client: validate streaming gRPC response content types

[EffortlessSteven]

What this does

Server-streaming and bidi receive initialization did not validate that a successful response's content-type matched the configured gRPC family or codec. In the trailers-only regression, a gRPC client accepted application/grpc-web+proto: call_server_stream returned Ok(ServerStream), then message() returned Ok(None).

make_server_stream now reuses the unary validator after response-status classification and before encoding or stream construction. Missing and bare-family content types remain accepted; Connect and non-200 HTTP precedence are unchanged.

Verification

Check	Result
public trailers-only witness	unpatched Ok(ServerStream) then Ok(None); patched Unknown before stream exposure
ordinary response heads	family and codec mismatches rejected without grpc-status; headers and compatibility cases preserved
mutation proof	six mutants killed: deleted or conditional validation, hard-coded selectors, wrong ordering, and wrong call site
compatibility runner	1,462 gRPC and 2,854 gRPC-Web cases passed with zero failures

Review map

• validate_grpc_response_content_type: takes protocol and codec directly.
• make_server_stream: shared server-streaming and bidi validation seam.
• Tests and changelog: rejection and compatibility tests, HTTP 502 precedence, and the public false-success regression.

[coderabbitai]

📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes
  • Improved content-type validation for server-streaming and bidirectional gRPC responses.
  • Incompatible protocol or codec declarations are now rejected earlier with appropriate errors.
  • Preserved compatibility for missing or bare content-type headers.
  • Maintained existing HTTP status handling and response-header behavior.

Walkthrough

The client now validates successful gRPC and gRPC-Web streaming response content types before exposing streams. The shared validator uses explicit protocol and codec values. Tests cover compatibility, rejection, error classification, status precedence, headers, and trailers-only responses.

Changes

gRPC content-type validation

Layer / File(s)	Summary
Validator contract and unary integration connectrpc/src/client/mod.rs	The validator now accepts explicit Protocol and CodecFormat values. Unary call sites and compatibility tests use the updated interface.
Streaming response validation connectrpc/src/client/mod.rs	Server-stream and bidirectional-stream construction validates successful gRPC and gRPC-Web responses. Connect responses remain unchanged.
Streaming validation coverage connectrpc/src/client/mod.rs, .changes/unreleased/*	Fixtures and tests cover compatible, incompatible, missing, and bare content types, error classification, status precedence, response headers, trailers-only responses, and the changelog records the behavior.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant GrpcClient
  participant make_server_stream
  participant validate_grpc_response_content_type
  GrpcClient->>make_server_stream: construct successful streaming response
  make_server_stream->>validate_grpc_response_content_type: validate protocol and codec content type
  validate_grpc_response_content_type-->>make_server_stream: accept response or return validation error
  make_server_stream-->>GrpcClient: expose stream or return error

Loading

Suggested reviewers: iainmcgin, fallintoplace, rpb-ant

Poem

A rabbit checks the stream with care,
For family and codec declared there.
Wrong headers stop before the run,
Bare or missing ones still pass on.
Tests hop softly, green and bright.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly identifies the main change: validation of streaming gRPC response content types.
Description check	✅ Passed	The description directly explains the streaming validation change, compatibility behavior, tests, and verification results.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch claude/grpc-stream-response-content-type

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_{Comment @coderabbitai help to get the list of available commands.}

[EffortlessSteven]

Mutation receipts retained for upstream review:

Local mutation	Discriminating failure
remove validation from make_server_stream	direct matrix and public trailers-only witness returned Ok(ServerStream)
require initial-header grpc-status before validation	ordinary response-head matrix returned Ok(ServerStream) while the trailers-only witness still passed
hard-code Protocol::Grpc	gRPC-Web cross-family row returned Ok(ServerStream)
hard-code CodecFormat::Proto	JSON-configured mismatch row returned Ok(ServerStream)
validate before non-200 handling	502 text/html became Unknown instead of Unavailable
validate only in call_server_stream	direct shared-construction matrix returned Ok(ServerStream)

All mutations were restored before the final test runs. The custom missing-terminal-status runner also completed with gRPC 1,462 passed and gRPC-Web 2,854 passed, zero failures.