fix: do not use ReadableStream async iterator in SSE stream parsing

[ilbertt]

Description

The async iterator in ReadableStream is not available in browsers like Safari: MDN. This PR changes it to a lower-level API which has better support across different environments.

Fixes #308.

[gemini-code-assist]

Summary of Changes

Hello @ilbertt, 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 resolves a critical browser compatibility issue related to ReadableStream objects lacking native Symbol.asyncIterator support in environments like Safari. By introducing a custom pipeThrough utility, it ensures that Server-Sent Events (SSE) parsing can consistently leverage for await...of syntax, thereby enhancing the robustness and cross-browser functionality of stream processing.

Highlights

• Browser Compatibility Fix: Implemented a fallback for ReadableStream to ensure Symbol.asyncIterator is available, addressing compatibility issues in browsers like Safari where it might be missing.
• New pipeThrough Utility: Introduced a pipeThrough function that wraps TextDecoderStream and conditionally adds a custom Symbol.asyncIterator to the stream if it's not natively present, ensuring for await...of loops work consistently.
• Custom Async Iterator Implementation: Added a createAsyncIterator helper function to provide a manual async iterator for ReadableStream instances, which is used by the new pipeThrough utility.
• Enhanced Test Coverage: Included new test cases to validate the async iterator fallback mechanism and confirm proper resource cleanup (e.g., reader.releaseLock()) when iterating streams is terminated early.

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[github-actions]

🧪 Code Coverage

⬇️ Download Full Report

	Main	PR	Delta
src/sse_utils.ts	90.9%	93.22%	🟢 +2.32%
Total	80%	80.06%	🟢 +0.06%

Generated by coverage-comment.yml

[gemini-code-assist]

Code Review

The pull request introduces a polyfill for "Symbol.asyncIterator" on "ReadableStream" to enhance compatibility across different browser environments, particularly Safari. This is a valuable improvement for robust SSE stream parsing. The new "createAsyncIterator" and "pipeThrough" functions are well-structured, and the "try...finally" block in "createAsyncIterator" ensures proper resource cleanup. The added test cases effectively validate the new fallback mechanism and early termination scenarios. The identified type inaccuracies should be addressed for improved type safety and clarity.

[ishymko]

Thank you for the prompt fix!

BTW were you able to test it on a real iOS? We don't have this kind of integration tests running on a real iOS so if you were able to confirm it it'd be great.

[ilbertt]

BTW were you able to test it on a real iOS? We don't have this kind of integration tests running on a real iOS so if you were able to confirm it it'd be great.

I tested the workaround from my comment, and it was working. If you can release a beta/patch version, I'm happy to pull it in and test it

[ishymko]

I tested the workaround from #308 (comment)

Sounds good, thank you!

A few minor comments and should be good to go.

[ilbertt]

@ishymko I've pushed some updates, let me know if I need to do anything else!

[ishymko]

Thank you for the contribution!

Should be released next week or the week after next at the latest.

[ilbertt]

@ishymko to close the loop, I've just bumped the @a2a-js/sdk to v0.3.10 for our production app and everything works.

Thanks again for the help!