fix(cloudflare): Keep http root span alive until streaming responses are consumed #18087

RulaKhaled · 2025-11-04T09:57:48Z

Fixes: https://linear.app/getsentry/issue/JS-1103/spans-are-not-flushed-to-dashboard-when-using-streamtext-with-vercel

The Cloudflare request wrapper was ending the root HTTP span immediately when the handler returned a streaming Response (e.g. result.toTextStreamResponse()). Since Vercel AI child spans only finish after the stream is consumed by the client, they were filtered out by Sentry's isFullFinishedSpan check, resulting in transactions with 0 spans.

This PR implements a streaming response detection and handles this from within the http handler:

Created classifyResponseStreaming() helper
- Detects streaming vs non streaming, via Content-Type (SSE), Content-Length
Updated request wrapper
- Changed from startSpan() to startSpanManual() for manual span control
- Monitors streaming response consumption in background
- Ends root span only after stream fully consumed by client

…onsumed

linear · 2025-11-04T12:29:45Z

JS-1103 Spans are not flushed to dashboard when using streamText() with Vercel AI SDK in Cloudflare Workers

github-actions · 2025-11-04T13:46:42Z

size-limit report 📦

Path	Size	% Change	Change
@sentry/browser	24.8 kB	-	-
@sentry/browser - with treeshaking flags	23.31 kB	-	-
@sentry/browser (incl. Tracing)	41.54 kB	-	-
@sentry/browser (incl. Tracing, Profiling)	46.13 kB	-	-
@sentry/browser (incl. Tracing, Replay)	79.96 kB	-	-
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	69.69 kB	-	-
@sentry/browser (incl. Tracing, Replay with Canvas)	84.64 kB	-	-
@sentry/browser (incl. Tracing, Replay, Feedback)	96.88 kB	-	-
@sentry/browser (incl. Feedback)	41.48 kB	-	-
@sentry/browser (incl. sendFeedback)	29.49 kB	-	-
@sentry/browser (incl. FeedbackAsync)	34.47 kB	-	-
@sentry/react	26.52 kB	-	-
@sentry/react (incl. Tracing)	43.74 kB	-	-
@sentry/vue	29.25 kB	-	-
@sentry/vue (incl. Tracing)	43.34 kB	-	-
@sentry/svelte	24.82 kB	-	-
CDN Bundle	27.21 kB	-	-
CDN Bundle (incl. Tracing)	42.21 kB	-	-
CDN Bundle (incl. Tracing, Replay)	78.75 kB	-	-
CDN Bundle (incl. Tracing, Replay, Feedback)	84.2 kB	-	-
CDN Bundle - uncompressed	79.96 kB	-	-
CDN Bundle (incl. Tracing) - uncompressed	125.34 kB	-	-
CDN Bundle (incl. Tracing, Replay) - uncompressed	241.37 kB	-	-
CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed	254.13 kB	-	-
@sentry/nextjs (client)	45.96 kB	-	-
@sentry/sveltekit (client)	41.9 kB	-	-
@sentry/node-core	51.19 kB	-	-
@sentry/node	159.36 kB	-	-
@sentry/node - without tracing	92.83 kB	-	-
@sentry/aws-serverless	108.08 kB	-	-

View base workflow run

github-actions · 2025-11-17T10:08:50Z

node-overhead report 🧳

Note: This is a synthetic benchmark with a minimal express app and does not necessarily reflect the real-world performance impact in an application.

Scenario	Requests/s	% of Baseline	Prev. Requests/s	Change %
GET Baseline	10,618	-	8,853	+20%
GET With Sentry	1,792	17%	1,777	+1%
GET With Sentry (error only)	6,867	65%	6,031	+14%
POST Baseline	1,061	-	1,207	-12%
POST With Sentry	472	44%	597	-21%
POST With Sentry (error only)	907	85%	1,060	-14%
MYSQL Baseline	3,575	-	3,301	+8%
MYSQL With Sentry	420	12%	490	-14%
MYSQL With Sentry (error only)	3,034	85%	2,724	+11%

View base workflow run

Lms24 · 2025-11-28T11:58:02Z

packages/cloudflare/src/request.ts

+                  const result = await reader.read();
+                  done = result.done;
+                }
+              } catch {
+                // Stream error or cancellation - will end span in finally
+              } finally {
+                reader.releaseLock();
+                span.end();
+                waitUntil?.(flush(2000));
+              }
+            })();


This is a good point, let's try to be extra-careful here :)

Lms24 · 2025-11-28T11:52:41Z

packages/cloudflare/src/request.ts

+              }
+            })();
+
+            waitUntil?.(streamMonitor);


q: why do we need this call? (just asking, no objections)

I'll add a comment here! We just have to wait for stream consumption and end span when complete

Lms24 · 2025-11-28T11:58:02Z

packages/cloudflare/src/request.ts

+                  const result = await reader.read();
+                  done = result.done;
+                }
+              } catch {
+                // Stream error or cancellation - will end span in finally
+              } finally {
+                reader.releaseLock();
+                span.end();
+                waitUntil?.(flush(2000));
+              }
+            })();


This is a good point, let's try to be extra-careful here :)

Lms24 · 2025-11-28T11:59:16Z

packages/cloudflare/src/request.ts

+          }
+
+          // Classify response to detect actual streaming
+          const classification = classifyResponseStreaming(res);


m: what happens if we mis-classify a non-streaming response as a stream response? Would we break anything with creating the stream readers?

