rpc_util: Reuse memory buffer for receiving message

rpc_util.go

@@ -540,6 +540,9 @@ type parser struct {
 	// The header of a gRPC message. Find more detail at
 	// https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md
 	header [5]byte
+
+	// buffer is recycled memory used to read the message.
+	buffer []byte
 }
 
 // recvMsg reads a complete gRPC message from the stream.
@@ -573,9 +576,10 @@ func (p *parser) recvMsg(maxReceiveMessageSize int) (pf payloadFormat, msg []byt
 	if int(length) > maxReceiveMessageSize {
 		return 0, nil, status.Errorf(codes.ResourceExhausted, "grpc: received message larger than max (%d vs. %d)", length, maxReceiveMessageSize)
 	}
-	// TODO(bradfitz,zhaoq): garbage. reuse buffer after proto decoding instead
-	// of making it for each message:
-	msg = make([]byte, int(length))
+	if uint32(cap(p.buffer)) < length {
+		p.buffer = make([]byte, int(length))
+	}
+	msg = p.buffer[:length]
 	if _, err := p.r.Read(msg); err != nil {
 		if err == io.EOF {
 			err = io.ErrUnexpectedEOF
@@ -688,12 +692,12 @@ type payloadInfo struct {
 }
 
 func recvAndDecompress(p *parser, s *transport.Stream, dc Decompressor, maxReceiveMessageSize int, payInfo *payloadInfo, compressor encoding.Compressor) ([]byte, error) {
-	pf, d, err := p.recvMsg(maxReceiveMessageSize)
+	pf, buf, err := p.recvMsg(maxReceiveMessageSize)
 	if err != nil {
 		return nil, err
 	}
 	if payInfo != nil {
-		payInfo.wireLength = len(d)
+		payInfo.wireLength = len(buf)
 	}
 
 	if st := checkRecvPayload(pf, s.RecvCompress(), compressor != nil || dc != nil); st != nil {
@@ -705,10 +709,10 @@ func recvAndDecompress(p *parser, s *transport.Stream, dc Decompressor, maxRecei
 		// To match legacy behavior, if the decompressor is set by WithDecompressor or RPCDecompressor,
 		// use this decompressor as the default.
 		if dc != nil {
-			d, err = dc.Do(bytes.NewReader(d))
-			size = len(d)
+			buf, err = dc.Do(bytes.NewReader(buf))
+			size = len(buf)
 		} else {
-			d, size, err = decompress(compressor, d, maxReceiveMessageSize)
+			buf, size, err = decompress(compressor, buf, maxReceiveMessageSize)
 		}
 		if err != nil {
 			return nil, status.Errorf(codes.Internal, "grpc: failed to decompress the received message %v", err)
@@ -719,7 +723,7 @@ func recvAndDecompress(p *parser, s *transport.Stream, dc Decompressor, maxRecei
 			return nil, status.Errorf(codes.ResourceExhausted, "grpc: received message after decompression larger than max (%d vs. %d)", size, maxReceiveMessageSize)
 		}
 	}
-	return d, nil
+	return buf, nil
 }
 
 // Using compressor, decompress d, returning data and size.
@@ -754,15 +758,16 @@ func decompress(compressor encoding.Compressor, d []byte, maxReceiveMessageSize
 // dc takes precedence over compressor.
 // TODO(dfawley): wrap the old compressor/decompressor using the new API?
 func recv(p *parser, c baseCodec, s *transport.Stream, dc Decompressor, m interface{}, maxReceiveMessageSize int, payInfo *payloadInfo, compressor encoding.Compressor) error {
-	d, err := recvAndDecompress(p, s, dc, maxReceiveMessageSize, payInfo, compressor)
+	buf, err := recvAndDecompress(p, s, dc, maxReceiveMessageSize, payInfo, compressor)
 	if err != nil {
 		return err
 	}
-	if err := c.Unmarshal(d, m); err != nil {
+	if err := c.Unmarshal(buf, m); err != nil {
 		return status.Errorf(codes.Internal, "grpc: failed to unmarshal the received message %v", err)
 	}
-	if payInfo != nil {
-		payInfo.uncompressedBytes = d
+	if payInfo != nil && buf != nil {
+		payInfo.uncompressedBytes = make([]byte, len(buf))
+		copy(payInfo.uncompressedBytes, buf)
 	}
 	return nil
 }