Bump github.com/SevereCloud/vksdk/v2 from 2.11.0 to 2.13.0 (#1698)

Bumps [github.com/SevereCloud/vksdk/v2](https://github.com/SevereCloud/vksdk) from 2.11.0 to 2.13.0.
- [Release notes](https://github.com/SevereCloud/vksdk/releases)
- [Commits](https://github.com/SevereCloud/vksdk/compare/v2.11.0...v2.13.0)

---
updated-dependencies:
- dependency-name: github.com/SevereCloud/vksdk/v2
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

go.mod

@@ -6,7 +6,7 @@ require (
 	github.com/Benau/tgsconverter v0.0.0-20210809170556-99f4a4f6337f
 	github.com/Philipp15b/go-steam v1.0.1-0.20200727090957-6ae9b3c0a560
 	github.com/Rhymen/go-whatsapp v0.1.2-0.20211102134409-31a2e740845c
-	github.com/SevereCloud/vksdk/v2 v2.11.0
+	github.com/SevereCloud/vksdk/v2 v2.13.0
 	github.com/d5/tengo/v2 v2.10.0
 	github.com/davecgh/go-spew v1.1.1
 	github.com/fsnotify/fsnotify v1.5.1
@@ -73,7 +73,7 @@ require (
 	github.com/hashicorp/hcl v1.0.0 // indirect
 	github.com/json-iterator/go v1.1.12 // indirect
 	github.com/kettek/apng v0.0.0-20191108220231-414630eed80f // indirect
-	github.com/klauspost/compress v1.13.6 // indirect
+	github.com/klauspost/compress v1.14.1 // indirect
 	github.com/klauspost/cpuid/v2 v2.0.9 // indirect
 	github.com/labstack/gommon v0.3.1 // indirect
 	github.com/magiconair/properties v1.8.5 // indirect

go.sum

@@ -153,8 +153,8 @@ github.com/Rhymen/go-whatsapp v0.1.2-0.20211102134409-31a2e740845c/go.mod h1:DNS
 github.com/RoaringBitmap/roaring v0.4.23/go.mod h1:D0gp8kJQgE1A4LQ5wFLggQEyvDi06Mq5mKs52e1TwOo=
 github.com/RoaringBitmap/roaring v0.8.0/go.mod h1:jdT9ykXwHFNdJbEtxePexlFYH9LXucApeS0/+/g+p1I=
 github.com/RoaringBitmap/roaring v0.9.4/go.mod h1:icnadbWcNyfEHlYdr+tDlOTih1Bf/h+rzPpv4sbomAA=
-github.com/SevereCloud/vksdk/v2 v2.11.0 h1:9O85YicxktQB6sh1nmRKig1EZM+jHrdtST5FnOIiDGk=
-github.com/SevereCloud/vksdk/v2 v2.11.0/go.mod h1:o3pBTvwhvzDQhi1Uu+MuTk8TRWosWrGmxeySTGsYKYA=
+github.com/SevereCloud/vksdk/v2 v2.13.0 h1:sXAGkWRHCsPUDitiiPBU7PqzoTSdF7vdXZjLnHzYZQc=
+github.com/SevereCloud/vksdk/v2 v2.13.0/go.mod h1:skoTmXOqmQIESWnNKSpkWhpNdFK2Jjp1GxGZDElOKUw=
 github.com/Shopify/goreferrer v0.0.0-20181106222321-ec9c9a553398/go.mod h1:a1uqRtAwp2Xwc6WNPJEufxJ7fx3npB4UV/JOLmbu5I0=
 github.com/Shopify/logrus-bugsnag v0.0.0-20171204204709-577dee27f20d/go.mod h1:HI8ITrYtUY+O+ZhtlqUnD8+KwNPOyugEhfP9fdUIaEQ=
 github.com/Shopify/sarama v1.19.0/go.mod h1:FVkBWblsNy7DGZRfXLU0O9RCGt5g3g3yEuWXgklEdEo=
@@ -1004,8 +1004,9 @@ github.com/klauspost/compress v1.11.13/go.mod h1:aoV0uJVorq1K+umq18yTdKaF57EivdY
 github.com/klauspost/compress v1.13.1/go.mod h1:8dP1Hq4DHOhN9w426knH3Rhby4rFm6D8eO+e+Dq5Gzg=
 github.com/klauspost/compress v1.13.4/go.mod h1:8dP1Hq4DHOhN9w426knH3Rhby4rFm6D8eO+e+Dq5Gzg=
 github.com/klauspost/compress v1.13.5/go.mod h1:/3/Vjq9QcHkK5uEr5lBEmyoZ1iFhe47etQ6QUkpK6sk=
-github.com/klauspost/compress v1.13.6 h1:P76CopJELS0TiO2mebmnzgWaajssP/EszplttgQxcgc=
 github.com/klauspost/compress v1.13.6/go.mod h1:/3/Vjq9QcHkK5uEr5lBEmyoZ1iFhe47etQ6QUkpK6sk=
+github.com/klauspost/compress v1.14.1 h1:hLQYb23E8/fO+1u53d02A97a8UnsddcvYzq4ERRU4ds=
+github.com/klauspost/compress v1.14.1/go.mod h1:/3/Vjq9QcHkK5uEr5lBEmyoZ1iFhe47etQ6QUkpK6sk=
 github.com/klauspost/cpuid v1.2.0/go.mod h1:Pj4uuM528wm8OyEC2QMXAi2YiTZ96dNQPGgoMS4s3ek=
 github.com/klauspost/cpuid v1.2.1/go.mod h1:Pj4uuM528wm8OyEC2QMXAi2YiTZ96dNQPGgoMS4s3ek=
 github.com/klauspost/cpuid v1.2.3/go.mod h1:Pj4uuM528wm8OyEC2QMXAi2YiTZ96dNQPGgoMS4s3ek=

vendor/github.com/SevereCloud/vksdk/v2/.golangci.yml

@@ -53,10 +53,10 @@ linters:
     - ireturn
     - nilnil
     - tenv
+    - nestif
 
 # - wrapcheck # TODO: v3 Fix
 # - testpackage # TODO: Fix testpackage
-# - nestif # TODO: Fix nestif
 # - noctx # TODO: Fix noctx
 
 # don't enable:

vendor/github.com/SevereCloud/vksdk/v2/.markdownlint.yml

@@ -1,2 +1,3 @@
 ---
 no-hard-tabs: false
+no-duplicate-heading: false

vendor/github.com/SevereCloud/vksdk/v2/CONTRIBUTING.md

@@ -6,7 +6,7 @@
 
 Требования:
 
-- [Go 1.13+](https://golang.org/doc/install)
+- [Go 1.16+](https://golang.org/doc/install)
 - [golangci-lint](https://github.com/golangci/golangci-lint)
 - [global .gitignore](https://help.github.com/en/articles/ignoring-files#create-a-global-gitignore)
 

vendor/github.com/SevereCloud/vksdk/v2/README.md

@@ -16,11 +16,13 @@
 Version API 5.131.
 
 - [API](https://pkg.go.dev/github.com/SevereCloud/vksdk/v2/api)
-  - 400+ methods
-  - Ability to change the request handler
+  - 500+ methods
   - Ability to modify HTTP client
   - Request Limiter
+  - Support [zstd](https://pkg.go.dev/github.com/SevereCloud/vksdk/v2/api#VK.EnableZstd)
+and [MessagePack](https://pkg.go.dev/github.com/SevereCloud/vksdk/v2/api#VK.EnableMessagePack)
   - Token pool
+  - [OAuth](https://pkg.go.dev/github.com/SevereCloud/vksdk/v2/api/oauth)
 - [Callback API](https://pkg.go.dev/github.com/SevereCloud/vksdk/v2/callback)
   - Tracking tool for users activity in your VK communities
   - Supports all events
@@ -60,6 +62,7 @@ go get github.com/SevereCloud/vksdk/v2@latest
 
 ## Use by
 
+- A simple chat bridge: <https://github.com/42wim/matterbridge>
 - [Joe](https://github.com/go-joe/joe) adapter: <https://github.com/tdakkota/joe-vk-adapter>
 - [Logrus](https://github.com/sirupsen/logrus) hook: <https://github.com/SevereCloud/vkrus>
 

vendor/github.com/SevereCloud/vksdk/v2/api/README.md

@@ -3,7 +3,7 @@
 [![PkgGoDev](https://pkg.go.dev/badge/github.com/SevereCloud/vksdk/v2/api)](https://pkg.go.dev/github.com/SevereCloud/vksdk/v2/api)
 [![VK](https://img.shields.io/badge/developers-%234a76a8.svg?logo=VK&logoColor=white)](https://vk.com/dev/first_guide)
 
-Данная библиотека поддерживает версию API **5.122**.
+Данная библиотека поддерживает версию API **5.131**.
 
 ## Запросы
 
@@ -80,6 +80,54 @@ if errors.As(err, &e) {
 
 Для Execute существует отдельная ошибка `ExecuteErrors`
 
+### Поддержка MessagePack и zstd
+
+> Результат перехода с gzip (JSON) на zstd (msgpack):
+>
+> - в 7 раз быстрее сжатие (–1 мкс);
+> - на 10% меньше размер данных (8 Кбайт вместо 9 Кбайт);
+> - продуктовый эффект не статзначимый :(
+>
+> [Как мы отказались от JPEG, JSON, TCP и ускорили ВКонтакте в два раза](https://habr.com/ru/company/vk/blog/594633/)
+
+VK API способно возвращать ответ в виде [MessagePack](https://msgpack.org/).
+Это эффективный формат двоичной сериализации, похожий на JSON, только быстрее
+и меньше по размеру.
+
+ВНИМАНИЕ, C MessagePack НЕКОТОРЫЕ МЕТОДЫ МОГУТ ВОЗВРАЩАТЬ
+СЛОМАННУЮ КОДИРОВКУ.
+
+Для сжатия, вместо классического gzip, можно использовать
+[zstd](https://github.com/facebook/zstd). Сейчас vksdk поддерживает zstd без
+словаря. Если кто знает как получать словарь,
+[отпишитесь сюда](https://github.com/SevereCloud/vksdk/issues/180).
+
+```go
+vk := api.NewVK(os.Getenv("USER_TOKEN"))
+
+method := "store.getStickersKeywords"
+params := api.Params{
+	"aliases":       true,
+	"all_products":  true,
+	"need_stickers": true,
+}
+
+r, err := vk.Request(method, params) // Content-Length: 44758
+if err != nil {
+	log.Fatal(err)
+}
+log.Println("json:", len(r)) // json: 814231
+
+vk.EnableMessagePack() // Включаем поддержку MessagePack
+vk.EnableZstd() // Включаем поддержку zstd
+
+r, err = vk.Request(method, params) // Content-Length: 35755
+if err != nil {
+	log.Fatal(err)
+}
+log.Println("msgpack:", len(r)) // msgpack: 650775
+```
+
 ### Запрос любого метода
 
 Пример запроса [users.get](https://vk.com/dev/users.get)

vendor/github.com/SevereCloud/vksdk/v2/api/ads.go

@@ -1,9 +1,11 @@
 package api // import "github.com/SevereCloud/vksdk/v2/api"
 
 import (
+	"bytes"
 	"encoding/json"
 
 	"github.com/SevereCloud/vksdk/v2/object"
+	"github.com/vmihailenco/msgpack/v5"
 )
 
 // AdsAddOfficeUsersItem struct.
@@ -21,6 +23,23 @@ func (r *AdsAddOfficeUsersItem) UnmarshalJSON(data []byte) (err error) {
 	return
 }
 
+// DecodeMsgpack func.
+func (r *AdsAddOfficeUsersItem) DecodeMsgpack(dec *msgpack.Decoder) error {
+	data, err := dec.DecodeRaw()
+	if err != nil {
+		return err
+	}
+
+	if msgpack.Unmarshal(data, &r.OK) != nil {
+		d := msgpack.NewDecoder(bytes.NewReader(data))
+		d.SetCustomStructTag("json")
+
+		return d.Decode(&r.Error)
+	}
+
+	return nil
+}
+
 // AdsAddOfficeUsersResponse struct.
 type AdsAddOfficeUsersResponse []AdsAddOfficeUsersItem
 
@@ -349,7 +368,7 @@ func (vk *VK) AdsGetAdsLayout(params Params) (response AdsGetAdsLayoutResponse,
 
 // AdsGetMusiciansResponse struct.
 type AdsGetMusiciansResponse struct {
-	Items []object.BaseObjectWithName
+	Items []object.AdsMusician
 }
 
 // AdsGetMusicians returns a list of musicians.

vendor/github.com/SevereCloud/vksdk/v2/api/api.go

@@ -7,9 +7,11 @@ package api // import "github.com/SevereCloud/vksdk/v2/api"
 
 import (
 	"bytes"
+	"compress/gzip"
 	"context"
 	"encoding/json"
 	"fmt"
+	"io"
 	"mime"
 	"net/http"
 	"net/url"
@@ -21,6 +23,8 @@ import (
 	"github.com/SevereCloud/vksdk/v2"
 	"github.com/SevereCloud/vksdk/v2/internal"
 	"github.com/SevereCloud/vksdk/v2/object"
+	"github.com/klauspost/compress/zstd"
+	"github.com/vmihailenco/msgpack/v5"
 )
 
 // Api constants.
@@ -91,6 +95,9 @@ type VK struct {
 	UserAgent    string
 	Handler      func(method string, params ...Params) (Response, error)
 
+	msgpack bool
+	zstd    bool
+
 	mux      sync.Mutex
 	lastTime time.Time
 	rps      int
@@ -98,9 +105,9 @@ type VK struct {
 
 // Response struct.
 type Response struct {
-	Response      json.RawMessage `json:"response"`
-	Error         Error           `json:"error"`
-	ExecuteErrors ExecuteErrors   `json:"execute_errors"`
+	Response      object.RawMessage `json:"response"`
+	Error         Error             `json:"error"`
+	ExecuteErrors ExecuteErrors     `json:"execute_errors"`
 }
 
 // NewVK returns a new VK.
@@ -121,7 +128,7 @@ func NewVK(tokens ...string) *VK {
 	vk.accessTokens = tokens
 	vk.Version = Version
 
-	vk.Handler = vk.defaultHandler
+	vk.Handler = vk.DefaultHandler
 
 	vk.MethodURL = MethodURL
 	vk.Client = http.DefaultClient
@@ -207,8 +214,8 @@ func buildQuery(sliceParams ...Params) (context.Context, url.Values) {
 	return ctx, query
 }
 
-// defaultHandler provides access to VK API methods.
-func (vk *VK) defaultHandler(method string, sliceParams ...Params) (Response, error) {
+// DefaultHandler provides access to VK API methods.
+func (vk *VK) DefaultHandler(method string, sliceParams ...Params) (Response, error) {
 	u := vk.MethodURL + method
 	ctx, query := buildQuery(sliceParams...)
 	attempt := 0
@@ -243,24 +250,52 @@ func (vk *VK) defaultHandler(method string, sliceParams ...Params) (Response, er
 			return response, err
 		}
 
+		acceptEncoding := "gzip"
+		if vk.zstd {
+			acceptEncoding = "zstd"
+		}
+
 		req.Header.Set("User-Agent", vk.UserAgent)
 		req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
 
+		req.Header.Set("Accept-Encoding", acceptEncoding)
+
+		var reader io.Reader
+
 		resp, err := vk.Client.Do(req)
 		if err != nil {
 			return response, err
 		}
 
-		mediatype, _, _ := mime.ParseMediaType(resp.Header.Get("Content-Type"))
-		if mediatype != "application/json" {
-			_ = resp.Body.Close()
-			return response, &InvalidContentType{mediatype}
+		switch resp.Header.Get("Content-Encoding") {
+		case "zstd":
+			reader, _ = zstd.NewReader(resp.Body)
+		case "gzip":
+			reader, _ = gzip.NewReader(resp.Body)
+		default:
+			reader = resp.Body
 		}
 
-		err = json.NewDecoder(resp.Body).Decode(&response)
-		if err != nil {
+		mediatype, _, _ := mime.ParseMediaType(resp.Header.Get("Content-Type"))
+		switch mediatype {
+		case "application/json":
+			err = json.NewDecoder(reader).Decode(&response)
+			if err != nil {
+				_ = resp.Body.Close()
+				return response, err
+			}
+		case "application/x-msgpack":
+			dec := msgpack.NewDecoder(reader)
+			dec.SetCustomStructTag("json")
+
+			err = dec.Decode(&response)
+			if err != nil {
+				_ = resp.Body.Close()
+				return response, err
+			}
+		default:
 			_ = resp.Body.Close()
-			return response, err
+			return response, &InvalidContentType{mediatype}
 		}
 
 		_ = resp.Body.Close()
@@ -291,6 +326,10 @@ func (vk *VK) Request(method string, sliceParams ...Params) ([]byte, error) {
 
 	sliceParams = append(sliceParams, reqParams)
 
+	if vk.msgpack {
+		method += ".msgpack"
+	}
+
 	resp, err := vk.Handler(method, sliceParams...)
 
 	return resp.Response, err
@@ -303,7 +342,32 @@ func (vk *VK) RequestUnmarshal(method string, obj interface{}, sliceParams ...Pa
 		return err
 	}
 
-	return json.Unmarshal(rawResponse, &obj)
+	if vk.msgpack {
+		dec := msgpack.NewDecoder(bytes.NewReader(rawResponse))
+		dec.SetCustomStructTag("json")
+
+		err = dec.Decode(&obj)
+	} else {
+		err = json.Unmarshal(rawResponse, &obj)
+	}
+
+	return err
+}
+
+// EnableMessagePack enable using MessagePack instead of JSON.
+//
+// THIS IS EXPERIMENTAL FUNCTION! Broken encoding returned in some methods.
+//
+// See https://msgpack.org
+func (vk *VK) EnableMessagePack() {
+	vk.msgpack = true
+}
+
+// EnableZstd enable using zstd instead of gzip.
+//
+// This not use dict.
+func (vk *VK) EnableZstd() {
+	vk.zstd = true
 }
 
 func fmtReflectValue(value reflect.Value, depth int) string {

vendor/github.com/SevereCloud/vksdk/v2/api/auth.go

@@ -1,5 +1,9 @@
 package api // import "github.com/SevereCloud/vksdk/v2/api"
 
+import (
+	"github.com/SevereCloud/vksdk/v2/object"
+)
+
 // AuthCheckPhone checks a user's phone number for correctness.
 //
 // https://vk.com/dev/auth.checkPhone
@@ -24,3 +28,58 @@ func (vk *VK) AuthRestore(params Params) (response AuthRestoreResponse, err erro
 	err = vk.RequestUnmarshal("auth.restore", &response, params)
 	return
 }
+
+// AuthGetProfileInfoBySilentTokenResponse struct.
+type AuthGetProfileInfoBySilentTokenResponse struct {
+	Success []object.AuthSilentTokenProfile `json:"success"`
+	Errors  []AuthSilentTokenError          `json:"errors"`
+}
+
+// AuthGetProfileInfoBySilentToken method.
+//
+// https://platform.vk.com/?p=DocsDashboard&docs=tokens_silent-token
+func (vk *VK) AuthGetProfileInfoBySilentToken(params Params) (response AuthGetProfileInfoBySilentTokenResponse, err error) {
+	err = vk.RequestUnmarshal("auth.getProfileInfoBySilentToken", &response, params)
+	return
+}
+
+// ExchangeSilentTokenSource call conditions exchangeSilentToken.
+//
+// 	0	Unknown
+// 	1	Silent authentication
+// 	2	Auth by login and password
+// 	3	Extended registration
+// 	4	Auth by exchange token
+// 	5	Auth by exchange token on reset password
+// 	6	Auth by exchange token on unblock
+// 	7	Auth by exchange token on reset session
+// 	8	Auth by exchange token on change password
+// 	9	Finish phone validation on authentication
+// 	10	Auth by code
+// 	11	Auth by external oauth
+// 	12	Reactivation
+// 	15	Auth by SDK temporary access-token
+type ExchangeSilentTokenSource int
+
+// AuthExchangeSilentAuthTokenResponse struct.
+type AuthExchangeSilentAuthTokenResponse struct {
+	AccessToken              string                    `json:"access_token"`
+	AccessTokenID            string                    `json:"access_token_id"`
+	UserID                   int                       `json:"user_id"`
+	Phone                    string                    `json:"phone"`
+	PhoneValidated           interface{}               `json:"phone_validated"`
+	IsPartial                bool                      `json:"is_partial"`
+	IsService                bool                      `json:"is_service"`
+	AdditionalSignupRequired bool                      `json:"additional_signup_required"`
+	Email                    string                    `json:"email"`
+	Source                   ExchangeSilentTokenSource `json:"source"`
+	SourceDescription        string                    `json:"source_description"`
+}
+
+// AuthExchangeSilentAuthToken method.
+//
+// https://platform.vk.com/?p=DocsDashboard&docs=tokens_access-token
+func (vk *VK) AuthExchangeSilentAuthToken(params Params) (response AuthExchangeSilentAuthTokenResponse, err error) {
+	err = vk.RequestUnmarshal("auth.exchangeSilentAuthToken", &response, params)
+	return
+}

vendor/github.com/SevereCloud/vksdk/v2/api/errors.go

@@ -598,6 +598,12 @@ const (
 	// This user can't be added to the work chat, as they aren't an employe.
 	ErrMessagesAccessWorkChat ErrorType = 967
 
+	// Message cannot be forwarded.
+	ErrMessagesCantForwarded ErrorType = 969
+
+	// Cannot pin an expiring message.
+	ErrMessagesPinExpiringMessage ErrorType = 970
+
 	// Invalid phone number.
 	ErrParamPhone ErrorType = 1000
 
@@ -994,3 +1000,31 @@ func (e AdsError) Is(target error) bool {
 
 	return false
 }
+
+// AuthSilentTokenError struct.
+type AuthSilentTokenError struct {
+	Token       string    `json:"token"`
+	Code        ErrorType `json:"code"`
+	Description string    `json:"description"`
+}
+
+// Error returns the description of a AuthSilentTokenError.
+func (e AuthSilentTokenError) Error() string {
+	return "api: " + e.Description
+}
+
+// Is unwraps its first argument sequentially looking for an error that matches
+// the second.
+func (e AuthSilentTokenError) Is(target error) bool {
+	var tError *AuthSilentTokenError
+	if errors.As(target, &tError) {
+		return e.Code == tError.Code && e.Description == tError.Description
+	}
+
+	var tErrorType ErrorType
+	if errors.As(target, &tErrorType) {
+		return e.Code == tErrorType
+	}
+
+	return false
+}

vendor/github.com/SevereCloud/vksdk/v2/api/execute.go

@@ -1,6 +1,11 @@
 package api
 
-import "encoding/json"
+import (
+	"bytes"
+	"encoding/json"
+
+	"github.com/vmihailenco/msgpack/v5"
+)
 
 // ExecuteWithArgs a universal method for calling a sequence of other methods
 // while saving and filtering interim results.
@@ -26,9 +31,19 @@ func (vk *VK) ExecuteWithArgs(code string, params Params, obj interface{}) error
 		return err
 	}
 
-	jsonErr := json.Unmarshal(resp.Response, &obj)
-	if jsonErr != nil {
-		return jsonErr
+	var decoderErr error
+
+	if vk.msgpack {
+		dec := msgpack.NewDecoder(bytes.NewReader(resp.Response))
+		dec.SetCustomStructTag("json")
+
+		decoderErr = dec.Decode(&obj)
+	} else {
+		decoderErr = json.Unmarshal(resp.Response, &obj)
+	}
+
+	if decoderErr != nil {
+		return decoderErr
 	}
 
 	if resp.ExecuteErrors != nil {

vendor/github.com/SevereCloud/vksdk/v2/api/market.go

@@ -20,6 +20,7 @@ func (vk *VK) MarketAdd(params Params) (response MarketAddResponse, err error) {
 // MarketAddAlbumResponse struct.
 type MarketAddAlbumResponse struct {
 	MarketAlbumID int `json:"market_album_id"` // Album ID
+	AlbumsCount   int `json:"albums_count"`
 }
 
 // MarketAddAlbum creates new collection of items.

vendor/github.com/SevereCloud/vksdk/v2/api/messages.go

@@ -1,7 +1,10 @@
 package api // import "github.com/SevereCloud/vksdk/v2/api"
 
 import (
+	"strconv"
+
 	"github.com/SevereCloud/vksdk/v2/object"
+	"github.com/vmihailenco/msgpack/v5"
 )
 
 // MessagesAddChatUser adds a new user to a chat.
@@ -31,11 +34,34 @@ func (vk *VK) MessagesCreateChat(params Params) (response int, err error) {
 // MessagesDeleteResponse struct.
 type MessagesDeleteResponse map[string]int
 
+// DecodeMsgpack funcion.
+func (resp *MessagesDeleteResponse) DecodeMsgpack(dec *msgpack.Decoder) error {
+	data, err := dec.DecodeRaw()
+	if err != nil {
+		return err
+	}
+
+	var respMap map[int]int
+
+	err = msgpack.Unmarshal(data, &respMap)
+	if err != nil {
+		return err
+	}
+
+	*resp = make(MessagesDeleteResponse)
+	for key, val := range respMap {
+		(*resp)[strconv.Itoa(key)] = val
+	}
+
+	return nil
+}
+
 // MessagesDelete deletes one or more messages.
 //
 // https://vk.com/dev/messages.delete
 func (vk *VK) MessagesDelete(params Params) (response MessagesDeleteResponse, err error) {
 	err = vk.RequestUnmarshal("messages.delete", &response, params)
+
 	return
 }
 

vendor/github.com/SevereCloud/vksdk/v2/api/photos.go

@@ -571,12 +571,13 @@ func (vk *VK) PhotosSaveOwnerCoverPhoto(params Params) (response PhotosSaveOwner
 
 // PhotosSaveOwnerPhotoResponse struct.
 type PhotosSaveOwnerPhotoResponse struct {
-	PhotoHash     string `json:"photo_hash"`
-	PhotoSrc      string `json:"photo_src"`
-	PhotoSrcBig   string `json:"photo_src_big"`
-	PhotoSrcSmall string `json:"photo_src_small"`
-	Saved         int    `json:"saved"`
-	PostID        int    `json:"post_id"`
+	PhotoHash string `json:"photo_hash"`
+	// BUG(VK): returns false
+	// PhotoSrc      string `json:"photo_src"`
+	// PhotoSrcBig   string `json:"photo_src_big"`
+	// PhotoSrcSmall string `json:"photo_src_small"`
+	Saved  int `json:"saved"`
+	PostID int `json:"post_id"`
 }
 
 // PhotosSaveOwnerPhoto saves a profile or community photo.

vendor/github.com/SevereCloud/vksdk/v2/api/utils.go

@@ -1,9 +1,8 @@
 package api // import "github.com/SevereCloud/vksdk/v2/api"
 
 import (
-	"encoding/json"
-
 	"github.com/SevereCloud/vksdk/v2/object"
+	"github.com/vmihailenco/msgpack/v5"
 )
 
 // UtilsCheckLinkResponse struct.
@@ -89,17 +88,34 @@ func (vk *VK) UtilsGetShortLink(params Params) (response UtilsGetShortLinkRespon
 // UtilsResolveScreenNameResponse struct.
 type UtilsResolveScreenNameResponse object.UtilsDomainResolved
 
+// UnmarshalJSON UtilsResolveScreenNameResponse.
+//
+// BUG(VK): UtilsResolveScreenNameResponse return [].
+func (resp *UtilsResolveScreenNameResponse) UnmarshalJSON(data []byte) error {
+	var p object.UtilsDomainResolved
+	err := p.UnmarshalJSON(data)
+
+	*resp = UtilsResolveScreenNameResponse(p)
+
+	return err
+}
+
+// DecodeMsgpack UtilsResolveScreenNameResponse.
+//
+// BUG(VK): UtilsResolveScreenNameResponse return [].
+func (resp *UtilsResolveScreenNameResponse) DecodeMsgpack(dec *msgpack.Decoder) error {
+	var p object.UtilsDomainResolved
+	err := p.DecodeMsgpack(dec)
+
+	*resp = UtilsResolveScreenNameResponse(p)
+
+	return err
+}
+
 // UtilsResolveScreenName detects a type of object (e.g., user, community, application) and its ID by screen name.
 //
 // https://vk.com/dev/utils.resolveScreenName
 func (vk *VK) UtilsResolveScreenName(params Params) (response UtilsResolveScreenNameResponse, err error) {
-	rawResponse, err := vk.Request("utils.resolveScreenName", params)
-	// Если короткое имя screen_name не занято, то будет возвращён пустой объект.
-	if err != nil || string(rawResponse) == "[]" {
-		return
-	}
-
-	err = json.Unmarshal(rawResponse, &response)
-
+	err = vk.RequestUnmarshal("utils.resolveScreenName", &response, params)
 	return
 }

vendor/github.com/SevereCloud/vksdk/v2/doc.go

@@ -7,6 +7,6 @@ package vksdk
 
 // Module constants.
 const (
-	Version = "2.11.0"
+	Version = "2.13.0"
 	API     = "5.131"
 )

vendor/github.com/SevereCloud/vksdk/v2/longpoll-bot/README.md

@@ -10,7 +10,7 @@ Long Poll настраивается автоматически. Вам не т
 
 ### Версия API
 
-Данная библиотека поддерживает версию API **5.122**.
+Данная библиотека поддерживает версию API **5.131**.
 
 ### Инициализация
 

vendor/github.com/SevereCloud/vksdk/v2/longpoll-bot/longpoll.go

@@ -8,8 +8,11 @@ package longpoll // import "github.com/SevereCloud/vksdk/v2/longpoll-bot"
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
+	"io"
 	"net/http"
+	"strconv"
 
 	"github.com/SevereCloud/vksdk/v2"
 	"github.com/SevereCloud/vksdk/v2/api"
@@ -117,7 +120,7 @@ func (lp *LongPoll) check(ctx context.Context) (response Response, err error) {
 	}
 	defer resp.Body.Close()
 
-	err = json.NewDecoder(resp.Body).Decode(&response)
+	response, err = parseResponse(resp.Body)
 	if err != nil {
 		return response, err
 	}
@@ -127,6 +130,59 @@ func (lp *LongPoll) check(ctx context.Context) (response Response, err error) {
 	return response, err
 }
 
+func parseResponse(reader io.Reader) (response Response, err error) {
+	decoder := json.NewDecoder(reader)
+	for decoder.More() {
+		token, err := decoder.Token()
+		if err != nil {
+			if errors.Is(err, io.EOF) {
+				break
+			}
+
+			return response, err
+		}
+
+		t, ok := token.(string)
+		if !ok {
+			continue
+		}
+
+		switch t {
+		case "failed":
+			raw, err := decoder.Token()
+			if err != nil {
+				return response, err
+			}
+
+			response.Failed = int(raw.(float64))
+		case "updates":
+			var updates []events.GroupEvent
+
+			err = decoder.Decode(&updates)
+			if err != nil {
+				return response, err
+			}
+
+			response.Updates = updates
+		case "ts":
+			// can be a number in the response with "failed" field: {"ts":8,"failed":1}
+			// or string, e.g. {"ts":"8","updates":[]}
+			rawTs, err := decoder.Token()
+			if err != nil {
+				return response, err
+			}
+
+			if ts, isNumber := rawTs.(float64); isNumber {
+				response.Ts = strconv.Itoa(int(ts))
+			} else {
+				response.Ts = rawTs.(string)
+			}
+		}
+	}
+
+	return response, err
+}
+
 func (lp *LongPoll) checkResponse(response Response) (err error) {
 	switch response.Failed {
 	case 0:

vendor/github.com/SevereCloud/vksdk/v2/object/account.go

@@ -62,21 +62,24 @@ type AccountOffer struct {
 
 // AccountAccountCounters struct.
 type AccountAccountCounters struct {
-	AppRequests            int `json:"app_requests"`            // New app requests number
-	Events                 int `json:"events"`                  // New events number
-	Friends                int `json:"friends"`                 // New friends requests number
-	FriendsRecommendations int `json:"friends_recommendations"` // New friends recommendations number
-	FriendsSuggestions     int `json:"friends_suggestions"`     // New friends suggestions number
-	Gifts                  int `json:"gifts"`                   // New gifts number
-	Groups                 int `json:"groups"`                  // New groups number
-	Messages               int `json:"messages"`                // New messages number
-	Notifications          int `json:"notifications"`           // New notifications number
-	Photos                 int `json:"photos"`                  // New photo tags number
-	SDK                    int `json:"sdk"`                     // New SDK number
-	MenuDiscoverBadge      int `json:"menu_discover_badge"`     // New menu discover badge number
-	MenuClipsBadge         int `json:"menu_clips_badge"`        // New menu clips badge number
-	Videos                 int `json:"videos"`                  // New video tags number
-	Faves                  int `json:"faves"`                   // New faves number
+	AppRequests              int `json:"app_requests"`            // New app requests number
+	Events                   int `json:"events"`                  // New events number
+	Friends                  int `json:"friends"`                 // New friends requests number
+	FriendsRecommendations   int `json:"friends_recommendations"` // New friends recommendations number
+	FriendsSuggestions       int `json:"friends_suggestions"`     // New friends suggestions number
+	Gifts                    int `json:"gifts"`                   // New gifts number
+	Groups                   int `json:"groups"`                  // New groups number
+	Messages                 int `json:"messages"`                // New messages number
+	Notifications            int `json:"notifications"`           // New notifications number
+	Photos                   int `json:"photos"`                  // New photo tags number
+	SDK                      int `json:"sdk"`                     // New SDK number
+	MenuDiscoverBadge        int `json:"menu_discover_badge"`     // New menu discover badge number
+	MenuClipsBadge           int `json:"menu_clips_badge"`        // New menu clips badge number
+	Videos                   int `json:"videos"`                  // New video tags number
+	Faves                    int `json:"faves"`                   // New faves number
+	Calls                    int `json:"calls"`                   // New calls number
+	MenuSuperappFriendsBadge int `json:"menu_superapp_friends_badge"`
+	MenuNewClipsBadge        int `json:"menu_new_clips_badge"`
 }
 
 // AccountInfo struct.
@@ -107,6 +110,7 @@ type AccountInfo struct {
 	IsLiveStreamingEnabled    BaseBoolInt       `json:"is_live_streaming_enabled"`
 	IsNewLiveStreamingEnabled BaseBoolInt       `json:"is_new_live_streaming_enabled"`
 	LinkRedirects             map[string]string `json:"link_redirects"`
+	VkPayEndpointV2           string            `json:"vk_pay_endpoint_v2"`
 }
 
 // AccountPushSettings struct.

vendor/github.com/SevereCloud/vksdk/v2/object/ads.go

@@ -8,12 +8,13 @@ type AdsAccesses struct {
 
 // AdsAccount struct.
 type AdsAccount struct {
-	AccessRole    string      `json:"access_role"`
-	AccountID     int         `json:"account_id"` // Account ID
-	AccountName   string      `json:"account_name"`
-	AccountStatus BaseBoolInt `json:"account_status"` // Information whether account is active
-	CanViewBudget BaseBoolInt `json:"can_view_budget"`
-	AccountType   string      `json:"account_type"`
+	AccessRole                  string      `json:"access_role"`
+	AccountID                   int         `json:"account_id"` // Account ID
+	AccountName                 string      `json:"account_name"`
+	AccountStatus               BaseBoolInt `json:"account_status"` // Information whether account is active
+	CanViewBudget               BaseBoolInt `json:"can_view_budget"`
+	AdNetworkAllowedPotentially BaseBoolInt `json:"ad_network_allowed_potentially"`
+	AccountType                 string      `json:"account_type"`
 }
 
 // AdsAdLayout struct.
@@ -318,3 +319,10 @@ type AdsPromotedPostReach struct {
 	VideoViews75p    int `json:"video_views_75p"`   // Video views for 75 percent
 	VideoViewsStart  int `json:"video_views_start"` // Video starts
 }
+
+// AdsMusician struct.
+type AdsMusician struct {
+	ID     int    `json:"id"`               // Targeting music artist ID
+	Name   string `json:"name"`             // Music artist name
+	Avatar string `json:"avatar,omitempty"` // Music artist photo.
+}

vendor/github.com/SevereCloud/vksdk/v2/object/apps.go

@@ -60,6 +60,7 @@ type AppsApp struct {
 	IsNew           BaseBoolInt `json:"is_new"`
 	New             BaseBoolInt `json:"new"`
 	IsInstalled     BaseBoolInt `json:"is_installed"`
+	HasVkConnect    BaseBoolInt `json:"has_vk_connect"`
 	LeaderboardType int         `json:"leaderboard_type"`
 	MembersCount    int         `json:"members_count"` // Members number
 	PlatformID      int         `json:"platform_id"`   // Application ID in store
@@ -78,7 +79,7 @@ type AppsApp struct {
 
 	// mobile_controls_type = 0 - прозрачный элемент управления поверх области с игрой;
 	// mobile_controls_type = 1 - чёрная полоска над областью с игрой;
-	// mobile_controls_type = 2 - только для vk apps, без контроллов.
+	// mobile_controls_type = 2 - только для vk apps, без элементов управления'.
 	MobileControlsType int `json:"mobile_controls_type"`
 
 	// mobile_view_support_type = 0 - игра не использует нижнюю часть экрана на iPhoneX, черная полоса есть.

vendor/github.com/SevereCloud/vksdk/v2/object/auth.go

@@ -0,0 +1,17 @@
+package object // import "github.com/SevereCloud/vksdk/v2/object"
+
+// AuthSilentTokenProfile struct.
+type AuthSilentTokenProfile struct {
+	Token          string      `json:"token"`
+	Expires        int         `json:"expires"`
+	FirstName      string      `json:"first_name"`
+	LastName       string      `json:"last_name"`
+	Photo50        string      `json:"photo_50"`
+	Photo100       string      `json:"photo_100"`
+	Photo200       string      `json:"photo_200"`
+	Phone          string      `json:"phone"`
+	PhoneValidated interface{} `json:"phone_validated"` // int | bool
+	UserID         int         `json:"user_id"`
+	IsPartial      BaseBoolInt `json:"is_partial"`
+	IsService      BaseBoolInt `json:"is_service"`
+}

vendor/github.com/SevereCloud/vksdk/v2/object/database.go

@@ -4,9 +4,9 @@ package object // import "github.com/SevereCloud/vksdk/v2/object"
 type DatabaseCity struct {
 	ID        int         `json:"id"`    // City ID
 	Title     string      `json:"title"` // City title
-	Area      string      `json:"area"`
-	Region    string      `json:"region"`
-	Important BaseBoolInt `json:"important"`
+	Area      string      `json:"area,omitempty"`
+	Region    string      `json:"region,omitempty"`
+	Important BaseBoolInt `json:"important,omitempty"`
 }
 
 // DatabaseMetroStation  struct.

vendor/github.com/SevereCloud/vksdk/v2/object/groups.go

@@ -1,9 +1,13 @@
 package object // import "github.com/SevereCloud/vksdk/v2/object"
 
 import (
+	"bytes"
 	"encoding/json"
 	"fmt"
 	"reflect"
+
+	"github.com/vmihailenco/msgpack/v5"
+	"github.com/vmihailenco/msgpack/v5/msgpcode"
 )
 
 // GroupsAddress WorkInfoStatus of information about timetable.
@@ -110,112 +114,113 @@ const (
 
 // GroupsGroup struct.
 type GroupsGroup struct {
-	AdminLevel   int              `json:"admin_level"`
-	Deactivated  string           `json:"deactivated"` // Information whether community is banned
-	FinishDate   int              `json:"finish_date"` // Finish date in Unixtime format
 	ID           int              `json:"id"`          // Community ID
 	Name         string           `json:"name"`        // Community name
-	Photo100     string           `json:"photo_100"`   // URL of square photo of the community with 100 pixels in width
-	Photo200     string           `json:"photo_200"`   // URL of square photo of the community with 200 pixels in width
-	Photo50      string           `json:"photo_50"`    // URL of square photo of the community with 50 pixels in width
 	ScreenName   string           `json:"screen_name"` // Domain of the community page
-	StartDate    int              `json:"start_date"`  // Start date in Unixtime format
 	Type         string           `json:"type"`
-	Market       GroupsMarketInfo `json:"market"`
-	MemberStatus int              `json:"member_status"` // Current user's member status
 	IsClosed     int              `json:"is_closed"`
-	City         BaseObject       `json:"city"`
-	Country      BaseCountry      `json:"country"`
+	AdminLevel   int              `json:"admin_level,omitempty"`
+	Deactivated  string           `json:"deactivated,omitempty"` // Information whether community is banned
+	FinishDate   int              `json:"finish_date,omitempty"` // Finish date in Unixtime format
+	Photo100     string           `json:"photo_100,omitempty"`   // URL of square photo of the community with 100 pixels in width
+	Photo200     string           `json:"photo_200,omitempty"`   // URL of square photo of the community with 200 pixels in width
+	Photo50      string           `json:"photo_50,omitempty"`    // URL of square photo of the community with 50 pixels in width
+	StartDate    int              `json:"start_date,omitempty"`  // Start date in Unixtime format
+	Market       GroupsMarketInfo `json:"market,omitempty"`
+	MemberStatus int              `json:"member_status,omitempty"` // Current user's member status
+	City         BaseObject       `json:"city,omitempty"`
+	Country      BaseCountry      `json:"country,omitempty"`
 
 	// Information whether current user is administrator.
 	IsAdmin BaseBoolInt `json:"is_admin"`
 
 	// Information whether current user is advertiser.
-	IsAdvertiser BaseBoolInt `json:"is_advertiser"`
+	IsAdvertiser BaseBoolInt `json:"is_advertiser,omitempty"`
 
 	// Information whether current user is member.
-	IsMember BaseBoolInt `json:"is_member"`
+	IsMember BaseBoolInt `json:"is_member,omitempty"`
 
 	// Information whether community is in faves.
-	IsFavorite BaseBoolInt `json:"is_favorite"`
+	IsFavorite BaseBoolInt `json:"is_favorite,omitempty"`
 
 	// Information whether community is adult.
-	IsAdult BaseBoolInt `json:"is_adult"`
+	IsAdult BaseBoolInt `json:"is_adult,omitempty"`
 
 	// Information whether current user is subscribed.
-	IsSubscribed BaseBoolInt `json:"is_subscribed"`
+	IsSubscribed BaseBoolInt `json:"is_subscribed,omitempty"`
 
 	// Information whether current user can post on community's wall.
-	CanPost BaseBoolInt `json:"can_post"`
+	CanPost BaseBoolInt `json:"can_post,omitempty"`
 
 	// Information whether current user can see all posts on community's wall.
-	CanSeeAllPosts BaseBoolInt `json:"can_see_all_posts"`
+	CanSeeAllPosts BaseBoolInt `json:"can_see_all_posts,omitempty"`
 
 	// Information whether current user can create topic.
-	CanCreateTopic BaseBoolInt `json:"can_create_topic"`
+	CanCreateTopic BaseBoolInt `json:"can_create_topic,omitempty"`
 
 	// Information whether current user can upload video.
-	CanUploadVideo BaseBoolInt `json:"can_upload_video"`
+	CanUploadVideo BaseBoolInt `json:"can_upload_video,omitempty"`
 
 	// Information whether current user can upload doc.
-	CanUploadDoc BaseBoolInt `json:"can_upload_doc"`
+	CanUploadDoc BaseBoolInt `json:"can_upload_doc,omitempty"`
 
 	// Information whether community has photo.
-	HasPhoto BaseBoolInt `json:"has_photo"`
+	HasPhoto BaseBoolInt `json:"has_photo,omitempty"`
 
 	// Information whether current user can send a message to community.
-	CanMessage BaseBoolInt `json:"can_message"`
+	CanMessage BaseBoolInt `json:"can_message,omitempty"`
 
 	// Information whether community can send a message to current user.
-	IsMessagesBlocked BaseBoolInt `json:"is_messages_blocked"`
+	IsMessagesBlocked BaseBoolInt `json:"is_messages_blocked,omitempty"`
 
 	// Information whether community can send notifications by phone number to current user.
-	CanSendNotify BaseBoolInt `json:"can_send_notify"`
+	CanSendNotify BaseBoolInt `json:"can_send_notify,omitempty"`
 
 	// Information whether current user is subscribed to podcasts.
-	IsSubscribedPodcasts BaseBoolInt `json:"is_subscribed_podcasts"`
+	IsSubscribedPodcasts BaseBoolInt `json:"is_subscribed_podcasts,omitempty"`
 
 	// Owner in whitelist or not.
-	CanSubscribePodcasts BaseBoolInt `json:"can_subscribe_podcasts"`
+	CanSubscribePodcasts BaseBoolInt `json:"can_subscribe_podcasts,omitempty"`
 
 	// Can subscribe to wall.
-	CanSubscribePosts BaseBoolInt `json:"can_subscribe_posts"`
+	CanSubscribePosts BaseBoolInt `json:"can_subscribe_posts,omitempty"`
 
 	// Information whether community has market app.
-	HasMarketApp        BaseBoolInt `json:"has_market_app"`
-	IsHiddenFromFeed    BaseBoolInt `json:"is_hidden_from_feed"`
-	IsMarketCartEnabled BaseBoolInt `json:"is_market_cart_enabled"`
-	Verified            BaseBoolInt `json:"verified"` // Information whether community is verified
+	HasMarketApp        BaseBoolInt `json:"has_market_app,omitempty"`
+	IsHiddenFromFeed    BaseBoolInt `json:"is_hidden_from_feed,omitempty"`
+	IsMarketCartEnabled BaseBoolInt `json:"is_market_cart_enabled,omitempty"`
+	Verified            BaseBoolInt `json:"verified,omitempty"` // Information whether community is verified
 
 	// Information whether the community has a fire pictogram.
-	Trending     BaseBoolInt         `json:"trending"`
-	Description  string              `json:"description"`   // Community description
-	WikiPage     string              `json:"wiki_page"`     // Community's main wiki page title
-	MembersCount int                 `json:"members_count"` // Community members number
-	Counters     GroupsCountersGroup `json:"counters"`
-	Cover        GroupsCover         `json:"cover"`
+	Trending     BaseBoolInt         `json:"trending,omitempty"`
+	Description  string              `json:"description,omitempty"`   // Community description
+	WikiPage     string              `json:"wiki_page,omitempty"`     // Community's main wiki page title
+	MembersCount int                 `json:"members_count,omitempty"` // Community members number
+	Counters     GroupsCountersGroup `json:"counters,omitempty"`
+	Cover        GroupsCover         `json:"cover,omitempty"`
 
 	// Type of group, start date of event or category of public page.
-	Activity        string               `json:"activity"`
-	FixedPost       int                  `json:"fixed_post"`    // Fixed post ID
-	Status          string               `json:"status"`        // Community status
-	MainAlbumID     int                  `json:"main_album_id"` // Community's main photo album ID
-	Links           []GroupsLinksItem    `json:"links"`
-	Contacts        []GroupsContactsItem `json:"contacts"`
-	Site            string               `json:"site"` // Community's website
-	MainSection     int                  `json:"main_section"`
-	OnlineStatus    GroupsOnlineStatus   `json:"online_status"` // Status of replies in community messages
-	AgeLimits       int                  `json:"age_limits"`    // Information whether age limit
-	BanInfo         GroupsGroupBanInfo   `json:"ban_info"`      // User ban info
-	Addresses       GroupsAddressesInfo  `json:"addresses"`     // Info about addresses in Groups
-	LiveCovers      GroupsLiveCovers     `json:"live_covers"`
-	CropPhoto       UsersCropPhoto       `json:"crop_photo"`
-	Wall            int                  `json:"wall"`
-	ActionButton    GroupsActionButton   `json:"action_button"`
-	TrackCode       string               `json:"track_code"`
-	PublicDateLabel string               `json:"public_date_label"`
-	AuthorID        int                  `json:"author_id"`
-	Phone           string               `json:"phone"`
+	Activity        string               `json:"activity,omitempty"`
+	FixedPost       int                  `json:"fixed_post,omitempty"`    // Fixed post ID
+	Status          string               `json:"status,omitempty"`        // Community status
+	MainAlbumID     int                  `json:"main_album_id,omitempty"` // Community's main photo album ID
+	Links           []GroupsLinksItem    `json:"links,omitempty"`
+	Contacts        []GroupsContactsItem `json:"contacts,omitempty"`
+	Site            string               `json:"site,omitempty"` // Community's website
+	MainSection     int                  `json:"main_section,omitempty"`
+	OnlineStatus    GroupsOnlineStatus   `json:"online_status,omitempty"` // Status of replies in community messages
+	AgeLimits       int                  `json:"age_limits,omitempty"`    // Information whether age limit
+	BanInfo         GroupsGroupBanInfo   `json:"ban_info,omitempty"`      // User ban info
+	Addresses       GroupsAddressesInfo  `json:"addresses,omitempty"`     // Info about addresses in Groups
+	LiveCovers      GroupsLiveCovers     `json:"live_covers,omitempty"`
+	CropPhoto       UsersCropPhoto       `json:"crop_photo,omitempty"`
+	Wall            int                  `json:"wall,omitempty"`
+	ActionButton    GroupsActionButton   `json:"action_button,omitempty"`
+	TrackCode       string               `json:"track_code,omitempty"`
+	PublicDateLabel string               `json:"public_date_label,omitempty"`
+	AuthorID        int                  `json:"author_id,omitempty"`
+	Phone           string               `json:"phone,omitempty"`
+	Like            GroupsGroupLike      `json:"like"`
 }
 
 // ToMention return mention.
@@ -223,6 +228,18 @@ func (group GroupsGroup) ToMention() string {
 	return fmt.Sprintf("[club%d|%s]", group.ID, group.Name)
 }
 
+// GroupsGroupLike struct.
+type GroupsGroupLike struct {
+	IsLiked BaseBoolInt            `json:"is_liked"`
+	Friends GroupsGroupLikeFriends `json:"friends"`
+}
+
+// GroupsGroupLikeFriends struct.
+type GroupsGroupLikeFriends struct {
+	Count   int   `json:"count"`
+	Preview []int `json:"preview"`
+}
+
 // GroupsLiveCovers struct.
 type GroupsLiveCovers struct {
 	IsEnabled  BaseBoolInt `json:"is_enabled"`
@@ -275,16 +292,70 @@ type GroupsContactsItem struct {
 
 // GroupsCountersGroup struct.
 type GroupsCountersGroup struct {
-	Addresses  int `json:"addresses"`  // Addresses number
-	Albums     int `json:"albums"`     // Photo albums number
-	Articles   int `json:"articles"`   // Articles number
-	Audios     int `json:"audios"`     // Audios number
-	Docs       int `json:"docs"`       // Docs number
-	Market     int `json:"market"`     // Market items number
-	Photos     int `json:"photos"`     // Photos number
-	Topics     int `json:"topics"`     // Topics number
-	Videos     int `json:"videos"`     // Videos number
-	Narratives int `json:"narratives"` // Narratives number
+	Addresses      int `json:"addresses"`       // Addresses number
+	Albums         int `json:"albums"`          // Photo albums number
+	Articles       int `json:"articles"`        // Articles number
+	Audios         int `json:"audios"`          // Audios number
+	Docs           int `json:"docs"`            // Docs number
+	Market         int `json:"market"`          // Market items number
+	Photos         int `json:"photos"`          // Photos number
+	Topics         int `json:"topics"`          // Topics number
+	Videos         int `json:"videos"`          // Videos number
+	Narratives     int `json:"narratives"`      // Narratives number
+	Clips          int `json:"clips"`           // Clips number
+	ClipsFollowers int `json:"clips_followers"` // Clips followers number
+}
+
+// UnmarshalJSON GroupsCountersGroup.
+//
+// BUG(VK): GroupsCountersGroup return [].
+func (personal *GroupsCountersGroup) UnmarshalJSON(data []byte) error {
+	if bytes.Equal(data, []byte("[]")) {
+		return nil
+	}
+
+	type renamedGroupsCountersGroup GroupsCountersGroup
+
+	var r renamedGroupsCountersGroup
+
+	err := json.Unmarshal(data, &r)
+	if err != nil {
+		return err
+	}
+
+	*personal = GroupsCountersGroup(r)
+
+	return nil
+}
+
+// DecodeMsgpack GroupsCountersGroup.
+//
+// BUG(VK): GroupsCountersGroup return [].
+func (personal *GroupsCountersGroup) DecodeMsgpack(dec *msgpack.Decoder) error {
+	data, err := dec.DecodeRaw()
+	if err != nil {
+		return err
+	}
+
+	if bytes.Equal(data, []byte{msgpcode.FixedArrayLow}) {
+		return nil
+	}
+
+	type renamedGroupsCountersGroup GroupsCountersGroup
+
+	var r renamedGroupsCountersGroup
+
+	d := msgpack.NewDecoder(bytes.NewReader(data))
+	d.SetCustomStructTag("json")
+
+	err = d.Decode(&r)
+	if err != nil {
+		return err
+	}
+
+	*personal = GroupsCountersGroup(r)
+
+	return nil
 }
 
 // GroupsCover struct.
@@ -479,6 +550,70 @@ type GroupsGroupSettings struct {
 	SecondarySection int                  `json:"secondary_section"`
 	ActionButton     GroupsActionButton   `json:"action_button"`
 	Phone            string               `json:"phone"`
+
+	RecognizePhoto int `json:"recognize_photo"`
+
+	MarketServices GroupsMarketServices `json:"market_services"`
+	Narratives     int                  `json:"narratives"`
+	Clips          int                  `json:"clips"`
+	Textlives      int                  `json:"textlives"`
+	Youla          GroupsYoula          `json:"youla"`
+}
+
+// GroupsMarketServices struct.
+type GroupsMarketServices struct {
+	Enabled         BaseBoolInt         `json:"enabled"`
+	CanMessage      BaseBoolInt         `json:"can_message"`
+	CommentsEnabled BaseBoolInt         `json:"comments_enabled"`
+	ContactID       int                 `json:"contact_id"`
+	Currency        MarketCurrency      `json:"currency"`
+	ViewType        GroupsSelectedItems `json:"view_type"`
+	BlockName       GroupsSelectedItems `json:"block_name"`
+	ButtonLabel     GroupsSelectedItems `json:"button_label"`
+}
+
+// GroupsSelectedItems struct.
+type GroupsSelectedItems struct {
+	SelectedItemID int64                `json:"selected_item_id"`
+	Items          []BaseObjectWithName `json:"items"`
+}
+
+// GroupsYoula struct.
+type GroupsYoula struct {
+	CategoryTree  GroupsYoulaCategory `json:"category_tree"`
+	GroupSettings GroupsYoulaSettings `json:"group_settings"`
+}
+
+// GroupsYoulaCategory struct.
+type GroupsYoulaCategory struct {
+	ID            int                      `json:"id"`
+	Title         string                   `json:"title"`
+	Subcategories []GroupsYoulaSubcategory `json:"subcategories"`
+}
+
+// GroupsYoulaSubcategory struct.
+type GroupsYoulaSubcategory struct {
+	ID            int                      `json:"id"`
+	Title         string                   `json:"title"`
+	ParentID      int                      `json:"parent_id"`
+	Subcategories []GroupsYoulaSubcategory `json:"subcategories"`
+}
+
+// GroupsYoulaSettings struct.
+type GroupsYoulaSettings struct {
+	IsActive              BaseBoolInt `json:"is_active"`
+	IsModerated           BaseBoolInt `json:"is_moderated"`
+	ShowModerationSetting BaseBoolInt `json:"show_moderation_setting"`
+	ModerationStatus      int         `json:"moderation_status"`
+	DeclineReason         string      `json:"decline_reason"`
+	GroupMode             int         `json:"group_mode"`
+	SelectedCategoryIDS   []int       `json:"selected_category_ids"`
+	Lat                   float64     `json:"lat"`
+	Long                  float64     `json:"long"`
+	Radius                float64     `json:"radius"`
+	RadiusArea            string      `json:"radius_area"`
+	Address               string      `json:"address"`
+	Radiuses              []float64   `json:"radiuses"`
 }
 
 // GroupsSectionsList struct.
@@ -532,6 +667,53 @@ func (g *GroupsSectionsList) UnmarshalJSON(data []byte) error {
 	return nil
 }
 
+// DecodeMsgpack need for decode dynamic array (Example: [1, "Фотографии"]) to struct.
+func (g *GroupsSectionsList) DecodeMsgpack(dec *msgpack.Decoder) error {
+	data, err := dec.DecodeRaw()
+	if err != nil {
+		return err
+	}
+
+	var alias []interface{}
+
+	err = msgpack.Unmarshal(data, &alias)
+	if err != nil {
+		return err
+	}
+
+	if len(alias) != 2 {
+		return &json.UnmarshalTypeError{
+			Value: string(data),
+			Type:  reflect.TypeOf((*GroupsSectionsList)(nil)),
+		}
+	}
+
+	id, ok := alias[0].(int8)
+	if !ok {
+		return &json.UnmarshalTypeError{
+			Value:  string(data),
+			Type:   reflect.TypeOf((*GroupsSectionsList)(nil)),
+			Struct: "GroupsSectionsList",
+			Field:  "ID",
+		}
+	}
+
+	name, ok := alias[1].(string)
+	if !ok {
+		return &json.UnmarshalTypeError{
+			Value:  string(data),
+			Type:   reflect.TypeOf((*GroupsSectionsList)(nil)),
+			Struct: "GroupsSectionsList",
+			Field:  "Name",
+		}
+	}
+
+	g.ID = int(id)
+	g.Name = name
+
+	return nil
+}
+
 // GroupsActionType for action_button in groups.
 type GroupsActionType string
 
@@ -685,7 +867,10 @@ type GroupsLongPollServer struct {
 	Ts     string `json:"ts"`     // Number of the last event
 }
 
-// TODO: func (g GroupsLongPollServer) GetURL() string {
+// GetURL return link.
+func (lp GroupsLongPollServer) GetURL(wait int) string {
+	return fmt.Sprintf("%s?act=a_check&key=%s&ts=%s&wait=%d", lp.Server, lp.Key, lp.Ts, wait)
+}
 
 // GroupsLongPollSettings struct.
 type GroupsLongPollSettings struct {
@@ -714,12 +899,14 @@ type GroupsMarketInfo struct {
 	Enabled         BaseBoolInt       `json:"enabled"`                 // Information whether the market is enabled
 	CommentsEnabled BaseBoolInt       `json:"comments_enabled,omitempty"`
 	CanMessage      BaseBoolInt       `json:"can_message,omitempty"`
+	IsHsEnabled     BaseBoolInt       `json:"is_hs_enabled,omitempty"`
 	MainAlbumID     int               `json:"main_album_id,omitempty"` // Main market album ID
 	PriceMax        string            `json:"price_max,omitempty"`     // Maximum price
 	PriceMin        string            `json:"price_min,omitempty"`     // Minimum price
 	Wiki            PagesWikipageFull `json:"wiki,omitempty"`
 	CityIDs         []int             `json:"city_ids"`
 	CountryIDs      []int             `json:"country_ids,omitempty"`
+	MinOrderPrice   MarketPrice       `json:"min_order_price,omitempty"`
 }
 
 // GroupsGroupRole Role type.

vendor/github.com/SevereCloud/vksdk/v2/object/market.go

@@ -4,6 +4,9 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
+
+	"github.com/vmihailenco/msgpack/v5"
+	"github.com/vmihailenco/msgpack/v5/msgpcode"
 )
 
 // Information whether the MarketMarketItem is available.
@@ -100,6 +103,36 @@ func (market *MarketMarketItem) UnmarshalJSON(data []byte) error {
 	return nil
 }
 
+// DecodeMsgpack MarketMarketItem.
+//
+// BUG(VK): https://github.com/SevereCloud/vksdk/issues/147
+func (market *MarketMarketItem) DecodeMsgpack(dec *msgpack.Decoder) error {
+	data, err := dec.DecodeRaw()
+	if err != nil {
+		return err
+	}
+
+	if bytes.Equal(data, []byte{msgpcode.False}) {
+		return nil
+	}
+
+	type renamedMarketMarketItem MarketMarketItem
+
+	var r renamedMarketMarketItem
+
+	d := msgpack.NewDecoder(bytes.NewReader(data))
+	d.SetCustomStructTag("json")
+
+	err = d.Decode(&r)
+	if err != nil {
+		return err
+	}
+
+	*market = MarketMarketItem(r)
+
+	return nil
+}
+
 // MarketMarketItemProperty struct.
 type MarketMarketItemProperty struct {
 	VariantID    int    `json:"variant_id"`
@@ -151,6 +184,36 @@ func (m *MarketPrice) UnmarshalJSON(data []byte) error {
 	return nil
 }
 
+// DecodeMsgpack MarketPrice.
+//
+// BUG(VK): unavailable product, in fave.get return [].
+func (m *MarketPrice) DecodeMsgpack(dec *msgpack.Decoder) error {
+	data, err := dec.DecodeRaw()
+	if err != nil {
+		return err
+	}
+
+	if bytes.Equal(data, []byte{msgpcode.FixedArrayLow}) {
+		return nil
+	}
+
+	type renamedMarketPrice MarketPrice
+
+	var r renamedMarketPrice
+
+	d := msgpack.NewDecoder(bytes.NewReader(data))
+	d.SetCustomStructTag("json")
+
+	err = d.Decode(&r)
+	if err != nil {
+		return err
+	}
+
+	*m = MarketPrice(r)
+
+	return nil
+}
+
 // MarketSection struct.
 type MarketSection struct {
 	ID   int    `json:"id"`   // Section ID

vendor/github.com/SevereCloud/vksdk/v2/object/messages.go

@@ -79,6 +79,7 @@ type MessagesMessage struct {
 	UpdateTime   int    `json:"update_time"`   // Date when the message has been updated in Unixtime
 	MembersCount int    `json:"members_count"` // Members number
 	ExpireTTL    int    `json:"expire_ttl"`
+	MessageTag   string `json:"message_tag"` // for https://notify.mail.ru/
 }
 
 // MessagesBasePayload struct.
@@ -378,7 +379,8 @@ type MessagesTemplateElementCarousel struct {
 	Title       string                                `json:"title,omitempty"`
 	Action      MessagesTemplateElementCarouselAction `json:"action,omitempty"`
 	Description string                                `json:"description,omitempty"`
-	Photo       *PhotosPhoto                          `json:"photo,omitempty"`
+	Photo       *PhotosPhoto                          `json:"photo,omitempty"`    // Only read
+	PhotoID     string                                `json:"photo_id,omitempty"` // Only for send
 	Buttons     []MessagesKeyboardButton              `json:"buttons,omitempty"`
 }
 
@@ -474,20 +476,24 @@ type MessagesChatPushSettings struct {
 
 // MessagesChatSettingsPhoto struct.
 type MessagesChatSettingsPhoto struct {
-	Photo100       string      `json:"photo_100"`
-	Photo200       string      `json:"photo_200"`
-	Photo50        string      `json:"photo_50"`
-	IsDefaultPhoto BaseBoolInt `json:"is_default_photo"`
+	Photo100           string      `json:"photo_100"`
+	Photo200           string      `json:"photo_200"`
+	Photo50            string      `json:"photo_50"`
+	IsDefaultPhoto     BaseBoolInt `json:"is_default_photo"`
+	IsDefaultCallPhoto bool        `json:"is_default_call_photo"`
 }
 
 // MessagesConversation struct.
 type MessagesConversation struct {
-	CanWrite       MessagesConversationCanWrite     `json:"can_write"`
-	ChatSettings   MessagesConversationChatSettings `json:"chat_settings"`
-	InRead         int                              `json:"in_read"`         // Last message user have read
-	LastMessageID  int                              `json:"last_message_id"` // ID of the last message in conversation
-	Mentions       []int                            `json:"mentions"`        // IDs of messages with mentions
-	MessageRequest string                           `json:"message_request"`
+	CanWrite                  MessagesConversationCanWrite     `json:"can_write"`
+	ChatSettings              MessagesConversationChatSettings `json:"chat_settings"`
+	InRead                    int                              `json:"in_read"`         // Last message user have read
+	LastMessageID             int                              `json:"last_message_id"` // ID of the last message in conversation
+	Mentions                  []int                            `json:"mentions"`        // IDs of messages with mentions
+	MessageRequest            string                           `json:"message_request"`
+	LastConversationMessageID int                              `json:"last_conversation_message_id"`
+	InReadCMID                int                              `json:"in_read_cmid"`
+	OutReadCMID               int                              `json:"out_read_cmid"`
 
 	// Last outcoming message have been read by the opponent.
 	OutRead         int                              `json:"out_read"`
@@ -496,6 +502,10 @@ type MessagesConversation struct {
 	Important       BaseBoolInt                      `json:"important"`
 	Unanswered      BaseBoolInt                      `json:"unanswered"`
 	IsMarkedUnread  BaseBoolInt                      `json:"is_marked_unread"`
+	CanSendMoney    BaseBoolInt                      `json:"can_send_money"`
+	CanReceiveMoney BaseBoolInt                      `json:"can_receive_money"`
+	IsNew           BaseBoolInt                      `json:"is_new"`
+	IsArchived      BaseBoolInt                      `json:"is_archived"`
 	UnreadCount     int                              `json:"unread_count"` // Unread messages number
 	CurrentKeyboard MessagesKeyboard                 `json:"current_keyboard"`
 	SortID          struct {
@@ -531,6 +541,7 @@ type MessagesConversationChatSettings struct {
 		CanCall              BaseBoolInt `json:"can_call"`
 		CanUseMassMentions   BaseBoolInt `json:"can_use_mass_mentions"`
 		CanChangeServiceType BaseBoolInt `json:"can_change_service_type"`
+		CanChangeStyle       BaseBoolInt `json:"can_change_style"`
 	} `json:"acl"`
 	IsGroupChannel   BaseBoolInt             `json:"is_group_channel"`
 	IsDisappearing   BaseBoolInt             `json:"is_disappearing"`
@@ -560,6 +571,7 @@ type MessagesChatPermissions struct {
 	SeeInviteLink   MessagesChatPermission `json:"see_invite_link"`
 	Call            MessagesChatPermission `json:"call"`
 	ChangeAdmins    MessagesChatPermission `json:"change_admins"`
+	ChangeStyle     MessagesChatPermission `json:"change_style"`
 }
 
 // MessagesConversationPeer struct.
@@ -571,9 +583,11 @@ type MessagesConversationPeer struct {
 
 // MessagesConversationPushSettings struct.
 type MessagesConversationPushSettings struct {
-	DisabledUntil   int         `json:"disabled_until"`
-	DisabledForever BaseBoolInt `json:"disabled_forever"`
-	NoSound         BaseBoolInt `json:"no_sound"`
+	DisabledUntil        int         `json:"disabled_until"`
+	DisabledForever      BaseBoolInt `json:"disabled_forever"`
+	NoSound              BaseBoolInt `json:"no_sound"`
+	DisabledMentions     BaseBoolInt `json:"disabled_mentions"`
+	DisabledMassMentions BaseBoolInt `json:"disabled_mass_mentions"`
 }
 
 // MessagesConversationWithMessage struct.

vendor/github.com/SevereCloud/vksdk/v2/object/notifications.go

@@ -1,7 +1,5 @@
 package object // import "github.com/SevereCloud/vksdk/v2/object"
 
-import "encoding/json"
-
 // NotificationsFeedback struct.
 type NotificationsFeedback struct {
 	Attachments []WallWallpostAttachment `json:"attachments"`
@@ -16,8 +14,8 @@ type NotificationsFeedback struct {
 // NotificationsNotification struct.
 type NotificationsNotification struct {
 	Date     int                `json:"date"` // Date when the event has been occurred
-	Feedback json.RawMessage    `json:"feedback"`
-	Parent   json.RawMessage    `json:"parent"`
+	Feedback RawMessage         `json:"feedback"`
+	Parent   RawMessage         `json:"parent"`
 	Reply    NotificationsReply `json:"reply"`
 	Type     string             `json:"type"` // Notification type
 }

vendor/github.com/SevereCloud/vksdk/v2/object/object.go

@@ -9,6 +9,8 @@ import (
 	"bytes"
 	"encoding/json"
 	"reflect"
+
+	"github.com/vmihailenco/msgpack/v5"
 )
 
 // Attachment interface.
@@ -42,6 +44,44 @@ func (b *BaseBoolInt) UnmarshalJSON(data []byte) (err error) {
 	return
 }
 
+// DecodeMsgpack func.
+func (b *BaseBoolInt) DecodeMsgpack(dec *msgpack.Decoder) (err error) {
+	data, err := dec.DecodeRaw()
+	if err != nil {
+		return err
+	}
+
+	var (
+		valueInt  int
+		valueBool bool
+	)
+
+	switch {
+	case msgpack.Unmarshal(data, &valueBool) == nil:
+		*b = BaseBoolInt(valueBool)
+	case msgpack.Unmarshal(data, &valueInt) == nil:
+		if valueInt == 1 {
+			*b = true
+			break
+		}
+
+		if valueInt == 0 {
+			*b = false
+			break
+		}
+
+		fallthrough
+	default:
+		// return msgpack error
+		err = &json.UnmarshalTypeError{
+			Value: string(data),
+			Type:  reflect.TypeOf((*BaseBoolInt)(nil)),
+		}
+	}
+
+	return err
+}
+
 // BaseCountry struct.
 type BaseCountry struct {
 	ID    int    `json:"id"`
@@ -151,6 +191,33 @@ func (obj *BaseImage) UnmarshalJSON(data []byte) (err error) {
 	return err
 }
 
+// DecodeMsgpack is required to support images with `src` field.
+func (obj *BaseImage) DecodeMsgpack(dec *msgpack.Decoder) (err error) {
+	type renamedBaseImage struct {
+		Height float64 `msgpack:"height"`
+		URL    string  `msgpack:"url"`
+		Src    string  `msgpack:"src"`
+		Width  float64 `msgpack:"width"`
+		Type   string  `msgpack:"type"`
+	}
+
+	var renamedObj renamedBaseImage
+
+	err = dec.Decode(&renamedObj)
+
+	obj.Height = renamedObj.Height
+	obj.Width = renamedObj.Width
+	obj.Type = renamedObj.Type
+
+	if renamedObj.Src == "" {
+		obj.URL = renamedObj.URL
+	} else {
+		obj.URL = renamedObj.Src
+	}
+
+	return err
+}
+
 // BaseLikes struct.
 type BaseLikes struct {
 	UserLikes BaseBoolInt `json:"user_likes"` // Information whether current user likes
@@ -346,9 +413,11 @@ const (
 type Privacy struct {
 	Category PrivacyCategory `json:"category,omitempty"`
 	Lists    struct {
-		Allowed []int `json:"allowed"`
+		Allowed  []int `json:"allowed"`
+		Excluded []int `json:"excluded"`
 	} `json:"lists,omitempty"`
 	Owners struct {
+		Allowed  []int `json:"allowed"`
 		Excluded []int `json:"excluded"`
 	} `json:"owners,omitempty"`
 }

vendor/github.com/SevereCloud/vksdk/v2/object/photos.go

@@ -239,6 +239,7 @@ type PhotosPhotoFull struct {
 	Photo1280  string             `json:"photo_1280"` // URL of image with 1280 px width
 	Photo2560  string             `json:"photo_2560"` // URL of image with 2560 px width
 	Sizes      []PhotosPhotoSizes `json:"sizes"`
+	OrigPhoto  PhotosPhotoSizes   `json:"orig_photo"`
 }
 
 // ToAttachment return attachment format.

vendor/github.com/SevereCloud/vksdk/v2/object/raw.go

@@ -0,0 +1,39 @@
+package object // import "github.com/SevereCloud/vksdk/v2/object"
+
+import "github.com/vmihailenco/msgpack/v5"
+
+// RawMessage is a raw encoded JSON or MessagePack value.
+type RawMessage []byte
+
+// MarshalJSON returns m as the JSON encoding of m.
+func (m RawMessage) MarshalJSON() ([]byte, error) {
+	if m == nil {
+		return []byte("null"), nil
+	}
+
+	return m, nil
+}
+
+// UnmarshalJSON sets *m to a copy of data.
+func (m *RawMessage) UnmarshalJSON(data []byte) error {
+	*m = append((*m)[0:0], data...)
+	return nil
+}
+
+// EncodeMsgpack write m as the MessagePack encoding of m.
+func (m RawMessage) EncodeMsgpack(enc *msgpack.Encoder) error {
+	_, err := enc.Writer().Write(m)
+	return err
+}
+
+// DecodeMsgpack sets *m to a copy of data.
+func (m *RawMessage) DecodeMsgpack(dec *msgpack.Decoder) error {
+	msg, err := dec.DecodeRaw()
+	if err != nil {
+		return err
+	}
+
+	*m = RawMessage(msg)
+
+	return nil
+}

vendor/github.com/SevereCloud/vksdk/v2/object/stories.go

@@ -127,6 +127,7 @@ type StoriesStory struct {
 	Seen                 BaseBoolInt              `json:"seen"`
 	IsOwnerPinned        BaseBoolInt              `json:"is_owner_pinned"`
 	IsOneTime            BaseBoolInt              `json:"is_one_time"`
+	IsAdvice             BaseBoolInt              `json:"is_advice,omitempty"`
 	NeedMute             BaseBoolInt              `json:"need_mute"`
 	MuteReply            BaseBoolInt              `json:"mute_reply"`
 	CanLike              BaseBoolInt              `json:"can_like"`
@@ -152,6 +153,7 @@ type StoriesStory struct {
 	NarrativesCount      int                      `json:"narratives_count"`
 	FirstNarrativeTitle  string                   `json:"first_narrative_title"`
 	Questions            StoriesQuestions         `json:"questions"`
+	ReactionSetID        string                   `json:"reaction_set_id"`
 }
 
 // StoriesFeedItemType type.

vendor/github.com/SevereCloud/vksdk/v2/object/users.go

@@ -4,6 +4,9 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
+
+	"github.com/vmihailenco/msgpack/v5"
+	"github.com/vmihailenco/msgpack/v5/msgpcode"
 )
 
 // User relationship status.
@@ -258,6 +261,36 @@ func (personal *UsersPersonal) UnmarshalJSON(data []byte) error {
 	return nil
 }
 
+// DecodeMsgpack UsersPersonal.
+//
+// BUG(VK): UsersPersonal return [].
+func (personal *UsersPersonal) DecodeMsgpack(dec *msgpack.Decoder) error {
+	data, err := dec.DecodeRaw()
+	if err != nil {
+		return err
+	}
+
+	if bytes.Equal(data, []byte{msgpcode.FixedArrayLow}) {
+		return nil
+	}
+
+	type renamedUsersPersonal UsersPersonal
+
+	var r renamedUsersPersonal
+
+	d := msgpack.NewDecoder(bytes.NewReader(data))
+	d.SetCustomStructTag("json")
+
+	err = d.Decode(&r)
+	if err != nil {
+		return err
+	}
+
+	*personal = UsersPersonal(r)
+
+	return nil
+}
+
 // UsersRelative struct.
 type UsersRelative struct {
 	BirthDate string `json:"birth_date"` // Date of child birthday (format dd.mm.yyyy)

vendor/github.com/SevereCloud/vksdk/v2/object/utils.go

@@ -1,5 +1,13 @@
 package object // import "github.com/SevereCloud/vksdk/v2/object"
 
+import (
+	"bytes"
+	"encoding/json"
+
+	"github.com/vmihailenco/msgpack/v5"
+	"github.com/vmihailenco/msgpack/v5/msgpcode"
+)
+
 // UtilsDomainResolvedType object type.
 const (
 	UtilsDomainResolvedTypeUser        = "user"
@@ -15,6 +23,58 @@ type UtilsDomainResolved struct {
 	Type     string `json:"type"`
 }
 
+// UnmarshalJSON UtilsDomainResolved.
+//
+// BUG(VK): UtilsDomainResolved return [].
+func (link *UtilsDomainResolved) UnmarshalJSON(data []byte) error {
+	if bytes.Equal(data, []byte("[]")) {
+		return nil
+	}
+
+	type renamedUtilsDomainResolved UtilsDomainResolved
+
+	var r renamedUtilsDomainResolved
+
+	err := json.Unmarshal(data, &r)
+	if err != nil {
+		return err
+	}
+
+	*link = UtilsDomainResolved(r)
+
+	return nil
+}
+
+// DecodeMsgpack UtilsDomainResolved.
+//
+// BUG(VK): UtilsDomainResolved return [].
+func (link *UtilsDomainResolved) DecodeMsgpack(dec *msgpack.Decoder) error {
+	data, err := dec.DecodeRaw()
+	if err != nil {
+		return err
+	}
+
+	if bytes.Equal(data, []byte{msgpcode.FixedArrayLow}) {
+		return nil
+	}
+
+	type renamedUtilsDomainResolved UtilsDomainResolved
+
+	var r renamedUtilsDomainResolved
+
+	d := msgpack.NewDecoder(bytes.NewReader(data))
+	d.SetCustomStructTag("json")
+
+	err = d.Decode(&r)
+	if err != nil {
+		return err
+	}
+
+	*link = UtilsDomainResolved(r)
+
+	return nil
+}
+
 // UtilsLastShortenedLink struct.
 type UtilsLastShortenedLink struct {
 	AccessKey string `json:"access_key"` // Access key for private stats

vendor/github.com/SevereCloud/vksdk/v2/object/video.go

@@ -12,6 +12,9 @@ type VideoVideo struct {
 	// Date when the video has been added in Unixtime.
 	AddingDate int `json:"adding_date"`
 
+	// Date when the video has been released in Unixtime.
+	ReleaseDate int `json:"release_date"`
+
 	// Information whether current user can add the video.
 	CanAdd BaseBoolInt `json:"can_add"`
 
@@ -27,12 +30,17 @@ type VideoVideo struct {
 	// Information whether current user can like the video.
 	CanLike BaseBoolInt `json:"can_like"`
 
