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fix: memory leak from cloneResponse #82678

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Merged
wyattjoh merged 3 commits into from
Aug 15, 2025
Merged

fix: memory leak from cloneResponse #82678

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e06e27c
fix: memory leak from cloneResponse
snyamathi Aug 15, 2025
26140a9
Update clone-response.ts
snyamathi Aug 15, 2025
c8be8bc
Merge branch 'vercel:canary' into mem-leak
snyamathi Aug 15, 2025
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37 changes: 37 additions & 0 deletions packages/next/src/server/lib/clone-response.ts
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Original file line number Diff line number Diff line change
@@ -1,3 +1,22 @@
// @ts-ignore https://nodejs.org/api/stream.html#streamreadableisdisturbedstream
import { isDisturbed, isErrored } from 'node:stream'
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@eps1lon eps1lon Aug 15, 2025

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If I read the docs correctly, these are statics on Readable. Can't use node: either since it needs to work in Edge runtimes.

Suggested change
import { isDisturbed, isErrored } from 'node:stream'
import { Readable } from 'stream'

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@snyamathi snyamathi Aug 15, 2025

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Thank you, let me update this

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@snyamathi snyamathi Aug 15, 2025

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image

I'm still not able to get the isDisturbed or isErrored checks working type-wise. However, I'm also not certain they're needed at all.

The stream you are trying to cancel is not a ReadableStream, or it is locked.

https://developer.mozilla.org/en-US/docs/Web/API/ReadableStream/cancel#exceptions

Additionally, we're also catching the error, if one were to occur.


// https://github.com/nodejs/undici/blob/c399fdf4246be4992e89efe42aa83062edd0609f/lib/web/fetch/body.js#L32
const noop = () => {}
const registry = new FinalizationRegistry(
(weakRef: WeakRef<ReadableStream>) => {
const stream = weakRef.deref()
if (
stream &&
!stream.locked &&
!isDisturbed(stream) &&
!isErrored(stream as any as NodeJS.ReadableStream)
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@eps1lon eps1lon Aug 15, 2025 •
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Suggested change
!isDisturbed(stream) &&
!isErrored(stream as any as NodeJS.ReadableStream)
!Readable.isDisturbed(stream) &&
!Readable.isErrored(stream)

) {
stream.cancel('Response object has been garbage collected').then(noop)
}
}
)

/**
* Clones a response by teeing the body so we can return two independent
* ReadableStreams from it. This avoids the bug in the undici library around
Expand Down Expand Up @@ -33,6 +52,24 @@ export function cloneResponse(original: Response): [Response, Response] {
writable: false,
})

// The Fetch Standard allows users to skip consuming the response body by
// relying on garbage collection to release connection resources.
// https://github.com/nodejs/undici?tab=readme-ov-file#garbage-collection
//
// To cancel the stream you then need to cancel both resulting branches.
// Teeing a stream will generally lock it for the duration, preventing other
// readers from locking it.
// https://developer.mozilla.org/en-US/docs/Web/API/ReadableStream/tee

// cloned2 is stored in a react cache and cloned for subsequent requests.
// It is the original request, and is is garbage collected by a
// FinalizationRegistry in Undici, but since we're tee-ing the stream
// ourselves, we need to cancel clone1's stream (the response returned from
// our dedupe fetch) when clone1 is reclaimed, otherwise we leak memory.
if (cloned1.body) {
registry.register(cloned1, new WeakRef(cloned1.body))
}

const cloned2 = new Response(body2, {
status: original.status,
statusText: original.statusText,
Expand Down
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