fix: Return UnsupportedOperationError when extendedAgentCard capabili… by kabir · Pull Request #736 · a2aproject/a2a-java

kabir · 2026-03-12T13:55:27Z

…ty is disabled

GetExtendedAgentCard now checks if the capability is enabled before checking if the card is configured. When capability is false, returns 501/UNIMPLEMENTED with UnsupportedOperationError instead of 400/FAILED_PRECONDITION.

Applied to all three transports: HTTP+JSON, JSON-RPC, and gRPC.

Fixes #733

…ty is disabled GetExtendedAgentCard now checks if the capability is enabled before checking if the card is configured. When capability is false, returns 501/UNIMPLEMENTED with UnsupportedOperationError instead of 400/FAILED_PRECONDITION. Applied to all three transports: HTTP+JSON, JSON-RPC, and gRPC. Fixes a2aproject#733 Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

gemini-code-assist · 2026-03-12T13:55:47Z

Summary of Changes

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This pull request refines the error handling for the GetExtendedAgentCard functionality by ensuring that if the extendedAgentCard capability is explicitly disabled, an UnsupportedOperationError is returned. This change standardizes the error response across gRPC, JSON-RPC, and HTTP+JSON transports, providing a clearer indication that the operation itself is not supported rather than merely misconfigured.

Highlights

Error Handling Logic: The GetExtendedAgentCard method across all transports (gRPC, JSON-RPC, HTTP+JSON) now first checks if the extendedAgentCard capability is enabled. If it is disabled, an UnsupportedOperationError is returned.
Standardized Error Response: Instead of returning a 400/FAILED_PRECONDITION (or ExtendedAgentCardNotConfiguredError) when the capability is disabled, the system now returns a 501/UNIMPLEMENTED status with an UnsupportedOperationError, providing a more accurate error type for disabled features.
Test Coverage: A test case in JSONRPCHandlerTest was updated to reflect the new error handling, ensuring that UnsupportedOperationError is correctly returned when the capability is not enabled.

Changelog

transport/grpc/src/main/java/io/a2a/transport/grpc/handler/GrpcHandler.java
- Added a check for the extendedAgentCard capability at the beginning of the getExtendedAgentCard method.
- Returned an UnsupportedOperationError via handleError if the capability is found to be disabled.
transport/jsonrpc/src/main/java/io/a2a/transport/jsonrpc/handler/JSONRPCHandler.java
- Imported UnsupportedOperationError.
- Modified the onGetExtendedCardRequest method to prioritize checking the extendedAgentCard capability.
- Returned a GetExtendedAgentCardResponse with UnsupportedOperationError if the capability is disabled.
transport/jsonrpc/src/test/java/io/a2a/transport/jsonrpc/handler/JSONRPCHandlerTest.java
- Updated the testOnGetExtendedAgentCard test to assert that an UnsupportedOperationError is returned when the extended agent card capability is not enabled.
transport/rest/src/main/java/io/a2a/transport/rest/handler/RestHandler.java
- Modified the getExtendedAgentCard method to check for the extendedAgentCard capability first.
- Threw an UnsupportedOperationError if the capability is disabled, before checking for card configuration.

Activity

The pull request addresses and fixes issue [Bug]: GetExtendedAgentCard fails with the incorrect error when the capability is not available #733.

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Code Review

The pull request refactors error handling for the getExtendedAgentCard operation across gRPC, JSON-RPC, and REST transports. It introduces an UnsupportedOperationError to specifically address cases where the extendedAgentCard capability is not enabled, differentiating this from scenarios where the card is simply not configured. This change involves adding a capability check before the configuration check in the respective handlers and updating a JSON-RPC test case to reflect the new error type.

gemini-code-assist · 2026-03-12T13:58:22Z

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

+            if (!getAgentCard().capabilities().extendedAgentCard()) {
+                handleError(responseObserver, new UnsupportedOperationError());
+                return;


This new check correctly identifies when the extendedAgentCard capability is not enabled and returns an UnsupportedOperationException. This is a more accurate exception than ExtendedAgentCardNotConfiguredError, as it indicates that the operation itself is not supported by the agent's capabilities, rather than just a configuration issue.

@gemini-code-assist This isn't an error right? It is the point of the PR

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gemini-code-assist · 2026-03-12T13:58:22Z

transport/jsonrpc/src/main/java/io/a2a/transport/jsonrpc/handler/JSONRPCHandler.java

+        if (!agentCard.capabilities().extendedAgentCard()) {
+            return new GetExtendedAgentCardResponse(request.getId(), new UnsupportedOperationError());
+        }


Separating the capability check from the configuration check improves the clarity and precision of error reporting. Returning UnsupportedOperationException when the capability is disabled is more appropriate than ExtendedAgentCardNotConfiguredError, as it directly communicates that the operation is not supported by the agent's current capabilities.

@gemini-code-assist This isn't an error right? It is the point of the PR

You are absolutely correct, kabir. My apologies if my previous comment was unclear. I was indeed highlighting that the change to return UnsupportedOperationError when the capability is disabled is a significant improvement, as it accurately reflects the nature of the issue (lack of capability, not just misconfiguration). This change aligns perfectly with the objective of this pull request.

gemini-code-assist · 2026-03-12T13:58:22Z

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

+            if (!agentCard.capabilities().extendedAgentCard()) {
+                throw new UnsupportedOperationError();
+            }


Similar to the other transports, this change correctly prioritizes the capability check. Throwing UnsupportedOperationException when the extendedAgentCard capability is not enabled provides a more precise and actionable error message to the client.

@gemini-code-assist This isn't an error right? It is the point of the PR

You are absolutely right, kabir. My apologies for the potential confusion. When I referred to "error message," I was specifically referring to the UnsupportedOperationException itself as a type of error that is now being correctly thrown. This change is indeed the core point of the PR and a significant improvement, providing a more accurate and actionable response when the extendedAgentCard capability is not enabled. The change is correct and aligns perfectly with the PR's objective.

gemini-code-assist bot reviewed Mar 12, 2026

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jmesnil approved these changes Mar 12, 2026

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kabir merged commit 5f742ae into a2aproject:main Mar 12, 2026
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fix: Return UnsupportedOperationError when extendedAgentCard capabili…#736

fix: Return UnsupportedOperationError when extendedAgentCard capabili…#736
kabir merged 1 commit intoa2aproject:mainfrom
kabir:issue-733

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