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Ensure we cancel consumeUint8ArrayReadableStream if iteration breaks #428

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merged 2 commits into from Jun 26, 2023

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jridgewell
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Right now, consumeUint8ArrayReadableStream never explicitly closes the the readable stream we're consuming from. Unfortunately that means that devs aren't able to release their resources, leaking them until the GC eventually runs.

This is important for the AI streaming use case, so that devs can detect that a client has disconnected the stream and in turn disconnect the fetch they're maintaining to the AI service.

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changeset-bot bot commented Jun 23, 2023

🦋 Changeset detected

Latest commit: 6ffc30e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package
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edge-runtime Patch

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vercel bot commented Jun 23, 2023

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@Kikobeats Kikobeats merged commit ac97ee1 into vercel:main Jun 26, 2023
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@github-actions github-actions bot mentioned this pull request Jun 26, 2023
@jridgewell jridgewell deleted the jrl-cancel-stream branch June 27, 2023 02:18
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@jridgewell: the amount of real-world dollars that this change will save (not transfer to OpenAI but keep in the dev's pockets) cannot be overstated :)

kodiakhq bot pushed a commit to vercel/next.js that referenced this pull request Jun 29, 2023
### What?

The updates `edge-runtime` to the latest version

### Why?

vercel/edge-runtime#428 fixes `consumeUint8ArrayReadableStream` so that when we break iteration early (due to client disconnect), we cleanup the inner stream. That will fire the stream's `cancel` handler, and allow devs to disconnect from an AI service fetch.

### How?

`edge-runtime` maintain a `try {} finally {}` over the inner stream's iteration. When we early break, JS will call `it.return()`, and that will resume `consumeUint8ArrayReadableStream` with an abrupt completion (essentially, the `yield` turns into a `return`). We'll be able to trigger the `finally {}` block with that, and we call `inner.cancel()` to cleanup.

Fixes vercel/ai#90
enricoros added a commit to enricoros/big-AGI that referenced this pull request Jul 5, 2023
Thanks to the Vercel team (@jridgewell), an interruption of the stream on the client
side will lead to the cancellation of the TransformStream on the servers side, which
in turns cancels the open fetch() to the upstream. This was a long needed change and
we are happy to report it works well.

Related: #114
 - vercel/ai#90
 - vercel/edge-runtime#428
 - trpc/trpc#4586 (enormous thanks to the tRPC team to issue
   a quick release as well)
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3 participants