fix(fetch): properly release fetch during long-lived stream handling #13967

Lei-k · 2024-10-12T18:22:59Z

Hi,
I saw that the trackFetchStreamPerformance option was introduced in PR #13951 to bypass this issue, and Issue #13950 was closed as a result. However, this hasn't fully resolved the problem, so I attempted to address it in this PR.

Here is my modified test result after applying the changes:

…tream is cancelled - Modified `resolveResponse` to properly handle the cancellation of child streams by overriding the `cancel` method on the parent response's body. - Updated unit tests to cover scenarios for both successful stream resolution and error cases involving stream cancellation.

chargome · 2024-10-14T08:24:17Z

@Lei-k we have not released #13951 yet, can you specify why this does not resolve the issue?

Lei-k · 2024-10-14T08:33:40Z

@chargome From what I understand, in #13951 only adds the trackFetchStreamPerformance option and sets it to false by default to bypass the issue. However, when this option is enabled, the problem still persists.

…ry-javascript into fix/fetch-not-release

Lei-k · 2024-10-16T14:28:00Z

I saw some errors in the CI. I'll deal with them later

Lei-k · 2024-10-18T07:31:54Z

It seems that there are no further errors related to this PR. Can you please help confirm this, @chargome .

Lei-k · 2024-10-18T09:48:26Z

@chargome

Response was already in the code before, but now it's triggering a TS2304 error. Do you have any idea why this is happening?

It looks like only the TS2304 error and the file size check remain to be solved now.

chargome · 2024-10-18T10:53:15Z

@Lei-k not sure, but the same error is also crashing node-otel-sdk-node and node-otel-custom-sampler tests

Lei-k · 2024-10-20T07:02:19Z

@chargome

All tests have passed on my side. Please check, thanks!

Lei-k · 2024-10-21T11:46:34Z

Hi, @chargome

There’s one remaining bundle size check that failed due to the size limit. Could you assist me in adjusting the size, or do you have any suggestions for resolving this?

chargome

Hey @Lei-k sorry for the silence on this one, could you please have a look at my review and potentially also merge develop into your pr? We had some changes to our package structure lately, e.g. @sentry/types got deprecated.

chargome · 2024-12-02T15:06:05Z

packages/utils/src/instrument/fetch.ts

-  if (res && res.body) {
-    const body = res.body;
-    const responseReader = body.getReader();
+async function resloveReader(reader: WebReadableStreamDefaultReader, onFinishedResolving: () => void): Promise<void> {


Suggested change

async function resloveReader(reader: WebReadableStreamDefaultReader, onFinishedResolving: () => void): Promise<void> {

async function resolveReader(reader: WebReadableStreamDefaultReader, onFinishedResolving: () => void): Promise<void> {

Thank for reply. I’m merging the develop branch now and will check for any issues caused by the recent package structure changes.

chargome · 2024-12-02T15:13:17Z

packages/utils/src/instrument/fetch.ts

+ *
+ * Export For Test Only
+ */
+export function resolveResponse(


I think we might be introducing a potential memory leak within this function. Previously we were cancelling the resolving after a max timeout plus a timeout for individual chunk resolving. Could you explain why you removed these?

Hi,

Based on WHATWG specification, getReader returns a ReadableStreamDefaultReader. When using an asynchronous method to repeatedly call read, the ReadableStreamDefaultReader will respond as long as data is available, and it will appropriately handle cases where no data is available or an error occurs. A memory leak would only occur if responses are not properly handled—for example, using a recursive approach to read data, which is also noted in the WHATWG specification.

On the other hand, the previous implementation, which added a timeout for each chunk, could lead to issues. If the network is unstable or experiences jitter, chunks might not be retrieved within the specified timeout, causing the program to incorrectly cancel the reader prematurely.

Furthermore, adding a timeout to address a memory leak issue doesn’t make sense. If a timeout occurs, it means there wasn’t enough data available for us to read within the given time frame. If there isn’t sufficient data to read, there’s no accumulation of unhandled data, and therefore, a memory leak cannot happen.

Hi, I am Here.

Hi @chargome

I can understand your concerns.

Here are the patches I applied to Sentry 8.30.0, which are similar to this PR.
After running in production for more than 2 months, we have not encountered any memory leak issues.
The memory usage remains stable, and all monitored streams are properly canceled and released as expected.
I’ve also attached the memory test results and patches for reference.

@sentry+utils+8.30.0.patch
@sentry-internal+replay+8.30.0.patch

@Lei-k could you address this concern?

chargome · 2025-05-20T09:06:35Z

Closing this one for now, we might need to re-visit the entire fetch instrumentation for streams

Lei-k · 2024-10-16T14:32:40Z

packages/utils/src/instrument/fetch.ts

-          body.cancel().then(null, () => {
-            // noop on error
-          });
-        }, 5000);


I think removing the 5-second chunkTimeout is fine, but if there is any reason to keep it, please let me know. Thanks!

Lei-k · 2024-10-20T06:32:45Z

packages/types/src/whatwg/fetch.ts

+  arrayBuffer(): Promise<ArrayBuffer>; // Reads response body as ArrayBuffer
+  blob(): Promise<object>; // Reads response body as Blob
+  formData(): Promise<object>; // Reads response body as FormData
+}


Looks like we need to define the DOM types, maybe according to the WHATWG spec?

