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103 lines
2.9 KiB
Go
103 lines
2.9 KiB
Go
// Copyright 2017 The Gorilla WebSocket Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package websocket
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import (
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"bytes"
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"net"
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"sync"
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"time"
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)
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// PreparedMessage caches on the wire representations of a message payload.
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// Use PreparedMessage to efficiently send a message payload to multiple
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// connections. PreparedMessage is especially useful when compression is used
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// because the CPU and memory expensive compression operation can be executed
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// once for a given set of compression options.
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type PreparedMessage struct {
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messageType int
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data []byte
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mu sync.Mutex
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frames map[prepareKey]*preparedFrame
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}
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// prepareKey defines a unique set of options to cache prepared frames in PreparedMessage.
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type prepareKey struct {
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isServer bool
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compress bool
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compressionLevel int
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}
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// preparedFrame contains data in wire representation.
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type preparedFrame struct {
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once sync.Once
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data []byte
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}
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// NewPreparedMessage returns an initialized PreparedMessage. You can then send
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// it to connection using WritePreparedMessage method. Valid wire
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// representation will be calculated lazily only once for a set of current
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// connection options.
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func NewPreparedMessage(messageType int, data []byte) (*PreparedMessage, error) {
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pm := &PreparedMessage{
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messageType: messageType,
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frames: make(map[prepareKey]*preparedFrame),
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data: data,
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}
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// Prepare a plain server frame.
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_, frameData, err := pm.frame(prepareKey{isServer: true, compress: false})
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if err != nil {
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return nil, err
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}
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// To protect against caller modifying the data argument, remember the data
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// copied to the plain server frame.
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pm.data = frameData[len(frameData)-len(data):]
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return pm, nil
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}
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func (pm *PreparedMessage) frame(key prepareKey) (int, []byte, error) {
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pm.mu.Lock()
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frame, ok := pm.frames[key]
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if !ok {
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frame = &preparedFrame{}
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pm.frames[key] = frame
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}
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pm.mu.Unlock()
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var err error
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frame.once.Do(func() {
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// Prepare a frame using a 'fake' connection.
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// TODO: Refactor code in conn.go to allow more direct construction of
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// the frame.
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mu := make(chan struct{}, 1)
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mu <- struct{}{}
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var nc prepareConn
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c := &Conn{
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conn: &nc,
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mu: mu,
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isServer: key.isServer,
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compressionLevel: key.compressionLevel,
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enableWriteCompression: true,
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writeBuf: make([]byte, defaultWriteBufferSize+maxFrameHeaderSize),
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}
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if key.compress {
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c.newCompressionWriter = compressNoContextTakeover
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}
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err = c.WriteMessage(pm.messageType, pm.data)
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frame.data = nc.buf.Bytes()
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})
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return pm.messageType, frame.data, err
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}
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type prepareConn struct {
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buf bytes.Buffer
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net.Conn
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}
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func (pc *prepareConn) Write(p []byte) (int, error) { return pc.buf.Write(p) }
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func (pc *prepareConn) SetWriteDeadline(t time.Time) error { return nil }
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