feat: Adding stand-alone support for RESTful API serving #297

pstephengoogle · 2025-07-11T15:51:31Z

Adding stand-alone support for RESTful API serving

Though the RESTful API (JSON+HTTP) can be served from an envoy transcoding of the gRPC service that may not always make sense in all cases. Instead, this PR also adds the ability to serve the RESTful API stand-alone, without needing to also setup the gRPC service.

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Summary of Changes

Hello @pstephengoogle, 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 introduces the capability to serve the A2A RESTful API as a standalone service, offering an alternative to gRPC-based serving with Envoy transcoding. It achieves this by adding new application and request handler components that directly process REST (JSON+HTTP) requests, map them to the core A2A logic, and manage responses, including Server-Sent Events.

Highlights

Standalone REST API Support: Introduces new RESTApplication and A2ARESTFastAPIApplication classes to enable serving the A2A RESTful API independently, without reliance on gRPC or Envoy transcoding.
REST Request Handling: Adds a dedicated RESTHandler that maps incoming REST (JSON+HTTP) requests to the appropriate underlying A2A request handler methods, ensuring consistency with existing gRPC service definitions by leveraging protobuf for data serialization/deserialization.
FastAPI Integration: Implements A2ARESTFastAPIApplication to build a FastAPI application, providing concrete endpoints for A2A operations such as message sending (including streaming), task retrieval, and push notification management.

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Code Review

This pull request introduces stand-alone support for serving the RESTful API. Several critical and high-severity issues concerning attribute access, routing logic, error handling, and type safety were identified.

src/a2a/server/apps/rest/fastapi_app.py

src/a2a/server/apps/rest/rest_app.py

src/a2a/server/request_handlers/rest_handler.py

src/a2a/server/apps/rest/rest_app.py

src/a2a/server/request_handlers/rest_handler.py

# Description Push notifications are not being triggered for message/send operations without an initial task.

Fixes #301 🦕

# Description This update improves the robustness of the `new_task` function by adding explicit error handling for invalid `Message` objects. Previously, `new_task` did not validate its input, which could lead to unexpected `TypeError` or `ValueError` exceptions when a malformed `Message` was passed. This change introduces checks to ensure that a `Message` has a valid `role` and a non-empty `parts` list before a `Task` is created. Additionally, this update includes corresponding unit tests to verify the new error handling and ensures that the correct exceptions are raised for invalid inputs.

# Description Refactored `tests/client/test_auth_middleware.py` and added test cases to improve coverage for `credentials.py` and `interceptor.py`. - `src/a2a/client/auth/credentials.py`: 94% -> 100% - `src/a2a/client/auth/interceptor.py`: 71% -> 94% Signed-off-by: Shingo OKAWA <shingo.okawa.g.h.c@gmail.com>

🤖 I have created a release *beep* *boop* --- ## [0.2.12](v0.2.11...v0.2.12) (2025-07-14) ### Features * add `metadata` property to `RequestContext` ([#302](#302)) ([e781ced](e781ced)) * add A2ABaseModel ([#292](#292)) ([24f2eb0](24f2eb0)) * add support for notification tokens in PushNotificationSender ([#266](#266)) ([75aa4ed](75aa4ed)) * Update A2A types from specification 🤖 ([#289](#289)) ([ecb321a](ecb321a)) ### Bug Fixes * add proper a2a request body documentation to Swagger UI ([#276](#276)) ([4343be9](4343be9)), closes [#274](#274) * Handle asyncio.cancellederror and raise to propagate back ([#293](#293)) ([9d6cb68](9d6cb68)) * Improve error handling in task creation ([#294](#294)) ([6412c75](6412c75)) * Resolve dependency issue with sql stores ([#303](#303)) ([2126828](2126828)) * Send push notifications for message/send ([#298](#298)) ([0274112](0274112)) * **server:** Improve event consumer error handling ([#282](#282)) ([a5786a1](a5786a1)) --- This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please). Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>

# Description Introduces support for Database backed Push Notification Config Store. Push Notification Config persisted to the database table gets encrypted when encryption_key param is set for the DatabasePushNotificationConfigStore. Usage: ```py httpx_client = httpx.AsyncClient() engine = create_async_engine( "sqlite+aiosqlite:///file::memory:?cache=shared", echo=False ) push_config_store = DatabasePushNotificationConfigStore(engine=engine, encryption_key=Fernet.generate_key()) push_sender = BasePushNotificationSender( httpx_client=httpx_client, config_store=push_config_store) request_handler = DefaultRequestHandler( agent_executor=CurrencyAgentExecutor(), task_store=DatabaseTaskStore(engine=engine), push_config_store=push_config_store, push_sender=push_sender) ```

