strings: Make Nickname profile not actually case-sensitive

irc/strings.go

@@ -8,8 +8,6 @@ package irc
 import (
 	"errors"
 	"strings"
-
-	"golang.org/x/text/secure/precis"
 )
 
 var (
@@ -18,12 +16,12 @@ var (
 
 // Casefold returns a casefolded string, without doing any name or channel character checks.
 func Casefold(str string) (string, error) {
-	return precis.Nickname.String(str)
+	return NicknameProfile.String(str)
 }
 
 // CasefoldChannel returns a casefolded version of a channel name.
 func CasefoldChannel(name string) (string, error) {
-	lowered, err := precis.Nickname.String(name)
+	lowered, err := NicknameProfile.String(name)
 
 	if err != nil {
 		return "", err
@@ -47,7 +45,7 @@ func CasefoldChannel(name string) (string, error) {
 
 // CasefoldName returns a casefolded version of a nick/user name.
 func CasefoldName(name string) (string, error) {
-	lowered, err := precis.Nickname.String(name)
+	lowered, err := NicknameProfile.String(name)
 
 	if err != nil {
 		return "", err

irc/strings_nickname.go

@@ -0,0 +1,89 @@
+// Copyright 2015 The 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.
+
+//NOTE(dan): I need this because the default PRECIS API does not allow a way to retrieve the casefolded version of strings.
+// See also: https://github.com/golang/go/issues/17386
+
+// the content of this file is taken wholesale from the proper PRECIS API:
+// https://github.com/golang/text/tree/master/secure/precis
+
+package irc
+
+import (
+	"unicode"
+	"unicode/utf8"
+
+	"golang.org/x/text/secure/precis"
+	"golang.org/x/text/transform"
+	"golang.org/x/text/unicode/norm"
+)
+
+type nickAdditionalMapping struct {
+	// TODO: This transformer needs to be stateless somehow…
+	notStart  bool
+	prevSpace bool
+}
+
+func (t *nickAdditionalMapping) Reset() {
+	t.prevSpace = false
+	t.notStart = false
+}
+
+func (t *nickAdditionalMapping) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
+	// RFC 7700 §2.1.  Rules
+	//
+	// 2.  Additional Mapping Rule: The additional mapping rule consists of
+	//                              the following sub-rules.
+	//
+	//        1.  Any instances of non-ASCII space MUST be mapped to ASCII
+	//            space (U+0020); a non-ASCII space is any Unicode code point
+	//            having a general category of "Zs", naturally with the
+	//            exception of U+0020.
+	//
+	//        2.  Any instances of the ASCII space character at the beginning
+	//            or end of a nickname MUST be removed (e.g., "stpeter " is
+	//            mapped to "stpeter").
+	//
+	//        3.  Interior sequences of more than one ASCII space character
+	//            MUST be mapped to a single ASCII space character (e.g.,
+	//            "St  Peter" is mapped to "St Peter").
+
+	for nSrc < len(src) {
+		r, size := utf8.DecodeRune(src[nSrc:])
+		if size == 0 { // Incomplete UTF-8 encoding
+			if !atEOF {
+				return nDst, nSrc, transform.ErrShortSrc
+			}
+			size = 1
+		}
+		if unicode.Is(unicode.Zs, r) {
+			t.prevSpace = true
+		} else {
+			if t.prevSpace && t.notStart {
+				dst[nDst] = ' '
+				nDst += 1
+			}
+			if size != copy(dst[nDst:], src[nSrc:nSrc+size]) {
+				nDst += size
+				return nDst, nSrc, transform.ErrShortDst
+			}
+			nDst += size
+			t.prevSpace = false
+			t.notStart = true
+		}
+		nSrc += size
+	}
+	return nDst, nSrc, nil
+}
+
+var (
+	NicknameProfile = precis.NewFreeform(
+		precis.AdditionalMapping(func() transform.Transformer {
+			return &nickAdditionalMapping{}
+		}),
+		precis.LowerCase(),
+		precis.Norm(norm.NFKC),
+		precis.DisallowEmpty,
+	)
+)