fix: Reject SendMessage with mismatching contextId and taskId

[jmesnil]

When a message references an existing task but provides a contextId that doesn't match the task's context, reject it with an InvalidParamsError.

This fixes #723

[gemini-code-assist]

Summary of Changes

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This pull request introduces a crucial validation step to enhance the integrity of message processing within the system. It ensures that messages intended for existing tasks are correctly routed by verifying that their contextId aligns with the task's contextId. This prevents potential data corruption or misdirection of messages, improving the robustness of the message handling mechanism.

Highlights

• Context ID Validation: Implemented a new validation check in DefaultRequestHandler to ensure that when a SendMessage operation references an existing task, the contextId provided in the message matches the contextId of the task.
• Error Handling: Requests with a contextId mismatch will now be rejected with an InvalidParamsError, preventing messages from being incorrectly associated with tasks.
• Test Coverage: Added a new unit test (testRejectMismatchingContextId) in DefaultRequestHandlerTest to verify the correct behavior of the contextId mismatch validation and error throwing.

Changelog

• server-common/src/main/java/io/a2a/server/requesthandlers/DefaultRequestHandler.java
  • Added a check to validate if the contextId in an incoming message matches the contextId of an existing task.
  • Introduced an InvalidParamsError to be thrown when a contextId mismatch is detected.
• server-common/src/test/java/io/a2a/server/requesthandlers/DefaultRequestHandlerTest.java
  • Imported assertThrows for testing expected exceptions.
  • Imported InvalidParamsError for use in the test.
  • Added testRejectMismatchingContextId to test the new validation logic for mismatched contextIds.

Activity

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[gemini-code-assist]

Code Review

This pull request correctly implements the validation to reject messages with a mismatched contextId for an existing task. The added logic in DefaultRequestHandler prevents associating a message with a task in a different context, and the new test case in DefaultRequestHandlerTest effectively verifies this behavior. I have a couple of suggestions for minor improvements to enhance code clarity and test robustness.