fix: fix error handling for gRPC and SSE streaming

[ishymko]

Reproduced in test_client_server_integration.py.

gRPC

validate_async_generator decorator was applied on top of the method above A2A error handling. Compat handler was already refactored in a way which made it possible to apply it on a nested function. It was done there and v1 handler was refactored in the same way.

SSE streaming

Iterator wrapped into validate_async_generator is assigned to EventSourceResponse and is returned from the method, so when it throws rest_stream_error_handler has no effect on it.

a2a-python/src/a2a/server/apps/rest/rest_adapter.py

Lines 155 to 163 in 4630efd

	async def event_generator(
	stream: AsyncIterable[Any],
	) -> AsyncIterator[str]:
	async for item in stream:
	yield json.dumps(item)
	return EventSourceResponse(
	event_generator(method(request, call_context))
	)

Instead of throwing on the first iteration, throw on the method invocation itself to avoid more sophisticated error handling (i.e. reading one item to trigger error) by removing separate handling for async generator.

Client-level handling is also updated to properly handle non-200 status code for streaming and non-streaming response in case of JSON-RPC error.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the gRPC request handling mechanism to centralize error management and context building. By introducing generic helper methods for unary and streaming calls, it standardizes how errors are caught and processed across all gRPC endpoints. This change improves code maintainability and ensures consistent error responses, while also enhancing test coverage for various error conditions.

Highlights

• Centralized gRPC Error Handling: Introduced new _handle_unary and _handle_stream helper methods in GrpcHandler to centralize error handling, context building, and metadata setting for all gRPC service methods. This significantly reduces boilerplate and improves consistency.
• Decorator Relocation for A2A Compat Handler: Moved @validate_async_generator and @validate decorators from the main gRPC service methods to their nested _handler functions within CompatGrpcHandler. This ensures validation occurs at the correct stage of the request lifecycle.
• Refactored gRPC Service Methods: All individual gRPC service methods in GrpcHandler were refactored to utilize the new _handle_unary or _handle_stream helper methods, streamlining their implementation and error management.
• Expanded Integration Tests: Added new fixtures and integration tests to cover error handling scenarios, including UnsupportedOperationError for disabled streaming and push notifications, and VersionNotSupportedError, ensuring robust error propagation.

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[gemini-code-assist]

Code Review

The pull request effectively refactors the gRPC handlers to centralize error handling and context management, improving code organization and reducing duplication. The changes in src/a2a/compat/v0_3/grpc_handler.py correctly move validation decorators to nested functions, aligning with the new error handling strategy. The addition of new fixtures and integration tests in tests/integration/test_client_server_integration.py demonstrates a commitment to robust testing, particularly for the new error handling and compatibility features. The overall direction of the changes is positive for maintainability and reliability.

[github-actions]

🧪 Code Coverage (vs 1.0-dev)

⬇️ Download Full Report

	Base	PR	Delta
src/a2a/client/transports/grpc.py	88.46%	89.23%	🟢 +0.77%
src/a2a/client/transports/http_helpers.py	95.65%	94.64%	🔴 -1.01%
src/a2a/client/transports/jsonrpc.py	83.92%	86.71%	🟢 +2.80%
src/a2a/compat/v0_3/grpc_handler.py	95.52%	97.01%	🟢 +1.49%
src/a2a/compat/v0_3/grpc_transport.py	41.84%	59.57%	🟢 +17.73%
src/a2a/server/request_handlers/grpc_handler.py	81.55%	94.48%	🟢 +12.93%
src/a2a/utils/helpers.py	97.42%	97.19%	🔴 -0.23%
Total	90.77%	91.45%	🟢 +0.68%

Generated by coverage-comment.yml

[ishymko]

/gemini review

[gemini-code-assist]

Code Review

This pull request refactors error handling for gRPC and SSE streaming. The gRPC handler refactoring significantly improves code clarity and maintainability by centralizing error handling. The SSE error handling improvements in http_helpers.py are also a good addition for robustness.

However, there is a critical issue introduced by replacing @validate_async_generator with @validate on async generator methods. The current @validate decorator is not designed to handle async generators and will cause a TypeError at runtime. This affects gRPC, REST, and JSON-RPC streaming handlers. I've left a detailed comment on this issue. Additionally, the new integration tests for this feature are incomplete as they only test the failure path, which masks this bug.