feat: Check transports in AgentCard match those on classpath by kabir · Pull Request #251 · a2aproject/a2a-java

kabir · 2025-09-03T13:49:07Z

Fixes #246 🦕

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Summary of Changes

Hello @kabir, 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 potential runtime issue by implementing a robust validation system for AgentCards. It ensures that any transport protocols declared within an AgentCard are genuinely supported and available on the classpath, thereby improving the reliability and preventing errors related to missing transport dependencies. The changes involve new interfaces, a dedicated validator, and integration points within existing transport handlers.

Highlights

AgentCard Transport Validation: Introduced a new validation mechanism to ensure that the transport protocols specified in an AgentCard are actually available on the application's classpath. This prevents misconfigurations and ensures runtime stability.
New TransportMetadata Interface: Defined a new TransportMetadata interface that transport implementations must implement to expose their supported protocols, enabling dynamic discovery via Java's ServiceLoader.
Integration with Existing Handlers: Integrated the new validation logic into the GrpcHandler and JSONRPCHandler initialization processes, ensuring that AgentCards are validated when handlers are set up.
Enhanced Test Coverage: Added new unit tests for the AgentCardValidator and updated existing test infrastructure to support the new transport discovery and validation, including the use of properties files for preferred transport configuration in tests.

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Code Review

This pull request introduces a validation mechanism to ensure that transports specified in an AgentCard are available on the classpath. This is achieved by using Java's ServiceLoader to discover TransportMetadata implementations. The core logic is in the new AgentCardValidator class, which is then integrated into the gRPC and JSON-RPC transport handlers.

The implementation is solid, but I've identified a potential design issue with how ServiceLoader interacts with dependency injection, which could lead to NullPointerExceptions in the future. I've left comments with suggestions on how to make this more robust. I also noticed some code duplication in test helper methods that could be refactored for better maintainability.

reference/grpc/src/main/java/io/a2a/server/grpc/quarkus/QuarkusGrpcHandler.java

reference/jsonrpc/src/main/java/io/a2a/server/apps/quarkus/A2AServerRoutes.java

gemini-code-assist · 2025-09-03T13:52:12Z

tests/server-common/src/test/java/io/a2a/server/apps/common/AgentCardProducer.java

+    private static String loadPreferredTransportFromProperties() {
+        URL url = AgentCardProducer.class.getResource(A2A_REQUESTHANDLER_TEST_PROPERTIES);
+        if (url == null) {
+            return null;
+        }
+        Properties properties = new Properties();
+        try {
+            try (InputStream in = url.openStream()){
+                properties.load(in);
+            }
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+
+        String preferredTransport = properties.getProperty(PREFERRED_TRANSPORT);
+        Assertions.assertNotNull(preferredTransport);
+        return preferredTransport;
    }


This loadDefaultTransportFromProperties method is nearly identical to the one in AbstractA2ARequestHandlerTest. To improve maintainability and avoid code duplication, consider extracting this logic into a shared test utility class.

The two implementations also have a slight difference in handling a missing properties file (url == null): one returns null while the other fails with an assertion. Consolidating them would also unify this behavior.

I don't think this makes sense. It is only test code, and dependencies between those is a bit tricky

kabir · 2025-09-03T15:53:07Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces a valuable feature for validating AgentCard transport configurations against available transports on the classpath. The implementation correctly uses the ServiceLoader pattern for discovering transport metadata, making it extensible. The validation logic is sound, and the integration into the transport handlers is well-thought-out. I've identified one potential race condition in the GrpcHandler's initialization logic that should be addressed to ensure thread safety.

transport/grpc/src/main/java/io/a2a/transport/grpc/handler/GrpcHandler.java

kabir · 2025-09-03T15:59:02Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces a valuable feature to validate that the transports specified in an AgentCard are available on the classpath, improving the robustness of agent configurations. The implementation correctly uses Java's ServiceLoader for discovering transport metadata, and includes a good set of unit tests. My review found a logical error in the one-time validation for the gRPC handler and a minor case of code duplication in the test helpers. Overall, this is a solid contribution.

transport/grpc/src/main/java/io/a2a/transport/grpc/handler/GrpcHandler.java

gemini-code-assist · 2025-09-03T16:00:52Z

tests/server-common/src/test/java/io/a2a/server/apps/common/AgentCardProducer.java

+    private static String loadPreferredTransportFromProperties() {
+        URL url = AgentCardProducer.class.getResource(A2A_REQUESTHANDLER_TEST_PROPERTIES);
+        if (url == null) {
+            return null;
+        }
+        Properties properties = new Properties();
+        try {
+            try (InputStream in = url.openStream()){
+                properties.load(in);
+            }
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+
+        String preferredTransport = properties.getProperty(PREFERRED_TRANSPORT);
+        Assertions.assertNotNull(preferredTransport);
+        return preferredTransport;
    }


The loadPreferredTransportFromProperties method is very similar to the one in server-common/src/test/java/io/a2a/server/requesthandlers/AbstractA2ARequestHandlerTest.java. To improve maintainability and avoid code duplication, consider extracting this logic into a shared test utility class.

server-common/src/main/java/io/a2a/server/TransportMetadata.java

reference/jsonrpc/src/main/java/io/a2a/server/apps/quarkus/A2AServerRoutes.java

kabir · 2025-09-04T10:41:37Z

@fjuma Should be fixed now

…ect#251) Fixes a2aproject#246 🦕

gemini-code-assist bot reviewed Sep 3, 2025

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kabir force-pushed the transport-warning branch from 523f593 to c8a14af Compare September 3, 2025 13:51

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kabir force-pushed the transport-warning branch from 438d08d to 6e13ad6 Compare September 3, 2025 15:51

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transport/grpc/src/main/java/io/a2a/transport/grpc/handler/GrpcHandler.java Outdated Show resolved Hide resolved

kabir force-pushed the transport-warning branch from 6e13ad6 to 9ac1e19 Compare September 3, 2025 15:57

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kabir force-pushed the transport-warning branch from 9ac1e19 to d186f8c Compare September 3, 2025 16:01

fjuma reviewed Sep 3, 2025

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server-common/src/main/java/io/a2a/server/TransportMetadata.java Outdated Show resolved Hide resolved

fjuma reviewed Sep 3, 2025

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reference/jsonrpc/src/main/java/io/a2a/server/apps/quarkus/A2AServerRoutes.java Outdated Show resolved Hide resolved

kabir added 3 commits September 4, 2025 11:31

feat: Check transports in AgentCard match those on classpath

1f51af5

Optimise imports

b7642b5

Use String rather than TransportProtocol

8c6c718

kabir force-pushed the transport-warning branch from d186f8c to 8c6c718 Compare September 4, 2025 10:41

fjuma approved these changes Sep 4, 2025

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fjuma merged commit 8e70e48 into a2aproject:main Sep 4, 2025
3 of 4 checks passed

kabir mentioned this pull request Sep 11, 2025

[Feat]: Add ability to skip transport validation #264

Closed

1 task

fjuma mentioned this pull request Sep 16, 2025

Validate that the primary URL specified in the AgentCard matches the URL for the preferred transport #272

Closed

kabir added a commit to kabir/a2a-java that referenced this pull request Dec 23, 2025

feat: Check transports in AgentCard match those on classpath (a2aproj…

b7b0de0

…ect#251) Fixes a2aproject#246 🦕

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