fix(client): prevent ClientFactory.create() from mutating shared config extensions

[matanweks]

Summary

• Fix: ClientFactory.create() was mutating self._config.extensions when called with per-client extensions, causing extensions to silently accumulate across calls.
• Solution: Use dataclasses.replace() to create a per-call config copy instead of mutating the shared ClientConfig. This matches the immutability pattern from fix: use default_factory for mutable field defaults in ServerCallContext #744.
• Test: Added regression test verifying that config.extensions remains unchanged after multiple create() calls with different extensions.

Fixes #858

Test plan

• New test test_client_factory_create_does_not_mutate_config_extensions verifies no mutation
• All existing test_client_factory.py tests pass
• ruff check and ruff format pass
• mypy passes with no issues

[gemini-code-assist]

Summary of Changes

Hello, 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 critical bug where the ClientFactory was mutating its internal configuration's extension list when creating new clients. The fix ensures that the factory's base configuration remains immutable, preventing unexpected behavior and maintaining data integrity across client creation calls. This change aligns the client creation process with an immutable pattern, making the system more robust and predictable.

Highlights

• Bug Fix: Resolved an issue where ClientFactory.create() was inadvertently modifying the shared self._config.extensions when client-specific extensions were provided, leading to unintended accumulation across calls.
• Solution Implementation: Implemented dataclasses.replace() to generate a per-call copy of the configuration, ensuring that the original ClientConfig remains immutable and preventing side effects.
• Regression Test: Added a new regression test to explicitly confirm that the config.extensions attribute remains unchanged after multiple create() calls with varying extensions.

Changelog

• src/a2a/client/client_factory.py
  • Imported the dataclasses module.
  • Modified the create method to use dataclasses.replace() for creating a new ClientConfig instance with updated extensions, rather than directly modifying the factory's shared configuration.
• tests/client/test_client_factory.py
  • Added a new test test_client_factory_create_does_not_mutate_config_extensions to verify that the factory's configuration extensions are not mutated by create() calls.

Activity

• Addressed issue ClientFactory.create() mutates shared ClientConfig.extensions across calls #858.
• A new test test_client_factory_create_does_not_mutate_config_extensions was added and passes.
• All existing test_client_factory.py tests pass.
• ruff check and ruff format pass.
• mypy passes with no issues.

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[gemini-code-assist]

Code Review

This pull request effectively resolves a critical bug where ClientFactory.create() mutated the shared configuration's extensions, leading to unintended accumulation across multiple calls. The solution, which involves using dataclasses.replace() to create an immutable, per-call configuration copy, is robust and aligns with best practices for immutability. The addition of a regression test is excellent, as it verifies the fix and prevents future regressions. The changes are correct and well-implemented. I have one minor suggestion to improve the conciseness of the code by using a ternary operator.

[gemini-code-assist]

While the current implementation correctly fixes the mutation bug, the logic for creating the per-call configuration can be simplified for better readability and conciseness. For consistency, prefer using a conditional expression (ternary operator) for this assignment over an if/else block, as per repository guidelines.

config = dataclasses.replace(self._config, extensions=self._config.extensions + extensions) if extensions else self._config

References

1. For consistency, prefer using conditional expressions (ternary operators) for simple assignments over if/else blocks.

[github-actions]

🧪 Code Coverage (vs main)

⬇️ Download Full Report

	Base	PR	Delta
src/a2a/client/client_factory.py	89.09%	91.82%	🟢 +2.73%
Total	91.73%	91.79%	🟢 +0.06%

Generated by coverage-comment.yml