feat: add support for JSON+HTTP/REST #229

ehsavoie · 2025-08-14T14:03:04Z

Create JSON+HTTP/REST Client.
Integrate PR from @ronantakizawa using regexp for server routing.
Update server code to use proper JSON (de)serialization with Proto.

gemini-code-assist

Summary of Changes

Hello @ehsavoie, 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 a significant refactoring of the client-side A2A SDK, shifting from monolithic client implementations to a modular architecture that supports multiple transport protocols. It establishes a flexible client factory, abstract client interfaces, and dedicated transport implementations for JSON-RPC, gRPC, and a new HTTP+JSON REST client. This change enhances the SDK's extensibility and maintainability by decoupling transport logic from core client functionalities.

Highlights

Modular Client Architecture: The old monolithic client implementations ('A2AClient' and 'A2AGrpcClient') have been replaced by a flexible 'AbstractClient' and 'Client' structure, supported by a 'ClientFactory' and 'ClientTransport' interfaces. This significantly improves modularity and extensibility.
Multi-Transport Protocol Support: New dedicated transport implementations for JSON-RPC, gRPC, and a new HTTP+JSON REST client have been introduced. This allows the SDK to dynamically select the appropriate communication protocol based on agent capabilities.
Enhanced Client-Side Event Handling: A new event processing mechanism, including 'ClientEvent' and 'ClientTaskManager', ensures consistent handling of messages, tasks, and updates across all supported transport protocols.
Standardized Agent Card Path: The standard path for agent card discovery has been updated from '.well-known/agent.json' to '.well-known/agent-card.json' for consistency.
Integration of New Protocol Features: The SDK now includes support for new protocol features such as Agent Card Signatures and Mutual TLS security schemes, enhancing security and verification capabilities.

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gemini-code-assist

Code Review

This pull request introduces a major refactoring of the client-side implementation, abstracting the transport layer to support JSON-RPC, gRPC, and a new REST+JSON transport. This is a significant architectural improvement that enhances modularity and extensibility. The changes include removing the old monolithic clients and introducing a transport-agnostic Client with a ClientFactory and SPI for transport providers. The protobuf definitions and spec classes have been updated to align with version 0.3.0 of the A2A protocol.

My review focuses on the new REST+JSON transport implementation. I've found that it is currently incomplete, with several methods throwing UnsupportedOperationException. There are also some areas for improvement regarding logging consistency and error handling. Overall, this is a great step forward for the SDK's architecture.

client/src/main/java/io/a2a/client/transport/JSONRestTransport.java

client/src/main/java/io/a2a/client/sse/JSONRestSSEEventListener.java

client/src/test/java/io/a2a/client/transport/JSONRestTransportTest.java

spec/src/main/java/io/a2a/util/Utils.java

client/src/main/java/io/a2a/client/transport/JSONRestTransport.java

ehsavoie · 2025-08-19T10:03:20Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces a major refactoring of the A2A client, abstracting the transport layer to support multiple protocols like JSON-RPC, gRPC, and a new REST+JSON implementation. The changes are extensive, including the removal of old client classes and the addition of a new modular structure with a client factory, abstract client, and transport-specific implementations. The code is also updated to align with a newer version of the A2A specification. My feedback focuses on a couple of minor issues in the new implementation, such as a parameter typo and leftover debugging code. Overall, this is a significant improvement to the SDK's architecture and capabilities.

client/src/main/java/io/a2a/client/Client.java

client/src/main/java/io/a2a/client/transport/JSONRestTransport.java

fjuma · 2025-08-19T13:26:04Z

@ehsavoie Just FYI, I've merged the v0.3.0 PR so this one can be rebased now.

ehsavoie · 2025-08-19T17:31:31Z

/gemini-review

gemini-code-assist · 2025-08-19T17:31:59Z

It looks like you might have intended to use the /gemini review command. Please try that if you'd like me to perform a review of the pull request.

fjuma

Thanks @ehsavoie! I'm starting to review this so adding an initial set of comments.

client/transport/jsonrest/pom.xml

...ansport/jsonrest/src/main/java/io/a2a/client/transport/jsonrest/JSONRestTransportConfig.java

client/transport/jsonrest/src/main/java/io/a2a/client/transport/jsonrest/JSONRestTransport.java

...transport/jsonrest/src/test/java/io/a2a/client/transport/jsonrest/JSONRestTransportTest.java

server-common/src/main/java/io/a2a/server/requesthandlers/RequestHandler.java

spec-grpc/src/main/java/io/a2a/grpc/A2A.java

transport/rest/src/main/java/io/a2a/transport/rest/handler/RestHandler.java

spec-grpc/src/main/java/io/a2a/grpc/FilePart.java

priyanshus1 · 2025-09-01T00:37:19Z

Question:
This PR only covers a REST client(as I understand), Is their a plan to introduce REST support for A2A server soon ?
Is their a contribution needed if this is not already planned by someone.

ehsavoie · 2025-09-01T07:45:17Z

@priyanshus1 it covers all the rest part (client and server)

priyanshus1 · 2025-09-01T13:33:47Z

@ehsavoie Do we know an ETA on this PR, we are waiting for either adopt this or self implement :)

kabir · 2025-09-01T14:18:53Z

@priyanshus1 We're aiming to get it in for the next release (hopefully later this week)

README.md

@ronantakizawa

* Create JSON+HTTP/REST Client. * Integrate PR from @ronantakizawa using regexp for server routing. * Update server code to use proper JSON (de)serialization with Proto. * Create Reference Implementation * Removing the listTasks since it has been removed from the specs * Removing io.grpc:* as direct dependencies for a2a-java-sdk-spec-grpc. * Support client preferences. * Running the TCK Signed-off-by: Emmanuel Hugonnet <[email protected]>

gemini-code-assist bot reviewed Aug 14, 2025

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ehsavoie force-pushed the rest_json branch 3 times, most recently from 7e4ec93 to a72f662 Compare August 14, 2025 17:27

fjuma mentioned this pull request Aug 14, 2025

feat: Make the client transport agnostic #231

Merged

3 tasks

ehsavoie force-pushed the rest_json branch from a72f662 to afe2050 Compare August 18, 2025 10:33

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ehsavoie force-pushed the rest_json branch from afe2050 to 06905cf Compare August 19, 2025 09:42

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ehsavoie force-pushed the rest_json branch 2 times, most recently from 67c8163 to 13367c4 Compare August 19, 2025 17:29

ehsavoie force-pushed the rest_json branch 4 times, most recently from eb68867 to 9700c25 Compare August 26, 2025 12:35

ehsavoie changed the title ~~Rest json~~ feat: add support for JSON+HTTP/REST Aug 26, 2025

ehsavoie marked this pull request as ready for review August 26, 2025 12:39

ehsavoie force-pushed the rest_json branch 4 times, most recently from 9ffdeb5 to 83add84 Compare August 26, 2025 14:24

fjuma requested changes Aug 27, 2025

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fjuma requested a review from kabir August 29, 2025 18:51

ehsavoie force-pushed the rest_json branch 2 times, most recently from 1ac5baa to 4a70fbf Compare September 1, 2025 13:32

ehsavoie force-pushed the rest_json branch from 4a70fbf to 8b08e23 Compare September 1, 2025 13:34

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