refactor: unify transport name constants usage

[ishymko]

Use enum everywhere, data model uses str for protocol names, so custom protocols won't be constrained with the enum.

Fixes #705

[gemini-code-assist]

Summary of Changes

Hello @ishymko, 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 refactors the handling of transport protocol constants by migrating from individual string constants to a unified TransportProtocol str Enum. This change, which addresses issue #705, improves code consistency, type safety, and maintainability by centralizing the definition and usage of transport protocols throughout the A2A SDK.

Highlights

• Unified Transport Constants: Converted the TransportProtocol class into a str Enum in src/a2a/utils/constants.py to centralize and standardize transport protocol definitions.
• Codebase-Wide Constant Replacement: Replaced all instances of the old string constants (TRANSPORT_GRPC, TRANSPORT_HTTP_JSON, TRANSPORT_JSONRPC) with their corresponding TransportProtocol enum members across the entire codebase, including client factories, transports, and test files.
• Improved Type Safety and Readability: Enhanced type safety and code readability by ensuring that transport protocols are consistently referenced through enum members, which also helps prevent potential errors from string mismatches.

Changelog

• src/a2a/client/client_factory.py
  • Updated transport protocol references to use TransportProtocol enum members.
• src/a2a/client/transports/rest.py
  • Updated transport protocol references to use TransportProtocol enum members.
• src/a2a/utils/init.py
  • Removed deprecated transport string constants from imports and __all__ export list.
• src/a2a/utils/constants.py
  • Refactored TransportProtocol into a str Enum.
  • Removed old, individual transport string constants.
• tests/client/test_auth_middleware.py
  • Updated AgentInterface protocol binding and ClientConfig supported protocols to use TransportProtocol enum members.
• tests/client/test_client_factory.py
  • Updated AgentInterface protocol binding and ClientConfig supported protocols to use TransportProtocol enum members.
  • Adjusted an assertion for extensions.
• tests/client/transports/test_rest_client.py
  • Updated AgentInterface protocol binding to use TransportProtocol enum members.
  • Reordered an import.
• tests/e2e/push_notifications/test_default_push_notification_support.py
  • Updated ClientConfig supported protocols and minimal_agent_card calls to use TransportProtocol enum members.
• tests/integration/test_client_server_integration.py
  • Updated AgentInterface protocol binding to use TransportProtocol enum members.
  • Removed deprecated transport constants from imports.
• tests/integration/test_end_to_end.py
  • Updated AgentInterface protocol binding to use TransportProtocol enum members.
  • Removed deprecated transport constants from imports.

Activity

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[gemini-code-assist]

Code Review

This pull request is a well-executed refactoring that unifies the usage of transport protocol constants into a TransportProtocol enum. This change significantly improves code clarity, maintainability, and type safety. The refactoring has been applied consistently across both the application logic and the test suite. I have one minor suggestion to improve the readability of a type hint, but overall, the changes are excellent.