Fixes #249

holtskinner

Can you also add tests for these new handlers?

holtskinner · 2025-07-15T16:13:21Z

src/a2a/server/apps/rest/fastapi_app.py

+
+    def build(
+        self,
+        agent_card_url: str = '/.well-known/agent.json',


Suggested change

agent_card_url: str = '/.well-known/agent.json',

agent_card_url: str = AGENT_CARD_WELL_KNOWN_PATH,

Also add import:

from a2a.utils.constants import AGENT_CARD_WELL_KNOWN_PATH

holtskinner · 2025-07-15T16:13:54Z

src/a2a/server/apps/rest/rest_app.py

+logger = logging.getLogger(__name__)
+
+
+class RESTApplication:


Should this be called A2ARESTApplication?

This update addresses an issue where the `completed_task` function in `a2a/utils/task.py` did not perform any validation on the `artifacts` list. This could lead to unexpected behavior if an empty or invalid list was provided. This change introduces a validation check to ensure that the `artifacts` list is a non-empty list of `Artifact` objects, raising a `ValueError` if the validation fails. **Changes:** - Modified `a2a/utils/task.py` to add a validation check for the `artifacts` parameter in the `completed_task` function. - Updated `tests/utils/test_task.py` to include tests for the new validation logic, covering cases with empty lists and lists containing invalid items.

…updates

swapydapy · 2025-07-15T23:26:36Z

src/a2a/server/apps/rest/fastapi_app.py

+    def __init__(
+        self,
+        agent_card: AgentCard,
+        http_handler: RequestHandler,


nit: this param should be called request_handler, right? As it is the base request handler, there's nothing related to HTTP.

swapydapy · 2025-07-15T23:30:39Z

src/a2a/server/apps/rest/rest_app.py

+        )
+        return JSONResponse(
+            '{"message": ' + error.message + '}',
+            status_code=404,


This would not be 404. Default value would be 500. But we should check for error and attach 4XX or 5XX HTTP error codes.

swapydapy · 2025-07-15T23:35:20Z

Not sure why, but this PR seems to have Krishna's persistence store changes as well.

swapydapy · 2025-07-15T23:36:33Z

src/a2a/server/apps/rest/rest_app.py

+
+    def routes(self) -> dict[tuple[str, str], Callable[[Request], Any]]:
+        routes = {
+            ('/v1/message:send', 'POST'): (


Might want to check with Google AIP readability.

Since this is effectively creating a new message, do we need the ":send" custom operation. Can't we just call it ('/v1/message', 'POST')

feat: [WIP] Add dedicated RESTful handler

03a0fbe

pstephengoogle requested a review from a team as a code owner July 11, 2025 15:51

gemini-code-assist bot reviewed Jul 11, 2025

View reviewed changes

pstephengoogle and others added 9 commits July 11, 2025 18:02

Address gemini comments

661db10

add to allowlist

f7bbfc4

fix: Send push notifications for message/send (#298)

0274112

# Description Push notifications are not being triggered for message/send operations without an initial task.

fix: Resolve dependency issue with sql stores (#303)

2126828

feat: add metadata property to RequestContext (#302)

e781ced

Fixes #301 🦕

chore: Move docker/postgres/init.sql to tests/ (#304)

dc95e2a

pstephengoogle changed the title ~~feat: [WIP] Adding stand-alone support for RESTful API serving~~ feat: Adding stand-alone support for RESTful API serving Jul 15, 2025

kthota-g added 2 commits July 15, 2025 17:10

fix: Handle readtimeout errors. (#305)

b94b8f5

Fixes #249

holtskinner requested changes Jul 15, 2025

View reviewed changes

holtskinner and others added 4 commits July 15, 2025 17:19

Formatting

2482059

ci: Add ruff format checking (#309)

ecbbb7e

Merge branch 'main' of https://github.com/google-a2a/a2a-python into …

45b148e

…updates

swapydapy requested changes Jul 15, 2025

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swapydapy reviewed Jul 15, 2025

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feat: Adding stand-alone support for RESTful API serving #297

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	agent_card_url: str = '/.well-known/agent.json',
	agent_card_url: str = AGENT_CARD_WELL_KNOWN_PATH,

		logger = logging.getLogger(__name__)


		class RESTApplication:

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pstephengoogle commented Jul 11, 2025

Adding stand-alone support for RESTful API serving

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