Retries on xds:/// channels (or with RawMessageClientInterceptor) send empty 0-byte payload on retry

[alfredomusumeci]

What version of gRPC-Java are you using?

Broken: 1.83.0/1.83.1
Working: 1.82.2

What is your environment?

Azul Zulu JDK 26

Summary

When an RPC is retried on an 'xds:///' channel (or any channel with raw 'InputStream' pass-through marshalling), retry attempts send an empty 0-byte payload (a 5-byte gRPC frame '00 00 00 00 00') rather than replying with the original request payload. If the backend server is configured to also accept an empty protobuf message (e.g. a batch request containing 0 items) and returns 'OK', this results in silent false positives, ie the replayed (now) empty message doesn't throw any error.

RetriableStream replays messages via 'method.streamRequest(message)'. When 'method' uses a raw 'InputStream' pass-through marshaller, the already consumed 'InputStream' is passed to subsequent retry attempts without being re-buffered. Starting on version 1.83.0, 'XdsNameResolver' introduced 'RawMessageClientInterceptor' on every 'xds:///' call. In turn, that rebuilds the method with a pass-through InputStream marshaller. As a result, all retried calls on 'xds:///' channels transmit empty request bodies.
The retry itself comes from Traffic Director over xDS.

What did you expect to see?

On retry, the client should replay the full original payload buffer
user-agent: grpc-java-netty/1.83.0
Attempt 1 (StreamId=3): sends 857 bytes -> server returns grpc-status: 13
Retry 1 (streamId=3 on second connection): sends 857 bytes -> server returns grpc-status: 13
Retry 2 (streamId=5): sends 857 bytes -> server returns grpc-status: 13
Retry 3 (streamId=5): sends 857 bytes -> server returns grpc-status: 13
Retry 4 (streamId=7): sends 857 bytes -> server returns grpc-status: 13
StatusRuntimeException(INTERNAL) -> MyServiceInternalException

What did you see instead?

user-agent: grpc-java-netty/1.83.0
Attempt 1 (StreamId=3): sends 857 bytes -> server returns grpc-status: 13
Retry (streamId=5): sends 5 bytes (0000000000 - empty body) -> server returns grpc-status: 0 (OK) with empty response

Steps to reproduce the bug

1. Using grpc-java 1.83.0+, create an xds:// channel (or a channel with XdsNameResolver.RawMessageClientInterceptor) with RetryPolicy configured in serviceConfig
2. Issue a unary or batch RPC (with a non-empty payload)
3. Have the server return a retryable status (INTERNAL/UNAVAILABLE) on attempt 1
4. Attempt 2 will transmit an empty 5-byte frame with 0 payload bytes.