fix: support complete agent card URL in A2ACardResolver by ehsavoie · Pull Request #837 · a2aproject/a2a-java · GitHub
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fix: support complete agent card URL in A2ACardResolver - #837

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kabir merged 1 commit into
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ehsavoie:issue_771
Jun 2, 2026
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kabir merged 1 commit into
a2aproject:mainfrom
ehsavoie:issue_771

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@ehsavoie

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URI.resolve() silently drops intermediate path segments when the
resolved path starts with '/', causing incorrect URLs for agents
hosted under a path prefix (e.g. /spec03). Replace with direct
concatenation and add a pass-through guard when the supplied URL
already ends with the agent card path.

Fixes #771 🦕

@ehsavoie
ehsavoie requested a review from jmesnil April 29, 2026 09:59

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Code Review

The pull request enhances A2ACardResolver to accept either a base URL or a complete agent card URL, updating the internal URL construction logic to handle these variations correctly. It also introduces several unit tests to validate URL resolution with tenants, custom paths, and authentication headers, while improving error handling in the test suite. Feedback was provided to address a potential double-slash issue when concatenating the base URL and the agent card path.

Comment thread http-client/src/main/java/org/a2aproject/sdk/client/http/A2ACardResolver.java Outdated
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Code Review

This pull request updates the A2ACardResolver to support base URLs that already include the agent card path, ensuring the resolver uses such URLs verbatim. The URL construction logic was modified to handle manual concatenation when URI.resolve() is insufficient, and comprehensive unit tests were added to cover new functionality and error cases. Feedback was provided regarding a potential double-slash issue in the manual URL concatenation logic, along with a suggestion for a more robust normalization approach.

Comment thread http-client/src/main/java/org/a2aproject/sdk/client/http/A2ACardResolver.java Outdated

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I'm not sure if we should make the card resolver more complex.
I see 2 use case for fetching an agent card:

  • use the spec's well-known endpoint that is appended to whatever the baseUrl is (it can be http://example.com, http://example.com/agents/v1/foo)
  • point to a specific URL that returns an agent card. This does not have to end with .well-known/.agent-card.json. This URL can be fetched from a registry for example. In that case, there is no URL resolution at all, it's used verbatim.

So the API would be:

  • A2AResolver(String url) (and all its variant)
  • AgentCard getWellKnownAgentCard() -> append `.well-known/.agent-card.json to the base URL
  • AgentCard getAgentCard() -> use the URL verbatim

That's be a API break change so maybe we could have just a new method:

  • AgentCard getAgentCard(boolean fromWellKnownLocation)
    • getAgentCard() delegates to getAgentCard(true)
    • the resolution of the URL is deferred until getAgentCard(boolean) is called to figure out which URL to connect to.

@ehsavoie

ehsavoie commented May 4, 2026 •

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@jmesnil I broke the API because I think it is cleaner and clearer that way

@kabir

kabir commented May 18, 2026

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/gemini review

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Code Review

This pull request refactors the A2ACardResolver utility to use a builder pattern and introduces separate methods for retrieving well-known and configured agent cards. It also adds logging, improves URL resolution logic, and updates relevant tests and examples. Feedback was provided regarding the authHeader builder method, which could throw an UnsupportedOperationException if an immutable map is used, and a suggestion was made to normalize the Authorization header casing for consistency.

@ehsavoie

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/gemini review

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Code Review

This pull request refactors the A2ACardResolver to use a builder pattern and introduces distinct methods for fetching well-known versus configured agent cards. It includes URL normalization logic to handle trailing slashes and path prefixes more robustly, along with enhanced logging and updated test coverage. Feedback was provided regarding the resolveAgentCardUrl method, noting that its path-matching guard is currently hardcoded to the default path and should instead dynamically check against the specific path being resolved to avoid incorrect results when custom paths are used.

