write: Zero alloc writes with Writer

Closes #354

ci/bench.sh

@@ -2,8 +2,8 @@
 set -eu
 cd -- "$(dirname "$0")/.."
 
-go test --run=^$ --bench=. "$@" ./...
+go test --run=^$ --bench=. --benchmem --memprofile ci/out/prof.mem --cpuprofile ci/out/prof.cpu -o ci/out/websocket.test "$@" .
 (
   cd ./internal/thirdparty
-  go test --run=^$ --bench=. "$@" ./...
+  go test --run=^$ --bench=. --benchmem --memprofile ../../ci/out/prof-thirdparty.mem --cpuprofile ../../ci/out/prof-thirdparty.cpu -o ../../ci/out/thirdparty.test "$@" .
 )

conn.go

@@ -63,7 +63,7 @@ type Conn struct {
 	readCloseFrameErr error
 
 	// Write state.
-	msgWriterState *msgWriterState
+	msgWriter      *msgWriter
 	writeFrameMu   *mu
 	writeBuf       []byte
 	writeHeaderBuf [8]byte
@@ -113,14 +113,14 @@ func newConn(cfg connConfig) *Conn {
 
 	c.msgReader = newMsgReader(c)
 
-	c.msgWriterState = newMsgWriterState(c)
+	c.msgWriter = newMsgWriter(c)
 	if c.client {
 		c.writeBuf = extractBufioWriterBuf(c.bw, c.rwc)
 	}
 
 	if c.flate() && c.flateThreshold == 0 {
 		c.flateThreshold = 128
-		if !c.msgWriterState.flateContextTakeover() {
+		if !c.msgWriter.flateContextTakeover() {
 			c.flateThreshold = 512
 		}
 	}
@@ -157,8 +157,7 @@ func (c *Conn) close(err error) {
 	c.rwc.Close()
 
 	go func() {
-		c.msgWriterState.close()
-
+		c.msgWriter.close()
 		c.msgReader.close()
 	}()
 }

write.go

@@ -49,30 +49,11 @@ func (c *Conn) Write(ctx context.Context, typ MessageType, p []byte) error {
 }
 
 type msgWriter struct {
-	mw     *msgWriterState
-	closed bool
-}
-
-func (mw *msgWriter) Write(p []byte) (int, error) {
-	if mw.closed {
-		return 0, errors.New("cannot use closed writer")
-	}
-	return mw.mw.Write(p)
-}
-
-func (mw *msgWriter) Close() error {
-	if mw.closed {
-		return errors.New("cannot use closed writer")
-	}
-	mw.closed = true
-	return mw.mw.Close()
-}
-
-type msgWriterState struct {
 	c *Conn
 
 	mu      *mu
 	writeMu *mu
+	closed  bool
 
 	ctx    context.Context
 	opcode opcode
@@ -82,16 +63,16 @@ type msgWriterState struct {
 	flateWriter *flate.Writer
 }
 
-func newMsgWriterState(c *Conn) *msgWriterState {
-	mw := &msgWriterState{
+func newMsgWriter(c *Conn) *msgWriter {
+	mw := &msgWriter{
 		c:       c,
 		mu:      newMu(c),
 		writeMu: newMu(c),
 	}
 	return mw
 }
 
-func (mw *msgWriterState) ensureFlate() {
+func (mw *msgWriter) ensureFlate() {
 	if mw.trimWriter == nil {
 		mw.trimWriter = &trimLastFourBytesWriter{
 			w: util.WriterFunc(mw.write),
@@ -104,22 +85,19 @@ func (mw *msgWriterState) ensureFlate() {
 	mw.flate = true
 }
 
