`return` in a generator function crashes after iterating an `@azure/core-sse` `EventMessageStream` to the end

[jaked]

• Package Name: @azure/core-sse
• Package Version: 2.1.2
• Operating system: MacOS
• nodejs
  • version: 20.10.0
• browser
  • name/version:
• typescript
  • version:
• Is the bug related to documentation in
  • README.md
  • source code documentation
  • SDK API docs on https://learn.microsoft.com

Describe the bug
Returning from an iteration over an EventMessageStream crashes if the entire stream has already been consumed.

To Reproduce
Steps to reproduce the behavior:

1. obtain a stream with createSseStream (e.g. from an @azure-rest/ai-inference response body)
2. iterate the stream in a generator function (with for await (const event of stream))
3. return from the iterator when complete (e.g. with if (event.data === "[DONE]") return)
4. observe exception:

TypeError: Cannot read properties of null (reading 'end')
    at Object.cancel (file:///Users/jaked/repos/githubnext/vitale/node_modules/.pnpm/@azure+core-sse@2.1.2/node_modules/@azure/core-sse/dist/esm/utils.js:54:31)
    at readableStreamDefaultControllerCancelSteps (node:internal/webstreams/readablestream:2383:39)
    at ReadableStreamDefaultController.[kCancel] (node:internal/webstreams/readablestream:1079:12)
    at ensureIsPromise (node:internal/webstreams/util:185:19)
    at readableStreamCancel (node:internal/webstreams/readablestream:1984:5)
    at readableStreamReaderGenericCancel (node:internal/webstreams/readablestream:2124:10)
    at returnSteps (node:internal/webstreams/readablestream:524:24)
    at Object.return (node:internal/webstreams/readablestream:568:11)
    at main (/Users/jaked/repos/githubnext/vitale/packages/examples/azure-ai.vnb-cellId=fUdPs5uLJxWHELOq-T1-8.tsx:40:3)
    at main.next (<anonymous>)

Expected behavior
Iteration completes normally without exception.

Screenshots
If applicable, add screenshots to help explain your problem.

Additional context
The exception is coming from the cancel function in @azure/core-sse/utils.js, which calls stream.socket.end() when an EventMessageStream iteration returns in a generator function (since #28111). But Node sets stream.socket to null when the underlying message has been consumed (I think since nodejs/node#38505 / nodejs/undici#834), so the call fails.

Replacing stream.socket.end() with stream.socket?.end() fixes the issue for me.

[github-actions]

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @xgithubtriage.

[deyaaeldeen]

Hi @jaked, thanks for opening this report and apologies for the delay. I agree with your analysis and proposed remedy and I opened #30707. I'll let you know once we make a release. Again, thanks for your patience!