Comment thread http-client/src/main/java/org/a2aproject/sdk/client/http/A2ACardResolver.java Outdated
@ehsavoie
ehsavoie force-pushed the issue_771 branch 2 times, most recently from e915a3b to 103105c Compare May 19, 2026 15:03

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Also since I think this changes the API the prefix to the PR title should be "fix!" rather than "fix"

* @deprecated Use {@link #getConfiguredAgentCard()} for fetching the configured card URL, or
* {@link #getWellKnownAgentCard()} for the standard well-known endpoint.
*/
@Deprecated

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Could we just not keep this method and remove the two new methods?
It seems a bit cumbersome to have the user choose between getConfiguredAgentCard() and getWellKnownAgentCard().
In my mind, if one is configured we return that, and if not we fallback to the well known one

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We always have both since both are based on the builtBaseUri

Comment thread http-client/src/main/java/org/a2aproject/sdk/client/http/A2ACardResolver.java Outdated
Comment thread http-client/src/main/java/org/a2aproject/sdk/client/http/A2ACardResolver.java Outdated
Comment thread http-client/src/main/java/org/a2aproject/sdk/client/http/A2ACardResolver.java Outdated
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/gemini review

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Code Review

This pull request refactors A2ACardResolver to use a builder pattern and introduces separate methods for fetching well-known and configured agent cards, updating all client usages and tests accordingly. The review feedback points out a critical breaking change from removing public constructors and a bug where configuredAgentCardUrl incorrectly defaults to the base URL instead of the well-known URL when the card path is empty. Additional suggestions include allowing authHeaders to be explicitly cleared in the builder and simplifying the resolver logic in A2A.java once the default URL bug is resolved.

Comment on lines +187 to +192
public Builder authHeaders(@Nullable Map<String, String> authHeaders) {
if (authHeaders != null) {
this.authHeaders = new HashMap<>(authHeaders);
}
return this;
}

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medium

If authHeaders is null, the builder currently leaves this.authHeaders unmodified. To allow clearing headers or setting them to null explicitly, we should assign null when the parameter is null.

        public Builder authHeaders(@Nullable Map<String, String> authHeaders) {
            this.authHeaders = authHeaders != null ? new HashMap<>(authHeaders) : null;
            return this;
        }

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We don't want null headers

Comment thread client/base/src/main/java/org/a2aproject/sdk/A2A.java Outdated
URI.resolve() silently drops intermediate path segments when the
resolved path starts with '/', producing wrong URLs for agents under
a path prefix. Replace with direct concatenation and add a guard when
the supplied URL already includes the agent card path.

Signed-off-by: Emmanuel Hugonnet <ehugonne@redhat.com>
@ehsavoie

ehsavoie commented Jun 1, 2026

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Code Review

This pull request refactors A2ACardResolver to use a fluent builder pattern, replacing its public constructors. It also introduces several URL normalization and validation helper methods in Utils to prevent malformed URL construction when handling tenant paths, custom card paths, and well-known suffixes. Additionally, the changes improve exception handling for thread interrupts and expand test coverage across the HTTP client and utility classes. The review feedback highlights an issue in the builder's authHeaders setter, where passing null fails to clear previously set headers due to a conditional guard.

@kabir
kabir merged commit 3ced57f into a2aproject:main Jun 2, 2026
11 checks passed
salaboy pushed a commit to salaboy/a2a-java that referenced this pull request Jun 19, 2026
feat!: support complete agent card URL in A2ACardResolver

URI.resolve() silently drops intermediate path segments when the
resolved path starts with '/', producing wrong URLs for agents under
a path prefix. Replace with direct concatenation and add a guard when
the supplied URL already includes the agent card path.

Signed-off-by: Emmanuel Hugonnet <ehugonne@redhat.com>
@ehsavoie
ehsavoie deleted the issue_771 branch July 28, 2026 12:36
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[Bug]: spec.AgentCard does not allow many agents on same domain

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