+	// Information whether current user can download the video.
+	CanDownload BaseBoolInt `json:"can_download"`
+
 	// Information whether current user can repost this video.
 	CanRepost         BaseBoolInt       `json:"can_repost"`
 	CanSubscribe      BaseBoolInt       `json:"can_subscribe"`
 	CanAttachLink     BaseBoolInt       `json:"can_attach_link"`
 	IsFavorite        BaseBoolInt       `json:"is_favorite"`
 	IsPrivate         BaseBoolInt       `json:"is_private"`
+	IsExplicit        BaseBoolInt       `json:"is_explicit"`
+	IsSubscribed      BaseBoolInt       `json:"is_subscribed"`
 	Added             BaseBoolInt       `json:"added"`
 	Repeat            BaseBoolInt       `json:"repeat"` // Information whether the video is repeated
 	ContentRestricted int               `json:"content_restricted"`
@@ -43,6 +51,7 @@ type VideoVideo struct {
 	Description       string            `json:"description"` // Video description
 	Duration          int               `json:"duration"`    // Video duration in seconds
 	Files             VideoVideoFiles   `json:"files"`
+	Trailer           VideoVideoFiles   `json:"trailer,omitempty"`
 	FirstFrame        []VideoVideoImage `json:"first_frame"`
 	Image             []VideoVideoImage `json:"image"`
 	Height            int               `json:"height"`   // Video height
@@ -56,22 +65,27 @@ type VideoVideo struct {
 	Photo1280         string            `json:"photo_1280"` // URL of the preview image with 1280 px in width
 
 	// URL of the page with a player that can be used to play the video in the browser.
-	Player                   string            `json:"player"`
-	Processing               int               `json:"processing"` // Returns if the video is processing
-	Title                    string            `json:"title"`      // Video title
-	Type                     string            `json:"type"`
-	Views                    int               `json:"views"` // Number of views
-	Width                    int               `json:"width"` // Video width
-	Platform                 string            `json:"platform"`
-	LocalViews               int               `json:"local_views"`
-	Likes                    BaseLikesInfo     `json:"likes"`   // Count of likes
-	Reposts                  BaseRepostsInfo   `json:"reposts"` // Count of views
-	TrackCode                string            `json:"track_code"`
-	PrivacyView              Privacy           `json:"privacy_view"`
-	PrivacyComment           Privacy           `json:"privacy_comment"`
-	ActionButton             VideoActionButton `json:"action_button"`
-	Restriction              VideoRestriction  `json:"restriction"`
-	ContentRestrictedMessage string            `json:"content_restricted_message"`
+	Player                   string               `json:"player"`
+	Processing               int                  `json:"processing"` // Returns if the video is processing
+	Title                    string               `json:"title"`      // Video title
+	Subtitle                 string               `json:"subtitle"`   // Video subtitle
+	Type                     string               `json:"type"`
+	Views                    int                  `json:"views"` // Number of views
+	Width                    int                  `json:"width"` // Video width
+	Platform                 string               `json:"platform"`
+	LocalViews               int                  `json:"local_views"`
+	Likes                    BaseLikesInfo        `json:"likes"`   // Count of likes
+	Reposts                  BaseRepostsInfo      `json:"reposts"` // Count of views
+	TrackCode                string               `json:"track_code"`
+	PrivacyView              Privacy              `json:"privacy_view"`
+	PrivacyComment           Privacy              `json:"privacy_comment"`
+	ActionButton             VideoActionButton    `json:"action_button"`
+	Restriction              VideoRestriction     `json:"restriction"`
+	ContentRestrictedMessage string               `json:"content_restricted_message"`
+	MainArtists              []AudioAudioArtist   `json:"main_artists"`
+	FeaturedArtists          []AudioAudioArtist   `json:"featured_artists"`
+	Genres                   []BaseObjectWithName `json:"genres"`
+	OvID                     string               `json:"ov_id,omitempty"`
 }
 
 // ToAttachment return attachment format.
@@ -112,16 +126,20 @@ type VideoSnippet struct {
 
 // VideoVideoFiles struct.
 type VideoVideoFiles struct {
-	External string `json:"external"` // URL of the external player
-	Mp4_1080 string `json:"mp4_1080"` // URL of the mpeg4 file with 1080p quality
-	Mp4_1440 string `json:"mp4_1440"` // URL of the mpeg4 file with 2k quality
-	Mp4_2160 string `json:"mp4_2160"` // URL of the mpeg4 file with 4k quality
-	Mp4_240  string `json:"mp4_240"`  // URL of the mpeg4 file with 240p quality
-	Mp4_360  string `json:"mp4_360"`  // URL of the mpeg4 file with 360p quality
-	Mp4_480  string `json:"mp4_480"`  // URL of the mpeg4 file with 480p quality
-	Mp4_720  string `json:"mp4_720"`  // URL of the mpeg4 file with 720p quality
-	Live     string `json:"live"`
-	HLS      string `json:"hls"`
+	External     string `json:"external,omitempty"` // URL of the external player
+	Mp4_1080     string `json:"mp4_1080,omitempty"` // URL of the mpeg4 file with 1080p quality
+	Mp4_1440     string `json:"mp4_1440,omitempty"` // URL of the mpeg4 file with 2k quality
+	Mp4_2160     string `json:"mp4_2160,omitempty"` // URL of the mpeg4 file with 4k quality
+	Mp4_240      string `json:"mp4_240,omitempty"`  // URL of the mpeg4 file with 240p quality
+	Mp4_360      string `json:"mp4_360,omitempty"`  // URL of the mpeg4 file with 360p quality
+	Mp4_480      string `json:"mp4_480,omitempty"`  // URL of the mpeg4 file with 480p quality
+	Mp4_720      string `json:"mp4_720,omitempty"`  // URL of the mpeg4 file with 720p quality
+	Live         string `json:"live,omitempty"`
+	HLS          string `json:"hls,omitempty"`
+	DashUni      string `json:"dash_uni,omitempty"`
+	DashSep      string `json:"dash_sep,omitempty"`
+	DashWebm     string `json:"dash_webm,omitempty"`
+	FailoverHost string `json:"failover_host,omitempty"`
 }
 
 // VideoCatBlock struct.

vendor/github.com/SevereCloud/vksdk/v2/object/wall.go

@@ -128,7 +128,7 @@ const (
 	WallPostTypeSuggest  = "suggest"
 )
 
-// WallWallpost  struct.
+// WallWallpost struct.
 type WallWallpost struct {
 	AccessKey      string                   `json:"access_key"` // Access key to private object
 	ID             int                      `json:"id"`         // Post ID
@@ -156,14 +156,17 @@ type WallWallpost struct {
 	IsPinned       BaseBoolInt              `json:"is_pinned"`
 	IsFavorite     BaseBoolInt              `json:"is_favorite"` // Information whether the post in favorites list
 	IsArchived     BaseBoolInt              `json:"is_archived"` // Is post archived, only for post owners
+	IsDeleted      BaseBoolInt              `json:"is_deleted"`
 	MarkedAsAds    BaseBoolInt              `json:"marked_as_ads"`
 	Edited         int                      `json:"edited"` // Date of editing in Unixtime
 	Copyright      WallPostCopyright        `json:"copyright"`
 	PostID         int                      `json:"post_id"`
 	ParentsStack   []int                    `json:"parents_stack"`
-	Donut          WallWallpostDonut        `json:"donut"` // need api v5.125
+	Donut          WallWallpostDonut        `json:"donut"`
 	ShortTextRate  float64                  `json:"short_text_rate"`
 	CarouselOffset int                      `json:"carousel_offset"`
+	Header         WallWallpostHeader       `json:"header"`
+	Hash           string                   `json:"hash"`
 }
 
 // Attachment type.
@@ -235,8 +238,10 @@ type WallWallpostToID struct {
 	IsFavorite    BaseBoolInt              `json:"is_favorite"` // Information whether the post in favorites list
 	MarkedAsAds   BaseBoolInt              `json:"marked_as_ads"`
 	ParentsStack  []int                    `json:"parents_stack"`
-	Donut         WallWallpostDonut        `json:"donut"` // need api v5.125
+	Donut         WallWallpostDonut        `json:"donut"`
 	ShortTextRate float64                  `json:"short_text_rate"`
+	Views         WallViews                `json:"views"` // Count of views
+	Header        WallWallpostHeader       `json:"header"`
 }
 
 // WallWallpostDonut info about VK Donut.
@@ -255,3 +260,15 @@ type WallPostCopyright struct {
 	Type string `json:"type"`
 	Name string `json:"name"`
 }
+
+// WallWallpostHeader struct.
+type WallWallpostHeader struct {
+	Type              string                              `json:"type"`
+	CustomDescription WallWallpostHeaderCustomDescription `json:"custom_description"`
+}
+
+// WallWallpostHeaderCustomDescription struct.
+type WallWallpostHeaderCustomDescription struct {
+	SourceID int `json:"source_id"`
+	Date     int `json:"date"`
+}

vendor/github.com/SevereCloud/vksdk/v2/object/widgets.go

@@ -45,6 +45,9 @@ type WidgetsWidgetComment struct {
 	Views       struct {
 		Count int `json:"count"`
 	} `json:"views"`
+	Donut         WallWallpostDonut  `json:"donut"`
+	ShortTextRate float64            `json:"short_text_rate"`
+	Header        WallWallpostHeader `json:"header"`
 }
 
 // WidgetsWidgetLikes struct.

vendor/github.com/klauspost/compress/.gitattributes

@@ -0,0 +1,2 @@
+* -text
+*.bin -text -diff

vendor/github.com/klauspost/compress/.gitignore

@@ -0,0 +1,25 @@
+# Compiled Object files, Static and Dynamic libs (Shared Objects)
+*.o
+*.a
+*.so
+
+# Folders
+_obj
+_test
+
+# Architecture specific extensions/prefixes
+*.[568vq]
+[568vq].out
+
+*.cgo1.go
+*.cgo2.c
+_cgo_defun.c
+_cgo_gotypes.go
+_cgo_export.*
+
+_testmain.go
+
+*.exe
+*.test
+*.prof
+/s2/cmd/_s2sx/sfx-exe

vendor/github.com/klauspost/compress/.goreleaser.yml

@@ -0,0 +1,141 @@
+# This is an example goreleaser.yaml file with some sane defaults.
+# Make sure to check the documentation at http://goreleaser.com
+before:
+  hooks:
+    - ./gen.sh
+    - go install mvdan.cc/garble@latest
+
+builds:
+  -
+    id: "s2c"
+    binary: s2c
+    main: ./s2/cmd/s2c/main.go
+    flags:
+      - -trimpath
+    env:
+      - CGO_ENABLED=0
+    goos:
+      - aix
+      - linux
+      - freebsd
+      - netbsd
+      - windows
+      - darwin
+    goarch:
+      - 386
+      - amd64
+      - arm
+      - arm64
+      - ppc64
+      - ppc64le
+      - mips64
+      - mips64le
+    goarm:
+      - 7
+    gobinary: garble
+  -
+    id: "s2d"
+    binary: s2d
+    main: ./s2/cmd/s2d/main.go
+    flags:
+      - -trimpath
+    env:
+      - CGO_ENABLED=0
+    goos:
+      - aix
+      - linux
+      - freebsd
+      - netbsd
+      - windows
+      - darwin
+    goarch:
+      - 386
+      - amd64
+      - arm
+      - arm64
+      - ppc64
+      - ppc64le
+      - mips64
+      - mips64le
+    goarm:
+      - 7
+    gobinary: garble
+  -
+    id: "s2sx"
+    binary: s2sx
+    main: ./s2/cmd/_s2sx/main.go
+    flags:
+      - -modfile=s2sx.mod
+      - -trimpath
+    env:
+      - CGO_ENABLED=0
+    goos:
+      - aix
+      - linux
+      - freebsd
+      - netbsd
+      - windows
+      - darwin
+    goarch:
+      - 386
+      - amd64
+      - arm
+      - arm64
+      - ppc64
+      - ppc64le
+      - mips64
+      - mips64le
+    goarm:
+      - 7
+    gobinary: garble
+
+archives:
+  -
+    id: s2-binaries
+    name_template: "s2-{{ .Os }}_{{ .Arch }}_{{ .Version }}"
+    replacements:
+      aix: AIX
+      darwin: OSX
+      linux: Linux
+      windows: Windows
+      386: i386
+      amd64: x86_64
+      freebsd: FreeBSD
+      netbsd: NetBSD
+    format_overrides:
+      - goos: windows
+        format: zip
+    files:
+      - unpack/*
+      - s2/LICENSE
+      - s2/README.md
+checksum:
+  name_template: 'checksums.txt'
+snapshot:
+  name_template: "{{ .Tag }}-next"
+changelog:
+  sort: asc
+  filters:
+    exclude:
+    - '^doc:'
+    - '^docs:'
+    - '^test:'
+    - '^tests:'
+    - '^Update\sREADME.md'
+
+nfpms:
+  -
+    file_name_template: "s2_package_{{ .Version }}_{{ .Os }}_{{ .Arch }}"
+    vendor: Klaus Post
+    homepage: https://github.com/klauspost/compress
+    maintainer: Klaus Post <klauspost@gmail.com>
+    description: S2 Compression Tool
+    license: BSD 3-Clause
+    formats:
+      - deb
+      - rpm
+    replacements:
+      darwin: Darwin
+      linux: Linux
+      freebsd: FreeBSD
+      amd64: x86_64

vendor/github.com/klauspost/compress/README.md

@@ -0,0 +1,452 @@
+# compress
+
+This package provides various compression algorithms.
+
+* [zstandard](https://github.com/klauspost/compress/tree/master/zstd#zstd) compression and decompression in pure Go.
+* [S2](https://github.com/klauspost/compress/tree/master/s2#s2-compression) is a high performance replacement for Snappy.
+* Optimized [deflate](https://godoc.org/github.com/klauspost/compress/flate) packages which can be used as a dropin replacement for [gzip](https://godoc.org/github.com/klauspost/compress/gzip), [zip](https://godoc.org/github.com/klauspost/compress/zip) and [zlib](https://godoc.org/github.com/klauspost/compress/zlib).
+* [snappy](https://github.com/klauspost/compress/tree/master/snappy) is a drop-in replacement for `github.com/golang/snappy` offering better compression and concurrent streams.
+* [huff0](https://github.com/klauspost/compress/tree/master/huff0) and [FSE](https://github.com/klauspost/compress/tree/master/fse) implementations for raw entropy encoding.
+* [gzhttp](https://github.com/klauspost/compress/tree/master/gzhttp) Provides client and server wrappers for handling gzipped requests efficiently.
+* [pgzip](https://github.com/klauspost/pgzip) is a separate package that provides a very fast parallel gzip implementation.
+* [fuzz package](https://github.com/klauspost/compress-fuzz) for fuzz testing all compressors/decompressors here.
+
+[![Go Reference](https://pkg.go.dev/badge/klauspost/compress.svg)](https://pkg.go.dev/github.com/klauspost/compress?tab=subdirectories)
+[![Go](https://github.com/klauspost/compress/actions/workflows/go.yml/badge.svg)](https://github.com/klauspost/compress/actions/workflows/go.yml)
+[![Sourcegraph Badge](https://sourcegraph.com/github.com/klauspost/compress/-/badge.svg)](https://sourcegraph.com/github.com/klauspost/compress?badge)
+
+# changelog
+
+* Jan 11, 2022 (v1.14.1)
+	* s2: Add stream index in [#462](https://github.com/klauspost/compress/pull/462)
+	* flate: Speed and efficiency improvements in [#439](https://github.com/klauspost/compress/pull/439) [#461](https://github.com/klauspost/compress/pull/461) [#455](https://github.com/klauspost/compress/pull/455) [#452](https://github.com/klauspost/compress/pull/452) [#458](https://github.com/klauspost/compress/pull/458)
+	* zstd: Performance improvement in [#420]( https://github.com/klauspost/compress/pull/420) [#456](https://github.com/klauspost/compress/pull/456) [#437](https://github.com/klauspost/compress/pull/437) [#467](https://github.com/klauspost/compress/pull/467) [#468](https://github.com/klauspost/compress/pull/468)
+	* zstd: add arm64 xxhash assembly in [#464](https://github.com/klauspost/compress/pull/464)
+	* Add garbled for binaries for s2 in [#445](https://github.com/klauspost/compress/pull/445)
+
+* Aug 30, 2021 (v1.13.5)
+	* gz/zlib/flate: Alias stdlib errors [#425](https://github.com/klauspost/compress/pull/425)
+	* s2: Add block support to commandline tools [#413](https://github.com/klauspost/compress/pull/413)
+	* zstd: pooledZipWriter should return Writers to the same pool [#426](https://github.com/klauspost/compress/pull/426)
+	* Removed golang/snappy as external dependency for tests [#421](https://github.com/klauspost/compress/pull/421)
+
+* Aug 12, 2021 (v1.13.4)
+	* Add [snappy replacement package](https://github.com/klauspost/compress/tree/master/snappy).
+	* zstd: Fix incorrect encoding in "best" mode [#415](https://github.com/klauspost/compress/pull/415)
+
+* Aug 3, 2021 (v1.13.3) 
+	* zstd: Improve Best compression [#404](https://github.com/klauspost/compress/pull/404)
+	* zstd: Fix WriteTo error forwarding [#411](https://github.com/klauspost/compress/pull/411)
+	* gzhttp: Return http.HandlerFunc instead of http.Handler. Unlikely breaking change. [#406](https://github.com/klauspost/compress/pull/406)
+	* s2sx: Fix max size error [#399](https://github.com/klauspost/compress/pull/399)
+	* zstd: Add optional stream content size on reset [#401](https://github.com/klauspost/compress/pull/401)
+	* zstd: use SpeedBestCompression for level >= 10 [#410](https://github.com/klauspost/compress/pull/410)
+
+* Jun 14, 2021 (v1.13.1)
+	* s2: Add full Snappy output support  [#396](https://github.com/klauspost/compress/pull/396)
+	* zstd: Add configurable [Decoder window](https://pkg.go.dev/github.com/klauspost/compress/zstd#WithDecoderMaxWindow) size [#394](https://github.com/klauspost/compress/pull/394)
+	* gzhttp: Add header to skip compression  [#389](https://github.com/klauspost/compress/pull/389)
+	* s2: Improve speed with bigger output margin  [#395](https://github.com/klauspost/compress/pull/395)
+
+* Jun 3, 2021 (v1.13.0)
+	* Added [gzhttp](https://github.com/klauspost/compress/tree/master/gzhttp#gzip-handler) which allows wrapping HTTP servers and clients with GZIP compressors.
+	* zstd: Detect short invalid signatures [#382](https://github.com/klauspost/compress/pull/382)
+	* zstd: Spawn decoder goroutine only if needed. [#380](https://github.com/klauspost/compress/pull/380)
+
+* May 25, 2021 (v1.12.3)
+	* deflate: Better/faster Huffman encoding [#374](https://github.com/klauspost/compress/pull/374)
+	* deflate: Allocate less for history. [#375](https://github.com/klauspost/compress/pull/375)
+	* zstd: Forward read errors [#373](https://github.com/klauspost/compress/pull/373) 
+
+* Apr 27, 2021 (v1.12.2)
+	* zstd: Improve better/best compression [#360](https://github.com/klauspost/compress/pull/360) [#364](https://github.com/klauspost/compress/pull/364) [#365](https://github.com/klauspost/compress/pull/365)
+	* zstd: Add helpers to compress/decompress zstd inside zip files [#363](https://github.com/klauspost/compress/pull/363)
+	* deflate: Improve level 5+6 compression [#367](https://github.com/klauspost/compress/pull/367)
+	* s2: Improve better/best compression [#358](https://github.com/klauspost/compress/pull/358) [#359](https://github.com/klauspost/compress/pull/358)
+	* s2: Load after checking src limit on amd64. [#362](https://github.com/klauspost/compress/pull/362)
+	* s2sx: Limit max executable size [#368](https://github.com/klauspost/compress/pull/368) 
+
+* Apr 14, 2021 (v1.12.1)
+	* snappy package removed. Upstream added as dependency.
+	* s2: Better compression in "best" mode [#353](https://github.com/klauspost/compress/pull/353)
+	* s2sx: Add stdin input and detect pre-compressed from signature [#352](https://github.com/klauspost/compress/pull/352)
+	* s2c/s2d: Add http as possible input [#348](https://github.com/klauspost/compress/pull/348)
+	* s2c/s2d/s2sx: Always truncate when writing files [#352](https://github.com/klauspost/compress/pull/352)
+	* zstd: Reduce memory usage further when using [WithLowerEncoderMem](https://pkg.go.dev/github.com/klauspost/compress/zstd#WithLowerEncoderMem) [#346](https://github.com/klauspost/compress/pull/346)
+	* s2: Fix potential problem with amd64 assembly and profilers [#349](https://github.com/klauspost/compress/pull/349)
+
+<details>
+	<summary>See changes prior to v1.12.1</summary>
+	
+* Mar 26, 2021 (v1.11.13)
+	* zstd: Big speedup on small dictionary encodes [#344](https://github.com/klauspost/compress/pull/344) [#345](https://github.com/klauspost/compress/pull/345)
+	* zstd: Add [WithLowerEncoderMem](https://pkg.go.dev/github.com/klauspost/compress/zstd#WithLowerEncoderMem) encoder option [#336](https://github.com/klauspost/compress/pull/336)
+	* deflate: Improve entropy compression [#338](https://github.com/klauspost/compress/pull/338)
+	* s2: Clean up and minor performance improvement in best [#341](https://github.com/klauspost/compress/pull/341)
+
+* Mar 5, 2021 (v1.11.12)
+	* s2: Add `s2sx` binary that creates [self extracting archives](https://github.com/klauspost/compress/tree/master/s2#s2sx-self-extracting-archives).
+	* s2: Speed up decompression on non-assembly platforms [#328](https://github.com/klauspost/compress/pull/328)
+
+* Mar 1, 2021 (v1.11.9)
+	* s2: Add ARM64 decompression assembly. Around 2x output speed. [#324](https://github.com/klauspost/compress/pull/324)
+	* s2: Improve "better" speed and efficiency. [#325](https://github.com/klauspost/compress/pull/325)
+	* s2: Fix binaries.
+
+* Feb 25, 2021 (v1.11.8)
+	* s2: Fixed occational out-of-bounds write on amd64. Upgrade recommended.
+	* s2: Add AMD64 assembly for better mode. 25-50% faster. [#315](https://github.com/klauspost/compress/pull/315)
+	* s2: Less upfront decoder allocation. [#322](https://github.com/klauspost/compress/pull/322)
+	* zstd: Faster "compression" of incompressible data. [#314](https://github.com/klauspost/compress/pull/314)
+	* zip: Fix zip64 headers. [#313](https://github.com/klauspost/compress/pull/313)
+  
+* Jan 14, 2021 (v1.11.7)
+	* Use Bytes() interface to get bytes across packages. [#309](https://github.com/klauspost/compress/pull/309)
+	* s2: Add 'best' compression option.  [#310](https://github.com/klauspost/compress/pull/310)
+	* s2: Add ReaderMaxBlockSize, changes `s2.NewReader` signature to include varargs. [#311](https://github.com/klauspost/compress/pull/311)
+	* s2: Fix crash on small better buffers. [#308](https://github.com/klauspost/compress/pull/308)
+	* s2: Clean up decoder. [#312](https://github.com/klauspost/compress/pull/312)
+
+* Jan 7, 2021 (v1.11.6)
+	* zstd: Make decoder allocations smaller [#306](https://github.com/klauspost/compress/pull/306)
+	* zstd: Free Decoder resources when Reset is called with a nil io.Reader  [#305](https://github.com/klauspost/compress/pull/305)
+
+* Dec 20, 2020 (v1.11.4)
+	* zstd: Add Best compression mode [#304](https://github.com/klauspost/compress/pull/304)
+	* Add header decoder [#299](https://github.com/klauspost/compress/pull/299)
+	* s2: Add uncompressed stream option [#297](https://github.com/klauspost/compress/pull/297)
+	* Simplify/speed up small blocks with known max size. [#300](https://github.com/klauspost/compress/pull/300)
+	* zstd: Always reset literal dict encoder [#303](https://github.com/klauspost/compress/pull/303)
+
+* Nov 15, 2020 (v1.11.3)
+	* inflate: 10-15% faster decompression  [#293](https://github.com/klauspost/compress/pull/293)
+	* zstd: Tweak DecodeAll default allocation [#295](https://github.com/klauspost/compress/pull/295)
+
+* Oct 11, 2020 (v1.11.2)
+	* s2: Fix out of bounds read in "better" block compression [#291](https://github.com/klauspost/compress/pull/291)
+
+* Oct 1, 2020 (v1.11.1)
+	* zstd: Set allLitEntropy true in default configuration [#286](https://github.com/klauspost/compress/pull/286)
+
+* Sept 8, 2020 (v1.11.0)
+	* zstd: Add experimental compression [dictionaries](https://github.com/klauspost/compress/tree/master/zstd#dictionaries) [#281](https://github.com/klauspost/compress/pull/281)
+	* zstd: Fix mixed Write and ReadFrom calls [#282](https://github.com/klauspost/compress/pull/282)
+	* inflate/gz: Limit variable shifts, ~5% faster decompression [#274](https://github.com/klauspost/compress/pull/274)
+</details>
+
+<details>
+	<summary>See changes prior to v1.11.0</summary>
+ 
+* July 8, 2020 (v1.10.11) 
+	* zstd: Fix extra block when compressing with ReadFrom. [#278](https://github.com/klauspost/compress/pull/278)
+	* huff0: Also populate compression table when reading decoding table. [#275](https://github.com/klauspost/compress/pull/275)
+	
+* June 23, 2020 (v1.10.10) 
+	* zstd: Skip entropy compression in fastest mode when no matches. [#270](https://github.com/klauspost/compress/pull/270)
+	
+* June 16, 2020 (v1.10.9): 
+	* zstd: API change for specifying dictionaries. See [#268](https://github.com/klauspost/compress/pull/268)
+	* zip: update CreateHeaderRaw to handle zip64 fields. [#266](https://github.com/klauspost/compress/pull/266)
+	* Fuzzit tests removed. The service has been purchased and is no longer available.
+	
+* June 5, 2020 (v1.10.8): 
+	* 1.15x faster zstd block decompression. [#265](https://github.com/klauspost/compress/pull/265)
+	
+* June 1, 2020 (v1.10.7): 
+	* Added zstd decompression [dictionary support](https://github.com/klauspost/compress/tree/master/zstd#dictionaries)
+	* Increase zstd decompression speed up to 1.19x.  [#259](https://github.com/klauspost/compress/pull/259)
+	* Remove internal reset call in zstd compression and reduce allocations. [#263](https://github.com/klauspost/compress/pull/263)
+	
+* May 21, 2020: (v1.10.6) 
+	* zstd: Reduce allocations while decoding. [#258](https://github.com/klauspost/compress/pull/258), [#252](https://github.com/klauspost/compress/pull/252)
+	* zstd: Stricter decompression checks.
+	
+* April 12, 2020: (v1.10.5)
+	* s2-commands: Flush output when receiving SIGINT. [#239](https://github.com/klauspost/compress/pull/239)
+	
+* Apr 8, 2020: (v1.10.4) 
+	* zstd: Minor/special case optimizations. [#251](https://github.com/klauspost/compress/pull/251),  [#250](https://github.com/klauspost/compress/pull/250),  [#249](https://github.com/klauspost/compress/pull/249),  [#247](https://github.com/klauspost/compress/pull/247)
+* Mar 11, 2020: (v1.10.3) 
+	* s2: Use S2 encoder in pure Go mode for Snappy output as well. [#245](https://github.com/klauspost/compress/pull/245)
+	* s2: Fix pure Go block encoder. [#244](https://github.com/klauspost/compress/pull/244)
+	* zstd: Added "better compression" mode. [#240](https://github.com/klauspost/compress/pull/240)
+	* zstd: Improve speed of fastest compression mode by 5-10% [#241](https://github.com/klauspost/compress/pull/241)
+	* zstd: Skip creating encoders when not needed. [#238](https://github.com/klauspost/compress/pull/238)
+	
+* Feb 27, 2020: (v1.10.2) 
+	* Close to 50% speedup in inflate (gzip/zip decompression). [#236](https://github.com/klauspost/compress/pull/236) [#234](https://github.com/klauspost/compress/pull/234) [#232](https://github.com/klauspost/compress/pull/232)
+	* Reduce deflate level 1-6 memory usage up to 59%. [#227](https://github.com/klauspost/compress/pull/227)
+	
+* Feb 18, 2020: (v1.10.1)
+	* Fix zstd crash when resetting multiple times without sending data. [#226](https://github.com/klauspost/compress/pull/226)
+	* deflate: Fix dictionary use on level 1-6. [#224](https://github.com/klauspost/compress/pull/224)
+	* Remove deflate writer reference when closing. [#224](https://github.com/klauspost/compress/pull/224)
+	
+* Feb 4, 2020: (v1.10.0) 
+	* Add optional dictionary to [stateless deflate](https://pkg.go.dev/github.com/klauspost/compress/flate?tab=doc#StatelessDeflate). Breaking change, send `nil` for previous behaviour. [#216](https://github.com/klauspost/compress/pull/216)
+	* Fix buffer overflow on repeated small block deflate.  [#218](https://github.com/klauspost/compress/pull/218)
+	* Allow copying content from an existing ZIP file without decompressing+compressing. [#214](https://github.com/klauspost/compress/pull/214)
+	* Added [S2](https://github.com/klauspost/compress/tree/master/s2#s2-compression) AMD64 assembler and various optimizations. Stream speed >10GB/s.  [#186](https://github.com/klauspost/compress/pull/186)
+
+</details>
+
+<details>
+	<summary>See changes prior to v1.10.0</summary>
+
+* Jan 20,2020 (v1.9.8) Optimize gzip/deflate with better size estimates and faster table generation. [#207](https://github.com/klauspost/compress/pull/207) by [luyu6056](https://github.com/luyu6056),  [#206](https://github.com/klauspost/compress/pull/206).
+* Jan 11, 2020: S2 Encode/Decode will use provided buffer if capacity is big enough. [#204](https://github.com/klauspost/compress/pull/204) 
+* Jan 5, 2020: (v1.9.7) Fix another zstd regression in v1.9.5 - v1.9.6 removed.
+* Jan 4, 2020: (v1.9.6) Regression in v1.9.5 fixed causing corrupt zstd encodes in rare cases.
+* Jan 4, 2020: Faster IO in [s2c + s2d commandline tools](https://github.com/klauspost/compress/tree/master/s2#commandline-tools) compression/decompression. [#192](https://github.com/klauspost/compress/pull/192)
+* Dec 29, 2019: Removed v1.9.5 since fuzz tests showed a compatibility problem with the reference zstandard decoder.
+* Dec 29, 2019: (v1.9.5) zstd: 10-20% faster block compression. [#199](https://github.com/klauspost/compress/pull/199)
+* Dec 29, 2019: [zip](https://godoc.org/github.com/klauspost/compress/zip) package updated with latest Go features
+* Dec 29, 2019: zstd: Single segment flag condintions tweaked. [#197](https://github.com/klauspost/compress/pull/197)
+* Dec 18, 2019: s2: Faster compression when ReadFrom is used. [#198](https://github.com/klauspost/compress/pull/198)
+* Dec 10, 2019: s2: Fix repeat length output when just above at 16MB limit.
+* Dec 10, 2019: zstd: Add function to get decoder as io.ReadCloser. [#191](https://github.com/klauspost/compress/pull/191)
+* Dec 3, 2019: (v1.9.4) S2: limit max repeat length. [#188](https://github.com/klauspost/compress/pull/188)
+* Dec 3, 2019: Add [WithNoEntropyCompression](https://godoc.org/github.com/klauspost/compress/zstd#WithNoEntropyCompression) to zstd [#187](https://github.com/klauspost/compress/pull/187)
+* Dec 3, 2019: Reduce memory use for tests. Check for leaked goroutines.
+* Nov 28, 2019 (v1.9.3) Less allocations in stateless deflate.
+* Nov 28, 2019: 5-20% Faster huff0 decode. Impacts zstd as well. [#184](https://github.com/klauspost/compress/pull/184)
+* Nov 12, 2019 (v1.9.2) Added [Stateless Compression](#stateless-compression) for gzip/deflate.
+* Nov 12, 2019: Fixed zstd decompression of large single blocks. [#180](https://github.com/klauspost/compress/pull/180)
+* Nov 11, 2019: Set default  [s2c](https://github.com/klauspost/compress/tree/master/s2#commandline-tools) block size to 4MB.
+* Nov 11, 2019: Reduce inflate memory use by 1KB.
+* Nov 10, 2019: Less allocations in deflate bit writer.
+* Nov 10, 2019: Fix inconsistent error returned by zstd decoder.
+* Oct 28, 2019 (v1.9.1) ztsd: Fix crash when compressing blocks. [#174](https://github.com/klauspost/compress/pull/174)
+* Oct 24, 2019 (v1.9.0) zstd: Fix rare data corruption [#173](https://github.com/klauspost/compress/pull/173)
+* Oct 24, 2019 zstd: Fix huff0 out of buffer write [#171](https://github.com/klauspost/compress/pull/171) and always return errors [#172](https://github.com/klauspost/compress/pull/172) 
+* Oct 10, 2019: Big deflate rewrite, 30-40% faster with better compression [#105](https://github.com/klauspost/compress/pull/105)
+
+</details>
+
+<details>
+	<summary>See changes prior to v1.9.0</summary>
+
+* Oct 10, 2019: (v1.8.6) zstd: Allow partial reads to get flushed data. [#169](https://github.com/klauspost/compress/pull/169)
+* Oct 3, 2019: Fix inconsistent results on broken zstd streams.
+* Sep 25, 2019: Added `-rm` (remove source files) and `-q` (no output except errors) to `s2c` and `s2d` [commands](https://github.com/klauspost/compress/tree/master/s2#commandline-tools)
+* Sep 16, 2019: (v1.8.4) Add `s2c` and `s2d` [commandline tools](https://github.com/klauspost/compress/tree/master/s2#commandline-tools).
+* Sep 10, 2019: (v1.8.3) Fix s2 decoder [Skip](https://godoc.org/github.com/klauspost/compress/s2#Reader.Skip).
+* Sep 7, 2019: zstd: Added [WithWindowSize](https://godoc.org/github.com/klauspost/compress/zstd#WithWindowSize), contributed by [ianwilkes](https://github.com/ianwilkes).
+* Sep 5, 2019: (v1.8.2) Add [WithZeroFrames](https://godoc.org/github.com/klauspost/compress/zstd#WithZeroFrames) which adds full zero payload block encoding option.
+* Sep 5, 2019: Lazy initialization of zstandard predefined en/decoder tables.
+* Aug 26, 2019: (v1.8.1) S2: 1-2% compression increase in "better" compression mode.
+* Aug 26, 2019: zstd: Check maximum size of Huffman 1X compressed literals while decoding.
+* Aug 24, 2019: (v1.8.0) Added [S2 compression](https://github.com/klauspost/compress/tree/master/s2#s2-compression), a high performance replacement for Snappy. 
+* Aug 21, 2019: (v1.7.6) Fixed minor issues found by fuzzer. One could lead to zstd not decompressing.
+* Aug 18, 2019: Add [fuzzit](https://fuzzit.dev/) continuous fuzzing.
+* Aug 14, 2019: zstd: Skip incompressible data 2x faster.  [#147](https://github.com/klauspost/compress/pull/147)
+* Aug 4, 2019 (v1.7.5): Better literal compression. [#146](https://github.com/klauspost/compress/pull/146)
+* Aug 4, 2019: Faster zstd compression. [#143](https://github.com/klauspost/compress/pull/143) [#144](https://github.com/klauspost/compress/pull/144)
+* Aug 4, 2019: Faster zstd decompression. [#145](https://github.com/klauspost/compress/pull/145) [#143](https://github.com/klauspost/compress/pull/143) [#142](https://github.com/klauspost/compress/pull/142)
+* July 15, 2019 (v1.7.4): Fix double EOF block in rare cases on zstd encoder.
+* July 15, 2019 (v1.7.3): Minor speedup/compression increase in default zstd encoder.
+* July 14, 2019: zstd decoder: Fix decompression error on multiple uses with mixed content.
+* July 7, 2019 (v1.7.2): Snappy update, zstd decoder potential race fix.
+* June 17, 2019: zstd decompression bugfix.
+* June 17, 2019: fix 32 bit builds.
+* June 17, 2019: Easier use in modules (less dependencies).
+* June 9, 2019: New stronger "default" [zstd](https://github.com/klauspost/compress/tree/master/zstd#zstd) compression mode. Matches zstd default compression ratio.
+* June 5, 2019: 20-40% throughput in [zstandard](https://github.com/klauspost/compress/tree/master/zstd#zstd) compression and better compression.
+* June 5, 2019: deflate/gzip compression: Reduce memory usage of lower compression levels.
+* June 2, 2019: Added [zstandard](https://github.com/klauspost/compress/tree/master/zstd#zstd) compression!
+* May 25, 2019: deflate/gzip: 10% faster bit writer, mostly visible in lower levels.
+* Apr 22, 2019: [zstd](https://github.com/klauspost/compress/tree/master/zstd#zstd) decompression added.
+* Aug 1, 2018: Added [huff0 README](https://github.com/klauspost/compress/tree/master/huff0#huff0-entropy-compression).
+* Jul 8, 2018: Added [Performance Update 2018](#performance-update-2018) below.
+* Jun 23, 2018: Merged [Go 1.11 inflate optimizations](https://go-review.googlesource.com/c/go/+/102235). Go 1.9 is now required. Backwards compatible version tagged with [v1.3.0](https://github.com/klauspost/compress/releases/tag/v1.3.0).
+* Apr 2, 2018: Added [huff0](https://godoc.org/github.com/klauspost/compress/huff0) en/decoder. Experimental for now, API may change.
+* Mar 4, 2018: Added [FSE Entropy](https://godoc.org/github.com/klauspost/compress/fse) en/decoder. Experimental for now, API may change.
+* Nov 3, 2017: Add compression [Estimate](https://godoc.org/github.com/klauspost/compress#Estimate) function.
+* May 28, 2017: Reduce allocations when resetting decoder.
+* Apr 02, 2017: Change back to official crc32, since changes were merged in Go 1.7.
+* Jan 14, 2017: Reduce stack pressure due to array copies. See [Issue #18625](https://github.com/golang/go/issues/18625).
+* Oct 25, 2016: Level 2-4 have been rewritten and now offers significantly better performance than before.
+* Oct 20, 2016: Port zlib changes from Go 1.7 to fix zlib writer issue. Please update.
+* Oct 16, 2016: Go 1.7 changes merged. Apples to apples this package is a few percent faster, but has a significantly better balance between speed and compression per level. 
+* Mar 24, 2016: Always attempt Huffman encoding on level 4-7. This improves base 64 encoded data compression.
+* Mar 24, 2016: Small speedup for level 1-3.
+* Feb 19, 2016: Faster bit writer, level -2 is 15% faster, level 1 is 4% faster.
+* Feb 19, 2016: Handle small payloads faster in level 1-3.
+* Feb 19, 2016: Added faster level 2 + 3 compression modes.
+* Feb 19, 2016: [Rebalanced compression levels](https://blog.klauspost.com/rebalancing-deflate-compression-levels/), so there is a more even progresssion in terms of compression. New default level is 5.
+* Feb 14, 2016: Snappy: Merge upstream changes. 
+* Feb 14, 2016: Snappy: Fix aggressive skipping.
+* Feb 14, 2016: Snappy: Update benchmark.
+* Feb 13, 2016: Deflate: Fixed assembler problem that could lead to sub-optimal compression.
+* Feb 12, 2016: Snappy: Added AMD64 SSE 4.2 optimizations to matching, which makes easy to compress material run faster. Typical speedup is around 25%.
+* Feb 9, 2016: Added Snappy package fork. This version is 5-7% faster, much more on hard to compress content.
+* Jan 30, 2016: Optimize level 1 to 3 by not considering static dictionary or storing uncompressed. ~4-5% speedup.
+* Jan 16, 2016: Optimization on deflate level 1,2,3 compression.
+* Jan 8 2016: Merge [CL 18317](https://go-review.googlesource.com/#/c/18317): fix reading, writing of zip64 archives.
+* Dec 8 2015: Make level 1 and -2 deterministic even if write size differs.
+* Dec 8 2015: Split encoding functions, so hashing and matching can potentially be inlined. 1-3% faster on AMD64. 5% faster on other platforms.
+* Dec 8 2015: Fixed rare [one byte out-of bounds read](https://github.com/klauspost/compress/issues/20). Please update!
+* Nov 23 2015: Optimization on token writer. ~2-4% faster. Contributed by [@dsnet](https://github.com/dsnet).
+* Nov 20 2015: Small optimization to bit writer on 64 bit systems.
+* Nov 17 2015: Fixed out-of-bound errors if the underlying Writer returned an error. See [#15](https://github.com/klauspost/compress/issues/15).
+* Nov 12 2015: Added [io.WriterTo](https://golang.org/pkg/io/#WriterTo) support to gzip/inflate.
+* Nov 11 2015: Merged [CL 16669](https://go-review.googlesource.com/#/c/16669/4): archive/zip: enable overriding (de)compressors per file
+* Oct 15 2015: Added skipping on uncompressible data. Random data speed up >5x.
+
+</details>
+
+# deflate usage
+
+* [High Throughput Benchmark](http://blog.klauspost.com/go-gzipdeflate-benchmarks/).
+* [Small Payload/Webserver Benchmarks](http://blog.klauspost.com/gzip-performance-for-go-webservers/).
+* [Linear Time Compression](http://blog.klauspost.com/constant-time-gzipzip-compression/).
+* [Re-balancing Deflate Compression Levels](https://blog.klauspost.com/rebalancing-deflate-compression-levels/)
+
+The packages are drop-in replacements for standard libraries. Simply replace the import path to use them:
+
+| old import         | new import                              | Documentation
+|--------------------|-----------------------------------------|--------------------|
+| `compress/gzip`    | `github.com/klauspost/compress/gzip`    | [gzip](https://pkg.go.dev/github.com/klauspost/compress/gzip?tab=doc)
+| `compress/zlib`    | `github.com/klauspost/compress/zlib`    | [zlib](https://pkg.go.dev/github.com/klauspost/compress/zlib?tab=doc)
+| `archive/zip`      | `github.com/klauspost/compress/zip`     | [zip](https://pkg.go.dev/github.com/klauspost/compress/zip?tab=doc)
+| `compress/flate`   | `github.com/klauspost/compress/flate`   | [flate](https://pkg.go.dev/github.com/klauspost/compress/flate?tab=doc)
+
+* Optimized [deflate](https://godoc.org/github.com/klauspost/compress/flate) packages which can be used as a dropin replacement for [gzip](https://godoc.org/github.com/klauspost/compress/gzip), [zip](https://godoc.org/github.com/klauspost/compress/zip) and [zlib](https://godoc.org/github.com/klauspost/compress/zlib).
+
+You may also be interested in [pgzip](https://github.com/klauspost/pgzip), which is a drop in replacement for gzip, which support multithreaded compression on big files and the optimized [crc32](https://github.com/klauspost/crc32) package used by these packages.
+
+The packages contains the same as the standard library, so you can use the godoc for that: [gzip](http://golang.org/pkg/compress/gzip/), [zip](http://golang.org/pkg/archive/zip/),  [zlib](http://golang.org/pkg/compress/zlib/), [flate](http://golang.org/pkg/compress/flate/).
+
+Currently there is only minor speedup on decompression (mostly CRC32 calculation).
+
+Memory usage is typically 1MB for a Writer. stdlib is in the same range. 
+If you expect to have a lot of concurrently allocated Writers consider using 
+the stateless compress described below.
+
+# Stateless compression
+
+This package offers stateless compression as a special option for gzip/deflate. 
+It will do compression but without maintaining any state between Write calls.
+
+This means there will be no memory kept between Write calls, but compression and speed will be suboptimal.
+
+This is only relevant in cases where you expect to run many thousands of compressors concurrently, 
+but with very little activity. This is *not* intended for regular web servers serving individual requests.  
+
+Because of this, the size of actual Write calls will affect output size.
+
+In gzip, specify level `-3` / `gzip.StatelessCompression` to enable.
+
+For direct deflate use, NewStatelessWriter and StatelessDeflate are available. See [documentation](https://godoc.org/github.com/klauspost/compress/flate#NewStatelessWriter)
+
+A `bufio.Writer` can of course be used to control write sizes. For example, to use a 4KB buffer:
+
+```
+	// replace 'ioutil.Discard' with your output.
+	gzw, err := gzip.NewWriterLevel(ioutil.Discard, gzip.StatelessCompression)
+	if err != nil {
+		return err
+	}
+	defer gzw.Close()
+
+	w := bufio.NewWriterSize(gzw, 4096)
+	defer w.Flush()
+	
+	// Write to 'w' 
+```
+
+This will only use up to 4KB in memory when the writer is idle. 
+
+Compression is almost always worse than the fastest compression level 
+and each write will allocate (a little) memory. 
+
+# Performance Update 2018
+
+It has been a while since we have been looking at the speed of this package compared to the standard library, so I thought I would re-do my tests and give some overall recommendations based on the current state. All benchmarks have been performed with Go 1.10 on my Desktop Intel(R) Core(TM) i7-2600 CPU @3.40GHz. Since I last ran the tests, I have gotten more RAM, which means tests with big files are no longer limited by my SSD.
+
+The raw results are in my [updated spreadsheet](https://docs.google.com/spreadsheets/d/1nuNE2nPfuINCZJRMt6wFWhKpToF95I47XjSsc-1rbPQ/edit?usp=sharing). Due to cgo changes and upstream updates i could not get the cgo version of gzip to compile. Instead I included the [zstd](https://github.com/datadog/zstd) cgo implementation. If I get cgo gzip to work again, I might replace the results in the sheet.
+
+The columns to take note of are: *MB/s* - the throughput. *Reduction* - the data size reduction in percent of the original. *Rel Speed* relative speed compared to the standard library at the same level. *Smaller* - how many percent smaller is the compressed output compared to stdlib. Negative means the output was bigger. *Loss* means the loss (or gain) in compression as a percentage difference of the input.
+
+The `gzstd` (standard library gzip) and `gzkp` (this package gzip) only uses one CPU core. [`pgzip`](https://github.com/klauspost/pgzip), [`bgzf`](https://github.com/biogo/hts/tree/master/bgzf) uses all 4 cores. [`zstd`](https://github.com/DataDog/zstd) uses one core, and is a beast (but not Go, yet).
+
+
+## Overall differences.
+
+There appears to be a roughly 5-10% speed advantage over the standard library when comparing at similar compression levels.
+
+The biggest difference you will see is the result of [re-balancing](https://blog.klauspost.com/rebalancing-deflate-compression-levels/) the compression levels. I wanted by library to give a smoother transition between the compression levels than the standard library.
+
+This package attempts to provide a more smooth transition, where "1" is taking a lot of shortcuts, "5" is the reasonable trade-off and "9" is the "give me the best compression", and the values in between gives something reasonable in between. The standard library has big differences in levels 1-4, but levels 5-9 having no significant gains - often spending a lot more time than can be justified by the achieved compression.
+
+There are links to all the test data in the [spreadsheet](https://docs.google.com/spreadsheets/d/1nuNE2nPfuINCZJRMt6wFWhKpToF95I47XjSsc-1rbPQ/edit?usp=sharing) in the top left field on each tab.
+
+## Web Content
+
+This test set aims to emulate typical use in a web server. The test-set is 4GB data in 53k files, and is a mixture of (mostly) HTML, JS, CSS.
+
+Since level 1 and 9 are close to being the same code, they are quite close. But looking at the levels in-between the differences are quite big.
+
+Looking at level 6, this package is 88% faster, but will output about 6% more data. For a web server, this means you can serve 88% more data, but have to pay for 6% more bandwidth. You can draw your own conclusions on what would be the most expensive for your case.
+
+## Object files
+
+This test is for typical data files stored on a server. In this case it is a collection of Go precompiled objects. They are very compressible.
+
+The picture is similar to the web content, but with small differences since this is very compressible. Levels 2-3 offer good speed, but is sacrificing quite a bit of compression. 
+
+The standard library seems suboptimal on level 3 and 4 - offering both worse compression and speed than level 6 & 7 of this package respectively.
+
+## Highly Compressible File
+
+This is a JSON file with very high redundancy. The reduction starts at 95% on level 1, so in real life terms we are dealing with something like a highly redundant stream of data, etc.
+
+It is definitely visible that we are dealing with specialized content here, so the results are very scattered. This package does not do very well at levels 1-4, but picks up significantly at level 5 and levels 7 and 8 offering great speed for the achieved compression.
+
+So if you know you content is extremely compressible you might want to go slightly higher than the defaults. The standard library has a huge gap between levels 3 and 4 in terms of speed (2.75x slowdown), so it offers little "middle ground".
+
+## Medium-High Compressible
+
+This is a pretty common test corpus: [enwik9](http://mattmahoney.net/dc/textdata.html). It contains the first 10^9 bytes of the English Wikipedia dump on Mar. 3, 2006. This is a very good test of typical text based compression and more data heavy streams.
+
+We see a similar picture here as in "Web Content". On equal levels some compression is sacrificed for more speed. Level 5 seems to be the best trade-off between speed and size, beating stdlib level 3 in both.
+
+## Medium Compressible
+
+I will combine two test sets, one [10GB file set](http://mattmahoney.net/dc/10gb.html) and a VM disk image (~8GB). Both contain different data types and represent a typical backup scenario.
+
+The most notable thing is how quickly the standard library drops to very low compression speeds around level 5-6 without any big gains in compression. Since this type of data is fairly common, this does not seem like good behavior.
+
+
+## Un-compressible Content
+
+This is mainly a test of how good the algorithms are at detecting un-compressible input. The standard library only offers this feature with very conservative settings at level 1. Obviously there is no reason for the algorithms to try to compress input that cannot be compressed.  The only downside is that it might skip some compressible data on false detections.
+
+
+## Huffman only compression
+
+This compression library adds a special compression level, named `HuffmanOnly`, which allows near linear time compression. This is done by completely disabling matching of previous data, and only reduce the number of bits to represent each character. 
+
+This means that often used characters, like 'e' and ' ' (space) in text use the fewest bits to represent, and rare characters like '¤' takes more bits to represent. For more information see [wikipedia](https://en.wikipedia.org/wiki/Huffman_coding) or this nice [video](https://youtu.be/ZdooBTdW5bM).
+
+Since this type of compression has much less variance, the compression speed is mostly unaffected by the input data, and is usually more than *180MB/s* for a single core.
+
+The downside is that the compression ratio is usually considerably worse than even the fastest conventional compression. The compression ratio can never be better than 8:1 (12.5%). 
+
+The linear time compression can be used as a "better than nothing" mode, where you cannot risk the encoder to slow down on some content. For comparison, the size of the "Twain" text is *233460 bytes* (+29% vs. level 1) and encode speed is 144MB/s (4.5x level 1). So in this case you trade a 30% size increase for a 4 times speedup.
+
+For more information see my blog post on [Fast Linear Time Compression](http://blog.klauspost.com/constant-time-gzipzip-compression/).
+
+This is implemented on Go 1.7 as "Huffman Only" mode, though not exposed for gzip.
+
+# Other packages
+
+Here are other packages of good quality and pure Go (no cgo wrappers or autoconverted code):
+
+* [github.com/pierrec/lz4](https://github.com/pierrec/lz4) - strong multithreaded LZ4 compression.
+* [github.com/cosnicolaou/pbzip2](https://github.com/cosnicolaou/pbzip2) - multithreaded bzip2 decompression.
+* [github.com/dsnet/compress](https://github.com/dsnet/compress) - brotli decompression, bzip2 writer.
+
+# license
+
+This code is licensed under the same conditions as the original Go code. See LICENSE file.

vendor/github.com/klauspost/compress/compressible.go

@@ -0,0 +1,85 @@
+package compress
+
+import "math"
+
+// Estimate returns a normalized compressibility estimate of block b.
+// Values close to zero are likely uncompressible.
+// Values above 0.1 are likely to be compressible.
+// Values above 0.5 are very compressible.
+// Very small lengths will return 0.
+func Estimate(b []byte) float64 {
+	if len(b) < 16 {
+		return 0
+	}
+
+	// Correctly predicted order 1
+	hits := 0
+	lastMatch := false
+	var o1 [256]byte
+	var hist [256]int
+	c1 := byte(0)
+	for _, c := range b {
+		if c == o1[c1] {
+			// We only count a hit if there was two correct predictions in a row.
+			if lastMatch {
+				hits++
+			}
+			lastMatch = true
+		} else {
+			lastMatch = false
+		}
+		o1[c1] = c
+		c1 = c
+		hist[c]++
+	}
+
+	// Use x^0.6 to give better spread
+	prediction := math.Pow(float64(hits)/float64(len(b)), 0.6)
+
+	// Calculate histogram distribution
+	variance := float64(0)
+	avg := float64(len(b)) / 256
+
+	for _, v := range hist {
+		Δ := float64(v) - avg
+		variance += Δ * Δ
+	}
+
+	stddev := math.Sqrt(float64(variance)) / float64(len(b))
+	exp := math.Sqrt(1 / float64(len(b)))
+
+	// Subtract expected stddev
+	stddev -= exp
+	if stddev < 0 {
+		stddev = 0
+	}
+	stddev *= 1 + exp
+
+	// Use x^0.4 to give better spread
+	entropy := math.Pow(stddev, 0.4)
+
+	// 50/50 weight between prediction and histogram distribution
+	return math.Pow((prediction+entropy)/2, 0.9)
+}
+
+// ShannonEntropyBits returns the number of bits minimum required to represent
+// an entropy encoding of the input bytes.
+// https://en.wiktionary.org/wiki/Shannon_entropy
+func ShannonEntropyBits(b []byte) int {
+	if len(b) == 0 {
+		return 0
+	}
+	var hist [256]int
+	for _, c := range b {
+		hist[c]++
+	}
+	shannon := float64(0)
+	invTotal := 1.0 / float64(len(b))
+	for _, v := range hist[:] {
+		if v > 0 {
+			n := float64(v)
+			shannon += math.Ceil(-math.Log2(n*invTotal) * n)
+		}
+	}
+	return int(math.Ceil(shannon))
+}

vendor/github.com/klauspost/compress/fse/README.md

@@ -0,0 +1,79 @@
+# Finite State Entropy
+
+This package provides Finite State Entropy encoding and decoding.
+            
+Finite State Entropy (also referenced as [tANS](https://en.wikipedia.org/wiki/Asymmetric_numeral_systems#tANS)) 
+encoding provides a fast near-optimal symbol encoding/decoding
+for byte blocks as implemented in [zstandard](https://github.com/facebook/zstd).
+
+This can be used for compressing input with a lot of similar input values to the smallest number of bytes.
+This does not perform any multi-byte [dictionary coding](https://en.wikipedia.org/wiki/Dictionary_coder) as LZ coders,
+but it can be used as a secondary step to compressors (like Snappy) that does not do entropy encoding. 
+
+* [Godoc documentation](https://godoc.org/github.com/klauspost/compress/fse)
+
+## News
+
+ * Feb 2018: First implementation released. Consider this beta software for now.
+
+# Usage
+
+This package provides a low level interface that allows to compress single independent blocks. 
+
+Each block is separate, and there is no built in integrity checks. 
+This means that the caller should keep track of block sizes and also do checksums if needed.  
+
+Compressing a block is done via the [`Compress`](https://godoc.org/github.com/klauspost/compress/fse#Compress) function.
+You must provide input and will receive the output and maybe an error.
+
+These error values can be returned:
+
+| Error               | Description                                                                 |
+|---------------------|-----------------------------------------------------------------------------|
+| `<nil>`             | Everything ok, output is returned                                           |
+| `ErrIncompressible` | Returned when input is judged to be too hard to compress                    |
+| `ErrUseRLE`         | Returned from the compressor when the input is a single byte value repeated |
+| `(error)`           | An internal error occurred.                                                 |
+
+As can be seen above there are errors that will be returned even under normal operation so it is important to handle these.
+
+To reduce allocations you can provide a [`Scratch`](https://godoc.org/github.com/klauspost/compress/fse#Scratch) object 
+that can be re-used for successive calls. Both compression and decompression accepts a `Scratch` object, and the same 
+object can be used for both.   
+
+Be aware, that when re-using a `Scratch` object that the *output* buffer is also re-used, so if you are still using this
+you must set the `Out` field in the scratch to nil. The same buffer is used for compression and decompression output.
+
+Decompressing is done by calling the [`Decompress`](https://godoc.org/github.com/klauspost/compress/fse#Decompress) function.
+You must provide the output from the compression stage, at exactly the size you got back. If you receive an error back
+your input was likely corrupted. 
+
+It is important to note that a successful decoding does *not* mean your output matches your original input. 
+There are no integrity checks, so relying on errors from the decompressor does not assure your data is valid.
+
+For more detailed usage, see examples in the [godoc documentation](https://godoc.org/github.com/klauspost/compress/fse#pkg-examples).
+
+# Performance
+
+A lot of factors are affecting speed. Block sizes and compressibility of the material are primary factors.  
+All compression functions are currently only running on the calling goroutine so only one core will be used per block.  
+
+The compressor is significantly faster if symbols are kept as small as possible. The highest byte value of the input
+is used to reduce some of the processing, so if all your input is above byte value 64 for instance, it may be 
+beneficial to transpose all your input values down by 64.   
+
+With moderate block sizes around 64k speed are typically 200MB/s per core for compression and 
+around 300MB/s decompression speed. 
+
+The same hardware typically does Huffman (deflate) encoding at 125MB/s and decompression at 100MB/s. 
+
+# Plans
+
+At one point, more internals will be exposed to facilitate more "expert" usage of the components. 
+
+A streaming interface is also likely to be implemented. Likely compatible with [FSE stream format](https://github.com/Cyan4973/FiniteStateEntropy/blob/dev/programs/fileio.c#L261).  
+
+# Contributing
+
+Contributions are always welcome. Be aware that adding public functions will require good justification and breaking 
+changes will likely not be accepted. If in doubt open an issue before writing the PR.  

vendor/github.com/klauspost/compress/fse/bitreader.go

@@ -0,0 +1,122 @@
+// Copyright 2018 Klaus Post. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+// Based on work Copyright (c) 2013, Yann Collet, released under BSD License.
+
+package fse
+
+import (
+	"encoding/binary"
+	"errors"
+	"io"
+)
+
+// bitReader reads a bitstream in reverse.
+// The last set bit indicates the start of the stream and is used
+// for aligning the input.
+type bitReader struct {
+	in       []byte
+	off      uint // next byte to read is at in[off - 1]
+	value    uint64
+	bitsRead uint8
+}
+
+// init initializes and resets the bit reader.
+func (b *bitReader) init(in []byte) error {
+	if len(in) < 1 {
+		return errors.New("corrupt stream: too short")
+	}
+	b.in = in
+	b.off = uint(len(in))
+	// The highest bit of the last byte indicates where to start
+	v := in[len(in)-1]
+	if v == 0 {
+		return errors.New("corrupt stream, did not find end of stream")
+	}
+	b.bitsRead = 64
+	b.value = 0
+	if len(in) >= 8 {
+		b.fillFastStart()
+	} else {
+		b.fill()
+		b.fill()
+	}
+	b.bitsRead += 8 - uint8(highBits(uint32(v)))
+	return nil
+}
+
+// getBits will return n bits. n can be 0.
+func (b *bitReader) getBits(n uint8) uint16 {
+	if n == 0 || b.bitsRead >= 64 {
+		return 0
+	}
+	return b.getBitsFast(n)
+}
+
+// getBitsFast requires that at least one bit is requested every time.
+// There are no checks if the buffer is filled.
+func (b *bitReader) getBitsFast(n uint8) uint16 {
+	const regMask = 64 - 1
+	v := uint16((b.value << (b.bitsRead & regMask)) >> ((regMask + 1 - n) & regMask))
+	b.bitsRead += n
+	return v
+}
+
+// fillFast() will make sure at least 32 bits are available.
+// There must be at least 4 bytes available.
+func (b *bitReader) fillFast() {
+	if b.bitsRead < 32 {
+		return
+	}
+	// 2 bounds checks.
+	v := b.in[b.off-4:]
+	v = v[:4]
+	low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+	b.value = (b.value << 32) | uint64(low)
+	b.bitsRead -= 32
+	b.off -= 4
+}
+
+// fill() will make sure at least 32 bits are available.
+func (b *bitReader) fill() {
+	if b.bitsRead < 32 {
+		return
+	}
+	if b.off > 4 {
+		v := b.in[b.off-4:]
+		v = v[:4]
+		low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+		b.value = (b.value << 32) | uint64(low)
+		b.bitsRead -= 32
+		b.off -= 4
+		return
+	}
+	for b.off > 0 {
+		b.value = (b.value << 8) | uint64(b.in[b.off-1])
+		b.bitsRead -= 8
+		b.off--
+	}
+}
+
+// fillFastStart() assumes the bitreader is empty and there is at least 8 bytes to read.
+func (b *bitReader) fillFastStart() {
+	// Do single re-slice to avoid bounds checks.
+	b.value = binary.LittleEndian.Uint64(b.in[b.off-8:])
+	b.bitsRead = 0
+	b.off -= 8
+}
+
+// finished returns true if all bits have been read from the bit stream.
+func (b *bitReader) finished() bool {
+	return b.bitsRead >= 64 && b.off == 0
+}
+
+// close the bitstream and returns an error if out-of-buffer reads occurred.
+func (b *bitReader) close() error {
+	// Release reference.
+	b.in = nil
+	if b.bitsRead > 64 {
+		return io.ErrUnexpectedEOF
+	}
+	return nil
+}

vendor/github.com/klauspost/compress/fse/bitwriter.go

@@ -0,0 +1,168 @@
+// Copyright 2018 Klaus Post. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+// Based on work Copyright (c) 2013, Yann Collet, released under BSD License.
+
+package fse
+
+import "fmt"
+
+// bitWriter will write bits.
+// First bit will be LSB of the first byte of output.
+type bitWriter struct {
+	bitContainer uint64
+	nBits        uint8
+	out          []byte
+}
+
+// bitMask16 is bitmasks. Has extra to avoid bounds check.
+var bitMask16 = [32]uint16{
+	0, 1, 3, 7, 0xF, 0x1F,
+	0x3F, 0x7F, 0xFF, 0x1FF, 0x3FF, 0x7FF,
+	0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF, 0xFFFF,
+	0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF,
+	0xFFFF, 0xFFFF} /* up to 16 bits */
+
+// addBits16NC will add up to 16 bits.
+// It will not check if there is space for them,
+// so the caller must ensure that it has flushed recently.
+func (b *bitWriter) addBits16NC(value uint16, bits uint8) {
+	b.bitContainer |= uint64(value&bitMask16[bits&31]) << (b.nBits & 63)
+	b.nBits += bits
+}
+
+// addBits16Clean will add up to 16 bits. value may not contain more set bits than indicated.
+// It will not check if there is space for them, so the caller must ensure that it has flushed recently.
+func (b *bitWriter) addBits16Clean(value uint16, bits uint8) {
+	b.bitContainer |= uint64(value) << (b.nBits & 63)
+	b.nBits += bits
+}
+
+// addBits16ZeroNC will add up to 16 bits.
+// It will not check if there is space for them,
+// so the caller must ensure that it has flushed recently.
+// This is fastest if bits can be zero.
+func (b *bitWriter) addBits16ZeroNC(value uint16, bits uint8) {
+	if bits == 0 {
+		return
+	}
+	value <<= (16 - bits) & 15
+	value >>= (16 - bits) & 15
+	b.bitContainer |= uint64(value) << (b.nBits & 63)
+	b.nBits += bits
+}
+
+// flush will flush all pending full bytes.
+// There will be at least 56 bits available for writing when this has been called.
+// Using flush32 is faster, but leaves less space for writing.
+func (b *bitWriter) flush() {
+	v := b.nBits >> 3
+	switch v {
+	case 0:
+	case 1:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+		)
+	case 2:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+		)
+	case 3:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+		)
+	case 4:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+			byte(b.bitContainer>>24),
+		)
+	case 5:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+			byte(b.bitContainer>>24),
+			byte(b.bitContainer>>32),
+		)
+	case 6:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+			byte(b.bitContainer>>24),
+			byte(b.bitContainer>>32),
+			byte(b.bitContainer>>40),
+		)
+	case 7:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+			byte(b.bitContainer>>24),
+			byte(b.bitContainer>>32),
+			byte(b.bitContainer>>40),
+			byte(b.bitContainer>>48),
+		)
+	case 8:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+			byte(b.bitContainer>>24),
+			byte(b.bitContainer>>32),
+			byte(b.bitContainer>>40),
+			byte(b.bitContainer>>48),
+			byte(b.bitContainer>>56),
+		)
+	default:
+		panic(fmt.Errorf("bits (%d) > 64", b.nBits))
+	}
+	b.bitContainer >>= v << 3
+	b.nBits &= 7
+}
+
+// flush32 will flush out, so there are at least 32 bits available for writing.
+func (b *bitWriter) flush32() {
+	if b.nBits < 32 {
+		return
+	}
+	b.out = append(b.out,
+		byte(b.bitContainer),
+		byte(b.bitContainer>>8),
+		byte(b.bitContainer>>16),
+		byte(b.bitContainer>>24))
+	b.nBits -= 32
+	b.bitContainer >>= 32
+}
+
+// flushAlign will flush remaining full bytes and align to next byte boundary.
+func (b *bitWriter) flushAlign() {
+	nbBytes := (b.nBits + 7) >> 3
+	for i := uint8(0); i < nbBytes; i++ {
+		b.out = append(b.out, byte(b.bitContainer>>(i*8)))
+	}
+	b.nBits = 0
+	b.bitContainer = 0
+}
+
+// close will write the alignment bit and write the final byte(s)
+// to the output.
+func (b *bitWriter) close() error {
+	// End mark
+	b.addBits16Clean(1, 1)
+	// flush until next byte.
+	b.flushAlign()
+	return nil
+}
+
+// reset and continue writing by appending to out.
+func (b *bitWriter) reset(out []byte) {
+	b.bitContainer = 0
+	b.nBits = 0
+	b.out = out
+}

vendor/github.com/klauspost/compress/fse/bytereader.go

@@ -0,0 +1,47 @@
+// Copyright 2018 Klaus Post. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+// Based on work Copyright (c) 2013, Yann Collet, released under BSD License.
+
+package fse
+
+// byteReader provides a byte reader that reads
+// little endian values from a byte stream.
+// The input stream is manually advanced.
+// The reader performs no bounds checks.
+type byteReader struct {
+	b   []byte
+	off int
+}
+
+// init will initialize the reader and set the input.
+func (b *byteReader) init(in []byte) {
+	b.b = in
+	b.off = 0
+}
+
+// advance the stream b n bytes.
+func (b *byteReader) advance(n uint) {
+	b.off += int(n)
+}
+
+// Uint32 returns a little endian uint32 starting at current offset.
+func (b byteReader) Uint32() uint32 {
+	b2 := b.b[b.off:]
+	b2 = b2[:4]
+	v3 := uint32(b2[3])
+	v2 := uint32(b2[2])
+	v1 := uint32(b2[1])
+	v0 := uint32(b2[0])
+	return v0 | (v1 << 8) | (v2 << 16) | (v3 << 24)
+}
+
+// unread returns the unread portion of the input.
+func (b byteReader) unread() []byte {
+	return b.b[b.off:]
+}
+
+// remain will return the number of bytes remaining.
+func (b byteReader) remain() int {
+	return len(b.b) - b.off
+}

vendor/github.com/klauspost/compress/fse/compress.go

@@ -0,0 +1,683 @@
+// Copyright 2018 Klaus Post. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+// Based on work Copyright (c) 2013, Yann Collet, released under BSD License.
+
+package fse
+
+import (
+	"errors"
+	"fmt"
+)
+
+// Compress the input bytes. Input must be < 2GB.
+// Provide a Scratch buffer to avoid memory allocations.
+// Note that the output is also kept in the scratch buffer.
+// If input is too hard to compress, ErrIncompressible is returned.
+// If input is a single byte value repeated ErrUseRLE is returned.
+func Compress(in []byte, s *Scratch) ([]byte, error) {
+	if len(in) <= 1 {
+		return nil, ErrIncompressible
+	}
+	if len(in) > (2<<30)-1 {
+		return nil, errors.New("input too big, must be < 2GB")
+	}
+	s, err := s.prepare(in)
+	if err != nil {
+		return nil, err
+	}
+
+	// Create histogram, if none was provided.
+	maxCount := s.maxCount
+	if maxCount == 0 {
+		maxCount = s.countSimple(in)
+	}
+	// Reset for next run.
+	s.clearCount = true
+	s.maxCount = 0
+	if maxCount == len(in) {
+		// One symbol, use RLE
+		return nil, ErrUseRLE
+	}
+	if maxCount == 1 || maxCount < (len(in)>>7) {
+		// Each symbol present maximum once or too well distributed.
+		return nil, ErrIncompressible
+	}
+	s.optimalTableLog()
+	err = s.normalizeCount()
+	if err != nil {
+		return nil, err
+	}
+	err = s.writeCount()
+	if err != nil {
+		return nil, err
+	}
+
+	if false {
+		err = s.validateNorm()
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	err = s.buildCTable()
+	if err != nil {
+		return nil, err
+	}
+	err = s.compress(in)
+	if err != nil {
+		return nil, err
+	}
+	s.Out = s.bw.out
+	// Check if we compressed.
+	if len(s.Out) >= len(in) {
+		return nil, ErrIncompressible
+	}
+	return s.Out, nil
+}
+
+// cState contains the compression state of a stream.
+type cState struct {
+	bw         *bitWriter
+	stateTable []uint16
+	state      uint16
+}
+
+// init will initialize the compression state to the first symbol of the stream.
+func (c *cState) init(bw *bitWriter, ct *cTable, tableLog uint8, first symbolTransform) {
+	c.bw = bw
+	c.stateTable = ct.stateTable
+
+	nbBitsOut := (first.deltaNbBits + (1 << 15)) >> 16
+	im := int32((nbBitsOut << 16) - first.deltaNbBits)
+	lu := (im >> nbBitsOut) + first.deltaFindState
+	c.state = c.stateTable[lu]
+}
+
+// encode the output symbol provided and write it to the bitstream.
+func (c *cState) encode(symbolTT symbolTransform) {
+	nbBitsOut := (uint32(c.state) + symbolTT.deltaNbBits) >> 16
+	dstState := int32(c.state>>(nbBitsOut&15)) + symbolTT.deltaFindState
+	c.bw.addBits16NC(c.state, uint8(nbBitsOut))
+	c.state = c.stateTable[dstState]
+}
+
+// encode the output symbol provided and write it to the bitstream.
+func (c *cState) encodeZero(symbolTT symbolTransform) {
+	nbBitsOut := (uint32(c.state) + symbolTT.deltaNbBits) >> 16
+	dstState := int32(c.state>>(nbBitsOut&15)) + symbolTT.deltaFindState
+	c.bw.addBits16ZeroNC(c.state, uint8(nbBitsOut))
+	c.state = c.stateTable[dstState]
+}
+
+// flush will write the tablelog to the output and flush the remaining full bytes.
+func (c *cState) flush(tableLog uint8) {
+	c.bw.flush32()
+	c.bw.addBits16NC(c.state, tableLog)
+	c.bw.flush()
+}
+
+// compress is the main compression loop that will encode the input from the last byte to the first.
+func (s *Scratch) compress(src []byte) error {
+	if len(src) <= 2 {
+		return errors.New("compress: src too small")
+	}
+	tt := s.ct.symbolTT[:256]
+	s.bw.reset(s.Out)
+
+	// Our two states each encodes every second byte.
+	// Last byte encoded (first byte decoded) will always be encoded by c1.
+	var c1, c2 cState
+
+	// Encode so remaining size is divisible by 4.
+	ip := len(src)
+	if ip&1 == 1 {
+		c1.init(&s.bw, &s.ct, s.actualTableLog, tt[src[ip-1]])
+		c2.init(&s.bw, &s.ct, s.actualTableLog, tt[src[ip-2]])
+		c1.encodeZero(tt[src[ip-3]])
+		ip -= 3
+	} else {
+		c2.init(&s.bw, &s.ct, s.actualTableLog, tt[src[ip-1]])
+		c1.init(&s.bw, &s.ct, s.actualTableLog, tt[src[ip-2]])
+		ip -= 2
+	}
+	if ip&2 != 0 {
+		c2.encodeZero(tt[src[ip-1]])
+		c1.encodeZero(tt[src[ip-2]])
+		ip -= 2
+	}
+
+	// Main compression loop.
+	switch {
+	case !s.zeroBits && s.actualTableLog <= 8:
+		// We can encode 4 symbols without requiring a flush.
+		// We do not need to check if any output is 0 bits.
+		for ip >= 4 {
+			s.bw.flush32()
+			v3, v2, v1, v0 := src[ip-4], src[ip-3], src[ip-2], src[ip-1]
+			c2.encode(tt[v0])
+			c1.encode(tt[v1])
+			c2.encode(tt[v2])
+			c1.encode(tt[v3])
+			ip -= 4
+		}
+	case !s.zeroBits:
+		// We do not need to check if any output is 0 bits.
+		for ip >= 4 {
+			s.bw.flush32()
+			v3, v2, v1, v0 := src[ip-4], src[ip-3], src[ip-2], src[ip-1]
+			c2.encode(tt[v0])
+			c1.encode(tt[v1])
+			s.bw.flush32()
+			c2.encode(tt[v2])
+			c1.encode(tt[v3])
+			ip -= 4
+		}
+	case s.actualTableLog <= 8:
+		// We can encode 4 symbols without requiring a flush
+		for ip >= 4 {
+			s.bw.flush32()
+			v3, v2, v1, v0 := src[ip-4], src[ip-3], src[ip-2], src[ip-1]
+			c2.encodeZero(tt[v0])
+			c1.encodeZero(tt[v1])
+			c2.encodeZero(tt[v2])
+			c1.encodeZero(tt[v3])
+			ip -= 4
+		}
+	default:
+		for ip >= 4 {
+			s.bw.flush32()
+			v3, v2, v1, v0 := src[ip-4], src[ip-3], src[ip-2], src[ip-1]
+			c2.encodeZero(tt[v0])
+			c1.encodeZero(tt[v1])
+			s.bw.flush32()
+			c2.encodeZero(tt[v2])
+			c1.encodeZero(tt[v3])
+			ip -= 4
+		}
+	}
+
+	// Flush final state.
+	// Used to initialize state when decoding.
+	c2.flush(s.actualTableLog)
+	c1.flush(s.actualTableLog)
+
+	return s.bw.close()
+}
+
+// writeCount will write the normalized histogram count to header.
+// This is read back by readNCount.
+func (s *Scratch) writeCount() error {
+	var (
+		tableLog  = s.actualTableLog
+		tableSize = 1 << tableLog
+		previous0 bool
+		charnum   uint16
+
+		maxHeaderSize = ((int(s.symbolLen) * int(tableLog)) >> 3) + 3
+
+		// Write Table Size
+		bitStream = uint32(tableLog - minTablelog)
+		bitCount  = uint(4)
+		remaining = int16(tableSize + 1) /* +1 for extra accuracy */
+		threshold = int16(tableSize)
+		nbBits    = uint(tableLog + 1)
+	)
+	if cap(s.Out) < maxHeaderSize {
+		s.Out = make([]byte, 0, s.br.remain()+maxHeaderSize)
+	}
+	outP := uint(0)
+	out := s.Out[:maxHeaderSize]
+
+	// stops at 1
+	for remaining > 1 {
+		if previous0 {
+			start := charnum
+			for s.norm[charnum] == 0 {
+				charnum++
+			}
+			for charnum >= start+24 {
+				start += 24
+				bitStream += uint32(0xFFFF) << bitCount
+				out[outP] = byte(bitStream)
+				out[outP+1] = byte(bitStream >> 8)
+				outP += 2
+				bitStream >>= 16
+			}
+			for charnum >= start+3 {
+				start += 3
+				bitStream += 3 << bitCount
+				bitCount += 2
+			}
+			bitStream += uint32(charnum-start) << bitCount
+			bitCount += 2
+			if bitCount > 16 {
+				out[outP] = byte(bitStream)
+				out[outP+1] = byte(bitStream >> 8)
+				outP += 2
+				bitStream >>= 16
+				bitCount -= 16
+			}
+		}
+
+		count := s.norm[charnum]
+		charnum++
+		max := (2*threshold - 1) - remaining
+		if count < 0 {
+			remaining += count
+		} else {
+			remaining -= count
+		}
+		count++ // +1 for extra accuracy
+		if count >= threshold {
+			count += max // [0..max[ [max..threshold[ (...) [threshold+max 2*threshold[
+		}
+		bitStream += uint32(count) << bitCount
+		bitCount += nbBits
+		if count < max {
+			bitCount--
+		}
+
+		previous0 = count == 1
+		if remaining < 1 {
+			return errors.New("internal error: remaining<1")
+		}
+		for remaining < threshold {
+			nbBits--
+			threshold >>= 1
+		}
+
+		if bitCount > 16 {
+			out[outP] = byte(bitStream)
+			out[outP+1] = byte(bitStream >> 8)
+			outP += 2
+			bitStream >>= 16
+			bitCount -= 16
+		}
+	}
+
+	out[outP] = byte(bitStream)
+	out[outP+1] = byte(bitStream >> 8)
+	outP += (bitCount + 7) / 8
+
+	if charnum > s.symbolLen {
+		return errors.New("internal error: charnum > s.symbolLen")
+	}
+	s.Out = out[:outP]
+	return nil
+}
+
+// symbolTransform contains the state transform for a symbol.
+type symbolTransform struct {
+	deltaFindState int32
+	deltaNbBits    uint32
+}
+
+// String prints values as a human readable string.
+func (s symbolTransform) String() string {
+	return fmt.Sprintf("dnbits: %08x, fs:%d", s.deltaNbBits, s.deltaFindState)
+}
+
+// cTable contains tables used for compression.
+type cTable struct {
+	tableSymbol []byte
+	stateTable  []uint16
+	symbolTT    []symbolTransform
+}
+
+// allocCtable will allocate tables needed for compression.
+// If existing tables a re big enough, they are simply re-used.
+func (s *Scratch) allocCtable() {
+	tableSize := 1 << s.actualTableLog
+	// get tableSymbol that is big enough.
+	if cap(s.ct.tableSymbol) < tableSize {
+		s.ct.tableSymbol = make([]byte, tableSize)
+	}
+	s.ct.tableSymbol = s.ct.tableSymbol[:tableSize]
+
+	ctSize := tableSize
+	if cap(s.ct.stateTable) < ctSize {
+		s.ct.stateTable = make([]uint16, ctSize)
+	}
+	s.ct.stateTable = s.ct.stateTable[:ctSize]
+
+	if cap(s.ct.symbolTT) < 256 {
+		s.ct.symbolTT = make([]symbolTransform, 256)
+	}
+	s.ct.symbolTT = s.ct.symbolTT[:256]
+}
+
+// buildCTable will populate the compression table so it is ready to be used.
+func (s *Scratch) buildCTable() error {
+	tableSize := uint32(1 << s.actualTableLog)
+	highThreshold := tableSize - 1
+	var cumul [maxSymbolValue + 2]int16
+
+	s.allocCtable()
+	tableSymbol := s.ct.tableSymbol[:tableSize]
+	// symbol start positions
+	{
+		cumul[0] = 0
+		for ui, v := range s.norm[:s.symbolLen-1] {
+			u := byte(ui) // one less than reference
+			if v == -1 {
+				// Low proba symbol
+				cumul[u+1] = cumul[u] + 1
+				tableSymbol[highThreshold] = u
+				highThreshold--
+			} else {
+				cumul[u+1] = cumul[u] + v
+			}
+		}
+		// Encode last symbol separately to avoid overflowing u
+		u := int(s.symbolLen - 1)
+		v := s.norm[s.symbolLen-1]
+		if v == -1 {
+			// Low proba symbol
+			cumul[u+1] = cumul[u] + 1
+			tableSymbol[highThreshold] = byte(u)
+			highThreshold--
+		} else {
+			cumul[u+1] = cumul[u] + v
+		}
+		if uint32(cumul[s.symbolLen]) != tableSize {
+			return fmt.Errorf("internal error: expected cumul[s.symbolLen] (%d) == tableSize (%d)", cumul[s.symbolLen], tableSize)
+		}
+		cumul[s.symbolLen] = int16(tableSize) + 1
+	}
+	// Spread symbols
+	s.zeroBits = false
+	{
+		step := tableStep(tableSize)
+		tableMask := tableSize - 1
+		var position uint32
+		// if any symbol > largeLimit, we may have 0 bits output.
+		largeLimit := int16(1 << (s.actualTableLog - 1))
+		for ui, v := range s.norm[:s.symbolLen] {
+			symbol := byte(ui)
+			if v > largeLimit {
+				s.zeroBits = true
+			}
+			for nbOccurrences := int16(0); nbOccurrences < v; nbOccurrences++ {
+				tableSymbol[position] = symbol
+				position = (position + step) & tableMask
+				for position > highThreshold {
+					position = (position + step) & tableMask
+				} /* Low proba area */
+			}
+		}
+
+		// Check if we have gone through all positions
+		if position != 0 {
+			return errors.New("position!=0")
+		}
+	}
+
+	// Build table
+	table := s.ct.stateTable
+	{
+		tsi := int(tableSize)
+		for u, v := range tableSymbol {
+			// TableU16 : sorted by symbol order; gives next state value
+			table[cumul[v]] = uint16(tsi + u)
+			cumul[v]++
+		}
+	}
+
+	// Build Symbol Transformation Table
+	{
+		total := int16(0)
+		symbolTT := s.ct.symbolTT[:s.symbolLen]
+		tableLog := s.actualTableLog
+		tl := (uint32(tableLog) << 16) - (1 << tableLog)
+		for i, v := range s.norm[:s.symbolLen] {
+			switch v {
+			case 0:
+			case -1, 1:
+				symbolTT[i].deltaNbBits = tl
+				symbolTT[i].deltaFindState = int32(total - 1)
+				total++
+			default:
+				maxBitsOut := uint32(tableLog) - highBits(uint32(v-1))
+				minStatePlus := uint32(v) << maxBitsOut
+				symbolTT[i].deltaNbBits = (maxBitsOut << 16) - minStatePlus
+				symbolTT[i].deltaFindState = int32(total - v)
+				total += v
+			}
+		}
+		if total != int16(tableSize) {
+			return fmt.Errorf("total mismatch %d (got) != %d (want)", total, tableSize)
+		}
+	}
+	return nil
+}
+
+// countSimple will create a simple histogram in s.count.
+// Returns the biggest count.
+// Does not update s.clearCount.
+func (s *Scratch) countSimple(in []byte) (max int) {
+	for _, v := range in {
+		s.count[v]++
+	}
+	m := uint32(0)
+	for i, v := range s.count[:] {
+		if v > m {
+			m = v
+		}
+		if v > 0 {
+			s.symbolLen = uint16(i) + 1
+		}
+	}
+	return int(m)
+}
+
+// minTableLog provides the minimum logSize to safely represent a distribution.
+func (s *Scratch) minTableLog() uint8 {
+	minBitsSrc := highBits(uint32(s.br.remain()-1)) + 1
+	minBitsSymbols := highBits(uint32(s.symbolLen-1)) + 2
+	if minBitsSrc < minBitsSymbols {
+		return uint8(minBitsSrc)
+	}
+	return uint8(minBitsSymbols)
+}
+
+// optimalTableLog calculates and sets the optimal tableLog in s.actualTableLog
+func (s *Scratch) optimalTableLog() {
+	tableLog := s.TableLog
+	minBits := s.minTableLog()
+	maxBitsSrc := uint8(highBits(uint32(s.br.remain()-1))) - 2
+	if maxBitsSrc < tableLog {
+		// Accuracy can be reduced
+		tableLog = maxBitsSrc
+	}
+	if minBits > tableLog {
+		tableLog = minBits
+	}
+	// Need a minimum to safely represent all symbol values
+	if tableLog < minTablelog {
+		tableLog = minTablelog
+	}
+	if tableLog > maxTableLog {
+		tableLog = maxTableLog
+	}
+	s.actualTableLog = tableLog
+}
+
+var rtbTable = [...]uint32{0, 473195, 504333, 520860, 550000, 700000, 750000, 830000}
+
+// normalizeCount will normalize the count of the symbols so
+// the total is equal to the table size.
+func (s *Scratch) normalizeCount() error {
+	var (
+		tableLog          = s.actualTableLog
+		scale             = 62 - uint64(tableLog)
+		step              = (1 << 62) / uint64(s.br.remain())
+		vStep             = uint64(1) << (scale - 20)
+		stillToDistribute = int16(1 << tableLog)
+		largest           int
+		largestP          int16
+		lowThreshold      = (uint32)(s.br.remain() >> tableLog)
+	)
+
+	for i, cnt := range s.count[:s.symbolLen] {
+		// already handled
+		// if (count[s] == s.length) return 0;   /* rle special case */
+
+		if cnt == 0 {
+			s.norm[i] = 0
+			continue
+		}
+		if cnt <= lowThreshold {
+			s.norm[i] = -1
+			stillToDistribute--
+		} else {
+			proba := (int16)((uint64(cnt) * step) >> scale)
+			if proba < 8 {
+				restToBeat := vStep * uint64(rtbTable[proba])
+				v := uint64(cnt)*step - (uint64(proba) << scale)
+				if v > restToBeat {
+					proba++
+				}
+			}
+			if proba > largestP {
+				largestP = proba
+				largest = i
+			}
+			s.norm[i] = proba
+			stillToDistribute -= proba
+		}
+	}
+
+	if -stillToDistribute >= (s.norm[largest] >> 1) {
+		// corner case, need another normalization method
+		return s.normalizeCount2()
+	}
+	s.norm[largest] += stillToDistribute
+	return nil
+}
+
+// Secondary normalization method.
+// To be used when primary method fails.
+func (s *Scratch) normalizeCount2() error {
+	const notYetAssigned = -2
+	var (
+		distributed  uint32
+		total        = uint32(s.br.remain())
+		tableLog     = s.actualTableLog
+		lowThreshold = total >> tableLog
+		lowOne       = (total * 3) >> (tableLog + 1)
+	)
+	for i, cnt := range s.count[:s.symbolLen] {
+		if cnt == 0 {
+			s.norm[i] = 0
+			continue
+		}
+		if cnt <= lowThreshold {
+			s.norm[i] = -1
+			distributed++
+			total -= cnt
+			continue
+		}
+		if cnt <= lowOne {
+			s.norm[i] = 1
+			distributed++
+			total -= cnt
+			continue
+		}
+		s.norm[i] = notYetAssigned
+	}
+	toDistribute := (1 << tableLog) - distributed
+
+	if (total / toDistribute) > lowOne {
+		// risk of rounding to zero
+		lowOne = (total * 3) / (toDistribute * 2)
+		for i, cnt := range s.count[:s.symbolLen] {
+			if (s.norm[i] == notYetAssigned) && (cnt <= lowOne) {
+				s.norm[i] = 1
+				distributed++
+				total -= cnt
+				continue
+			}
+		}
+		toDistribute = (1 << tableLog) - distributed
+	}
+	if distributed == uint32(s.symbolLen)+1 {
+		// all values are pretty poor;
+		//   probably incompressible data (should have already been detected);
+		//   find max, then give all remaining points to max
+		var maxV int
+		var maxC uint32
+		for i, cnt := range s.count[:s.symbolLen] {
+			if cnt > maxC {
+				maxV = i
+				maxC = cnt
+			}
+		}
+		s.norm[maxV] += int16(toDistribute)
+		return nil
+	}
+
+	if total == 0 {
+		// all of the symbols were low enough for the lowOne or lowThreshold
+		for i := uint32(0); toDistribute > 0; i = (i + 1) % (uint32(s.symbolLen)) {
+			if s.norm[i] > 0 {
+				toDistribute--
+				s.norm[i]++
+			}
+		}
+		return nil
+	}
+
+	var (
+		vStepLog = 62 - uint64(tableLog)
+		mid      = uint64((1 << (vStepLog - 1)) - 1)
+		rStep    = (((1 << vStepLog) * uint64(toDistribute)) + mid) / uint64(total) // scale on remaining
+		tmpTotal = mid
+	)
+	for i, cnt := range s.count[:s.symbolLen] {
+		if s.norm[i] == notYetAssigned {
+			var (
+				end    = tmpTotal + uint64(cnt)*rStep
+				sStart = uint32(tmpTotal >> vStepLog)
+				sEnd   = uint32(end >> vStepLog)
+				weight = sEnd - sStart
+			)
+			if weight < 1 {
+				return errors.New("weight < 1")
+			}
+			s.norm[i] = int16(weight)
+			tmpTotal = end
+		}
+	}
+	return nil
+}
+
+// validateNorm validates the normalized histogram table.
+func (s *Scratch) validateNorm() (err error) {
+	var total int
+	for _, v := range s.norm[:s.symbolLen] {
+		if v >= 0 {
+			total += int(v)
+		} else {
+			total -= int(v)
+		}
+	}
+	defer func() {
+		if err == nil {
+			return
+		}
+		fmt.Printf("selected TableLog: %d, Symbol length: %d\n", s.actualTableLog, s.symbolLen)
+		for i, v := range s.norm[:s.symbolLen] {
+			fmt.Printf("%3d: %5d -> %4d \n", i, s.count[i], v)
+		}
+	}()
+	if total != (1 << s.actualTableLog) {
+		return fmt.Errorf("warning: Total == %d != %d", total, 1<<s.actualTableLog)
+	}
+	for i, v := range s.count[s.symbolLen:] {
+		if v != 0 {
+			return fmt.Errorf("warning: Found symbol out of range, %d after cut", i)
+		}
+	}
+	return nil
+}