-func (mw *msgWriterState) flateContextTakeover() bool {
+func (mw *msgWriter) flateContextTakeover() bool {
 	if mw.c.client {
 		return !mw.c.copts.clientNoContextTakeover
 	}
 	return !mw.c.copts.serverNoContextTakeover
 }
 
 func (c *Conn) writer(ctx context.Context, typ MessageType) (io.WriteCloser, error) {
-	err := c.msgWriterState.reset(ctx, typ)
+	err := c.msgWriter.reset(ctx, typ)
 	if err != nil {
 		return nil, err
 	}
-	return &msgWriter{
-		mw:     c.msgWriterState,
-		closed: false,
-	}, nil
+	return c.msgWriter, nil
 }
 
 func (c *Conn) write(ctx context.Context, typ MessageType, p []byte) (int, error) {
@@ -129,8 +107,8 @@ func (c *Conn) write(ctx context.Context, typ MessageType, p []byte) (int, error
 	}
 
 	if !c.flate() {
-		defer c.msgWriterState.mu.unlock()
-		return c.writeFrame(ctx, true, false, c.msgWriterState.opcode, p)
+		defer c.msgWriter.mu.unlock()
+		return c.writeFrame(ctx, true, false, c.msgWriter.opcode, p)
 	}
 
 	n, err := mw.Write(p)
@@ -142,7 +120,7 @@ func (c *Conn) write(ctx context.Context, typ MessageType, p []byte) (int, error
 	return n, err
 }
 
-func (mw *msgWriterState) reset(ctx context.Context, typ MessageType) error {
+func (mw *msgWriter) reset(ctx context.Context, typ MessageType) error {
 	err := mw.mu.lock(ctx)
 	if err != nil {
 		return err
@@ -151,21 +129,26 @@ func (mw *msgWriterState) reset(ctx context.Context, typ MessageType) error {
 	mw.ctx = ctx
 	mw.opcode = opcode(typ)
 	mw.flate = false
+	mw.closed = false
 
 	mw.trimWriter.reset()
 
 	return nil
 }
 
-func (mw *msgWriterState) putFlateWriter() {
+func (mw *msgWriter) putFlateWriter() {
 	if mw.flateWriter != nil {
 		putFlateWriter(mw.flateWriter)
 		mw.flateWriter = nil
 	}
 }
 
 // Write writes the given bytes to the WebSocket connection.
-func (mw *msgWriterState) Write(p []byte) (_ int, err error) {
+func (mw *msgWriter) Write(p []byte) (_ int, err error) {
+	if mw.closed {
+		return 0, errors.New("cannot use closed writer")
+	}
+
 	err = mw.writeMu.lock(mw.ctx)
 	if err != nil {
 		return 0, fmt.Errorf("failed to write: %w", err)
@@ -194,7 +177,7 @@ func (mw *msgWriterState) Write(p []byte) (_ int, err error) {
 	return mw.write(p)
 }
 
-func (mw *msgWriterState) write(p []byte) (int, error) {
+func (mw *msgWriter) write(p []byte) (int, error) {
 	n, err := mw.c.writeFrame(mw.ctx, false, mw.flate, mw.opcode, p)
 	if err != nil {
 		return n, fmt.Errorf("failed to write data frame: %w", err)
@@ -204,9 +187,14 @@ func (mw *msgWriterState) write(p []byte) (int, error) {
 }
 
 // Close flushes the frame to the connection.
-func (mw *msgWriterState) Close() (err error) {
+func (mw *msgWriter) Close() (err error) {
 	defer errd.Wrap(&err, "failed to close writer")
 
+	if mw.closed {
+		return errors.New("writer already closed")
+	}
+	mw.closed = true
+
 	err = mw.writeMu.lock(mw.ctx)
 	if err != nil {
 		return err
@@ -232,7 +220,7 @@ func (mw *msgWriterState) Close() (err error) {
 	return nil
 }
 
-func (mw *msgWriterState) close() {
+func (mw *msgWriter) close() {
 	if mw.c.client {
 		mw.c.writeFrameMu.forceLock()
 		putBufioWriter(mw.c.bw)