feat(xmtp_api_grpc): bidi_stream transport primitive

[tylerhawkes]

Stack 2/4 of the XIP-83 bidi client lane: #3769 → #3770 → #3771 → #3772.

Adds one primitive to the protocol-agnostic Client trait: bidi_stream(request, path, BoxDynStream<Bytes>) -> http::Response<BytesStream> — outbound stream of encoded protobuf messages in, inbound message stream out. Default implementation errors ("not supported by this transport"), so gRPC-Web/wasm and mocks are untouched; forwarded through the &T/Box/Arc/boxed-client impls. GrpcClient overrides it natively via tonic Grpc::streaming + the existing TransparentCodec, reusing the NonBlocking stream machinery verbatim. build_tonic_request made generic over the body type.

🤖 Generated with Claude Code

Note

Add bidi_stream bidirectional streaming transport primitive to GrpcClient

• Adds bidi_stream to the Client trait in traits.rs with a default implementation that returns an unretryable error, so existing transports don't break.
• Implements bidi_stream on GrpcClient (non-wasm only) in client.rs, sending an outbound BoxDynStream<Bytes> and returning an inbound BytesStream over HTTP/2.
• Makes build_tonic_request generic over the body type to support both unary/server-streaming (Bytes) and bidirectional (stream of frames) use cases.
• Forwards bidi_stream through blanket impls for &T, &mut T, Arc<T>, and BoxedClient<C>.

^{Macroscope summarized 74f05a8.}

[claude]

Claude finished @tylerhawkes's task —— View job

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Code Review - June 24, 2026 20:31 UTC

• Read changed files
• Analyze code quality and best practices
• Check for potential bugs or issues
• Review performance and security considerations
• Assess test coverage

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Findings

Code Quality & Best Practices ✅

• Clean implementation following existing patterns (mirrors stream method structure)
• Proper delegation through wrapper types (&T, Box, Arc, BoxedClient)
• Good use of #[cfg(not(target_arch = "wasm32"))] to limit bidi to native platforms
• Generic build_tonic_request<B> is elegant and reuses existing code

Potential Issues ⚠️

1. Missing #[cfg] guard in blanket impls (crates/xmtp_proto/src/traits.rs:199-206, 232-239, 265-272)

   • The blanket Client impls for &T, Box<T>, and Arc<T> unconditionally forward bidi_stream
   • On wasm, this will forward to the trait's default impl (which errors), but it's inconsistent with GrpcClient having an explicit #[cfg(not(target_arch = "wasm32"))]
   • Consider: Either add #[cfg(not(target_arch = "wasm32"))] to these forwarding impls OR document why unconditional forwarding is intentional

2. Code duplication (crates/xmtp_api_grpc/src/grpc_client/client.rs:196-224)

   • bidi_stream is nearly identical to stream (lines 169-194), differing only in:
     • Body type: BoxDynStream<'static, Bytes> vs Bytes
     • Codec call: client.streaming vs client.server_streaming
   • Consider: Extract shared logic into a helper method to reduce duplication and maintenance burden

Performance & Security ✅

• Reuses proven NonBlockingStreamRequest + TransparentCodec machinery
• No obvious security concerns
• Cloning self and client.inner is consistent with existing stream implementation

Test Coverage ⚠️

• Codecov reports 14.28% patch coverage (24/28 new lines uncovered)
• Missing coverage for:
  • bidi_stream happy path execution (client.rs:199-224)
  • Default error path in trait (traits.rs:150-160)
  • Forwarding impls (traits.rs, boxed_client.rs)
• Stack PR 3/4 or 4/4 likely adds integration tests, but unit-level coverage gap remains

Minor Nit

• Line 215 (client.rs): Type ascription as crate::streams::ResponseFuture is duplicated from stream — if extracted to a helper, this would be deduplicated

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Summary: Solid implementation with no blocking issues. Main concerns are code duplication and test coverage, both addressable in follow-ups if needed for this stack.

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[codecov]

Codecov Report

❌ Patch coverage is 14.28571% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.43%. Comparing base (1e1a195) to head (74f05a8).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/xmtp_api_grpc/src/grpc_client/client.rs	22.22%	14 Missing ⚠️
crates/xmtp_proto/src/traits.rs	0.00%	8 Missing ⚠️
crates/xmtp_proto/src/traits/boxed_client.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3770      +/-   ##
==========================================
- Coverage   84.44%   84.43%   -0.02%     
==========================================
  Files         408      408              
  Lines       59880    59904      +24     
==========================================
+ Hits        50567    50578      +11     
- Misses       9313     9326      +13     

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[macroscopeapp]

Approvability

Verdict: Needs human review

This PR introduces a new bidirectional streaming transport primitive (XIP-83), adding new capability to the Client trait. While well-scoped and authored by the code owner, new transport infrastructure warrants human review to validate the design and integration approach.

^{You can customize Macroscope's approvability policy. Learn more.}