Lei-k · 2024-12-17T13:25:27Z

packages/utils/src/instrument/fetch.ts

-  if (res && res.body) {
-    const body = res.body;
-    const responseReader = body.getReader();
+async function resloveReader(reader: WebReadableStreamDefaultReader, onFinishedResolving: () => void): Promise<void> {


Thank for reply. I’m merging the develop branch now and will check for any issues caused by the recent package structure changes.

Lei-k · 2024-12-17T14:17:53Z

packages/utils/src/instrument/fetch.ts

+ *
+ * Export For Test Only
+ */
+export function resolveResponse(


Hi,

Based on WHATWG specification, getReader returns a ReadableStreamDefaultReader. When using an asynchronous method to repeatedly call read, the ReadableStreamDefaultReader will respond as long as data is available, and it will appropriately handle cases where no data is available or an error occurs. A memory leak would only occur if responses are not properly handled—for example, using a recursive approach to read data, which is also noted in the WHATWG specification.

On the other hand, the previous implementation, which added a timeout for each chunk, could lead to issues. If the network is unstable or experiences jitter, chunks might not be retrieved within the specified timeout, causing the program to incorrectly cancel the reader prematurely.

Lei-k · 2024-12-17T14:30:08Z

packages/utils/src/instrument/fetch.ts

+ *
+ * Export For Test Only
+ */
+export function resolveResponse(


Furthermore, adding a timeout to address a memory leak issue doesn’t make sense. If a timeout occurs, it means there wasn’t enough data available for us to read within the given time frame. If there isn’t sufficient data to read, there’s no accumulation of unhandled data, and therefore, a memory leak cannot happen.

Lei-k · 2024-12-17T16:10:24Z

packages/utils/src/instrument/fetch.ts

+ *
+ * Export For Test Only
+ */
+export function resolveResponse(


Hi, I am Here.

Lei-k · 2024-12-18T16:21:50Z

packages/utils/src/instrument/fetch.ts

+ *
+ * Export For Test Only
+ */
+export function resolveResponse(


Hi @chargome

I can understand your concerns.

Here are the patches I applied to Sentry 8.30.0, which are similar to this PR.
After running in production for more than 2 months, we have not encountered any memory leak issues.
The memory usage remains stable, and all monitored streams are properly canceled and released as expected.
I’ve also attached the memory test results and patches for reference.

@sentry+utils+8.30.0.patch
@sentry-internal+replay+8.30.0.patch

Lei-k · 2025-08-26T19:06:37Z

Hi @chargome,
Sorry, I just realized that my earlier comments were not actually submitted. I’ll sync with the latest branch and check the situation, and if needed, I’ll open a new PR to address it.

Lei-k added 3 commits October 13, 2024 02:05

style(fetch): fix formatting

f878695

Merge branch 'develop' into fix/fetch-not-release

d0282f4

Lei-k added 3 commits October 15, 2024 02:40

fix: resolve multiple ESLint issues

2c6d34e

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Merge branch 'develop' into fix/fetch-not-release

c7c943f

Lei-k changed the title ~~fix(fetch): fix fetch not release~~ fix(fetch): properly release fetch during long-lived stream handling Oct 15, 2024

Lei-k added 3 commits October 15, 2024 18:10

Merge branch 'develop' into fix/fetch-not-release

643a342

Immediate stream cancellation after timeout in _tryGetResponseText

f3aaa5d

Merge branch 'fix/fetch-not-release' of https://github.com/Lei-k/sent…

7f92ea3

…ry-javascript into fix/fetch-not-release

Lei-k requested a review from a team as a code owner October 15, 2024 14:36

Lei-k added 2 commits October 15, 2024 22:40

fix conflicts

9b83669

Merge branch 'develop' into fix/fetch-not-release

1d29564

Lei-k mentioned this pull request Oct 16, 2024

Improve Fetch Stream Handling for Long-lived Streams to Ensure Connection Closure #13996

Closed

3 tasks

Merge branch 'develop' into fix/fetch-not-release

80aa60d

Lei-k added 3 commits October 18, 2024 09:40

Merge branch 'develop' into fix/fetch-not-release

0cf8645

fix file formatting

6d66814

Update test cases to handle new logic in fetchUtils

0d10106

Lei-k added 3 commits October 19, 2024 06:48

Merge branch 'develop' into fix/fetch-not-release

536cc02

feat: define whatwg's stream types

78ac956

fix type error for tests

7fd0ffe

chargome requested a review from lforst October 21, 2024 11:53

Lei-k added 10 commits October 29, 2024 14:33

Merge branch 'develop' into fix/fetch-not-release

5ec50f6

Merge branch 'getsentry:develop' into fix/fetch-not-release

3923ecb

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chargome reviewed Dec 2, 2024

View reviewed changes

Lei-k added 15 commits December 17, 2024 14:58

ref: Resolve merge conflict between develop and fix/fetch-not-release

9ce2d8e

ref: fix typo

5c6ce1d

ref: prettify file format

2ed739d

ref: fix file format

02c2448

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b0b096a

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chore: resolve conflict from PR getsentry#14745

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chargome closed this May 20, 2025

Lei-k commented Aug 26, 2025

View reviewed changes

	async function resloveReader(reader: WebReadableStreamDefaultReader, onFinishedResolving: () => void): Promise<void> {
	async function resolveReader(reader: WebReadableStreamDefaultReader, onFinishedResolving: () => void): Promise<void> {

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fix(fetch): properly release fetch during long-lived stream handling #13967

fix(fetch): properly release fetch during long-lived stream handling #13967

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