PROTOCOL_ERROR when grpc-java connects over Unix socket

[UsatovPavel]

What version of gRPC-Java are you using?

1.79.0 (grpc-netty, Netty 4.1.130)

What is your environment?

• OS: Linux x86_64 (Ubuntu 24)
• Server: tonic (Rust gRPC, e.g. Dragonfly dfdaemon)
• Transport: Unix domain socket

What did you expect to see?

Successful gRPC calls over Unix domain socket, same as grpc-go.

What did you see instead?

io.grpc.StatusRuntimeException: INTERNAL: RST_STREAM closed stream. HTTP/2 error code: PROTOCOL_ERROR

Steps to reproduce the bug

1. Run a tonic gRPC server on a Unix socket (e.g. Dragonfly dfdaemon at /var/run/dragonfly/dfdaemon.sock).
2. Connect with grpc-java:

ManagedChannel ch = NettyChannelBuilder
    .forAddress(new DomainSocketAddress("/var/run/dragonfly/dfdaemon.sock"))
    .eventLoopGroup(new EpollEventLoopGroup())
    .channelType(EpollDomainSocketChannel.class)
    .usePlaintext()
    .build();
// Any RPC call fails with PROTOCOL_ERROR

3. Same server works with grpc-go over the same socket.
4. Same grpc-java client works if server is reached via TCP (e.g. socat proxy).

Additional context

strace: grpc-java sends :authority = socket path (/var/run/dragonfly/dfdaemon.sock). grpc-go sends localhost or empty for UDS. tonic uses hyperium/h2, which rejects non-RFC authority. See h2#487, tonic#742.

Workaround: socat TCP-LISTEN:50051,fork UNIX-CONNECT:/path/to/sock then connect to 127.0.0.1:50051.

Suggestion: Add overrideAuthority() (or similar) to NettyChannelBuilder for UDS, like grpc-go's WithAuthority("localhost").