fix(a2a-server): add missing return after 501 in /tasks/metadata endpoint

[yashodipmore]

Summary

Fixes #21729

Adds a missing return statement after the res.status(501).send() in the GET /tasks/metadata endpoint. Without this return, when using a non-InMemory task store (e.g., GCSTaskStore), the handler falls through into the try block and attempts to send a second response, causing ERR_HTTP_HEADERS_SENT and crashing the server.

Changes

packages/a2a-server/src/http/app.ts

• Added return; after res.status(501).send() in the /tasks/metadata route handler
• Consistent with the pattern used in the adjacent /tasks/:taskId/metadata endpoint and all other early-exit guards in the file

packages/a2a-server/src/http/endpoints.test.ts

• Added @google-cloud/storage mock to support GCS task store testing
• Added new Agent Server Endpoints (GCS Task Store) describe block
• Added test: verifies GET /tasks/metadata returns 501 (not crash) when using GCS task store

Testing

All 26 tests pass (6 endpoints + 20 app tests):

✓ Agent Server Endpoints > should create a new task via POST /tasks
✓ Agent Server Endpoints > should get metadata for a specific task via GET /tasks/:taskId/metadata
✓ Agent Server Endpoints > should get metadata for all tasks via GET /tasks/metadata
✓ Agent Server Endpoints > should return 404 for a non-existent task
✓ Agent Server Endpoints > should return agent metadata via GET /.well-known/agent-card.json
✓ Agent Server Endpoints (GCS Task Store) > should return 501 for GET /tasks/metadata when not using InMemoryTaskStore  ← NEW

Impact

• Before: Every GET /tasks/metadata call crashes A2A server when GCS_BUCKET_NAME is set
• After: Returns clean 501 with descriptive error message

[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 addresses a critical bug in the A2A server where the GET /tasks/metadata endpoint would crash the server if a task store other than InMemoryTaskStore (e.g., GCSTaskStore) was configured. The fix ensures that the server gracefully handles this scenario by returning a 501 status and preventing subsequent response attempts, thereby improving the server's stability and reliability.

Highlights

• API Endpoint Fix: Added a crucial "return" statement after sending a 501 status in the GET /tasks/metadata endpoint to prevent the server from crashing when a non-InMemory task store is used.
• Testing Enhancements: Introduced a mock for @google-cloud/storage and a new test suite to verify the correct 501 behavior of the /tasks/metadata endpoint when using a GCS task store.

Changelog

• packages/a2a-server/src/http/app.ts
  • Added a "return;" statement after res.status(501).send() in the /tasks/metadata route handler.
• packages/a2a-server/src/http/endpoints.test.ts
  • Added a mock for @google-cloud/storage to enable testing with GCS task stores without a real connection.
  • Introduced a new describe block for "Agent Server Endpoints (GCS Task Store)".
  • Added a test case to verify that GET /tasks/metadata returns a 501 status and does not crash when a GCS task store is in use.

Activity

• The pull request was created by yashodipmore to fix issue Bug: A2A server GET /tasks/metadata missing return after 501 response — causes ERR_HTTP_HEADERS_SENT crash with GCS task store #21729.
• The author provided a detailed summary, changes, testing information, and impact analysis.

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[gemini-code-assist]

Code Review

This pull request correctly addresses a server crash in the /tasks/metadata endpoint by adding a missing return statement after sending a 501 error. This prevents the code from attempting to send a second response, which previously caused an ERR_HTTP_HEADERS_SENT error. The fix is accompanied by a well-written test case that mocks the GCS task store and verifies that the endpoint now correctly returns a 501 status without crashing. The changes are correct and effectively resolve the issue.

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