avoid per-frame cleanup closures on read to remove 2 allocs per frame read

read.go

@@ -217,51 +217,48 @@ func (c *Conn) readLoop(ctx context.Context) (header, error) {
 	}
 }
 
-// prepareRead sets the readTimeout context and returns a done function
-// to be called after the read is done. It also returns an error if the
-// connection is closed. The reference to the error is used to assign
-// an error depending on if the connection closed or the context timed
-// out during use. Typically, the referenced error is a named return
-// variable of the function calling this method.
-func (c *Conn) prepareRead(ctx context.Context, err *error) (func(), error) {
+// prepareRead sets the read timeout and checks whether the connection is closed.
+func (c *Conn) prepareRead(ctx context.Context) error {
 	select {
 	case <-c.closed:
-		return nil, net.ErrClosed
+		return net.ErrClosed
 	default:
 	}
 	c.setupReadTimeout(ctx)
 
-	done := func() {
-		c.clearReadTimeout()
-		select {
-		case <-c.closed:
-			if *err != nil {
-				*err = net.ErrClosed
-			}
-		default:
-		}
-		if *err != nil && ctx.Err() != nil {
-			*err = ctx.Err()
-		}
-	}
-
 	c.closeStateMu.Lock()
 	closeReceivedErr := c.closeReceivedErr
 	c.closeStateMu.Unlock()
 	if closeReceivedErr != nil {
-		defer done()
-		return nil, closeReceivedErr
+		c.clearReadTimeout()
+		return closeReceivedErr
 	}
 
-	return done, nil
+	return nil
+}
+
+// finishRead clears the read timeout and reports whether the connection or
+// operation context ended while the read was in progress.
+func (c *Conn) finishRead(ctx context.Context, err *error) {
+	c.clearReadTimeout()
+	select {
+	case <-c.closed:
+		if *err != nil {
+			*err = net.ErrClosed
+		}
+	default:
+	}
+	if *err != nil && ctx.Err() != nil {
+		*err = ctx.Err()
+	}
 }
 
 func (c *Conn) readFrameHeader(ctx context.Context) (_ header, err error) {
-	readDone, err := c.prepareRead(ctx, &err)
+	err = c.prepareRead(ctx)
 	if err != nil {
 		return header{}, err
 	}
-	defer readDone()
+	defer c.finishRead(ctx, &err)
 
 	h, err := readFrameHeader(c.br, c.readHeaderBuf[:])
 	if err != nil {
@@ -272,11 +269,11 @@ func (c *Conn) readFrameHeader(ctx context.Context) (_ header, err error) {
 }
 
 func (c *Conn) readFramePayload(ctx context.Context, p []byte) (_ int, err error) {
-	readDone, err := c.prepareRead(ctx, &err)
+	err = c.prepareRead(ctx)
 	if err != nil {
 		return 0, err
 	}
-	defer readDone()
+	defer c.finishRead(ctx, &err)
 
 	n, err := io.ReadFull(c.br, p)
 	if err != nil {