test: Correct JSON-RPC serialization tests and add edge case coverage

[pankaj-bind]

Description

This update addresses a failing test in tests/server/apps/jsonrpc/test_serialization.py and significantly enhances the test coverage for the JSON-RPC serialization layer to ensure robustness against various edge cases.

The test_handle_unicode_characters test was previously failing due to an invalid JSON-RPC request payload. This has been corrected to use a valid message/send request, allowing the test to properly validate Unicode handling.

Additionally, new tests have been added to cover scenarios that were previously untested:

• Malformed JSON: Ensures the server correctly identifies and rejects invalid JSON structures, returning a JSONParseError.
• Oversized Payloads: Checks how the application handles requests that exceed size limits, now gracefully handled as an InvalidRequestError.
• Unicode Characters: The corrected test now properly validates that the application can handle Unicode characters in request payloads without serialization issues.

A minor improvement was also made to src/a2a/server/apps/jsonrpc/jsonrpc_app.py to explicitly catch HTTPException (like the one for oversized payloads) and convert it into a standard JSON-RPC error response, ensuring consistent error reporting to clients.

These changes ensure more robust and reliable JSON-RPC communication, which is critical for agentic applications.

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[gemini-code-assist]

Summary of Changes

Hello @pankaj-bind, 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 significantly enhances the robustness and reliability of the JSON-RPC communication layer. It addresses a failing test, adds comprehensive test coverage for critical edge cases like malformed JSON and oversized payloads, and improves the server's error handling to provide consistent JSON-RPC error responses for HTTP-level issues.

Highlights

• Test Correction: The test_handle_unicode_characters test in tests/server/apps/jsonrpc/test_serialization.py was fixed by correcting its JSON-RPC request payload to be valid, allowing it to properly validate Unicode handling.
• New Test Coverage (Malformed JSON): Added a new test, test_handle_invalid_json, to ensure the server correctly identifies and rejects invalid JSON structures, returning a JSONParseError.
• New Test Coverage (Oversized Payloads): Introduced test_handle_oversized_payload to check how the application handles requests that exceed size limits, expecting either a 413 HTTP status or a graceful JSON-RPC InvalidRequestError.
• Enhanced Test Coverage (Unicode Characters): The test_handle_unicode_characters test was enhanced to properly validate that the application can handle Unicode characters in request payloads without serialization issues, using a more realistic message/send request.
• Improved Error Handling: Modified src/a2a/server/apps/jsonrpc/jsonrpc_app.py to explicitly catch HTTPException (specifically for 413 Payload Too Large errors) and convert it into a standard JSON-RPC InvalidRequestError response, ensuring consistent error reporting.

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[gemini-code-assist]

Code Review

This pull request fixes a failing test for Unicode handling and enhances test coverage for malformed JSON and oversized payloads. The application change to handle oversized payloads gracefully with a JSON-RPC error is a good improvement. The review suggests using named constants for HTTP status codes and making the oversized payload test more specific.