vendor/github.com/klauspost/compress/fse/decompress.go

@@ -0,0 +1,374 @@
+package fse
+
+import (
+	"errors"
+	"fmt"
+)
+
+const (
+	tablelogAbsoluteMax = 15
+)
+
+// Decompress a block of data.
+// You can provide a scratch buffer to avoid allocations.
+// If nil is provided a temporary one will be allocated.
+// It is possible, but by no way guaranteed that corrupt data will
+// return an error.
+// It is up to the caller to verify integrity of the returned data.
+// Use a predefined Scrach to set maximum acceptable output size.
+func Decompress(b []byte, s *Scratch) ([]byte, error) {
+	s, err := s.prepare(b)
+	if err != nil {
+		return nil, err
+	}
+	s.Out = s.Out[:0]
+	err = s.readNCount()
+	if err != nil {
+		return nil, err
+	}
+	err = s.buildDtable()
+	if err != nil {
+		return nil, err
+	}
+	err = s.decompress()
+	if err != nil {
+		return nil, err
+	}
+
+	return s.Out, nil
+}
+
+// readNCount will read the symbol distribution so decoding tables can be constructed.
+func (s *Scratch) readNCount() error {
+	var (
+		charnum   uint16
+		previous0 bool
+		b         = &s.br
+	)
+	iend := b.remain()
+	if iend < 4 {
+		return errors.New("input too small")
+	}
+	bitStream := b.Uint32()
+	nbBits := uint((bitStream & 0xF) + minTablelog) // extract tableLog
+	if nbBits > tablelogAbsoluteMax {
+		return errors.New("tableLog too large")
+	}
+	bitStream >>= 4
+	bitCount := uint(4)
+
+	s.actualTableLog = uint8(nbBits)
+	remaining := int32((1 << nbBits) + 1)
+	threshold := int32(1 << nbBits)
+	gotTotal := int32(0)
+	nbBits++
+
+	for remaining > 1 {
+		if previous0 {
+			n0 := charnum
+			for (bitStream & 0xFFFF) == 0xFFFF {
+				n0 += 24
+				if b.off < iend-5 {
+					b.advance(2)
+					bitStream = b.Uint32() >> bitCount
+				} else {
+					bitStream >>= 16
+					bitCount += 16
+				}
+			}
+			for (bitStream & 3) == 3 {
+				n0 += 3
+				bitStream >>= 2
+				bitCount += 2
+			}
+			n0 += uint16(bitStream & 3)
+			bitCount += 2
+			if n0 > maxSymbolValue {
+				return errors.New("maxSymbolValue too small")
+			}
+			for charnum < n0 {
+				s.norm[charnum&0xff] = 0
+				charnum++
+			}
+
+			if b.off <= iend-7 || b.off+int(bitCount>>3) <= iend-4 {
+				b.advance(bitCount >> 3)
+				bitCount &= 7
+				bitStream = b.Uint32() >> bitCount
+			} else {
+				bitStream >>= 2
+			}
+		}
+
+		max := (2*(threshold) - 1) - (remaining)
+		var count int32
+
+		if (int32(bitStream) & (threshold - 1)) < max {
+			count = int32(bitStream) & (threshold - 1)
+			bitCount += nbBits - 1
+		} else {
+			count = int32(bitStream) & (2*threshold - 1)
+			if count >= threshold {
+				count -= max
+			}
+			bitCount += nbBits
+		}
+
+		count-- // extra accuracy
+		if count < 0 {
+			// -1 means +1
+			remaining += count
+			gotTotal -= count
+		} else {
+			remaining -= count
+			gotTotal += count
+		}
+		s.norm[charnum&0xff] = int16(count)
+		charnum++
+		previous0 = count == 0
+		for remaining < threshold {
+			nbBits--
+			threshold >>= 1
+		}
+		if b.off <= iend-7 || b.off+int(bitCount>>3) <= iend-4 {
+			b.advance(bitCount >> 3)
+			bitCount &= 7
+		} else {
+			bitCount -= (uint)(8 * (len(b.b) - 4 - b.off))
+			b.off = len(b.b) - 4
+		}
+		bitStream = b.Uint32() >> (bitCount & 31)
+	}
+	s.symbolLen = charnum
+
+	if s.symbolLen <= 1 {
+		return fmt.Errorf("symbolLen (%d) too small", s.symbolLen)
+	}
+	if s.symbolLen > maxSymbolValue+1 {
+		return fmt.Errorf("symbolLen (%d) too big", s.symbolLen)
+	}
+	if remaining != 1 {
+		return fmt.Errorf("corruption detected (remaining %d != 1)", remaining)
+	}
+	if bitCount > 32 {
+		return fmt.Errorf("corruption detected (bitCount %d > 32)", bitCount)
+	}
+	if gotTotal != 1<<s.actualTableLog {
+		return fmt.Errorf("corruption detected (total %d != %d)", gotTotal, 1<<s.actualTableLog)
+	}
+	b.advance((bitCount + 7) >> 3)
+	return nil
+}
+
+// decSymbol contains information about a state entry,
+// Including the state offset base, the output symbol and
+// the number of bits to read for the low part of the destination state.
+type decSymbol struct {
+	newState uint16
+	symbol   uint8
+	nbBits   uint8
+}
+
+// allocDtable will allocate decoding tables if they are not big enough.
+func (s *Scratch) allocDtable() {
+	tableSize := 1 << s.actualTableLog
+	if cap(s.decTable) < tableSize {
+		s.decTable = make([]decSymbol, tableSize)
+	}
+	s.decTable = s.decTable[:tableSize]
+
+	if cap(s.ct.tableSymbol) < 256 {
+		s.ct.tableSymbol = make([]byte, 256)
+	}
+	s.ct.tableSymbol = s.ct.tableSymbol[:256]
+
+	if cap(s.ct.stateTable) < 256 {
+		s.ct.stateTable = make([]uint16, 256)
+	}
+	s.ct.stateTable = s.ct.stateTable[:256]
+}
+
+// buildDtable will build the decoding table.
+func (s *Scratch) buildDtable() error {
+	tableSize := uint32(1 << s.actualTableLog)
+	highThreshold := tableSize - 1
+	s.allocDtable()
+	symbolNext := s.ct.stateTable[:256]
+
+	// Init, lay down lowprob symbols
+	s.zeroBits = false
+	{
+		largeLimit := int16(1 << (s.actualTableLog - 1))
+		for i, v := range s.norm[:s.symbolLen] {
+			if v == -1 {
+				s.decTable[highThreshold].symbol = uint8(i)
+				highThreshold--
+				symbolNext[i] = 1
+			} else {
+				if v >= largeLimit {
+					s.zeroBits = true
+				}
+				symbolNext[i] = uint16(v)
+			}
+		}
+	}
+	// Spread symbols
+	{
+		tableMask := tableSize - 1
+		step := tableStep(tableSize)
+		position := uint32(0)
+		for ss, v := range s.norm[:s.symbolLen] {
+			for i := 0; i < int(v); i++ {
+				s.decTable[position].symbol = uint8(ss)
+				position = (position + step) & tableMask
+				for position > highThreshold {
+					// lowprob area
+					position = (position + step) & tableMask
+				}
+			}
+		}
+		if position != 0 {
+			// position must reach all cells once, otherwise normalizedCounter is incorrect
+			return errors.New("corrupted input (position != 0)")
+		}
+	}
+
+	// Build Decoding table
+	{
+		tableSize := uint16(1 << s.actualTableLog)
+		for u, v := range s.decTable {
+			symbol := v.symbol
+			nextState := symbolNext[symbol]
+			symbolNext[symbol] = nextState + 1
+			nBits := s.actualTableLog - byte(highBits(uint32(nextState)))
+			s.decTable[u].nbBits = nBits
+			newState := (nextState << nBits) - tableSize
+			if newState >= tableSize {
+				return fmt.Errorf("newState (%d) outside table size (%d)", newState, tableSize)
+			}
+			if newState == uint16(u) && nBits == 0 {
+				// Seems weird that this is possible with nbits > 0.
+				return fmt.Errorf("newState (%d) == oldState (%d) and no bits", newState, u)
+			}
+			s.decTable[u].newState = newState
+		}
+	}
+	return nil
+}
+
+// decompress will decompress the bitstream.
+// If the buffer is over-read an error is returned.
+func (s *Scratch) decompress() error {
+	br := &s.bits
+	br.init(s.br.unread())
+
+	var s1, s2 decoder
+	// Initialize and decode first state and symbol.
+	s1.init(br, s.decTable, s.actualTableLog)
+	s2.init(br, s.decTable, s.actualTableLog)
+
+	// Use temp table to avoid bound checks/append penalty.
+	var tmp = s.ct.tableSymbol[:256]
+	var off uint8
+
+	// Main part
+	if !s.zeroBits {
+		for br.off >= 8 {
+			br.fillFast()
+			tmp[off+0] = s1.nextFast()
+			tmp[off+1] = s2.nextFast()
+			br.fillFast()
+			tmp[off+2] = s1.nextFast()
+			tmp[off+3] = s2.nextFast()
+			off += 4
+			// When off is 0, we have overflowed and should write.
+			if off == 0 {
+				s.Out = append(s.Out, tmp...)
+				if len(s.Out) >= s.DecompressLimit {
+					return fmt.Errorf("output size (%d) > DecompressLimit (%d)", len(s.Out), s.DecompressLimit)
+				}
+			}
+		}
+	} else {
+		for br.off >= 8 {
+			br.fillFast()
+			tmp[off+0] = s1.next()
+			tmp[off+1] = s2.next()
+			br.fillFast()
+			tmp[off+2] = s1.next()
+			tmp[off+3] = s2.next()
+			off += 4
+			if off == 0 {
+				s.Out = append(s.Out, tmp...)
+				// When off is 0, we have overflowed and should write.
+				if len(s.Out) >= s.DecompressLimit {
+					return fmt.Errorf("output size (%d) > DecompressLimit (%d)", len(s.Out), s.DecompressLimit)
+				}
+			}
+		}
+	}
+	s.Out = append(s.Out, tmp[:off]...)
+
+	// Final bits, a bit more expensive check
+	for {
+		if s1.finished() {
+			s.Out = append(s.Out, s1.final(), s2.final())
+			break
+		}
+		br.fill()
+		s.Out = append(s.Out, s1.next())
+		if s2.finished() {
+			s.Out = append(s.Out, s2.final(), s1.final())
+			break
+		}
+		s.Out = append(s.Out, s2.next())
+		if len(s.Out) >= s.DecompressLimit {
+			return fmt.Errorf("output size (%d) > DecompressLimit (%d)", len(s.Out), s.DecompressLimit)
+		}
+	}
+	return br.close()
+}
+
+// decoder keeps track of the current state and updates it from the bitstream.
+type decoder struct {
+	state uint16
+	br    *bitReader
+	dt    []decSymbol
+}
+
+// init will initialize the decoder and read the first state from the stream.
+func (d *decoder) init(in *bitReader, dt []decSymbol, tableLog uint8) {
+	d.dt = dt
+	d.br = in
+	d.state = in.getBits(tableLog)
+}
+
+// next returns the next symbol and sets the next state.
+// At least tablelog bits must be available in the bit reader.
+func (d *decoder) next() uint8 {
+	n := &d.dt[d.state]
+	lowBits := d.br.getBits(n.nbBits)
+	d.state = n.newState + lowBits
+	return n.symbol
+}
+
+// finished returns true if all bits have been read from the bitstream
+// and the next state would require reading bits from the input.
+func (d *decoder) finished() bool {
+	return d.br.finished() && d.dt[d.state].nbBits > 0
+}
+
+// final returns the current state symbol without decoding the next.
+func (d *decoder) final() uint8 {
+	return d.dt[d.state].symbol
+}
+
+// nextFast returns the next symbol and sets the next state.
+// This can only be used if no symbols are 0 bits.
+// At least tablelog bits must be available in the bit reader.
+func (d *decoder) nextFast() uint8 {
+	n := d.dt[d.state]
+	lowBits := d.br.getBitsFast(n.nbBits)
+	d.state = n.newState + lowBits
+	return n.symbol
+}

vendor/github.com/klauspost/compress/fse/fse.go

@@ -0,0 +1,144 @@
+// Copyright 2018 Klaus Post. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+// Based on work Copyright (c) 2013, Yann Collet, released under BSD License.
+
+// Package fse provides Finite State Entropy encoding and decoding.
+//
+// Finite State Entropy encoding provides a fast near-optimal symbol encoding/decoding
+// for byte blocks as implemented in zstd.
+//
+// See https://github.com/klauspost/compress/tree/master/fse for more information.
+package fse
+
+import (
+	"errors"
+	"fmt"
+	"math/bits"
+)
+
+const (
+	/*!MEMORY_USAGE :
+	 *  Memory usage formula : N->2^N Bytes (examples : 10 -> 1KB; 12 -> 4KB ; 16 -> 64KB; 20 -> 1MB; etc.)
+	 *  Increasing memory usage improves compression ratio
+	 *  Reduced memory usage can improve speed, due to cache effect
+	 *  Recommended max value is 14, for 16KB, which nicely fits into Intel x86 L1 cache */
+	maxMemoryUsage     = 14
+	defaultMemoryUsage = 13
+
+	maxTableLog     = maxMemoryUsage - 2
+	maxTablesize    = 1 << maxTableLog
+	defaultTablelog = defaultMemoryUsage - 2
+	minTablelog     = 5
+	maxSymbolValue  = 255
+)
+
+var (
+	// ErrIncompressible is returned when input is judged to be too hard to compress.
+	ErrIncompressible = errors.New("input is not compressible")
+
+	// ErrUseRLE is returned from the compressor when the input is a single byte value repeated.
+	ErrUseRLE = errors.New("input is single value repeated")
+)
+
+// Scratch provides temporary storage for compression and decompression.
+type Scratch struct {
+	// Private
+	count    [maxSymbolValue + 1]uint32
+	norm     [maxSymbolValue + 1]int16
+	br       byteReader
+	bits     bitReader
+	bw       bitWriter
+	ct       cTable      // Compression tables.
+	decTable []decSymbol // Decompression table.
+	maxCount int         // count of the most probable symbol
+
+	// Per block parameters.
+	// These can be used to override compression parameters of the block.
+	// Do not touch, unless you know what you are doing.
+
+	// Out is output buffer.
+	// If the scratch is re-used before the caller is done processing the output,
+	// set this field to nil.
+	// Otherwise the output buffer will be re-used for next Compression/Decompression step
+	// and allocation will be avoided.
+	Out []byte
+
+	// DecompressLimit limits the maximum decoded size acceptable.
+	// If > 0 decompression will stop when approximately this many bytes
+	// has been decoded.
+	// If 0, maximum size will be 2GB.
+	DecompressLimit int
+
+	symbolLen      uint16 // Length of active part of the symbol table.
+	actualTableLog uint8  // Selected tablelog.
+	zeroBits       bool   // no bits has prob > 50%.
+	clearCount     bool   // clear count
+
+	// MaxSymbolValue will override the maximum symbol value of the next block.
+	MaxSymbolValue uint8
+
+	// TableLog will attempt to override the tablelog for the next block.
+	TableLog uint8
+}
+
+// Histogram allows to populate the histogram and skip that step in the compression,
+// It otherwise allows to inspect the histogram when compression is done.
+// To indicate that you have populated the histogram call HistogramFinished
+// with the value of the highest populated symbol, as well as the number of entries
+// in the most populated entry. These are accepted at face value.
+// The returned slice will always be length 256.
+func (s *Scratch) Histogram() []uint32 {
+	return s.count[:]
+}
+
+// HistogramFinished can be called to indicate that the histogram has been populated.
+// maxSymbol is the index of the highest set symbol of the next data segment.
+// maxCount is the number of entries in the most populated entry.
+// These are accepted at face value.
+func (s *Scratch) HistogramFinished(maxSymbol uint8, maxCount int) {
+	s.maxCount = maxCount
+	s.symbolLen = uint16(maxSymbol) + 1
+	s.clearCount = maxCount != 0
+}
+
+// prepare will prepare and allocate scratch tables used for both compression and decompression.
+func (s *Scratch) prepare(in []byte) (*Scratch, error) {
+	if s == nil {
+		s = &Scratch{}
+	}
+	if s.MaxSymbolValue == 0 {
+		s.MaxSymbolValue = 255
+	}
+	if s.TableLog == 0 {
+		s.TableLog = defaultTablelog
+	}
+	if s.TableLog > maxTableLog {
+		return nil, fmt.Errorf("tableLog (%d) > maxTableLog (%d)", s.TableLog, maxTableLog)
+	}
+	if cap(s.Out) == 0 {
+		s.Out = make([]byte, 0, len(in))
+	}
+	if s.clearCount && s.maxCount == 0 {
+		for i := range s.count {
+			s.count[i] = 0
+		}
+		s.clearCount = false
+	}
+	s.br.init(in)
+	if s.DecompressLimit == 0 {
+		// Max size 2GB.
+		s.DecompressLimit = (2 << 30) - 1
+	}
+
+	return s, nil
+}
+
+// tableStep returns the next table index.
+func tableStep(tableSize uint32) uint32 {
+	return (tableSize >> 1) + (tableSize >> 3) + 3
+}
+
+func highBits(val uint32) (n uint32) {
+	return uint32(bits.Len32(val) - 1)
+}

vendor/github.com/klauspost/compress/gen.sh

@@ -0,0 +1,4 @@
+#!/bin/sh
+
+cd s2/cmd/_s2sx/ || exit 1
+go generate .

vendor/github.com/klauspost/compress/huff0/.gitignore

@@ -0,0 +1 @@
+/huff0-fuzz.zip

vendor/github.com/klauspost/compress/huff0/README.md

@@ -0,0 +1,89 @@
+# Huff0 entropy compression
+
+This package provides Huff0 encoding and decoding as used in zstd.
+            
+[Huff0](https://github.com/Cyan4973/FiniteStateEntropy#new-generation-entropy-coders), 
+a Huffman codec designed for modern CPU, featuring OoO (Out of Order) operations on multiple ALU 
+(Arithmetic Logic Unit), achieving extremely fast compression and decompression speeds.
+
+This can be used for compressing input with a lot of similar input values to the smallest number of bytes.
+This does not perform any multi-byte [dictionary coding](https://en.wikipedia.org/wiki/Dictionary_coder) as LZ coders,
+but it can be used as a secondary step to compressors (like Snappy) that does not do entropy encoding. 
+
+* [Godoc documentation](https://godoc.org/github.com/klauspost/compress/huff0)
+
+## News
+
+This is used as part of the [zstandard](https://github.com/klauspost/compress/tree/master/zstd#zstd) compression and decompression package.
+
+This ensures that most functionality is well tested.
+
+# Usage
+
+This package provides a low level interface that allows to compress single independent blocks. 
+
+Each block is separate, and there is no built in integrity checks. 
+This means that the caller should keep track of block sizes and also do checksums if needed.  
+
+Compressing a block is done via the [`Compress1X`](https://godoc.org/github.com/klauspost/compress/huff0#Compress1X) and 
+[`Compress4X`](https://godoc.org/github.com/klauspost/compress/huff0#Compress4X) functions.
+You must provide input and will receive the output and maybe an error.
+
+These error values can be returned:
+
+| Error               | Description                                                                 |
+|---------------------|-----------------------------------------------------------------------------|
+| `<nil>`             | Everything ok, output is returned                                           |
+| `ErrIncompressible` | Returned when input is judged to be too hard to compress                    |
+| `ErrUseRLE`         | Returned from the compressor when the input is a single byte value repeated |
+| `ErrTooBig`         | Returned if the input block exceeds the maximum allowed size (128 Kib)      |
+| `(error)`           | An internal error occurred.                                                 |
+
+
+As can be seen above some of there are errors that will be returned even under normal operation so it is important to handle these.
+
+To reduce allocations you can provide a [`Scratch`](https://godoc.org/github.com/klauspost/compress/huff0#Scratch) object 
+that can be re-used for successive calls. Both compression and decompression accepts a `Scratch` object, and the same 
+object can be used for both.   
+
+Be aware, that when re-using a `Scratch` object that the *output* buffer is also re-used, so if you are still using this
+you must set the `Out` field in the scratch to nil. The same buffer is used for compression and decompression output.
+
+The `Scratch` object will retain state that allows to re-use previous tables for encoding and decoding.  
+
+## Tables and re-use
+
+Huff0 allows for reusing tables from the previous block to save space if that is expected to give better/faster results. 
+
+The Scratch object allows you to set a [`ReusePolicy`](https://godoc.org/github.com/klauspost/compress/huff0#ReusePolicy) 
+that controls this behaviour. See the documentation for details. This can be altered between each block.
+
+Do however note that this information is *not* stored in the output block and it is up to the users of the package to
+record whether [`ReadTable`](https://godoc.org/github.com/klauspost/compress/huff0#ReadTable) should be called,
+based on the boolean reported back from the CompressXX call. 
+
+If you want to store the table separate from the data, you can access them as `OutData` and `OutTable` on the 
+[`Scratch`](https://godoc.org/github.com/klauspost/compress/huff0#Scratch) object.
+
+## Decompressing
+
+The first part of decoding is to initialize the decoding table through [`ReadTable`](https://godoc.org/github.com/klauspost/compress/huff0#ReadTable).
+This will initialize the decoding tables. 
+You can supply the complete block to `ReadTable` and it will return the data part of the block 
+which can be given to the decompressor. 
+
+Decompressing is done by calling the [`Decompress1X`](https://godoc.org/github.com/klauspost/compress/huff0#Scratch.Decompress1X) 
+or [`Decompress4X`](https://godoc.org/github.com/klauspost/compress/huff0#Scratch.Decompress4X) function.
+
+For concurrently decompressing content with a fixed table a stateless [`Decoder`](https://godoc.org/github.com/klauspost/compress/huff0#Decoder) can be requested which will remain correct as long as the scratch is unchanged. The capacity of the provided slice indicates the expected output size.
+
+You must provide the output from the compression stage, at exactly the size you got back. If you receive an error back
+your input was likely corrupted. 
+
+It is important to note that a successful decoding does *not* mean your output matches your original input. 
+There are no integrity checks, so relying on errors from the decompressor does not assure your data is valid.
+
+# Contributing
+
+Contributions are always welcome. Be aware that adding public functions will require good justification and breaking 
+changes will likely not be accepted. If in doubt open an issue before writing the PR.

vendor/github.com/klauspost/compress/huff0/bitreader.go

@@ -0,0 +1,329 @@
+// Copyright 2018 Klaus Post. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+// Based on work Copyright (c) 2013, Yann Collet, released under BSD License.
+
+package huff0
+
+import (
+	"encoding/binary"
+	"errors"
+	"io"
+)
+
+// bitReader reads a bitstream in reverse.
+// The last set bit indicates the start of the stream and is used
+// for aligning the input.
+type bitReader struct {
+	in       []byte
+	off      uint // next byte to read is at in[off - 1]
+	value    uint64
+	bitsRead uint8
+}
+
+// init initializes and resets the bit reader.
+func (b *bitReader) init(in []byte) error {
+	if len(in) < 1 {
+		return errors.New("corrupt stream: too short")
+	}
+	b.in = in
+	b.off = uint(len(in))
+	// The highest bit of the last byte indicates where to start
+	v := in[len(in)-1]
+	if v == 0 {
+		return errors.New("corrupt stream, did not find end of stream")
+	}
+	b.bitsRead = 64
+	b.value = 0
+	if len(in) >= 8 {
+		b.fillFastStart()
+	} else {
+		b.fill()
+		b.fill()
+	}
+	b.bitsRead += 8 - uint8(highBit32(uint32(v)))
+	return nil
+}
+
+// peekBitsFast requires that at least one bit is requested every time.
+// There are no checks if the buffer is filled.
+func (b *bitReader) peekBitsFast(n uint8) uint16 {
+	const regMask = 64 - 1
+	v := uint16((b.value << (b.bitsRead & regMask)) >> ((regMask + 1 - n) & regMask))
+	return v
+}
+
+// fillFast() will make sure at least 32 bits are available.
+// There must be at least 4 bytes available.
+func (b *bitReader) fillFast() {
+	if b.bitsRead < 32 {
+		return
+	}
+
+	// 2 bounds checks.
+	v := b.in[b.off-4 : b.off]
+	v = v[:4]
+	low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+	b.value = (b.value << 32) | uint64(low)
+	b.bitsRead -= 32
+	b.off -= 4
+}
+
+func (b *bitReader) advance(n uint8) {
+	b.bitsRead += n
+}
+
+// fillFastStart() assumes the bitreader is empty and there is at least 8 bytes to read.
+func (b *bitReader) fillFastStart() {
+	// Do single re-slice to avoid bounds checks.
+	b.value = binary.LittleEndian.Uint64(b.in[b.off-8:])
+	b.bitsRead = 0
+	b.off -= 8
+}
+
+// fill() will make sure at least 32 bits are available.
+func (b *bitReader) fill() {
+	if b.bitsRead < 32 {
+		return
+	}
+	if b.off > 4 {
+		v := b.in[b.off-4:]
+		v = v[:4]
+		low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+		b.value = (b.value << 32) | uint64(low)
+		b.bitsRead -= 32
+		b.off -= 4
+		return
+	}
+	for b.off > 0 {
+		b.value = (b.value << 8) | uint64(b.in[b.off-1])
+		b.bitsRead -= 8
+		b.off--
+	}
+}
+
+// finished returns true if all bits have been read from the bit stream.
+func (b *bitReader) finished() bool {
+	return b.off == 0 && b.bitsRead >= 64
+}
+
+// close the bitstream and returns an error if out-of-buffer reads occurred.
+func (b *bitReader) close() error {
+	// Release reference.
+	b.in = nil
+	if b.bitsRead > 64 {
+		return io.ErrUnexpectedEOF
+	}
+	return nil
+}
+
+// bitReader reads a bitstream in reverse.
+// The last set bit indicates the start of the stream and is used
+// for aligning the input.
+type bitReaderBytes struct {
+	in       []byte
+	off      uint // next byte to read is at in[off - 1]
+	value    uint64
+	bitsRead uint8
+}
+
+// init initializes and resets the bit reader.
+func (b *bitReaderBytes) init(in []byte) error {
+	if len(in) < 1 {
+		return errors.New("corrupt stream: too short")
+	}
+	b.in = in
+	b.off = uint(len(in))
+	// The highest bit of the last byte indicates where to start
+	v := in[len(in)-1]
+	if v == 0 {
+		return errors.New("corrupt stream, did not find end of stream")
+	}
+	b.bitsRead = 64
+	b.value = 0
+	if len(in) >= 8 {
+		b.fillFastStart()
+	} else {
+		b.fill()
+		b.fill()
+	}
+	b.advance(8 - uint8(highBit32(uint32(v))))
+	return nil
+}
+
+// peekBitsFast requires that at least one bit is requested every time.
+// There are no checks if the buffer is filled.
+func (b *bitReaderBytes) peekByteFast() uint8 {
+	got := uint8(b.value >> 56)
+	return got
+}
+
+func (b *bitReaderBytes) advance(n uint8) {
+	b.bitsRead += n
+	b.value <<= n & 63
+}
+
+// fillFast() will make sure at least 32 bits are available.
+// There must be at least 4 bytes available.
+func (b *bitReaderBytes) fillFast() {
+	if b.bitsRead < 32 {
+		return
+	}
+
+	// 2 bounds checks.
+	v := b.in[b.off-4 : b.off]
+	v = v[:4]
+	low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+	b.value |= uint64(low) << (b.bitsRead - 32)
+	b.bitsRead -= 32
+	b.off -= 4
+}
+
+// fillFastStart() assumes the bitReaderBytes is empty and there is at least 8 bytes to read.
+func (b *bitReaderBytes) fillFastStart() {
+	// Do single re-slice to avoid bounds checks.
+	b.value = binary.LittleEndian.Uint64(b.in[b.off-8:])
+	b.bitsRead = 0
+	b.off -= 8
+}
+
+// fill() will make sure at least 32 bits are available.
+func (b *bitReaderBytes) fill() {
+	if b.bitsRead < 32 {
+		return
+	}
+	if b.off > 4 {
+		v := b.in[b.off-4:]
+		v = v[:4]
+		low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+		b.value |= uint64(low) << (b.bitsRead - 32)
+		b.bitsRead -= 32
+		b.off -= 4
+		return
+	}
+	for b.off > 0 {
+		b.value |= uint64(b.in[b.off-1]) << (b.bitsRead - 8)
+		b.bitsRead -= 8
+		b.off--
+	}
+}
+
+// finished returns true if all bits have been read from the bit stream.
+func (b *bitReaderBytes) finished() bool {
+	return b.off == 0 && b.bitsRead >= 64
+}
+
+// close the bitstream and returns an error if out-of-buffer reads occurred.
+func (b *bitReaderBytes) close() error {
+	// Release reference.
+	b.in = nil
+	if b.bitsRead > 64 {
+		return io.ErrUnexpectedEOF
+	}
+	return nil
+}
+
+// bitReaderShifted reads a bitstream in reverse.
+// The last set bit indicates the start of the stream and is used
+// for aligning the input.
+type bitReaderShifted struct {
+	in       []byte
+	off      uint // next byte to read is at in[off - 1]
+	value    uint64
+	bitsRead uint8
+}
+
+// init initializes and resets the bit reader.
+func (b *bitReaderShifted) init(in []byte) error {
+	if len(in) < 1 {
+		return errors.New("corrupt stream: too short")
+	}
+	b.in = in
+	b.off = uint(len(in))
+	// The highest bit of the last byte indicates where to start
+	v := in[len(in)-1]
+	if v == 0 {
+		return errors.New("corrupt stream, did not find end of stream")
+	}
+	b.bitsRead = 64
+	b.value = 0
+	if len(in) >= 8 {
+		b.fillFastStart()
+	} else {
+		b.fill()
+		b.fill()
+	}
+	b.advance(8 - uint8(highBit32(uint32(v))))
+	return nil
+}
+
+// peekBitsFast requires that at least one bit is requested every time.
+// There are no checks if the buffer is filled.
+func (b *bitReaderShifted) peekBitsFast(n uint8) uint16 {
+	return uint16(b.value >> ((64 - n) & 63))
+}
+
+func (b *bitReaderShifted) advance(n uint8) {
+	b.bitsRead += n
+	b.value <<= n & 63
+}
+
+// fillFast() will make sure at least 32 bits are available.
+// There must be at least 4 bytes available.
+func (b *bitReaderShifted) fillFast() {
+	if b.bitsRead < 32 {
+		return
+	}
+
+	// 2 bounds checks.
+	v := b.in[b.off-4 : b.off]
+	v = v[:4]
+	low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+	b.value |= uint64(low) << ((b.bitsRead - 32) & 63)
+	b.bitsRead -= 32
+	b.off -= 4
+}
+
+// fillFastStart() assumes the bitReaderShifted is empty and there is at least 8 bytes to read.
+func (b *bitReaderShifted) fillFastStart() {
+	// Do single re-slice to avoid bounds checks.
+	b.value = binary.LittleEndian.Uint64(b.in[b.off-8:])
+	b.bitsRead = 0
+	b.off -= 8
+}
+
+// fill() will make sure at least 32 bits are available.
+func (b *bitReaderShifted) fill() {
+	if b.bitsRead < 32 {
+		return
+	}
+	if b.off > 4 {
+		v := b.in[b.off-4:]
+		v = v[:4]
+		low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+		b.value |= uint64(low) << ((b.bitsRead - 32) & 63)
+		b.bitsRead -= 32
+		b.off -= 4
+		return
+	}
+	for b.off > 0 {
+		b.value |= uint64(b.in[b.off-1]) << ((b.bitsRead - 8) & 63)
+		b.bitsRead -= 8
+		b.off--
+	}
+}
+
+// finished returns true if all bits have been read from the bit stream.
+func (b *bitReaderShifted) finished() bool {
+	return b.off == 0 && b.bitsRead >= 64
+}
+
+// close the bitstream and returns an error if out-of-buffer reads occurred.
+func (b *bitReaderShifted) close() error {
+	// Release reference.
+	b.in = nil
+	if b.bitsRead > 64 {
+		return io.ErrUnexpectedEOF
+	}
+	return nil
+}

vendor/github.com/klauspost/compress/huff0/bitwriter.go

@@ -0,0 +1,210 @@
+// Copyright 2018 Klaus Post. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+// Based on work Copyright (c) 2013, Yann Collet, released under BSD License.
+
+package huff0
+
+import "fmt"
+
+// bitWriter will write bits.
+// First bit will be LSB of the first byte of output.
+type bitWriter struct {
+	bitContainer uint64
+	nBits        uint8
+	out          []byte
+}
+
+// bitMask16 is bitmasks. Has extra to avoid bounds check.
+var bitMask16 = [32]uint16{
+	0, 1, 3, 7, 0xF, 0x1F,
+	0x3F, 0x7F, 0xFF, 0x1FF, 0x3FF, 0x7FF,
+	0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF, 0xFFFF,
+	0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF,
+	0xFFFF, 0xFFFF} /* up to 16 bits */
+
+// addBits16NC will add up to 16 bits.
+// It will not check if there is space for them,
+// so the caller must ensure that it has flushed recently.
+func (b *bitWriter) addBits16NC(value uint16, bits uint8) {
+	b.bitContainer |= uint64(value&bitMask16[bits&31]) << (b.nBits & 63)
+	b.nBits += bits
+}
+
+// addBits16Clean will add up to 16 bits. value may not contain more set bits than indicated.
+// It will not check if there is space for them, so the caller must ensure that it has flushed recently.
+func (b *bitWriter) addBits16Clean(value uint16, bits uint8) {
+	b.bitContainer |= uint64(value) << (b.nBits & 63)
+	b.nBits += bits
+}
+
+// encSymbol will add up to 16 bits. value may not contain more set bits than indicated.
+// It will not check if there is space for them, so the caller must ensure that it has flushed recently.
+func (b *bitWriter) encSymbol(ct cTable, symbol byte) {
+	enc := ct[symbol]
+	b.bitContainer |= uint64(enc.val) << (b.nBits & 63)
+	if false {
+		if enc.nBits == 0 {
+			panic("nbits 0")
+		}
+	}
+	b.nBits += enc.nBits
+}
+
+// encTwoSymbols will add up to 32 bits. value may not contain more set bits than indicated.
+// It will not check if there is space for them, so the caller must ensure that it has flushed recently.
+func (b *bitWriter) encTwoSymbols(ct cTable, av, bv byte) {
+	encA := ct[av]
+	encB := ct[bv]
+	sh := b.nBits & 63
+	combined := uint64(encA.val) | (uint64(encB.val) << (encA.nBits & 63))
+	b.bitContainer |= combined << sh
+	if false {
+		if encA.nBits == 0 {
+			panic("nbitsA 0")
+		}
+		if encB.nBits == 0 {
+			panic("nbitsB 0")
+		}
+	}
+	b.nBits += encA.nBits + encB.nBits
+}
+
+// addBits16ZeroNC will add up to 16 bits.
+// It will not check if there is space for them,
+// so the caller must ensure that it has flushed recently.
+// This is fastest if bits can be zero.
+func (b *bitWriter) addBits16ZeroNC(value uint16, bits uint8) {
+	if bits == 0 {
+		return
+	}
+	value <<= (16 - bits) & 15
+	value >>= (16 - bits) & 15
+	b.bitContainer |= uint64(value) << (b.nBits & 63)
+	b.nBits += bits
+}
+
+// flush will flush all pending full bytes.
+// There will be at least 56 bits available for writing when this has been called.
+// Using flush32 is faster, but leaves less space for writing.
+func (b *bitWriter) flush() {
+	v := b.nBits >> 3
+	switch v {
+	case 0:
+		return
+	case 1:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+		)
+		b.bitContainer >>= 1 << 3
+	case 2:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+		)
+		b.bitContainer >>= 2 << 3
+	case 3:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+		)
+		b.bitContainer >>= 3 << 3
+	case 4:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+			byte(b.bitContainer>>24),
+		)
+		b.bitContainer >>= 4 << 3
+	case 5:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+			byte(b.bitContainer>>24),
+			byte(b.bitContainer>>32),
+		)
+		b.bitContainer >>= 5 << 3
+	case 6:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+			byte(b.bitContainer>>24),
+			byte(b.bitContainer>>32),
+			byte(b.bitContainer>>40),
+		)
+		b.bitContainer >>= 6 << 3
+	case 7:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+			byte(b.bitContainer>>24),
+			byte(b.bitContainer>>32),
+			byte(b.bitContainer>>40),
+			byte(b.bitContainer>>48),
+		)
+		b.bitContainer >>= 7 << 3
+	case 8:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+			byte(b.bitContainer>>24),
+			byte(b.bitContainer>>32),
+			byte(b.bitContainer>>40),
+			byte(b.bitContainer>>48),
+			byte(b.bitContainer>>56),
+		)
+		b.bitContainer = 0
+		b.nBits = 0
+		return
+	default:
+		panic(fmt.Errorf("bits (%d) > 64", b.nBits))
+	}
+	b.nBits &= 7
+}
+
+// flush32 will flush out, so there are at least 32 bits available for writing.
+func (b *bitWriter) flush32() {
+	if b.nBits < 32 {
+		return
+	}
+	b.out = append(b.out,
+		byte(b.bitContainer),
+		byte(b.bitContainer>>8),
+		byte(b.bitContainer>>16),
+		byte(b.bitContainer>>24))
+	b.nBits -= 32
+	b.bitContainer >>= 32
+}
+
+// flushAlign will flush remaining full bytes and align to next byte boundary.
+func (b *bitWriter) flushAlign() {
+	nbBytes := (b.nBits + 7) >> 3
+	for i := uint8(0); i < nbBytes; i++ {
+		b.out = append(b.out, byte(b.bitContainer>>(i*8)))
+	}
+	b.nBits = 0
+	b.bitContainer = 0
+}
+
+// close will write the alignment bit and write the final byte(s)
+// to the output.
+func (b *bitWriter) close() error {
+	// End mark
+	b.addBits16Clean(1, 1)
+	// flush until next byte.
+	b.flushAlign()
+	return nil
+}
+
+// reset and continue writing by appending to out.
+func (b *bitWriter) reset(out []byte) {
+	b.bitContainer = 0
+	b.nBits = 0
+	b.out = out
+}

vendor/github.com/klauspost/compress/huff0/bytereader.go

@@ -0,0 +1,54 @@
+// Copyright 2018 Klaus Post. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+// Based on work Copyright (c) 2013, Yann Collet, released under BSD License.
+
+package huff0
+
+// byteReader provides a byte reader that reads
+// little endian values from a byte stream.
+// The input stream is manually advanced.
+// The reader performs no bounds checks.
+type byteReader struct {
+	b   []byte
+	off int
+}
+
+// init will initialize the reader and set the input.
+func (b *byteReader) init(in []byte) {
+	b.b = in
+	b.off = 0
+}
+
+// advance the stream b n bytes.
+func (b *byteReader) advance(n uint) {
+	b.off += int(n)
+}
+
+// Int32 returns a little endian int32 starting at current offset.
+func (b byteReader) Int32() int32 {
+	v3 := int32(b.b[b.off+3])
+	v2 := int32(b.b[b.off+2])
+	v1 := int32(b.b[b.off+1])
+	v0 := int32(b.b[b.off])
+	return (v3 << 24) | (v2 << 16) | (v1 << 8) | v0
+}
+
+// Uint32 returns a little endian uint32 starting at current offset.
+func (b byteReader) Uint32() uint32 {
+	v3 := uint32(b.b[b.off+3])
+	v2 := uint32(b.b[b.off+2])
+	v1 := uint32(b.b[b.off+1])
+	v0 := uint32(b.b[b.off])
+	return (v3 << 24) | (v2 << 16) | (v1 << 8) | v0
+}
+
+// unread returns the unread portion of the input.
+func (b byteReader) unread() []byte {
+	return b.b[b.off:]
+}
+
+// remain will return the number of bytes remaining.
+func (b byteReader) remain() int {
+	return len(b.b) - b.off
+}

vendor/github.com/klauspost/compress/huff0/compress.go

@@ -0,0 +1,720 @@
+package huff0
+
+import (
+	"fmt"
+	"runtime"
+	"sync"
+)
+
+// Compress1X will compress the input.
+// The output can be decoded using Decompress1X.
+// Supply a Scratch object. The scratch object contains state about re-use,
+// So when sharing across independent encodes, be sure to set the re-use policy.
+func Compress1X(in []byte, s *Scratch) (out []byte, reUsed bool, err error) {
+	s, err = s.prepare(in)
+	if err != nil {
+		return nil, false, err
+	}
+	return compress(in, s, s.compress1X)
+}
+
+// Compress4X will compress the input. The input is split into 4 independent blocks
+// and compressed similar to Compress1X.
+// The output can be decoded using Decompress4X.
+// Supply a Scratch object. The scratch object contains state about re-use,
+// So when sharing across independent encodes, be sure to set the re-use policy.
+func Compress4X(in []byte, s *Scratch) (out []byte, reUsed bool, err error) {
+	s, err = s.prepare(in)
+	if err != nil {
+		return nil, false, err
+	}
+	if false {
+		// TODO: compress4Xp only slightly faster.
+		const parallelThreshold = 8 << 10
+		if len(in) < parallelThreshold || runtime.GOMAXPROCS(0) == 1 {
+			return compress(in, s, s.compress4X)
+		}
+		return compress(in, s, s.compress4Xp)
+	}
+	return compress(in, s, s.compress4X)
+}
+
+func compress(in []byte, s *Scratch, compressor func(src []byte) ([]byte, error)) (out []byte, reUsed bool, err error) {
+	// Nuke previous table if we cannot reuse anyway.
+	if s.Reuse == ReusePolicyNone {
+		s.prevTable = s.prevTable[:0]
+	}
+
+	// Create histogram, if none was provided.
+	maxCount := s.maxCount
+	var canReuse = false
+	if maxCount == 0 {
+		maxCount, canReuse = s.countSimple(in)
+	} else {
+		canReuse = s.canUseTable(s.prevTable)
+	}
+
+	// We want the output size to be less than this:
+	wantSize := len(in)
+	if s.WantLogLess > 0 {
+		wantSize -= wantSize >> s.WantLogLess
+	}
+
+	// Reset for next run.
+	s.clearCount = true
+	s.maxCount = 0
+	if maxCount >= len(in) {
+		if maxCount > len(in) {
+			return nil, false, fmt.Errorf("maxCount (%d) > length (%d)", maxCount, len(in))
+		}
+		if len(in) == 1 {
+			return nil, false, ErrIncompressible
+		}
+		// One symbol, use RLE
+		return nil, false, ErrUseRLE
+	}
+	if maxCount == 1 || maxCount < (len(in)>>7) {
+		// Each symbol present maximum once or too well distributed.
+		return nil, false, ErrIncompressible
+	}
+	if s.Reuse == ReusePolicyMust && !canReuse {
+		// We must reuse, but we can't.
+		return nil, false, ErrIncompressible
+	}
+	if (s.Reuse == ReusePolicyPrefer || s.Reuse == ReusePolicyMust) && canReuse {
+		keepTable := s.cTable
+		keepTL := s.actualTableLog
+		s.cTable = s.prevTable
+		s.actualTableLog = s.prevTableLog
+		s.Out, err = compressor(in)
+		s.cTable = keepTable
+		s.actualTableLog = keepTL
+		if err == nil && len(s.Out) < wantSize {
+			s.OutData = s.Out
+			return s.Out, true, nil
+		}
+		if s.Reuse == ReusePolicyMust {
+			return nil, false, ErrIncompressible
+		}
+		// Do not attempt to re-use later.
+		s.prevTable = s.prevTable[:0]
+	}
+
+	// Calculate new table.
+	err = s.buildCTable()
+	if err != nil {
+		return nil, false, err
+	}
+
+	if false && !s.canUseTable(s.cTable) {
+		panic("invalid table generated")
+	}
+
+	if s.Reuse == ReusePolicyAllow && canReuse {
+		hSize := len(s.Out)
+		oldSize := s.prevTable.estimateSize(s.count[:s.symbolLen])
+		newSize := s.cTable.estimateSize(s.count[:s.symbolLen])
+		if oldSize <= hSize+newSize || hSize+12 >= wantSize {
+			// Retain cTable even if we re-use.
+			keepTable := s.cTable
+			keepTL := s.actualTableLog
+
+			s.cTable = s.prevTable
+			s.actualTableLog = s.prevTableLog
+			s.Out, err = compressor(in)
+
+			// Restore ctable.
+			s.cTable = keepTable
+			s.actualTableLog = keepTL
+			if err != nil {
+				return nil, false, err
+			}
+			if len(s.Out) >= wantSize {
+				return nil, false, ErrIncompressible
+			}
+			s.OutData = s.Out
+			return s.Out, true, nil
+		}
+	}
+
+	// Use new table
+	err = s.cTable.write(s)
+	if err != nil {
+		s.OutTable = nil
+		return nil, false, err
+	}
+	s.OutTable = s.Out
+
+	// Compress using new table
+	s.Out, err = compressor(in)
+	if err != nil {
+		s.OutTable = nil
+		return nil, false, err
+	}
+	if len(s.Out) >= wantSize {
+		s.OutTable = nil
+		return nil, false, ErrIncompressible
+	}
+	// Move current table into previous.
+	s.prevTable, s.prevTableLog, s.cTable = s.cTable, s.actualTableLog, s.prevTable[:0]
+	s.OutData = s.Out[len(s.OutTable):]
+	return s.Out, false, nil
+}
+
+// EstimateSizes will estimate the data sizes
+func EstimateSizes(in []byte, s *Scratch) (tableSz, dataSz, reuseSz int, err error) {
+	s, err = s.prepare(in)
+	if err != nil {
+		return 0, 0, 0, err
+	}
+
+	// Create histogram, if none was provided.
+	tableSz, dataSz, reuseSz = -1, -1, -1
+	maxCount := s.maxCount
+	var canReuse = false
+	if maxCount == 0 {
+		maxCount, canReuse = s.countSimple(in)
+	} else {
+		canReuse = s.canUseTable(s.prevTable)
+	}
+
+	// We want the output size to be less than this:
+	wantSize := len(in)
+	if s.WantLogLess > 0 {
+		wantSize -= wantSize >> s.WantLogLess
+	}
+
+	// Reset for next run.
+	s.clearCount = true
+	s.maxCount = 0
+	if maxCount >= len(in) {
+		if maxCount > len(in) {
+			return 0, 0, 0, fmt.Errorf("maxCount (%d) > length (%d)", maxCount, len(in))
+		}
+		if len(in) == 1 {
+			return 0, 0, 0, ErrIncompressible
+		}
+		// One symbol, use RLE
+		return 0, 0, 0, ErrUseRLE
+	}
+	if maxCount == 1 || maxCount < (len(in)>>7) {
+		// Each symbol present maximum once or too well distributed.
+		return 0, 0, 0, ErrIncompressible
+	}
+
+	// Calculate new table.
+	err = s.buildCTable()
+	if err != nil {
+		return 0, 0, 0, err
+	}
+
+	if false && !s.canUseTable(s.cTable) {
+		panic("invalid table generated")
+	}
+
+	tableSz, err = s.cTable.estTableSize(s)
+	if err != nil {
+		return 0, 0, 0, err
+	}
+	if canReuse {
+		reuseSz = s.prevTable.estimateSize(s.count[:s.symbolLen])
+	}
+	dataSz = s.cTable.estimateSize(s.count[:s.symbolLen])
+
+	// Restore
+	return tableSz, dataSz, reuseSz, nil
+}
+
+func (s *Scratch) compress1X(src []byte) ([]byte, error) {
+	return s.compress1xDo(s.Out, src)
+}
+
+func (s *Scratch) compress1xDo(dst, src []byte) ([]byte, error) {
+	var bw = bitWriter{out: dst}
+
+	// N is length divisible by 4.
+	n := len(src)
+	n -= n & 3
+	cTable := s.cTable[:256]
+
+	// Encode last bytes.
+	for i := len(src) & 3; i > 0; i-- {
+		bw.encSymbol(cTable, src[n+i-1])
+	}
+	n -= 4
+	if s.actualTableLog <= 8 {
+		for ; n >= 0; n -= 4 {
+			tmp := src[n : n+4]
+			// tmp should be len 4
+			bw.flush32()
+			bw.encTwoSymbols(cTable, tmp[3], tmp[2])
+			bw.encTwoSymbols(cTable, tmp[1], tmp[0])
+		}
+	} else {
+		for ; n >= 0; n -= 4 {
+			tmp := src[n : n+4]
+			// tmp should be len 4
+			bw.flush32()
+			bw.encTwoSymbols(cTable, tmp[3], tmp[2])
+			bw.flush32()
+			bw.encTwoSymbols(cTable, tmp[1], tmp[0])
+		}
+	}
+	err := bw.close()
+	return bw.out, err
+}
+
+var sixZeros [6]byte
+
+func (s *Scratch) compress4X(src []byte) ([]byte, error) {
+	if len(src) < 12 {
+		return nil, ErrIncompressible
+	}
+	segmentSize := (len(src) + 3) / 4
+
+	// Add placeholder for output length
+	offsetIdx := len(s.Out)
+	s.Out = append(s.Out, sixZeros[:]...)
+
+	for i := 0; i < 4; i++ {
+		toDo := src
+		if len(toDo) > segmentSize {
+			toDo = toDo[:segmentSize]
+		}
+		src = src[len(toDo):]
+
+		var err error
+		idx := len(s.Out)
+		s.Out, err = s.compress1xDo(s.Out, toDo)
+		if err != nil {
+			return nil, err
+		}
+		// Write compressed length as little endian before block.
+		if i < 3 {
+			// Last length is not written.
+			length := len(s.Out) - idx
+			s.Out[i*2+offsetIdx] = byte(length)
+			s.Out[i*2+offsetIdx+1] = byte(length >> 8)
+		}
+	}
+
+	return s.Out, nil
+}
+
+// compress4Xp will compress 4 streams using separate goroutines.
+func (s *Scratch) compress4Xp(src []byte) ([]byte, error) {
+	if len(src) < 12 {
+		return nil, ErrIncompressible
+	}
+	// Add placeholder for output length
+	s.Out = s.Out[:6]
+
+	segmentSize := (len(src) + 3) / 4
+	var wg sync.WaitGroup
+	var errs [4]error
+	wg.Add(4)
+	for i := 0; i < 4; i++ {
+		toDo := src
+		if len(toDo) > segmentSize {
+			toDo = toDo[:segmentSize]
+		}
+		src = src[len(toDo):]
+
+		// Separate goroutine for each block.
+		go func(i int) {
+			s.tmpOut[i], errs[i] = s.compress1xDo(s.tmpOut[i][:0], toDo)
+			wg.Done()
+		}(i)
+	}
+	wg.Wait()
+	for i := 0; i < 4; i++ {
+		if errs[i] != nil {
+			return nil, errs[i]
+		}
+		o := s.tmpOut[i]
+		// Write compressed length as little endian before block.
+		if i < 3 {
+			// Last length is not written.
+			s.Out[i*2] = byte(len(o))
+			s.Out[i*2+1] = byte(len(o) >> 8)
+		}
+
+		// Write output.
+		s.Out = append(s.Out, o...)
+	}
+	return s.Out, nil
+}
+
+// countSimple will create a simple histogram in s.count.
+// Returns the biggest count.
+// Does not update s.clearCount.
+func (s *Scratch) countSimple(in []byte) (max int, reuse bool) {
+	reuse = true
+	for _, v := range in {
+		s.count[v]++
+	}
+	m := uint32(0)
+	if len(s.prevTable) > 0 {
+		for i, v := range s.count[:] {
+			if v > m {
+				m = v
+			}
+			if v > 0 {
+				s.symbolLen = uint16(i) + 1
+				if i >= len(s.prevTable) {
+					reuse = false
+				} else {
+					if s.prevTable[i].nBits == 0 {
+						reuse = false
+					}
+				}
+			}
+		}
+		return int(m), reuse
+	}
+	for i, v := range s.count[:] {
+		if v > m {
+			m = v
+		}
+		if v > 0 {
+			s.symbolLen = uint16(i) + 1
+		}
+	}
+	return int(m), false
+}
+
+func (s *Scratch) canUseTable(c cTable) bool {
+	if len(c) < int(s.symbolLen) {
+		return false
+	}
+	for i, v := range s.count[:s.symbolLen] {
+		if v != 0 && c[i].nBits == 0 {
+			return false
+		}
+	}
+	return true
+}
+
+func (s *Scratch) validateTable(c cTable) bool {
+	if len(c) < int(s.symbolLen) {
+		return false
+	}
+	for i, v := range s.count[:s.symbolLen] {
+		if v != 0 {
+			if c[i].nBits == 0 {
+				return false
+			}
+			if c[i].nBits > s.actualTableLog {
+				return false
+			}
+		}
+	}
+	return true
+}
+
+// minTableLog provides the minimum logSize to safely represent a distribution.
+func (s *Scratch) minTableLog() uint8 {
+	minBitsSrc := highBit32(uint32(s.br.remain())) + 1
+	minBitsSymbols := highBit32(uint32(s.symbolLen-1)) + 2
+	if minBitsSrc < minBitsSymbols {
+		return uint8(minBitsSrc)
+	}
+	return uint8(minBitsSymbols)
+}
+
+// optimalTableLog calculates and sets the optimal tableLog in s.actualTableLog
+func (s *Scratch) optimalTableLog() {
+	tableLog := s.TableLog
+	minBits := s.minTableLog()
+	maxBitsSrc := uint8(highBit32(uint32(s.br.remain()-1))) - 1
+	if maxBitsSrc < tableLog {
+		// Accuracy can be reduced
+		tableLog = maxBitsSrc
+	}
+	if minBits > tableLog {
+		tableLog = minBits
+	}
+	// Need a minimum to safely represent all symbol values
+	if tableLog < minTablelog {
+		tableLog = minTablelog
+	}
+	if tableLog > tableLogMax {
+		tableLog = tableLogMax
+	}
+	s.actualTableLog = tableLog
+}
+
+type cTableEntry struct {
+	val   uint16
+	nBits uint8
+	// We have 8 bits extra
+}
+
+const huffNodesMask = huffNodesLen - 1
+
+func (s *Scratch) buildCTable() error {
+	s.optimalTableLog()
+	s.huffSort()
+	if cap(s.cTable) < maxSymbolValue+1 {
+		s.cTable = make([]cTableEntry, s.symbolLen, maxSymbolValue+1)
+	} else {
+		s.cTable = s.cTable[:s.symbolLen]
+		for i := range s.cTable {
+			s.cTable[i] = cTableEntry{}
+		}
+	}
+
+	var startNode = int16(s.symbolLen)
+	nonNullRank := s.symbolLen - 1
+
+	nodeNb := startNode
+	huffNode := s.nodes[1 : huffNodesLen+1]
+
+	// This overlays the slice above, but allows "-1" index lookups.
+	// Different from reference implementation.
+	huffNode0 := s.nodes[0 : huffNodesLen+1]
+
+	for huffNode[nonNullRank].count == 0 {
+		nonNullRank--
+	}
+
+	lowS := int16(nonNullRank)
+	nodeRoot := nodeNb + lowS - 1
+	lowN := nodeNb
+	huffNode[nodeNb].count = huffNode[lowS].count + huffNode[lowS-1].count
+	huffNode[lowS].parent, huffNode[lowS-1].parent = uint16(nodeNb), uint16(nodeNb)
+	nodeNb++
+	lowS -= 2
+	for n := nodeNb; n <= nodeRoot; n++ {
+		huffNode[n].count = 1 << 30
+	}
+	// fake entry, strong barrier
+	huffNode0[0].count = 1 << 31
+
+	// create parents
+	for nodeNb <= nodeRoot {
+		var n1, n2 int16
+		if huffNode0[lowS+1].count < huffNode0[lowN+1].count {
+			n1 = lowS
+			lowS--
+		} else {
+			n1 = lowN
+			lowN++
+		}
+		if huffNode0[lowS+1].count < huffNode0[lowN+1].count {
+			n2 = lowS
+			lowS--
+		} else {
+			n2 = lowN
+			lowN++
+		}
+
+		huffNode[nodeNb].count = huffNode0[n1+1].count + huffNode0[n2+1].count
+		huffNode0[n1+1].parent, huffNode0[n2+1].parent = uint16(nodeNb), uint16(nodeNb)
+		nodeNb++
+	}
+
+	// distribute weights (unlimited tree height)
+	huffNode[nodeRoot].nbBits = 0
+	for n := nodeRoot - 1; n >= startNode; n-- {
+		huffNode[n].nbBits = huffNode[huffNode[n].parent].nbBits + 1
+	}
+	for n := uint16(0); n <= nonNullRank; n++ {
+		huffNode[n].nbBits = huffNode[huffNode[n].parent].nbBits + 1
+	}
+	s.actualTableLog = s.setMaxHeight(int(nonNullRank))
+	maxNbBits := s.actualTableLog
+
+	// fill result into tree (val, nbBits)
+	if maxNbBits > tableLogMax {
+		return fmt.Errorf("internal error: maxNbBits (%d) > tableLogMax (%d)", maxNbBits, tableLogMax)
+	}
+	var nbPerRank [tableLogMax + 1]uint16
+	var valPerRank [16]uint16
+	for _, v := range huffNode[:nonNullRank+1] {
+		nbPerRank[v.nbBits]++
+	}
+	// determine stating value per rank
+	{
+		min := uint16(0)
+		for n := maxNbBits; n > 0; n-- {
+			// get starting value within each rank
+			valPerRank[n] = min
+			min += nbPerRank[n]
+			min >>= 1
+		}
+	}
+
+	// push nbBits per symbol, symbol order
+	for _, v := range huffNode[:nonNullRank+1] {
+		s.cTable[v.symbol].nBits = v.nbBits
+	}
+
+	// assign value within rank, symbol order
+	t := s.cTable[:s.symbolLen]
+	for n, val := range t {
+		nbits := val.nBits & 15
+		v := valPerRank[nbits]
+		t[n].val = v
+		valPerRank[nbits] = v + 1
+	}
+
+	return nil
+}
+
+// huffSort will sort symbols, decreasing order.
+func (s *Scratch) huffSort() {
+	type rankPos struct {
+		base    uint32
+		current uint32
+	}
+
+	// Clear nodes
+	nodes := s.nodes[:huffNodesLen+1]
+	s.nodes = nodes
+	nodes = nodes[1 : huffNodesLen+1]
+
+	// Sort into buckets based on length of symbol count.
+	var rank [32]rankPos
+	for _, v := range s.count[:s.symbolLen] {
+		r := highBit32(v+1) & 31
+		rank[r].base++
+	}
+	// maxBitLength is log2(BlockSizeMax) + 1
+	const maxBitLength = 18 + 1
+	for n := maxBitLength; n > 0; n-- {
+		rank[n-1].base += rank[n].base
+	}
+	for n := range rank[:maxBitLength] {
+		rank[n].current = rank[n].base
+	}
+	for n, c := range s.count[:s.symbolLen] {
+		r := (highBit32(c+1) + 1) & 31
+		pos := rank[r].current
+		rank[r].current++
+		prev := nodes[(pos-1)&huffNodesMask]
+		for pos > rank[r].base && c > prev.count {
+			nodes[pos&huffNodesMask] = prev
+			pos--
+			prev = nodes[(pos-1)&huffNodesMask]
+		}
+		nodes[pos&huffNodesMask] = nodeElt{count: c, symbol: byte(n)}
+	}
+}
+
+func (s *Scratch) setMaxHeight(lastNonNull int) uint8 {
+	maxNbBits := s.actualTableLog
+	huffNode := s.nodes[1 : huffNodesLen+1]
+	//huffNode = huffNode[: huffNodesLen]
+
+	largestBits := huffNode[lastNonNull].nbBits
+
+	// early exit : no elt > maxNbBits
+	if largestBits <= maxNbBits {
+		return largestBits
+	}
+	totalCost := int(0)
+	baseCost := int(1) << (largestBits - maxNbBits)
+	n := uint32(lastNonNull)
+
+	for huffNode[n].nbBits > maxNbBits {
+		totalCost += baseCost - (1 << (largestBits - huffNode[n].nbBits))
+		huffNode[n].nbBits = maxNbBits
+		n--
+	}
+	// n stops at huffNode[n].nbBits <= maxNbBits
+
+	for huffNode[n].nbBits == maxNbBits {
+		n--
+	}
+	// n end at index of smallest symbol using < maxNbBits
+
+	// renorm totalCost
+	totalCost >>= largestBits - maxNbBits /* note : totalCost is necessarily a multiple of baseCost */
+
+	// repay normalized cost
+	{
+		const noSymbol = 0xF0F0F0F0
+		var rankLast [tableLogMax + 2]uint32
+
+		for i := range rankLast[:] {
+			rankLast[i] = noSymbol
+		}
+
+		// Get pos of last (smallest) symbol per rank
+		{
+			currentNbBits := maxNbBits
+			for pos := int(n); pos >= 0; pos-- {
+				if huffNode[pos].nbBits >= currentNbBits {
+					continue
+				}
+				currentNbBits = huffNode[pos].nbBits // < maxNbBits
+				rankLast[maxNbBits-currentNbBits] = uint32(pos)
+			}
+		}
+
+		for totalCost > 0 {
+			nBitsToDecrease := uint8(highBit32(uint32(totalCost))) + 1
+
+			for ; nBitsToDecrease > 1; nBitsToDecrease-- {
+				highPos := rankLast[nBitsToDecrease]
+				lowPos := rankLast[nBitsToDecrease-1]
+				if highPos == noSymbol {
+					continue
+				}
+				if lowPos == noSymbol {
+					break
+				}
+				highTotal := huffNode[highPos].count
+				lowTotal := 2 * huffNode[lowPos].count
+				if highTotal <= lowTotal {
+					break
+				}
+			}
+			// only triggered when no more rank 1 symbol left => find closest one (note : there is necessarily at least one !)
+			// HUF_MAX_TABLELOG test just to please gcc 5+; but it should not be necessary
+			// FIXME: try to remove
+			for (nBitsToDecrease <= tableLogMax) && (rankLast[nBitsToDecrease] == noSymbol) {
+				nBitsToDecrease++
+			}
+			totalCost -= 1 << (nBitsToDecrease - 1)
+			if rankLast[nBitsToDecrease-1] == noSymbol {
+				// this rank is no longer empty
+				rankLast[nBitsToDecrease-1] = rankLast[nBitsToDecrease]
+			}
+			huffNode[rankLast[nBitsToDecrease]].nbBits++
+			if rankLast[nBitsToDecrease] == 0 {
+				/* special case, reached largest symbol */
+				rankLast[nBitsToDecrease] = noSymbol
+			} else {
+				rankLast[nBitsToDecrease]--
+				if huffNode[rankLast[nBitsToDecrease]].nbBits != maxNbBits-nBitsToDecrease {
+					rankLast[nBitsToDecrease] = noSymbol /* this rank is now empty */
+				}
+			}
+		}
+
+		for totalCost < 0 { /* Sometimes, cost correction overshoot */
+			if rankLast[1] == noSymbol { /* special case : no rank 1 symbol (using maxNbBits-1); let's create one from largest rank 0 (using maxNbBits) */
+				for huffNode[n].nbBits == maxNbBits {
+					n--
+				}
+				huffNode[n+1].nbBits--
+				rankLast[1] = n + 1
+				totalCost++
+				continue
+			}
+			huffNode[rankLast[1]+1].nbBits--
+			rankLast[1]++
+			totalCost++
+		}
+	}
+	return maxNbBits
+}
+
+type nodeElt struct {
+	count  uint32
+	parent uint16
+	symbol byte
+	nbBits uint8
+}

