write buffer pooling

client.go

@@ -83,6 +83,15 @@ type Dialer struct {
 	// If Jar is nil, cookies are not sent in requests and ignored
 	// in responses.
 	Jar http.CookieJar
+
+	// WriteBufferPool specifies a pool of buffers to use for write methods. A
+	// nil value will cause a buffer to be allocated per connection. It is
+	// recommended to use a buffer pool for applications that have a large number
+	// of connections and a modest volume of writes. The provided buffer pool
+	// must not implement a new value instatiator (e.g. Do not implement
+	// sync.Pool.New()), and must not be shared across connections that have
+	// different values of WriteBufferSize.
+	WriteBufferPool BufferPool
 }
 
 var errMalformedURL = errors.New("malformed ws or wss URL")
@@ -339,6 +348,7 @@ func (d *Dialer) Dial(urlStr string, requestHeader http.Header) (*Conn, *http.Re
 	}
 
 	conn := newConn(netConn, false, d.ReadBufferSize, d.WriteBufferSize)
+	conn.writePool = d.WriteBufferPool
 
 	if err := req.Write(netConn); err != nil {
 		return nil, nil, err

conn.go

@@ -109,6 +109,12 @@ type CloseError struct {
 	Text string
 }
 
+// BufferPool represents a pool of buffers.
+type BufferPool interface {
+	Get() interface{}
+	Put(interface{})
+}
+
 func (e *CloseError) Error() string {
 	s := []byte("websocket: close ")
 	s = strconv.AppendInt(s, int64(e.Code), 10)
@@ -225,11 +231,13 @@ type Conn struct {
 	subprotocol string
 
 	// Write fields
-	mu            chan bool // used as mutex to protect write to conn
-	writeBuf      []byte    // frame is constructed in this buffer.
-	writeDeadline time.Time
-	writer        io.WriteCloser // the current writer returned to the application
-	isWriting     bool           // for best-effort concurrent write detection
+	mu              chan bool // used as mutex to protect write to conn
+	writeBuf        []byte    // frame is constructed in this buffer.
+	writeBufferSize int
+	writePool       BufferPool
+	writeDeadline   time.Time
+	writer          io.WriteCloser // the current writer returned to the application
+	isWriting       bool           // for best-effort concurrent write detection
 
 	writeErrMu sync.Mutex
 	writeErr   error
@@ -276,7 +284,7 @@ func newConn(conn net.Conn, isServer bool, readBufferSize, writeBufferSize int)
 		conn:                   conn,
 		mu:                     mu,
 		readFinal:              true,
-		writeBuf:               make([]byte, writeBufferSize+maxFrameHeaderSize),
+		writeBufferSize:        writeBufferSize,
 		enableWriteCompression: true,
 	}
 	c.SetCloseHandler(nil)
@@ -441,6 +449,9 @@ func (c *Conn) NextWriter(messageType int) (io.WriteCloser, error) {
 		frameType: messageType,
 		pos:       maxFrameHeaderSize,
 	}
+	if err := c.acquireWriteBuf(); err != nil {
+		return nil, err
+	}
 	c.writer = mw
 	if c.newCompressionWriter != nil && c.enableWriteCompression && isData(messageType) {
 		w, err := c.newCompressionWriter(c.writer)
@@ -644,6 +655,7 @@ func (w *messageWriter) ReadFrom(r io.Reader) (nn int64, err error) {
 }
 
 func (w *messageWriter) Close() error {
+	defer w.c.releaseWriteBuf()
 	if w.err != nil {
 		return w.err
 	}
@@ -666,6 +678,9 @@ func (c *Conn) WriteMessage(messageType int, data []byte) error {
 			return err
 		}
 		mw := messageWriter{c: c, frameType: messageType, pos: maxFrameHeaderSize}
+		if err := c.acquireWriteBuf(); err != nil {
+			return err
+		}
 		n := copy(c.writeBuf[mw.pos:], data)
 		mw.pos += n
 		data = data[n:]
@@ -1041,3 +1056,29 @@ func FormatCloseMessage(closeCode int, text string) []byte {
 	copy(buf[2:], text)
 	return buf
 }
+
+func (c *Conn) acquireWriteBuf() error {
+	if c.writeBuf != nil {
+		return nil
+	}
+	n := c.writeBufferSize + maxFrameHeaderSize
+	if c.writePool != nil {
+		if i := c.writePool.Get(); i != nil {
+			p, ok := i.([]byte)
+			if !ok || len(p) != n {
+				return errors.New("bad value from write buffer pool")
+			}
+			c.writeBuf = p
+			return nil
+		}
+	}
+	c.writeBuf = make([]byte, n)
+	return nil
+}
+
+func (c *Conn) releaseWriteBuf() {
+	if c.writePool != nil && c.writeBuf != nil {
+		c.writePool.Put(c.writeBuf)
+		c.writeBuf = nil
+	}
+}

server.go

@@ -52,6 +52,15 @@ type Upgrader struct {
 	// guarantee that compression will be supported. Currently only "no context
 	// takeover" modes are supported.
 	EnableCompression bool
+
+	// WriteBufferPool specifies a pool of buffers to use for write methods. A
+	// nil value will cause a buffer to be allocated per connection. It is
+	// recommended to use a buffer pool for applications that have a large number
+	// of connections and a modest volume of writes. The provided buffer pool
+	// must not implement a new value instatiator (e.g. Do not implement
+	// sync.Pool.New()), and must not be shared across connections that have
+	// different values of WriteBufferSize.
+	WriteBufferPool BufferPool
 }
 
 func (u *Upgrader) returnError(w http.ResponseWriter, r *http.Request, status int, reason string) (*Conn, error) {
@@ -173,13 +182,19 @@ func (u *Upgrader) Upgrade(w http.ResponseWriter, r *http.Request, responseHeade
 	}
 
 	c := newConn(netConn, true, u.ReadBufferSize, u.WriteBufferSize)
+	c.writePool = u.WriteBufferPool
 	c.subprotocol = subprotocol
 
 	if compress {
 		c.newCompressionWriter = compressNoContextTakeover
 		c.newDecompressionReader = decompressNoContextTakeover
 	}
 
+	if err = c.acquireWriteBuf(); err != nil {
+		netConn.Close()
+		return nil, err
+	}
+	defer c.releaseWriteBuf()
 	p := c.writeBuf[:0]
 	p = append(p, "HTTP/1.1 101 Switching Protocols\r\nUpgrade: websocket\r\nConnection: Upgrade\r\nSec-WebSocket-Accept: "...)
 	p = append(p, computeAcceptKey(challengeKey)...)