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feat: Add pluggable A2AHttpClient with Vert.x implementation #584

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@ehsavoie ehsavoie commented Jan 13, 2026

Introduce ServiceLoader-based A2AHttpClient client architecture with two implementations:

  • JDK HttpClient (core, always available)
  • Vert.x WebClient (optional, high-performance)

Changes:

  • Create http-client-vertx module for Vert.x implementation
  • Add ServiceLoader infrastructure (A2AHttpClientFactory, providers)
  • Update dependent modules to use Vert.x client by default
  • Add comprehensive tests and usage examples

Users can choose implementation via Maven dependencies. Priority-based selection: Vert.x (100) > JDK (0).

Fixes #583 🦕

@ehsavoie ehsavoie requested review from jmesnil and kabir January 13, 2026 14:16
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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 significantly enhances the HTTP client capabilities by introducing a pluggable architecture. It allows the system to dynamically select the most performant HTTP client available, with a new Vert.x-based client offering high-performance asynchronous operations, while retaining the JDK client as a reliable default. This change provides greater flexibility and potential for performance improvements without requiring explicit configuration from the end-user.

Highlights

  • Pluggable HTTP Client Architecture: Introduced a new ServiceLoader-based architecture for A2AHttpClient, allowing for flexible and extensible HTTP client implementations.
  • Vert.x WebClient Implementation: Added a high-performance Vert.x WebClient-based implementation, VertxA2AHttpClient, which is now the preferred default when Vert.x dependencies are available.
  • JDK HttpClient as Fallback: The existing JdkA2AHttpClient has been integrated into the new architecture as a fallback, ensuring a functional client is always available.
  • Automatic Client Selection: Implemented a priority-based selection mechanism where VertxA2AHttpClient (priority 100) is chosen over JdkA2AHttpClient (priority 0) by default.
  • Refactoring for Factory Usage: Updated various modules (client/base, client/transport/jsonrpc, client/transport/rest, server-common, http-client) to use the new A2AHttpClientFactory for client instantiation, promoting consistency and modularity.
  • New Module and Comprehensive Testing: A new http-client-vertx module was created, complete with unit, integration, and SSE-specific tests to ensure the robustness and correctness of the Vert.x implementation.
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ehsavoie commented Jan 13, 2026

@brasseld It has been quite some time but if you want to take a look at this PR :)

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Code Review

This pull request introduces a pluggable HTTP client architecture using Java's ServiceLoader, with a new Vert.x implementation and a JDK fallback. The changes are well-integrated across the codebase, updating dependencies, imports, and client instantiation to leverage the new A2AHttpClientFactory. The new Vert.x client and its provider are well-documented and include comprehensive tests. The overall design significantly improves flexibility by allowing users to choose or provide their preferred HTTP client implementation.

@ehsavoie ehsavoie force-pushed the vertx branch 2 times, most recently from bf5b44b to ed6d055 Compare January 13, 2026 14:40
jmesnil
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@ehsavoie ehsavoie force-pushed the vertx branch 2 times, most recently from a28dae0 to 7a778c8 Compare January 14, 2026 08:48
@ehsavoie ehsavoie requested a review from jmesnil January 14, 2026 09:35
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jmesnil commented Jan 14, 2026

/gemini review

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Code Review

This pull request introduces a pluggable A2AHttpClient architecture using Java's ServiceLoader, which is a great improvement for flexibility. The new Vert.x-based implementation is a valuable addition for high-performance scenarios. The code is well-structured, and the changes are consistently applied across the modules. The inclusion of comprehensive tests for the new implementation is also commendable. I've found a critical bug in RestTransportProvider.java that could lead to a NullPointerException, and a few minor areas for improvement in the new VertxA2AHttpClient implementation for code clarity and correctness. Overall, this is a solid contribution.

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brasseld commented Jan 14, 2026

Hey @ehsavoie , thanks for adding me here, it's been a while indeed.

Some general comments:

Good work in general, I will be giving it a try later today (US TZ).

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ehsavoie commented Jan 14, 2026

@brasseld :
You can still provide the client directly, this SPI is the default fallback behaviour.
The provider enables the use of the vertx client with a fallback to the jdk client if vertx classes are not available.
Yeah, the issue was the connection could be closed (onComplete called) before the onError was called iirc

@ehsavoie
feat: Add pluggable A2AHttpClient with Vert.x implementation
94e4ae5 
Introduce ServiceLoader-based A2AHttpClient client architecture with two implementations:
- JDK HttpClient (core, always available)
- Vert.x WebClient (optional, high-performance)

Changes:
- Create http-client-vertx module for Vert.x implementation
- Add ServiceLoader infrastructure (A2AHttpClientFactory, providers)
- Update dependent modules to use Vert.x client by default
- Add comprehensive tests and usage examples

Users can choose implementation via Maven dependencies.
Priority-based selection: Vert.x (100) > JDK (0).

Signed-off-by: Emmanuel Hugonnet <ehugonne@redhat.com>
@ehsavoie ehsavoie requested a review from jmesnil January 14, 2026 14:03
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LGTM

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brasseld commented Jan 14, 2026

Sounds good.

Should the extras README be updated as well maybe ? https://github.com/a2aproject/a2a-java/blob/main/extras/README.md

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@jmesnil jmesnil jmesnil approved these changes

@kabir kabir Awaiting requested review from kabir

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[Feat]: Provide another other A2AHttpClient implementation

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