vendor/github.com/klauspost/compress/huff0/huff0.go

@@ -0,0 +1,335 @@
+// Package huff0 provides fast huffman encoding as used in zstd.
+//
+// See README.md at https://github.com/klauspost/compress/tree/master/huff0 for details.
+package huff0
+
+import (
+	"errors"
+	"fmt"
+	"math"
+	"math/bits"
+
+	"github.com/klauspost/compress/fse"
+)
+
+const (
+	maxSymbolValue = 255
+
+	// zstandard limits tablelog to 11, see:
+	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#huffman-tree-description
+	tableLogMax     = 11
+	tableLogDefault = 11
+	minTablelog     = 5
+	huffNodesLen    = 512
+
+	// BlockSizeMax is maximum input size for a single block uncompressed.
+	BlockSizeMax = 1<<18 - 1
+)
+
+var (
+	// ErrIncompressible is returned when input is judged to be too hard to compress.
+	ErrIncompressible = errors.New("input is not compressible")
+
+	// ErrUseRLE is returned from the compressor when the input is a single byte value repeated.
+	ErrUseRLE = errors.New("input is single value repeated")
+
+	// ErrTooBig is return if input is too large for a single block.
+	ErrTooBig = errors.New("input too big")
+
+	// ErrMaxDecodedSizeExceeded is return if input is too large for a single block.
+	ErrMaxDecodedSizeExceeded = errors.New("maximum output size exceeded")
+)
+
+type ReusePolicy uint8
+
+const (
+	// ReusePolicyAllow will allow reuse if it produces smaller output.
+	ReusePolicyAllow ReusePolicy = iota
+
+	// ReusePolicyPrefer will re-use aggressively if possible.
+	// This will not check if a new table will produce smaller output,
+	// except if the current table is impossible to use or
+	// compressed output is bigger than input.
+	ReusePolicyPrefer
+
+	// ReusePolicyNone will disable re-use of tables.
+	// This is slightly faster than ReusePolicyAllow but may produce larger output.
+	ReusePolicyNone
+
+	// ReusePolicyMust must allow reuse and produce smaller output.
+	ReusePolicyMust
+)
+
+type Scratch struct {
+	count [maxSymbolValue + 1]uint32
+
+	// Per block parameters.
+	// These can be used to override compression parameters of the block.
+	// Do not touch, unless you know what you are doing.
+
+	// Out is output buffer.
+	// If the scratch is re-used before the caller is done processing the output,
+	// set this field to nil.
+	// Otherwise the output buffer will be re-used for next Compression/Decompression step
+	// and allocation will be avoided.
+	Out []byte
+
+	// OutTable will contain the table data only, if a new table has been generated.
+	// Slice of the returned data.
+	OutTable []byte
+
+	// OutData will contain the compressed data.
+	// Slice of the returned data.
+	OutData []byte
+
+	// MaxDecodedSize will set the maximum allowed output size.
+	// This value will automatically be set to BlockSizeMax if not set.
+	// Decoders will return ErrMaxDecodedSizeExceeded is this limit is exceeded.
+	MaxDecodedSize int
+
+	br byteReader
+
+	// MaxSymbolValue will override the maximum symbol value of the next block.
+	MaxSymbolValue uint8
+
+	// TableLog will attempt to override the tablelog for the next block.
+	// Must be <= 11 and >= 5.
+	TableLog uint8
+
+	// Reuse will specify the reuse policy
+	Reuse ReusePolicy
+
+	// WantLogLess allows to specify a log 2 reduction that should at least be achieved,
+	// otherwise the block will be returned as incompressible.
+	// The reduction should then at least be (input size >> WantLogLess)
+	// If WantLogLess == 0 any improvement will do.
+	WantLogLess uint8
+
+	symbolLen      uint16 // Length of active part of the symbol table.
+	maxCount       int    // count of the most probable symbol
+	clearCount     bool   // clear count
+	actualTableLog uint8  // Selected tablelog.
+	prevTableLog   uint8  // Tablelog for previous table
+	prevTable      cTable // Table used for previous compression.
+	cTable         cTable // compression table
+	dt             dTable // decompression table
+	nodes          []nodeElt
+	tmpOut         [4][]byte
+	fse            *fse.Scratch
+	huffWeight     [maxSymbolValue + 1]byte
+}
+
+// TransferCTable will transfer the previously used compression table.
+func (s *Scratch) TransferCTable(src *Scratch) {
+	if cap(s.prevTable) < len(src.prevTable) {
+		s.prevTable = make(cTable, 0, maxSymbolValue+1)
+	}
+	s.prevTable = s.prevTable[:len(src.prevTable)]
+	copy(s.prevTable, src.prevTable)
+	s.prevTableLog = src.prevTableLog
+}
+
+func (s *Scratch) prepare(in []byte) (*Scratch, error) {
+	if len(in) > BlockSizeMax {
+		return nil, ErrTooBig
+	}
+	if s == nil {
+		s = &Scratch{}
+	}
+	if s.MaxSymbolValue == 0 {
+		s.MaxSymbolValue = maxSymbolValue
+	}
+	if s.TableLog == 0 {
+		s.TableLog = tableLogDefault
+	}
+	if s.TableLog > tableLogMax || s.TableLog < minTablelog {
+		return nil, fmt.Errorf(" invalid tableLog %d (%d -> %d)", s.TableLog, minTablelog, tableLogMax)
+	}
+	if s.MaxDecodedSize <= 0 || s.MaxDecodedSize > BlockSizeMax {
+		s.MaxDecodedSize = BlockSizeMax
+	}
+	if s.clearCount && s.maxCount == 0 {
+		for i := range s.count {
+			s.count[i] = 0
+		}
+		s.clearCount = false
+	}
+	if cap(s.Out) == 0 {
+		s.Out = make([]byte, 0, len(in))
+	}
+	s.Out = s.Out[:0]
+
+	s.OutTable = nil
+	s.OutData = nil
+	if cap(s.nodes) < huffNodesLen+1 {
+		s.nodes = make([]nodeElt, 0, huffNodesLen+1)
+	}
+	s.nodes = s.nodes[:0]
+	if s.fse == nil {
+		s.fse = &fse.Scratch{}
+	}
+	s.br.init(in)
+
+	return s, nil
+}
+
+type cTable []cTableEntry
+
+func (c cTable) write(s *Scratch) error {
+	var (
+		// precomputed conversion table
+		bitsToWeight [tableLogMax + 1]byte
+		huffLog      = s.actualTableLog
+		// last weight is not saved.
+		maxSymbolValue = uint8(s.symbolLen - 1)
+		huffWeight     = s.huffWeight[:256]
+	)
+	const (
+		maxFSETableLog = 6
+	)
+	// convert to weight
+	bitsToWeight[0] = 0
+	for n := uint8(1); n < huffLog+1; n++ {
+		bitsToWeight[n] = huffLog + 1 - n
+	}
+
+	// Acquire histogram for FSE.
+	hist := s.fse.Histogram()
+	hist = hist[:256]
+	for i := range hist[:16] {
+		hist[i] = 0
+	}
+	for n := uint8(0); n < maxSymbolValue; n++ {
+		v := bitsToWeight[c[n].nBits] & 15
+		huffWeight[n] = v
+		hist[v]++
+	}
+
+	// FSE compress if feasible.
+	if maxSymbolValue >= 2 {
+		huffMaxCnt := uint32(0)
+		huffMax := uint8(0)
+		for i, v := range hist[:16] {
+			if v == 0 {
+				continue
+			}
+			huffMax = byte(i)
+			if v > huffMaxCnt {
+				huffMaxCnt = v
+			}
+		}
+		s.fse.HistogramFinished(huffMax, int(huffMaxCnt))
+		s.fse.TableLog = maxFSETableLog
+		b, err := fse.Compress(huffWeight[:maxSymbolValue], s.fse)
+		if err == nil && len(b) < int(s.symbolLen>>1) {
+			s.Out = append(s.Out, uint8(len(b)))
+			s.Out = append(s.Out, b...)
+			return nil
+		}
+		// Unable to compress (RLE/uncompressible)
+	}
+	// write raw values as 4-bits (max : 15)
+	if maxSymbolValue > (256 - 128) {
+		// should not happen : likely means source cannot be compressed
+		return ErrIncompressible
+	}
+	op := s.Out
+	// special case, pack weights 4 bits/weight.
+	op = append(op, 128|(maxSymbolValue-1))
+	// be sure it doesn't cause msan issue in final combination
+	huffWeight[maxSymbolValue] = 0
+	for n := uint16(0); n < uint16(maxSymbolValue); n += 2 {
+		op = append(op, (huffWeight[n]<<4)|huffWeight[n+1])
+	}
+	s.Out = op
+	return nil
+}
+
+func (c cTable) estTableSize(s *Scratch) (sz int, err error) {
+	var (
+		// precomputed conversion table
+		bitsToWeight [tableLogMax + 1]byte
+		huffLog      = s.actualTableLog
+		// last weight is not saved.
+		maxSymbolValue = uint8(s.symbolLen - 1)
+		huffWeight     = s.huffWeight[:256]
+	)
+	const (
+		maxFSETableLog = 6
+	)
+	// convert to weight
+	bitsToWeight[0] = 0
+	for n := uint8(1); n < huffLog+1; n++ {
+		bitsToWeight[n] = huffLog + 1 - n
+	}
+
+	// Acquire histogram for FSE.
+	hist := s.fse.Histogram()
+	hist = hist[:256]
+	for i := range hist[:16] {
+		hist[i] = 0
+	}
+	for n := uint8(0); n < maxSymbolValue; n++ {
+		v := bitsToWeight[c[n].nBits] & 15
+		huffWeight[n] = v
+		hist[v]++
+	}
+
+	// FSE compress if feasible.
+	if maxSymbolValue >= 2 {
+		huffMaxCnt := uint32(0)
+		huffMax := uint8(0)
+		for i, v := range hist[:16] {
+			if v == 0 {
+				continue
+			}
+			huffMax = byte(i)
+			if v > huffMaxCnt {
+				huffMaxCnt = v
+			}
+		}
+		s.fse.HistogramFinished(huffMax, int(huffMaxCnt))
+		s.fse.TableLog = maxFSETableLog
+		b, err := fse.Compress(huffWeight[:maxSymbolValue], s.fse)
+		if err == nil && len(b) < int(s.symbolLen>>1) {
+			sz += 1 + len(b)
+			return sz, nil
+		}
+		// Unable to compress (RLE/uncompressible)
+	}
+	// write raw values as 4-bits (max : 15)
+	if maxSymbolValue > (256 - 128) {
+		// should not happen : likely means source cannot be compressed
+		return 0, ErrIncompressible
+	}
+	// special case, pack weights 4 bits/weight.
+	sz += 1 + int(maxSymbolValue/2)
+	return sz, nil
+}
+
+// estimateSize returns the estimated size in bytes of the input represented in the
+// histogram supplied.
+func (c cTable) estimateSize(hist []uint32) int {
+	nbBits := uint32(7)
+	for i, v := range c[:len(hist)] {
+		nbBits += uint32(v.nBits) * hist[i]
+	}
+	return int(nbBits >> 3)
+}
+
+// minSize returns the minimum possible size considering the shannon limit.
+func (s *Scratch) minSize(total int) int {
+	nbBits := float64(7)
+	fTotal := float64(total)
+	for _, v := range s.count[:s.symbolLen] {
+		n := float64(v)
+		if n > 0 {
+			nbBits += math.Log2(fTotal/n) * n
+		}
+	}
+	return int(nbBits) >> 3
+}
+
+func highBit32(val uint32) (n uint32) {
+	return uint32(bits.Len32(val) - 1)
+}

vendor/github.com/klauspost/compress/internal/snapref/LICENSE

@@ -0,0 +1,27 @@
+Copyright (c) 2011 The Snappy-Go Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Google Inc. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

vendor/github.com/klauspost/compress/internal/snapref/decode.go

@@ -0,0 +1,264 @@
+// Copyright 2011 The Snappy-Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package snapref
+
+import (
+	"encoding/binary"
+	"errors"
+	"io"
+)
+
+var (
+	// ErrCorrupt reports that the input is invalid.
+	ErrCorrupt = errors.New("snappy: corrupt input")
+	// ErrTooLarge reports that the uncompressed length is too large.
+	ErrTooLarge = errors.New("snappy: decoded block is too large")
+	// ErrUnsupported reports that the input isn't supported.
+	ErrUnsupported = errors.New("snappy: unsupported input")
+
+	errUnsupportedLiteralLength = errors.New("snappy: unsupported literal length")
+)
+
+// DecodedLen returns the length of the decoded block.
+func DecodedLen(src []byte) (int, error) {
+	v, _, err := decodedLen(src)
+	return v, err
+}
+
+// decodedLen returns the length of the decoded block and the number of bytes
+// that the length header occupied.
+func decodedLen(src []byte) (blockLen, headerLen int, err error) {
+	v, n := binary.Uvarint(src)
+	if n <= 0 || v > 0xffffffff {
+		return 0, 0, ErrCorrupt
+	}
+
+	const wordSize = 32 << (^uint(0) >> 32 & 1)
+	if wordSize == 32 && v > 0x7fffffff {
+		return 0, 0, ErrTooLarge
+	}
+	return int(v), n, nil
+}
+
+const (
+	decodeErrCodeCorrupt                  = 1
+	decodeErrCodeUnsupportedLiteralLength = 2
+)
+
+// Decode returns the decoded form of src. The returned slice may be a sub-
+// slice of dst if dst was large enough to hold the entire decoded block.
+// Otherwise, a newly allocated slice will be returned.
+//
+// The dst and src must not overlap. It is valid to pass a nil dst.
+//
+// Decode handles the Snappy block format, not the Snappy stream format.
+func Decode(dst, src []byte) ([]byte, error) {
+	dLen, s, err := decodedLen(src)
+	if err != nil {
+		return nil, err
+	}
+	if dLen <= len(dst) {
+		dst = dst[:dLen]
+	} else {
+		dst = make([]byte, dLen)
+	}
+	switch decode(dst, src[s:]) {
+	case 0:
+		return dst, nil
+	case decodeErrCodeUnsupportedLiteralLength:
+		return nil, errUnsupportedLiteralLength
+	}
+	return nil, ErrCorrupt
+}
+
+// NewReader returns a new Reader that decompresses from r, using the framing
+// format described at
+// https://github.com/google/snappy/blob/master/framing_format.txt
+func NewReader(r io.Reader) *Reader {
+	return &Reader{
+		r:       r,
+		decoded: make([]byte, maxBlockSize),
+		buf:     make([]byte, maxEncodedLenOfMaxBlockSize+checksumSize),
+	}
+}
+
+// Reader is an io.Reader that can read Snappy-compressed bytes.
+//
+// Reader handles the Snappy stream format, not the Snappy block format.
+type Reader struct {
+	r       io.Reader
+	err     error
+	decoded []byte
+	buf     []byte
+	// decoded[i:j] contains decoded bytes that have not yet been passed on.
+	i, j       int
+	readHeader bool
+}
+
+// Reset discards any buffered data, resets all state, and switches the Snappy
+// reader to read from r. This permits reusing a Reader rather than allocating
+// a new one.
+func (r *Reader) Reset(reader io.Reader) {
+	r.r = reader
+	r.err = nil
+	r.i = 0
+	r.j = 0
+	r.readHeader = false
+}
+
+func (r *Reader) readFull(p []byte, allowEOF bool) (ok bool) {
+	if _, r.err = io.ReadFull(r.r, p); r.err != nil {
+		if r.err == io.ErrUnexpectedEOF || (r.err == io.EOF && !allowEOF) {
+			r.err = ErrCorrupt
+		}
+		return false
+	}
+	return true
+}
+
+func (r *Reader) fill() error {
+	for r.i >= r.j {
+		if !r.readFull(r.buf[:4], true) {
+			return r.err
+		}
+		chunkType := r.buf[0]
+		if !r.readHeader {
+			if chunkType != chunkTypeStreamIdentifier {
+				r.err = ErrCorrupt
+				return r.err
+			}
+			r.readHeader = true
+		}
+		chunkLen := int(r.buf[1]) | int(r.buf[2])<<8 | int(r.buf[3])<<16
+		if chunkLen > len(r.buf) {
+			r.err = ErrUnsupported
+			return r.err
+		}
+
+		// The chunk types are specified at
+		// https://github.com/google/snappy/blob/master/framing_format.txt
+		switch chunkType {
+		case chunkTypeCompressedData:
+			// Section 4.2. Compressed data (chunk type 0x00).
+			if chunkLen < checksumSize {
+				r.err = ErrCorrupt
+				return r.err
+			}
+			buf := r.buf[:chunkLen]
+			if !r.readFull(buf, false) {
+				return r.err
+			}
+			checksum := uint32(buf[0]) | uint32(buf[1])<<8 | uint32(buf[2])<<16 | uint32(buf[3])<<24
+			buf = buf[checksumSize:]
+
+			n, err := DecodedLen(buf)
+			if err != nil {
+				r.err = err
+				return r.err
+			}
+			if n > len(r.decoded) {
+				r.err = ErrCorrupt
+				return r.err
+			}
+			if _, err := Decode(r.decoded, buf); err != nil {
+				r.err = err
+				return r.err
+			}
+			if crc(r.decoded[:n]) != checksum {
+				r.err = ErrCorrupt
+				return r.err
+			}
+			r.i, r.j = 0, n
+			continue
+
+		case chunkTypeUncompressedData:
+			// Section 4.3. Uncompressed data (chunk type 0x01).
+			if chunkLen < checksumSize {
+				r.err = ErrCorrupt
+				return r.err
+			}
+			buf := r.buf[:checksumSize]
+			if !r.readFull(buf, false) {
+				return r.err
+			}
+			checksum := uint32(buf[0]) | uint32(buf[1])<<8 | uint32(buf[2])<<16 | uint32(buf[3])<<24
+			// Read directly into r.decoded instead of via r.buf.
+			n := chunkLen - checksumSize
+			if n > len(r.decoded) {
+				r.err = ErrCorrupt
+				return r.err
+			}
+			if !r.readFull(r.decoded[:n], false) {
+				return r.err
+			}
+			if crc(r.decoded[:n]) != checksum {
+				r.err = ErrCorrupt
+				return r.err
+			}
+			r.i, r.j = 0, n
+			continue
+
+		case chunkTypeStreamIdentifier:
+			// Section 4.1. Stream identifier (chunk type 0xff).
+			if chunkLen != len(magicBody) {
+				r.err = ErrCorrupt
+				return r.err
+			}
+			if !r.readFull(r.buf[:len(magicBody)], false) {
+				return r.err
+			}
+			for i := 0; i < len(magicBody); i++ {
+				if r.buf[i] != magicBody[i] {
+					r.err = ErrCorrupt
+					return r.err
+				}
+			}
+			continue
+		}
+
+		if chunkType <= 0x7f {
+			// Section 4.5. Reserved unskippable chunks (chunk types 0x02-0x7f).
+			r.err = ErrUnsupported
+			return r.err
+		}
+		// Section 4.4 Padding (chunk type 0xfe).
+		// Section 4.6. Reserved skippable chunks (chunk types 0x80-0xfd).
+		if !r.readFull(r.buf[:chunkLen], false) {
+			return r.err
+		}
+	}
+
+	return nil
+}
+
+// Read satisfies the io.Reader interface.
+func (r *Reader) Read(p []byte) (int, error) {
+	if r.err != nil {
+		return 0, r.err
+	}
+
+	if err := r.fill(); err != nil {
+		return 0, err
+	}
+
+	n := copy(p, r.decoded[r.i:r.j])
+	r.i += n
+	return n, nil
+}
+
+// ReadByte satisfies the io.ByteReader interface.
+func (r *Reader) ReadByte() (byte, error) {
+	if r.err != nil {
+		return 0, r.err
+	}
+
+	if err := r.fill(); err != nil {
+		return 0, err
+	}
+
+	c := r.decoded[r.i]
+	r.i++
+	return c, nil
+}

vendor/github.com/klauspost/compress/internal/snapref/decode_other.go

@@ -0,0 +1,113 @@
+// Copyright 2016 The Snappy-Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package snapref
+
+// decode writes the decoding of src to dst. It assumes that the varint-encoded
+// length of the decompressed bytes has already been read, and that len(dst)
+// equals that length.
+//
+// It returns 0 on success or a decodeErrCodeXxx error code on failure.
+func decode(dst, src []byte) int {
+	var d, s, offset, length int
+	for s < len(src) {
+		switch src[s] & 0x03 {
+		case tagLiteral:
+			x := uint32(src[s] >> 2)
+			switch {
+			case x < 60:
+				s++
+			case x == 60:
+				s += 2
+				if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
+					return decodeErrCodeCorrupt
+				}
+				x = uint32(src[s-1])
+			case x == 61:
+				s += 3
+				if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
+					return decodeErrCodeCorrupt
+				}
+				x = uint32(src[s-2]) | uint32(src[s-1])<<8
+			case x == 62:
+				s += 4
+				if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
+					return decodeErrCodeCorrupt
+				}
+				x = uint32(src[s-3]) | uint32(src[s-2])<<8 | uint32(src[s-1])<<16
+			case x == 63:
+				s += 5
+				if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
+					return decodeErrCodeCorrupt
+				}
+				x = uint32(src[s-4]) | uint32(src[s-3])<<8 | uint32(src[s-2])<<16 | uint32(src[s-1])<<24
+			}
+			length = int(x) + 1
+			if length <= 0 {
+				return decodeErrCodeUnsupportedLiteralLength
+			}
+			if length > len(dst)-d || length > len(src)-s {
+				return decodeErrCodeCorrupt
+			}
+			copy(dst[d:], src[s:s+length])
+			d += length
+			s += length
+			continue
+
+		case tagCopy1:
+			s += 2
+			if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
+				return decodeErrCodeCorrupt
+			}
+			length = 4 + int(src[s-2])>>2&0x7
+			offset = int(uint32(src[s-2])&0xe0<<3 | uint32(src[s-1]))
+
+		case tagCopy2:
+			s += 3
+			if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
+				return decodeErrCodeCorrupt
+			}
+			length = 1 + int(src[s-3])>>2
+			offset = int(uint32(src[s-2]) | uint32(src[s-1])<<8)
+
+		case tagCopy4:
+			s += 5
+			if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
+				return decodeErrCodeCorrupt
+			}
+			length = 1 + int(src[s-5])>>2
+			offset = int(uint32(src[s-4]) | uint32(src[s-3])<<8 | uint32(src[s-2])<<16 | uint32(src[s-1])<<24)
+		}
+
+		if offset <= 0 || d < offset || length > len(dst)-d {
+			return decodeErrCodeCorrupt
+		}
+		// Copy from an earlier sub-slice of dst to a later sub-slice.
+		// If no overlap, use the built-in copy:
+		if offset >= length {
+			copy(dst[d:d+length], dst[d-offset:])
+			d += length
+			continue
+		}
+
+		// Unlike the built-in copy function, this byte-by-byte copy always runs
+		// forwards, even if the slices overlap. Conceptually, this is:
+		//
+		// d += forwardCopy(dst[d:d+length], dst[d-offset:])
+		//
+		// We align the slices into a and b and show the compiler they are the same size.
+		// This allows the loop to run without bounds checks.
+		a := dst[d : d+length]
+		b := dst[d-offset:]
+		b = b[:len(a)]
+		for i := range a {
+			a[i] = b[i]
+		}
+		d += length
+	}
+	if d != len(dst) {
+		return decodeErrCodeCorrupt
+	}
+	return 0
+}

vendor/github.com/klauspost/compress/internal/snapref/encode.go

@@ -0,0 +1,289 @@
+// Copyright 2011 The Snappy-Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package snapref
+
+import (
+	"encoding/binary"
+	"errors"
+	"io"
+)
+
+// Encode returns the encoded form of src. The returned slice may be a sub-
+// slice of dst if dst was large enough to hold the entire encoded block.
+// Otherwise, a newly allocated slice will be returned.
+//
+// The dst and src must not overlap. It is valid to pass a nil dst.
+//
+// Encode handles the Snappy block format, not the Snappy stream format.
+func Encode(dst, src []byte) []byte {
+	if n := MaxEncodedLen(len(src)); n < 0 {
+		panic(ErrTooLarge)
+	} else if len(dst) < n {
+		dst = make([]byte, n)
+	}
+
+	// The block starts with the varint-encoded length of the decompressed bytes.
+	d := binary.PutUvarint(dst, uint64(len(src)))
+
+	for len(src) > 0 {
+		p := src
+		src = nil
+		if len(p) > maxBlockSize {
+			p, src = p[:maxBlockSize], p[maxBlockSize:]
+		}
+		if len(p) < minNonLiteralBlockSize {
+			d += emitLiteral(dst[d:], p)
+		} else {
+			d += encodeBlock(dst[d:], p)
+		}
+	}
+	return dst[:d]
+}
+
+// inputMargin is the minimum number of extra input bytes to keep, inside
+// encodeBlock's inner loop. On some architectures, this margin lets us
+// implement a fast path for emitLiteral, where the copy of short (<= 16 byte)
+// literals can be implemented as a single load to and store from a 16-byte
+// register. That literal's actual length can be as short as 1 byte, so this
+// can copy up to 15 bytes too much, but that's OK as subsequent iterations of
+// the encoding loop will fix up the copy overrun, and this inputMargin ensures
+// that we don't overrun the dst and src buffers.
+const inputMargin = 16 - 1
+
+// minNonLiteralBlockSize is the minimum size of the input to encodeBlock that
+// could be encoded with a copy tag. This is the minimum with respect to the
+// algorithm used by encodeBlock, not a minimum enforced by the file format.
+//
+// The encoded output must start with at least a 1 byte literal, as there are
+// no previous bytes to copy. A minimal (1 byte) copy after that, generated
+// from an emitCopy call in encodeBlock's main loop, would require at least
+// another inputMargin bytes, for the reason above: we want any emitLiteral
+// calls inside encodeBlock's main loop to use the fast path if possible, which
+// requires being able to overrun by inputMargin bytes. Thus,
+// minNonLiteralBlockSize equals 1 + 1 + inputMargin.
+//
+// The C++ code doesn't use this exact threshold, but it could, as discussed at
+// https://groups.google.com/d/topic/snappy-compression/oGbhsdIJSJ8/discussion
+// The difference between Go (2+inputMargin) and C++ (inputMargin) is purely an
+// optimization. It should not affect the encoded form. This is tested by
+// TestSameEncodingAsCppShortCopies.
+const minNonLiteralBlockSize = 1 + 1 + inputMargin
+
+// MaxEncodedLen returns the maximum length of a snappy block, given its
+// uncompressed length.
+//
+// It will return a negative value if srcLen is too large to encode.
+func MaxEncodedLen(srcLen int) int {
+	n := uint64(srcLen)
+	if n > 0xffffffff {
+		return -1
+	}
+	// Compressed data can be defined as:
+	//    compressed := item* literal*
+	//    item       := literal* copy
+	//
+	// The trailing literal sequence has a space blowup of at most 62/60
+	// since a literal of length 60 needs one tag byte + one extra byte
+	// for length information.
+	//
+	// Item blowup is trickier to measure. Suppose the "copy" op copies
+	// 4 bytes of data. Because of a special check in the encoding code,
+	// we produce a 4-byte copy only if the offset is < 65536. Therefore
+	// the copy op takes 3 bytes to encode, and this type of item leads
+	// to at most the 62/60 blowup for representing literals.
+	//
+	// Suppose the "copy" op copies 5 bytes of data. If the offset is big
+	// enough, it will take 5 bytes to encode the copy op. Therefore the
+	// worst case here is a one-byte literal followed by a five-byte copy.
+	// That is, 6 bytes of input turn into 7 bytes of "compressed" data.
+	//
+	// This last factor dominates the blowup, so the final estimate is:
+	n = 32 + n + n/6
+	if n > 0xffffffff {
+		return -1
+	}
+	return int(n)
+}
+
+var errClosed = errors.New("snappy: Writer is closed")
+
+// NewWriter returns a new Writer that compresses to w.
+//
+// The Writer returned does not buffer writes. There is no need to Flush or
+// Close such a Writer.
+//
+// Deprecated: the Writer returned is not suitable for many small writes, only
+// for few large writes. Use NewBufferedWriter instead, which is efficient
+// regardless of the frequency and shape of the writes, and remember to Close
+// that Writer when done.
+func NewWriter(w io.Writer) *Writer {
+	return &Writer{
+		w:    w,
+		obuf: make([]byte, obufLen),
+	}
+}
+
+// NewBufferedWriter returns a new Writer that compresses to w, using the
+// framing format described at
+// https://github.com/google/snappy/blob/master/framing_format.txt
+//
+// The Writer returned buffers writes. Users must call Close to guarantee all
+// data has been forwarded to the underlying io.Writer. They may also call
+// Flush zero or more times before calling Close.
+func NewBufferedWriter(w io.Writer) *Writer {
+	return &Writer{
+		w:    w,
+		ibuf: make([]byte, 0, maxBlockSize),
+		obuf: make([]byte, obufLen),
+	}
+}
+
+// Writer is an io.Writer that can write Snappy-compressed bytes.
+//
+// Writer handles the Snappy stream format, not the Snappy block format.
+type Writer struct {
+	w   io.Writer
+	err error
+
+	// ibuf is a buffer for the incoming (uncompressed) bytes.
+	//
+	// Its use is optional. For backwards compatibility, Writers created by the
+	// NewWriter function have ibuf == nil, do not buffer incoming bytes, and
+	// therefore do not need to be Flush'ed or Close'd.
+	ibuf []byte
+
+	// obuf is a buffer for the outgoing (compressed) bytes.
+	obuf []byte
+
+	// wroteStreamHeader is whether we have written the stream header.
+	wroteStreamHeader bool
+}
+
+// Reset discards the writer's state and switches the Snappy writer to write to
+// w. This permits reusing a Writer rather than allocating a new one.
+func (w *Writer) Reset(writer io.Writer) {
+	w.w = writer
+	w.err = nil
+	if w.ibuf != nil {
+		w.ibuf = w.ibuf[:0]
+	}
+	w.wroteStreamHeader = false
+}
+
+// Write satisfies the io.Writer interface.
+func (w *Writer) Write(p []byte) (nRet int, errRet error) {
+	if w.ibuf == nil {
+		// Do not buffer incoming bytes. This does not perform or compress well
+		// if the caller of Writer.Write writes many small slices. This
+		// behavior is therefore deprecated, but still supported for backwards
+		// compatibility with code that doesn't explicitly Flush or Close.
+		return w.write(p)
+	}
+
+	// The remainder of this method is based on bufio.Writer.Write from the
+	// standard library.
+
+	for len(p) > (cap(w.ibuf)-len(w.ibuf)) && w.err == nil {
+		var n int
+		if len(w.ibuf) == 0 {
+			// Large write, empty buffer.
+			// Write directly from p to avoid copy.
+			n, _ = w.write(p)
+		} else {
+			n = copy(w.ibuf[len(w.ibuf):cap(w.ibuf)], p)
+			w.ibuf = w.ibuf[:len(w.ibuf)+n]
+			w.Flush()
+		}
+		nRet += n
+		p = p[n:]
+	}
+	if w.err != nil {
+		return nRet, w.err
+	}
+	n := copy(w.ibuf[len(w.ibuf):cap(w.ibuf)], p)
+	w.ibuf = w.ibuf[:len(w.ibuf)+n]
+	nRet += n
+	return nRet, nil
+}
+
+func (w *Writer) write(p []byte) (nRet int, errRet error) {
+	if w.err != nil {
+		return 0, w.err
+	}
+	for len(p) > 0 {
+		obufStart := len(magicChunk)
+		if !w.wroteStreamHeader {
+			w.wroteStreamHeader = true
+			copy(w.obuf, magicChunk)
+			obufStart = 0
+		}
+
+		var uncompressed []byte
+		if len(p) > maxBlockSize {
+			uncompressed, p = p[:maxBlockSize], p[maxBlockSize:]
+		} else {
+			uncompressed, p = p, nil
+		}
+		checksum := crc(uncompressed)
+
+		// Compress the buffer, discarding the result if the improvement
+		// isn't at least 12.5%.
+		compressed := Encode(w.obuf[obufHeaderLen:], uncompressed)
+		chunkType := uint8(chunkTypeCompressedData)
+		chunkLen := 4 + len(compressed)
+		obufEnd := obufHeaderLen + len(compressed)
+		if len(compressed) >= len(uncompressed)-len(uncompressed)/8 {
+			chunkType = chunkTypeUncompressedData
+			chunkLen = 4 + len(uncompressed)
+			obufEnd = obufHeaderLen
+		}
+
+		// Fill in the per-chunk header that comes before the body.
+		w.obuf[len(magicChunk)+0] = chunkType
+		w.obuf[len(magicChunk)+1] = uint8(chunkLen >> 0)
+		w.obuf[len(magicChunk)+2] = uint8(chunkLen >> 8)
+		w.obuf[len(magicChunk)+3] = uint8(chunkLen >> 16)
+		w.obuf[len(magicChunk)+4] = uint8(checksum >> 0)
+		w.obuf[len(magicChunk)+5] = uint8(checksum >> 8)
+		w.obuf[len(magicChunk)+6] = uint8(checksum >> 16)
+		w.obuf[len(magicChunk)+7] = uint8(checksum >> 24)
+
+		if _, err := w.w.Write(w.obuf[obufStart:obufEnd]); err != nil {
+			w.err = err
+			return nRet, err
+		}
+		if chunkType == chunkTypeUncompressedData {
+			if _, err := w.w.Write(uncompressed); err != nil {
+				w.err = err
+				return nRet, err
+			}
+		}
+		nRet += len(uncompressed)
+	}
+	return nRet, nil
+}
+
+// Flush flushes the Writer to its underlying io.Writer.
+func (w *Writer) Flush() error {
+	if w.err != nil {
+		return w.err
+	}
+	if len(w.ibuf) == 0 {
+		return nil
+	}
+	w.write(w.ibuf)
+	w.ibuf = w.ibuf[:0]
+	return w.err
+}
+
+// Close calls Flush and then closes the Writer.
+func (w *Writer) Close() error {
+	w.Flush()
+	ret := w.err
+	if w.err == nil {
+		w.err = errClosed
+	}
+	return ret
+}

vendor/github.com/klauspost/compress/internal/snapref/encode_other.go

@@ -0,0 +1,236 @@
+// Copyright 2016 The Snappy-Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package snapref
+
+func load32(b []byte, i int) uint32 {
+	b = b[i : i+4 : len(b)] // Help the compiler eliminate bounds checks on the next line.
+	return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
+}
+
+func load64(b []byte, i int) uint64 {
+	b = b[i : i+8 : len(b)] // Help the compiler eliminate bounds checks on the next line.
+	return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
+		uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
+}
+
+// emitLiteral writes a literal chunk and returns the number of bytes written.
+//
+// It assumes that:
+//	dst is long enough to hold the encoded bytes
+//	1 <= len(lit) && len(lit) <= 65536
+func emitLiteral(dst, lit []byte) int {
+	i, n := 0, uint(len(lit)-1)
+	switch {
+	case n < 60:
+		dst[0] = uint8(n)<<2 | tagLiteral
+		i = 1
+	case n < 1<<8:
+		dst[0] = 60<<2 | tagLiteral
+		dst[1] = uint8(n)
+		i = 2
+	default:
+		dst[0] = 61<<2 | tagLiteral
+		dst[1] = uint8(n)
+		dst[2] = uint8(n >> 8)
+		i = 3
+	}
+	return i + copy(dst[i:], lit)
+}
+
+// emitCopy writes a copy chunk and returns the number of bytes written.
+//
+// It assumes that:
+//	dst is long enough to hold the encoded bytes
+//	1 <= offset && offset <= 65535
+//	4 <= length && length <= 65535
+func emitCopy(dst []byte, offset, length int) int {
+	i := 0
+	// The maximum length for a single tagCopy1 or tagCopy2 op is 64 bytes. The
+	// threshold for this loop is a little higher (at 68 = 64 + 4), and the
+	// length emitted down below is is a little lower (at 60 = 64 - 4), because
+	// it's shorter to encode a length 67 copy as a length 60 tagCopy2 followed
+	// by a length 7 tagCopy1 (which encodes as 3+2 bytes) than to encode it as
+	// a length 64 tagCopy2 followed by a length 3 tagCopy2 (which encodes as
+	// 3+3 bytes). The magic 4 in the 64±4 is because the minimum length for a
+	// tagCopy1 op is 4 bytes, which is why a length 3 copy has to be an
+	// encodes-as-3-bytes tagCopy2 instead of an encodes-as-2-bytes tagCopy1.
+	for length >= 68 {
+		// Emit a length 64 copy, encoded as 3 bytes.
+		dst[i+0] = 63<<2 | tagCopy2
+		dst[i+1] = uint8(offset)
+		dst[i+2] = uint8(offset >> 8)
+		i += 3
+		length -= 64
+	}
+	if length > 64 {
+		// Emit a length 60 copy, encoded as 3 bytes.
+		dst[i+0] = 59<<2 | tagCopy2
+		dst[i+1] = uint8(offset)
+		dst[i+2] = uint8(offset >> 8)
+		i += 3
+		length -= 60
+	}
+	if length >= 12 || offset >= 2048 {
+		// Emit the remaining copy, encoded as 3 bytes.
+		dst[i+0] = uint8(length-1)<<2 | tagCopy2
+		dst[i+1] = uint8(offset)
+		dst[i+2] = uint8(offset >> 8)
+		return i + 3
+	}
+	// Emit the remaining copy, encoded as 2 bytes.
+	dst[i+0] = uint8(offset>>8)<<5 | uint8(length-4)<<2 | tagCopy1
+	dst[i+1] = uint8(offset)
+	return i + 2
+}
+
+// extendMatch returns the largest k such that k <= len(src) and that
+// src[i:i+k-j] and src[j:k] have the same contents.
+//
+// It assumes that:
+//	0 <= i && i < j && j <= len(src)
+func extendMatch(src []byte, i, j int) int {
+	for ; j < len(src) && src[i] == src[j]; i, j = i+1, j+1 {
+	}
+	return j
+}
+
+func hash(u, shift uint32) uint32 {
+	return (u * 0x1e35a7bd) >> shift
+}
+
+// encodeBlock encodes a non-empty src to a guaranteed-large-enough dst. It
+// assumes that the varint-encoded length of the decompressed bytes has already
+// been written.
+//
+// It also assumes that:
+//	len(dst) >= MaxEncodedLen(len(src)) &&
+// 	minNonLiteralBlockSize <= len(src) && len(src) <= maxBlockSize
+func encodeBlock(dst, src []byte) (d int) {
+	// Initialize the hash table. Its size ranges from 1<<8 to 1<<14 inclusive.
+	// The table element type is uint16, as s < sLimit and sLimit < len(src)
+	// and len(src) <= maxBlockSize and maxBlockSize == 65536.
+	const (
+		maxTableSize = 1 << 14
+		// tableMask is redundant, but helps the compiler eliminate bounds
+		// checks.
+		tableMask = maxTableSize - 1
+	)
+	shift := uint32(32 - 8)
+	for tableSize := 1 << 8; tableSize < maxTableSize && tableSize < len(src); tableSize *= 2 {
+		shift--
+	}
+	// In Go, all array elements are zero-initialized, so there is no advantage
+	// to a smaller tableSize per se. However, it matches the C++ algorithm,
+	// and in the asm versions of this code, we can get away with zeroing only
+	// the first tableSize elements.
+	var table [maxTableSize]uint16
+
+	// sLimit is when to stop looking for offset/length copies. The inputMargin
+	// lets us use a fast path for emitLiteral in the main loop, while we are
+	// looking for copies.
+	sLimit := len(src) - inputMargin
+
+	// nextEmit is where in src the next emitLiteral should start from.
+	nextEmit := 0
+
+	// The encoded form must start with a literal, as there are no previous
+	// bytes to copy, so we start looking for hash matches at s == 1.
+	s := 1
+	nextHash := hash(load32(src, s), shift)
+
+	for {
+		// Copied from the C++ snappy implementation:
+		//
+		// Heuristic match skipping: If 32 bytes are scanned with no matches
+		// found, start looking only at every other byte. If 32 more bytes are
+		// scanned (or skipped), look at every third byte, etc.. When a match
+		// is found, immediately go back to looking at every byte. This is a
+		// small loss (~5% performance, ~0.1% density) for compressible data
+		// due to more bookkeeping, but for non-compressible data (such as
+		// JPEG) it's a huge win since the compressor quickly "realizes" the
+		// data is incompressible and doesn't bother looking for matches
+		// everywhere.
+		//
+		// The "skip" variable keeps track of how many bytes there are since
+		// the last match; dividing it by 32 (ie. right-shifting by five) gives
+		// the number of bytes to move ahead for each iteration.
+		skip := 32
+
+		nextS := s
+		candidate := 0
+		for {
+			s = nextS
+			bytesBetweenHashLookups := skip >> 5
+			nextS = s + bytesBetweenHashLookups
+			skip += bytesBetweenHashLookups
+			if nextS > sLimit {
+				goto emitRemainder
+			}
+			candidate = int(table[nextHash&tableMask])
+			table[nextHash&tableMask] = uint16(s)
+			nextHash = hash(load32(src, nextS), shift)
+			if load32(src, s) == load32(src, candidate) {
+				break
+			}
+		}
+
+		// A 4-byte match has been found. We'll later see if more than 4 bytes
+		// match. But, prior to the match, src[nextEmit:s] are unmatched. Emit
+		// them as literal bytes.
+		d += emitLiteral(dst[d:], src[nextEmit:s])
+
+		// Call emitCopy, and then see if another emitCopy could be our next
+		// move. Repeat until we find no match for the input immediately after
+		// what was consumed by the last emitCopy call.
+		//
+		// If we exit this loop normally then we need to call emitLiteral next,
+		// though we don't yet know how big the literal will be. We handle that
+		// by proceeding to the next iteration of the main loop. We also can
+		// exit this loop via goto if we get close to exhausting the input.
+		for {
+			// Invariant: we have a 4-byte match at s, and no need to emit any
+			// literal bytes prior to s.
+			base := s
+
+			// Extend the 4-byte match as long as possible.
+			//
+			// This is an inlined version of:
+			//	s = extendMatch(src, candidate+4, s+4)
+			s += 4
+			for i := candidate + 4; s < len(src) && src[i] == src[s]; i, s = i+1, s+1 {
+			}
+
+			d += emitCopy(dst[d:], base-candidate, s-base)
+			nextEmit = s
+			if s >= sLimit {
+				goto emitRemainder
+			}
+
+			// We could immediately start working at s now, but to improve
+			// compression we first update the hash table at s-1 and at s. If
+			// another emitCopy is not our next move, also calculate nextHash
+			// at s+1. At least on GOARCH=amd64, these three hash calculations
+			// are faster as one load64 call (with some shifts) instead of
+			// three load32 calls.
+			x := load64(src, s-1)
+			prevHash := hash(uint32(x>>0), shift)
+			table[prevHash&tableMask] = uint16(s - 1)
+			currHash := hash(uint32(x>>8), shift)
+			candidate = int(table[currHash&tableMask])
+			table[currHash&tableMask] = uint16(s)
+			if uint32(x>>8) != load32(src, candidate) {
+				nextHash = hash(uint32(x>>16), shift)
+				s++
+				break
+			}
+		}
+	}
+
+emitRemainder:
+	if nextEmit < len(src) {
+		d += emitLiteral(dst[d:], src[nextEmit:])
+	}
+	return d
+}

vendor/github.com/klauspost/compress/internal/snapref/snappy.go

@@ -0,0 +1,98 @@
+// Copyright 2011 The Snappy-Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package snapref implements the Snappy compression format. It aims for very
+// high speeds and reasonable compression.
+//
+// There are actually two Snappy formats: block and stream. They are related,
+// but different: trying to decompress block-compressed data as a Snappy stream
+// will fail, and vice versa. The block format is the Decode and Encode
+// functions and the stream format is the Reader and Writer types.
+//
+// The block format, the more common case, is used when the complete size (the
+// number of bytes) of the original data is known upfront, at the time
+// compression starts. The stream format, also known as the framing format, is
+// for when that isn't always true.
+//
+// The canonical, C++ implementation is at https://github.com/google/snappy and
+// it only implements the block format.
+package snapref
+
+import (
+	"hash/crc32"
+)
+
+/*
+Each encoded block begins with the varint-encoded length of the decoded data,
+followed by a sequence of chunks. Chunks begin and end on byte boundaries. The
+first byte of each chunk is broken into its 2 least and 6 most significant bits
+called l and m: l ranges in [0, 4) and m ranges in [0, 64). l is the chunk tag.
+Zero means a literal tag. All other values mean a copy tag.
+
+For literal tags:
+  - If m < 60, the next 1 + m bytes are literal bytes.
+  - Otherwise, let n be the little-endian unsigned integer denoted by the next
+    m - 59 bytes. The next 1 + n bytes after that are literal bytes.
+
+For copy tags, length bytes are copied from offset bytes ago, in the style of
+Lempel-Ziv compression algorithms. In particular:
+  - For l == 1, the offset ranges in [0, 1<<11) and the length in [4, 12).
+    The length is 4 + the low 3 bits of m. The high 3 bits of m form bits 8-10
+    of the offset. The next byte is bits 0-7 of the offset.
+  - For l == 2, the offset ranges in [0, 1<<16) and the length in [1, 65).
+    The length is 1 + m. The offset is the little-endian unsigned integer
+    denoted by the next 2 bytes.
+  - For l == 3, this tag is a legacy format that is no longer issued by most
+    encoders. Nonetheless, the offset ranges in [0, 1<<32) and the length in
+    [1, 65). The length is 1 + m. The offset is the little-endian unsigned
+    integer denoted by the next 4 bytes.
+*/
+const (
+	tagLiteral = 0x00
+	tagCopy1   = 0x01
+	tagCopy2   = 0x02
+	tagCopy4   = 0x03
+)
+
+const (
+	checksumSize    = 4
+	chunkHeaderSize = 4
+	magicChunk      = "\xff\x06\x00\x00" + magicBody
+	magicBody       = "sNaPpY"
+
+	// maxBlockSize is the maximum size of the input to encodeBlock. It is not
+	// part of the wire format per se, but some parts of the encoder assume
+	// that an offset fits into a uint16.
+	//
+	// Also, for the framing format (Writer type instead of Encode function),
+	// https://github.com/google/snappy/blob/master/framing_format.txt says
+	// that "the uncompressed data in a chunk must be no longer than 65536
+	// bytes".
+	maxBlockSize = 65536
+
+	// maxEncodedLenOfMaxBlockSize equals MaxEncodedLen(maxBlockSize), but is
+	// hard coded to be a const instead of a variable, so that obufLen can also
+	// be a const. Their equivalence is confirmed by
+	// TestMaxEncodedLenOfMaxBlockSize.
+	maxEncodedLenOfMaxBlockSize = 76490
+
+	obufHeaderLen = len(magicChunk) + checksumSize + chunkHeaderSize
+	obufLen       = obufHeaderLen + maxEncodedLenOfMaxBlockSize
+)
+
+const (
+	chunkTypeCompressedData   = 0x00
+	chunkTypeUncompressedData = 0x01
+	chunkTypePadding          = 0xfe
+	chunkTypeStreamIdentifier = 0xff
+)
+
+var crcTable = crc32.MakeTable(crc32.Castagnoli)
+
+// crc implements the checksum specified in section 3 of
+// https://github.com/google/snappy/blob/master/framing_format.txt
+func crc(b []byte) uint32 {
+	c := crc32.Update(0, crcTable, b)
+	return uint32(c>>15|c<<17) + 0xa282ead8
+}

vendor/github.com/klauspost/compress/s2/README.md

@@ -20,6 +20,7 @@ This is important, so you don't have to worry about spending CPU cycles on alrea
 * Concurrent stream compression
 * Faster decompression, even for Snappy compatible content
 * Ability to quickly skip forward in compressed stream
+* Random seeking with indexes
 * Compatible with reading Snappy compressed content
 * Smaller block size overhead on incompressible blocks
 * Block concatenation
@@ -29,8 +30,8 @@ This is important, so you don't have to worry about spending CPU cycles on alrea
 
 ## Drawbacks over Snappy
 
-* Not optimized for 32 bit systems.
-* Streams use slightly more memory due to larger blocks and concurrency (configurable).
+* Not optimized for 32 bit systems
+* Streams use slightly more memory due to larger blocks and concurrency (configurable)
 
 # Usage
 
@@ -141,7 +142,7 @@ Binaries can be downloaded on the [Releases Page](https://github.com/klauspost/c
 
 Installing then requires Go to be installed. To install them, use:
 
-`go install github.com/klauspost/compress/s2/cmd/s2c && go install github.com/klauspost/compress/s2/cmd/s2d`
+`go install github.com/klauspost/compress/s2/cmd/s2c@latest && go install github.com/klauspost/compress/s2/cmd/s2d@latest`
 
 To build binaries to the current folder use:
 
