Compress behavior difference between grpc-java and grpc-go

[yann9]

Client:
grpc-java append grpc-accept-encoding header even if compress calloption has not set.

grpc-java/core/src/main/java/io/grpc/internal/ClientCallImpl.java

Line 196 in cc2d376

headers.put(MESSAGE_ACCEPT_ENCODING_KEY, advertisedEncodings);

    byte[] advertisedEncodings =
        InternalDecompressorRegistry.getRawAdvertisedMessageEncodings(decompressorRegistry);
    if (advertisedEncodings.length != 0) {
      headers.put(MESSAGE_ACCEPT_ENCODING_KEY, advertisedEncodings);
    }

grpc-go append grpc-accept-encoding header only if compress calloption has set.
https://github.com/grpc/grpc-go/blob/a6ab4473c5a469332c1bdee691293affeaaece25/internal/transport/http2_client.go#L444

 if callHdr.SendCompress != "" {
	headerFields = append(headerFields, hpack.HeaderField{Name: "grpc-encoding", Value: callHdr.SendCompress})
	headerFields = append(headerFields, hpack.HeaderField{Name: "grpc-accept-encoding", Value: callHdr.SendCompress})
 }

Server:

grpc-java will check the grpc-accept-encoding header which client send to server and compression is not enabled by default. Compressor will be set with the grpc-accept-encoding message compression method

grpc-java/core/src/main/java/io/grpc/internal/ServerCallImpl.java

Line 114 in cc2d376

if (messageAcceptEncoding != null) {

    if (compressor == null) {
      compressor = Codec.Identity.NONE;
    } else {
      if (messageAcceptEncoding != null) {
        // TODO(carl-mastrangelo): remove the string allocation.
        if (!GrpcUtil.iterableContains(
            ACCEPT_ENCODING_SPLITTER.split(new String(messageAcceptEncoding, GrpcUtil.US_ASCII)),
            compressor.getMessageEncoding())) {
          // resort to using no compression.
          compressor = Codec.Identity.NONE;
        }
      } else {
        compressor = Codec.Identity.NONE;
      }
    }

grpc-go will not check the grpc-accept-encoding header which client send to server and compression is enabled by default. Compressor will be set with the grpc-encoding message compression method
https://github.com/grpc/grpc-go/blob/a6ab4473c5a469332c1bdee691293affeaaece25/server.go#L1123

if s.opts.cp != nil {
	cp = s.opts.cp
	stream.SetSendCompress(cp.Type())
} else if rc := stream.RecvCompress(); rc != "" && rc != encoding.Identity {
	// Legacy compressor not specified; attempt to respond with same encoding.
	comp = encoding.GetCompressor(rc)
	if comp != nil {
		stream.SetSendCompress(rc)
	}
} 

Why? Are there any other reasons for the inconsistency？

[ericgribkoff]

I believe the discrepancy is due to grpc/grpc-go#2786. Go only recently (grpc/grpc-go#3139) added the client-side setting of grpc-accept-encoding, and the open issue identifies that some more items still remain to be done there.

Since this seems to be more of a gRPC Go question - as far as I can tell, gRPC Java is compliant with the spec and compression is advertised/configured as expected - I'm going to mark this closed here. If there's other Java-specific concerns feel free to comment and I will reopen; otherwise for the Go side of things adding a comment to grpc/grpc-go#2786 is probably the right place.