@@ -176,6 +177,8 @@ Options:
     	Compress faster, but with a minor compression loss
   -help
     	Display help
+  -index
+        Add seek index (default true)    	
   -o string
         Write output to another file. Single input file only
   -pad string
@@ -217,11 +220,15 @@ Options:
     	Display help
   -o string
         Write output to another file. Single input file only
-  -q	Don't write any output to terminal, except errors
+  -offset string
+        Start at offset. Examples: 92, 64K, 256K, 1M, 4M. Requires Index
+  -q    Don't write any output to terminal, except errors
   -rm
-    	Delete source file(s) after successful decompression
+        Delete source file(s) after successful decompression
   -safe
-    	Do not overwrite output files
+        Do not overwrite output files
+  -tail string
+        Return last of compressed file. Examples: 92, 64K, 256K, 1M, 4M. Requires Index
   -verify
     	Verify files, but do not write output                                      
 ```
@@ -633,12 +640,12 @@ Compression and speed is typically a bit better `MaxEncodedLen` is also smaller
 Comparison of [`webdevdata.org-2015-01-07-subset`](https://files.klauspost.com/compress/webdevdata.org-2015-01-07-4GB-subset.7z),
 53927 files, total input size: 4,014,735,833 bytes. amd64, single goroutine used:
 
-| Encoder               | Size       | MB/s   | Reduction |
-|-----------------------|------------|--------|------------
-| snappy.Encode         | 1128706759 | 725.59 | 71.89%    |
-| s2.EncodeSnappy       | 1093823291 | 899.16 | 72.75%    |
-| s2.EncodeSnappyBetter | 1001158548 | 578.49 | 75.06%    |
-| s2.EncodeSnappyBest   | 944507998  | 66.00  | 76.47%    |
+| Encoder               | Size       | MB/s       | Reduction |
+|-----------------------|------------|------------|------------
+| snappy.Encode         | 1128706759 | 725.59     | 71.89%    |
+| s2.EncodeSnappy       | 1093823291 | **899.16** | 72.75%    |
+| s2.EncodeSnappyBetter | 1001158548 | 578.49     | 75.06%    |
+| s2.EncodeSnappyBest   | 944507998  | 66.00      | **76.47%**|
 
 ## Streams
 
@@ -649,11 +656,11 @@ Comparison of different streams, AMD Ryzen 3950x, 16 cores. Size and throughput:
 
 | File                        | snappy.NewWriter         | S2 Snappy                 | S2 Snappy, Better        | S2 Snappy, Best         |
 |-----------------------------|--------------------------|---------------------------|--------------------------|-------------------------|
-| nyc-taxi-data-10M.csv       | 1316042016 - 517.54MB/s  | 1307003093 - 8406.29MB/s  | 1174534014 - 4984.35MB/s | 1115904679 - 177.81MB/s |
-| enwik10                     | 5088294643 - 433.45MB/s  | 5175840939 - 8454.52MB/s  | 4560784526 - 4403.10MB/s | 4340299103 - 159.71MB/s |
-| 10gb.tar                    | 6056946612 - 703.25MB/s  | 6208571995 - 9035.75MB/s  | 5741646126 - 2402.08MB/s | 5548973895 - 171.17MB/s |
-| github-june-2days-2019.json | 1525176492 - 908.11MB/s  | 1476519054 - 12625.93MB/s | 1400547532 - 6163.61MB/s | 1321887137 - 200.71MB/s |
-| consensus.db.10gb           | 5412897703 - 1054.38MB/s | 5354073487 - 12634.82MB/s | 5335069899 - 2472.23MB/s | 5201000954 - 166.32MB/s |
+| nyc-taxi-data-10M.csv       | 1316042016 - 539.47MB/s  | 1307003093 - 10132.73MB/s | 1174534014 - 5002.44MB/s | 1115904679 - 177.97MB/s |
+| enwik10 (xml)               | 5088294643 - 451.13MB/s  | 5175840939 -  9440.69MB/s | 4560784526 - 4487.21MB/s | 4340299103 - 158.92MB/s |
+| 10gb.tar (mixed)            | 6056946612 - 729.73MB/s  | 6208571995 -  9978.05MB/s | 5741646126 - 4919.98MB/s | 5548973895 - 180.44MB/s |
+| github-june-2days-2019.json | 1525176492 - 933.00MB/s  | 1476519054 - 13150.12MB/s | 1400547532 - 5803.40MB/s | 1321887137 - 204.29MB/s |
+| consensus.db.10gb (db)      | 5412897703 - 1102.14MB/s | 5354073487 - 13562.91MB/s | 5335069899 - 5294.73MB/s | 5201000954 - 175.72MB/s |
 
 # Decompression
 
@@ -679,7 +686,220 @@ The 10 byte 'stream identifier' of the second stream can optionally be stripped,
 
 Blocks can be concatenated using the `ConcatBlocks` function.
 
-Snappy blocks/streams can safely be concatenated with S2 blocks and streams. 
+Snappy blocks/streams can safely be concatenated with S2 blocks and streams.
+Streams with indexes (see below) will currently not work on concatenated streams.
+
+# Stream Seek Index
+
+S2 and Snappy streams can have indexes. These indexes will allow random seeking within the compressed data.
+
+The index can either be appended to the stream as a skippable block or returned for separate storage.
+
+When the index is appended to a stream it will be skipped by regular decoders, 
+so the output remains compatible with other decoders. 
+
+## Creating an Index
+
+To automatically add an index to a stream, add `WriterAddIndex()` option to your writer.
+Then the index will be added to the stream when `Close()` is called.
+
+```
+    // Add Index to stream...
+	enc := s2.NewWriter(w, s2.WriterAddIndex())
+	io.Copy(enc, r)
+	enc.Close()
+```
+
+If you want to store the index separately, you can use `CloseIndex()` instead of the regular `Close()`.
+This will return the index. Note that `CloseIndex()` should only be called once, and you shouldn't call `Close()`.
+
+```
+    // Get index for separate storage... 
+	enc := s2.NewWriter(w)
+	io.Copy(enc, r)
+	index, err := enc.CloseIndex()
+```
+
+The `index` can then be used needing to read from the stream. 
+This means the index can be used without needing to seek to the end of the stream 
+or for manually forwarding streams. See below.
+
+Finally, an existing S2/Snappy stream can be indexed using the `s2.IndexStream(r io.Reader)` function.
+
+## Using Indexes
+
+To use indexes there is a `ReadSeeker(random bool, index []byte) (*ReadSeeker, error)` function available.
+
+Calling ReadSeeker will return an [io.ReadSeeker](https://pkg.go.dev/io#ReadSeeker) compatible version of the reader.
+
+If 'random' is specified the returned io.Seeker can be used for random seeking, otherwise only forward seeking is supported.
+Enabling random seeking requires the original input to support the [io.Seeker](https://pkg.go.dev/io#Seeker) interface.
+
+```
+	dec := s2.NewReader(r)
+	rs, err := dec.ReadSeeker(false, nil)
+	rs.Seek(wantOffset, io.SeekStart)	
+```
+
+Get a seeker to seek forward. Since no index is provided, the index is read from the stream.
+This requires that an index was added and that `r` supports the [io.Seeker](https://pkg.go.dev/io#Seeker) interface.
+
+A custom index can be specified which will be used if supplied.
+When using a custom index, it will not be read from the input stream.
+
+```
+	dec := s2.NewReader(r)
+	rs, err := dec.ReadSeeker(false, index)
+	rs.Seek(wantOffset, io.SeekStart)	
+```
+
+This will read the index from `index`. Since we specify non-random (forward only) seeking `r` does not have to be an io.Seeker
+
+```
+	dec := s2.NewReader(r)
+	rs, err := dec.ReadSeeker(true, index)
+	rs.Seek(wantOffset, io.SeekStart)	
+```
+
+Finally, since we specify that we want to do random seeking `r` must be an io.Seeker. 
+
+The returned [ReadSeeker](https://pkg.go.dev/github.com/klauspost/compress/s2#ReadSeeker) contains a shallow reference to the existing Reader,
+meaning changes performed to one is reflected in the other.
+
+To check if a stream contains an index at the end, the `(*Index).LoadStream(rs io.ReadSeeker) error` can be used.
+
+## Manually Forwarding Streams
+
+Indexes can also be read outside the decoder using the [Index](https://pkg.go.dev/github.com/klauspost/compress/s2#Index) type.
+This can be used for parsing indexes, either separate or in streams.
+
+In some cases it may not be possible to serve a seekable stream.
+This can for instance be an HTTP stream, where the Range request 
+is sent at the start of the stream. 
+
+With a little bit of extra code it is still possible to use indexes
+to forward to specific offset with a single forward skip. 
+
+It is possible to load the index manually like this: 
+```
+	var index s2.Index
+	_, err = index.Load(idxBytes)
+```
+
+This can be used to figure out how much to offset the compressed stream:
+
+```
+	compressedOffset, uncompressedOffset, err := index.Find(wantOffset)
+```
+
+The `compressedOffset` is the number of bytes that should be skipped 
+from the beginning of the compressed file.
+
+The `uncompressedOffset` will then be offset of the uncompressed bytes returned
+when decoding from that position. This will always be <= wantOffset.
+
+When creating a decoder it must be specified that it should *not* expect a stream identifier
+at the beginning of the stream. Assuming the io.Reader `r` has been forwarded to `compressedOffset`
+we create the decoder like this:
+
+```
+	dec := s2.NewReader(r, s2.ReaderIgnoreStreamIdentifier())
+```
+
+We are not completely done. We still need to forward the stream the uncompressed bytes we didn't want.
+This is done using the regular "Skip" function:
+
+```
+	err = dec.Skip(wantOffset - uncompressedOffset)
+```
+
+This will ensure that we are at exactly the offset we want, and reading from `dec` will start at the requested offset.
+
+## Index Format:
+
+Each block is structured as a snappy skippable block, with the chunk ID 0x99.
+
+The block can be read from the front, but contains information so it can be read from the back as well.
+
+Numbers are stored as fixed size little endian values or [zigzag encoded](https://developers.google.com/protocol-buffers/docs/encoding#signed_integers) [base 128 varints](https://developers.google.com/protocol-buffers/docs/encoding), 
+with un-encoded value length of 64 bits, unless other limits are specified. 
+
+| Content                                                                   | Format                                                                                                                      |
+|---------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------|
+| ID, `[1]byte`                                                           | Always 0x99.                                                                                                                  |
+| Data Length, `[3]byte`                                                  | 3 byte little-endian length of the chunk in bytes, following this.                                                            |
+| Header `[6]byte`                                                        | Header, must be `[115, 50, 105, 100, 120, 0]` or in text: "s2idx\x00".                                                        |
+| UncompressedSize, Varint                                                | Total Uncompressed size.                                                                                                      |
+| CompressedSize, Varint                                                  | Total Compressed size if known. Should be -1 if unknown.                                                                      |
+| EstBlockSize, Varint                                                    | Block Size, used for guessing uncompressed offsets. Must be >= 0.                                                             |
+| Entries, Varint                                                         | Number of Entries in index, must be < 65536 and >=0.                                                                          |
+| HasUncompressedOffsets `byte`                                           | 0 if no uncompressed offsets are present, 1 if present. Other values are invalid.                                             |
+| UncompressedOffsets, [Entries]VarInt                                    | Uncompressed offsets. See below how to decode.                                                                                |
+| CompressedOffsets, [Entries]VarInt                                      | Compressed offsets. See below how to decode.                                                                                  |
+| Block Size, `[4]byte`                                                   | Little Endian total encoded size (including header and trailer). Can be used for searching backwards to start of block.       |
+| Trailer `[6]byte`                                                       | Trailer, must be `[0, 120, 100, 105, 50, 115]` or in text: "\x00xdi2s". Can be used for identifying block from end of stream. |
+
+For regular streams the uncompressed offsets are fully predictable,
+so `HasUncompressedOffsets` allows to specify that compressed blocks all have 
+exactly `EstBlockSize` bytes of uncompressed content.
+
+Entries *must* be in order, starting with the lowest offset, 
+and there *must* be no uncompressed offset duplicates.  
+Entries *may* point to the start of a skippable block, 
+but it is then not allowed to also have an entry for the next block since 
+that would give an uncompressed offset duplicate.
+
+There is no requirement for all blocks to be represented in the index. 
+In fact there is a maximum of 65536 block entries in an index.
+
+The writer can use any method to reduce the number of entries.
+An implicit block start at 0,0 can be assumed.
+
+### Decoding entries:
+
+```
+// Read Uncompressed entries.
+// Each assumes EstBlockSize delta from previous.
+for each entry {
+    uOff = 0
+    if HasUncompressedOffsets == 1 {
+        uOff = ReadVarInt // Read value from stream
+    }
+   
+    // Except for the first entry, use previous values.
+    if entryNum == 0 {
+        entry[entryNum].UncompressedOffset = uOff
+        continue
+    }
+    
+    // Uncompressed uses previous offset and adds EstBlockSize
+    entry[entryNum].UncompressedOffset = entry[entryNum-1].UncompressedOffset + EstBlockSize
+}
+
+
+// Guess that the first block will be 50% of uncompressed size.
+// Integer truncating division must be used.
+CompressGuess := EstBlockSize / 2
+
+// Read Compressed entries.
+// Each assumes CompressGuess delta from previous.
+// CompressGuess is adjusted for each value.
+for each entry {
+    cOff = ReadVarInt // Read value from stream
+    
+    // Except for the first entry, use previous values.
+    if entryNum == 0 {
+        entry[entryNum].CompressedOffset = cOff
+        continue
+    }
+    
+    // Compressed uses previous and our estimate.
+    entry[entryNum].CompressedOffset = entry[entryNum-1].CompressedOffset + CompressGuess
+        
+     // Adjust compressed offset for next loop, integer truncating division must be used. 
+     CompressGuess += cOff/2               
+}
+```
 
 # Format Extensions
 

vendor/github.com/klauspost/compress/s2/decode.go

@@ -8,7 +8,9 @@ package s2
 import (
 	"encoding/binary"
 	"errors"
+	"fmt"
 	"io"
+	"io/ioutil"
 )
 
 var (
@@ -22,6 +24,16 @@ var (
 	ErrUnsupported = errors.New("s2: unsupported input")
 )
 
+// ErrCantSeek is returned if the stream cannot be seeked.
+type ErrCantSeek struct {
+	Reason string
+}
+
+// Error returns the error as string.
+func (e ErrCantSeek) Error() string {
+	return fmt.Sprintf("s2: Can't seek because %s", e.Reason)
+}
+
 // DecodedLen returns the length of the decoded block.
 func DecodedLen(src []byte) (int, error) {
 	v, _, err := decodedLen(src)
@@ -88,6 +100,7 @@ func NewReader(r io.Reader, opts ...ReaderOption) *Reader {
 	} else {
 		nr.buf = make([]byte, MaxEncodedLen(defaultBlockSize)+checksumSize)
 	}
+	nr.readHeader = nr.ignoreStreamID
 	nr.paramsOK = true
 	return &nr
 }
@@ -131,12 +144,41 @@ func ReaderAllocBlock(blockSize int) ReaderOption {
 	}
 }
 
+// ReaderIgnoreStreamIdentifier will make the reader skip the expected
+// stream identifier at the beginning of the stream.
+// This can be used when serving a stream that has been forwarded to a specific point.
+func ReaderIgnoreStreamIdentifier() ReaderOption {
+	return func(r *Reader) error {
+		r.ignoreStreamID = true
+		return nil
+	}
+}
+
+// ReaderSkippableCB will register a callback for chuncks with the specified ID.
+// ID must be a Reserved skippable chunks ID, 0x80-0xfd (inclusive).
+// For each chunk with the ID, the callback is called with the content.
+// Any returned non-nil error will abort decompression.
+// Only one callback per ID is supported, latest sent will be used.
+func ReaderSkippableCB(id uint8, fn func(r io.Reader) error) ReaderOption {
+	return func(r *Reader) error {
+		if id < 0x80 || id > 0xfd {
+			return fmt.Errorf("ReaderSkippableCB: Invalid id provided, must be 0x80-0xfd (inclusive)")
+		}
+		r.skippableCB[id] = fn
+		return nil
+	}
+}
+
 // Reader is an io.Reader that can read Snappy-compressed bytes.
 type Reader struct {
-	r       io.Reader
-	err     error
-	decoded []byte
-	buf     []byte
+	r           io.Reader
+	err         error
+	decoded     []byte
+	buf         []byte
+	skippableCB [0x80]func(r io.Reader) error
+	blockStart  int64 // Uncompressed offset at start of current.
+	index       *Index
+
 	// decoded[i:j] contains decoded bytes that have not yet been passed on.
 	i, j int
 	// maximum block size allowed.
@@ -144,10 +186,11 @@ type Reader struct {
 	// maximum expected buffer size.
 	maxBufSize int
 	// alloc a buffer this size if > 0.
-	lazyBuf     int
-	readHeader  bool
-	paramsOK    bool
-	snappyFrame bool
+	lazyBuf        int
+	readHeader     bool
+	paramsOK       bool
+	snappyFrame    bool
+	ignoreStreamID bool
 }
 
 // ensureBufferSize will ensure that the buffer can take at least n bytes.
@@ -172,11 +215,12 @@ func (r *Reader) Reset(reader io.Reader) {
 	if !r.paramsOK {
 		return
 	}
+	r.index = nil
 	r.r = reader
 	r.err = nil
 	r.i = 0
 	r.j = 0
-	r.readHeader = false
+	r.readHeader = r.ignoreStreamID
 }
 
 func (r *Reader) readFull(p []byte, allowEOF bool) (ok bool) {
@@ -189,11 +233,24 @@ func (r *Reader) readFull(p []byte, allowEOF bool) (ok bool) {
 	return true
 }
 
-// skipN will skip n bytes.
+// skippable will skip n bytes.
 // If the supplied reader supports seeking that is used.
 // tmp is used as a temporary buffer for reading.
 // The supplied slice does not need to be the size of the read.
-func (r *Reader) skipN(tmp []byte, n int, allowEOF bool) (ok bool) {
+func (r *Reader) skippable(tmp []byte, n int, allowEOF bool, id uint8) (ok bool) {
+	if id < 0x80 {
+		r.err = fmt.Errorf("interbal error: skippable id < 0x80")
+		return false
+	}
+	if fn := r.skippableCB[id-0x80]; fn != nil {
+		rd := io.LimitReader(r.r, int64(n))
+		r.err = fn(rd)
+		if r.err != nil {
+			return false
+		}
+		_, r.err = io.CopyBuffer(ioutil.Discard, rd, tmp)
+		return r.err == nil
+	}
 	if rs, ok := r.r.(io.ReadSeeker); ok {
 		_, err := rs.Seek(int64(n), io.SeekCurrent)
 		if err == nil {
@@ -247,6 +304,7 @@ func (r *Reader) Read(p []byte) (int, error) {
 		// https://github.com/google/snappy/blob/master/framing_format.txt
 		switch chunkType {
 		case chunkTypeCompressedData:
+			r.blockStart += int64(r.j)
 			// Section 4.2. Compressed data (chunk type 0x00).
 			if chunkLen < checksumSize {
 				r.err = ErrCorrupt
@@ -294,6 +352,7 @@ func (r *Reader) Read(p []byte) (int, error) {
 			continue
 
 		case chunkTypeUncompressedData:
+			r.blockStart += int64(r.j)
 			// Section 4.3. Uncompressed data (chunk type 0x01).
 			if chunkLen < checksumSize {
 				r.err = ErrCorrupt
@@ -357,17 +416,20 @@ func (r *Reader) Read(p []byte) (int, error) {
 
 		if chunkType <= 0x7f {
 			// Section 4.5. Reserved unskippable chunks (chunk types 0x02-0x7f).
+			// fmt.Printf("ERR chunktype: 0x%x\n", chunkType)
 			r.err = ErrUnsupported
 			return 0, r.err
 		}
 		// Section 4.4 Padding (chunk type 0xfe).
 		// Section 4.6. Reserved skippable chunks (chunk types 0x80-0xfd).
-		if chunkLen > maxBlockSize {
+		if chunkLen > maxChunkSize {
+			// fmt.Printf("ERR chunkLen: 0x%x\n", chunkLen)
 			r.err = ErrUnsupported
 			return 0, r.err
 		}
 
-		if !r.skipN(r.buf, chunkLen, false) {
+		// fmt.Printf("skippable: ID: 0x%x, len: 0x%x\n", chunkType, chunkLen)
+		if !r.skippable(r.buf, chunkLen, false, chunkType) {
 			return 0, r.err
 		}
 	}
@@ -396,7 +458,7 @@ func (r *Reader) Skip(n int64) error {
 				return nil
 			}
 			n -= int64(r.j - r.i)
-			r.i, r.j = 0, 0
+			r.i = r.j
 		}
 
 		// Buffer empty; read blocks until we have content.
@@ -420,6 +482,7 @@ func (r *Reader) Skip(n int64) error {
 		// https://github.com/google/snappy/blob/master/framing_format.txt
 		switch chunkType {
 		case chunkTypeCompressedData:
+			r.blockStart += int64(r.j)
 			// Section 4.2. Compressed data (chunk type 0x00).
 			if chunkLen < checksumSize {
 				r.err = ErrCorrupt
@@ -468,6 +531,7 @@ func (r *Reader) Skip(n int64) error {
 			r.i, r.j = 0, dLen
 			continue
 		case chunkTypeUncompressedData:
+			r.blockStart += int64(r.j)
 			// Section 4.3. Uncompressed data (chunk type 0x01).
 			if chunkLen < checksumSize {
 				r.err = ErrCorrupt
@@ -528,19 +592,138 @@ func (r *Reader) Skip(n int64) error {
 			r.err = ErrUnsupported
 			return r.err
 		}
-		if chunkLen > maxBlockSize {
+		if chunkLen > maxChunkSize {
 			r.err = ErrUnsupported
 			return r.err
 		}
 		// Section 4.4 Padding (chunk type 0xfe).
 		// Section 4.6. Reserved skippable chunks (chunk types 0x80-0xfd).
-		if !r.skipN(r.buf, chunkLen, false) {
+		if !r.skippable(r.buf, chunkLen, false, chunkType) {
 			return r.err
 		}
 	}
 	return nil
 }
 
+// ReadSeeker provides random or forward seeking in compressed content.
+// See Reader.ReadSeeker
+type ReadSeeker struct {
+	*Reader
+}
+
+// ReadSeeker will return an io.ReadSeeker compatible version of the reader.
+// If 'random' is specified the returned io.Seeker can be used for
+// random seeking, otherwise only forward seeking is supported.
+// Enabling random seeking requires the original input to support
+// the io.Seeker interface.
+// A custom index can be specified which will be used if supplied.
+// When using a custom index, it will not be read from the input stream.
+// The returned ReadSeeker contains a shallow reference to the existing Reader,
+// meaning changes performed to one is reflected in the other.
+func (r *Reader) ReadSeeker(random bool, index []byte) (*ReadSeeker, error) {
+	// Read index if provided.
+	if len(index) != 0 {
+		if r.index == nil {
+			r.index = &Index{}
+		}
+		if _, err := r.index.Load(index); err != nil {
+			return nil, ErrCantSeek{Reason: "loading index returned: " + err.Error()}
+		}
+	}
+
+	// Check if input is seekable
+	rs, ok := r.r.(io.ReadSeeker)
+	if !ok {
+		if !random {
+			return &ReadSeeker{Reader: r}, nil
+		}
+		return nil, ErrCantSeek{Reason: "input stream isn't seekable"}
+	}
+
+	if r.index != nil {
+		// Seekable and index, ok...
+		return &ReadSeeker{Reader: r}, nil
+	}
+
+	// Load from stream.
+	r.index = &Index{}
+
+	// Read current position.
+	pos, err := rs.Seek(0, io.SeekCurrent)
+	if err != nil {
+		return nil, ErrCantSeek{Reason: "seeking input returned: " + err.Error()}
+	}
+	err = r.index.LoadStream(rs)
+	if err != nil {
+		if err == ErrUnsupported {
+			return nil, ErrCantSeek{Reason: "input stream does not contain an index"}
+		}
+		return nil, ErrCantSeek{Reason: "reading index returned: " + err.Error()}
+	}
+
+	// reset position.
+	_, err = rs.Seek(pos, io.SeekStart)
+	if err != nil {
+		return nil, ErrCantSeek{Reason: "seeking input returned: " + err.Error()}
+	}
+	return &ReadSeeker{Reader: r}, nil
+}
+
+// Seek allows seeking in compressed data.
+func (r *ReadSeeker) Seek(offset int64, whence int) (int64, error) {
+	if r.err != nil {
+		return 0, r.err
+	}
+	if offset == 0 && whence == io.SeekCurrent {
+		return r.blockStart + int64(r.i), nil
+	}
+	if !r.readHeader {
+		// Make sure we read the header.
+		_, r.err = r.Read([]byte{})
+	}
+	rs, ok := r.r.(io.ReadSeeker)
+	if r.index == nil || !ok {
+		if whence == io.SeekCurrent && offset >= 0 {
+			err := r.Skip(offset)
+			return r.blockStart + int64(r.i), err
+		}
+		if whence == io.SeekStart && offset >= r.blockStart+int64(r.i) {
+			err := r.Skip(offset - r.blockStart - int64(r.i))
+			return r.blockStart + int64(r.i), err
+		}
+		return 0, ErrUnsupported
+
+	}
+
+	switch whence {
+	case io.SeekCurrent:
+		offset += r.blockStart + int64(r.i)
+	case io.SeekEnd:
+		offset = -offset
+	}
+	c, u, err := r.index.Find(offset)
+	if err != nil {
+		return r.blockStart + int64(r.i), err
+	}
+
+	// Seek to next block
+	_, err = rs.Seek(c, io.SeekStart)
+	if err != nil {
+		return 0, err
+	}
+
+	if offset < 0 {
+		offset = r.index.TotalUncompressed + offset
+	}
+
+	r.i = r.j // Remove rest of current block.
+	if u < offset {
+		// Forward inside block
+		return offset, r.Skip(offset - u)
+	}
+	return offset, nil
+}
+
 // ReadByte satisfies the io.ByteReader interface.
 func (r *Reader) ReadByte() (byte, error) {
 	if r.err != nil {
@@ -563,3 +746,17 @@ func (r *Reader) ReadByte() (byte, error) {
 	}
 	return 0, io.ErrNoProgress
 }
+
+// SkippableCB will register a callback for chunks with the specified ID.
+// ID must be a Reserved skippable chunks ID, 0x80-0xfe (inclusive).
+// For each chunk with the ID, the callback is called with the content.
+// Any returned non-nil error will abort decompression.
+// Only one callback per ID is supported, latest sent will be used.
+// Sending a nil function will disable previous callbacks.
+func (r *Reader) SkippableCB(id uint8, fn func(r io.Reader) error) error {
+	if id < 0x80 || id > chunkTypePadding {
+		return fmt.Errorf("ReaderSkippableCB: Invalid id provided, must be 0x80-0xfe (inclusive)")
+	}
+	r.skippableCB[id] = fn
+	return nil
+}

vendor/github.com/klauspost/compress/s2/encode.go

@@ -395,23 +395,26 @@ type Writer struct {
 	// ibuf is a buffer for the incoming (uncompressed) bytes.
 	ibuf []byte
 
-	blockSize   int
-	obufLen     int
-	concurrency int
-	written     int64
-	output      chan chan result
-	buffers     sync.Pool
-	pad         int
+	blockSize     int
+	obufLen       int
+	concurrency   int
+	written       int64
+	uncompWritten int64 // Bytes sent to compression
+	output        chan chan result
+	buffers       sync.Pool
+	pad           int
 
 	writer   io.Writer
 	randSrc  io.Reader
 	writerWg sync.WaitGroup
+	index    Index
 
 	// wroteStreamHeader is whether we have written the stream header.
 	wroteStreamHeader bool
 	paramsOK          bool
 	snappy            bool
 	flushOnWrite      bool
+	appendIndex       bool
 	level             uint8
 }
 
@@ -422,7 +425,11 @@ const (
 	levelBest
 )
 
-type result []byte
+type result struct {
+	b []byte
+	// Uncompressed start offset
+	startOffset int64
+}
 
 // err returns the previously set error.
 // If no error has been set it is set to err if not nil.
@@ -454,6 +461,9 @@ func (w *Writer) Reset(writer io.Writer) {
 	w.wroteStreamHeader = false
 	w.written = 0
 	w.writer = writer
+	w.uncompWritten = 0
+	w.index.reset(w.blockSize)
+
 	// If we didn't get a writer, stop here.
 	if writer == nil {
 		return
@@ -474,7 +484,8 @@ func (w *Writer) Reset(writer io.Writer) {
 		// Get a queued write.
 		for write := range toWrite {
 			// Wait for the data to be available.
-			in := <-write
+			input := <-write
+			in := input.b
 			if len(in) > 0 {
 				if w.err(nil) == nil {
 					// Don't expose data from previous buffers.
@@ -485,11 +496,12 @@ func (w *Writer) Reset(writer io.Writer) {
 						err = io.ErrShortBuffer
 					}
 					_ = w.err(err)
+					w.err(w.index.add(w.written, input.startOffset))
 					w.written += int64(n)
 				}
 			}
 			if cap(in) >= w.obufLen {
-				w.buffers.Put([]byte(in))
+				w.buffers.Put(in)
 			}
 			// close the incoming write request.
 			// This can be used for synchronizing flushes.
@@ -500,6 +512,9 @@ func (w *Writer) Reset(writer io.Writer) {
 
 // Write satisfies the io.Writer interface.
 func (w *Writer) Write(p []byte) (nRet int, errRet error) {
+	if err := w.err(nil); err != nil {
+		return 0, err
+	}
 	if w.flushOnWrite {
 		return w.write(p)
 	}
@@ -535,6 +550,9 @@ func (w *Writer) Write(p []byte) (nRet int, errRet error) {
 // The return value n is the number of bytes read.
 // Any error except io.EOF encountered during the read is also returned.
 func (w *Writer) ReadFrom(r io.Reader) (n int64, err error) {
+	if err := w.err(nil); err != nil {
+		return 0, err
+	}
 	if len(w.ibuf) > 0 {
 		err := w.Flush()
 		if err != nil {
@@ -577,6 +595,85 @@ func (w *Writer) ReadFrom(r io.Reader) (n int64, err error) {
 	return n, w.err(nil)
 }
 
+// AddSkippableBlock will add a skippable block to the stream.
+// The ID must be 0x80-0xfe (inclusive).
+// Length of the skippable block must be <= 16777215 bytes.
+func (w *Writer) AddSkippableBlock(id uint8, data []byte) (err error) {
+	if err := w.err(nil); err != nil {
+		return err
+	}
+	if len(data) == 0 {
+		return nil
+	}
+	if id < 0x80 || id > chunkTypePadding {
+		return fmt.Errorf("invalid skippable block id %x", id)
+	}
+	if len(data) > maxChunkSize {
+		return fmt.Errorf("skippable block excessed maximum size")
+	}
+	var header [4]byte
+	chunkLen := 4 + len(data)
+	header[0] = id
+	header[1] = uint8(chunkLen >> 0)
+	header[2] = uint8(chunkLen >> 8)
+	header[3] = uint8(chunkLen >> 16)
+	if w.concurrency == 1 {
+		write := func(b []byte) error {
+			n, err := w.writer.Write(b)
+			if err = w.err(err); err != nil {
+				return err
+			}
+			if n != len(data) {
+				return w.err(io.ErrShortWrite)
+			}
+			w.written += int64(n)
+			return w.err(nil)
+		}
+		if !w.wroteStreamHeader {
+			w.wroteStreamHeader = true
+			if w.snappy {
+				if err := write([]byte(magicChunkSnappy)); err != nil {
+					return err
+				}
+			} else {
+				if err := write([]byte(magicChunk)); err != nil {
+					return err
+				}
+			}
+		}
+		if err := write(header[:]); err != nil {
+			return err
+		}
+		if err := write(data); err != nil {
+			return err
+		}
+	}
+
+	// Create output...
+	if !w.wroteStreamHeader {
+		w.wroteStreamHeader = true
+		hWriter := make(chan result)
+		w.output <- hWriter
+		if w.snappy {
+			hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunkSnappy)}
+		} else {
+			hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunk)}
+		}
+	}
+
+	// Copy input.
+	inbuf := w.buffers.Get().([]byte)[:4]
+	copy(inbuf, header[:])
+	inbuf = append(inbuf, data...)
+
+	output := make(chan result, 1)
+	// Queue output.
+	w.output <- output
+	output <- result{startOffset: w.uncompWritten, b: inbuf}
+
+	return nil
+}
+
 // EncodeBuffer will add a buffer to the stream.
 // This is the fastest way to encode a stream,
 // but the input buffer cannot be written to by the caller
@@ -614,9 +711,9 @@ func (w *Writer) EncodeBuffer(buf []byte) (err error) {
 		hWriter := make(chan result)
 		w.output <- hWriter
 		if w.snappy {
-			hWriter <- []byte(magicChunkSnappy)
+			hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunkSnappy)}
 		} else {
-			hWriter <- []byte(magicChunk)
+			hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunk)}
 		}
 	}
 
@@ -632,6 +729,10 @@ func (w *Writer) EncodeBuffer(buf []byte) (err error) {
 		output := make(chan result)
 		// Queue output now, so we keep order.
 		w.output <- output
+		res := result{
+			startOffset: w.uncompWritten,
+		}
+		w.uncompWritten += int64(len(uncompressed))
 		go func() {
 			checksum := crc(uncompressed)
 
@@ -664,7 +765,8 @@ func (w *Writer) EncodeBuffer(buf []byte) (err error) {
 			obuf[7] = uint8(checksum >> 24)
 
 			// Queue final output.
-			output <- obuf
+			res.b = obuf
+			output <- res
 		}()
 	}
 	return nil
@@ -708,9 +810,9 @@ func (w *Writer) write(p []byte) (nRet int, errRet error) {
 			hWriter := make(chan result)
 			w.output <- hWriter
 			if w.snappy {
-				hWriter <- []byte(magicChunkSnappy)
+				hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunkSnappy)}
 			} else {
-				hWriter <- []byte(magicChunk)
+				hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunk)}
 			}
 		}
 
@@ -731,6 +833,11 @@ func (w *Writer) write(p []byte) (nRet int, errRet error) {
 		output := make(chan result)
 		// Queue output now, so we keep order.
 		w.output <- output
+		res := result{
+			startOffset: w.uncompWritten,
+		}
+		w.uncompWritten += int64(len(uncompressed))
+
 		go func() {
 			checksum := crc(uncompressed)
 
@@ -763,7 +870,8 @@ func (w *Writer) write(p []byte) (nRet int, errRet error) {
 			obuf[7] = uint8(checksum >> 24)
 
 			// Queue final output.
-			output <- obuf
+			res.b = obuf
+			output <- res
 
 			// Put unused buffer back in pool.
 			w.buffers.Put(inbuf)
@@ -793,9 +901,9 @@ func (w *Writer) writeFull(inbuf []byte) (errRet error) {
 		hWriter := make(chan result)
 		w.output <- hWriter
 		if w.snappy {
-			hWriter <- []byte(magicChunkSnappy)
+			hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunkSnappy)}
 		} else {
-			hWriter <- []byte(magicChunk)
+			hWriter <- result{startOffset: w.uncompWritten, b: []byte(magicChunk)}
 		}
 	}
 
@@ -806,6 +914,11 @@ func (w *Writer) writeFull(inbuf []byte) (errRet error) {
 	output := make(chan result)
 	// Queue output now, so we keep order.
 	w.output <- output
+	res := result{
+		startOffset: w.uncompWritten,
+	}
+	w.uncompWritten += int64(len(uncompressed))
+
 	go func() {
 		checksum := crc(uncompressed)
 
@@ -838,7 +951,8 @@ func (w *Writer) writeFull(inbuf []byte) (errRet error) {
 		obuf[7] = uint8(checksum >> 24)
 
 		// Queue final output.
-		output <- obuf
+		res.b = obuf
+		output <- res
 
 		// Put unused buffer back in pool.
 		w.buffers.Put(inbuf)
@@ -912,7 +1026,10 @@ func (w *Writer) writeSync(p []byte) (nRet int, errRet error) {
 		if n != len(obuf) {
 			return 0, w.err(io.ErrShortWrite)
 		}
+		w.err(w.index.add(w.written, w.uncompWritten))
 		w.written += int64(n)
+		w.uncompWritten += int64(len(uncompressed))
+
 		if chunkType == chunkTypeUncompressedData {
 			// Write uncompressed data.
 			n, err := w.writer.Write(uncompressed)
@@ -961,38 +1078,87 @@ func (w *Writer) Flush() error {
 	res := make(chan result)
 	w.output <- res
 	// Block until this has been picked up.
-	res <- nil
+	res <- result{b: nil, startOffset: w.uncompWritten}
 	// When it is closed, we have flushed.
 	<-res
 	return w.err(nil)
 }
 
 // Close calls Flush and then closes the Writer.
-// Calling Close multiple times is ok.
+// Calling Close multiple times is ok,
+// but calling CloseIndex after this will make it not return the index.
 func (w *Writer) Close() error {
+	_, err := w.closeIndex(w.appendIndex)
+	return err
+}
+
+// CloseIndex calls Close and returns an index on first call.
+// This is not required if you are only adding index to a stream.
+func (w *Writer) CloseIndex() ([]byte, error) {
+	return w.closeIndex(true)
+}
+
+func (w *Writer) closeIndex(idx bool) ([]byte, error) {
 	err := w.Flush()
 	if w.output != nil {
 		close(w.output)
 		w.writerWg.Wait()
 		w.output = nil
 	}
-	if w.err(nil) == nil && w.writer != nil && w.pad > 0 {
-		add := calcSkippableFrame(w.written, int64(w.pad))
-		frame, err := skippableFrame(w.ibuf[:0], add, w.randSrc)
-		if err = w.err(err); err != nil {
-			return err
-		}
-		_, err2 := w.writer.Write(frame)
-		_ = w.err(err2)
-	}
-	_ = w.err(errClosed)
-	if err == errClosed {
-		return nil
-	}
-	return err
-}
 
-const skippableFrameHeader = 4
+	var index []byte
+	if w.err(nil) == nil && w.writer != nil {
+		// Create index.
+		if idx {
+			compSize := int64(-1)
+			if w.pad <= 1 {
+				compSize = w.written
+			}
+			index = w.index.appendTo(w.ibuf[:0], w.uncompWritten, compSize)
+			// Count as written for padding.
+			if w.appendIndex {
+				w.written += int64(len(index))
+			}
+			if true {
+				_, err := w.index.Load(index)
+				if err != nil {
+					panic(err)
+				}
+			}
+		}
+
+		if w.pad > 1 {
+			tmp := w.ibuf[:0]
+			if len(index) > 0 {
+				// Allocate another buffer.
+				tmp = w.buffers.Get().([]byte)[:0]
+				defer w.buffers.Put(tmp)
+			}
+			add := calcSkippableFrame(w.written, int64(w.pad))
+			frame, err := skippableFrame(tmp, add, w.randSrc)
+			if err = w.err(err); err != nil {
+				return nil, err
+			}
+			n, err2 := w.writer.Write(frame)
+			if err2 == nil && n != len(frame) {
+				err2 = io.ErrShortWrite
+			}
+			_ = w.err(err2)
+		}
+		if len(index) > 0 && w.appendIndex {
+			n, err2 := w.writer.Write(index)
+			if err2 == nil && n != len(index) {
+				err2 = io.ErrShortWrite
+			}
+			_ = w.err(err2)
+		}
+	}
+	err = w.err(errClosed)
+	if err == errClosed {
+		return index, nil
+	}
+	return nil, err
+}
 
 // calcSkippableFrame will return a total size to be added for written
 // to be divisible by multiple.
@@ -1057,6 +1223,15 @@ func WriterConcurrency(n int) WriterOption {
 	}
 }
 
+// WriterAddIndex will append an index to the end of a stream
+// when it is closed.
+func WriterAddIndex() WriterOption {
+	return func(w *Writer) error {
+		w.appendIndex = true
+		return nil
+	}
+}
+
 // WriterBetterCompression will enable better compression.
 // EncodeBetter compresses better than Encode but typically with a
 // 10-40% speed decrease on both compression and decompression.

vendor/github.com/klauspost/compress/s2/index.go

@@ -0,0 +1,525 @@
+// Copyright (c) 2022+ Klaus Post. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package s2
+
+import (
+	"bytes"
+	"encoding/binary"
+	"encoding/json"
+	"fmt"
+	"io"
+)
+
+const (
+	S2IndexHeader   = "s2idx\x00"
+	S2IndexTrailer  = "\x00xdi2s"
+	maxIndexEntries = 1 << 16
+)
+
+// Index represents an S2/Snappy index.
+type Index struct {
+	TotalUncompressed int64 // Total Uncompressed size if known. Will be -1 if unknown.
+	TotalCompressed   int64 // Total Compressed size if known. Will be -1 if unknown.
+	info              []struct {
+		compressedOffset   int64
+		uncompressedOffset int64
+	}
+	estBlockUncomp int64
+}
+
+func (i *Index) reset(maxBlock int) {
+	i.estBlockUncomp = int64(maxBlock)
+	i.TotalCompressed = -1
+	i.TotalUncompressed = -1
+	if len(i.info) > 0 {
+		i.info = i.info[:0]
+	}
+}
+
+// allocInfos will allocate an empty slice of infos.
+func (i *Index) allocInfos(n int) {
+	if n > maxIndexEntries {
+		panic("n > maxIndexEntries")
+	}
+	i.info = make([]struct {
+		compressedOffset   int64
+		uncompressedOffset int64
+	}, 0, n)
+}
+
+// add an uncompressed and compressed pair.
+// Entries must be sent in order.
+func (i *Index) add(compressedOffset, uncompressedOffset int64) error {
+	if i == nil {
+		return nil
+	}
+	lastIdx := len(i.info) - 1
+	if lastIdx >= 0 {
+		latest := i.info[lastIdx]
+		if latest.uncompressedOffset == uncompressedOffset {
+			// Uncompressed didn't change, don't add entry,
+			// but update start index.
+			latest.compressedOffset = compressedOffset
+			i.info[lastIdx] = latest
+			return nil
+		}
+		if latest.uncompressedOffset > uncompressedOffset {
+			return fmt.Errorf("internal error: Earlier uncompressed received (%d > %d)", latest.uncompressedOffset, uncompressedOffset)
+		}
+		if latest.compressedOffset > compressedOffset {
+			return fmt.Errorf("internal error: Earlier compressed received (%d > %d)", latest.uncompressedOffset, uncompressedOffset)
+		}
+	}
+	i.info = append(i.info, struct {
+		compressedOffset   int64
+		uncompressedOffset int64
+	}{compressedOffset: compressedOffset, uncompressedOffset: uncompressedOffset})
+	return nil
+}
+
+// Find the offset at or before the wanted (uncompressed) offset.
+// If offset is 0 or positive it is the offset from the beginning of the file.
+// If the uncompressed size is known, the offset must be within the file.
+// If an offset outside the file is requested io.ErrUnexpectedEOF is returned.
+// If the offset is negative, it is interpreted as the distance from the end of the file,
+// where -1 represents the last byte.
+// If offset from the end of the file is requested, but size is unknown,
+// ErrUnsupported will be returned.
+func (i *Index) Find(offset int64) (compressedOff, uncompressedOff int64, err error) {
+	if i.TotalUncompressed < 0 {
+		return 0, 0, ErrCorrupt
+	}
+	if offset < 0 {
+		offset = i.TotalUncompressed + offset
+		if offset < 0 {
+			return 0, 0, io.ErrUnexpectedEOF
+		}
+	}
+	if offset > i.TotalUncompressed {
+		return 0, 0, io.ErrUnexpectedEOF
+	}
+	for _, info := range i.info {
+		if info.uncompressedOffset > offset {
+			break
+		}
+		compressedOff = info.compressedOffset
+		uncompressedOff = info.uncompressedOffset
+	}
+	return compressedOff, uncompressedOff, nil
+}
+
+// reduce to stay below maxIndexEntries
+func (i *Index) reduce() {
+	if len(i.info) < maxIndexEntries && i.estBlockUncomp >= 1<<20 {
+		return
+	}
+
+	// Algorithm, keep 1, remove removeN entries...
+	removeN := (len(i.info) + 1) / maxIndexEntries
+	src := i.info
+	j := 0
+
+	// Each block should be at least 1MB, but don't reduce below 1000 entries.
+	for i.estBlockUncomp*(int64(removeN)+1) < 1<<20 && len(i.info)/(removeN+1) > 1000 {
+		removeN++
+	}
+	for idx := 0; idx < len(src); idx++ {
+		i.info[j] = src[idx]
+		j++
+		idx += removeN
+	}
+	i.info = i.info[:j]
+	// Update maxblock estimate.
+	i.estBlockUncomp += i.estBlockUncomp * int64(removeN)
+}
+
+func (i *Index) appendTo(b []byte, uncompTotal, compTotal int64) []byte {
+	i.reduce()
+	var tmp [binary.MaxVarintLen64]byte
+
+	initSize := len(b)
+	// We make the start a skippable header+size.
+	b = append(b, ChunkTypeIndex, 0, 0, 0)
+	b = append(b, []byte(S2IndexHeader)...)
+	// Total Uncompressed size
+	n := binary.PutVarint(tmp[:], uncompTotal)
+	b = append(b, tmp[:n]...)
+	// Total Compressed size
+	n = binary.PutVarint(tmp[:], compTotal)
+	b = append(b, tmp[:n]...)
+	// Put EstBlockUncomp size
+	n = binary.PutVarint(tmp[:], i.estBlockUncomp)
+	b = append(b, tmp[:n]...)
+	// Put length
+	n = binary.PutVarint(tmp[:], int64(len(i.info)))
+	b = append(b, tmp[:n]...)
+
+	// Check if we should add uncompressed offsets
+	var hasUncompressed byte
+	for idx, info := range i.info {
+		if idx == 0 {
+			if info.uncompressedOffset != 0 {
+				hasUncompressed = 1
+				break
+			}
+			continue
+		}
+		if info.uncompressedOffset != i.info[idx-1].uncompressedOffset+i.estBlockUncomp {
+			hasUncompressed = 1
+			break
+		}
+	}
+	b = append(b, hasUncompressed)
+
+	// Add each entry
+	if hasUncompressed == 1 {
+		for idx, info := range i.info {
+			uOff := info.uncompressedOffset
+			if idx > 0 {
+				prev := i.info[idx-1]
+				uOff -= prev.uncompressedOffset + (i.estBlockUncomp)
+			}
+			n = binary.PutVarint(tmp[:], uOff)
+			b = append(b, tmp[:n]...)
+		}
+	}
+
+	// Initial compressed size estimate.
+	cPredict := i.estBlockUncomp / 2
+
+	for idx, info := range i.info {
+		cOff := info.compressedOffset
+		if idx > 0 {
+			prev := i.info[idx-1]
+			cOff -= prev.compressedOffset + cPredict
+			// Update compressed size prediction, with half the error.
+			cPredict += cOff / 2
+		}
+		n = binary.PutVarint(tmp[:], cOff)
+		b = append(b, tmp[:n]...)
+	}
+
+	// Add Total Size.
+	// Stored as fixed size for easier reading.
+	binary.LittleEndian.PutUint32(tmp[:], uint32(len(b)-initSize+4+len(S2IndexTrailer)))
+	b = append(b, tmp[:4]...)
+	// Trailer
+	b = append(b, []byte(S2IndexTrailer)...)
+
+	// Update size
+	chunkLen := len(b) - initSize - skippableFrameHeader
+	b[initSize+1] = uint8(chunkLen >> 0)
+	b[initSize+2] = uint8(chunkLen >> 8)
+	b[initSize+3] = uint8(chunkLen >> 16)
+	//fmt.Printf("chunklen: 0x%x Uncomp:%d, Comp:%d\n", chunkLen, uncompTotal, compTotal)
+	return b
+}
+
+// Load a binary index.
+// A zero value Index can be used or a previous one can be reused.
+func (i *Index) Load(b []byte) ([]byte, error) {
+	if len(b) <= 4+len(S2IndexHeader)+len(S2IndexTrailer) {
+		return b, io.ErrUnexpectedEOF
+	}
+	if b[0] != ChunkTypeIndex {
+		return b, ErrCorrupt
+	}
+	chunkLen := int(b[1]) | int(b[2])<<8 | int(b[3])<<16
+	b = b[4:]
+
+	// Validate we have enough...
+	if len(b) < chunkLen {
+		return b, io.ErrUnexpectedEOF
+	}
+	if !bytes.Equal(b[:len(S2IndexHeader)], []byte(S2IndexHeader)) {
+		return b, ErrUnsupported
+	}
+	b = b[len(S2IndexHeader):]
+
+	// Total Uncompressed
+	if v, n := binary.Varint(b); n <= 0 || v < 0 {
+		return b, ErrCorrupt
+	} else {
+		i.TotalUncompressed = v
+		b = b[n:]
+	}
+
+	// Total Compressed
+	if v, n := binary.Varint(b); n <= 0 {
+		return b, ErrCorrupt
+	} else {
+		i.TotalCompressed = v
+		b = b[n:]
+	}
+
+	// Read EstBlockUncomp
+	if v, n := binary.Varint(b); n <= 0 {
+		return b, ErrCorrupt
+	} else {
+		if v < 0 {
+			return b, ErrCorrupt
+		}
+		i.estBlockUncomp = v
+		b = b[n:]
+	}
+
+	var entries int
+	if v, n := binary.Varint(b); n <= 0 {
+		return b, ErrCorrupt
+	} else {
+		if v < 0 || v > maxIndexEntries {
+			return b, ErrCorrupt
+		}
+		entries = int(v)
+		b = b[n:]
+	}
+	if cap(i.info) < entries {
+		i.allocInfos(entries)
+	}
+	i.info = i.info[:entries]
+
+	if len(b) < 1 {
+		return b, io.ErrUnexpectedEOF
+	}
+	hasUncompressed := b[0]
+	b = b[1:]
+	if hasUncompressed&1 != hasUncompressed {
+		return b, ErrCorrupt
+	}
+
+	// Add each uncompressed entry
+	for idx := range i.info {
+		var uOff int64
+		if hasUncompressed != 0 {
+			// Load delta
+			if v, n := binary.Varint(b); n <= 0 {
+				return b, ErrCorrupt
+			} else {
+				uOff = v
+				b = b[n:]
+			}
+		}
+
+		if idx > 0 {
+			prev := i.info[idx-1].uncompressedOffset
+			uOff += prev + (i.estBlockUncomp)
+			if uOff <= prev {
+				return b, ErrCorrupt
+			}
+		}
+		if uOff < 0 {
+			return b, ErrCorrupt
+		}
+		i.info[idx].uncompressedOffset = uOff
+	}
+
+	// Initial compressed size estimate.
+	cPredict := i.estBlockUncomp / 2
+
+	// Add each compressed entry
+	for idx := range i.info {
+		var cOff int64
+		if v, n := binary.Varint(b); n <= 0 {
+			return b, ErrCorrupt
+		} else {
+			cOff = v
+			b = b[n:]
+		}
+
+		if idx > 0 {
+			// Update compressed size prediction, with half the error.
+			cPredictNew := cPredict + cOff/2
+
+			prev := i.info[idx-1].compressedOffset
+			cOff += prev + cPredict
+			if cOff <= prev {
+				return b, ErrCorrupt
+			}
+			cPredict = cPredictNew
+		}
+		if cOff < 0 {
+			return b, ErrCorrupt
+		}
+		i.info[idx].compressedOffset = cOff
+	}
+	if len(b) < 4+len(S2IndexTrailer) {
+		return b, io.ErrUnexpectedEOF
+	}
+	// Skip size...
+	b = b[4:]
+
+	// Check trailer...
+	if !bytes.Equal(b[:len(S2IndexTrailer)], []byte(S2IndexTrailer)) {
+		return b, ErrCorrupt
+	}
+	return b[len(S2IndexTrailer):], nil
+}
+
+// LoadStream will load an index from the end of the supplied stream.
+// ErrUnsupported will be returned if the signature cannot be found.
+// ErrCorrupt will be returned if unexpected values are found.
+// io.ErrUnexpectedEOF is returned if there are too few bytes.
+// IO errors are returned as-is.
+func (i *Index) LoadStream(rs io.ReadSeeker) error {
+	// Go to end.
+	_, err := rs.Seek(-10, io.SeekEnd)
+	if err != nil {
+		return err
+	}
+	var tmp [10]byte
+	_, err = io.ReadFull(rs, tmp[:])
+	if err != nil {
+		return err
+	}
+	// Check trailer...
+	if !bytes.Equal(tmp[4:4+len(S2IndexTrailer)], []byte(S2IndexTrailer)) {
+		return ErrUnsupported
+	}
+	sz := binary.LittleEndian.Uint32(tmp[:4])
+	if sz > maxChunkSize+skippableFrameHeader {
+		return ErrCorrupt
+	}
+	_, err = rs.Seek(-int64(sz), io.SeekEnd)
+	if err != nil {
+		return err
+	}
+
+	// Read index.
+	buf := make([]byte, sz)
+	_, err = io.ReadFull(rs, buf)
+	if err != nil {
+		return err
+	}
+	_, err = i.Load(buf)
+	return err
+}
+
+// IndexStream will return an index for a stream.
+// The stream structure will be checked, but
+// data within blocks is not verified.
+// The returned index can either be appended to the end of the stream
+// or stored separately.
+func IndexStream(r io.Reader) ([]byte, error) {
+	var i Index
+	var buf [maxChunkSize]byte
+	var readHeader bool
+	for {
+		_, err := io.ReadFull(r, buf[:4])
+		if err != nil {
+			if err == io.EOF {
+				return i.appendTo(nil, i.TotalUncompressed, i.TotalCompressed), nil
+			}
+			return nil, err
+		}
+		// Start of this chunk.
+		startChunk := i.TotalCompressed
+		i.TotalCompressed += 4
+
+		chunkType := buf[0]
+		if !readHeader {
+			if chunkType != chunkTypeStreamIdentifier {
+				return nil, ErrCorrupt
+			}
+			readHeader = true
+		}
+		chunkLen := int(buf[1]) | int(buf[2])<<8 | int(buf[3])<<16
+		if chunkLen < checksumSize {
+			return nil, ErrCorrupt
+		}
+
+		i.TotalCompressed += int64(chunkLen)
+		_, err = io.ReadFull(r, buf[:chunkLen])
+		if err != nil {
+			return nil, io.ErrUnexpectedEOF
+		}
+		// The chunk types are specified at
+		// https://github.com/google/snappy/blob/master/framing_format.txt
+		switch chunkType {
+		case chunkTypeCompressedData:
+			// Section 4.2. Compressed data (chunk type 0x00).
+			// Skip checksum.
+			dLen, err := DecodedLen(buf[checksumSize:])
+			if err != nil {
+				return nil, err
+			}
+			if dLen > maxBlockSize {
+				return nil, ErrCorrupt
+			}
+			if i.estBlockUncomp == 0 {
+				// Use first block for estimate...
+				i.estBlockUncomp = int64(dLen)
+			}
+			err = i.add(startChunk, i.TotalUncompressed)
+			if err != nil {
+				return nil, err
+			}
+			i.TotalUncompressed += int64(dLen)
+			continue
+		case chunkTypeUncompressedData:
+			n2 := chunkLen - checksumSize
+			if n2 > maxBlockSize {
+				return nil, ErrCorrupt
+			}
+			if i.estBlockUncomp == 0 {
+				// Use first block for estimate...
+				i.estBlockUncomp = int64(n2)
+			}
+			err = i.add(startChunk, i.TotalUncompressed)
+			if err != nil {
+				return nil, err
+			}
+			i.TotalUncompressed += int64(n2)
+			continue
+		case chunkTypeStreamIdentifier:
+			// Section 4.1. Stream identifier (chunk type 0xff).
+			if chunkLen != len(magicBody) {
+				return nil, ErrCorrupt
+			}
+
+			if string(buf[:len(magicBody)]) != magicBody {
+				if string(buf[:len(magicBody)]) != magicBodySnappy {
+					return nil, ErrCorrupt
+				}
+			}
+
+			continue
+		}
+
+		if chunkType <= 0x7f {
+			// Section 4.5. Reserved unskippable chunks (chunk types 0x02-0x7f).
+			return nil, ErrUnsupported
+		}
+		if chunkLen > maxChunkSize {
+			return nil, ErrUnsupported
+		}
+		// Section 4.4 Padding (chunk type 0xfe).
+		// Section 4.6. Reserved skippable chunks (chunk types 0x80-0xfd).
+	}
+}
+
+// JSON returns the index as JSON text.
+func (i *Index) JSON() []byte {
+	x := struct {
+		TotalUncompressed int64 `json:"total_uncompressed"` // Total Uncompressed size if known. Will be -1 if unknown.
+		TotalCompressed   int64 `json:"total_compressed"`   // Total Compressed size if known. Will be -1 if unknown.
+		Offsets           []struct {
+			CompressedOffset   int64 `json:"compressed"`
+			UncompressedOffset int64 `json:"uncompressed"`
+		} `json:"offsets"`
+		EstBlockUncomp int64 `json:"est_block_uncompressed"`
+	}{
+		TotalUncompressed: i.TotalUncompressed,
+		TotalCompressed:   i.TotalCompressed,
+		EstBlockUncomp:    i.estBlockUncomp,
+	}
+	for _, v := range i.info {
+		x.Offsets = append(x.Offsets, struct {
+			CompressedOffset   int64 `json:"compressed"`
+			UncompressedOffset int64 `json:"uncompressed"`
+		}{CompressedOffset: v.compressedOffset, UncompressedOffset: v.uncompressedOffset})
+	}
+	b, _ := json.MarshalIndent(x, "", "  ")
+	return b
+}

vendor/github.com/klauspost/compress/s2/s2.go

@@ -87,6 +87,9 @@ const (
 	// minBlockSize is the minimum size of block setting when creating a writer.
 	minBlockSize = 4 << 10
 
+	skippableFrameHeader = 4
+	maxChunkSize         = 1<<24 - 1 // 16777215
+
 	// Default block size
 	defaultBlockSize = 1 << 20
 
@@ -99,6 +102,7 @@ const (
 const (
 	chunkTypeCompressedData   = 0x00
 	chunkTypeUncompressedData = 0x01
+	ChunkTypeIndex            = 0x99
 	chunkTypePadding          = 0xfe
 	chunkTypeStreamIdentifier = 0xff
 )

vendor/github.com/klauspost/compress/s2sx.mod

@@ -0,0 +1,4 @@
+module github.com/klauspost/compress
+
+go 1.16
+

vendor/github.com/klauspost/compress/zstd/README.md

@@ -0,0 +1,441 @@
+# zstd 
+
+[Zstandard](https://facebook.github.io/zstd/) is a real-time compression algorithm, providing high compression ratios. 
+It offers a very wide range of compression / speed trade-off, while being backed by a very fast decoder.
+A high performance compression algorithm is implemented. For now focused on speed. 
+
+This package provides [compression](#Compressor) to and [decompression](#Decompressor) of Zstandard content. 
+
+This package is pure Go and without use of "unsafe". 
+
+The `zstd` package is provided as open source software using a Go standard license.
+
+Currently the package is heavily optimized for 64 bit processors and will be significantly slower on 32 bit processors.
+
+## Installation
+
+Install using `go get -u github.com/klauspost/compress`. The package is located in `github.com/klauspost/compress/zstd`.
+
+[![Go Reference](https://pkg.go.dev/badge/github.com/klauspost/compress/zstd.svg)](https://pkg.go.dev/github.com/klauspost/compress/zstd)
+
+## Compressor
+
+### Status: 
+
+STABLE - there may always be subtle bugs, a wide variety of content has been tested and the library is actively 
+used by several projects. This library is being [fuzz-tested](https://github.com/klauspost/compress-fuzz) for all updates.
+
+There may still be specific combinations of data types/size/settings that could lead to edge cases, 
+so as always, testing is recommended.  
+
+For now, a high speed (fastest) and medium-fast (default) compressor has been implemented. 
+
+* The "Fastest" compression ratio is roughly equivalent to zstd level 1. 
+* The "Default" compression ratio is roughly equivalent to zstd level 3 (default).
+* The "Better" compression ratio is roughly equivalent to zstd level 7.
+* The "Best" compression ratio is roughly equivalent to zstd level 11.
+
+In terms of speed, it is typically 2x as fast as the stdlib deflate/gzip in its fastest mode. 
+The compression ratio compared to stdlib is around level 3, but usually 3x as fast.
+
+ 
+### Usage
+
+An Encoder can be used for either compressing a stream via the
+`io.WriteCloser` interface supported by the Encoder or as multiple independent
+tasks via the `EncodeAll` function.
+Smaller encodes are encouraged to use the EncodeAll function.
+Use `NewWriter` to create a new instance that can be used for both.
+
+To create a writer with default options, do like this:
+
+```Go
+// Compress input to output.
+func Compress(in io.Reader, out io.Writer) error {
+    enc, err := zstd.NewWriter(out)
+    if err != nil {
+        return err
+    }
+    _, err = io.Copy(enc, in)
+    if err != nil {
+        enc.Close()
+        return err
+    }
+    return enc.Close()
+}
+```
+
+Now you can encode by writing data to `enc`. The output will be finished writing when `Close()` is called.
+Even if your encode fails, you should still call `Close()` to release any resources that may be held up.  
+
+The above is fine for big encodes. However, whenever possible try to *reuse* the writer.
+
+To reuse the encoder, you can use the `Reset(io.Writer)` function to change to another output. 
+This will allow the encoder to reuse all resources and avoid wasteful allocations. 
+
+Currently stream encoding has 'light' concurrency, meaning up to 2 goroutines can be working on part 
+of a stream. This is independent of the `WithEncoderConcurrency(n)`, but that is likely to change 
+in the future. So if you want to limit concurrency for future updates, specify the concurrency
+you would like.
+
+You can specify your desired compression level using `WithEncoderLevel()` option. Currently only pre-defined 
+compression settings can be specified.
+
+#### Future Compatibility Guarantees
+
+This will be an evolving project. When using this package it is important to note that both the compression efficiency and speed may change.
+
+The goal will be to keep the default efficiency at the default zstd (level 3). 
+However the encoding should never be assumed to remain the same, 
+and you should not use hashes of compressed output for similarity checks.
+
+The Encoder can be assumed to produce the same output from the exact same code version.
+However, the may be modes in the future that break this, 
+although they will not be enabled without an explicit option.   
+
+This encoder is not designed to (and will probably never) output the exact same bitstream as the reference encoder.
+
+Also note, that the cgo decompressor currently does not [report all errors on invalid input](https://github.com/DataDog/zstd/issues/59),
+[omits error checks](https://github.com/DataDog/zstd/issues/61), [ignores checksums](https://github.com/DataDog/zstd/issues/43) 
+and seems to ignore concatenated streams, even though [it is part of the spec](https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#frames).
+
+#### Blocks
+
+For compressing small blocks, the returned encoder has a function called `EncodeAll(src, dst []byte) []byte`.
+
+`EncodeAll` will encode all input in src and append it to dst.
+This function can be called concurrently, but each call will only run on a single goroutine.
+
+Encoded blocks can be concatenated and the result will be the combined input stream.
+Data compressed with EncodeAll can be decoded with the Decoder, using either a stream or `DecodeAll`.
+
+Especially when encoding blocks you should take special care to reuse the encoder. 
+This will effectively make it run without allocations after a warmup period. 
+To make it run completely without allocations, supply a destination buffer with space for all content.   
+
+```Go
+import "github.com/klauspost/compress/zstd"
+
+// Create a writer that caches compressors.
+// For this operation type we supply a nil Reader.
+var encoder, _ = zstd.NewWriter(nil)
+
+// Compress a buffer. 
+// If you have a destination buffer, the allocation in the call can also be eliminated.
+func Compress(src []byte) []byte {
+    return encoder.EncodeAll(src, make([]byte, 0, len(src)))
+} 
+```
+
+You can control the maximum number of concurrent encodes using the `WithEncoderConcurrency(n)` 
+option when creating the writer.
+
+Using the Encoder for both a stream and individual blocks concurrently is safe. 
+
+### Performance
+
+I have collected some speed examples to compare speed and compression against other compressors.
+
+* `file` is the input file.
+* `out` is the compressor used. `zskp` is this package. `zstd` is the Datadog cgo library. `gzstd/gzkp` is gzip standard and this library.
+* `level` is the compression level used. For `zskp` level 1 is "fastest", level 2 is "default"; 3 is "better", 4 is "best".
+* `insize`/`outsize` is the input/output size.
+* `millis` is the number of milliseconds used for compression.
+* `mb/s` is megabytes (2^20 bytes) per second.
+
+```
+Silesia Corpus:
+http://sun.aei.polsl.pl/~sdeor/corpus/silesia.zip
+
+This package:
+file    out     level   insize      outsize     millis  mb/s
+silesia.tar zskp    1   211947520   73101992    643     313.87
+silesia.tar zskp    2   211947520   67504318    969     208.38
+silesia.tar zskp    3   211947520   64595893    2007    100.68
+silesia.tar zskp    4   211947520   60995370    8825    22.90
+
+cgo zstd:
+silesia.tar zstd    1   211947520   73605392    543     371.56
+silesia.tar zstd    3   211947520   66793289    864     233.68
+silesia.tar zstd    6   211947520   62916450    1913    105.66
+silesia.tar zstd    9   211947520   60212393    5063    39.92
+
+gzip, stdlib/this package:
+silesia.tar gzstd   1   211947520   80007735    1654    122.21
+silesia.tar gzkp    1   211947520   80136201    1152    175.45
+
+GOB stream of binary data. Highly compressible.
+https://files.klauspost.com/compress/gob-stream.7z
+
+file        out     level   insize  outsize     millis  mb/s
+gob-stream  zskp    1   1911399616  235022249   3088    590.30
+gob-stream  zskp    2   1911399616  205669791   3786    481.34
+gob-stream  zskp    3   1911399616  175034659   9636    189.17
+gob-stream  zskp    4   1911399616  165609838   50369   36.19
+
+gob-stream  zstd    1   1911399616  249810424   2637    691.26
+gob-stream  zstd    3   1911399616  208192146   3490    522.31
+gob-stream  zstd    6   1911399616  193632038   6687    272.56
+gob-stream  zstd    9   1911399616  177620386   16175   112.70
+
+gob-stream  gzstd   1   1911399616  357382641   10251   177.82
+gob-stream  gzkp    1   1911399616  359753026   5438    335.20
+
+The test data for the Large Text Compression Benchmark is the first
+10^9 bytes of the English Wikipedia dump on Mar. 3, 2006.
+http://mattmahoney.net/dc/textdata.html
+
+file    out level   insize      outsize     millis  mb/s
+enwik9  zskp    1   1000000000  343848582   3609    264.18
+enwik9  zskp    2   1000000000  317276632   5746    165.97
+enwik9  zskp    3   1000000000  292243069   12162   78.41
+enwik9  zskp    4   1000000000  262183768   82837   11.51
+
+enwik9  zstd    1   1000000000  358072021   3110    306.65
+enwik9  zstd    3   1000000000  313734672   4784    199.35
+enwik9  zstd    6   1000000000  295138875   10290   92.68
+enwik9  zstd    9   1000000000  278348700   28549   33.40
+
+enwik9  gzstd   1   1000000000  382578136   9604    99.30
+enwik9  gzkp    1   1000000000  383825945   6544    145.73
+
+Highly compressible JSON file.
+https://files.klauspost.com/compress/github-june-2days-2019.json.zst
+
+file                        out level   insize      outsize     millis  mb/s
+github-june-2days-2019.json zskp    1   6273951764  699045015   10620   563.40
+github-june-2days-2019.json zskp    2   6273951764  617881763   11687   511.96
+github-june-2days-2019.json zskp    3   6273951764  524340691   34043   175.75
+github-june-2days-2019.json zskp    4   6273951764  470320075   170190  35.16
+
+github-june-2days-2019.json zstd    1   6273951764  766284037   8450    708.00
+github-june-2days-2019.json zstd    3   6273951764  661889476   10927   547.57
+github-june-2days-2019.json zstd    6   6273951764  642756859   22996   260.18
+github-june-2days-2019.json zstd    9   6273951764  601974523   52413   114.16
+
+github-june-2days-2019.json gzstd   1   6273951764  1164400847  29948   199.79
+github-june-2days-2019.json gzkp    1   6273951764  1125417694  21788   274.61
+
+VM Image, Linux mint with a few installed applications:
+https://files.klauspost.com/compress/rawstudio-mint14.7z
+
+file                    out level   insize      outsize     millis  mb/s
+rawstudio-mint14.tar    zskp    1   8558382592  3667489370  20210   403.84
+rawstudio-mint14.tar    zskp    2   8558382592  3364592300  31873   256.07
+rawstudio-mint14.tar    zskp    3   8558382592  3158085214  77675   105.08
+rawstudio-mint14.tar    zskp    4   8558382592  2965110639  857750  9.52
+
+rawstudio-mint14.tar    zstd    1   8558382592  3609250104  17136   476.27
+rawstudio-mint14.tar    zstd    3   8558382592  3341679997  29262   278.92
+rawstudio-mint14.tar    zstd    6   8558382592  3235846406  77904   104.77
+rawstudio-mint14.tar    zstd    9   8558382592  3160778861  140946  57.91
+
+rawstudio-mint14.tar    gzstd   1   8558382592  3926257486  57722   141.40
+rawstudio-mint14.tar    gzkp    1   8558382592  3962605659  45113   180.92
+
+CSV data:
+https://files.klauspost.com/compress/nyc-taxi-data-10M.csv.zst
+
+file                    out level   insize      outsize     millis  mb/s
+nyc-taxi-data-10M.csv   zskp    1   3325605752  641339945   8925    355.35
+nyc-taxi-data-10M.csv   zskp    2   3325605752  591748091   11268   281.44
+nyc-taxi-data-10M.csv   zskp    3   3325605752  530289687   25239   125.66
+nyc-taxi-data-10M.csv   zskp    4   3325605752  476268884   135958  23.33
+
+nyc-taxi-data-10M.csv   zstd    1   3325605752  687399637   8233    385.18
+nyc-taxi-data-10M.csv   zstd    3   3325605752  598514411   10065   315.07
+nyc-taxi-data-10M.csv   zstd    6   3325605752  570522953   20038   158.27
+nyc-taxi-data-10M.csv   zstd    9   3325605752  517554797   64565   49.12
+
+nyc-taxi-data-10M.csv   gzstd   1   3325605752  928656485   23876   132.83
+nyc-taxi-data-10M.csv   gzkp    1   3325605752  922257165   16780   189.00
+```
+
+## Decompressor
+
+Staus: STABLE - there may still be subtle bugs, but a wide variety of content has been tested.
+
+This library is being continuously [fuzz-tested](https://github.com/klauspost/compress-fuzz),
+kindly supplied by [fuzzit.dev](https://fuzzit.dev/). 
+The main purpose of the fuzz testing is to ensure that it is not possible to crash the decoder, 
+or run it past its limits with ANY input provided.  
+ 
+### Usage
+
+The package has been designed for two main usages, big streams of data and smaller in-memory buffers. 
+There are two main usages of the package for these. Both of them are accessed by creating a `Decoder`.
+
+For streaming use a simple setup could look like this:
+
+```Go
+import "github.com/klauspost/compress/zstd"
+
+func Decompress(in io.Reader, out io.Writer) error {
+    d, err := zstd.NewReader(in)
+    if err != nil {
+        return err
+    }
+    defer d.Close()
+    
+    // Copy content...
+    _, err = io.Copy(out, d)
+    return err
+}
+```
+
+It is important to use the "Close" function when you no longer need the Reader to stop running goroutines. 
+See "Allocation-less operation" below.
+
+For decoding buffers, it could look something like this:
+
+```Go
+import "github.com/klauspost/compress/zstd"
+
+// Create a reader that caches decompressors.
+// For this operation type we supply a nil Reader.
+var decoder, _ = zstd.NewReader(nil)
+
+// Decompress a buffer. We don't supply a destination buffer,
+// so it will be allocated by the decoder.
+func Decompress(src []byte) ([]byte, error) {
+    return decoder.DecodeAll(src, nil)
+} 
+```
+
+Both of these cases should provide the functionality needed. 
+The decoder can be used for *concurrent* decompression of multiple buffers. 
+It will only allow a certain number of concurrent operations to run. 
+To tweak that yourself use the `WithDecoderConcurrency(n)` option when creating the decoder.   
+
+### Dictionaries
+
+Data compressed with [dictionaries](https://github.com/facebook/zstd#the-case-for-small-data-compression) can be decompressed.
+
+Dictionaries are added individually to Decoders.
+Dictionaries are generated by the `zstd --train` command and contains an initial state for the decoder.
+To add a dictionary use the `WithDecoderDicts(dicts ...[]byte)` option with the dictionary data.
+Several dictionaries can be added at once.
+
+The dictionary will be used automatically for the data that specifies them.
+A re-used Decoder will still contain the dictionaries registered.
+
+When registering multiple dictionaries with the same ID, the last one will be used.
+
+It is possible to use dictionaries when compressing data.
+
+To enable a dictionary use `WithEncoderDict(dict []byte)`. Here only one dictionary will be used 
+and it will likely be used even if it doesn't improve compression. 
+
+The used dictionary must be used to decompress the content.
+
+For any real gains, the dictionary should be built with similar data. 
+If an unsuitable dictionary is used the output may be slightly larger than using no dictionary.
+Use the [zstd commandline tool](https://github.com/facebook/zstd/releases) to build a dictionary from sample data.
+For information see [zstd dictionary information](https://github.com/facebook/zstd#the-case-for-small-data-compression). 
+
+For now there is a fixed startup performance penalty for compressing content with dictionaries. 
+This will likely be improved over time. Just be aware to test performance when implementing.  
+
+### Allocation-less operation
+
+The decoder has been designed to operate without allocations after a warmup. 
+
+This means that you should *store* the decoder for best performance. 
+To re-use a stream decoder, use the `Reset(r io.Reader) error` to switch to another stream.
+A decoder can safely be re-used even if the previous stream failed.
+
+To release the resources, you must call the `Close()` function on a decoder.
+After this it can *no longer be reused*, but all running goroutines will be stopped.
+So you *must* use this if you will no longer need the Reader.
+
+For decompressing smaller buffers a single decoder can be used.
+When decoding buffers, you can supply a destination slice with length 0 and your expected capacity.
+In this case no unneeded allocations should be made. 
+
+### Concurrency
+
+The buffer decoder does everything on the same goroutine and does nothing concurrently.
+It can however decode several buffers concurrently. Use `WithDecoderConcurrency(n)` to limit that.
+
+The stream decoder operates on
+
+* One goroutine reads input and splits the input to several block decoders.
+* A number of decoders will decode blocks.
+* A goroutine coordinates these blocks and sends history from one to the next.
+
+So effectively this also means the decoder will "read ahead" and prepare data to always be available for output.
+
+Since "blocks" are quite dependent on the output of the previous block stream decoding will only have limited concurrency.
+
+In practice this means that concurrency is often limited to utilizing about 2 cores effectively.
+ 
+ 
+### Benchmarks
+
+These are some examples of performance compared to [datadog cgo library](https://github.com/DataDog/zstd).
+
+The first two are streaming decodes and the last are smaller inputs. 
+ 
+```
+BenchmarkDecoderSilesia-8                          3     385000067 ns/op     550.51 MB/s        5498 B/op          8 allocs/op
+BenchmarkDecoderSilesiaCgo-8                       6     197666567 ns/op    1072.25 MB/s      270672 B/op          8 allocs/op
+
+BenchmarkDecoderEnwik9-8                           1    2027001600 ns/op     493.34 MB/s       10496 B/op         18 allocs/op
+BenchmarkDecoderEnwik9Cgo-8                        2     979499200 ns/op    1020.93 MB/s      270672 B/op          8 allocs/op
+
+Concurrent performance:
+
+BenchmarkDecoder_DecodeAllParallel/kppkn.gtb.zst-16                28915         42469 ns/op    4340.07 MB/s         114 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallel/geo.protodata.zst-16           116505          9965 ns/op    11900.16 MB/s         16 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallel/plrabn12.txt.zst-16              8952        134272 ns/op    3588.70 MB/s         915 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallel/lcet10.txt.zst-16               11820        102538 ns/op    4161.90 MB/s         594 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallel/asyoulik.txt.zst-16             34782         34184 ns/op    3661.88 MB/s          60 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallel/alice29.txt.zst-16              27712         43447 ns/op    3500.58 MB/s          99 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallel/html_x_4.zst-16                 62826         18750 ns/op    21845.10 MB/s        104 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallel/paper-100k.pdf.zst-16          631545          1794 ns/op    57078.74 MB/s          2 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallel/fireworks.jpeg.zst-16         1690140           712 ns/op    172938.13 MB/s         1 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallel/urls.10K.zst-16                 10432        113593 ns/op    6180.73 MB/s        1143 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallel/html.zst-16                    113206         10671 ns/op    9596.27 MB/s          15 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallel/comp-data.bin.zst-16          1530615           779 ns/op    5229.49 MB/s           0 B/op          0 allocs/op
+
+BenchmarkDecoder_DecodeAllParallelCgo/kppkn.gtb.zst-16             65217         16192 ns/op    11383.34 MB/s         46 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallelCgo/geo.protodata.zst-16        292671          4039 ns/op    29363.19 MB/s          6 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallelCgo/plrabn12.txt.zst-16          26314         46021 ns/op    10470.43 MB/s        293 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallelCgo/lcet10.txt.zst-16            33897         34900 ns/op    12227.96 MB/s        205 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallelCgo/asyoulik.txt.zst-16         104348         11433 ns/op    10949.01 MB/s         20 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallelCgo/alice29.txt.zst-16           75949         15510 ns/op    9805.60 MB/s          32 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallelCgo/html_x_4.zst-16             173910          6756 ns/op    60624.29 MB/s         37 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallelCgo/paper-100k.pdf.zst-16       923076          1339 ns/op    76474.87 MB/s          1 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallelCgo/fireworks.jpeg.zst-16       922920          1351 ns/op    91102.57 MB/s          2 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallelCgo/urls.10K.zst-16              27649         43618 ns/op    16096.19 MB/s        407 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallelCgo/html.zst-16                 279073          4160 ns/op    24614.18 MB/s          6 B/op          0 allocs/op
+BenchmarkDecoder_DecodeAllParallelCgo/comp-data.bin.zst-16        749938          1579 ns/op    2581.71 MB/s           0 B/op          0 allocs/op
+```
+
+This reflects the performance around May 2020, but this may be out of date.
+
+## Zstd inside ZIP files
+
+It is possible to use zstandard to compress individual files inside zip archives.
+While this isn't widely supported it can be useful for internal files.
+
+To support the compression and decompression of these files you must register a compressor and decompressor.
+
+It is highly recommended registering the (de)compressors on individual zip Reader/Writer and NOT
+use the global registration functions. The main reason for this is that 2 registrations from 
+different packages will result in a panic.
+
+It is a good idea to only have a single compressor and decompressor, since they can be used for multiple zip
+files concurrently, and using a single instance will allow reusing some resources.
+
+See [this example](https://pkg.go.dev/github.com/klauspost/compress/zstd#example-ZipCompressor) for 
+how to compress and decompress files inside zip archives.
+
+# Contributions
+
+Contributions are always welcome. 
+For new features/fixes, remember to add tests and for performance enhancements include benchmarks.
+
+For general feedback and experience reports, feel free to open an issue or write me on [Twitter](https://twitter.com/sh0dan).
+
+This package includes the excellent [`github.com/cespare/xxhash`](https://github.com/cespare/xxhash) package Copyright (c) 2016 Caleb Spare.

vendor/github.com/klauspost/compress/zstd/bitreader.go

@@ -0,0 +1,143 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+import (
+	"encoding/binary"
+	"errors"
+	"io"
+	"math/bits"
+)
+
+// bitReader reads a bitstream in reverse.
+// The last set bit indicates the start of the stream and is used
+// for aligning the input.
+type bitReader struct {
+	in       []byte
+	off      uint   // next byte to read is at in[off - 1]
+	value    uint64 // Maybe use [16]byte, but shifting is awkward.
+	bitsRead uint8
+}
+
+// init initializes and resets the bit reader.
+func (b *bitReader) init(in []byte) error {
+	if len(in) < 1 {
+		return errors.New("corrupt stream: too short")
+	}
+	b.in = in
+	b.off = uint(len(in))
+	// The highest bit of the last byte indicates where to start
+	v := in[len(in)-1]
+	if v == 0 {
+		return errors.New("corrupt stream, did not find end of stream")
+	}
+	b.bitsRead = 64
+	b.value = 0
+	if len(in) >= 8 {
+		b.fillFastStart()
+	} else {
+		b.fill()
+		b.fill()
+	}
+	b.bitsRead += 8 - uint8(highBits(uint32(v)))
+	return nil
+}
+
+// getBits will return n bits. n can be 0.
+func (b *bitReader) getBits(n uint8) int {
+	if n == 0 /*|| b.bitsRead >= 64 */ {
+		return 0
+	}
+	return int(b.get32BitsFast(n))
+}
+
+// get32BitsFast requires that at least one bit is requested every time.
+// There are no checks if the buffer is filled.
+func (b *bitReader) get32BitsFast(n uint8) uint32 {
+	const regMask = 64 - 1
+	v := uint32((b.value << (b.bitsRead & regMask)) >> ((regMask + 1 - n) & regMask))
+	b.bitsRead += n
+	return v
+}
+
+func (b *bitReader) get16BitsFast(n uint8) uint16 {
+	const regMask = 64 - 1
+	v := uint16((b.value << (b.bitsRead & regMask)) >> ((regMask + 1 - n) & regMask))
+	b.bitsRead += n
+	return v
+}
+
+// fillFast() will make sure at least 32 bits are available.
+// There must be at least 4 bytes available.
+func (b *bitReader) fillFast() {
+	if b.bitsRead < 32 {
+		return
+	}
+	// 2 bounds checks.
+	v := b.in[b.off-4:]
+	v = v[:4]
+	low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+	b.value = (b.value << 32) | uint64(low)
+	b.bitsRead -= 32
+	b.off -= 4
+}
+
+// fillFastStart() assumes the bitreader is empty and there is at least 8 bytes to read.
+func (b *bitReader) fillFastStart() {
+	// Do single re-slice to avoid bounds checks.
+	b.value = binary.LittleEndian.Uint64(b.in[b.off-8:])
+	b.bitsRead = 0
+	b.off -= 8
+}
+
+// fill() will make sure at least 32 bits are available.
+func (b *bitReader) fill() {
+	if b.bitsRead < 32 {
+		return
+	}
+	if b.off >= 4 {
+		v := b.in[b.off-4:]
+		v = v[:4]
+		low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+		b.value = (b.value << 32) | uint64(low)
+		b.bitsRead -= 32
+		b.off -= 4
+		return
+	}
+	for b.off > 0 {
+		b.value = (b.value << 8) | uint64(b.in[b.off-1])
+		b.bitsRead -= 8
+		b.off--
+	}
+}
+
+// finished returns true if all bits have been read from the bit stream.
+func (b *bitReader) finished() bool {
+	return b.off == 0 && b.bitsRead >= 64
+}
+
+// overread returns true if more bits have been requested than is on the stream.
+func (b *bitReader) overread() bool {
+	return b.bitsRead > 64
+}
+
+// remain returns the number of bits remaining.
+func (b *bitReader) remain() uint {
+	return b.off*8 + 64 - uint(b.bitsRead)
+}
+
+// close the bitstream and returns an error if out-of-buffer reads occurred.
+func (b *bitReader) close() error {
+	// Release reference.
+	b.in = nil
+	if b.bitsRead > 64 {
+		return io.ErrUnexpectedEOF
+	}
+	return nil
+}
+
+func highBits(val uint32) (n uint32) {
+	return uint32(bits.Len32(val) - 1)
+}

vendor/github.com/klauspost/compress/zstd/bitwriter.go

@@ -0,0 +1,189 @@
+// Copyright 2018 Klaus Post. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+// Based on work Copyright (c) 2013, Yann Collet, released under BSD License.
+
+package zstd
+
+import "fmt"
+
+// bitWriter will write bits.
+// First bit will be LSB of the first byte of output.
+type bitWriter struct {
+	bitContainer uint64
+	nBits        uint8
+	out          []byte
+}
+
+// bitMask16 is bitmasks. Has extra to avoid bounds check.
+var bitMask16 = [32]uint16{
+	0, 1, 3, 7, 0xF, 0x1F,
+	0x3F, 0x7F, 0xFF, 0x1FF, 0x3FF, 0x7FF,
+	0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF, 0xFFFF,
+	0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF,
+	0xFFFF, 0xFFFF} /* up to 16 bits */
+
+var bitMask32 = [32]uint32{
+	0, 1, 3, 7, 0xF, 0x1F, 0x3F, 0x7F, 0xFF,
+	0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF,
+	0x1ffff, 0x3ffff, 0x7FFFF, 0xfFFFF, 0x1fFFFF, 0x3fFFFF, 0x7fFFFF, 0xffFFFF,
+	0x1ffFFFF, 0x3ffFFFF, 0x7ffFFFF, 0xfffFFFF, 0x1fffFFFF, 0x3fffFFFF, 0x7fffFFFF,
+} // up to 32 bits
+
+// addBits16NC will add up to 16 bits.
+// It will not check if there is space for them,
+// so the caller must ensure that it has flushed recently.
+func (b *bitWriter) addBits16NC(value uint16, bits uint8) {
+	b.bitContainer |= uint64(value&bitMask16[bits&31]) << (b.nBits & 63)
+	b.nBits += bits
+}
+
+// addBits32NC will add up to 31 bits.
+// It will not check if there is space for them,
+// so the caller must ensure that it has flushed recently.
+func (b *bitWriter) addBits32NC(value uint32, bits uint8) {
+	b.bitContainer |= uint64(value&bitMask32[bits&31]) << (b.nBits & 63)
+	b.nBits += bits
+}
+
+// addBits64NC will add up to 64 bits.
+// There must be space for 32 bits.
+func (b *bitWriter) addBits64NC(value uint64, bits uint8) {
+	if bits <= 31 {
+		b.addBits32Clean(uint32(value), bits)
+		return
+	}
+	b.addBits32Clean(uint32(value), 32)
+	b.flush32()
+	b.addBits32Clean(uint32(value>>32), bits-32)
+}
+
+// addBits32Clean will add up to 32 bits.
+// It will not check if there is space for them.
+// The input must not contain more bits than specified.
+func (b *bitWriter) addBits32Clean(value uint32, bits uint8) {
+	b.bitContainer |= uint64(value) << (b.nBits & 63)
+	b.nBits += bits
+}
+
+// addBits16Clean will add up to 16 bits. value may not contain more set bits than indicated.
+// It will not check if there is space for them, so the caller must ensure that it has flushed recently.
+func (b *bitWriter) addBits16Clean(value uint16, bits uint8) {
+	b.bitContainer |= uint64(value) << (b.nBits & 63)
+	b.nBits += bits
+}
+
+// flush will flush all pending full bytes.
+// There will be at least 56 bits available for writing when this has been called.
+// Using flush32 is faster, but leaves less space for writing.
+func (b *bitWriter) flush() {
+	v := b.nBits >> 3
+	switch v {
+	case 0:
+	case 1:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+		)
+	case 2:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+		)
+	case 3:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+		)
+	case 4:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+			byte(b.bitContainer>>24),
+		)
+	case 5:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+			byte(b.bitContainer>>24),
+			byte(b.bitContainer>>32),
+		)
+	case 6:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+			byte(b.bitContainer>>24),
+			byte(b.bitContainer>>32),
+			byte(b.bitContainer>>40),
+		)
+	case 7:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+			byte(b.bitContainer>>24),
+			byte(b.bitContainer>>32),
+			byte(b.bitContainer>>40),
+			byte(b.bitContainer>>48),
+		)
+	case 8:
+		b.out = append(b.out,
+			byte(b.bitContainer),
+			byte(b.bitContainer>>8),
+			byte(b.bitContainer>>16),
+			byte(b.bitContainer>>24),
+			byte(b.bitContainer>>32),
+			byte(b.bitContainer>>40),
+			byte(b.bitContainer>>48),
+			byte(b.bitContainer>>56),
+		)
+	default:
+		panic(fmt.Errorf("bits (%d) > 64", b.nBits))
+	}
+	b.bitContainer >>= v << 3
+	b.nBits &= 7
+}
+
+// flush32 will flush out, so there are at least 32 bits available for writing.
+func (b *bitWriter) flush32() {
+	if b.nBits < 32 {
+		return
+	}
+	b.out = append(b.out,
+		byte(b.bitContainer),
+		byte(b.bitContainer>>8),
+		byte(b.bitContainer>>16),
+		byte(b.bitContainer>>24))
+	b.nBits -= 32
+	b.bitContainer >>= 32
+}
+
+// flushAlign will flush remaining full bytes and align to next byte boundary.
+func (b *bitWriter) flushAlign() {
+	nbBytes := (b.nBits + 7) >> 3
+	for i := uint8(0); i < nbBytes; i++ {
+		b.out = append(b.out, byte(b.bitContainer>>(i*8)))
+	}
+	b.nBits = 0
+	b.bitContainer = 0
+}
+
+// close will write the alignment bit and write the final byte(s)
+// to the output.
+func (b *bitWriter) close() error {
+	// End mark
+	b.addBits16Clean(1, 1)
+	// flush until next byte.
+	b.flushAlign()
+	return nil
+}
+
+// reset and continue writing by appending to out.
+func (b *bitWriter) reset(out []byte) {
+	b.bitContainer = 0
+	b.nBits = 0
+	b.out = out
+}

vendor/github.com/klauspost/compress/zstd/blockdec.go

@@ -0,0 +1,736 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"sync"
+
+	"github.com/klauspost/compress/huff0"
+	"github.com/klauspost/compress/zstd/internal/xxhash"
+)
+
+type blockType uint8
+
+//go:generate stringer -type=blockType,literalsBlockType,seqCompMode,tableIndex
+
+const (
+	blockTypeRaw blockType = iota
+	blockTypeRLE
+	blockTypeCompressed
+	blockTypeReserved
+)
+
+type literalsBlockType uint8
+
+const (
+	literalsBlockRaw literalsBlockType = iota
+	literalsBlockRLE
+	literalsBlockCompressed
+	literalsBlockTreeless
+)
+
+const (
+	// maxCompressedBlockSize is the biggest allowed compressed block size (128KB)
+	maxCompressedBlockSize = 128 << 10
+
+	// Maximum possible block size (all Raw+Uncompressed).
+	maxBlockSize = (1 << 21) - 1
+
+	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#literals_section_header
+	maxCompressedLiteralSize = 1 << 18
+	maxRLELiteralSize        = 1 << 20
+	maxMatchLen              = 131074
+	maxSequences             = 0x7f00 + 0xffff
+
+	// We support slightly less than the reference decoder to be able to
+	// use ints on 32 bit archs.
+	maxOffsetBits = 30
+)
+
+var (
+	huffDecoderPool = sync.Pool{New: func() interface{} {
+		return &huff0.Scratch{}
+	}}
+
+	fseDecoderPool = sync.Pool{New: func() interface{} {
+		return &fseDecoder{}
+	}}
+)
+
+type blockDec struct {
+	// Raw source data of the block.
+	data        []byte
+	dataStorage []byte
+
+	// Destination of the decoded data.
+	dst []byte
+
+	// Buffer for literals data.
+	literalBuf []byte
+
+	// Window size of the block.
+	WindowSize uint64
+
+	history     chan *history
+	input       chan struct{}
+	result      chan decodeOutput
+	sequenceBuf []seq
+	err         error
+	decWG       sync.WaitGroup
+
+	// Frame to use for singlethreaded decoding.
+	// Should not be used by the decoder itself since parent may be another frame.
+	localFrame *frameDec
+
+	// Block is RLE, this is the size.
+	RLESize uint32
+	tmp     [4]byte
+
+	Type blockType
+
+	// Is this the last block of a frame?
+	Last bool
+
+	// Use less memory
+	lowMem bool
+}
+
+func (b *blockDec) String() string {
+	if b == nil {
+		return "<nil>"
+	}
+	return fmt.Sprintf("Steam Size: %d, Type: %v, Last: %t, Window: %d", len(b.data), b.Type, b.Last, b.WindowSize)
+}
+
+func newBlockDec(lowMem bool) *blockDec {
+	b := blockDec{
+		lowMem:  lowMem,
+		result:  make(chan decodeOutput, 1),
+		input:   make(chan struct{}, 1),
+		history: make(chan *history, 1),
+	}
+	b.decWG.Add(1)
+	go b.startDecoder()
+	return &b
+}
+
+// reset will reset the block.
+// Input must be a start of a block and will be at the end of the block when returned.
+func (b *blockDec) reset(br byteBuffer, windowSize uint64) error {
+	b.WindowSize = windowSize
+	tmp, err := br.readSmall(3)
+	if err != nil {
+		println("Reading block header:", err)
+		return err
+	}
+	bh := uint32(tmp[0]) | (uint32(tmp[1]) << 8) | (uint32(tmp[2]) << 16)
+	b.Last = bh&1 != 0
+	b.Type = blockType((bh >> 1) & 3)
+	// find size.
+	cSize := int(bh >> 3)
+	maxSize := maxBlockSize
+	switch b.Type {
+	case blockTypeReserved:
+		return ErrReservedBlockType
+	case blockTypeRLE:
+		b.RLESize = uint32(cSize)
+		if b.lowMem {
+			maxSize = cSize
+		}
+		cSize = 1
+	case blockTypeCompressed:
+		if debugDecoder {
+			println("Data size on stream:", cSize)
+		}
+		b.RLESize = 0
+		maxSize = maxCompressedBlockSize
+		if windowSize < maxCompressedBlockSize && b.lowMem {
+			maxSize = int(windowSize)
+		}
+		if cSize > maxCompressedBlockSize || uint64(cSize) > b.WindowSize {
+			if debugDecoder {
+				printf("compressed block too big: csize:%d block: %+v\n", uint64(cSize), b)
+			}
+			return ErrCompressedSizeTooBig
+		}
+	case blockTypeRaw:
+		b.RLESize = 0
+		// We do not need a destination for raw blocks.
+		maxSize = -1
+	default:
+		panic("Invalid block type")
+	}
+
+	// Read block data.
+	if cap(b.dataStorage) < cSize {
+		if b.lowMem || cSize > maxCompressedBlockSize {
+			b.dataStorage = make([]byte, 0, cSize)
+		} else {
+			b.dataStorage = make([]byte, 0, maxCompressedBlockSize)
+		}
+	}
+	if cap(b.dst) <= maxSize {
+		b.dst = make([]byte, 0, maxSize+1)
+	}
+	b.data, err = br.readBig(cSize, b.dataStorage)
+	if err != nil {
+		if debugDecoder {
+			println("Reading block:", err, "(", cSize, ")", len(b.data))
+			printf("%T", br)
+		}
+		return err
+	}
+	return nil
+}
+
+// sendEOF will make the decoder send EOF on this frame.
+func (b *blockDec) sendErr(err error) {
+	b.Last = true
+	b.Type = blockTypeReserved
+	b.err = err
+	b.input <- struct{}{}
+}
+
+// Close will release resources.
+// Closed blockDec cannot be reset.
+func (b *blockDec) Close() {
+	close(b.input)
+	close(b.history)
+	close(b.result)
+	b.decWG.Wait()
+}
+
+// decodeAsync will prepare decoding the block when it receives input.
+// This will separate output and history.
+func (b *blockDec) startDecoder() {
+	defer b.decWG.Done()
+	for range b.input {
+		//println("blockDec: Got block input")
+		switch b.Type {
+		case blockTypeRLE:
+			if cap(b.dst) < int(b.RLESize) {
+				if b.lowMem {
+					b.dst = make([]byte, b.RLESize)
+				} else {
+					b.dst = make([]byte, maxBlockSize)
+				}
+			}
+			o := decodeOutput{
+				d:   b,
+				b:   b.dst[:b.RLESize],
+				err: nil,
+			}
+			v := b.data[0]
+			for i := range o.b {
+				o.b[i] = v
+			}
+			hist := <-b.history
+			hist.append(o.b)
+			b.result <- o
+		case blockTypeRaw:
+			o := decodeOutput{
+				d:   b,
+				b:   b.data,
+				err: nil,
+			}
+			hist := <-b.history
+			hist.append(o.b)
+			b.result <- o
+		case blockTypeCompressed:
+			b.dst = b.dst[:0]
+			err := b.decodeCompressed(nil)
+			o := decodeOutput{
+				d:   b,
+				b:   b.dst,
+				err: err,
+			}
+			if debugDecoder {
+				println("Decompressed to", len(b.dst), "bytes, error:", err)
+			}
+			b.result <- o
+		case blockTypeReserved:
+			// Used for returning errors.
+			<-b.history
+			b.result <- decodeOutput{
+				d:   b,
+				b:   nil,
+				err: b.err,
+			}
+		default:
+			panic("Invalid block type")
+		}
+		if debugDecoder {
+			println("blockDec: Finished block")
+		}
+	}
+}
+
+// decodeAsync will prepare decoding the block when it receives the history.
+// If history is provided, it will not fetch it from the channel.
+func (b *blockDec) decodeBuf(hist *history) error {
+	switch b.Type {
+	case blockTypeRLE:
+		if cap(b.dst) < int(b.RLESize) {
+			if b.lowMem {
+				b.dst = make([]byte, b.RLESize)
+			} else {
+				b.dst = make([]byte, maxBlockSize)
+			}
+		}
+		b.dst = b.dst[:b.RLESize]
+		v := b.data[0]
+		for i := range b.dst {
+			b.dst[i] = v
+		}
+		hist.appendKeep(b.dst)
+		return nil
+	case blockTypeRaw:
+		hist.appendKeep(b.data)
+		return nil
+	case blockTypeCompressed:
+		saved := b.dst
+		b.dst = hist.b
+		hist.b = nil
+		err := b.decodeCompressed(hist)
+		if debugDecoder {
+			println("Decompressed to total", len(b.dst), "bytes, hash:", xxhash.Sum64(b.dst), "error:", err)
+		}
+		hist.b = b.dst
+		b.dst = saved
+		return err
+	case blockTypeReserved:
+		// Used for returning errors.
+		return b.err
+	default:
+		panic("Invalid block type")
+	}
+}
+
+// decodeCompressed will start decompressing a block.
+// If no history is supplied the decoder will decodeAsync as much as possible
+// before fetching from blockDec.history
+func (b *blockDec) decodeCompressed(hist *history) error {
+	in := b.data
+	delayedHistory := hist == nil
+
+	if delayedHistory {
+		// We must always grab history.
+		defer func() {
+			if hist == nil {
+				<-b.history
+			}
+		}()
+	}
+	// There must be at least one byte for Literals_Block_Type and one for Sequences_Section_Header
+	if len(in) < 2 {
+		return ErrBlockTooSmall
+	}
+	litType := literalsBlockType(in[0] & 3)
+	var litRegenSize int
+	var litCompSize int
+	sizeFormat := (in[0] >> 2) & 3
+	var fourStreams bool
+	switch litType {
+	case literalsBlockRaw, literalsBlockRLE:
+		switch sizeFormat {
+		case 0, 2:
+			// Regenerated_Size uses 5 bits (0-31). Literals_Section_Header uses 1 byte.
+			litRegenSize = int(in[0] >> 3)
+			in = in[1:]
+		case 1:
+			// Regenerated_Size uses 12 bits (0-4095). Literals_Section_Header uses 2 bytes.
+			litRegenSize = int(in[0]>>4) + (int(in[1]) << 4)
+			in = in[2:]
+		case 3:
+			//  Regenerated_Size uses 20 bits (0-1048575). Literals_Section_Header uses 3 bytes.
+			if len(in) < 3 {
+				println("too small: litType:", litType, " sizeFormat", sizeFormat, len(in))
+				return ErrBlockTooSmall
+			}
+			litRegenSize = int(in[0]>>4) + (int(in[1]) << 4) + (int(in[2]) << 12)
+			in = in[3:]
+		}
+	case literalsBlockCompressed, literalsBlockTreeless:
+		switch sizeFormat {
+		case 0, 1:
+			// Both Regenerated_Size and Compressed_Size use 10 bits (0-1023).
+			if len(in) < 3 {
+				println("too small: litType:", litType, " sizeFormat", sizeFormat, len(in))
+				return ErrBlockTooSmall
+			}
+			n := uint64(in[0]>>4) + (uint64(in[1]) << 4) + (uint64(in[2]) << 12)
+			litRegenSize = int(n & 1023)
+			litCompSize = int(n >> 10)
+			fourStreams = sizeFormat == 1
+			in = in[3:]
+		case 2:
+			fourStreams = true
+			if len(in) < 4 {
+				println("too small: litType:", litType, " sizeFormat", sizeFormat, len(in))
+				return ErrBlockTooSmall
+			}
+			n := uint64(in[0]>>4) + (uint64(in[1]) << 4) + (uint64(in[2]) << 12) + (uint64(in[3]) << 20)
+			litRegenSize = int(n & 16383)
+			litCompSize = int(n >> 14)
+			in = in[4:]
+		case 3:
+			fourStreams = true
+			if len(in) < 5 {
+				println("too small: litType:", litType, " sizeFormat", sizeFormat, len(in))
+				return ErrBlockTooSmall
+			}
+			n := uint64(in[0]>>4) + (uint64(in[1]) << 4) + (uint64(in[2]) << 12) + (uint64(in[3]) << 20) + (uint64(in[4]) << 28)
+			litRegenSize = int(n & 262143)
+			litCompSize = int(n >> 18)
+			in = in[5:]
+		}
+	}
+	if debugDecoder {
+		println("literals type:", litType, "litRegenSize:", litRegenSize, "litCompSize:", litCompSize, "sizeFormat:", sizeFormat, "4X:", fourStreams)
+	}
+	var literals []byte
+	var huff *huff0.Scratch
+	switch litType {
+	case literalsBlockRaw:
+		if len(in) < litRegenSize {
+			println("too small: litType:", litType, " sizeFormat", sizeFormat, "remain:", len(in), "want:", litRegenSize)
+			return ErrBlockTooSmall
+		}
+		literals = in[:litRegenSize]
+		in = in[litRegenSize:]
+		//printf("Found %d uncompressed literals\n", litRegenSize)
+	case literalsBlockRLE:
+		if len(in) < 1 {
+			println("too small: litType:", litType, " sizeFormat", sizeFormat, "remain:", len(in), "want:", 1)
+			return ErrBlockTooSmall
+		}
+		if cap(b.literalBuf) < litRegenSize {
+			if b.lowMem {
+				b.literalBuf = make([]byte, litRegenSize)
+			} else {
+				if litRegenSize > maxCompressedLiteralSize {
+					// Exceptional
+					b.literalBuf = make([]byte, litRegenSize)
+				} else {
+					b.literalBuf = make([]byte, litRegenSize, maxCompressedLiteralSize)
+
+				}
+			}
+		}
+		literals = b.literalBuf[:litRegenSize]
+		v := in[0]
+		for i := range literals {
+			literals[i] = v
+		}
+		in = in[1:]
+		if debugDecoder {
+			printf("Found %d RLE compressed literals\n", litRegenSize)
+		}
+	case literalsBlockTreeless:
+		if len(in) < litCompSize {
+			println("too small: litType:", litType, " sizeFormat", sizeFormat, "remain:", len(in), "want:", litCompSize)
+			return ErrBlockTooSmall
+		}
+		// Store compressed literals, so we defer decoding until we get history.
+		literals = in[:litCompSize]
+		in = in[litCompSize:]
+		if debugDecoder {
+			printf("Found %d compressed literals\n", litCompSize)
+		}
+	case literalsBlockCompressed:
+		if len(in) < litCompSize {
+			println("too small: litType:", litType, " sizeFormat", sizeFormat, "remain:", len(in), "want:", litCompSize)
+			return ErrBlockTooSmall
+		}
+		literals = in[:litCompSize]
+		in = in[litCompSize:]
+		huff = huffDecoderPool.Get().(*huff0.Scratch)
+		var err error
+		// Ensure we have space to store it.
+		if cap(b.literalBuf) < litRegenSize {
+			if b.lowMem {
+				b.literalBuf = make([]byte, 0, litRegenSize)
+			} else {
+				b.literalBuf = make([]byte, 0, maxCompressedLiteralSize)
+			}
+		}
+		if huff == nil {
+			huff = &huff0.Scratch{}
+		}
+		huff, literals, err = huff0.ReadTable(literals, huff)
+		if err != nil {
+			println("reading huffman table:", err)
+			return err
+		}
+		// Use our out buffer.
+		if fourStreams {
+			literals, err = huff.Decoder().Decompress4X(b.literalBuf[:0:litRegenSize], literals)
+		} else {
+			literals, err = huff.Decoder().Decompress1X(b.literalBuf[:0:litRegenSize], literals)
+		}
+		if err != nil {
+			println("decoding compressed literals:", err)
+			return err
+		}
+		// Make sure we don't leak our literals buffer
+		if len(literals) != litRegenSize {
+			return fmt.Errorf("literal output size mismatch want %d, got %d", litRegenSize, len(literals))
+		}
+		if debugDecoder {
+			printf("Decompressed %d literals into %d bytes\n", litCompSize, litRegenSize)
+		}
+	}
+
+	// Decode Sequences
+	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#sequences-section
+	if len(in) < 1 {
+		return ErrBlockTooSmall
+	}
+	seqHeader := in[0]
+	nSeqs := 0
+	switch {
+	case seqHeader == 0:
+		in = in[1:]
+	case seqHeader < 128:
+		nSeqs = int(seqHeader)
+		in = in[1:]
+	case seqHeader < 255:
+		if len(in) < 2 {
+			return ErrBlockTooSmall
+		}
+		nSeqs = int(seqHeader-128)<<8 | int(in[1])
+		in = in[2:]
+	case seqHeader == 255:
+		if len(in) < 3 {
+			return ErrBlockTooSmall
+		}
+		nSeqs = 0x7f00 + int(in[1]) + (int(in[2]) << 8)
+		in = in[3:]
+	}
+	// Allocate sequences
+	if cap(b.sequenceBuf) < nSeqs {
+		if b.lowMem {
+			b.sequenceBuf = make([]seq, nSeqs)
+		} else {
+			// Allocate max
+			b.sequenceBuf = make([]seq, nSeqs, maxSequences)
+		}
+	} else {
+		// Reuse buffer
+		b.sequenceBuf = b.sequenceBuf[:nSeqs]
+	}
+	var seqs = &sequenceDecs{}
+	if nSeqs > 0 {
+		if len(in) < 1 {
+			return ErrBlockTooSmall
+		}
+		br := byteReader{b: in, off: 0}
+		compMode := br.Uint8()
+		br.advance(1)
+		if debugDecoder {
+			printf("Compression modes: 0b%b", compMode)
+		}
+		for i := uint(0); i < 3; i++ {
+			mode := seqCompMode((compMode >> (6 - i*2)) & 3)
+			if debugDecoder {
+				println("Table", tableIndex(i), "is", mode)
+			}
+			var seq *sequenceDec
+			switch tableIndex(i) {
+			case tableLiteralLengths:
+				seq = &seqs.litLengths
+			case tableOffsets:
+				seq = &seqs.offsets
+			case tableMatchLengths:
+				seq = &seqs.matchLengths
+			default:
+				panic("unknown table")
+			}
+			switch mode {
+			case compModePredefined:
+				seq.fse = &fsePredef[i]
+			case compModeRLE:
+				if br.remain() < 1 {
+					return ErrBlockTooSmall
+				}
+				v := br.Uint8()
+				br.advance(1)
+				dec := fseDecoderPool.Get().(*fseDecoder)
+				symb, err := decSymbolValue(v, symbolTableX[i])
+				if err != nil {
+					printf("RLE Transform table (%v) error: %v", tableIndex(i), err)
+					return err
+				}
+				dec.setRLE(symb)
+				seq.fse = dec
+				if debugDecoder {
+					printf("RLE set to %+v, code: %v", symb, v)
+				}
+			case compModeFSE:
+				println("Reading table for", tableIndex(i))
+				dec := fseDecoderPool.Get().(*fseDecoder)
+				err := dec.readNCount(&br, uint16(maxTableSymbol[i]))
+				if err != nil {
+					println("Read table error:", err)
+					return err
+				}
+				err = dec.transform(symbolTableX[i])
+				if err != nil {
+					println("Transform table error:", err)
+					return err
+				}
+				if debugDecoder {
+					println("Read table ok", "symbolLen:", dec.symbolLen)
+				}
+				seq.fse = dec
+			case compModeRepeat:
+				seq.repeat = true
+			}
+			if br.overread() {
+				return io.ErrUnexpectedEOF
+			}
+		}
+		in = br.unread()
+	}
+
+	// Wait for history.
+	// All time spent after this is critical since it is strictly sequential.
+	if hist == nil {
+		hist = <-b.history
+		if hist.error {
+			return ErrDecoderClosed
+		}
+	}
+
+	// Decode treeless literal block.
+	if litType == literalsBlockTreeless {
+		// TODO: We could send the history early WITHOUT the stream history.
+		//   This would allow decoding treeless literals before the byte history is available.
+		//   Silencia stats: Treeless 4393, with: 32775, total: 37168, 11% treeless.
+		//   So not much obvious gain here.
+
+		if hist.huffTree == nil {
+			return errors.New("literal block was treeless, but no history was defined")
+		}
+		// Ensure we have space to store it.
+		if cap(b.literalBuf) < litRegenSize {
+			if b.lowMem {
+				b.literalBuf = make([]byte, 0, litRegenSize)
+			} else {
+				b.literalBuf = make([]byte, 0, maxCompressedLiteralSize)
+			}
+		}
+		var err error
+		// Use our out buffer.
+		huff = hist.huffTree
+		if fourStreams {
+			literals, err = huff.Decoder().Decompress4X(b.literalBuf[:0:litRegenSize], literals)
+		} else {
+			literals, err = huff.Decoder().Decompress1X(b.literalBuf[:0:litRegenSize], literals)
+		}
+		// Make sure we don't leak our literals buffer
+		if err != nil {
+			println("decompressing literals:", err)
+			return err
+		}
+		if len(literals) != litRegenSize {
+			return fmt.Errorf("literal output size mismatch want %d, got %d", litRegenSize, len(literals))
+		}
+	} else {
+		if hist.huffTree != nil && huff != nil {
+			if hist.dict == nil || hist.dict.litEnc != hist.huffTree {
+				huffDecoderPool.Put(hist.huffTree)
+			}
+			hist.huffTree = nil
+		}
+	}
+	if huff != nil {
+		hist.huffTree = huff
+	}
+	if debugDecoder {
+		println("Final literals:", len(literals), "hash:", xxhash.Sum64(literals), "and", nSeqs, "sequences.")
+	}
+
+	if nSeqs == 0 {
+		// Decompressed content is defined entirely as Literals Section content.
+		b.dst = append(b.dst, literals...)
+		if delayedHistory {
+			hist.append(literals)
+		}
+		return nil
+	}
+
+	seqs, err := seqs.mergeHistory(&hist.decoders)
+	if err != nil {
+		return err
+	}
+	if debugDecoder {
+		println("History merged ok")
+	}
+	br := &bitReader{}
+	if err := br.init(in); err != nil {
+		return err
+	}
+
+	// TODO: Investigate if sending history without decoders are faster.
+	//   This would allow the sequences to be decoded async and only have to construct stream history.
+	//   If only recent offsets were not transferred, this would be an obvious win.
+	// 	 Also, if first 3 sequences don't reference recent offsets, all sequences can be decoded.
+
+	hbytes := hist.b
+	if len(hbytes) > hist.windowSize {
+		hbytes = hbytes[len(hbytes)-hist.windowSize:]
+		// We do not need history any more.
+		if hist.dict != nil {
+			hist.dict.content = nil
+		}
+	}
+
+	if err := seqs.initialize(br, hist, literals, b.dst); err != nil {
+		println("initializing sequences:", err)
+		return err
+	}
+
+	err = seqs.decode(nSeqs, br, hbytes)
+	if err != nil {
+		return err
+	}
+	if !br.finished() {
+		return fmt.Errorf("%d extra bits on block, should be 0", br.remain())
+	}
+
+	err = br.close()
+	if err != nil {
+		printf("Closing sequences: %v, %+v\n", err, *br)
+	}
+	if len(b.data) > maxCompressedBlockSize {
+		return fmt.Errorf("compressed block size too large (%d)", len(b.data))
+	}
+	// Set output and release references.
+	b.dst = seqs.out
+	seqs.out, seqs.literals, seqs.hist = nil, nil, nil
+
+	if !delayedHistory {
+		// If we don't have delayed history, no need to update.
+		hist.recentOffsets = seqs.prevOffset
+		return nil
+	}
+	if b.Last {
+		// if last block we don't care about history.
+		println("Last block, no history returned")
+		hist.b = hist.b[:0]
+		return nil
+	}
+	hist.append(b.dst)
+	hist.recentOffsets = seqs.prevOffset
+	if debugDecoder {
+		println("Finished block with literals:", len(literals), "and", nSeqs, "sequences.")
+	}
+
+	return nil
+}

vendor/github.com/klauspost/compress/zstd/blockenc.go

@@ -0,0 +1,871 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+import (
+	"errors"
+	"fmt"
+	"math"
+	"math/bits"
+
+	"github.com/klauspost/compress/huff0"
+)
+
+type blockEnc struct {
+	size       int
+	literals   []byte
+	sequences  []seq
+	coders     seqCoders
+	litEnc     *huff0.Scratch
+	dictLitEnc *huff0.Scratch
+	wr         bitWriter
+
+	extraLits         int
+	output            []byte
+	recentOffsets     [3]uint32
+	prevRecentOffsets [3]uint32
+
+	last   bool
+	lowMem bool
+}
+
+// init should be used once the block has been created.
+// If called more than once, the effect is the same as calling reset.
+func (b *blockEnc) init() {
+	if b.lowMem {
+		// 1K literals
+		if cap(b.literals) < 1<<10 {
+			b.literals = make([]byte, 0, 1<<10)
+		}
+		const defSeqs = 20
+		if cap(b.sequences) < defSeqs {
+			b.sequences = make([]seq, 0, defSeqs)
+		}
+		// 1K
+		if cap(b.output) < 1<<10 {
+			b.output = make([]byte, 0, 1<<10)
+		}
+	} else {
+		if cap(b.literals) < maxCompressedBlockSize {
+			b.literals = make([]byte, 0, maxCompressedBlockSize)
+		}
+		const defSeqs = 2000
+		if cap(b.sequences) < defSeqs {
+			b.sequences = make([]seq, 0, defSeqs)
+		}
+		if cap(b.output) < maxCompressedBlockSize {
+			b.output = make([]byte, 0, maxCompressedBlockSize)
+		}
+	}
+
+	if b.coders.mlEnc == nil {
+		b.coders.mlEnc = &fseEncoder{}
+		b.coders.mlPrev = &fseEncoder{}
+		b.coders.ofEnc = &fseEncoder{}
+		b.coders.ofPrev = &fseEncoder{}
+		b.coders.llEnc = &fseEncoder{}
+		b.coders.llPrev = &fseEncoder{}
+	}
+	b.litEnc = &huff0.Scratch{WantLogLess: 4}
+	b.reset(nil)
+}
+
+// initNewEncode can be used to reset offsets and encoders to the initial state.
+func (b *blockEnc) initNewEncode() {
+	b.recentOffsets = [3]uint32{1, 4, 8}
+	b.litEnc.Reuse = huff0.ReusePolicyNone
+	b.coders.setPrev(nil, nil, nil)
+}
+
+// reset will reset the block for a new encode, but in the same stream,
+// meaning that state will be carried over, but the block content is reset.
+// If a previous block is provided, the recent offsets are carried over.
+func (b *blockEnc) reset(prev *blockEnc) {
+	b.extraLits = 0
+	b.literals = b.literals[:0]
+	b.size = 0
+	b.sequences = b.sequences[:0]
+	b.output = b.output[:0]
+	b.last = false
+	if prev != nil {
+		b.recentOffsets = prev.prevRecentOffsets
+	}
+	b.dictLitEnc = nil
+}
+
+// reset will reset the block for a new encode, but in the same stream,
+// meaning that state will be carried over, but the block content is reset.
+// If a previous block is provided, the recent offsets are carried over.
+func (b *blockEnc) swapEncoders(prev *blockEnc) {
+	b.coders.swap(&prev.coders)
+	b.litEnc, prev.litEnc = prev.litEnc, b.litEnc
+}
+
+// blockHeader contains the information for a block header.
+type blockHeader uint32
+
+// setLast sets the 'last' indicator on a block.
+func (h *blockHeader) setLast(b bool) {
+	if b {
+		*h = *h | 1
+	} else {
+		const mask = (1 << 24) - 2
+		*h = *h & mask
+	}
+}
+
+// setSize will store the compressed size of a block.
+func (h *blockHeader) setSize(v uint32) {
+	const mask = 7
+	*h = (*h)&mask | blockHeader(v<<3)
+}
+
+// setType sets the block type.
+func (h *blockHeader) setType(t blockType) {
+	const mask = 1 | (((1 << 24) - 1) ^ 7)
+	*h = (*h & mask) | blockHeader(t<<1)
+}
+
+// appendTo will append the block header to a slice.
+func (h blockHeader) appendTo(b []byte) []byte {
+	return append(b, uint8(h), uint8(h>>8), uint8(h>>16))
+}
+
+// String returns a string representation of the block.
+func (h blockHeader) String() string {
+	return fmt.Sprintf("Type: %d, Size: %d, Last:%t", (h>>1)&3, h>>3, h&1 == 1)
+}
+
+// literalsHeader contains literals header information.
+type literalsHeader uint64
+
+// setType can be used to set the type of literal block.
+func (h *literalsHeader) setType(t literalsBlockType) {
+	const mask = math.MaxUint64 - 3
+	*h = (*h & mask) | literalsHeader(t)
+}
+
+// setSize can be used to set a single size, for uncompressed and RLE content.
+func (h *literalsHeader) setSize(regenLen int) {
+	inBits := bits.Len32(uint32(regenLen))
+	// Only retain 2 bits
+	const mask = 3
+	lh := uint64(*h & mask)
+	switch {
+	case inBits < 5:
+		lh |= (uint64(regenLen) << 3) | (1 << 60)
+		if debugEncoder {
+			got := int(lh>>3) & 0xff
+			if got != regenLen {
+				panic(fmt.Sprint("litRegenSize = ", regenLen, "(want) != ", got, "(got)"))
+			}
+		}
+	case inBits < 12:
+		lh |= (1 << 2) | (uint64(regenLen) << 4) | (2 << 60)
+	case inBits < 20:
+		lh |= (3 << 2) | (uint64(regenLen) << 4) | (3 << 60)
+	default:
+		panic(fmt.Errorf("internal error: block too big (%d)", regenLen))
+	}
+	*h = literalsHeader(lh)
+}
+
+// setSizes will set the size of a compressed literals section and the input length.
+func (h *literalsHeader) setSizes(compLen, inLen int, single bool) {
+	compBits, inBits := bits.Len32(uint32(compLen)), bits.Len32(uint32(inLen))
+	// Only retain 2 bits
+	const mask = 3
+	lh := uint64(*h & mask)
+	switch {
+	case compBits <= 10 && inBits <= 10:
+		if !single {
+			lh |= 1 << 2
+		}
+		lh |= (uint64(inLen) << 4) | (uint64(compLen) << (10 + 4)) | (3 << 60)
+		if debugEncoder {
+			const mmask = (1 << 24) - 1
+			n := (lh >> 4) & mmask
+			if int(n&1023) != inLen {
+				panic(fmt.Sprint("regensize:", int(n&1023), "!=", inLen, inBits))
+			}
+			if int(n>>10) != compLen {
+				panic(fmt.Sprint("compsize:", int(n>>10), "!=", compLen, compBits))
+			}
+		}
+	case compBits <= 14 && inBits <= 14:
+		lh |= (2 << 2) | (uint64(inLen) << 4) | (uint64(compLen) << (14 + 4)) | (4 << 60)
+		if single {
+			panic("single stream used with more than 10 bits length.")
+		}
+	case compBits <= 18 && inBits <= 18:
+		lh |= (3 << 2) | (uint64(inLen) << 4) | (uint64(compLen) << (18 + 4)) | (5 << 60)
+		if single {
+			panic("single stream used with more than 10 bits length.")
+		}
+	default:
+		panic("internal error: block too big")
+	}
+	*h = literalsHeader(lh)
+}
+
+// appendTo will append the literals header to a byte slice.
+func (h literalsHeader) appendTo(b []byte) []byte {
+	size := uint8(h >> 60)
+	switch size {
+	case 1:
+		b = append(b, uint8(h))
+	case 2:
+		b = append(b, uint8(h), uint8(h>>8))
+	case 3:
+		b = append(b, uint8(h), uint8(h>>8), uint8(h>>16))
+	case 4:
+		b = append(b, uint8(h), uint8(h>>8), uint8(h>>16), uint8(h>>24))
+	case 5:
+		b = append(b, uint8(h), uint8(h>>8), uint8(h>>16), uint8(h>>24), uint8(h>>32))
+	default:
+		panic(fmt.Errorf("internal error: literalsHeader has invalid size (%d)", size))
+	}
+	return b
+}
+
+// size returns the output size with currently set values.
+func (h literalsHeader) size() int {
+	return int(h >> 60)
+}
+
+func (h literalsHeader) String() string {
+	return fmt.Sprintf("Type: %d, SizeFormat: %d, Size: 0x%d, Bytes:%d", literalsBlockType(h&3), (h>>2)&3, h&((1<<60)-1)>>4, h>>60)
+}
+
+// pushOffsets will push the recent offsets to the backup store.
+func (b *blockEnc) pushOffsets() {
+	b.prevRecentOffsets = b.recentOffsets
+}
+
+// pushOffsets will push the recent offsets to the backup store.
+func (b *blockEnc) popOffsets() {
+	b.recentOffsets = b.prevRecentOffsets
+}
+
+// matchOffset will adjust recent offsets and return the adjusted one,
+// if it matches a previous offset.
+func (b *blockEnc) matchOffset(offset, lits uint32) uint32 {
+	// Check if offset is one of the recent offsets.
+	// Adjusts the output offset accordingly.
+	// Gives a tiny bit of compression, typically around 1%.
+	if true {
+		if lits > 0 {
+			switch offset {
+			case b.recentOffsets[0]:
+				offset = 1
+			case b.recentOffsets[1]:
+				b.recentOffsets[1] = b.recentOffsets[0]
+				b.recentOffsets[0] = offset
+				offset = 2
+			case b.recentOffsets[2]:
+				b.recentOffsets[2] = b.recentOffsets[1]
+				b.recentOffsets[1] = b.recentOffsets[0]
+				b.recentOffsets[0] = offset
+				offset = 3
+			default:
+				b.recentOffsets[2] = b.recentOffsets[1]
+				b.recentOffsets[1] = b.recentOffsets[0]
+				b.recentOffsets[0] = offset
+				offset += 3
+			}
+		} else {
+			switch offset {
+			case b.recentOffsets[1]:
+				b.recentOffsets[1] = b.recentOffsets[0]
+				b.recentOffsets[0] = offset
+				offset = 1
+			case b.recentOffsets[2]:
+				b.recentOffsets[2] = b.recentOffsets[1]
+				b.recentOffsets[1] = b.recentOffsets[0]
+				b.recentOffsets[0] = offset
+				offset = 2
+			case b.recentOffsets[0] - 1:
+				b.recentOffsets[2] = b.recentOffsets[1]
+				b.recentOffsets[1] = b.recentOffsets[0]
+				b.recentOffsets[0] = offset
+				offset = 3
+			default:
+				b.recentOffsets[2] = b.recentOffsets[1]
+				b.recentOffsets[1] = b.recentOffsets[0]
+				b.recentOffsets[0] = offset
+				offset += 3
+			}
+		}
+	} else {
+		offset += 3
+	}
+	return offset
+}
+
+// encodeRaw can be used to set the output to a raw representation of supplied bytes.
+func (b *blockEnc) encodeRaw(a []byte) {
+	var bh blockHeader
+	bh.setLast(b.last)
+	bh.setSize(uint32(len(a)))
+	bh.setType(blockTypeRaw)
+	b.output = bh.appendTo(b.output[:0])
+	b.output = append(b.output, a...)
+	if debugEncoder {
+		println("Adding RAW block, length", len(a), "last:", b.last)
+	}
+}
+
+// encodeRaw can be used to set the output to a raw representation of supplied bytes.
+func (b *blockEnc) encodeRawTo(dst, src []byte) []byte {
+	var bh blockHeader
+	bh.setLast(b.last)
+	bh.setSize(uint32(len(src)))
+	bh.setType(blockTypeRaw)
+	dst = bh.appendTo(dst)
+	dst = append(dst, src...)
+	if debugEncoder {
+		println("Adding RAW block, length", len(src), "last:", b.last)
+	}
+	return dst
+}
+
+// encodeLits can be used if the block is only litLen.
+func (b *blockEnc) encodeLits(lits []byte, raw bool) error {
+	var bh blockHeader
+	bh.setLast(b.last)
+	bh.setSize(uint32(len(lits)))
+
+	// Don't compress extremely small blocks
+	if len(lits) < 8 || (len(lits) < 32 && b.dictLitEnc == nil) || raw {
+		if debugEncoder {
+			println("Adding RAW block, length", len(lits), "last:", b.last)
+		}
+		bh.setType(blockTypeRaw)
+		b.output = bh.appendTo(b.output)
+		b.output = append(b.output, lits...)
+		return nil
+	}
+
+	var (
+		out            []byte
+		reUsed, single bool
+		err            error
+	)
+	if b.dictLitEnc != nil {
+		b.litEnc.TransferCTable(b.dictLitEnc)
+		b.litEnc.Reuse = huff0.ReusePolicyAllow
+		b.dictLitEnc = nil
+	}
+	if len(lits) >= 1024 {
+		// Use 4 Streams.
+		out, reUsed, err = huff0.Compress4X(lits, b.litEnc)
+	} else if len(lits) > 32 {
+		// Use 1 stream
+		single = true
+		out, reUsed, err = huff0.Compress1X(lits, b.litEnc)
+	} else {
+		err = huff0.ErrIncompressible
+	}
+
+	switch err {
+	case huff0.ErrIncompressible:
+		if debugEncoder {
+			println("Adding RAW block, length", len(lits), "last:", b.last)
+		}
+		bh.setType(blockTypeRaw)
+		b.output = bh.appendTo(b.output)
+		b.output = append(b.output, lits...)
+		return nil
+	case huff0.ErrUseRLE:
+		if debugEncoder {
+			println("Adding RLE block, length", len(lits))
+		}
+		bh.setType(blockTypeRLE)
+		b.output = bh.appendTo(b.output)
+		b.output = append(b.output, lits[0])
+		return nil
+	case nil:
+	default:
+		return err
+	}
+	// Compressed...
+	// Now, allow reuse
+	b.litEnc.Reuse = huff0.ReusePolicyAllow
+	bh.setType(blockTypeCompressed)
+	var lh literalsHeader
+	if reUsed {
+		if debugEncoder {
+			println("Reused tree, compressed to", len(out))
+		}
+		lh.setType(literalsBlockTreeless)
+	} else {
+		if debugEncoder {
+			println("New tree, compressed to", len(out), "tree size:", len(b.litEnc.OutTable))
+		}
+		lh.setType(literalsBlockCompressed)
+	}
+	// Set sizes
+	lh.setSizes(len(out), len(lits), single)
+	bh.setSize(uint32(len(out) + lh.size() + 1))
+
+	// Write block headers.
+	b.output = bh.appendTo(b.output)
+	b.output = lh.appendTo(b.output)
+	// Add compressed data.
+	b.output = append(b.output, out...)
+	// No sequences.
+	b.output = append(b.output, 0)
+	return nil
+}
+
+// fuzzFseEncoder can be used to fuzz the FSE encoder.
+func fuzzFseEncoder(data []byte) int {
+	if len(data) > maxSequences || len(data) < 2 {
+		return 0
+	}
+	enc := fseEncoder{}
+	hist := enc.Histogram()
+	maxSym := uint8(0)
+	for i, v := range data {
+		v = v & 63
+		data[i] = v
+		hist[v]++
+		if v > maxSym {
+			maxSym = v
+		}
+	}
+	if maxSym == 0 {
+		// All 0
+		return 0
+	}
+	maxCount := func(a []uint32) int {
+		var max uint32
+		for _, v := range a {
+			if v > max {
+				max = v
+			}
+		}
+		return int(max)
+	}
+	cnt := maxCount(hist[:maxSym])
+	if cnt == len(data) {
+		// RLE
+		return 0
+	}
+	enc.HistogramFinished(maxSym, cnt)
+	err := enc.normalizeCount(len(data))
+	if err != nil {
+		return 0
+	}
+	_, err = enc.writeCount(nil)
+	if err != nil {
+		panic(err)
+	}
+	return 1
+}
+
+// encode will encode the block and append the output in b.output.
+// Previous offset codes must be pushed if more blocks are expected.
+func (b *blockEnc) encode(org []byte, raw, rawAllLits bool) error {
+	if len(b.sequences) == 0 {
+		return b.encodeLits(b.literals, rawAllLits)
+	}
+	// We want some difference to at least account for the headers.
+	saved := b.size - len(b.literals) - (b.size >> 5)
+	if saved < 16 {
+		if org == nil {
+			return errIncompressible
+		}
+		b.popOffsets()
+		return b.encodeLits(org, rawAllLits)
+	}
+
+	var bh blockHeader
+	var lh literalsHeader
+	bh.setLast(b.last)
+	bh.setType(blockTypeCompressed)
+	// Store offset of the block header. Needed when we know the size.
+	bhOffset := len(b.output)
+	b.output = bh.appendTo(b.output)
+
+	var (
+		out            []byte
+		reUsed, single bool
+		err            error
+	)
+	if b.dictLitEnc != nil {
+		b.litEnc.TransferCTable(b.dictLitEnc)
+		b.litEnc.Reuse = huff0.ReusePolicyAllow
+		b.dictLitEnc = nil
+	}
+	if len(b.literals) >= 1024 && !raw {
+		// Use 4 Streams.
+		out, reUsed, err = huff0.Compress4X(b.literals, b.litEnc)
+	} else if len(b.literals) > 32 && !raw {
+		// Use 1 stream
+		single = true
+		out, reUsed, err = huff0.Compress1X(b.literals, b.litEnc)
+	} else {
+		err = huff0.ErrIncompressible
+	}
+
+	switch err {
+	case huff0.ErrIncompressible:
+		lh.setType(literalsBlockRaw)
+		lh.setSize(len(b.literals))
+		b.output = lh.appendTo(b.output)
+		b.output = append(b.output, b.literals...)
+		if debugEncoder {
+			println("Adding literals RAW, length", len(b.literals))
+		}
+	case huff0.ErrUseRLE:
+		lh.setType(literalsBlockRLE)
+		lh.setSize(len(b.literals))
+		b.output = lh.appendTo(b.output)
+		b.output = append(b.output, b.literals[0])
+		if debugEncoder {
+			println("Adding literals RLE")
+		}
+	case nil:
+		// Compressed litLen...
+		if reUsed {
+			if debugEncoder {
+				println("reused tree")
+			}
+			lh.setType(literalsBlockTreeless)
+		} else {
+			if debugEncoder {
+				println("new tree, size:", len(b.litEnc.OutTable))
+			}
+			lh.setType(literalsBlockCompressed)
+			if debugEncoder {
+				_, _, err := huff0.ReadTable(out, nil)
+				if err != nil {
+					panic(err)
+				}
+			}
+		}
+		lh.setSizes(len(out), len(b.literals), single)
+		if debugEncoder {
+			printf("Compressed %d literals to %d bytes", len(b.literals), len(out))
+			println("Adding literal header:", lh)
+		}
+		b.output = lh.appendTo(b.output)
+		b.output = append(b.output, out...)
+		b.litEnc.Reuse = huff0.ReusePolicyAllow
+		if debugEncoder {
+			println("Adding literals compressed")
+		}
+	default:
+		if debugEncoder {
+			println("Adding literals ERROR:", err)
+		}
+		return err
+	}
+	// Sequence compression
+
+	// Write the number of sequences
+	switch {
+	case len(b.sequences) < 128:
+		b.output = append(b.output, uint8(len(b.sequences)))
+	case len(b.sequences) < 0x7f00: // TODO: this could be wrong
+		n := len(b.sequences)
+		b.output = append(b.output, 128+uint8(n>>8), uint8(n))
+	default:
+		n := len(b.sequences) - 0x7f00
+		b.output = append(b.output, 255, uint8(n), uint8(n>>8))
+	}
+	if debugEncoder {
+		println("Encoding", len(b.sequences), "sequences")
+	}
+	b.genCodes()
+	llEnc := b.coders.llEnc
+	ofEnc := b.coders.ofEnc
+	mlEnc := b.coders.mlEnc
+	err = llEnc.normalizeCount(len(b.sequences))
+	if err != nil {
+		return err
+	}
+	err = ofEnc.normalizeCount(len(b.sequences))
+	if err != nil {
+		return err
+	}
+	err = mlEnc.normalizeCount(len(b.sequences))
+	if err != nil {
+		return err
+	}
+
+	// Choose the best compression mode for each type.
+	// Will evaluate the new vs predefined and previous.
+	chooseComp := func(cur, prev, preDef *fseEncoder) (*fseEncoder, seqCompMode) {
+		// See if predefined/previous is better
+		hist := cur.count[:cur.symbolLen]
+		nSize := cur.approxSize(hist) + cur.maxHeaderSize()
+		predefSize := preDef.approxSize(hist)
+		prevSize := prev.approxSize(hist)
+
+		// Add a small penalty for new encoders.
+		// Don't bother with extremely small (<2 byte gains).
+		nSize = nSize + (nSize+2*8*16)>>4
+		switch {
+		case predefSize <= prevSize && predefSize <= nSize || forcePreDef:
+			if debugEncoder {
+				println("Using predefined", predefSize>>3, "<=", nSize>>3)
+			}
+			return preDef, compModePredefined
+		case prevSize <= nSize:
+			if debugEncoder {
+				println("Using previous", prevSize>>3, "<=", nSize>>3)
+			}
+			return prev, compModeRepeat
+		default:
+			if debugEncoder {
+				println("Using new, predef", predefSize>>3, ". previous:", prevSize>>3, ">", nSize>>3, "header max:", cur.maxHeaderSize()>>3, "bytes")
+				println("tl:", cur.actualTableLog, "symbolLen:", cur.symbolLen, "norm:", cur.norm[:cur.symbolLen], "hist", cur.count[:cur.symbolLen])
+			}
+			return cur, compModeFSE
+		}
+	}
+
+	// Write compression mode
+	var mode uint8
+	if llEnc.useRLE {
+		mode |= uint8(compModeRLE) << 6
+		llEnc.setRLE(b.sequences[0].llCode)
+		if debugEncoder {
+			println("llEnc.useRLE")
+		}
+	} else {
+		var m seqCompMode
+		llEnc, m = chooseComp(llEnc, b.coders.llPrev, &fsePredefEnc[tableLiteralLengths])
+		mode |= uint8(m) << 6
+	}
+	if ofEnc.useRLE {
+		mode |= uint8(compModeRLE) << 4
+		ofEnc.setRLE(b.sequences[0].ofCode)
+		if debugEncoder {
+			println("ofEnc.useRLE")
+		}
+	} else {
+		var m seqCompMode
+		ofEnc, m = chooseComp(ofEnc, b.coders.ofPrev, &fsePredefEnc[tableOffsets])
+		mode |= uint8(m) << 4
+	}
+
+	if mlEnc.useRLE {
+		mode |= uint8(compModeRLE) << 2
+		mlEnc.setRLE(b.sequences[0].mlCode)
+		if debugEncoder {
+			println("mlEnc.useRLE, code: ", b.sequences[0].mlCode, "value", b.sequences[0].matchLen)
+		}
+	} else {
+		var m seqCompMode
+		mlEnc, m = chooseComp(mlEnc, b.coders.mlPrev, &fsePredefEnc[tableMatchLengths])
+		mode |= uint8(m) << 2
+	}
+	b.output = append(b.output, mode)
+	if debugEncoder {
+		printf("Compression modes: 0b%b", mode)
+	}
+	b.output, err = llEnc.writeCount(b.output)
+	if err != nil {
+		return err
+	}
+	start := len(b.output)
+	b.output, err = ofEnc.writeCount(b.output)
+	if err != nil {
+		return err
+	}
+	if false {
+		println("block:", b.output[start:], "tablelog", ofEnc.actualTableLog, "maxcount:", ofEnc.maxCount)
+		fmt.Printf("selected TableLog: %d, Symbol length: %d\n", ofEnc.actualTableLog, ofEnc.symbolLen)
+		for i, v := range ofEnc.norm[:ofEnc.symbolLen] {
+			fmt.Printf("%3d: %5d -> %4d \n", i, ofEnc.count[i], v)
+		}
+	}
+	b.output, err = mlEnc.writeCount(b.output)
+	if err != nil {
+		return err
+	}
+
+	// Maybe in block?
+	wr := &b.wr
+	wr.reset(b.output)
+
+	var ll, of, ml cState
+
+	// Current sequence
+	seq := len(b.sequences) - 1
+	s := b.sequences[seq]
+	llEnc.setBits(llBitsTable[:])
+	mlEnc.setBits(mlBitsTable[:])
+	ofEnc.setBits(nil)
+
+	llTT, ofTT, mlTT := llEnc.ct.symbolTT[:256], ofEnc.ct.symbolTT[:256], mlEnc.ct.symbolTT[:256]
+
+	// We have 3 bounds checks here (and in the loop).
+	// Since we are iterating backwards it is kinda hard to avoid.
+	llB, ofB, mlB := llTT[s.llCode], ofTT[s.ofCode], mlTT[s.mlCode]
+	ll.init(wr, &llEnc.ct, llB)
+	of.init(wr, &ofEnc.ct, ofB)
+	wr.flush32()
+	ml.init(wr, &mlEnc.ct, mlB)
+
+	// Each of these lookups also generates a bounds check.
+	wr.addBits32NC(s.litLen, llB.outBits)
+	wr.addBits32NC(s.matchLen, mlB.outBits)
+	wr.flush32()
+	wr.addBits32NC(s.offset, ofB.outBits)
+	if debugSequences {
+		println("Encoded seq", seq, s, "codes:", s.llCode, s.mlCode, s.ofCode, "states:", ll.state, ml.state, of.state, "bits:", llB, mlB, ofB)
+	}
+	seq--
+	// Store sequences in reverse...
+	for seq >= 0 {
+		s = b.sequences[seq]
+
+		ofB := ofTT[s.ofCode]
+		wr.flush32() // tablelog max is below 8 for each, so it will fill max 24 bits.
+		//of.encode(ofB)
+		nbBitsOut := (uint32(of.state) + ofB.deltaNbBits) >> 16
+		dstState := int32(of.state>>(nbBitsOut&15)) + int32(ofB.deltaFindState)
+		wr.addBits16NC(of.state, uint8(nbBitsOut))
+		of.state = of.stateTable[dstState]
+
+		// Accumulate extra bits.
+		outBits := ofB.outBits & 31
+		extraBits := uint64(s.offset & bitMask32[outBits])
+		extraBitsN := outBits
+
+		mlB := mlTT[s.mlCode]
+		//ml.encode(mlB)
+		nbBitsOut = (uint32(ml.state) + mlB.deltaNbBits) >> 16
+		dstState = int32(ml.state>>(nbBitsOut&15)) + int32(mlB.deltaFindState)
+		wr.addBits16NC(ml.state, uint8(nbBitsOut))
+		ml.state = ml.stateTable[dstState]
+
+		outBits = mlB.outBits & 31
+		extraBits = extraBits<<outBits | uint64(s.matchLen&bitMask32[outBits])
+		extraBitsN += outBits
+
+		llB := llTT[s.llCode]
+		//ll.encode(llB)
+		nbBitsOut = (uint32(ll.state) + llB.deltaNbBits) >> 16
+		dstState = int32(ll.state>>(nbBitsOut&15)) + int32(llB.deltaFindState)
+		wr.addBits16NC(ll.state, uint8(nbBitsOut))
+		ll.state = ll.stateTable[dstState]
+
+		outBits = llB.outBits & 31
+		extraBits = extraBits<<outBits | uint64(s.litLen&bitMask32[outBits])
+		extraBitsN += outBits
+
+		wr.flush32()
+		wr.addBits64NC(extraBits, extraBitsN)
+
+		if debugSequences {
+			println("Encoded seq", seq, s)
+		}
+
+		seq--
+	}
+	ml.flush(mlEnc.actualTableLog)
+	of.flush(ofEnc.actualTableLog)
+	ll.flush(llEnc.actualTableLog)
+	err = wr.close()
+	if err != nil {
+		return err
+	}
+	b.output = wr.out
+
+	if len(b.output)-3-bhOffset >= b.size {
+		// Maybe even add a bigger margin.
+		b.litEnc.Reuse = huff0.ReusePolicyNone
+		return errIncompressible
+	}
+
+	// Size is output minus block header.
+	bh.setSize(uint32(len(b.output)-bhOffset) - 3)
+	if debugEncoder {
+		println("Rewriting block header", bh)
+	}
+	_ = bh.appendTo(b.output[bhOffset:bhOffset])
+	b.coders.setPrev(llEnc, mlEnc, ofEnc)
+	return nil
+}
+
+var errIncompressible = errors.New("incompressible")
+
+func (b *blockEnc) genCodes() {
+	if len(b.sequences) == 0 {
+		// nothing to do
+		return
+	}
+	if len(b.sequences) > math.MaxUint16 {
+		panic("can only encode up to 64K sequences")
+	}
+	// No bounds checks after here:
+	llH := b.coders.llEnc.Histogram()
+	ofH := b.coders.ofEnc.Histogram()
+	mlH := b.coders.mlEnc.Histogram()
+	for i := range llH {
+		llH[i] = 0
+	}
+	for i := range ofH {
+		ofH[i] = 0
+	}
+	for i := range mlH {
+		mlH[i] = 0
+	}
+
+	var llMax, ofMax, mlMax uint8
+	for i := range b.sequences {
+		seq := &b.sequences[i]
+		v := llCode(seq.litLen)
+		seq.llCode = v
+		llH[v]++
+		if v > llMax {
+			llMax = v
+		}
+
+		v = ofCode(seq.offset)
+		seq.ofCode = v
+		ofH[v]++
+		if v > ofMax {
+			ofMax = v
+		}
+
+		v = mlCode(seq.matchLen)
+		seq.mlCode = v
+		mlH[v]++
+		if v > mlMax {
+			mlMax = v
+			if debugAsserts && mlMax > maxMatchLengthSymbol {
+				panic(fmt.Errorf("mlMax > maxMatchLengthSymbol (%d), matchlen: %d", mlMax, seq.matchLen))
+			}
+		}
+	}
+	maxCount := func(a []uint32) int {
+		var max uint32
+		for _, v := range a {
+			if v > max {
+				max = v
+			}
+		}
+		return int(max)
+	}
+	if debugAsserts && mlMax > maxMatchLengthSymbol {
+		panic(fmt.Errorf("mlMax > maxMatchLengthSymbol (%d)", mlMax))
+	}
+	if debugAsserts && ofMax > maxOffsetBits {
+		panic(fmt.Errorf("ofMax > maxOffsetBits (%d)", ofMax))
+	}
+	if debugAsserts && llMax > maxLiteralLengthSymbol {
+		panic(fmt.Errorf("llMax > maxLiteralLengthSymbol (%d)", llMax))
+	}
+
+	b.coders.mlEnc.HistogramFinished(mlMax, maxCount(mlH[:mlMax+1]))
+	b.coders.ofEnc.HistogramFinished(ofMax, maxCount(ofH[:ofMax+1]))
+	b.coders.llEnc.HistogramFinished(llMax, maxCount(llH[:llMax+1]))
+}

vendor/github.com/klauspost/compress/zstd/blocktype_string.go

@@ -0,0 +1,85 @@
+// Code generated by "stringer -type=blockType,literalsBlockType,seqCompMode,tableIndex"; DO NOT EDIT.
+
+package zstd
+
+import "strconv"
+
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[blockTypeRaw-0]
+	_ = x[blockTypeRLE-1]
+	_ = x[blockTypeCompressed-2]
+	_ = x[blockTypeReserved-3]
+}
+
+const _blockType_name = "blockTypeRawblockTypeRLEblockTypeCompressedblockTypeReserved"
+
+var _blockType_index = [...]uint8{0, 12, 24, 43, 60}
+
+func (i blockType) String() string {
+	if i >= blockType(len(_blockType_index)-1) {
+		return "blockType(" + strconv.FormatInt(int64(i), 10) + ")"
+	}
+	return _blockType_name[_blockType_index[i]:_blockType_index[i+1]]
+}
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[literalsBlockRaw-0]
+	_ = x[literalsBlockRLE-1]
+	_ = x[literalsBlockCompressed-2]
+	_ = x[literalsBlockTreeless-3]
+}
+
+const _literalsBlockType_name = "literalsBlockRawliteralsBlockRLEliteralsBlockCompressedliteralsBlockTreeless"
+
+var _literalsBlockType_index = [...]uint8{0, 16, 32, 55, 76}
+
+func (i literalsBlockType) String() string {
+	if i >= literalsBlockType(len(_literalsBlockType_index)-1) {
+		return "literalsBlockType(" + strconv.FormatInt(int64(i), 10) + ")"
+	}
+	return _literalsBlockType_name[_literalsBlockType_index[i]:_literalsBlockType_index[i+1]]
+}
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[compModePredefined-0]
+	_ = x[compModeRLE-1]
+	_ = x[compModeFSE-2]
+	_ = x[compModeRepeat-3]
+}
+
+const _seqCompMode_name = "compModePredefinedcompModeRLEcompModeFSEcompModeRepeat"
+
+var _seqCompMode_index = [...]uint8{0, 18, 29, 40, 54}
+
+func (i seqCompMode) String() string {
+	if i >= seqCompMode(len(_seqCompMode_index)-1) {
+		return "seqCompMode(" + strconv.FormatInt(int64(i), 10) + ")"
+	}
+	return _seqCompMode_name[_seqCompMode_index[i]:_seqCompMode_index[i+1]]
+}
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[tableLiteralLengths-0]
+	_ = x[tableOffsets-1]
+	_ = x[tableMatchLengths-2]
+}
+
+const _tableIndex_name = "tableLiteralLengthstableOffsetstableMatchLengths"
+
+var _tableIndex_index = [...]uint8{0, 19, 31, 48}
+
+func (i tableIndex) String() string {
+	if i >= tableIndex(len(_tableIndex_index)-1) {
+		return "tableIndex(" + strconv.FormatInt(int64(i), 10) + ")"
+	}
+	return _tableIndex_name[_tableIndex_index[i]:_tableIndex_index[i+1]]
+}

vendor/github.com/klauspost/compress/zstd/bytebuf.go

@@ -0,0 +1,130 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+)
+
+type byteBuffer interface {
+	// Read up to 8 bytes.
+	// Returns io.ErrUnexpectedEOF if this cannot be satisfied.
+	readSmall(n int) ([]byte, error)
+
+	// Read >8 bytes.
+	// MAY use the destination slice.
+	readBig(n int, dst []byte) ([]byte, error)
+
+	// Read a single byte.
+	readByte() (byte, error)
+
+	// Skip n bytes.
+	skipN(n int) error
+}
+
+// in-memory buffer
+type byteBuf []byte
+
+func (b *byteBuf) readSmall(n int) ([]byte, error) {
+	if debugAsserts && n > 8 {
+		panic(fmt.Errorf("small read > 8 (%d). use readBig", n))
+	}
+	bb := *b
+	if len(bb) < n {
+		return nil, io.ErrUnexpectedEOF
+	}
+	r := bb[:n]
+	*b = bb[n:]
+	return r, nil
+}
+
+func (b *byteBuf) readBig(n int, dst []byte) ([]byte, error) {
+	bb := *b
+	if len(bb) < n {
+		return nil, io.ErrUnexpectedEOF
+	}
+	r := bb[:n]
+	*b = bb[n:]
+	return r, nil
+}
+
+func (b *byteBuf) remain() []byte {
+	return *b
+}
+
+func (b *byteBuf) readByte() (byte, error) {
+	bb := *b
+	if len(bb) < 1 {
+		return 0, nil
+	}
+	r := bb[0]
+	*b = bb[1:]
+	return r, nil
+}
+
+func (b *byteBuf) skipN(n int) error {
+	bb := *b
+	if len(bb) < n {
+		return io.ErrUnexpectedEOF
+	}
+	*b = bb[n:]
+	return nil
+}
+
+// wrapper around a reader.
+type readerWrapper struct {
+	r   io.Reader
+	tmp [8]byte
+}
+
+func (r *readerWrapper) readSmall(n int) ([]byte, error) {
+	if debugAsserts && n > 8 {
+		panic(fmt.Errorf("small read > 8 (%d). use readBig", n))
+	}
+	n2, err := io.ReadFull(r.r, r.tmp[:n])
+	// We only really care about the actual bytes read.
+	if err != nil {
+		if err == io.EOF {
+			return nil, io.ErrUnexpectedEOF
+		}
+		if debugDecoder {
+			println("readSmall: got", n2, "want", n, "err", err)
+		}
+		return nil, err
+	}
+	return r.tmp[:n], nil
+}
+
+func (r *readerWrapper) readBig(n int, dst []byte) ([]byte, error) {
+	if cap(dst) < n {
+		dst = make([]byte, n)
+	}
+	n2, err := io.ReadFull(r.r, dst[:n])
+	if err == io.EOF && n > 0 {
+		err = io.ErrUnexpectedEOF
+	}
+	return dst[:n2], err
+}
+
+func (r *readerWrapper) readByte() (byte, error) {
+	n2, err := r.r.Read(r.tmp[:1])
+	if err != nil {
+		return 0, err
+	}
+	if n2 != 1 {
+		return 0, io.ErrUnexpectedEOF
+	}
+	return r.tmp[0], nil
+}
+
+func (r *readerWrapper) skipN(n int) error {
+	n2, err := io.CopyN(ioutil.Discard, r.r, int64(n))
+	if n2 != int64(n) {
+		err = io.ErrUnexpectedEOF
+	}
+	return err
+}

vendor/github.com/klauspost/compress/zstd/bytereader.go

@@ -0,0 +1,88 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+// byteReader provides a byte reader that reads
+// little endian values from a byte stream.
+// The input stream is manually advanced.
+// The reader performs no bounds checks.
+type byteReader struct {
+	b   []byte
+	off int
+}
+
+// init will initialize the reader and set the input.
+func (b *byteReader) init(in []byte) {
+	b.b = in
+	b.off = 0
+}
+
+// advance the stream b n bytes.
+func (b *byteReader) advance(n uint) {
+	b.off += int(n)
+}
+
+// overread returns whether we have advanced too far.
+func (b *byteReader) overread() bool {
+	return b.off > len(b.b)
+}
+
+// Int32 returns a little endian int32 starting at current offset.
+func (b byteReader) Int32() int32 {
+	b2 := b.b[b.off:]
+	b2 = b2[:4]
+	v3 := int32(b2[3])
+	v2 := int32(b2[2])
+	v1 := int32(b2[1])
+	v0 := int32(b2[0])
+	return v0 | (v1 << 8) | (v2 << 16) | (v3 << 24)
+}
+
+// Uint8 returns the next byte
+func (b *byteReader) Uint8() uint8 {
+	v := b.b[b.off]
+	return v
+}
+
+// Uint32 returns a little endian uint32 starting at current offset.
+func (b byteReader) Uint32() uint32 {
+	if r := b.remain(); r < 4 {
+		// Very rare
+		v := uint32(0)
+		for i := 1; i <= r; i++ {
+			v = (v << 8) | uint32(b.b[len(b.b)-i])
+		}
+		return v
+	}
+	b2 := b.b[b.off:]
+	b2 = b2[:4]
+	v3 := uint32(b2[3])
+	v2 := uint32(b2[2])
+	v1 := uint32(b2[1])
+	v0 := uint32(b2[0])
+	return v0 | (v1 << 8) | (v2 << 16) | (v3 << 24)
+}
+
+// Uint32NC returns a little endian uint32 starting at current offset.
+// The caller must be sure if there are at least 4 bytes left.
+func (b byteReader) Uint32NC() uint32 {
+	b2 := b.b[b.off:]
+	b2 = b2[:4]
+	v3 := uint32(b2[3])
+	v2 := uint32(b2[2])
+	v1 := uint32(b2[1])
+	v0 := uint32(b2[0])
+	return v0 | (v1 << 8) | (v2 << 16) | (v3 << 24)
+}
+
+// unread returns the unread portion of the input.
+func (b byteReader) unread() []byte {
+	return b.b[b.off:]
+}
+
+// remain will return the number of bytes remaining.
+func (b byteReader) remain() int {
+	return len(b.b) - b.off
+}

vendor/github.com/klauspost/compress/zstd/decodeheader.go

@@ -0,0 +1,202 @@
+// Copyright 2020+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+
+package zstd
+
+import (
+	"bytes"
+	"errors"
+	"io"
+)
+
+// HeaderMaxSize is the maximum size of a Frame and Block Header.
+// If less is sent to Header.Decode it *may* still contain enough information.
+const HeaderMaxSize = 14 + 3
+
+// Header contains information about the first frame and block within that.
+type Header struct {
+	// Window Size the window of data to keep while decoding.
+	// Will only be set if HasFCS is false.
+	WindowSize uint64
+
+	// Frame content size.
+	// Expected size of the entire frame.
+	FrameContentSize uint64
+
+	// Dictionary ID.
+	// If 0, no dictionary.
+	DictionaryID uint32
+
+	// First block information.
+	FirstBlock struct {
+		// OK will be set if first block could be decoded.
+		OK bool
+
+		// Is this the last block of a frame?
+		Last bool
+
+		// Is the data compressed?
+		// If true CompressedSize will be populated.
+		// Unfortunately DecompressedSize cannot be determined
+		// without decoding the blocks.
+		Compressed bool
+
+		// DecompressedSize is the expected decompressed size of the block.
+		// Will be 0 if it cannot be determined.
+		DecompressedSize int
+
+		// CompressedSize of the data in the block.
+		// Does not include the block header.
+		// Will be equal to DecompressedSize if not Compressed.
+		CompressedSize int
+	}
+
+	// Skippable will be true if the frame is meant to be skipped.
+	// No other information will be populated.
+	Skippable bool
+
+	// If set there is a checksum present for the block content.
+	HasCheckSum bool
+
+	// If this is true FrameContentSize will have a valid value
+	HasFCS bool
+
+	SingleSegment bool
+}
+
+// Decode the header from the beginning of the stream.
+// This will decode the frame header and the first block header if enough bytes are provided.
+// It is recommended to provide at least HeaderMaxSize bytes.
+// If the frame header cannot be read an error will be returned.
+// If there isn't enough input, io.ErrUnexpectedEOF is returned.
+// The FirstBlock.OK will indicate if enough information was available to decode the first block header.
+func (h *Header) Decode(in []byte) error {
+	if len(in) < 4 {
+		return io.ErrUnexpectedEOF
+	}
+	b, in := in[:4], in[4:]
+	if !bytes.Equal(b, frameMagic) {
+		if !bytes.Equal(b[1:4], skippableFrameMagic) || b[0]&0xf0 != 0x50 {
+			return ErrMagicMismatch
+		}
+		*h = Header{Skippable: true}
+		return nil
+	}
+	if len(in) < 1 {
+		return io.ErrUnexpectedEOF
+	}
+
+	// Clear output
+	*h = Header{}
+	fhd, in := in[0], in[1:]
+	h.SingleSegment = fhd&(1<<5) != 0
+	h.HasCheckSum = fhd&(1<<2) != 0
+
+	if fhd&(1<<3) != 0 {
+		return errors.New("reserved bit set on frame header")
+	}
+
+	// Read Window_Descriptor
+	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#window_descriptor
+	if !h.SingleSegment {
+		if len(in) < 1 {
+			return io.ErrUnexpectedEOF
+		}
+		var wd byte
+		wd, in = in[0], in[1:]
+		windowLog := 10 + (wd >> 3)
+		windowBase := uint64(1) << windowLog
+		windowAdd := (windowBase / 8) * uint64(wd&0x7)
+		h.WindowSize = windowBase + windowAdd
+	}
+
+	// Read Dictionary_ID
+	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#dictionary_id
+	if size := fhd & 3; size != 0 {
+		if size == 3 {
+			size = 4
+		}
+		if len(in) < int(size) {
+			return io.ErrUnexpectedEOF
+		}
+		b, in = in[:size], in[size:]
+		if b == nil {
+			return io.ErrUnexpectedEOF
+		}
+		switch size {
+		case 1:
+			h.DictionaryID = uint32(b[0])
+		case 2:
+			h.DictionaryID = uint32(b[0]) | (uint32(b[1]) << 8)
+		case 4:
+			h.DictionaryID = uint32(b[0]) | (uint32(b[1]) << 8) | (uint32(b[2]) << 16) | (uint32(b[3]) << 24)
+		}
+	}
+
+	// Read Frame_Content_Size
+	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#frame_content_size
+	var fcsSize int
+	v := fhd >> 6
+	switch v {
+	case 0:
+		if h.SingleSegment {
+			fcsSize = 1
+		}
+	default:
+		fcsSize = 1 << v
+	}
+
+	if fcsSize > 0 {
+		h.HasFCS = true
+		if len(in) < fcsSize {
+			return io.ErrUnexpectedEOF
+		}
+		b, in = in[:fcsSize], in[fcsSize:]
+		if b == nil {
+			return io.ErrUnexpectedEOF
+		}
+		switch fcsSize {
+		case 1:
+			h.FrameContentSize = uint64(b[0])
+		case 2:
+			// When FCS_Field_Size is 2, the offset of 256 is added.
+			h.FrameContentSize = uint64(b[0]) | (uint64(b[1]) << 8) + 256
+		case 4:
+			h.FrameContentSize = uint64(b[0]) | (uint64(b[1]) << 8) | (uint64(b[2]) << 16) | (uint64(b[3]) << 24)
+		case 8:
+			d1 := uint32(b[0]) | (uint32(b[1]) << 8) | (uint32(b[2]) << 16) | (uint32(b[3]) << 24)
+			d2 := uint32(b[4]) | (uint32(b[5]) << 8) | (uint32(b[6]) << 16) | (uint32(b[7]) << 24)
+			h.FrameContentSize = uint64(d1) | (uint64(d2) << 32)
+		}
+	}
+
+	// Frame Header done, we will not fail from now on.
+	if len(in) < 3 {
+		return nil
+	}
+	tmp := in[:3]
+	bh := uint32(tmp[0]) | (uint32(tmp[1]) << 8) | (uint32(tmp[2]) << 16)
+	h.FirstBlock.Last = bh&1 != 0
+	blockType := blockType((bh >> 1) & 3)
+	// find size.
+	cSize := int(bh >> 3)
+	switch blockType {
+	case blockTypeReserved:
+		return nil
+	case blockTypeRLE:
+		h.FirstBlock.Compressed = true
+		h.FirstBlock.DecompressedSize = cSize
+		h.FirstBlock.CompressedSize = 1
+	case blockTypeCompressed:
+		h.FirstBlock.Compressed = true
+		h.FirstBlock.CompressedSize = cSize
+	case blockTypeRaw:
+		h.FirstBlock.DecompressedSize = cSize
+		h.FirstBlock.CompressedSize = cSize
+	default:
+		panic("Invalid block type")
+	}
+
+	h.FirstBlock.OK = true
+	return nil
+}

vendor/github.com/klauspost/compress/zstd/decoder.go

@@ -0,0 +1,555 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+import (
+	"errors"
+	"io"
+	"sync"
+)
+
+// Decoder provides decoding of zstandard streams.
+// The decoder has been designed to operate without allocations after a warmup.
+// This means that you should store the decoder for best performance.
+// To re-use a stream decoder, use the Reset(r io.Reader) error to switch to another stream.
+// A decoder can safely be re-used even if the previous stream failed.
+// To release the resources, you must call the Close() function on a decoder.
+type Decoder struct {
+	o decoderOptions
+
+	// Unreferenced decoders, ready for use.
+	decoders chan *blockDec
+
+	// Streams ready to be decoded.
+	stream chan decodeStream
+
+	// Current read position used for Reader functionality.
+	current decoderState
+
+	// Custom dictionaries.
+	// Always uses copies.
+	dicts map[uint32]dict
+
+	// streamWg is the waitgroup for all streams
+	streamWg sync.WaitGroup
+}
+
+// decoderState is used for maintaining state when the decoder
+// is used for streaming.
+type decoderState struct {
+	// current block being written to stream.
+	decodeOutput
+
+	// output in order to be written to stream.
+	output chan decodeOutput
+
+	// cancel remaining output.
+	cancel chan struct{}
+
+	flushed bool
+}
+
+var (
+	// Check the interfaces we want to support.
+	_ = io.WriterTo(&Decoder{})
+	_ = io.Reader(&Decoder{})
+)
+
+// NewReader creates a new decoder.
+// A nil Reader can be provided in which case Reset can be used to start a decode.
+//
+// A Decoder can be used in two modes:
+//
+// 1) As a stream, or
+// 2) For stateless decoding using DecodeAll.
+//
+// Only a single stream can be decoded concurrently, but the same decoder
+// can run multiple concurrent stateless decodes. It is even possible to
+// use stateless decodes while a stream is being decoded.
+//
+// The Reset function can be used to initiate a new stream, which is will considerably
+// reduce the allocations normally caused by NewReader.
+func NewReader(r io.Reader, opts ...DOption) (*Decoder, error) {
+	initPredefined()
+	var d Decoder
+	d.o.setDefault()
+	for _, o := range opts {
+		err := o(&d.o)
+		if err != nil {
+			return nil, err
+		}
+	}
+	d.current.output = make(chan decodeOutput, d.o.concurrent)
+	d.current.flushed = true
+
+	if r == nil {
+		d.current.err = ErrDecoderNilInput
+	}
+
+	// Transfer option dicts.
+	d.dicts = make(map[uint32]dict, len(d.o.dicts))
+	for _, dc := range d.o.dicts {
+		d.dicts[dc.id] = dc
+	}
+	d.o.dicts = nil
+
+	// Create decoders
+	d.decoders = make(chan *blockDec, d.o.concurrent)
+	for i := 0; i < d.o.concurrent; i++ {
+		dec := newBlockDec(d.o.lowMem)
+		dec.localFrame = newFrameDec(d.o)
+		d.decoders <- dec
+	}
+
+	if r == nil {
+		return &d, nil
+	}
+	return &d, d.Reset(r)
+}
+
+// Read bytes from the decompressed stream into p.
+// Returns the number of bytes written and any error that occurred.
+// When the stream is done, io.EOF will be returned.
+func (d *Decoder) Read(p []byte) (int, error) {
+	var n int
+	for {
+		if len(d.current.b) > 0 {
+			filled := copy(p, d.current.b)
+			p = p[filled:]
+			d.current.b = d.current.b[filled:]
+			n += filled
+		}
+		if len(p) == 0 {
+			break
+		}
+		if len(d.current.b) == 0 {
+			// We have an error and no more data
+			if d.current.err != nil {
+				break
+			}
+			if !d.nextBlock(n == 0) {
+				return n, nil
+			}
+		}
+	}
+	if len(d.current.b) > 0 {
+		if debugDecoder {
+			println("returning", n, "still bytes left:", len(d.current.b))
+		}
+		// Only return error at end of block
+		return n, nil
+	}
+	if d.current.err != nil {
+		d.drainOutput()
+	}
+	if debugDecoder {
+		println("returning", n, d.current.err, len(d.decoders))
+	}
+	return n, d.current.err
+}
+
+// Reset will reset the decoder the supplied stream after the current has finished processing.
+// Note that this functionality cannot be used after Close has been called.
+// Reset can be called with a nil reader to release references to the previous reader.
+// After being called with a nil reader, no other operations than Reset or DecodeAll or Close
+// should be used.
+func (d *Decoder) Reset(r io.Reader) error {
+	if d.current.err == ErrDecoderClosed {
+		return d.current.err
+	}
+
+	d.drainOutput()
+
+	if r == nil {
+		d.current.err = ErrDecoderNilInput
+		if len(d.current.b) > 0 {
+			d.current.b = d.current.b[:0]
+		}
+		d.current.flushed = true
+		return nil
+	}
+
+	// If bytes buffer and < 5MB, do sync decoding anyway.
+	if bb, ok := r.(byter); ok && bb.Len() < 5<<20 {
+		bb2 := bb
+		if debugDecoder {
+			println("*bytes.Buffer detected, doing sync decode, len:", bb.Len())
+		}
+		b := bb2.Bytes()
+		var dst []byte
+		if cap(d.current.b) > 0 {
+			dst = d.current.b
+		}
+
+		dst, err := d.DecodeAll(b, dst[:0])
+		if err == nil {
+			err = io.EOF
+		}
+		d.current.b = dst
+		d.current.err = err
+		d.current.flushed = true
+		if debugDecoder {
+			println("sync decode to", len(dst), "bytes, err:", err)
+		}
+		return nil
+	}
+
+	if d.stream == nil {
+		d.stream = make(chan decodeStream, 1)
+		d.streamWg.Add(1)
+		go d.startStreamDecoder(d.stream)
+	}
+
+	// Remove current block.
+	d.current.decodeOutput = decodeOutput{}
+	d.current.err = nil
+	d.current.cancel = make(chan struct{})
+	d.current.flushed = false
+	d.current.d = nil
+
+	d.stream <- decodeStream{
+		r:      r,
+		output: d.current.output,
+		cancel: d.current.cancel,
+	}
+	return nil
+}
+
+// drainOutput will drain the output until errEndOfStream is sent.
+func (d *Decoder) drainOutput() {
+	if d.current.cancel != nil {
+		println("cancelling current")
+		close(d.current.cancel)
+		d.current.cancel = nil
+	}
+	if d.current.d != nil {
+		if debugDecoder {
+			printf("re-adding current decoder %p, decoders: %d", d.current.d, len(d.decoders))
+		}
+		d.decoders <- d.current.d
+		d.current.d = nil
+		d.current.b = nil
+	}
+	if d.current.output == nil || d.current.flushed {
+		println("current already flushed")
+		return
+	}
+	for v := range d.current.output {
+		if v.d != nil {
+			if debugDecoder {
+				printf("re-adding decoder %p", v.d)
+			}
+			d.decoders <- v.d
+		}
+		if v.err == errEndOfStream {
+			println("current flushed")
+			d.current.flushed = true
+			return
+		}
+	}
+}
+
+// WriteTo writes data to w until there's no more data to write or when an error occurs.
+// The return value n is the number of bytes written.
+// Any error encountered during the write is also returned.
+func (d *Decoder) WriteTo(w io.Writer) (int64, error) {
+	var n int64
+	for {
+		if len(d.current.b) > 0 {
+			n2, err2 := w.Write(d.current.b)
+			n += int64(n2)
+			if err2 != nil && (d.current.err == nil || d.current.err == io.EOF) {
+				d.current.err = err2
+			} else if n2 != len(d.current.b) {
+				d.current.err = io.ErrShortWrite
+			}
+		}
+		if d.current.err != nil {
+			break
+		}
+		d.nextBlock(true)
+	}
+	err := d.current.err
+	if err != nil {
+		d.drainOutput()
+	}
+	if err == io.EOF {
+		err = nil
+	}
+	return n, err
+}
+
+// DecodeAll allows stateless decoding of a blob of bytes.
+// Output will be appended to dst, so if the destination size is known
+// you can pre-allocate the destination slice to avoid allocations.
+// DecodeAll can be used concurrently.
+// The Decoder concurrency limits will be respected.
+func (d *Decoder) DecodeAll(input, dst []byte) ([]byte, error) {
+	if d.current.err == ErrDecoderClosed {
+		return dst, ErrDecoderClosed
+	}
+
+	// Grab a block decoder and frame decoder.
+	block := <-d.decoders
+	frame := block.localFrame
+	defer func() {
+		if debugDecoder {
+			printf("re-adding decoder: %p", block)
+		}
+		frame.rawInput = nil
+		frame.bBuf = nil
+		d.decoders <- block
+	}()
+	frame.bBuf = input
+
+	for {
+		frame.history.reset()
+		err := frame.reset(&frame.bBuf)
+		if err == io.EOF {
+			if debugDecoder {
+				println("frame reset return EOF")
+			}
+			return dst, nil
+		}
+		if frame.DictionaryID != nil {
+			dict, ok := d.dicts[*frame.DictionaryID]
+			if !ok {
+				return nil, ErrUnknownDictionary
+			}
+			frame.history.setDict(&dict)
+		}
+		if err != nil {
+			return dst, err
+		}
+		if frame.FrameContentSize > d.o.maxDecodedSize-uint64(len(dst)) {
+			return dst, ErrDecoderSizeExceeded
+		}
+		if frame.FrameContentSize > 0 && frame.FrameContentSize < 1<<30 {
+			// Never preallocate moe than 1 GB up front.
+			if cap(dst)-len(dst) < int(frame.FrameContentSize) {
+				dst2 := make([]byte, len(dst), len(dst)+int(frame.FrameContentSize))
+				copy(dst2, dst)
+				dst = dst2
+			}
+		}
+		if cap(dst) == 0 {
+			// Allocate len(input) * 2 by default if nothing is provided
+			// and we didn't get frame content size.
+			size := len(input) * 2
+			// Cap to 1 MB.
+			if size > 1<<20 {
+				size = 1 << 20
+			}
+			if uint64(size) > d.o.maxDecodedSize {
+				size = int(d.o.maxDecodedSize)
+			}
+			dst = make([]byte, 0, size)
+		}
+
+		dst, err = frame.runDecoder(dst, block)
+		if err != nil {
+			return dst, err
+		}
+		if len(frame.bBuf) == 0 {
+			if debugDecoder {
+				println("frame dbuf empty")
+			}
+			break
+		}
+	}
+	return dst, nil
+}
+
+// nextBlock returns the next block.
+// If an error occurs d.err will be set.
+// Optionally the function can block for new output.
+// If non-blocking mode is used the returned boolean will be false
+// if no data was available without blocking.
+func (d *Decoder) nextBlock(blocking bool) (ok bool) {
+	if d.current.d != nil {
+		if debugDecoder {
+			printf("re-adding current decoder %p", d.current.d)
+		}
+		d.decoders <- d.current.d
+		d.current.d = nil
+	}
+	if d.current.err != nil {
+		// Keep error state.
+		return blocking
+	}
+
+	if blocking {
+		d.current.decodeOutput = <-d.current.output
+	} else {
+		select {
+		case d.current.decodeOutput = <-d.current.output:
+		default:
+			return false
+		}
+	}
+	if debugDecoder {
+		println("got", len(d.current.b), "bytes, error:", d.current.err)
+	}
+	return true
+}
+
+// Close will release all resources.
+// It is NOT possible to reuse the decoder after this.
+func (d *Decoder) Close() {
+	if d.current.err == ErrDecoderClosed {
+		return
+	}
+	d.drainOutput()
+	if d.stream != nil {
+		close(d.stream)
+		d.streamWg.Wait()
+		d.stream = nil
+	}
+	if d.decoders != nil {
+		close(d.decoders)
+		for dec := range d.decoders {
+			dec.Close()
+		}
+		d.decoders = nil
+	}
+	if d.current.d != nil {
+		d.current.d.Close()
+		d.current.d = nil
+	}
+	d.current.err = ErrDecoderClosed
+}
+
+// IOReadCloser returns the decoder as an io.ReadCloser for convenience.
+// Any changes to the decoder will be reflected, so the returned ReadCloser
+// can be reused along with the decoder.
+// io.WriterTo is also supported by the returned ReadCloser.
+func (d *Decoder) IOReadCloser() io.ReadCloser {
+	return closeWrapper{d: d}
+}
+
+// closeWrapper wraps a function call as a closer.
+type closeWrapper struct {
+	d *Decoder
+}
+
+// WriteTo forwards WriteTo calls to the decoder.
+func (c closeWrapper) WriteTo(w io.Writer) (n int64, err error) {
+	return c.d.WriteTo(w)
+}
+
+// Read forwards read calls to the decoder.
+func (c closeWrapper) Read(p []byte) (n int, err error) {
+	return c.d.Read(p)
+}
+
+// Close closes the decoder.
+func (c closeWrapper) Close() error {
+	c.d.Close()
+	return nil
+}
+
+type decodeOutput struct {
+	d   *blockDec
+	b   []byte
+	err error
+}
+
+type decodeStream struct {
+	r io.Reader
+
+	// Blocks ready to be written to output.
+	output chan decodeOutput
+
+	// cancel reading from the input
+	cancel chan struct{}
+}
+
+// errEndOfStream indicates that everything from the stream was read.
+var errEndOfStream = errors.New("end-of-stream")
+
+// Create Decoder:
+// Spawn n block decoders. These accept tasks to decode a block.
+// Create goroutine that handles stream processing, this will send history to decoders as they are available.
+// Decoders update the history as they decode.
+// When a block is returned:
+// 		a) history is sent to the next decoder,
+// 		b) content written to CRC.
+// 		c) return data to WRITER.
+// 		d) wait for next block to return data.
+// Once WRITTEN, the decoders reused by the writer frame decoder for re-use.
+func (d *Decoder) startStreamDecoder(inStream chan decodeStream) {
+	defer d.streamWg.Done()
+	frame := newFrameDec(d.o)
+	for stream := range inStream {
+		if debugDecoder {
+			println("got new stream")
+		}
+		br := readerWrapper{r: stream.r}
+	decodeStream:
+		for {
+			frame.history.reset()
+			err := frame.reset(&br)
+			if debugDecoder && err != nil {
+				println("Frame decoder returned", err)
+			}
+			if err == nil && frame.DictionaryID != nil {
+				dict, ok := d.dicts[*frame.DictionaryID]
+				if !ok {
+					err = ErrUnknownDictionary
+				} else {
+					frame.history.setDict(&dict)
+				}
+			}
+			if err != nil {
+				stream.output <- decodeOutput{
+					err: err,
+				}
+				break
+			}
+			if debugDecoder {
+				println("starting frame decoder")
+			}
+
+			// This goroutine will forward history between frames.
+			frame.frameDone.Add(1)
+			frame.initAsync()
+
+			go frame.startDecoder(stream.output)
+		decodeFrame:
+			// Go through all blocks of the frame.
+			for {
+				dec := <-d.decoders
+				select {
+				case <-stream.cancel:
+					if !frame.sendErr(dec, io.EOF) {
+						// To not let the decoder dangle, send it back.
+						stream.output <- decodeOutput{d: dec}
+					}
+					break decodeStream
+				default:
+				}
+				err := frame.next(dec)
+				switch err {
+				case io.EOF:
+					// End of current frame, no error
+					println("EOF on next block")
+					break decodeFrame
+				case nil:
+					continue
+				default:
+					println("block decoder returned", err)
+					break decodeStream
+				}
+			}
+			// All blocks have started decoding, check if there are more frames.
+			println("waiting for done")
+			frame.frameDone.Wait()
+			println("done waiting...")
+		}
+		frame.frameDone.Wait()
+		println("Sending EOS")
+		stream.output <- decodeOutput{err: errEndOfStream}
+	}
+}

vendor/github.com/klauspost/compress/zstd/decoder_options.go

@@ -0,0 +1,102 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+import (
+	"errors"
+	"runtime"
+)
+
+// DOption is an option for creating a decoder.
+type DOption func(*decoderOptions) error
+
+// options retains accumulated state of multiple options.
+type decoderOptions struct {
+	lowMem         bool
+	concurrent     int
+	maxDecodedSize uint64
+	maxWindowSize  uint64
+	dicts          []dict
+}
+
+func (o *decoderOptions) setDefault() {
+	*o = decoderOptions{
+		// use less ram: true for now, but may change.
+		lowMem:        true,
+		concurrent:    runtime.GOMAXPROCS(0),
+		maxWindowSize: MaxWindowSize,
+	}
+	o.maxDecodedSize = 1 << 63
+}
+
+// WithDecoderLowmem will set whether to use a lower amount of memory,
+// but possibly have to allocate more while running.
+func WithDecoderLowmem(b bool) DOption {
+	return func(o *decoderOptions) error { o.lowMem = b; return nil }
+}
+
+// WithDecoderConcurrency will set the concurrency,
+// meaning the maximum number of decoders to run concurrently.
+// The value supplied must be at least 1.
+// By default this will be set to GOMAXPROCS.
+func WithDecoderConcurrency(n int) DOption {
+	return func(o *decoderOptions) error {
+		if n <= 0 {
+			return errors.New("concurrency must be at least 1")
+		}
+		o.concurrent = n
+		return nil
+	}
+}
+
+// WithDecoderMaxMemory allows to set a maximum decoded size for in-memory
+// non-streaming operations or maximum window size for streaming operations.
+// This can be used to control memory usage of potentially hostile content.
+// Maximum and default is 1 << 63 bytes.
+func WithDecoderMaxMemory(n uint64) DOption {
+	return func(o *decoderOptions) error {
+		if n == 0 {
+			return errors.New("WithDecoderMaxMemory must be at least 1")
+		}
+		if n > 1<<63 {
+			return errors.New("WithDecoderMaxmemory must be less than 1 << 63")
+		}
+		o.maxDecodedSize = n
+		return nil
+	}
+}
+
+// WithDecoderDicts allows to register one or more dictionaries for the decoder.
+// If several dictionaries with the same ID is provided the last one will be used.
+func WithDecoderDicts(dicts ...[]byte) DOption {
+	return func(o *decoderOptions) error {
+		for _, b := range dicts {
+			d, err := loadDict(b)
+			if err != nil {
+				return err
+			}
+			o.dicts = append(o.dicts, *d)
+		}
+		return nil
+	}
+}
+
+// WithDecoderMaxWindow allows to set a maximum window size for decodes.
+// This allows rejecting packets that will cause big memory usage.
+// The Decoder will likely allocate more memory based on the WithDecoderLowmem setting.
+// If WithDecoderMaxMemory is set to a lower value, that will be used.
+// Default is 512MB, Maximum is ~3.75 TB as per zstandard spec.
+func WithDecoderMaxWindow(size uint64) DOption {
+	return func(o *decoderOptions) error {
+		if size < MinWindowSize {
+			return errors.New("WithMaxWindowSize must be at least 1KB, 1024 bytes")
+		}
+		if size > (1<<41)+7*(1<<38) {
+			return errors.New("WithMaxWindowSize must be less than (1<<41) + 7*(1<<38) ~ 3.75TB")
+		}
+		o.maxWindowSize = size
+		return nil
+	}
+}

vendor/github.com/klauspost/compress/zstd/dict.go

@@ -0,0 +1,122 @@
+package zstd
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+
+	"github.com/klauspost/compress/huff0"
+)
+
+type dict struct {
+	id uint32
+
+	litEnc              *huff0.Scratch
+	llDec, ofDec, mlDec sequenceDec
+	//llEnc, ofEnc, mlEnc []*fseEncoder
+	offsets [3]int
+	content []byte
+}
+
+var dictMagic = [4]byte{0x37, 0xa4, 0x30, 0xec}
+
+// ID returns the dictionary id or 0 if d is nil.
+func (d *dict) ID() uint32 {
+	if d == nil {
+		return 0
+	}
+	return d.id
+}
+
+// DictContentSize returns the dictionary content size or 0 if d is nil.
+func (d *dict) DictContentSize() int {
+	if d == nil {
+		return 0
+	}
+	return len(d.content)
+}
+
+// Load a dictionary as described in
+// https://github.com/facebook/zstd/blob/master/doc/zstd_compression_format.md#dictionary-format
+func loadDict(b []byte) (*dict, error) {
+	// Check static field size.
+	if len(b) <= 8+(3*4) {
+		return nil, io.ErrUnexpectedEOF
+	}
+	d := dict{
+		llDec: sequenceDec{fse: &fseDecoder{}},
+		ofDec: sequenceDec{fse: &fseDecoder{}},
+		mlDec: sequenceDec{fse: &fseDecoder{}},
+	}
+	if !bytes.Equal(b[:4], dictMagic[:]) {
+		return nil, ErrMagicMismatch
+	}
+	d.id = binary.LittleEndian.Uint32(b[4:8])
+	if d.id == 0 {
+		return nil, errors.New("dictionaries cannot have ID 0")
+	}
+
+	// Read literal table
+	var err error
+	d.litEnc, b, err = huff0.ReadTable(b[8:], nil)
+	if err != nil {
+		return nil, err
+	}
+	d.litEnc.Reuse = huff0.ReusePolicyMust
+
+	br := byteReader{
+		b:   b,
+		off: 0,
+	}
+	readDec := func(i tableIndex, dec *fseDecoder) error {
+		if err := dec.readNCount(&br, uint16(maxTableSymbol[i])); err != nil {
+			return err
+		}
+		if br.overread() {
+			return io.ErrUnexpectedEOF
+		}
+		err = dec.transform(symbolTableX[i])
+		if err != nil {
+			println("Transform table error:", err)
+			return err
+		}
+		if debugDecoder || debugEncoder {
+			println("Read table ok", "symbolLen:", dec.symbolLen)
+		}
+		// Set decoders as predefined so they aren't reused.
+		dec.preDefined = true
+		return nil
+	}
+
+	if err := readDec(tableOffsets, d.ofDec.fse); err != nil {
+		return nil, err
+	}
+	if err := readDec(tableMatchLengths, d.mlDec.fse); err != nil {
+		return nil, err
+	}
+	if err := readDec(tableLiteralLengths, d.llDec.fse); err != nil {
+		return nil, err
+	}
+	if br.remain() < 12 {
+		return nil, io.ErrUnexpectedEOF
+	}
+
+	d.offsets[0] = int(br.Uint32())
+	br.advance(4)
+	d.offsets[1] = int(br.Uint32())
+	br.advance(4)
+	d.offsets[2] = int(br.Uint32())
+	br.advance(4)
+	if d.offsets[0] <= 0 || d.offsets[1] <= 0 || d.offsets[2] <= 0 {
+		return nil, errors.New("invalid offset in dictionary")
+	}
+	d.content = make([]byte, br.remain())
+	copy(d.content, br.unread())
+	if d.offsets[0] > len(d.content) || d.offsets[1] > len(d.content) || d.offsets[2] > len(d.content) {
+		return nil, fmt.Errorf("initial offset bigger than dictionary content size %d, offsets: %v", len(d.content), d.offsets)
+	}
+
+	return &d, nil
+}

vendor/github.com/klauspost/compress/zstd/enc_base.go

@@ -0,0 +1,188 @@
+package zstd
+
+import (
+	"fmt"
+	"math/bits"
+
+	"github.com/klauspost/compress/zstd/internal/xxhash"
+)
+
+const (
+	dictShardBits = 6
+)
+
+type fastBase struct {
+	// cur is the offset at the start of hist
+	cur int32
+	// maximum offset. Should be at least 2x block size.
+	maxMatchOff int32
+	hist        []byte
+	crc         *xxhash.Digest
+	tmp         [8]byte
+	blk         *blockEnc
+	lastDictID  uint32
+	lowMem      bool
+}
+
+// CRC returns the underlying CRC writer.
+func (e *fastBase) CRC() *xxhash.Digest {
+	return e.crc
+}
+
+// AppendCRC will append the CRC to the destination slice and return it.
+func (e *fastBase) AppendCRC(dst []byte) []byte {
+	crc := e.crc.Sum(e.tmp[:0])
+	dst = append(dst, crc[7], crc[6], crc[5], crc[4])
+	return dst
+}
+
+// WindowSize returns the window size of the encoder,
+// or a window size small enough to contain the input size, if > 0.
+func (e *fastBase) WindowSize(size int64) int32 {
+	if size > 0 && size < int64(e.maxMatchOff) {
+		b := int32(1) << uint(bits.Len(uint(size)))
+		// Keep minimum window.
+		if b < 1024 {
+			b = 1024
+		}
+		return b
+	}
+	return e.maxMatchOff
+}
+
+// Block returns the current block.
+func (e *fastBase) Block() *blockEnc {
+	return e.blk
+}
+
+func (e *fastBase) addBlock(src []byte) int32 {
+	if debugAsserts && e.cur > bufferReset {
+		panic(fmt.Sprintf("ecur (%d) > buffer reset (%d)", e.cur, bufferReset))
+	}
+	// check if we have space already
+	if len(e.hist)+len(src) > cap(e.hist) {
+		if cap(e.hist) == 0 {
+			e.ensureHist(len(src))
+		} else {
+			if cap(e.hist) < int(e.maxMatchOff+maxCompressedBlockSize) {
+				panic(fmt.Errorf("unexpected buffer cap %d, want at least %d with window %d", cap(e.hist), e.maxMatchOff+maxCompressedBlockSize, e.maxMatchOff))
+			}
+			// Move down
+			offset := int32(len(e.hist)) - e.maxMatchOff
+			copy(e.hist[0:e.maxMatchOff], e.hist[offset:])
+			e.cur += offset
+			e.hist = e.hist[:e.maxMatchOff]
+		}
+	}
+	s := int32(len(e.hist))
+	e.hist = append(e.hist, src...)
+	return s
+}
+
+// ensureHist will ensure that history can keep at least this many bytes.
+func (e *fastBase) ensureHist(n int) {
+	if cap(e.hist) >= n {
+		return
+	}
+	l := e.maxMatchOff
+	if (e.lowMem && e.maxMatchOff > maxCompressedBlockSize) || e.maxMatchOff <= maxCompressedBlockSize {
+		l += maxCompressedBlockSize
+	} else {
+		l += e.maxMatchOff
+	}
+	// Make it at least 1MB.
+	if l < 1<<20 && !e.lowMem {
+		l = 1 << 20
+	}
+	// Make it at least the requested size.
+	if l < int32(n) {
+		l = int32(n)
+	}
+	e.hist = make([]byte, 0, l)
+}
+
+// useBlock will replace the block with the provided one,
+// but transfer recent offsets from the previous.
+func (e *fastBase) UseBlock(enc *blockEnc) {
+	enc.reset(e.blk)
+	e.blk = enc
+}
+
+func (e *fastBase) matchlen(s, t int32, src []byte) int32 {
+	if debugAsserts {
+		if s < 0 {
+			err := fmt.Sprintf("s (%d) < 0", s)
+			panic(err)
+		}
+		if t < 0 {
+			err := fmt.Sprintf("s (%d) < 0", s)
+			panic(err)
+		}
+		if s-t > e.maxMatchOff {
+			err := fmt.Sprintf("s (%d) - t (%d) > maxMatchOff (%d)", s, t, e.maxMatchOff)
+			panic(err)
+		}
+		if len(src)-int(s) > maxCompressedBlockSize {
+			panic(fmt.Sprintf("len(src)-s (%d) > maxCompressedBlockSize (%d)", len(src)-int(s), maxCompressedBlockSize))
+		}
+	}
+	a := src[s:]
+	b := src[t:]
+	b = b[:len(a)]
+	end := int32((len(a) >> 3) << 3)
+	for i := int32(0); i < end; i += 8 {
+		if diff := load6432(a, i) ^ load6432(b, i); diff != 0 {
+			return i + int32(bits.TrailingZeros64(diff)>>3)
+		}
+	}
+
+	a = a[end:]
+	b = b[end:]
+	for i := range a {
+		if a[i] != b[i] {
+			return int32(i) + end
+		}
+	}
+	return int32(len(a)) + end
+}
+
+// Reset the encoding table.
+func (e *fastBase) resetBase(d *dict, singleBlock bool) {
+	if e.blk == nil {
+		e.blk = &blockEnc{lowMem: e.lowMem}
+		e.blk.init()
+	} else {
+		e.blk.reset(nil)
+	}
+	e.blk.initNewEncode()
+	if e.crc == nil {
+		e.crc = xxhash.New()
+	} else {
+		e.crc.Reset()
+	}
+	if d != nil {
+		low := e.lowMem
+		if singleBlock {
+			e.lowMem = true
+		}
+		e.ensureHist(d.DictContentSize() + maxCompressedBlockSize)
+		e.lowMem = low
+	}
+
+	// We offset current position so everything will be out of reach.
+	// If above reset line, history will be purged.
+	if e.cur < bufferReset {
+		e.cur += e.maxMatchOff + int32(len(e.hist))
+	}
+	e.hist = e.hist[:0]
+	if d != nil {
+		// Set offsets (currently not used)
+		for i, off := range d.offsets {
+			e.blk.recentOffsets[i] = uint32(off)
+			e.blk.prevRecentOffsets[i] = e.blk.recentOffsets[i]
+		}
+		// Transfer litenc.
+		e.blk.dictLitEnc = d.litEnc
+		e.hist = append(e.hist, d.content...)
+	}
+}

vendor/github.com/klauspost/compress/zstd/enc_best.go

@@ -0,0 +1,558 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+import (
+	"bytes"
+	"fmt"
+
+	"github.com/klauspost/compress"
+)
+
+const (
+	bestLongTableBits = 22                     // Bits used in the long match table
+	bestLongTableSize = 1 << bestLongTableBits // Size of the table
+	bestLongLen       = 8                      // Bytes used for table hash
+
+	// Note: Increasing the short table bits or making the hash shorter
+	// can actually lead to compression degradation since it will 'steal' more from the
+	// long match table and match offsets are quite big.
+	// This greatly depends on the type of input.
+	bestShortTableBits = 18                      // Bits used in the short match table
+	bestShortTableSize = 1 << bestShortTableBits // Size of the table
+	bestShortLen       = 4                       // Bytes used for table hash
+
+)
+
+type match struct {
+	offset int32
+	s      int32
+	length int32
+	rep    int32
+	est    int32
+}
+
+const highScore = 25000
+
+// estBits will estimate output bits from predefined tables.
+func (m *match) estBits(bitsPerByte int32) {
+	mlc := mlCode(uint32(m.length - zstdMinMatch))
+	var ofc uint8
+	if m.rep < 0 {
+		ofc = ofCode(uint32(m.s-m.offset) + 3)
+	} else {
+		ofc = ofCode(uint32(m.rep))
+	}
+	// Cost, excluding
+	ofTT, mlTT := fsePredefEnc[tableOffsets].ct.symbolTT[ofc], fsePredefEnc[tableMatchLengths].ct.symbolTT[mlc]
+
+	// Add cost of match encoding...
+	m.est = int32(ofTT.outBits + mlTT.outBits)
+	m.est += int32(ofTT.deltaNbBits>>16 + mlTT.deltaNbBits>>16)
+	// Subtract savings compared to literal encoding...
+	m.est -= (m.length * bitsPerByte) >> 10
+	if m.est > 0 {
+		// Unlikely gain..
+		m.length = 0
+		m.est = highScore
+	}
+}
+
+// bestFastEncoder uses 2 tables, one for short matches (5 bytes) and one for long matches.
+// The long match table contains the previous entry with the same hash,
+// effectively making it a "chain" of length 2.
+// When we find a long match we choose between the two values and select the longest.
+// When we find a short match, after checking the long, we check if we can find a long at n+1
+// and that it is longer (lazy matching).
+type bestFastEncoder struct {
+	fastBase
+	table         [bestShortTableSize]prevEntry
+	longTable     [bestLongTableSize]prevEntry
+	dictTable     []prevEntry
+	dictLongTable []prevEntry
+}
+
+// Encode improves compression...
+func (e *bestFastEncoder) Encode(blk *blockEnc, src []byte) {
+	const (
+		// Input margin is the number of bytes we read (8)
+		// and the maximum we will read ahead (2)
+		inputMargin            = 8 + 4
+		minNonLiteralBlockSize = 16
+	)
+
+	// Protect against e.cur wraparound.
+	for e.cur >= bufferReset {
+		if len(e.hist) == 0 {
+			for i := range e.table[:] {
+				e.table[i] = prevEntry{}
+			}
+			for i := range e.longTable[:] {
+				e.longTable[i] = prevEntry{}
+			}
+			e.cur = e.maxMatchOff
+			break
+		}
+		// Shift down everything in the table that isn't already too far away.
+		minOff := e.cur + int32(len(e.hist)) - e.maxMatchOff
+		for i := range e.table[:] {
+			v := e.table[i].offset
+			v2 := e.table[i].prev
+			if v < minOff {
+				v = 0
+				v2 = 0
+			} else {
+				v = v - e.cur + e.maxMatchOff
+				if v2 < minOff {
+					v2 = 0
+				} else {
+					v2 = v2 - e.cur + e.maxMatchOff
+				}
+			}
+			e.table[i] = prevEntry{
+				offset: v,
+				prev:   v2,
+			}
+		}
+		for i := range e.longTable[:] {
+			v := e.longTable[i].offset
+			v2 := e.longTable[i].prev
+			if v < minOff {
+				v = 0
+				v2 = 0
+			} else {
+				v = v - e.cur + e.maxMatchOff
+				if v2 < minOff {
+					v2 = 0
+				} else {
+					v2 = v2 - e.cur + e.maxMatchOff
+				}
+			}
+			e.longTable[i] = prevEntry{
+				offset: v,
+				prev:   v2,
+			}
+		}
+		e.cur = e.maxMatchOff
+		break
+	}
+
+	s := e.addBlock(src)
+	blk.size = len(src)
+	if len(src) < minNonLiteralBlockSize {
+		blk.extraLits = len(src)
+		blk.literals = blk.literals[:len(src)]
+		copy(blk.literals, src)
+		return
+	}
+
+	// Use this to estimate literal cost.
+	// Scaled by 10 bits.
+	bitsPerByte := int32((compress.ShannonEntropyBits(src) * 1024) / len(src))
+	// Huffman can never go < 1 bit/byte
+	if bitsPerByte < 1024 {
+		bitsPerByte = 1024
+	}
+
+	// Override src
+	src = e.hist
+	sLimit := int32(len(src)) - inputMargin
+	const kSearchStrength = 10
+
+	// nextEmit is where in src the next emitLiteral should start from.
+	nextEmit := s
+	cv := load6432(src, s)
+
+	// Relative offsets
+	offset1 := int32(blk.recentOffsets[0])
+	offset2 := int32(blk.recentOffsets[1])
+	offset3 := int32(blk.recentOffsets[2])
+
+	addLiterals := func(s *seq, until int32) {
+		if until == nextEmit {
+			return
+		}
+		blk.literals = append(blk.literals, src[nextEmit:until]...)
+		s.litLen = uint32(until - nextEmit)
+	}
+	_ = addLiterals
+
+	if debugEncoder {
+		println("recent offsets:", blk.recentOffsets)
+	}
+
+encodeLoop:
+	for {
+		// We allow the encoder to optionally turn off repeat offsets across blocks
+		canRepeat := len(blk.sequences) > 2
+
+		if debugAsserts && canRepeat && offset1 == 0 {
+			panic("offset0 was 0")
+		}
+
+		bestOf := func(a, b match) match {
+			if a.est+(a.s-b.s)*bitsPerByte>>10 < b.est+(b.s-a.s)*bitsPerByte>>10 {
+				return a
+			}
+			return b
+		}
+		const goodEnough = 100
+
+		nextHashL := hashLen(cv, bestLongTableBits, bestLongLen)
+		nextHashS := hashLen(cv, bestShortTableBits, bestShortLen)
+		candidateL := e.longTable[nextHashL]
+		candidateS := e.table[nextHashS]
+
+		matchAt := func(offset int32, s int32, first uint32, rep int32) match {
+			if s-offset >= e.maxMatchOff || load3232(src, offset) != first {
+				return match{s: s, est: highScore}
+			}
+			if debugAsserts {
+				if !bytes.Equal(src[s:s+4], src[offset:offset+4]) {
+					panic(fmt.Sprintf("first match mismatch: %v != %v, first: %08x", src[s:s+4], src[offset:offset+4], first))
+				}
+			}
+			m := match{offset: offset, s: s, length: 4 + e.matchlen(s+4, offset+4, src), rep: rep}
+			m.estBits(bitsPerByte)
+			return m
+		}
+
+		best := bestOf(matchAt(candidateL.offset-e.cur, s, uint32(cv), -1), matchAt(candidateL.prev-e.cur, s, uint32(cv), -1))
+		best = bestOf(best, matchAt(candidateS.offset-e.cur, s, uint32(cv), -1))
+		best = bestOf(best, matchAt(candidateS.prev-e.cur, s, uint32(cv), -1))
+
+		if canRepeat && best.length < goodEnough {
+			cv32 := uint32(cv >> 8)
+			spp := s + 1
+			best = bestOf(best, matchAt(spp-offset1, spp, cv32, 1))
+			best = bestOf(best, matchAt(spp-offset2, spp, cv32, 2))
+			best = bestOf(best, matchAt(spp-offset3, spp, cv32, 3))
+			if best.length > 0 {
+				cv32 = uint32(cv >> 24)
+				spp += 2
+				best = bestOf(best, matchAt(spp-offset1, spp, cv32, 1))
+				best = bestOf(best, matchAt(spp-offset2, spp, cv32, 2))
+				best = bestOf(best, matchAt(spp-offset3, spp, cv32, 3))
+			}
+		}
+		// Load next and check...
+		e.longTable[nextHashL] = prevEntry{offset: s + e.cur, prev: candidateL.offset}
+		e.table[nextHashS] = prevEntry{offset: s + e.cur, prev: candidateS.offset}
+
+		// Look far ahead, unless we have a really long match already...
+		if best.length < goodEnough {
+			// No match found, move forward on input, no need to check forward...
+			if best.length < 4 {
+				s += 1 + (s-nextEmit)>>(kSearchStrength-1)
+				if s >= sLimit {
+					break encodeLoop
+				}
+				cv = load6432(src, s)
+				continue
+			}
+
+			s++
+			candidateS = e.table[hashLen(cv>>8, bestShortTableBits, bestShortLen)]
+			cv = load6432(src, s)
+			cv2 := load6432(src, s+1)
+			candidateL = e.longTable[hashLen(cv, bestLongTableBits, bestLongLen)]
+			candidateL2 := e.longTable[hashLen(cv2, bestLongTableBits, bestLongLen)]
+
+			// Short at s+1
+			best = bestOf(best, matchAt(candidateS.offset-e.cur, s, uint32(cv), -1))
+			// Long at s+1, s+2
+			best = bestOf(best, matchAt(candidateL.offset-e.cur, s, uint32(cv), -1))
+			best = bestOf(best, matchAt(candidateL.prev-e.cur, s, uint32(cv), -1))
+			best = bestOf(best, matchAt(candidateL2.offset-e.cur, s+1, uint32(cv2), -1))
+			best = bestOf(best, matchAt(candidateL2.prev-e.cur, s+1, uint32(cv2), -1))
+			if false {
+				// Short at s+3.
+				// Too often worse...
+				best = bestOf(best, matchAt(e.table[hashLen(cv2>>8, bestShortTableBits, bestShortLen)].offset-e.cur, s+2, uint32(cv2>>8), -1))
+			}
+			// See if we can find a better match by checking where the current best ends.
+			// Use that offset to see if we can find a better full match.
+			if sAt := best.s + best.length; sAt < sLimit {
+				nextHashL := hashLen(load6432(src, sAt), bestLongTableBits, bestLongLen)
+				candidateEnd := e.longTable[nextHashL]
+				if pos := candidateEnd.offset - e.cur - best.length; pos >= 0 {
+					bestEnd := bestOf(best, matchAt(pos, best.s, load3232(src, best.s), -1))
+					if pos := candidateEnd.prev - e.cur - best.length; pos >= 0 {
+						bestEnd = bestOf(bestEnd, matchAt(pos, best.s, load3232(src, best.s), -1))
+					}
+					best = bestEnd
+				}
+			}
+		}
+
+		if debugAsserts {
+			if !bytes.Equal(src[best.s:best.s+best.length], src[best.offset:best.offset+best.length]) {
+				panic(fmt.Sprintf("match mismatch: %v != %v", src[best.s:best.s+best.length], src[best.offset:best.offset+best.length]))
+			}
+		}
+
+		// We have a match, we can store the forward value
+		if best.rep > 0 {
+			s = best.s
+			var seq seq
+			seq.matchLen = uint32(best.length - zstdMinMatch)
+
+			// We might be able to match backwards.
+			// Extend as long as we can.
+			start := best.s
+			// We end the search early, so we don't risk 0 literals
+			// and have to do special offset treatment.
+			startLimit := nextEmit + 1
+
+			tMin := s - e.maxMatchOff
+			if tMin < 0 {
+				tMin = 0
+			}
+			repIndex := best.offset
+			for repIndex > tMin && start > startLimit && src[repIndex-1] == src[start-1] && seq.matchLen < maxMatchLength-zstdMinMatch-1 {
+				repIndex--
+				start--
+				seq.matchLen++
+			}
+			addLiterals(&seq, start)
+
+			// rep 0
+			seq.offset = uint32(best.rep)
+			if debugSequences {
+				println("repeat sequence", seq, "next s:", s)
+			}
+			blk.sequences = append(blk.sequences, seq)
+
+			// Index match start+1 (long) -> s - 1
+			index0 := s
+			s = best.s + best.length
+
+			nextEmit = s
+			if s >= sLimit {
+				if debugEncoder {
+					println("repeat ended", s, best.length)
+
+				}
+				break encodeLoop
+			}
+			// Index skipped...
+			off := index0 + e.cur
+			for index0 < s-1 {
+				cv0 := load6432(src, index0)
+				h0 := hashLen(cv0, bestLongTableBits, bestLongLen)
+				h1 := hashLen(cv0, bestShortTableBits, bestShortLen)
+				e.longTable[h0] = prevEntry{offset: off, prev: e.longTable[h0].offset}
+				e.table[h1] = prevEntry{offset: off, prev: e.table[h1].offset}
+				off++
+				index0++
+			}
+			switch best.rep {
+			case 2:
+				offset1, offset2 = offset2, offset1
+			case 3:
+				offset1, offset2, offset3 = offset3, offset1, offset2
+			}
+			cv = load6432(src, s)
+			continue
+		}
+
+		// A 4-byte match has been found. Update recent offsets.
+		// We'll later see if more than 4 bytes.
+		s = best.s
+		t := best.offset
+		offset1, offset2, offset3 = s-t, offset1, offset2
+
+		if debugAsserts && s <= t {
+			panic(fmt.Sprintf("s (%d) <= t (%d)", s, t))
+		}
+
+		if debugAsserts && int(offset1) > len(src) {
+			panic("invalid offset")
+		}
+
+		// Extend the n-byte match as long as possible.
+		l := best.length
+
+		// Extend backwards
+		tMin := s - e.maxMatchOff
+		if tMin < 0 {
+			tMin = 0
+		}
+		for t > tMin && s > nextEmit && src[t-1] == src[s-1] && l < maxMatchLength {
+			s--
+			t--
+			l++
+		}
+
+		// Write our sequence
+		var seq seq
+		seq.litLen = uint32(s - nextEmit)
+		seq.matchLen = uint32(l - zstdMinMatch)
+		if seq.litLen > 0 {
+			blk.literals = append(blk.literals, src[nextEmit:s]...)
+		}
+		seq.offset = uint32(s-t) + 3
+		s += l
+		if debugSequences {
+			println("sequence", seq, "next s:", s)
+		}
+		blk.sequences = append(blk.sequences, seq)
+		nextEmit = s
+		if s >= sLimit {
+			break encodeLoop
+		}
+
+		// Index match start+1 (long) -> s - 1
+		index0 := s - l + 1
+		// every entry
+		for index0 < s-1 {
+			cv0 := load6432(src, index0)
+			h0 := hashLen(cv0, bestLongTableBits, bestLongLen)
+			h1 := hashLen(cv0, bestShortTableBits, bestShortLen)
+			off := index0 + e.cur
+			e.longTable[h0] = prevEntry{offset: off, prev: e.longTable[h0].offset}
+			e.table[h1] = prevEntry{offset: off, prev: e.table[h1].offset}
+			index0++
+		}
+
+		cv = load6432(src, s)
+		if !canRepeat {
+			continue
+		}
+
+		// Check offset 2
+		for {
+			o2 := s - offset2
+			if load3232(src, o2) != uint32(cv) {
+				// Do regular search
+				break
+			}
+
+			// Store this, since we have it.
+			nextHashS := hashLen(cv, bestShortTableBits, bestShortLen)
+			nextHashL := hashLen(cv, bestLongTableBits, bestLongLen)
+
+			// We have at least 4 byte match.
+			// No need to check backwards. We come straight from a match
+			l := 4 + e.matchlen(s+4, o2+4, src)
+
+			e.longTable[nextHashL] = prevEntry{offset: s + e.cur, prev: e.longTable[nextHashL].offset}
+			e.table[nextHashS] = prevEntry{offset: s + e.cur, prev: e.table[nextHashS].offset}
+			seq.matchLen = uint32(l) - zstdMinMatch
+			seq.litLen = 0
+
+			// Since litlen is always 0, this is offset 1.
+			seq.offset = 1
+			s += l
+			nextEmit = s
+			if debugSequences {
+				println("sequence", seq, "next s:", s)
+			}
+			blk.sequences = append(blk.sequences, seq)
+
+			// Swap offset 1 and 2.
+			offset1, offset2 = offset2, offset1
+			if s >= sLimit {
+				// Finished
+				break encodeLoop
+			}
+			cv = load6432(src, s)
+		}
+	}
+
+	if int(nextEmit) < len(src) {
+		blk.literals = append(blk.literals, src[nextEmit:]...)
+		blk.extraLits = len(src) - int(nextEmit)
+	}
+	blk.recentOffsets[0] = uint32(offset1)
+	blk.recentOffsets[1] = uint32(offset2)
+	blk.recentOffsets[2] = uint32(offset3)
+	if debugEncoder {
+		println("returning, recent offsets:", blk.recentOffsets, "extra literals:", blk.extraLits)
+	}
+}
+
+// EncodeNoHist will encode a block with no history and no following blocks.
+// Most notable difference is that src will not be copied for history and
+// we do not need to check for max match length.
+func (e *bestFastEncoder) EncodeNoHist(blk *blockEnc, src []byte) {
+	e.ensureHist(len(src))
+	e.Encode(blk, src)
+}
+
+// Reset will reset and set a dictionary if not nil
+func (e *bestFastEncoder) Reset(d *dict, singleBlock bool) {
+	e.resetBase(d, singleBlock)
+	if d == nil {
+		return
+	}
+	// Init or copy dict table
+	if len(e.dictTable) != len(e.table) || d.id != e.lastDictID {
+		if len(e.dictTable) != len(e.table) {
+			e.dictTable = make([]prevEntry, len(e.table))
+		}
+		end := int32(len(d.content)) - 8 + e.maxMatchOff
+		for i := e.maxMatchOff; i < end; i += 4 {
+			const hashLog = bestShortTableBits
+
+			cv := load6432(d.content, i-e.maxMatchOff)
+			nextHash := hashLen(cv, hashLog, bestShortLen)      // 0 -> 4
+			nextHash1 := hashLen(cv>>8, hashLog, bestShortLen)  // 1 -> 5
+			nextHash2 := hashLen(cv>>16, hashLog, bestShortLen) // 2 -> 6
+			nextHash3 := hashLen(cv>>24, hashLog, bestShortLen) // 3 -> 7
+			e.dictTable[nextHash] = prevEntry{
+				prev:   e.dictTable[nextHash].offset,
+				offset: i,
+			}
+			e.dictTable[nextHash1] = prevEntry{
+				prev:   e.dictTable[nextHash1].offset,
+				offset: i + 1,
+			}
+			e.dictTable[nextHash2] = prevEntry{
+				prev:   e.dictTable[nextHash2].offset,
+				offset: i + 2,
+			}
+			e.dictTable[nextHash3] = prevEntry{
+				prev:   e.dictTable[nextHash3].offset,
+				offset: i + 3,
+			}
+		}
+		e.lastDictID = d.id
+	}
+
+	// Init or copy dict table
+	if len(e.dictLongTable) != len(e.longTable) || d.id != e.lastDictID {
+		if len(e.dictLongTable) != len(e.longTable) {
+			e.dictLongTable = make([]prevEntry, len(e.longTable))
+		}
+		if len(d.content) >= 8 {
+			cv := load6432(d.content, 0)
+			h := hashLen(cv, bestLongTableBits, bestLongLen)
+			e.dictLongTable[h] = prevEntry{
+				offset: e.maxMatchOff,
+				prev:   e.dictLongTable[h].offset,
+			}
+
+			end := int32(len(d.content)) - 8 + e.maxMatchOff
+			off := 8 // First to read
+			for i := e.maxMatchOff + 1; i < end; i++ {
+				cv = cv>>8 | (uint64(d.content[off]) << 56)
+				h := hashLen(cv, bestLongTableBits, bestLongLen)
+				e.dictLongTable[h] = prevEntry{
+					offset: i,
+					prev:   e.dictLongTable[h].offset,
+				}
+				off++
+			}
+		}
+		e.lastDictID = d.id
+	}
+	// Reset table to initial state
+	copy(e.longTable[:], e.dictLongTable)
+
+	e.cur = e.maxMatchOff
+	// Reset table to initial state
+	copy(e.table[:], e.dictTable)
+}

vendor/github.com/klauspost/compress/zstd/enc_fast.go

@@ -0,0 +1,898 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+import (
+	"fmt"
+)
+
+const (
+	tableBits        = 15                               // Bits used in the table
+	tableSize        = 1 << tableBits                   // Size of the table
+	tableShardCnt    = 1 << (tableBits - dictShardBits) // Number of shards in the table
+	tableShardSize   = tableSize / tableShardCnt        // Size of an individual shard
+	tableFastHashLen = 6
+	tableMask        = tableSize - 1 // Mask for table indices. Redundant, but can eliminate bounds checks.
+	maxMatchLength   = 131074
+)
+
+type tableEntry struct {
+	val    uint32
+	offset int32
+}
+
+type fastEncoder struct {
+	fastBase
+	table [tableSize]tableEntry
+}
+
+type fastEncoderDict struct {
+	fastEncoder
+	dictTable       []tableEntry
+	tableShardDirty [tableShardCnt]bool
+	allDirty        bool
+}
+
+// Encode mimmics functionality in zstd_fast.c
+func (e *fastEncoder) Encode(blk *blockEnc, src []byte) {
+	const (
+		inputMargin            = 8
+		minNonLiteralBlockSize = 1 + 1 + inputMargin
+	)
+
+	// Protect against e.cur wraparound.
+	for e.cur >= bufferReset {
+		if len(e.hist) == 0 {
+			for i := range e.table[:] {
+				e.table[i] = tableEntry{}
+			}
+			e.cur = e.maxMatchOff
+			break
+		}
+		// Shift down everything in the table that isn't already too far away.
+		minOff := e.cur + int32(len(e.hist)) - e.maxMatchOff
+		for i := range e.table[:] {
+			v := e.table[i].offset
+			if v < minOff {
+				v = 0
+			} else {
+				v = v - e.cur + e.maxMatchOff
+			}
+			e.table[i].offset = v
+		}
+		e.cur = e.maxMatchOff
+		break
+	}
+
+	s := e.addBlock(src)
+	blk.size = len(src)
+	if len(src) < minNonLiteralBlockSize {
+		blk.extraLits = len(src)
+		blk.literals = blk.literals[:len(src)]
+		copy(blk.literals, src)
+		return
+	}
+
+	// Override src
+	src = e.hist
+	sLimit := int32(len(src)) - inputMargin
+	// stepSize is the number of bytes to skip on every main loop iteration.
+	// It should be >= 2.
+	const stepSize = 2
+
+	// TEMPLATE
+	const hashLog = tableBits
+	// seems global, but would be nice to tweak.
+	const kSearchStrength = 7
+
+	// nextEmit is where in src the next emitLiteral should start from.
+	nextEmit := s
+	cv := load6432(src, s)
+
+	// Relative offsets
+	offset1 := int32(blk.recentOffsets[0])
+	offset2 := int32(blk.recentOffsets[1])
+
+	addLiterals := func(s *seq, until int32) {
+		if until == nextEmit {
+			return
+		}
+		blk.literals = append(blk.literals, src[nextEmit:until]...)
+		s.litLen = uint32(until - nextEmit)
+	}
+	if debugEncoder {
+		println("recent offsets:", blk.recentOffsets)
+	}
+
+encodeLoop:
+	for {
+		// t will contain the match offset when we find one.
+		// When existing the search loop, we have already checked 4 bytes.
+		var t int32
+
+		// We will not use repeat offsets across blocks.
+		// By not using them for the first 3 matches
+		canRepeat := len(blk.sequences) > 2
+
+		for {
+			if debugAsserts && canRepeat && offset1 == 0 {
+				panic("offset0 was 0")
+			}
+
+			nextHash := hashLen(cv, hashLog, tableFastHashLen)
+			nextHash2 := hashLen(cv>>8, hashLog, tableFastHashLen)
+			candidate := e.table[nextHash]
+			candidate2 := e.table[nextHash2]
+			repIndex := s - offset1 + 2
+
+			e.table[nextHash] = tableEntry{offset: s + e.cur, val: uint32(cv)}
+			e.table[nextHash2] = tableEntry{offset: s + e.cur + 1, val: uint32(cv >> 8)}
+
+			if canRepeat && repIndex >= 0 && load3232(src, repIndex) == uint32(cv>>16) {
+				// Consider history as well.
+				var seq seq
+				var length int32
+				length = 4 + e.matchlen(s+6, repIndex+4, src)
+				seq.matchLen = uint32(length - zstdMinMatch)
+
+				// We might be able to match backwards.
+				// Extend as long as we can.
+				start := s + 2
+				// We end the search early, so we don't risk 0 literals
+				// and have to do special offset treatment.
+				startLimit := nextEmit + 1
+
+				sMin := s - e.maxMatchOff
+				if sMin < 0 {
+					sMin = 0
+				}
+				for repIndex > sMin && start > startLimit && src[repIndex-1] == src[start-1] && seq.matchLen < maxMatchLength-zstdMinMatch {
+					repIndex--
+					start--
+					seq.matchLen++
+				}
+				addLiterals(&seq, start)
+
+				// rep 0
+				seq.offset = 1
+				if debugSequences {
+					println("repeat sequence", seq, "next s:", s)
+				}
+				blk.sequences = append(blk.sequences, seq)
+				s += length + 2
+				nextEmit = s
+				if s >= sLimit {
+					if debugEncoder {
+						println("repeat ended", s, length)
+
+					}
+					break encodeLoop
+				}
+				cv = load6432(src, s)
+				continue
+			}
+			coffset0 := s - (candidate.offset - e.cur)
+			coffset1 := s - (candidate2.offset - e.cur) + 1
+			if coffset0 < e.maxMatchOff && uint32(cv) == candidate.val {
+				// found a regular match
+				t = candidate.offset - e.cur
+				if debugAsserts && s <= t {
+					panic(fmt.Sprintf("s (%d) <= t (%d)", s, t))
+				}
+				if debugAsserts && s-t > e.maxMatchOff {
+					panic("s - t >e.maxMatchOff")
+				}
+				break
+			}
+
+			if coffset1 < e.maxMatchOff && uint32(cv>>8) == candidate2.val {
+				// found a regular match
+				t = candidate2.offset - e.cur
+				s++
+				if debugAsserts && s <= t {
+					panic(fmt.Sprintf("s (%d) <= t (%d)", s, t))
+				}
+				if debugAsserts && s-t > e.maxMatchOff {
+					panic("s - t >e.maxMatchOff")
+				}
+				if debugAsserts && t < 0 {
+					panic("t<0")
+				}
+				break
+			}
+			s += stepSize + ((s - nextEmit) >> (kSearchStrength - 1))
+			if s >= sLimit {
+				break encodeLoop
+			}
+			cv = load6432(src, s)
+		}
+		// A 4-byte match has been found. We'll later see if more than 4 bytes.
+		offset2 = offset1
+		offset1 = s - t
+
+		if debugAsserts && s <= t {
+			panic(fmt.Sprintf("s (%d) <= t (%d)", s, t))
+		}
+
+		if debugAsserts && canRepeat && int(offset1) > len(src) {
+			panic("invalid offset")
+		}
+
+		// Extend the 4-byte match as long as possible.
+		l := e.matchlen(s+4, t+4, src) + 4
+
+		// Extend backwards
+		tMin := s - e.maxMatchOff
+		if tMin < 0 {
+			tMin = 0
+		}
+		for t > tMin && s > nextEmit && src[t-1] == src[s-1] && l < maxMatchLength {
+			s--
+			t--
+			l++
+		}
+
+		// Write our sequence.
+		var seq seq
+		seq.litLen = uint32(s - nextEmit)
+		seq.matchLen = uint32(l - zstdMinMatch)
+		if seq.litLen > 0 {
+			blk.literals = append(blk.literals, src[nextEmit:s]...)
+		}
+		// Don't use repeat offsets
+		seq.offset = uint32(s-t) + 3
+		s += l
+		if debugSequences {
+			println("sequence", seq, "next s:", s)
+		}
+		blk.sequences = append(blk.sequences, seq)
+		nextEmit = s
+		if s >= sLimit {
+			break encodeLoop
+		}
+		cv = load6432(src, s)
+
+		// Check offset 2
+		if o2 := s - offset2; canRepeat && load3232(src, o2) == uint32(cv) {
+			// We have at least 4 byte match.
+			// No need to check backwards. We come straight from a match
+			l := 4 + e.matchlen(s+4, o2+4, src)
+
+			// Store this, since we have it.
+			nextHash := hashLen(cv, hashLog, tableFastHashLen)
+			e.table[nextHash] = tableEntry{offset: s + e.cur, val: uint32(cv)}
+			seq.matchLen = uint32(l) - zstdMinMatch
+			seq.litLen = 0
+			// Since litlen is always 0, this is offset 1.
+			seq.offset = 1
+			s += l
+			nextEmit = s
+			if debugSequences {
+				println("sequence", seq, "next s:", s)
+			}
+			blk.sequences = append(blk.sequences, seq)
+
+			// Swap offset 1 and 2.
+			offset1, offset2 = offset2, offset1
+			if s >= sLimit {
+				break encodeLoop
+			}
+			// Prepare next loop.
+			cv = load6432(src, s)
+		}
+	}
+
+	if int(nextEmit) < len(src) {
+		blk.literals = append(blk.literals, src[nextEmit:]...)
+		blk.extraLits = len(src) - int(nextEmit)
+	}
+	blk.recentOffsets[0] = uint32(offset1)
+	blk.recentOffsets[1] = uint32(offset2)
+	if debugEncoder {
+		println("returning, recent offsets:", blk.recentOffsets, "extra literals:", blk.extraLits)
+	}
+}
+
+// EncodeNoHist will encode a block with no history and no following blocks.
+// Most notable difference is that src will not be copied for history and
+// we do not need to check for max match length.
+func (e *fastEncoder) EncodeNoHist(blk *blockEnc, src []byte) {
+	const (
+		inputMargin            = 8
+		minNonLiteralBlockSize = 1 + 1 + inputMargin
+	)
+	if debugEncoder {
+		if len(src) > maxBlockSize {
+			panic("src too big")
+		}
+	}
+
+	// Protect against e.cur wraparound.
+	if e.cur >= bufferReset {
+		for i := range e.table[:] {
+			e.table[i] = tableEntry{}
+		}
+		e.cur = e.maxMatchOff
+	}
+
+	s := int32(0)
+	blk.size = len(src)
+	if len(src) < minNonLiteralBlockSize {
+		blk.extraLits = len(src)
+		blk.literals = blk.literals[:len(src)]
+		copy(blk.literals, src)
+		return
+	}
+
+	sLimit := int32(len(src)) - inputMargin
+	// stepSize is the number of bytes to skip on every main loop iteration.
+	// It should be >= 2.
+	const stepSize = 2
+
+	// TEMPLATE
+	const hashLog = tableBits
+	// seems global, but would be nice to tweak.
+	const kSearchStrength = 8
+
+	// nextEmit is where in src the next emitLiteral should start from.
+	nextEmit := s
+	cv := load6432(src, s)
+
+	// Relative offsets
+	offset1 := int32(blk.recentOffsets[0])
+	offset2 := int32(blk.recentOffsets[1])
+
+	addLiterals := func(s *seq, until int32) {
+		if until == nextEmit {
+			return
+		}
+		blk.literals = append(blk.literals, src[nextEmit:until]...)
+		s.litLen = uint32(until - nextEmit)
+	}
+	if debugEncoder {
+		println("recent offsets:", blk.recentOffsets)
+	}
+
+encodeLoop:
+	for {
+		// t will contain the match offset when we find one.
+		// When existing the search loop, we have already checked 4 bytes.
+		var t int32
+
+		// We will not use repeat offsets across blocks.
+		// By not using them for the first 3 matches
+
+		for {
+			nextHash := hashLen(cv, hashLog, tableFastHashLen)
+			nextHash2 := hashLen(cv>>8, hashLog, tableFastHashLen)
+			candidate := e.table[nextHash]
+			candidate2 := e.table[nextHash2]
+			repIndex := s - offset1 + 2
+
+			e.table[nextHash] = tableEntry{offset: s + e.cur, val: uint32(cv)}
+			e.table[nextHash2] = tableEntry{offset: s + e.cur + 1, val: uint32(cv >> 8)}
+
+			if len(blk.sequences) > 2 && load3232(src, repIndex) == uint32(cv>>16) {
+				// Consider history as well.
+				var seq seq
+				length := 4 + e.matchlen(s+6, repIndex+4, src)
+
+				seq.matchLen = uint32(length - zstdMinMatch)
+
+				// We might be able to match backwards.
+				// Extend as long as we can.
+				start := s + 2
+				// We end the search early, so we don't risk 0 literals
+				// and have to do special offset treatment.
+				startLimit := nextEmit + 1
+
+				sMin := s - e.maxMatchOff
+				if sMin < 0 {
+					sMin = 0
+				}
+				for repIndex > sMin && start > startLimit && src[repIndex-1] == src[start-1] {
+					repIndex--
+					start--
+					seq.matchLen++
+				}
+				addLiterals(&seq, start)
+
+				// rep 0
+				seq.offset = 1
+				if debugSequences {
+					println("repeat sequence", seq, "next s:", s)
+				}
+				blk.sequences = append(blk.sequences, seq)
+				s += length + 2
+				nextEmit = s
+				if s >= sLimit {
+					if debugEncoder {
+						println("repeat ended", s, length)
+
+					}
+					break encodeLoop
+				}
+				cv = load6432(src, s)
+				continue
+			}
+			coffset0 := s - (candidate.offset - e.cur)
+			coffset1 := s - (candidate2.offset - e.cur) + 1
+			if coffset0 < e.maxMatchOff && uint32(cv) == candidate.val {
+				// found a regular match
+				t = candidate.offset - e.cur
+				if debugAsserts && s <= t {
+					panic(fmt.Sprintf("s (%d) <= t (%d)", s, t))
+				}
+				if debugAsserts && s-t > e.maxMatchOff {
+					panic("s - t >e.maxMatchOff")
+				}
+				if debugAsserts && t < 0 {
+					panic(fmt.Sprintf("t (%d) < 0, candidate.offset: %d, e.cur: %d, coffset0: %d, e.maxMatchOff: %d", t, candidate.offset, e.cur, coffset0, e.maxMatchOff))
+				}
+				break
+			}
+
+			if coffset1 < e.maxMatchOff && uint32(cv>>8) == candidate2.val {
+				// found a regular match
+				t = candidate2.offset - e.cur
+				s++
+				if debugAsserts && s <= t {
+					panic(fmt.Sprintf("s (%d) <= t (%d)", s, t))
+				}
+				if debugAsserts && s-t > e.maxMatchOff {
+					panic("s - t >e.maxMatchOff")
+				}
+				if debugAsserts && t < 0 {
+					panic("t<0")
+				}
+				break
+			}
+			s += stepSize + ((s - nextEmit) >> (kSearchStrength - 1))
+			if s >= sLimit {
+				break encodeLoop
+			}
+			cv = load6432(src, s)
+		}
+		// A 4-byte match has been found. We'll later see if more than 4 bytes.
+		offset2 = offset1
+		offset1 = s - t
+
+		if debugAsserts && s <= t {
+			panic(fmt.Sprintf("s (%d) <= t (%d)", s, t))
+		}
+
+		if debugAsserts && t < 0 {
+			panic(fmt.Sprintf("t (%d) < 0 ", t))
+		}
+		// Extend the 4-byte match as long as possible.
+		l := e.matchlen(s+4, t+4, src) + 4
+
+		// Extend backwards
+		tMin := s - e.maxMatchOff
+		if tMin < 0 {
+			tMin = 0
+		}
+		for t > tMin && s > nextEmit && src[t-1] == src[s-1] {
+			s--
+			t--
+			l++
+		}
+
+		// Write our sequence.
+		var seq seq
+		seq.litLen = uint32(s - nextEmit)
+		seq.matchLen = uint32(l - zstdMinMatch)
+		if seq.litLen > 0 {
+			blk.literals = append(blk.literals, src[nextEmit:s]...)
+		}
+		// Don't use repeat offsets
+		seq.offset = uint32(s-t) + 3
+		s += l
+		if debugSequences {
+			println("sequence", seq, "next s:", s)
+		}
+		blk.sequences = append(blk.sequences, seq)
+		nextEmit = s
+		if s >= sLimit {
+			break encodeLoop
+		}
+		cv = load6432(src, s)
+
+		// Check offset 2
+		if o2 := s - offset2; len(blk.sequences) > 2 && load3232(src, o2) == uint32(cv) {
+			// We have at least 4 byte match.
+			// No need to check backwards. We come straight from a match
+			l := 4 + e.matchlen(s+4, o2+4, src)
+
+			// Store this, since we have it.
+			nextHash := hashLen(cv, hashLog, tableFastHashLen)
+			e.table[nextHash] = tableEntry{offset: s + e.cur, val: uint32(cv)}
+			seq.matchLen = uint32(l) - zstdMinMatch
+			seq.litLen = 0
+			// Since litlen is always 0, this is offset 1.
+			seq.offset = 1
+			s += l
+			nextEmit = s
+			if debugSequences {
+				println("sequence", seq, "next s:", s)
+			}
+			blk.sequences = append(blk.sequences, seq)
+
+			// Swap offset 1 and 2.
+			offset1, offset2 = offset2, offset1
+			if s >= sLimit {
+				break encodeLoop
+			}
+			// Prepare next loop.
+			cv = load6432(src, s)
+		}
+	}
+
+	if int(nextEmit) < len(src) {
+		blk.literals = append(blk.literals, src[nextEmit:]...)
+		blk.extraLits = len(src) - int(nextEmit)
+	}
+	if debugEncoder {
+		println("returning, recent offsets:", blk.recentOffsets, "extra literals:", blk.extraLits)
+	}
+	// We do not store history, so we must offset e.cur to avoid false matches for next user.
+	if e.cur < bufferReset {
+		e.cur += int32(len(src))
+	}
+}
+
+// Encode will encode the content, with a dictionary if initialized for it.
+func (e *fastEncoderDict) Encode(blk *blockEnc, src []byte) {
+	const (
+		inputMargin            = 8
+		minNonLiteralBlockSize = 1 + 1 + inputMargin
+	)
+	if e.allDirty || len(src) > 32<<10 {
+		e.fastEncoder.Encode(blk, src)
+		e.allDirty = true
+		return
+	}
+	// Protect against e.cur wraparound.
+	for e.cur >= bufferReset {
+		if len(e.hist) == 0 {
+			for i := range e.table[:] {
+				e.table[i] = tableEntry{}
+			}
+			e.cur = e.maxMatchOff
+			break
+		}
+		// Shift down everything in the table that isn't already too far away.
+		minOff := e.cur + int32(len(e.hist)) - e.maxMatchOff
+		for i := range e.table[:] {
+			v := e.table[i].offset
+			if v < minOff {
+				v = 0
+			} else {
+				v = v - e.cur + e.maxMatchOff
+			}
+			e.table[i].offset = v
+		}
+		e.cur = e.maxMatchOff
+		break
+	}
+
+	s := e.addBlock(src)
+	blk.size = len(src)
+	if len(src) < minNonLiteralBlockSize {
+		blk.extraLits = len(src)
+		blk.literals = blk.literals[:len(src)]
+		copy(blk.literals, src)
+		return
+	}
+
+	// Override src
+	src = e.hist
+	sLimit := int32(len(src)) - inputMargin
+	// stepSize is the number of bytes to skip on every main loop iteration.
+	// It should be >= 2.
+	const stepSize = 2
+
+	// TEMPLATE
+	const hashLog = tableBits
+	// seems global, but would be nice to tweak.
+	const kSearchStrength = 7
+
+	// nextEmit is where in src the next emitLiteral should start from.
+	nextEmit := s
+	cv := load6432(src, s)
+
+	// Relative offsets
+	offset1 := int32(blk.recentOffsets[0])
+	offset2 := int32(blk.recentOffsets[1])
+
+	addLiterals := func(s *seq, until int32) {
+		if until == nextEmit {
+			return
+		}
+		blk.literals = append(blk.literals, src[nextEmit:until]...)
+		s.litLen = uint32(until - nextEmit)
+	}
+	if debugEncoder {
+		println("recent offsets:", blk.recentOffsets)
+	}
+
+encodeLoop:
+	for {
+		// t will contain the match offset when we find one.
+		// When existing the search loop, we have already checked 4 bytes.
+		var t int32
+
+		// We will not use repeat offsets across blocks.
+		// By not using them for the first 3 matches
+		canRepeat := len(blk.sequences) > 2
+
+		for {
+			if debugAsserts && canRepeat && offset1 == 0 {
+				panic("offset0 was 0")
+			}
+
+			nextHash := hashLen(cv, hashLog, tableFastHashLen)
+			nextHash2 := hashLen(cv>>8, hashLog, tableFastHashLen)
+			candidate := e.table[nextHash]
+			candidate2 := e.table[nextHash2]
+			repIndex := s - offset1 + 2
+
+			e.table[nextHash] = tableEntry{offset: s + e.cur, val: uint32(cv)}
+			e.markShardDirty(nextHash)
+			e.table[nextHash2] = tableEntry{offset: s + e.cur + 1, val: uint32(cv >> 8)}
+			e.markShardDirty(nextHash2)
+
+			if canRepeat && repIndex >= 0 && load3232(src, repIndex) == uint32(cv>>16) {
+				// Consider history as well.
+				var seq seq
+				var length int32
+				length = 4 + e.matchlen(s+6, repIndex+4, src)
+
+				seq.matchLen = uint32(length - zstdMinMatch)
+
+				// We might be able to match backwards.
+				// Extend as long as we can.
+				start := s + 2
+				// We end the search early, so we don't risk 0 literals
+				// and have to do special offset treatment.
+				startLimit := nextEmit + 1
+
+				sMin := s - e.maxMatchOff
+				if sMin < 0 {
+					sMin = 0
+				}
+				for repIndex > sMin && start > startLimit && src[repIndex-1] == src[start-1] && seq.matchLen < maxMatchLength-zstdMinMatch {
+					repIndex--
+					start--
+					seq.matchLen++
+				}
+				addLiterals(&seq, start)
+
+				// rep 0
+				seq.offset = 1
+				if debugSequences {
+					println("repeat sequence", seq, "next s:", s)
+				}
+				blk.sequences = append(blk.sequences, seq)
+				s += length + 2
+				nextEmit = s
+				if s >= sLimit {
+					if debugEncoder {
+						println("repeat ended", s, length)
+
+					}
+					break encodeLoop
+				}
+				cv = load6432(src, s)
+				continue
+			}
+			coffset0 := s - (candidate.offset - e.cur)
+			coffset1 := s - (candidate2.offset - e.cur) + 1
+			if coffset0 < e.maxMatchOff && uint32(cv) == candidate.val {
+				// found a regular match
+				t = candidate.offset - e.cur
+				if debugAsserts && s <= t {
+					panic(fmt.Sprintf("s (%d) <= t (%d)", s, t))
+				}
+				if debugAsserts && s-t > e.maxMatchOff {
+					panic("s - t >e.maxMatchOff")
+				}
+				break
+			}
+
+			if coffset1 < e.maxMatchOff && uint32(cv>>8) == candidate2.val {
+				// found a regular match
+				t = candidate2.offset - e.cur
+				s++
+				if debugAsserts && s <= t {
+					panic(fmt.Sprintf("s (%d) <= t (%d)", s, t))
+				}
+				if debugAsserts && s-t > e.maxMatchOff {
+					panic("s - t >e.maxMatchOff")
+				}
+				if debugAsserts && t < 0 {
+					panic("t<0")
+				}
+				break
+			}
+			s += stepSize + ((s - nextEmit) >> (kSearchStrength - 1))
+			if s >= sLimit {
+				break encodeLoop
+			}
+			cv = load6432(src, s)
+		}
+		// A 4-byte match has been found. We'll later see if more than 4 bytes.
+		offset2 = offset1
+		offset1 = s - t
+
+		if debugAsserts && s <= t {
+			panic(fmt.Sprintf("s (%d) <= t (%d)", s, t))
+		}
+
+		if debugAsserts && canRepeat && int(offset1) > len(src) {
+			panic("invalid offset")
+		}
+
+		// Extend the 4-byte match as long as possible.
+		l := e.matchlen(s+4, t+4, src) + 4
+
+		// Extend backwards
+		tMin := s - e.maxMatchOff
+		if tMin < 0 {
+			tMin = 0
+		}
+		for t > tMin && s > nextEmit && src[t-1] == src[s-1] && l < maxMatchLength {
+			s--
+			t--
+			l++
+		}
+
+		// Write our sequence.
+		var seq seq
+		seq.litLen = uint32(s - nextEmit)
+		seq.matchLen = uint32(l - zstdMinMatch)
+		if seq.litLen > 0 {
+			blk.literals = append(blk.literals, src[nextEmit:s]...)
+		}
+		// Don't use repeat offsets
+		seq.offset = uint32(s-t) + 3
+		s += l
+		if debugSequences {
+			println("sequence", seq, "next s:", s)
+		}
+		blk.sequences = append(blk.sequences, seq)
+		nextEmit = s
+		if s >= sLimit {
+			break encodeLoop
+		}
+		cv = load6432(src, s)
+
+		// Check offset 2
+		if o2 := s - offset2; canRepeat && load3232(src, o2) == uint32(cv) {
+			// We have at least 4 byte match.
+			// No need to check backwards. We come straight from a match
+			l := 4 + e.matchlen(s+4, o2+4, src)
+
+			// Store this, since we have it.
+			nextHash := hashLen(cv, hashLog, tableFastHashLen)
+			e.table[nextHash] = tableEntry{offset: s + e.cur, val: uint32(cv)}
+			e.markShardDirty(nextHash)
+			seq.matchLen = uint32(l) - zstdMinMatch
+			seq.litLen = 0
+			// Since litlen is always 0, this is offset 1.
+			seq.offset = 1
+			s += l
+			nextEmit = s
+			if debugSequences {
+				println("sequence", seq, "next s:", s)
+			}
+			blk.sequences = append(blk.sequences, seq)
+
+			// Swap offset 1 and 2.
+			offset1, offset2 = offset2, offset1
+			if s >= sLimit {
+				break encodeLoop
+			}
+			// Prepare next loop.
+			cv = load6432(src, s)
+		}
+	}
+
+	if int(nextEmit) < len(src) {
+		blk.literals = append(blk.literals, src[nextEmit:]...)
+		blk.extraLits = len(src) - int(nextEmit)
+	}
+	blk.recentOffsets[0] = uint32(offset1)
+	blk.recentOffsets[1] = uint32(offset2)
+	if debugEncoder {
+		println("returning, recent offsets:", blk.recentOffsets, "extra literals:", blk.extraLits)
+	}
+}
+
+// ResetDict will reset and set a dictionary if not nil
+func (e *fastEncoder) Reset(d *dict, singleBlock bool) {
+	e.resetBase(d, singleBlock)
+	if d != nil {
+		panic("fastEncoder: Reset with dict")
+	}
+}
+
+// ResetDict will reset and set a dictionary if not nil
+func (e *fastEncoderDict) Reset(d *dict, singleBlock bool) {
+	e.resetBase(d, singleBlock)
+	if d == nil {
+		return
+	}
+
+	// Init or copy dict table
+	if len(e.dictTable) != len(e.table) || d.id != e.lastDictID {
+		if len(e.dictTable) != len(e.table) {
+			e.dictTable = make([]tableEntry, len(e.table))
+		}
+		if true {
+			end := e.maxMatchOff + int32(len(d.content)) - 8
+			for i := e.maxMatchOff; i < end; i += 3 {
+				const hashLog = tableBits
+
+				cv := load6432(d.content, i-e.maxMatchOff)
+				nextHash := hashLen(cv, hashLog, tableFastHashLen)      // 0 -> 5
+				nextHash1 := hashLen(cv>>8, hashLog, tableFastHashLen)  // 1 -> 6
+				nextHash2 := hashLen(cv>>16, hashLog, tableFastHashLen) // 2 -> 7
+				e.dictTable[nextHash] = tableEntry{
+					val:    uint32(cv),
+					offset: i,
+				}
+				e.dictTable[nextHash1] = tableEntry{
+					val:    uint32(cv >> 8),
+					offset: i + 1,
+				}
+				e.dictTable[nextHash2] = tableEntry{
+					val:    uint32(cv >> 16),
+					offset: i + 2,
+				}
+			}
+		}
+		e.lastDictID = d.id
+		e.allDirty = true
+	}
+
+	e.cur = e.maxMatchOff
+	dirtyShardCnt := 0
+	if !e.allDirty {
+		for i := range e.tableShardDirty {
+			if e.tableShardDirty[i] {
+				dirtyShardCnt++
+			}
+		}
+	}
+
+	const shardCnt = tableShardCnt
+	const shardSize = tableShardSize
+	if e.allDirty || dirtyShardCnt > shardCnt*4/6 {
+		copy(e.table[:], e.dictTable)
+		for i := range e.tableShardDirty {
+			e.tableShardDirty[i] = false
+		}
+		e.allDirty = false
+		return
+	}
+	for i := range e.tableShardDirty {
+		if !e.tableShardDirty[i] {
+			continue
+		}
+
+		copy(e.table[i*shardSize:(i+1)*shardSize], e.dictTable[i*shardSize:(i+1)*shardSize])
+		e.tableShardDirty[i] = false
+	}
+	e.allDirty = false
+}
+
+func (e *fastEncoderDict) markAllShardsDirty() {
+	e.allDirty = true
+}
+
+func (e *fastEncoderDict) markShardDirty(entryNum uint32) {
+	e.tableShardDirty[entryNum/tableShardSize] = true
+}

vendor/github.com/klauspost/compress/zstd/encoder.go

@@ -0,0 +1,599 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+import (
+	"crypto/rand"
+	"fmt"
+	"io"
+	rdebug "runtime/debug"
+	"sync"
+
+	"github.com/klauspost/compress/zstd/internal/xxhash"
+)
+
+// Encoder provides encoding to Zstandard.
+// An Encoder can be used for either compressing a stream via the
+// io.WriteCloser interface supported by the Encoder or as multiple independent
+// tasks via the EncodeAll function.
+// Smaller encodes are encouraged to use the EncodeAll function.
+// Use NewWriter to create a new instance.
+type Encoder struct {
+	o        encoderOptions
+	encoders chan encoder
+	state    encoderState
+	init     sync.Once
+}
+
+type encoder interface {
+	Encode(blk *blockEnc, src []byte)
+	EncodeNoHist(blk *blockEnc, src []byte)
+	Block() *blockEnc
+	CRC() *xxhash.Digest
+	AppendCRC([]byte) []byte
+	WindowSize(size int64) int32
+	UseBlock(*blockEnc)
+	Reset(d *dict, singleBlock bool)
+}
+
+type encoderState struct {
+	w                io.Writer
+	filling          []byte
+	current          []byte
+	previous         []byte
+	encoder          encoder
+	writing          *blockEnc
+	err              error
+	writeErr         error
+	nWritten         int64
+	nInput           int64
+	frameContentSize int64
+	headerWritten    bool
+	eofWritten       bool
+	fullFrameWritten bool
+
+	// This waitgroup indicates an encode is running.
+	wg sync.WaitGroup
+	// This waitgroup indicates we have a block encoding/writing.
+	wWg sync.WaitGroup
+}
+
+// NewWriter will create a new Zstandard encoder.
+// If the encoder will be used for encoding blocks a nil writer can be used.
+func NewWriter(w io.Writer, opts ...EOption) (*Encoder, error) {
+	initPredefined()
+	var e Encoder
+	e.o.setDefault()
+	for _, o := range opts {
+		err := o(&e.o)
+		if err != nil {
+			return nil, err
+		}
+	}
+	if w != nil {
+		e.Reset(w)
+	}
+	return &e, nil
+}
+
+func (e *Encoder) initialize() {
+	if e.o.concurrent == 0 {
+		e.o.setDefault()
+	}
+	e.encoders = make(chan encoder, e.o.concurrent)
+	for i := 0; i < e.o.concurrent; i++ {
+		enc := e.o.encoder()
+		e.encoders <- enc
+	}
+}
+
+// Reset will re-initialize the writer and new writes will encode to the supplied writer
+// as a new, independent stream.
+func (e *Encoder) Reset(w io.Writer) {
+	s := &e.state
+	s.wg.Wait()
+	s.wWg.Wait()
+	if cap(s.filling) == 0 {
+		s.filling = make([]byte, 0, e.o.blockSize)
+	}
+	if cap(s.current) == 0 {
+		s.current = make([]byte, 0, e.o.blockSize)
+	}
+	if cap(s.previous) == 0 {
+		s.previous = make([]byte, 0, e.o.blockSize)
+	}
+	if s.encoder == nil {
+		s.encoder = e.o.encoder()
+	}
+	if s.writing == nil {
+		s.writing = &blockEnc{lowMem: e.o.lowMem}
+		s.writing.init()
+	}
+	s.writing.initNewEncode()
+	s.filling = s.filling[:0]
+	s.current = s.current[:0]
+	s.previous = s.previous[:0]
+	s.encoder.Reset(e.o.dict, false)
+	s.headerWritten = false
+	s.eofWritten = false
+	s.fullFrameWritten = false
+	s.w = w
+	s.err = nil
+	s.nWritten = 0
+	s.nInput = 0
+	s.writeErr = nil
+	s.frameContentSize = 0
+}
+
+// ResetContentSize will reset and set a content size for the next stream.
+// If the bytes written does not match the size given an error will be returned
+// when calling Close().
+// This is removed when Reset is called.
+// Sizes <= 0 results in no content size set.
+func (e *Encoder) ResetContentSize(w io.Writer, size int64) {
+	e.Reset(w)
+	if size >= 0 {
+		e.state.frameContentSize = size
+	}
+}
+
+// Write data to the encoder.
+// Input data will be buffered and as the buffer fills up
+// content will be compressed and written to the output.
+// When done writing, use Close to flush the remaining output
+// and write CRC if requested.
+func (e *Encoder) Write(p []byte) (n int, err error) {
+	s := &e.state
+	for len(p) > 0 {
+		if len(p)+len(s.filling) < e.o.blockSize {
+			if e.o.crc {
+				_, _ = s.encoder.CRC().Write(p)
+			}
+			s.filling = append(s.filling, p...)
+			return n + len(p), nil
+		}
+		add := p
+		if len(p)+len(s.filling) > e.o.blockSize {
+			add = add[:e.o.blockSize-len(s.filling)]
+		}
+		if e.o.crc {
+			_, _ = s.encoder.CRC().Write(add)
+		}
+		s.filling = append(s.filling, add...)
+		p = p[len(add):]
+		n += len(add)
+		if len(s.filling) < e.o.blockSize {
+			return n, nil
+		}
+		err := e.nextBlock(false)
+		if err != nil {
+			return n, err
+		}
+		if debugAsserts && len(s.filling) > 0 {
+			panic(len(s.filling))
+		}
+	}
+	return n, nil
+}
+
+// nextBlock will synchronize and start compressing input in e.state.filling.
+// If an error has occurred during encoding it will be returned.
+func (e *Encoder) nextBlock(final bool) error {
+	s := &e.state
+	// Wait for current block.
+	s.wg.Wait()
+	if s.err != nil {
+		return s.err
+	}
+	if len(s.filling) > e.o.blockSize {
+		return fmt.Errorf("block > maxStoreBlockSize")
+	}
+	if !s.headerWritten {
+		// If we have a single block encode, do a sync compression.
+		if final && len(s.filling) == 0 && !e.o.fullZero {
+			s.headerWritten = true
+			s.fullFrameWritten = true
+			s.eofWritten = true
+			return nil
+		}
+		if final && len(s.filling) > 0 {
+			s.current = e.EncodeAll(s.filling, s.current[:0])
+			var n2 int
+			n2, s.err = s.w.Write(s.current)
+			if s.err != nil {
+				return s.err
+			}
+			s.nWritten += int64(n2)
+			s.nInput += int64(len(s.filling))
+			s.current = s.current[:0]
+			s.filling = s.filling[:0]
+			s.headerWritten = true
+			s.fullFrameWritten = true
+			s.eofWritten = true
+			return nil
+		}
+
+		var tmp [maxHeaderSize]byte
+		fh := frameHeader{
+			ContentSize:   uint64(s.frameContentSize),
+			WindowSize:    uint32(s.encoder.WindowSize(s.frameContentSize)),
+			SingleSegment: false,
+			Checksum:      e.o.crc,
+			DictID:        e.o.dict.ID(),
+		}
+
+		dst, err := fh.appendTo(tmp[:0])
+		if err != nil {
+			return err
+		}
+		s.headerWritten = true
+		s.wWg.Wait()
+		var n2 int
+		n2, s.err = s.w.Write(dst)
+		if s.err != nil {
+			return s.err
+		}
+		s.nWritten += int64(n2)
+	}
+	if s.eofWritten {
+		// Ensure we only write it once.
+		final = false
+	}
+
+	if len(s.filling) == 0 {
+		// Final block, but no data.
+		if final {
+			enc := s.encoder
+			blk := enc.Block()
+			blk.reset(nil)
+			blk.last = true
+			blk.encodeRaw(nil)
+			s.wWg.Wait()
+			_, s.err = s.w.Write(blk.output)
+			s.nWritten += int64(len(blk.output))
+			s.eofWritten = true
+		}
+		return s.err
+	}
+
+	// Move blocks forward.
+	s.filling, s.current, s.previous = s.previous[:0], s.filling, s.current
+	s.nInput += int64(len(s.current))
+	s.wg.Add(1)
+	go func(src []byte) {
+		if debugEncoder {
+			println("Adding block,", len(src), "bytes, final:", final)
+		}
+		defer func() {
+			if r := recover(); r != nil {
+				s.err = fmt.Errorf("panic while encoding: %v", r)
+				rdebug.PrintStack()
+			}
+			s.wg.Done()
+		}()
+		enc := s.encoder
+		blk := enc.Block()
+		enc.Encode(blk, src)
+		blk.last = final
+		if final {
+			s.eofWritten = true
+		}
+		// Wait for pending writes.
+		s.wWg.Wait()
+		if s.writeErr != nil {
+			s.err = s.writeErr
+			return
+		}
+		// Transfer encoders from previous write block.
+		blk.swapEncoders(s.writing)
+		// Transfer recent offsets to next.
+		enc.UseBlock(s.writing)
+		s.writing = blk
+		s.wWg.Add(1)
+		go func() {
+			defer func() {
+				if r := recover(); r != nil {
+					s.writeErr = fmt.Errorf("panic while encoding/writing: %v", r)
+					rdebug.PrintStack()
+				}
+				s.wWg.Done()
+			}()
+			err := errIncompressible
+			// If we got the exact same number of literals as input,
+			// assume the literals cannot be compressed.
+			if len(src) != len(blk.literals) || len(src) != e.o.blockSize {
+				err = blk.encode(src, e.o.noEntropy, !e.o.allLitEntropy)
+			}
+			switch err {
+			case errIncompressible:
+				if debugEncoder {
+					println("Storing incompressible block as raw")
+				}
+				blk.encodeRaw(src)
+				// In fast mode, we do not transfer offsets, so we don't have to deal with changing the.
+			case nil:
+			default:
+				s.writeErr = err
+				return
+			}
+			_, s.writeErr = s.w.Write(blk.output)
+			s.nWritten += int64(len(blk.output))
+		}()
+	}(s.current)
+	return nil
+}
+
+// ReadFrom reads data from r until EOF or error.
+// The return value n is the number of bytes read.
+// Any error except io.EOF encountered during the read is also returned.
+//
+// The Copy function uses ReaderFrom if available.
+func (e *Encoder) ReadFrom(r io.Reader) (n int64, err error) {
+	if debugEncoder {
+		println("Using ReadFrom")
+	}
+
+	// Flush any current writes.
+	if len(e.state.filling) > 0 {
+		if err := e.nextBlock(false); err != nil {
+			return 0, err
+		}
+	}
+	e.state.filling = e.state.filling[:e.o.blockSize]
+	src := e.state.filling
+	for {
+		n2, err := r.Read(src)
+		if e.o.crc {
+			_, _ = e.state.encoder.CRC().Write(src[:n2])
+		}
+		// src is now the unfilled part...
+		src = src[n2:]
+		n += int64(n2)
+		switch err {
+		case io.EOF:
+			e.state.filling = e.state.filling[:len(e.state.filling)-len(src)]
+			if debugEncoder {
+				println("ReadFrom: got EOF final block:", len(e.state.filling))
+			}
+			return n, nil
+		case nil:
+		default:
+			if debugEncoder {
+				println("ReadFrom: got error:", err)
+			}
+			e.state.err = err
+			return n, err
+		}
+		if len(src) > 0 {
+			if debugEncoder {
+				println("ReadFrom: got space left in source:", len(src))
+			}
+			continue
+		}
+		err = e.nextBlock(false)
+		if err != nil {
+			return n, err
+		}
+		e.state.filling = e.state.filling[:e.o.blockSize]
+		src = e.state.filling
+	}
+}
+
+// Flush will send the currently written data to output
+// and block until everything has been written.
+// This should only be used on rare occasions where pushing the currently queued data is critical.
+func (e *Encoder) Flush() error {
+	s := &e.state
+	if len(s.filling) > 0 {
+		err := e.nextBlock(false)
+		if err != nil {
+			return err
+		}
+	}
+	s.wg.Wait()
+	s.wWg.Wait()
+	if s.err != nil {
+		return s.err
+	}
+	return s.writeErr
+}
+
+// Close will flush the final output and close the stream.
+// The function will block until everything has been written.
+// The Encoder can still be re-used after calling this.
+func (e *Encoder) Close() error {
+	s := &e.state
+	if s.encoder == nil {
+		return nil
+	}
+	err := e.nextBlock(true)
+	if err != nil {
+		return err
+	}
+	if s.frameContentSize > 0 {
+		if s.nInput != s.frameContentSize {
+			return fmt.Errorf("frame content size %d given, but %d bytes was written", s.frameContentSize, s.nInput)
+		}
+	}
+	if e.state.fullFrameWritten {
+		return s.err
+	}
+	s.wg.Wait()
+	s.wWg.Wait()
+
+	if s.err != nil {
+		return s.err
+	}
+	if s.writeErr != nil {
+		return s.writeErr
+	}
+
+	// Write CRC
+	if e.o.crc && s.err == nil {
+		// heap alloc.
+		var tmp [4]byte
+		_, s.err = s.w.Write(s.encoder.AppendCRC(tmp[:0]))
+		s.nWritten += 4
+	}
+
+	// Add padding with content from crypto/rand.Reader
+	if s.err == nil && e.o.pad > 0 {
+		add := calcSkippableFrame(s.nWritten, int64(e.o.pad))
+		frame, err := skippableFrame(s.filling[:0], add, rand.Reader)
+		if err != nil {
+			return err
+		}
+		_, s.err = s.w.Write(frame)
+	}
+	return s.err
+}
+
+// EncodeAll will encode all input in src and append it to dst.
+// This function can be called concurrently, but each call will only run on a single goroutine.
+// If empty input is given, nothing is returned, unless WithZeroFrames is specified.
+// Encoded blocks can be concatenated and the result will be the combined input stream.
+// Data compressed with EncodeAll can be decoded with the Decoder,
+// using either a stream or DecodeAll.
+func (e *Encoder) EncodeAll(src, dst []byte) []byte {
+	if len(src) == 0 {
+		if e.o.fullZero {
+			// Add frame header.
+			fh := frameHeader{
+				ContentSize:   0,
+				WindowSize:    MinWindowSize,
+				SingleSegment: true,
+				// Adding a checksum would be a waste of space.
+				Checksum: false,
+				DictID:   0,
+			}
+			dst, _ = fh.appendTo(dst)
+
+			// Write raw block as last one only.
+			var blk blockHeader
+			blk.setSize(0)
+			blk.setType(blockTypeRaw)
+			blk.setLast(true)
+			dst = blk.appendTo(dst)
+		}
+		return dst
+	}
+	e.init.Do(e.initialize)
+	enc := <-e.encoders
+	defer func() {
+		// Release encoder reference to last block.
+		// If a non-single block is needed the encoder will reset again.
+		e.encoders <- enc
+	}()
+	// Use single segments when above minimum window and below 1MB.
+	single := len(src) < 1<<20 && len(src) > MinWindowSize
+	if e.o.single != nil {
+		single = *e.o.single
+	}
+	fh := frameHeader{
+		ContentSize:   uint64(len(src)),
+		WindowSize:    uint32(enc.WindowSize(int64(len(src)))),
+		SingleSegment: single,
+		Checksum:      e.o.crc,
+		DictID:        e.o.dict.ID(),
+	}
+
+	// If less than 1MB, allocate a buffer up front.
+	if len(dst) == 0 && cap(dst) == 0 && len(src) < 1<<20 && !e.o.lowMem {
+		dst = make([]byte, 0, len(src))
+	}
+	dst, err := fh.appendTo(dst)
+	if err != nil {
+		panic(err)
+	}
+
+	// If we can do everything in one block, prefer that.
+	if len(src) <= maxCompressedBlockSize {
+		enc.Reset(e.o.dict, true)
+		// Slightly faster with no history and everything in one block.
+		if e.o.crc {
+			_, _ = enc.CRC().Write(src)
+		}
+		blk := enc.Block()
+		blk.last = true
+		if e.o.dict == nil {
+			enc.EncodeNoHist(blk, src)
+		} else {
+			enc.Encode(blk, src)
+		}
+
+		// If we got the exact same number of literals as input,
+		// assume the literals cannot be compressed.
+		err := errIncompressible
+		oldout := blk.output
+		if len(blk.literals) != len(src) || len(src) != e.o.blockSize {
+			// Output directly to dst
+			blk.output = dst
+			err = blk.encode(src, e.o.noEntropy, !e.o.allLitEntropy)
+		}
+
+		switch err {
+		case errIncompressible:
+			if debugEncoder {
+				println("Storing incompressible block as raw")
+			}
+			dst = blk.encodeRawTo(dst, src)
+		case nil:
+			dst = blk.output
+		default:
+			panic(err)
+		}
+		blk.output = oldout
+	} else {
+		enc.Reset(e.o.dict, false)
+		blk := enc.Block()
+		for len(src) > 0 {
+			todo := src
+			if len(todo) > e.o.blockSize {
+				todo = todo[:e.o.blockSize]
+			}
+			src = src[len(todo):]
+			if e.o.crc {
+				_, _ = enc.CRC().Write(todo)
+			}
+			blk.pushOffsets()
+			enc.Encode(blk, todo)
+			if len(src) == 0 {
+				blk.last = true
+			}
+			err := errIncompressible
+			// If we got the exact same number of literals as input,
+			// assume the literals cannot be compressed.
+			if len(blk.literals) != len(todo) || len(todo) != e.o.blockSize {
+				err = blk.encode(todo, e.o.noEntropy, !e.o.allLitEntropy)
+			}
+
+			switch err {
+			case errIncompressible:
+				if debugEncoder {
+					println("Storing incompressible block as raw")
+				}
+				dst = blk.encodeRawTo(dst, todo)
+				blk.popOffsets()
+			case nil:
+				dst = append(dst, blk.output...)
+			default:
+				panic(err)
+			}
+			blk.reset(nil)
+		}
+	}
+	if e.o.crc {
+		dst = enc.AppendCRC(dst)
+	}
+	// Add padding with content from crypto/rand.Reader
+	if e.o.pad > 0 {
+		add := calcSkippableFrame(int64(len(dst)), int64(e.o.pad))
+		dst, err = skippableFrame(dst, add, rand.Reader)
+		if err != nil {
+			panic(err)
+		}
+	}
+	return dst
+}

vendor/github.com/klauspost/compress/zstd/encoder_options.go

@@ -0,0 +1,312 @@
+package zstd
+
+import (
+	"errors"
+	"fmt"
+	"runtime"
+	"strings"
+)
+
+// EOption is an option for creating a encoder.
+type EOption func(*encoderOptions) error
+
+// options retains accumulated state of multiple options.
+type encoderOptions struct {
+	concurrent      int
+	level           EncoderLevel
+	single          *bool
+	pad             int
+	blockSize       int
+	windowSize      int
+	crc             bool
+	fullZero        bool
+	noEntropy       bool
+	allLitEntropy   bool
+	customWindow    bool
+	customALEntropy bool
+	lowMem          bool
+	dict            *dict
+}
+
+func (o *encoderOptions) setDefault() {
+	*o = encoderOptions{
+		concurrent:    runtime.GOMAXPROCS(0),
+		crc:           true,
+		single:        nil,
+		blockSize:     1 << 16,
+		windowSize:    8 << 20,
+		level:         SpeedDefault,
+		allLitEntropy: true,
+		lowMem:        false,
+	}
+}
+
+// encoder returns an encoder with the selected options.
+func (o encoderOptions) encoder() encoder {
+	switch o.level {
+	case SpeedFastest:
+		if o.dict != nil {
+			return &fastEncoderDict{fastEncoder: fastEncoder{fastBase: fastBase{maxMatchOff: int32(o.windowSize), lowMem: o.lowMem}}}
+		}
+		return &fastEncoder{fastBase: fastBase{maxMatchOff: int32(o.windowSize), lowMem: o.lowMem}}
+
+	case SpeedDefault:
+		if o.dict != nil {
+			return &doubleFastEncoderDict{fastEncoderDict: fastEncoderDict{fastEncoder: fastEncoder{fastBase: fastBase{maxMatchOff: int32(o.windowSize), lowMem: o.lowMem}}}}
+		}
+		return &doubleFastEncoder{fastEncoder: fastEncoder{fastBase: fastBase{maxMatchOff: int32(o.windowSize), lowMem: o.lowMem}}}
+	case SpeedBetterCompression:
+		if o.dict != nil {
+			return &betterFastEncoderDict{betterFastEncoder: betterFastEncoder{fastBase: fastBase{maxMatchOff: int32(o.windowSize), lowMem: o.lowMem}}}
+		}
+		return &betterFastEncoder{fastBase: fastBase{maxMatchOff: int32(o.windowSize), lowMem: o.lowMem}}
+	case SpeedBestCompression:
+		return &bestFastEncoder{fastBase: fastBase{maxMatchOff: int32(o.windowSize), lowMem: o.lowMem}}
+	}
+	panic("unknown compression level")
+}
+
+// WithEncoderCRC will add CRC value to output.
+// Output will be 4 bytes larger.
+func WithEncoderCRC(b bool) EOption {
+	return func(o *encoderOptions) error { o.crc = b; return nil }
+}
+
+// WithEncoderConcurrency will set the concurrency,
+// meaning the maximum number of encoders to run concurrently.
+// The value supplied must be at least 1.
+// By default this will be set to GOMAXPROCS.
+func WithEncoderConcurrency(n int) EOption {
+	return func(o *encoderOptions) error {
+		if n <= 0 {
+			return fmt.Errorf("concurrency must be at least 1")
+		}
+		o.concurrent = n
+		return nil
+	}
+}
+
+// WithWindowSize will set the maximum allowed back-reference distance.
+// The value must be a power of two between MinWindowSize and MaxWindowSize.
+// A larger value will enable better compression but allocate more memory and,
+// for above-default values, take considerably longer.
+// The default value is determined by the compression level.
+func WithWindowSize(n int) EOption {
+	return func(o *encoderOptions) error {
+		switch {
+		case n < MinWindowSize:
+			return fmt.Errorf("window size must be at least %d", MinWindowSize)
+		case n > MaxWindowSize:
+			return fmt.Errorf("window size must be at most %d", MaxWindowSize)
+		case (n & (n - 1)) != 0:
+			return errors.New("window size must be a power of 2")
+		}
+
+		o.windowSize = n
+		o.customWindow = true
+		if o.blockSize > o.windowSize {
+			o.blockSize = o.windowSize
+		}
+		return nil
+	}
+}
+
+// WithEncoderPadding will add padding to all output so the size will be a multiple of n.
+// This can be used to obfuscate the exact output size or make blocks of a certain size.
+// The contents will be a skippable frame, so it will be invisible by the decoder.
+// n must be > 0 and <= 1GB, 1<<30 bytes.
+// The padded area will be filled with data from crypto/rand.Reader.
+// If `EncodeAll` is used with data already in the destination, the total size will be multiple of this.
+func WithEncoderPadding(n int) EOption {
+	return func(o *encoderOptions) error {
+		if n <= 0 {
+			return fmt.Errorf("padding must be at least 1")
+		}
+		// No need to waste our time.
+		if n == 1 {
+			o.pad = 0
+		}
+		if n > 1<<30 {
+			return fmt.Errorf("padding must less than 1GB (1<<30 bytes) ")
+		}
+		o.pad = n
+		return nil
+	}
+}
+
+// EncoderLevel predefines encoder compression levels.
+// Only use the constants made available, since the actual mapping
+// of these values are very likely to change and your compression could change
+// unpredictably when upgrading the library.
+type EncoderLevel int
+
+const (
+	speedNotSet EncoderLevel = iota
+
+	// SpeedFastest will choose the fastest reasonable compression.
+	// This is roughly equivalent to the fastest Zstandard mode.
+	SpeedFastest
+
+	// SpeedDefault is the default "pretty fast" compression option.
+	// This is roughly equivalent to the default Zstandard mode (level 3).
+	SpeedDefault
+
+	// SpeedBetterCompression will yield better compression than the default.
+	// Currently it is about zstd level 7-8 with ~ 2x-3x the default CPU usage.
+	// By using this, notice that CPU usage may go up in the future.
+	SpeedBetterCompression
+
+	// SpeedBestCompression will choose the best available compression option.
+	// This will offer the best compression no matter the CPU cost.
+	SpeedBestCompression
+
+	// speedLast should be kept as the last actual compression option.
+	// The is not for external usage, but is used to keep track of the valid options.
+	speedLast
+)
+
+// EncoderLevelFromString will convert a string representation of an encoding level back
+// to a compression level. The compare is not case sensitive.
+// If the string wasn't recognized, (false, SpeedDefault) will be returned.
+func EncoderLevelFromString(s string) (bool, EncoderLevel) {
+	for l := speedNotSet + 1; l < speedLast; l++ {
+		if strings.EqualFold(s, l.String()) {
+			return true, l
+		}
+	}
+	return false, SpeedDefault
+}
+
+// EncoderLevelFromZstd will return an encoder level that closest matches the compression
+// ratio of a specific zstd compression level.
+// Many input values will provide the same compression level.
+func EncoderLevelFromZstd(level int) EncoderLevel {
+	switch {
+	case level < 3:
+		return SpeedFastest
+	case level >= 3 && level < 6:
+		return SpeedDefault
+	case level >= 6 && level < 10:
+		return SpeedBetterCompression
+	case level >= 10:
+		return SpeedBestCompression
+	}
+	return SpeedDefault
+}
+
+// String provides a string representation of the compression level.
+func (e EncoderLevel) String() string {
+	switch e {
+	case SpeedFastest:
+		return "fastest"
+	case SpeedDefault:
+		return "default"
+	case SpeedBetterCompression:
+		return "better"
+	case SpeedBestCompression:
+		return "best"
+	default:
+		return "invalid"
+	}
+}
+
+// WithEncoderLevel specifies a predefined compression level.
+func WithEncoderLevel(l EncoderLevel) EOption {
+	return func(o *encoderOptions) error {
+		switch {
+		case l <= speedNotSet || l >= speedLast:
+			return fmt.Errorf("unknown encoder level")
+		}
+		o.level = l
+		if !o.customWindow {
+			switch o.level {
+			case SpeedFastest:
+				o.windowSize = 4 << 20
+			case SpeedDefault:
+				o.windowSize = 8 << 20
+			case SpeedBetterCompression:
+				o.windowSize = 16 << 20
+			case SpeedBestCompression:
+				o.windowSize = 32 << 20
+			}
+		}
+		if !o.customALEntropy {
+			o.allLitEntropy = l > SpeedFastest
+		}
+
+		return nil
+	}
+}
+
+// WithZeroFrames will encode 0 length input as full frames.
+// This can be needed for compatibility with zstandard usage,
+// but is not needed for this package.
+func WithZeroFrames(b bool) EOption {
+	return func(o *encoderOptions) error {
+		o.fullZero = b
+		return nil
+	}
+}
+
+// WithAllLitEntropyCompression will apply entropy compression if no matches are found.
+// Disabling this will skip incompressible data faster, but in cases with no matches but
+// skewed character distribution compression is lost.
+// Default value depends on the compression level selected.
+func WithAllLitEntropyCompression(b bool) EOption {
+	return func(o *encoderOptions) error {
+		o.customALEntropy = true
+		o.allLitEntropy = b
+		return nil
+	}
+}
+
+// WithNoEntropyCompression will always skip entropy compression of literals.
+// This can be useful if content has matches, but unlikely to benefit from entropy
+// compression. Usually the slight speed improvement is not worth enabling this.
+func WithNoEntropyCompression(b bool) EOption {
+	return func(o *encoderOptions) error {
+		o.noEntropy = b
+		return nil
+	}
+}
+
+// WithSingleSegment will set the "single segment" flag when EncodeAll is used.
+// If this flag is set, data must be regenerated within a single continuous memory segment.
+// In this case, Window_Descriptor byte is skipped, but Frame_Content_Size is necessarily present.
+// As a consequence, the decoder must allocate a memory segment of size equal or larger than size of your content.
+// In order to preserve the decoder from unreasonable memory requirements,
+// a decoder is allowed to reject a compressed frame which requests a memory size beyond decoder's authorized range.
+// For broader compatibility, decoders are recommended to support memory sizes of at least 8 MB.
+// This is only a recommendation, each decoder is free to support higher or lower limits, depending on local limitations.
+// If this is not specified, block encodes will automatically choose this based on the input size.
+// This setting has no effect on streamed encodes.
+func WithSingleSegment(b bool) EOption {
+	return func(o *encoderOptions) error {
+		o.single = &b
+		return nil
+	}
+}
+
+// WithLowerEncoderMem will trade in some memory cases trade less memory usage for
+// slower encoding speed.
+// This will not change the window size which is the primary function for reducing
+// memory usage. See WithWindowSize.
+func WithLowerEncoderMem(b bool) EOption {
+	return func(o *encoderOptions) error {
+		o.lowMem = b
+		return nil
+	}
+}
+
+// WithEncoderDict allows to register a dictionary that will be used for the encode.
+// The encoder *may* choose to use no dictionary instead for certain payloads.
+func WithEncoderDict(dict []byte) EOption {
+	return func(o *encoderOptions) error {
+		d, err := loadDict(dict)
+		if err != nil {
+			return err
+		}
+		o.dict = d
+		return nil
+	}
+}

vendor/github.com/klauspost/compress/zstd/framedec.go

@@ -0,0 +1,521 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+import (
+	"bytes"
+	"encoding/hex"
+	"errors"
+	"hash"
+	"io"
+	"sync"
+
+	"github.com/klauspost/compress/zstd/internal/xxhash"
+)
+
+type frameDec struct {
+	o      decoderOptions
+	crc    hash.Hash64
+	offset int64
+
+	WindowSize uint64
+
+	// In order queue of blocks being decoded.
+	decoding chan *blockDec
+
+	// Frame history passed between blocks
+	history history
+
+	rawInput byteBuffer
+
+	// Byte buffer that can be reused for small input blocks.
+	bBuf byteBuf
+
+	FrameContentSize uint64
+	frameDone        sync.WaitGroup
+
+	DictionaryID  *uint32
+	HasCheckSum   bool
+	SingleSegment bool
+
+	// asyncRunning indicates whether the async routine processes input on 'decoding'.
+	asyncRunningMu sync.Mutex
+	asyncRunning   bool
+}
+
+const (
+	// MinWindowSize is the minimum Window Size, which is 1 KB.
+	MinWindowSize = 1 << 10
+
+	// MaxWindowSize is the maximum encoder window size
+	// and the default decoder maximum window size.
+	MaxWindowSize = 1 << 29
+)
+
+var (
+	frameMagic          = []byte{0x28, 0xb5, 0x2f, 0xfd}
+	skippableFrameMagic = []byte{0x2a, 0x4d, 0x18}
+)
+
+func newFrameDec(o decoderOptions) *frameDec {
+	if o.maxWindowSize > o.maxDecodedSize {
+		o.maxWindowSize = o.maxDecodedSize
+	}
+	d := frameDec{
+		o: o,
+	}
+	return &d
+}
+
+// reset will read the frame header and prepare for block decoding.
+// If nothing can be read from the input, io.EOF will be returned.
+// Any other error indicated that the stream contained data, but
+// there was a problem.
+func (d *frameDec) reset(br byteBuffer) error {
+	d.HasCheckSum = false
+	d.WindowSize = 0
+	var signature [4]byte
+	for {
+		var err error
+		// Check if we can read more...
+		b, err := br.readSmall(1)
+		switch err {
+		case io.EOF, io.ErrUnexpectedEOF:
+			return io.EOF
+		default:
+			return err
+		case nil:
+			signature[0] = b[0]
+		}
+		// Read the rest, don't allow io.ErrUnexpectedEOF
+		b, err = br.readSmall(3)
+		switch err {
+		case io.EOF:
+			return io.EOF
+		default:
+			return err
+		case nil:
+			copy(signature[1:], b)
+		}
+
+		if !bytes.Equal(signature[1:4], skippableFrameMagic) || signature[0]&0xf0 != 0x50 {
+			if debugDecoder {
+				println("Not skippable", hex.EncodeToString(signature[:]), hex.EncodeToString(skippableFrameMagic))
+			}
+			// Break if not skippable frame.
+			break
+		}
+		// Read size to skip
+		b, err = br.readSmall(4)
+		if err != nil {
+			if debugDecoder {
+				println("Reading Frame Size", err)
+			}
+			return err
+		}
+		n := uint32(b[0]) | (uint32(b[1]) << 8) | (uint32(b[2]) << 16) | (uint32(b[3]) << 24)
+		println("Skipping frame with", n, "bytes.")
+		err = br.skipN(int(n))
+		if err != nil {
+			if debugDecoder {
+				println("Reading discarded frame", err)
+			}
+			return err
+		}
+	}
+	if !bytes.Equal(signature[:], frameMagic) {
+		if debugDecoder {
+			println("Got magic numbers: ", signature, "want:", frameMagic)
+		}
+		return ErrMagicMismatch
+	}
+
+	// Read Frame_Header_Descriptor
+	fhd, err := br.readByte()
+	if err != nil {
+		if debugDecoder {
+			println("Reading Frame_Header_Descriptor", err)
+		}
+		return err
+	}
+	d.SingleSegment = fhd&(1<<5) != 0
+
+	if fhd&(1<<3) != 0 {
+		return errors.New("reserved bit set on frame header")
+	}
+
+	// Read Window_Descriptor
+	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#window_descriptor
+	d.WindowSize = 0
+	if !d.SingleSegment {
+		wd, err := br.readByte()
+		if err != nil {
+			if debugDecoder {
+				println("Reading Window_Descriptor", err)
+			}
+			return err
+		}
+		printf("raw: %x, mantissa: %d, exponent: %d\n", wd, wd&7, wd>>3)
+		windowLog := 10 + (wd >> 3)
+		windowBase := uint64(1) << windowLog
+		windowAdd := (windowBase / 8) * uint64(wd&0x7)
+		d.WindowSize = windowBase + windowAdd
+	}
+
+	// Read Dictionary_ID
+	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#dictionary_id
+	d.DictionaryID = nil
+	if size := fhd & 3; size != 0 {
+		if size == 3 {
+			size = 4
+		}
+
+		b, err := br.readSmall(int(size))
+		if err != nil {
+			println("Reading Dictionary_ID", err)
+			return err
+		}
+		var id uint32
+		switch size {
+		case 1:
+			id = uint32(b[0])
+		case 2:
+			id = uint32(b[0]) | (uint32(b[1]) << 8)
+		case 4:
+			id = uint32(b[0]) | (uint32(b[1]) << 8) | (uint32(b[2]) << 16) | (uint32(b[3]) << 24)
+		}
+		if debugDecoder {
+			println("Dict size", size, "ID:", id)
+		}
+		if id > 0 {
+			// ID 0 means "sorry, no dictionary anyway".
+			// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#dictionary-format
+			d.DictionaryID = &id
+		}
+	}
+
+	// Read Frame_Content_Size
+	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#frame_content_size
+	var fcsSize int
+	v := fhd >> 6
+	switch v {
+	case 0:
+		if d.SingleSegment {
+			fcsSize = 1
+		}
+	default:
+		fcsSize = 1 << v
+	}
+	d.FrameContentSize = 0
+	if fcsSize > 0 {
+		b, err := br.readSmall(fcsSize)
+		if err != nil {
+			println("Reading Frame content", err)
+			return err
+		}
+		switch fcsSize {
+		case 1:
+			d.FrameContentSize = uint64(b[0])
+		case 2:
+			// When FCS_Field_Size is 2, the offset of 256 is added.
+			d.FrameContentSize = uint64(b[0]) | (uint64(b[1]) << 8) + 256
+		case 4:
+			d.FrameContentSize = uint64(b[0]) | (uint64(b[1]) << 8) | (uint64(b[2]) << 16) | (uint64(b[3]) << 24)
+		case 8:
+			d1 := uint32(b[0]) | (uint32(b[1]) << 8) | (uint32(b[2]) << 16) | (uint32(b[3]) << 24)
+			d2 := uint32(b[4]) | (uint32(b[5]) << 8) | (uint32(b[6]) << 16) | (uint32(b[7]) << 24)
+			d.FrameContentSize = uint64(d1) | (uint64(d2) << 32)
+		}
+		if debugDecoder {
+			println("field size bits:", v, "fcsSize:", fcsSize, "FrameContentSize:", d.FrameContentSize, hex.EncodeToString(b[:fcsSize]), "singleseg:", d.SingleSegment, "window:", d.WindowSize)
+		}
+	}
+	// Move this to shared.
+	d.HasCheckSum = fhd&(1<<2) != 0
+	if d.HasCheckSum {
+		if d.crc == nil {
+			d.crc = xxhash.New()
+		}
+		d.crc.Reset()
+	}
+
+	if d.WindowSize == 0 && d.SingleSegment {
+		// We may not need window in this case.
+		d.WindowSize = d.FrameContentSize
+		if d.WindowSize < MinWindowSize {
+			d.WindowSize = MinWindowSize
+		}
+	}
+
+	if d.WindowSize > uint64(d.o.maxWindowSize) {
+		if debugDecoder {
+			printf("window size %d > max %d\n", d.WindowSize, d.o.maxWindowSize)
+		}
+		return ErrWindowSizeExceeded
+	}
+	// The minimum Window_Size is 1 KB.
+	if d.WindowSize < MinWindowSize {
+		if debugDecoder {
+			println("got window size: ", d.WindowSize)
+		}
+		return ErrWindowSizeTooSmall
+	}
+	d.history.windowSize = int(d.WindowSize)
+	if d.o.lowMem && d.history.windowSize < maxBlockSize {
+		d.history.maxSize = d.history.windowSize * 2
+	} else {
+		d.history.maxSize = d.history.windowSize + maxBlockSize
+	}
+	// history contains input - maybe we do something
+	d.rawInput = br
+	return nil
+}
+
+// next will start decoding the next block from stream.
+func (d *frameDec) next(block *blockDec) error {
+	if debugDecoder {
+		printf("decoding new block %p:%p", block, block.data)
+	}
+	err := block.reset(d.rawInput, d.WindowSize)
+	if err != nil {
+		println("block error:", err)
+		// Signal the frame decoder we have a problem.
+		d.sendErr(block, err)
+		return err
+	}
+	block.input <- struct{}{}
+	if debugDecoder {
+		println("next block:", block)
+	}
+	d.asyncRunningMu.Lock()
+	defer d.asyncRunningMu.Unlock()
+	if !d.asyncRunning {
+		return nil
+	}
+	if block.Last {
+		// We indicate the frame is done by sending io.EOF
+		d.decoding <- block
+		return io.EOF
+	}
+	d.decoding <- block
+	return nil
+}
+
+// sendEOF will queue an error block on the frame.
+// This will cause the frame decoder to return when it encounters the block.
+// Returns true if the decoder was added.
+func (d *frameDec) sendErr(block *blockDec, err error) bool {
+	d.asyncRunningMu.Lock()
+	defer d.asyncRunningMu.Unlock()
+	if !d.asyncRunning {
+		return false
+	}
+
+	println("sending error", err.Error())
+	block.sendErr(err)
+	d.decoding <- block
+	return true
+}
+
+// checkCRC will check the checksum if the frame has one.
+// Will return ErrCRCMismatch if crc check failed, otherwise nil.
+func (d *frameDec) checkCRC() error {
+	if !d.HasCheckSum {
+		return nil
+	}
+	var tmp [4]byte
+	got := d.crc.Sum64()
+	// Flip to match file order.
+	tmp[0] = byte(got >> 0)
+	tmp[1] = byte(got >> 8)
+	tmp[2] = byte(got >> 16)
+	tmp[3] = byte(got >> 24)
+
+	// We can overwrite upper tmp now
+	want, err := d.rawInput.readSmall(4)
+	if err != nil {
+		println("CRC missing?", err)
+		return err
+	}
+
+	if !bytes.Equal(tmp[:], want) {
+		if debugDecoder {
+			println("CRC Check Failed:", tmp[:], "!=", want)
+		}
+		return ErrCRCMismatch
+	}
+	if debugDecoder {
+		println("CRC ok", tmp[:])
+	}
+	return nil
+}
+
+func (d *frameDec) initAsync() {
+	if !d.o.lowMem && !d.SingleSegment {
+		// set max extra size history to 2MB.
+		d.history.maxSize = d.history.windowSize + maxBlockSize
+	}
+	// re-alloc if more than one extra block size.
+	if d.o.lowMem && cap(d.history.b) > d.history.maxSize+maxBlockSize {
+		d.history.b = make([]byte, 0, d.history.maxSize)
+	}
+	if cap(d.history.b) < d.history.maxSize {
+		d.history.b = make([]byte, 0, d.history.maxSize)
+	}
+	if cap(d.decoding) < d.o.concurrent {
+		d.decoding = make(chan *blockDec, d.o.concurrent)
+	}
+	if debugDecoder {
+		h := d.history
+		printf("history init. len: %d, cap: %d", len(h.b), cap(h.b))
+	}
+	d.asyncRunningMu.Lock()
+	d.asyncRunning = true
+	d.asyncRunningMu.Unlock()
+}
+
+// startDecoder will start decoding blocks and write them to the writer.
+// The decoder will stop as soon as an error occurs or at end of frame.
+// When the frame has finished decoding the *bufio.Reader
+// containing the remaining input will be sent on frameDec.frameDone.
+func (d *frameDec) startDecoder(output chan decodeOutput) {
+	written := int64(0)
+
+	defer func() {
+		d.asyncRunningMu.Lock()
+		d.asyncRunning = false
+		d.asyncRunningMu.Unlock()
+
+		// Drain the currently decoding.
+		d.history.error = true
+	flushdone:
+		for {
+			select {
+			case b := <-d.decoding:
+				b.history <- &d.history
+				output <- <-b.result
+			default:
+				break flushdone
+			}
+		}
+		println("frame decoder done, signalling done")
+		d.frameDone.Done()
+	}()
+	// Get decoder for first block.
+	block := <-d.decoding
+	block.history <- &d.history
+	for {
+		var next *blockDec
+		// Get result
+		r := <-block.result
+		if r.err != nil {
+			println("Result contained error", r.err)
+			output <- r
+			return
+		}
+		if debugDecoder {
+			println("got result, from ", d.offset, "to", d.offset+int64(len(r.b)))
+			d.offset += int64(len(r.b))
+		}
+		if !block.Last {
+			// Send history to next block
+			select {
+			case next = <-d.decoding:
+				if debugDecoder {
+					println("Sending ", len(d.history.b), "bytes as history")
+				}
+				next.history <- &d.history
+			default:
+				// Wait until we have sent the block, so
+				// other decoders can potentially get the decoder.
+				next = nil
+			}
+		}
+
+		// Add checksum, async to decoding.
+		if d.HasCheckSum {
+			n, err := d.crc.Write(r.b)
+			if err != nil {
+				r.err = err
+				if n != len(r.b) {
+					r.err = io.ErrShortWrite
+				}
+				output <- r
+				return
+			}
+		}
+		written += int64(len(r.b))
+		if d.SingleSegment && uint64(written) > d.FrameContentSize {
+			println("runDecoder: single segment and", uint64(written), ">", d.FrameContentSize)
+			r.err = ErrFrameSizeExceeded
+			output <- r
+			return
+		}
+		if block.Last {
+			r.err = d.checkCRC()
+			output <- r
+			return
+		}
+		output <- r
+		if next == nil {
+			// There was no decoder available, we wait for one now that we have sent to the writer.
+			if debugDecoder {
+				println("Sending ", len(d.history.b), " bytes as history")
+			}
+			next = <-d.decoding
+			next.history <- &d.history
+		}
+		block = next
+	}
+}
+
+// runDecoder will create a sync decoder that will decode a block of data.
+func (d *frameDec) runDecoder(dst []byte, dec *blockDec) ([]byte, error) {
+	saved := d.history.b
+
+	// We use the history for output to avoid copying it.
+	d.history.b = dst
+	// Store input length, so we only check new data.
+	crcStart := len(dst)
+	var err error
+	for {
+		err = dec.reset(d.rawInput, d.WindowSize)
+		if err != nil {
+			break
+		}
+		if debugDecoder {
+			println("next block:", dec)
+		}
+		err = dec.decodeBuf(&d.history)
+		if err != nil || dec.Last {
+			break
+		}
+		if uint64(len(d.history.b)) > d.o.maxDecodedSize {
+			err = ErrDecoderSizeExceeded
+			break
+		}
+		if d.SingleSegment && uint64(len(d.history.b)) > d.o.maxDecodedSize {
+			println("runDecoder: single segment and", uint64(len(d.history.b)), ">", d.o.maxDecodedSize)
+			err = ErrFrameSizeExceeded
+			break
+		}
+	}
+	dst = d.history.b
+	if err == nil {
+		if d.HasCheckSum {
+			var n int
+			n, err = d.crc.Write(dst[crcStart:])
+			if err == nil {
+				if n != len(dst)-crcStart {
+					err = io.ErrShortWrite
+				} else {
+					err = d.checkCRC()
+				}
+			}
+		}
+	}
+	d.history.b = saved
+	return dst, err
+}

vendor/github.com/klauspost/compress/zstd/frameenc.go

@@ -0,0 +1,137 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+	"math"
+	"math/bits"
+)
+
+type frameHeader struct {
+	ContentSize   uint64
+	WindowSize    uint32
+	SingleSegment bool
+	Checksum      bool
+	DictID        uint32
+}
+
+const maxHeaderSize = 14
+
+func (f frameHeader) appendTo(dst []byte) ([]byte, error) {
+	dst = append(dst, frameMagic...)
+	var fhd uint8
+	if f.Checksum {
+		fhd |= 1 << 2
+	}
+	if f.SingleSegment {
+		fhd |= 1 << 5
+	}
+
+	var dictIDContent []byte
+	if f.DictID > 0 {
+		var tmp [4]byte
+		if f.DictID < 256 {
+			fhd |= 1
+			tmp[0] = uint8(f.DictID)
+			dictIDContent = tmp[:1]
+		} else if f.DictID < 1<<16 {
+			fhd |= 2
+			binary.LittleEndian.PutUint16(tmp[:2], uint16(f.DictID))
+			dictIDContent = tmp[:2]
+		} else {
+			fhd |= 3
+			binary.LittleEndian.PutUint32(tmp[:4], f.DictID)
+			dictIDContent = tmp[:4]
+		}
+	}
+	var fcs uint8
+	if f.ContentSize >= 256 {
+		fcs++
+	}
+	if f.ContentSize >= 65536+256 {
+		fcs++
+	}
+	if f.ContentSize >= 0xffffffff {
+		fcs++
+	}
+
+	fhd |= fcs << 6
+
+	dst = append(dst, fhd)
+	if !f.SingleSegment {
+		const winLogMin = 10
+		windowLog := (bits.Len32(f.WindowSize-1) - winLogMin) << 3
+		dst = append(dst, uint8(windowLog))
+	}
+	if f.DictID > 0 {
+		dst = append(dst, dictIDContent...)
+	}
+	switch fcs {
+	case 0:
+		if f.SingleSegment {
+			dst = append(dst, uint8(f.ContentSize))
+		}
+		// Unless SingleSegment is set, framessizes < 256 are nto stored.
+	case 1:
+		f.ContentSize -= 256
+		dst = append(dst, uint8(f.ContentSize), uint8(f.ContentSize>>8))
+	case 2:
+		dst = append(dst, uint8(f.ContentSize), uint8(f.ContentSize>>8), uint8(f.ContentSize>>16), uint8(f.ContentSize>>24))
+	case 3:
+		dst = append(dst, uint8(f.ContentSize), uint8(f.ContentSize>>8), uint8(f.ContentSize>>16), uint8(f.ContentSize>>24),
+			uint8(f.ContentSize>>32), uint8(f.ContentSize>>40), uint8(f.ContentSize>>48), uint8(f.ContentSize>>56))
+	default:
+		panic("invalid fcs")
+	}
+	return dst, nil
+}
+
+const skippableFrameHeader = 4 + 4
+
+// calcSkippableFrame will return a total size to be added for written
+// to be divisible by multiple.
+// The value will always be > skippableFrameHeader.
+// The function will panic if written < 0 or wantMultiple <= 0.
+func calcSkippableFrame(written, wantMultiple int64) int {
+	if wantMultiple <= 0 {
+		panic("wantMultiple <= 0")
+	}
+	if written < 0 {
+		panic("written < 0")
+	}
+	leftOver := written % wantMultiple
+	if leftOver == 0 {
+		return 0
+	}
+	toAdd := wantMultiple - leftOver
+	for toAdd < skippableFrameHeader {
+		toAdd += wantMultiple
+	}
+	return int(toAdd)
+}
+
+// skippableFrame will add a skippable frame with a total size of bytes.
+// total should be >= skippableFrameHeader and < math.MaxUint32.
+func skippableFrame(dst []byte, total int, r io.Reader) ([]byte, error) {
+	if total == 0 {
+		return dst, nil
+	}
+	if total < skippableFrameHeader {
+		return dst, fmt.Errorf("requested skippable frame (%d) < 8", total)
+	}
+	if int64(total) > math.MaxUint32 {
+		return dst, fmt.Errorf("requested skippable frame (%d) > max uint32", total)
+	}
+	dst = append(dst, 0x50, 0x2a, 0x4d, 0x18)
+	f := uint32(total - skippableFrameHeader)
+	dst = append(dst, uint8(f), uint8(f>>8), uint8(f>>16), uint8(f>>24))
+	start := len(dst)
+	dst = append(dst, make([]byte, f)...)
+	_, err := io.ReadFull(r, dst[start:])
+	return dst, err
+}

vendor/github.com/klauspost/compress/zstd/fse_decoder.go

@@ -0,0 +1,385 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+import (
+	"errors"
+	"fmt"
+)
+
+const (
+	tablelogAbsoluteMax = 9
+)
+
+const (
+	/*!MEMORY_USAGE :
+	 *  Memory usage formula : N->2^N Bytes (examples : 10 -> 1KB; 12 -> 4KB ; 16 -> 64KB; 20 -> 1MB; etc.)
+	 *  Increasing memory usage improves compression ratio
+	 *  Reduced memory usage can improve speed, due to cache effect
+	 *  Recommended max value is 14, for 16KB, which nicely fits into Intel x86 L1 cache */
+	maxMemoryUsage = tablelogAbsoluteMax + 2
+
+	maxTableLog    = maxMemoryUsage - 2
+	maxTablesize   = 1 << maxTableLog
+	maxTableMask   = (1 << maxTableLog) - 1
+	minTablelog    = 5
+	maxSymbolValue = 255
+)
+
+// fseDecoder provides temporary storage for compression and decompression.
+type fseDecoder struct {
+	dt             [maxTablesize]decSymbol // Decompression table.
+	symbolLen      uint16                  // Length of active part of the symbol table.
+	actualTableLog uint8                   // Selected tablelog.
+	maxBits        uint8                   // Maximum number of additional bits
+
+	// used for table creation to avoid allocations.
+	stateTable [256]uint16
+	norm       [maxSymbolValue + 1]int16
+	preDefined bool
+}
+
+// tableStep returns the next table index.
+func tableStep(tableSize uint32) uint32 {
+	return (tableSize >> 1) + (tableSize >> 3) + 3
+}
+
+// readNCount will read the symbol distribution so decoding tables can be constructed.
+func (s *fseDecoder) readNCount(b *byteReader, maxSymbol uint16) error {
+	var (
+		charnum   uint16
+		previous0 bool
+	)
+	if b.remain() < 4 {
+		return errors.New("input too small")
+	}
+	bitStream := b.Uint32NC()
+	nbBits := uint((bitStream & 0xF) + minTablelog) // extract tableLog
+	if nbBits > tablelogAbsoluteMax {
+		println("Invalid tablelog:", nbBits)
+		return errors.New("tableLog too large")
+	}
+	bitStream >>= 4
+	bitCount := uint(4)
+
+	s.actualTableLog = uint8(nbBits)
+	remaining := int32((1 << nbBits) + 1)
+	threshold := int32(1 << nbBits)
+	gotTotal := int32(0)
+	nbBits++
+
+	for remaining > 1 && charnum <= maxSymbol {
+		if previous0 {
+			//println("prev0")
+			n0 := charnum
+			for (bitStream & 0xFFFF) == 0xFFFF {
+				//println("24 x 0")
+				n0 += 24
+				if r := b.remain(); r > 5 {
+					b.advance(2)
+					// The check above should make sure we can read 32 bits
+					bitStream = b.Uint32NC() >> bitCount
+				} else {
+					// end of bit stream
+					bitStream >>= 16
+					bitCount += 16
+				}
+			}
+			//printf("bitstream: %d, 0b%b", bitStream&3, bitStream)
+			for (bitStream & 3) == 3 {
+				n0 += 3
+				bitStream >>= 2
+				bitCount += 2
+			}
+			n0 += uint16(bitStream & 3)
+			bitCount += 2
+
+			if n0 > maxSymbolValue {
+				return errors.New("maxSymbolValue too small")
+			}
+			//println("inserting ", n0-charnum, "zeroes from idx", charnum, "ending before", n0)
+			for charnum < n0 {
+				s.norm[uint8(charnum)] = 0
+				charnum++
+			}
+
+			if r := b.remain(); r >= 7 || r-int(bitCount>>3) >= 4 {
+				b.advance(bitCount >> 3)
+				bitCount &= 7
+				// The check above should make sure we can read 32 bits
+				bitStream = b.Uint32NC() >> bitCount
+			} else {
+				bitStream >>= 2
+			}
+		}
+
+		max := (2*threshold - 1) - remaining
+		var count int32
+
+		if int32(bitStream)&(threshold-1) < max {
+			count = int32(bitStream) & (threshold - 1)
+			if debugAsserts && nbBits < 1 {
+				panic("nbBits underflow")
+			}
+			bitCount += nbBits - 1
+		} else {
+			count = int32(bitStream) & (2*threshold - 1)
+			if count >= threshold {
+				count -= max
+			}
+			bitCount += nbBits
+		}
+
+		// extra accuracy
+		count--
+		if count < 0 {
+			// -1 means +1
+			remaining += count
+			gotTotal -= count
+		} else {
+			remaining -= count
+			gotTotal += count
+		}
+		s.norm[charnum&0xff] = int16(count)
+		charnum++
+		previous0 = count == 0
+		for remaining < threshold {
+			nbBits--
+			threshold >>= 1
+		}
+
+		if r := b.remain(); r >= 7 || r-int(bitCount>>3) >= 4 {
+			b.advance(bitCount >> 3)
+			bitCount &= 7
+			// The check above should make sure we can read 32 bits
+			bitStream = b.Uint32NC() >> (bitCount & 31)
+		} else {
+			bitCount -= (uint)(8 * (len(b.b) - 4 - b.off))
+			b.off = len(b.b) - 4
+			bitStream = b.Uint32() >> (bitCount & 31)
+		}
+	}
+	s.symbolLen = charnum
+	if s.symbolLen <= 1 {
+		return fmt.Errorf("symbolLen (%d) too small", s.symbolLen)
+	}
+	if s.symbolLen > maxSymbolValue+1 {
+		return fmt.Errorf("symbolLen (%d) too big", s.symbolLen)
+	}
+	if remaining != 1 {
+		return fmt.Errorf("corruption detected (remaining %d != 1)", remaining)
+	}
+	if bitCount > 32 {
+		return fmt.Errorf("corruption detected (bitCount %d > 32)", bitCount)
+	}
+	if gotTotal != 1<<s.actualTableLog {
+		return fmt.Errorf("corruption detected (total %d != %d)", gotTotal, 1<<s.actualTableLog)
+	}
+	b.advance((bitCount + 7) >> 3)
+	// println(s.norm[:s.symbolLen], s.symbolLen)
+	return s.buildDtable()
+}
+
+// decSymbol contains information about a state entry,
+// Including the state offset base, the output symbol and
+// the number of bits to read for the low part of the destination state.
+// Using a composite uint64 is faster than a struct with separate members.
+type decSymbol uint64
+
+func newDecSymbol(nbits, addBits uint8, newState uint16, baseline uint32) decSymbol {
+	return decSymbol(nbits) | (decSymbol(addBits) << 8) | (decSymbol(newState) << 16) | (decSymbol(baseline) << 32)
+}
+
+func (d decSymbol) nbBits() uint8 {
+	return uint8(d)
+}
+
+func (d decSymbol) addBits() uint8 {
+	return uint8(d >> 8)
+}
+
+func (d decSymbol) newState() uint16 {
+	return uint16(d >> 16)
+}
+
+func (d decSymbol) baseline() uint32 {
+	return uint32(d >> 32)
+}
+
+func (d decSymbol) baselineInt() int {
+	return int(d >> 32)
+}
+
+func (d *decSymbol) set(nbits, addBits uint8, newState uint16, baseline uint32) {
+	*d = decSymbol(nbits) | (decSymbol(addBits) << 8) | (decSymbol(newState) << 16) | (decSymbol(baseline) << 32)
+}
+
+func (d *decSymbol) setNBits(nBits uint8) {
+	const mask = 0xffffffffffffff00
+	*d = (*d & mask) | decSymbol(nBits)
+}
+
+func (d *decSymbol) setAddBits(addBits uint8) {
+	const mask = 0xffffffffffff00ff
+	*d = (*d & mask) | (decSymbol(addBits) << 8)
+}
+
+func (d *decSymbol) setNewState(state uint16) {
+	const mask = 0xffffffff0000ffff
+	*d = (*d & mask) | decSymbol(state)<<16
+}
+
+func (d *decSymbol) setBaseline(baseline uint32) {
+	const mask = 0xffffffff
+	*d = (*d & mask) | decSymbol(baseline)<<32
+}
+
+func (d *decSymbol) setExt(addBits uint8, baseline uint32) {
+	const mask = 0xffff00ff
+	*d = (*d & mask) | (decSymbol(addBits) << 8) | (decSymbol(baseline) << 32)
+}
+
+// decSymbolValue returns the transformed decSymbol for the given symbol.
+func decSymbolValue(symb uint8, t []baseOffset) (decSymbol, error) {
+	if int(symb) >= len(t) {
+		return 0, fmt.Errorf("rle symbol %d >= max %d", symb, len(t))
+	}
+	lu := t[symb]
+	return newDecSymbol(0, lu.addBits, 0, lu.baseLine), nil
+}
+
+// setRLE will set the decoder til RLE mode.
+func (s *fseDecoder) setRLE(symbol decSymbol) {
+	s.actualTableLog = 0
+	s.maxBits = symbol.addBits()
+	s.dt[0] = symbol
+}
+
+// buildDtable will build the decoding table.
+func (s *fseDecoder) buildDtable() error {
+	tableSize := uint32(1 << s.actualTableLog)
+	highThreshold := tableSize - 1
+	symbolNext := s.stateTable[:256]
+
+	// Init, lay down lowprob symbols
+	{
+		for i, v := range s.norm[:s.symbolLen] {
+			if v == -1 {
+				s.dt[highThreshold].setAddBits(uint8(i))
+				highThreshold--
+				symbolNext[i] = 1
+			} else {
+				symbolNext[i] = uint16(v)
+			}
+		}
+	}
+	// Spread symbols
+	{
+		tableMask := tableSize - 1
+		step := tableStep(tableSize)
+		position := uint32(0)
+		for ss, v := range s.norm[:s.symbolLen] {
+			for i := 0; i < int(v); i++ {
+				s.dt[position].setAddBits(uint8(ss))
+				position = (position + step) & tableMask
+				for position > highThreshold {
+					// lowprob area
+					position = (position + step) & tableMask
+				}
+			}
+		}
+		if position != 0 {
+			// position must reach all cells once, otherwise normalizedCounter is incorrect
+			return errors.New("corrupted input (position != 0)")
+		}
+	}
+
+	// Build Decoding table
+	{
+		tableSize := uint16(1 << s.actualTableLog)
+		for u, v := range s.dt[:tableSize] {
+			symbol := v.addBits()
+			nextState := symbolNext[symbol]
+			symbolNext[symbol] = nextState + 1
+			nBits := s.actualTableLog - byte(highBits(uint32(nextState)))
+			s.dt[u&maxTableMask].setNBits(nBits)
+			newState := (nextState << nBits) - tableSize
+			if newState > tableSize {
+				return fmt.Errorf("newState (%d) outside table size (%d)", newState, tableSize)
+			}
+			if newState == uint16(u) && nBits == 0 {
+				// Seems weird that this is possible with nbits > 0.
+				return fmt.Errorf("newState (%d) == oldState (%d) and no bits", newState, u)
+			}
+			s.dt[u&maxTableMask].setNewState(newState)
+		}
+	}
+	return nil
+}
+
+// transform will transform the decoder table into a table usable for
+// decoding without having to apply the transformation while decoding.
+// The state will contain the base value and the number of bits to read.
+func (s *fseDecoder) transform(t []baseOffset) error {
+	tableSize := uint16(1 << s.actualTableLog)
+	s.maxBits = 0
+	for i, v := range s.dt[:tableSize] {
+		add := v.addBits()
+		if int(add) >= len(t) {
+			return fmt.Errorf("invalid decoding table entry %d, symbol %d >= max (%d)", i, v.addBits(), len(t))
+		}
+		lu := t[add]
+		if lu.addBits > s.maxBits {
+			s.maxBits = lu.addBits
+		}
+		v.setExt(lu.addBits, lu.baseLine)
+		s.dt[i] = v
+	}
+	return nil
+}
+
+type fseState struct {
+	dt    []decSymbol
+	state decSymbol
+}
+
+// Initialize and decodeAsync first state and symbol.
+func (s *fseState) init(br *bitReader, tableLog uint8, dt []decSymbol) {
+	s.dt = dt
+	br.fill()
+	s.state = dt[br.getBits(tableLog)]
+}
+
+// next returns the current symbol and sets the next state.
+// At least tablelog bits must be available in the bit reader.
+func (s *fseState) next(br *bitReader) {
+	lowBits := uint16(br.getBits(s.state.nbBits()))
+	s.state = s.dt[s.state.newState()+lowBits]
+}
+
+// finished returns true if all bits have been read from the bitstream
+// and the next state would require reading bits from the input.
+func (s *fseState) finished(br *bitReader) bool {
+	return br.finished() && s.state.nbBits() > 0
+}
+
+// final returns the current state symbol without decoding the next.
+func (s *fseState) final() (int, uint8) {
+	return s.state.baselineInt(), s.state.addBits()
+}
+
+// final returns the current state symbol without decoding the next.
+func (s decSymbol) final() (int, uint8) {
+	return s.baselineInt(), s.addBits()
+}
+
+// nextFast returns the next symbol and sets the next state.
+// This can only be used if no symbols are 0 bits.
+// At least tablelog bits must be available in the bit reader.
+func (s *fseState) nextFast(br *bitReader) (uint32, uint8) {
+	lowBits := br.get16BitsFast(s.state.nbBits())
+	s.state = s.dt[s.state.newState()+lowBits]
+	return s.state.baseline(), s.state.addBits()
+}

vendor/github.com/klauspost/compress/zstd/fse_encoder.go

@@ -0,0 +1,724 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+import (
+	"errors"
+	"fmt"
+	"math"
+)
+
+const (
+	// For encoding we only support up to
+	maxEncTableLog    = 8
+	maxEncTablesize   = 1 << maxTableLog
+	maxEncTableMask   = (1 << maxTableLog) - 1
+	minEncTablelog    = 5
+	maxEncSymbolValue = maxMatchLengthSymbol
+)
+
+// Scratch provides temporary storage for compression and decompression.
+type fseEncoder struct {
+	symbolLen      uint16 // Length of active part of the symbol table.
+	actualTableLog uint8  // Selected tablelog.
+	ct             cTable // Compression tables.
+	maxCount       int    // count of the most probable symbol
+	zeroBits       bool   // no bits has prob > 50%.
+	clearCount     bool   // clear count
+	useRLE         bool   // This encoder is for RLE
+	preDefined     bool   // This encoder is predefined.
+	reUsed         bool   // Set to know when the encoder has been reused.
+	rleVal         uint8  // RLE Symbol
+	maxBits        uint8  // Maximum output bits after transform.
+
+	// TODO: Technically zstd should be fine with 64 bytes.
+	count [256]uint32
+	norm  [256]int16
+}
+
+// cTable contains tables used for compression.
+type cTable struct {
+	tableSymbol []byte
+	stateTable  []uint16
+	symbolTT    []symbolTransform
+}
+
+// symbolTransform contains the state transform for a symbol.
+type symbolTransform struct {
+	deltaNbBits    uint32
+	deltaFindState int16
+	outBits        uint8
+}
+
+// String prints values as a human readable string.
+func (s symbolTransform) String() string {
+	return fmt.Sprintf("{deltabits: %08x, findstate:%d outbits:%d}", s.deltaNbBits, s.deltaFindState, s.outBits)
+}
+
+// Histogram allows to populate the histogram and skip that step in the compression,
+// It otherwise allows to inspect the histogram when compression is done.
+// To indicate that you have populated the histogram call HistogramFinished
+// with the value of the highest populated symbol, as well as the number of entries
+// in the most populated entry. These are accepted at face value.
+func (s *fseEncoder) Histogram() *[256]uint32 {
+	return &s.count
+}
+
+// HistogramFinished can be called to indicate that the histogram has been populated.
+// maxSymbol is the index of the highest set symbol of the next data segment.
+// maxCount is the number of entries in the most populated entry.
+// These are accepted at face value.
+func (s *fseEncoder) HistogramFinished(maxSymbol uint8, maxCount int) {
+	s.maxCount = maxCount
+	s.symbolLen = uint16(maxSymbol) + 1
+	s.clearCount = maxCount != 0
+}
+
+// prepare will prepare and allocate scratch tables used for both compression and decompression.
+func (s *fseEncoder) prepare() (*fseEncoder, error) {
+	if s == nil {
+		s = &fseEncoder{}
+	}
+	s.useRLE = false
+	if s.clearCount && s.maxCount == 0 {
+		for i := range s.count {
+			s.count[i] = 0
+		}
+		s.clearCount = false
+	}
+	return s, nil
+}
+
+// allocCtable will allocate tables needed for compression.
+// If existing tables a re big enough, they are simply re-used.
+func (s *fseEncoder) allocCtable() {
+	tableSize := 1 << s.actualTableLog
+	// get tableSymbol that is big enough.
+	if cap(s.ct.tableSymbol) < tableSize {
+		s.ct.tableSymbol = make([]byte, tableSize)
+	}
+	s.ct.tableSymbol = s.ct.tableSymbol[:tableSize]
+
+	ctSize := tableSize
+	if cap(s.ct.stateTable) < ctSize {
+		s.ct.stateTable = make([]uint16, ctSize)
+	}
+	s.ct.stateTable = s.ct.stateTable[:ctSize]
+
+	if cap(s.ct.symbolTT) < 256 {
+		s.ct.symbolTT = make([]symbolTransform, 256)
+	}
+	s.ct.symbolTT = s.ct.symbolTT[:256]
+}
+
+// buildCTable will populate the compression table so it is ready to be used.
+func (s *fseEncoder) buildCTable() error {
+	tableSize := uint32(1 << s.actualTableLog)
+	highThreshold := tableSize - 1
+	var cumul [256]int16
+
+	s.allocCtable()
+	tableSymbol := s.ct.tableSymbol[:tableSize]
+	// symbol start positions
+	{
+		cumul[0] = 0
+		for ui, v := range s.norm[:s.symbolLen-1] {
+			u := byte(ui) // one less than reference
+			if v == -1 {
+				// Low proba symbol
+				cumul[u+1] = cumul[u] + 1
+				tableSymbol[highThreshold] = u
+				highThreshold--
+			} else {
+				cumul[u+1] = cumul[u] + v
+			}
+		}
+		// Encode last symbol separately to avoid overflowing u
+		u := int(s.symbolLen - 1)
+		v := s.norm[s.symbolLen-1]
+		if v == -1 {
+			// Low proba symbol
+			cumul[u+1] = cumul[u] + 1
+			tableSymbol[highThreshold] = byte(u)
+			highThreshold--
+		} else {
+			cumul[u+1] = cumul[u] + v
+		}
+		if uint32(cumul[s.symbolLen]) != tableSize {
+			return fmt.Errorf("internal error: expected cumul[s.symbolLen] (%d) == tableSize (%d)", cumul[s.symbolLen], tableSize)
+		}
+		cumul[s.symbolLen] = int16(tableSize) + 1
+	}
+	// Spread symbols
+	s.zeroBits = false
+	{
+		step := tableStep(tableSize)
+		tableMask := tableSize - 1
+		var position uint32
+		// if any symbol > largeLimit, we may have 0 bits output.
+		largeLimit := int16(1 << (s.actualTableLog - 1))
+		for ui, v := range s.norm[:s.symbolLen] {
+			symbol := byte(ui)
+			if v > largeLimit {
+				s.zeroBits = true
+			}
+			for nbOccurrences := int16(0); nbOccurrences < v; nbOccurrences++ {
+				tableSymbol[position] = symbol
+				position = (position + step) & tableMask
+				for position > highThreshold {
+					position = (position + step) & tableMask
+				} /* Low proba area */
+			}
+		}
+
+		// Check if we have gone through all positions
+		if position != 0 {
+			return errors.New("position!=0")
+		}
+	}
+
+	// Build table
+	table := s.ct.stateTable
+	{
+		tsi := int(tableSize)
+		for u, v := range tableSymbol {
+			// TableU16 : sorted by symbol order; gives next state value
+			table[cumul[v]] = uint16(tsi + u)
+			cumul[v]++
+		}
+	}
+
+	// Build Symbol Transformation Table
+	{
+		total := int16(0)
+		symbolTT := s.ct.symbolTT[:s.symbolLen]
+		tableLog := s.actualTableLog
+		tl := (uint32(tableLog) << 16) - (1 << tableLog)
+		for i, v := range s.norm[:s.symbolLen] {
+			switch v {
+			case 0:
+			case -1, 1:
+				symbolTT[i].deltaNbBits = tl
+				symbolTT[i].deltaFindState = total - 1
+				total++
+			default:
+				maxBitsOut := uint32(tableLog) - highBit(uint32(v-1))
+				minStatePlus := uint32(v) << maxBitsOut
+				symbolTT[i].deltaNbBits = (maxBitsOut << 16) - minStatePlus
+				symbolTT[i].deltaFindState = total - v
+				total += v
+			}
+		}
+		if total != int16(tableSize) {
+			return fmt.Errorf("total mismatch %d (got) != %d (want)", total, tableSize)
+		}
+	}
+	return nil
+}
+
+var rtbTable = [...]uint32{0, 473195, 504333, 520860, 550000, 700000, 750000, 830000}
+
+func (s *fseEncoder) setRLE(val byte) {
+	s.allocCtable()
+	s.actualTableLog = 0
+	s.ct.stateTable = s.ct.stateTable[:1]
+	s.ct.symbolTT[val] = symbolTransform{
+		deltaFindState: 0,
+		deltaNbBits:    0,
+	}
+	if debugEncoder {
+		println("setRLE: val", val, "symbolTT", s.ct.symbolTT[val])
+	}
+	s.rleVal = val
+	s.useRLE = true
+}
+
+// setBits will set output bits for the transform.
+// if nil is provided, the number of bits is equal to the index.
+func (s *fseEncoder) setBits(transform []byte) {
+	if s.reUsed || s.preDefined {
+		return
+	}
+	if s.useRLE {
+		if transform == nil {
+			s.ct.symbolTT[s.rleVal].outBits = s.rleVal
+			s.maxBits = s.rleVal
+			return
+		}
+		s.maxBits = transform[s.rleVal]
+		s.ct.symbolTT[s.rleVal].outBits = s.maxBits
+		return
+	}
+	if transform == nil {
+		for i := range s.ct.symbolTT[:s.symbolLen] {
+			s.ct.symbolTT[i].outBits = uint8(i)
+		}
+		s.maxBits = uint8(s.symbolLen - 1)
+		return
+	}
+	s.maxBits = 0
+	for i, v := range transform[:s.symbolLen] {
+		s.ct.symbolTT[i].outBits = v
+		if v > s.maxBits {
+			// We could assume bits always going up, but we play safe.
+			s.maxBits = v
+		}
+	}
+}
+
+// normalizeCount will normalize the count of the symbols so
+// the total is equal to the table size.
+// If successful, compression tables will also be made ready.
+func (s *fseEncoder) normalizeCount(length int) error {
+	if s.reUsed {
+		return nil
+	}
+	s.optimalTableLog(length)
+	var (
+		tableLog          = s.actualTableLog
+		scale             = 62 - uint64(tableLog)
+		step              = (1 << 62) / uint64(length)
+		vStep             = uint64(1) << (scale - 20)
+		stillToDistribute = int16(1 << tableLog)
+		largest           int
+		largestP          int16
+		lowThreshold      = (uint32)(length >> tableLog)
+	)
+	if s.maxCount == length {
+		s.useRLE = true
+		return nil
+	}
+	s.useRLE = false
+	for i, cnt := range s.count[:s.symbolLen] {
+		// already handled
+		// if (count[s] == s.length) return 0;   /* rle special case */
+
+		if cnt == 0 {
+			s.norm[i] = 0
+			continue
+		}
+		if cnt <= lowThreshold {
+			s.norm[i] = -1
+			stillToDistribute--
+		} else {
+			proba := (int16)((uint64(cnt) * step) >> scale)
+			if proba < 8 {
+				restToBeat := vStep * uint64(rtbTable[proba])
+				v := uint64(cnt)*step - (uint64(proba) << scale)
+				if v > restToBeat {
+					proba++
+				}
+			}
+			if proba > largestP {
+				largestP = proba
+				largest = i
+			}
+			s.norm[i] = proba
+			stillToDistribute -= proba
+		}
+	}
+
+	if -stillToDistribute >= (s.norm[largest] >> 1) {
+		// corner case, need another normalization method
+		err := s.normalizeCount2(length)
+		if err != nil {
+			return err
+		}
+		if debugAsserts {
+			err = s.validateNorm()
+			if err != nil {
+				return err
+			}
+		}
+		return s.buildCTable()
+	}
+	s.norm[largest] += stillToDistribute
+	if debugAsserts {
+		err := s.validateNorm()
+		if err != nil {
+			return err
+		}
+	}
+	return s.buildCTable()
+}
+
+// Secondary normalization method.
+// To be used when primary method fails.
+func (s *fseEncoder) normalizeCount2(length int) error {
+	const notYetAssigned = -2
+	var (
+		distributed  uint32
+		total        = uint32(length)
+		tableLog     = s.actualTableLog
+		lowThreshold = total >> tableLog
+		lowOne       = (total * 3) >> (tableLog + 1)
+	)
+	for i, cnt := range s.count[:s.symbolLen] {
+		if cnt == 0 {
+			s.norm[i] = 0
+			continue
+		}
+		if cnt <= lowThreshold {
+			s.norm[i] = -1
+			distributed++
+			total -= cnt
+			continue
+		}
+		if cnt <= lowOne {
+			s.norm[i] = 1
+			distributed++
+			total -= cnt
+			continue
+		}
+		s.norm[i] = notYetAssigned
+	}
+	toDistribute := (1 << tableLog) - distributed
+
+	if (total / toDistribute) > lowOne {
+		// risk of rounding to zero
+		lowOne = (total * 3) / (toDistribute * 2)
+		for i, cnt := range s.count[:s.symbolLen] {
+			if (s.norm[i] == notYetAssigned) && (cnt <= lowOne) {
+				s.norm[i] = 1
+				distributed++
+				total -= cnt
+				continue
+			}
+		}
+		toDistribute = (1 << tableLog) - distributed
+	}
+	if distributed == uint32(s.symbolLen)+1 {
+		// all values are pretty poor;
+		//   probably incompressible data (should have already been detected);
+		//   find max, then give all remaining points to max
+		var maxV int
+		var maxC uint32
+		for i, cnt := range s.count[:s.symbolLen] {
+			if cnt > maxC {
+				maxV = i
+				maxC = cnt
+			}
+		}
+		s.norm[maxV] += int16(toDistribute)
+		return nil
+	}
+
+	if total == 0 {
+		// all of the symbols were low enough for the lowOne or lowThreshold
+		for i := uint32(0); toDistribute > 0; i = (i + 1) % (uint32(s.symbolLen)) {
+			if s.norm[i] > 0 {
+				toDistribute--
+				s.norm[i]++
+			}
+		}
+		return nil
+	}
+
+	var (
+		vStepLog = 62 - uint64(tableLog)
+		mid      = uint64((1 << (vStepLog - 1)) - 1)
+		rStep    = (((1 << vStepLog) * uint64(toDistribute)) + mid) / uint64(total) // scale on remaining
+		tmpTotal = mid
+	)
+	for i, cnt := range s.count[:s.symbolLen] {
+		if s.norm[i] == notYetAssigned {
+			var (
+				end    = tmpTotal + uint64(cnt)*rStep
+				sStart = uint32(tmpTotal >> vStepLog)
+				sEnd   = uint32(end >> vStepLog)
+				weight = sEnd - sStart
+			)
+			if weight < 1 {
+				return errors.New("weight < 1")
+			}
+			s.norm[i] = int16(weight)
+			tmpTotal = end
+		}
+	}
+	return nil
+}
+
+// optimalTableLog calculates and sets the optimal tableLog in s.actualTableLog
+func (s *fseEncoder) optimalTableLog(length int) {
+	tableLog := uint8(maxEncTableLog)
+	minBitsSrc := highBit(uint32(length)) + 1
+	minBitsSymbols := highBit(uint32(s.symbolLen-1)) + 2
+	minBits := uint8(minBitsSymbols)
+	if minBitsSrc < minBitsSymbols {
+		minBits = uint8(minBitsSrc)
+	}
+
+	maxBitsSrc := uint8(highBit(uint32(length-1))) - 2
+	if maxBitsSrc < tableLog {
+		// Accuracy can be reduced
+		tableLog = maxBitsSrc
+	}
+	if minBits > tableLog {
+		tableLog = minBits
+	}
+	// Need a minimum to safely represent all symbol values
+	if tableLog < minEncTablelog {
+		tableLog = minEncTablelog
+	}
+	if tableLog > maxEncTableLog {
+		tableLog = maxEncTableLog
+	}
+	s.actualTableLog = tableLog
+}
+
+// validateNorm validates the normalized histogram table.
+func (s *fseEncoder) validateNorm() (err error) {
+	var total int
+	for _, v := range s.norm[:s.symbolLen] {
+		if v >= 0 {
+			total += int(v)
+		} else {
+			total -= int(v)
+		}
+	}
+	defer func() {
+		if err == nil {
+			return
+		}
+		fmt.Printf("selected TableLog: %d, Symbol length: %d\n", s.actualTableLog, s.symbolLen)
+		for i, v := range s.norm[:s.symbolLen] {
+			fmt.Printf("%3d: %5d -> %4d \n", i, s.count[i], v)
+		}
+	}()
+	if total != (1 << s.actualTableLog) {
+		return fmt.Errorf("warning: Total == %d != %d", total, 1<<s.actualTableLog)
+	}
+	for i, v := range s.count[s.symbolLen:] {
+		if v != 0 {
+			return fmt.Errorf("warning: Found symbol out of range, %d after cut", i)
+		}
+	}
+	return nil
+}
+
+// writeCount will write the normalized histogram count to header.
+// This is read back by readNCount.
+func (s *fseEncoder) writeCount(out []byte) ([]byte, error) {
+	if s.useRLE {
+		return append(out, s.rleVal), nil
+	}
+	if s.preDefined || s.reUsed {
+		// Never write predefined.
+		return out, nil
+	}
+
+	var (
+		tableLog  = s.actualTableLog
+		tableSize = 1 << tableLog
+		previous0 bool
+		charnum   uint16
+
+		// maximum header size plus 2 extra bytes for final output if bitCount == 0.
+		maxHeaderSize = ((int(s.symbolLen) * int(tableLog)) >> 3) + 3 + 2
+
+		// Write Table Size
+		bitStream = uint32(tableLog - minEncTablelog)
+		bitCount  = uint(4)
+		remaining = int16(tableSize + 1) /* +1 for extra accuracy */
+		threshold = int16(tableSize)
+		nbBits    = uint(tableLog + 1)
+		outP      = len(out)
+	)
+	if cap(out) < outP+maxHeaderSize {
+		out = append(out, make([]byte, maxHeaderSize*3)...)
+		out = out[:len(out)-maxHeaderSize*3]
+	}
+	out = out[:outP+maxHeaderSize]
+
+	// stops at 1
+	for remaining > 1 {
+		if previous0 {
+			start := charnum
+			for s.norm[charnum] == 0 {
+				charnum++
+			}
+			for charnum >= start+24 {
+				start += 24
+				bitStream += uint32(0xFFFF) << bitCount
+				out[outP] = byte(bitStream)
+				out[outP+1] = byte(bitStream >> 8)
+				outP += 2
+				bitStream >>= 16
+			}
+			for charnum >= start+3 {
+				start += 3
+				bitStream += 3 << bitCount
+				bitCount += 2
+			}
+			bitStream += uint32(charnum-start) << bitCount
+			bitCount += 2
+			if bitCount > 16 {
+				out[outP] = byte(bitStream)
+				out[outP+1] = byte(bitStream >> 8)
+				outP += 2
+				bitStream >>= 16
+				bitCount -= 16
+			}
+		}
+
+		count := s.norm[charnum]
+		charnum++
+		max := (2*threshold - 1) - remaining
+		if count < 0 {
+			remaining += count
+		} else {
+			remaining -= count
+		}
+		count++ // +1 for extra accuracy
+		if count >= threshold {
+			count += max // [0..max[ [max..threshold[ (...) [threshold+max 2*threshold[
+		}
+		bitStream += uint32(count) << bitCount
+		bitCount += nbBits
+		if count < max {
+			bitCount--
+		}
+
+		previous0 = count == 1
+		if remaining < 1 {
+			return nil, errors.New("internal error: remaining < 1")
+		}
+		for remaining < threshold {
+			nbBits--
+			threshold >>= 1
+		}
+
+		if bitCount > 16 {
+			out[outP] = byte(bitStream)
+			out[outP+1] = byte(bitStream >> 8)
+			outP += 2
+			bitStream >>= 16
+			bitCount -= 16
+		}
+	}
+
+	if outP+2 > len(out) {
+		return nil, fmt.Errorf("internal error: %d > %d, maxheader: %d, sl: %d, tl: %d, normcount: %v", outP+2, len(out), maxHeaderSize, s.symbolLen, int(tableLog), s.norm[:s.symbolLen])
+	}
+	out[outP] = byte(bitStream)
+	out[outP+1] = byte(bitStream >> 8)
+	outP += int((bitCount + 7) / 8)
+
+	if charnum > s.symbolLen {
+		return nil, errors.New("internal error: charnum > s.symbolLen")
+	}
+	return out[:outP], nil
+}
+
+// Approximate symbol cost, as fractional value, using fixed-point format (accuracyLog fractional bits)
+// note 1 : assume symbolValue is valid (<= maxSymbolValue)
+// note 2 : if freq[symbolValue]==0, @return a fake cost of tableLog+1 bits *
+func (s *fseEncoder) bitCost(symbolValue uint8, accuracyLog uint32) uint32 {
+	minNbBits := s.ct.symbolTT[symbolValue].deltaNbBits >> 16
+	threshold := (minNbBits + 1) << 16
+	if debugAsserts {
+		if !(s.actualTableLog < 16) {
+			panic("!s.actualTableLog < 16")
+		}
+		// ensure enough room for renormalization double shift
+		if !(uint8(accuracyLog) < 31-s.actualTableLog) {
+			panic("!uint8(accuracyLog) < 31-s.actualTableLog")
+		}
+	}
+	tableSize := uint32(1) << s.actualTableLog
+	deltaFromThreshold := threshold - (s.ct.symbolTT[symbolValue].deltaNbBits + tableSize)
+	// linear interpolation (very approximate)
+	normalizedDeltaFromThreshold := (deltaFromThreshold << accuracyLog) >> s.actualTableLog
+	bitMultiplier := uint32(1) << accuracyLog
+	if debugAsserts {
+		if s.ct.symbolTT[symbolValue].deltaNbBits+tableSize > threshold {
+			panic("s.ct.symbolTT[symbolValue].deltaNbBits+tableSize > threshold")
+		}
+		if normalizedDeltaFromThreshold > bitMultiplier {
+			panic("normalizedDeltaFromThreshold > bitMultiplier")
+		}
+	}
+	return (minNbBits+1)*bitMultiplier - normalizedDeltaFromThreshold
+}
+
+// Returns the cost in bits of encoding the distribution in count using ctable.
+// Histogram should only be up to the last non-zero symbol.
+// Returns an -1 if ctable cannot represent all the symbols in count.
+func (s *fseEncoder) approxSize(hist []uint32) uint32 {
+	if int(s.symbolLen) < len(hist) {
+		// More symbols than we have.
+		return math.MaxUint32
+	}
+	if s.useRLE {
+		// We will never reuse RLE encoders.
+		return math.MaxUint32
+	}
+	const kAccuracyLog = 8
+	badCost := (uint32(s.actualTableLog) + 1) << kAccuracyLog
+	var cost uint32
+	for i, v := range hist {
+		if v == 0 {
+			continue
+		}
+		if s.norm[i] == 0 {
+			return math.MaxUint32
+		}
+		bitCost := s.bitCost(uint8(i), kAccuracyLog)
+		if bitCost > badCost {
+			return math.MaxUint32
+		}
+		cost += v * bitCost
+	}
+	return cost >> kAccuracyLog
+}
+
+// maxHeaderSize returns the maximum header size in bits.
+// This is not exact size, but we want a penalty for new tables anyway.
+func (s *fseEncoder) maxHeaderSize() uint32 {
+	if s.preDefined {
+		return 0
+	}
+	if s.useRLE {
+		return 8
+	}
+	return (((uint32(s.symbolLen) * uint32(s.actualTableLog)) >> 3) + 3) * 8
+}
+
+// cState contains the compression state of a stream.
+type cState struct {
+	bw         *bitWriter
+	stateTable []uint16
+	state      uint16
+}
+
+// init will initialize the compression state to the first symbol of the stream.
+func (c *cState) init(bw *bitWriter, ct *cTable, first symbolTransform) {
+	c.bw = bw
+	c.stateTable = ct.stateTable
+	if len(c.stateTable) == 1 {
+		// RLE
+		c.stateTable[0] = uint16(0)
+		c.state = 0
+		return
+	}
+	nbBitsOut := (first.deltaNbBits + (1 << 15)) >> 16
+	im := int32((nbBitsOut << 16) - first.deltaNbBits)
+	lu := (im >> nbBitsOut) + int32(first.deltaFindState)
+	c.state = c.stateTable[lu]
+}
+
+// encode the output symbol provided and write it to the bitstream.
+func (c *cState) encode(symbolTT symbolTransform) {
+	nbBitsOut := (uint32(c.state) + symbolTT.deltaNbBits) >> 16
+	dstState := int32(c.state>>(nbBitsOut&15)) + int32(symbolTT.deltaFindState)
+	c.bw.addBits16NC(c.state, uint8(nbBitsOut))
+	c.state = c.stateTable[dstState]
+}
+
+// flush will write the tablelog to the output and flush the remaining full bytes.
+func (c *cState) flush(tableLog uint8) {
+	c.bw.flush32()
+	c.bw.addBits16NC(c.state, tableLog)
+}

vendor/github.com/klauspost/compress/zstd/fse_predefined.go

@@ -0,0 +1,158 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+import (
+	"fmt"
+	"math"
+	"sync"
+)
+
+var (
+	// fsePredef are the predefined fse tables as defined here:
+	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#default-distributions
+	// These values are already transformed.
+	fsePredef [3]fseDecoder
+
+	// fsePredefEnc are the predefined encoder based on fse tables as defined here:
+	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#default-distributions
+	// These values are already transformed.
+	fsePredefEnc [3]fseEncoder
+
+	// symbolTableX contain the transformations needed for each type as defined in
+	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#the-codes-for-literals-lengths-match-lengths-and-offsets
+	symbolTableX [3][]baseOffset
+
+	// maxTableSymbol is the biggest supported symbol for each table type
+	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#the-codes-for-literals-lengths-match-lengths-and-offsets
+	maxTableSymbol = [3]uint8{tableLiteralLengths: maxLiteralLengthSymbol, tableOffsets: maxOffsetLengthSymbol, tableMatchLengths: maxMatchLengthSymbol}
+
+	// bitTables is the bits table for each table.
+	bitTables = [3][]byte{tableLiteralLengths: llBitsTable[:], tableOffsets: nil, tableMatchLengths: mlBitsTable[:]}
+)
+
+type tableIndex uint8
+
+const (
+	// indexes for fsePredef and symbolTableX
+	tableLiteralLengths tableIndex = 0
+	tableOffsets        tableIndex = 1
+	tableMatchLengths   tableIndex = 2
+
+	maxLiteralLengthSymbol = 35
+	maxOffsetLengthSymbol  = 30
+	maxMatchLengthSymbol   = 52
+)
+
+// baseOffset is used for calculating transformations.
+type baseOffset struct {
+	baseLine uint32
+	addBits  uint8
+}
+
+// fillBase will precalculate base offsets with the given bit distributions.
+func fillBase(dst []baseOffset, base uint32, bits ...uint8) {
+	if len(bits) != len(dst) {
+		panic(fmt.Sprintf("len(dst) (%d) != len(bits) (%d)", len(dst), len(bits)))
+	}
+	for i, bit := range bits {
+		if base > math.MaxInt32 {
+			panic("invalid decoding table, base overflows int32")
+		}
+
+		dst[i] = baseOffset{
+			baseLine: base,
+			addBits:  bit,
+		}
+		base += 1 << bit
+	}
+}
+
+var predef sync.Once
+
+func initPredefined() {
+	predef.Do(func() {
+		// Literals length codes
+		tmp := make([]baseOffset, 36)
+		for i := range tmp[:16] {
+			tmp[i] = baseOffset{
+				baseLine: uint32(i),
+				addBits:  0,
+			}
+		}
+		fillBase(tmp[16:], 16, 1, 1, 1, 1, 2, 2, 3, 3, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
+		symbolTableX[tableLiteralLengths] = tmp
+
+		// Match length codes
+		tmp = make([]baseOffset, 53)
+		for i := range tmp[:32] {
+			tmp[i] = baseOffset{
+				// The transformation adds the 3 length.
+				baseLine: uint32(i) + 3,
+				addBits:  0,
+			}
+		}
+		fillBase(tmp[32:], 35, 1, 1, 1, 1, 2, 2, 3, 3, 4, 4, 5, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
+		symbolTableX[tableMatchLengths] = tmp
+
+		// Offset codes
+		tmp = make([]baseOffset, maxOffsetBits+1)
+		tmp[1] = baseOffset{
+			baseLine: 1,
+			addBits:  1,
+		}
+		fillBase(tmp[2:], 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)
+		symbolTableX[tableOffsets] = tmp
+
+		// Fill predefined tables and transform them.
+		// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#default-distributions
+		for i := range fsePredef[:] {
+			f := &fsePredef[i]
+			switch tableIndex(i) {
+			case tableLiteralLengths:
+				// https://github.com/facebook/zstd/blob/ededcfca57366461021c922720878c81a5854a0a/lib/decompress/zstd_decompress_block.c#L243
+				f.actualTableLog = 6
+				copy(f.norm[:], []int16{4, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1,
+					2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 1, 1, 1, 1, 1,
+					-1, -1, -1, -1})
+				f.symbolLen = 36
+			case tableOffsets:
+				// https://github.com/facebook/zstd/blob/ededcfca57366461021c922720878c81a5854a0a/lib/decompress/zstd_decompress_block.c#L281
+				f.actualTableLog = 5
+				copy(f.norm[:], []int16{
+					1, 1, 1, 1, 1, 1, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1,
+					1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1})
+				f.symbolLen = 29
+			case tableMatchLengths:
+				//https://github.com/facebook/zstd/blob/ededcfca57366461021c922720878c81a5854a0a/lib/decompress/zstd_decompress_block.c#L304
+				f.actualTableLog = 6
+				copy(f.norm[:], []int16{
+					1, 4, 3, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1,
+					1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+					1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1,
+					-1, -1, -1, -1, -1})
+				f.symbolLen = 53
+			}
+			if err := f.buildDtable(); err != nil {
+				panic(fmt.Errorf("building table %v: %v", tableIndex(i), err))
+			}
+			if err := f.transform(symbolTableX[i]); err != nil {
+				panic(fmt.Errorf("building table %v: %v", tableIndex(i), err))
+			}
+			f.preDefined = true
+
+			// Create encoder as well
+			enc := &fsePredefEnc[i]
+			copy(enc.norm[:], f.norm[:])
+			enc.symbolLen = f.symbolLen
+			enc.actualTableLog = f.actualTableLog
+			if err := enc.buildCTable(); err != nil {
+				panic(fmt.Errorf("building encoding table %v: %v", tableIndex(i), err))
+			}
+			enc.setBits(bitTables[i])
+			enc.preDefined = true
+		}
+	})
+}

vendor/github.com/klauspost/compress/zstd/hash.go

@@ -0,0 +1,41 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+const (
+	prime3bytes = 506832829
+	prime4bytes = 2654435761
+	prime5bytes = 889523592379
+	prime6bytes = 227718039650203
+	prime7bytes = 58295818150454627
+	prime8bytes = 0xcf1bbcdcb7a56463
+)
+
+// hashLen returns a hash of the lowest mls bytes of with length output bits.
+// mls must be >=3 and <=8. Any other value will return hash for 4 bytes.
+// length should always be < 32.
+// Preferably length and mls should be a constant for inlining.
+func hashLen(u uint64, length, mls uint8) uint32 {
+	switch mls {
+	case 3:
+		return (uint32(u<<8) * prime3bytes) >> (32 - length)
+	case 5:
+		return uint32(((u << (64 - 40)) * prime5bytes) >> (64 - length))
+	case 6:
+		return uint32(((u << (64 - 48)) * prime6bytes) >> (64 - length))
+	case 7:
+		return uint32(((u << (64 - 56)) * prime7bytes) >> (64 - length))
+	case 8:
+		return uint32((u * prime8bytes) >> (64 - length))
+	default:
+		return (uint32(u) * prime4bytes) >> (32 - length)
+	}
+}
+
+// hash3 returns the hash of the lower 3 bytes of u to fit in a hash table with h bits.
+// Preferably h should be a constant and should always be <32.
+func hash3(u uint32, h uint8) uint32 {
+	return ((u << (32 - 24)) * prime3bytes) >> ((32 - h) & 31)
+}

vendor/github.com/klauspost/compress/zstd/history.go

@@ -0,0 +1,89 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+// Based on work by Yann Collet, released under BSD License.
+
+package zstd
+
+import (
+	"github.com/klauspost/compress/huff0"
+)
+
+// history contains the information transferred between blocks.
+type history struct {
+	b             []byte
+	huffTree      *huff0.Scratch
+	recentOffsets [3]int
+	decoders      sequenceDecs
+	windowSize    int
+	maxSize       int
+	error         bool
+	dict          *dict
+}
+
+// reset will reset the history to initial state of a frame.
+// The history must already have been initialized to the desired size.
+func (h *history) reset() {
+	h.b = h.b[:0]
+	h.error = false
+	h.recentOffsets = [3]int{1, 4, 8}
+	if f := h.decoders.litLengths.fse; f != nil && !f.preDefined {
+		fseDecoderPool.Put(f)
+	}
+	if f := h.decoders.offsets.fse; f != nil && !f.preDefined {
+		fseDecoderPool.Put(f)
+	}
+	if f := h.decoders.matchLengths.fse; f != nil && !f.preDefined {
+		fseDecoderPool.Put(f)
+	}
+	h.decoders = sequenceDecs{}
+	if h.huffTree != nil {
+		if h.dict == nil || h.dict.litEnc != h.huffTree {
+			huffDecoderPool.Put(h.huffTree)
+		}
+	}
+	h.huffTree = nil
+	h.dict = nil
+	//printf("history created: %+v (l: %d, c: %d)", *h, len(h.b), cap(h.b))
+}
+
+func (h *history) setDict(dict *dict) {
+	if dict == nil {
+		return
+	}
+	h.dict = dict
+	h.decoders.litLengths = dict.llDec
+	h.decoders.offsets = dict.ofDec
+	h.decoders.matchLengths = dict.mlDec
+	h.recentOffsets = dict.offsets
+	h.huffTree = dict.litEnc
+}
+
+// append bytes to history.
+// This function will make sure there is space for it,
+// if the buffer has been allocated with enough extra space.
+func (h *history) append(b []byte) {
+	if len(b) >= h.windowSize {
+		// Discard all history by simply overwriting
+		h.b = h.b[:h.windowSize]
+		copy(h.b, b[len(b)-h.windowSize:])
+		return
+	}
+
+	// If there is space, append it.
+	if len(b) < cap(h.b)-len(h.b) {
+		h.b = append(h.b, b...)
+		return
+	}
+
+	// Move data down so we only have window size left.
+	// We know we have less than window size in b at this point.
+	discard := len(b) + len(h.b) - h.windowSize
+	copy(h.b, h.b[discard:])
+	h.b = h.b[:h.windowSize]
+	copy(h.b[h.windowSize-len(b):], b)
+}
+
+// append bytes to history without ever discarding anything.
+func (h *history) appendKeep(b []byte) {
+	h.b = append(h.b, b...)
+}

vendor/github.com/klauspost/compress/zstd/internal/xxhash/LICENSE.txt

@@ -0,0 +1,22 @@
+Copyright (c) 2016 Caleb Spare
+
+MIT License
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

vendor/github.com/klauspost/compress/zstd/internal/xxhash/README.md

@@ -0,0 +1,58 @@
+# xxhash
+
+VENDORED: Go to [github.com/cespare/xxhash](https://github.com/cespare/xxhash) for original package.
+
+
+[![GoDoc](https://godoc.org/github.com/cespare/xxhash?status.svg)](https://godoc.org/github.com/cespare/xxhash)
+[![Build Status](https://travis-ci.org/cespare/xxhash.svg?branch=master)](https://travis-ci.org/cespare/xxhash)
+
+xxhash is a Go implementation of the 64-bit
+[xxHash](http://cyan4973.github.io/xxHash/) algorithm, XXH64. This is a
+high-quality hashing algorithm that is much faster than anything in the Go
+standard library.
+
+This package provides a straightforward API:
+
+```
+func Sum64(b []byte) uint64
+func Sum64String(s string) uint64
+type Digest struct{ ... }
+    func New() *Digest
+```
+
+The `Digest` type implements hash.Hash64. Its key methods are:
+
+```
+func (*Digest) Write([]byte) (int, error)
+func (*Digest) WriteString(string) (int, error)
+func (*Digest) Sum64() uint64
+```
+
+This implementation provides a fast pure-Go implementation and an even faster
+assembly implementation for amd64.
+
+## Benchmarks
+
+Here are some quick benchmarks comparing the pure-Go and assembly
+implementations of Sum64.
+
+| input size | purego | asm |
+| --- | --- | --- |
+| 5 B   |  979.66 MB/s |  1291.17 MB/s  |
+| 100 B | 7475.26 MB/s | 7973.40 MB/s  |
+| 4 KB  | 17573.46 MB/s | 17602.65 MB/s |
+| 10 MB | 17131.46 MB/s | 17142.16 MB/s |
+
+These numbers were generated on Ubuntu 18.04 with an Intel i7-8700K CPU using
+the following commands under Go 1.11.2:
+
+```
+$ go test -tags purego -benchtime 10s -bench '/xxhash,direct,bytes'
+$ go test -benchtime 10s -bench '/xxhash,direct,bytes'
+```
+
+## Projects using this package
+
+- [InfluxDB](https://github.com/influxdata/influxdb)
+- [Prometheus](https://github.com/prometheus/prometheus)
+- [FreeCache](https://github.com/coocood/freecache)

vendor/github.com/klauspost/compress/zstd/internal/xxhash/xxhash.go

@@ -0,0 +1,237 @@
+// Package xxhash implements the 64-bit variant of xxHash (XXH64) as described
+// at http://cyan4973.github.io/xxHash/.
+// THIS IS VENDORED: Go to github.com/cespare/xxhash for original package.
+
+package xxhash
+
+import (
+	"encoding/binary"
+	"errors"
+	"math/bits"
+)
+
+const (
+	prime1 uint64 = 11400714785074694791
+	prime2 uint64 = 14029467366897019727
+	prime3 uint64 = 1609587929392839161
+	prime4 uint64 = 9650029242287828579
+	prime5 uint64 = 2870177450012600261
+)
+
+// NOTE(caleb): I'm using both consts and vars of the primes. Using consts where
+// possible in the Go code is worth a small (but measurable) performance boost
+// by avoiding some MOVQs. Vars are needed for the asm and also are useful for
+// convenience in the Go code in a few places where we need to intentionally
+// avoid constant arithmetic (e.g., v1 := prime1 + prime2 fails because the
+// result overflows a uint64).
+var (
+	prime1v = prime1
+	prime2v = prime2
+	prime3v = prime3
+	prime4v = prime4
+	prime5v = prime5
+)
+
+// Digest implements hash.Hash64.
+type Digest struct {
+	v1    uint64
+	v2    uint64
+	v3    uint64
+	v4    uint64
+	total uint64
+	mem   [32]byte
+	n     int // how much of mem is used
+}
+
+// New creates a new Digest that computes the 64-bit xxHash algorithm.
+func New() *Digest {
+	var d Digest
+	d.Reset()
+	return &d
+}
+
+// Reset clears the Digest's state so that it can be reused.
+func (d *Digest) Reset() {
+	d.v1 = prime1v + prime2
+	d.v2 = prime2
+	d.v3 = 0
+	d.v4 = -prime1v
+	d.total = 0
+	d.n = 0
+}
+
+// Size always returns 8 bytes.
+func (d *Digest) Size() int { return 8 }
+
+// BlockSize always returns 32 bytes.
+func (d *Digest) BlockSize() int { return 32 }
+
+// Write adds more data to d. It always returns len(b), nil.
+func (d *Digest) Write(b []byte) (n int, err error) {
+	n = len(b)
+	d.total += uint64(n)
+
+	if d.n+n < 32 {
+		// This new data doesn't even fill the current block.
+		copy(d.mem[d.n:], b)
+		d.n += n
+		return
+	}
+
+	if d.n > 0 {
+		// Finish off the partial block.
+		copy(d.mem[d.n:], b)
+		d.v1 = round(d.v1, u64(d.mem[0:8]))
+		d.v2 = round(d.v2, u64(d.mem[8:16]))
+		d.v3 = round(d.v3, u64(d.mem[16:24]))
+		d.v4 = round(d.v4, u64(d.mem[24:32]))
+		b = b[32-d.n:]
+		d.n = 0
+	}
+
+	if len(b) >= 32 {
+		// One or more full blocks left.
+		nw := writeBlocks(d, b)
+		b = b[nw:]
+	}
+
+	// Store any remaining partial block.
+	copy(d.mem[:], b)
+	d.n = len(b)
+
+	return
+}
+
+// Sum appends the current hash to b and returns the resulting slice.
+func (d *Digest) Sum(b []byte) []byte {
+	s := d.Sum64()
+	return append(
+		b,
+		byte(s>>56),
+		byte(s>>48),
+		byte(s>>40),
+		byte(s>>32),
+		byte(s>>24),
+		byte(s>>16),
+		byte(s>>8),
+		byte(s),
+	)
+}
+
+// Sum64 returns the current hash.
+func (d *Digest) Sum64() uint64 {
+	var h uint64
+
+	if d.total >= 32 {
+		v1, v2, v3, v4 := d.v1, d.v2, d.v3, d.v4
+		h = rol1(v1) + rol7(v2) + rol12(v3) + rol18(v4)
+		h = mergeRound(h, v1)
+		h = mergeRound(h, v2)
+		h = mergeRound(h, v3)
+		h = mergeRound(h, v4)
+	} else {
+		h = d.v3 + prime5
+	}
+
+	h += d.total
+
+	i, end := 0, d.n
+	for ; i+8 <= end; i += 8 {
+		k1 := round(0, u64(d.mem[i:i+8]))
+		h ^= k1
+		h = rol27(h)*prime1 + prime4
+	}
+	if i+4 <= end {
+		h ^= uint64(u32(d.mem[i:i+4])) * prime1
+		h = rol23(h)*prime2 + prime3
+		i += 4
+	}
+	for i < end {
+		h ^= uint64(d.mem[i]) * prime5
+		h = rol11(h) * prime1
+		i++
+	}
+
+	h ^= h >> 33
+	h *= prime2
+	h ^= h >> 29
+	h *= prime3
+	h ^= h >> 32
+
+	return h
+}
+
+const (
+	magic         = "xxh\x06"
+	marshaledSize = len(magic) + 8*5 + 32
+)
+
+// MarshalBinary implements the encoding.BinaryMarshaler interface.
+func (d *Digest) MarshalBinary() ([]byte, error) {
+	b := make([]byte, 0, marshaledSize)
+	b = append(b, magic...)
+	b = appendUint64(b, d.v1)
+	b = appendUint64(b, d.v2)
+	b = appendUint64(b, d.v3)
+	b = appendUint64(b, d.v4)
+	b = appendUint64(b, d.total)
+	b = append(b, d.mem[:d.n]...)
+	b = b[:len(b)+len(d.mem)-d.n]
+	return b, nil
+}
+
+// UnmarshalBinary implements the encoding.BinaryUnmarshaler interface.
+func (d *Digest) UnmarshalBinary(b []byte) error {
+	if len(b) < len(magic) || string(b[:len(magic)]) != magic {
+		return errors.New("xxhash: invalid hash state identifier")
+	}
+	if len(b) != marshaledSize {
+		return errors.New("xxhash: invalid hash state size")
+	}
+	b = b[len(magic):]
+	b, d.v1 = consumeUint64(b)
+	b, d.v2 = consumeUint64(b)
+	b, d.v3 = consumeUint64(b)
+	b, d.v4 = consumeUint64(b)
+	b, d.total = consumeUint64(b)
+	copy(d.mem[:], b)
+	d.n = int(d.total % uint64(len(d.mem)))
+	return nil
+}
+
+func appendUint64(b []byte, x uint64) []byte {
+	var a [8]byte
+	binary.LittleEndian.PutUint64(a[:], x)
+	return append(b, a[:]...)
+}
+
+func consumeUint64(b []byte) ([]byte, uint64) {
+	x := u64(b)
+	return b[8:], x
+}
+
+func u64(b []byte) uint64 { return binary.LittleEndian.Uint64(b) }
+func u32(b []byte) uint32 { return binary.LittleEndian.Uint32(b) }
+
+func round(acc, input uint64) uint64 {
+	acc += input * prime2
+	acc = rol31(acc)
+	acc *= prime1
+	return acc
+}
+
+func mergeRound(acc, val uint64) uint64 {
+	val = round(0, val)
+	acc ^= val
+	acc = acc*prime1 + prime4
+	return acc
+}
+
+func rol1(x uint64) uint64  { return bits.RotateLeft64(x, 1) }
+func rol7(x uint64) uint64  { return bits.RotateLeft64(x, 7) }
+func rol11(x uint64) uint64 { return bits.RotateLeft64(x, 11) }
+func rol12(x uint64) uint64 { return bits.RotateLeft64(x, 12) }
+func rol18(x uint64) uint64 { return bits.RotateLeft64(x, 18) }
+func rol23(x uint64) uint64 { return bits.RotateLeft64(x, 23) }
+func rol27(x uint64) uint64 { return bits.RotateLeft64(x, 27) }
+func rol31(x uint64) uint64 { return bits.RotateLeft64(x, 31) }