I guess the other way around isn't "dangerous", given we'd just end the span too early, correct?

so for false positives (non-streaming → classified as streaming) functionality wise it won't break anything, the only downside is slightly more overhead (creating an unnecessary stream monitor), and for false negatives yes you're correct, it would end span too early, but that's our best guess for now

Lms24 · 2025-11-28T12:00:23Z

packages/cloudflare/src/utils/streaming.ts

+ * We avoid probing the stream to prevent blocking on transform streams (like injectTraceMetaTags)
+ * or SSR streams that may not have data ready immediately.
+ */
+export function classifyResponseStreaming(res: Response): StreamingGuess {


l/nit: Is there a reason why we return the response as well? I don't see any changes being made to it, so could a caller just directly reuse res instead of using the returned response?

nice catch! I was mutating the res in a previous commit, these are just leftovers 😅

Lms24

Thanks for making the changes! I think with this, we can at least ensure that the http.server stays alive. I'm a bit worried about the span not being active long enough though (because startSpanManual keeps the span only active as long as the callback is executed). But I think we can give this a try because at least the span length should now be correct.

This PR contains the following updates: | Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) | |---|---|---|---| | [@sentry/react](https://github.com/getsentry/sentry-javascript/tree/master/packages/react) ([source](https://github.com/getsentry/sentry-javascript)) | [`10.27.0` -> `10.28.0`](https://renovatebot.com/diffs/npm/@sentry%2freact/10.27.0/10.28.0) | ![age](https://developer.mend.io/api/mc/badges/age/npm/@sentry%2freact/10.28.0?slim=true) | ![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/@sentry%2freact/10.27.0/10.28.0?slim=true) | --- ### Release Notes <details> <summary>getsentry/sentry-javascript (@sentry/react)</summary> ### [`v10.28.0`](https://github.com/getsentry/sentry-javascript/releases/tag/10.28.0) [Compare Source](getsentry/sentry-javascript@10.27.0...10.28.0) ##### Important Changes - **feat(core): Make `matcher` parameter optional in `makeMultiplexedTransport` ([#10798](getsentry/sentry-javascript#10798 The `matcher` parameter in `makeMultiplexedTransport` is now optional with a sensible default. This makes it much easier to use the multiplexed transport for sending events to multiple DSNs based on runtime configuration. **Before:** ```javascript import { makeFetchTransport, makeMultiplexedTransport } from '@sentry/browser'; const EXTRA_KEY = 'ROUTE_TO'; const transport = makeMultiplexedTransport(makeFetchTransport, args => { const event = args.getEvent(); if (event?.extra?.[EXTRA_KEY] && Array.isArray(event.extra[EXTRA_KEY])) { return event.extra[EXTRA_KEY]; } return []; }); Sentry.init({ transport, // ... other options }); // Capture events with routing info Sentry.captureException(error, { extra: { [EXTRA_KEY]: [ { dsn: 'https://key1@sentry.io/project1', release: 'v1.0.0' }, { dsn: 'https://key2@sentry.io/project2' }, ], }, }); ``` **After:** ```javascript import { makeFetchTransport, makeMultiplexedTransport, MULTIPLEXED_TRANSPORT_EXTRA_KEY } from '@sentry/browser'; // Just pass the transport generator - the default matcher handles the rest! Sentry.init({ transport: makeMultiplexedTransport(makeFetchTransport), // ... other options }); // Capture events with routing info using the exported constant Sentry.captureException(error, { extra: { [MULTIPLEXED_TRANSPORT_EXTRA_KEY]: [ { dsn: 'https://key1@sentry.io/project1', release: 'v1.0.0' }, { dsn: 'https://key2@sentry.io/project2' }, ], }, }); ``` The default matcher looks for routing information in `event.extra[MULTIPLEXED_TRANSPORT_EXTRA_KEY]`. You can still provide a custom matcher function for advanced use cases. - **feat(nextjs): Support cacheComponents on turbopack ([#18304](getsentry/sentry-javascript#18304 This release adds support for `cacheComponents` on turbopack builds. We are working on adding support for this feature in webpack builds as well. ##### Other Changes - feat: Publish AWS Lambda Layer for Node 24 ([#18327](getsentry/sentry-javascript#18327)) - feat(browser): Expose langchain instrumentation ([#18342](getsentry/sentry-javascript#18342)) - feat(browser): Expose langgraph instrumentation ([#18345](getsentry/sentry-javascript#18345)) - feat(cloudflare): Allow specifying a custom fetch in Cloudflare transport options ([#18335](getsentry/sentry-javascript#18335)) - feat(core): Add `isolateTrace` option to `Sentry.withMonitor()` ([#18079](getsentry/sentry-javascript#18079)) - feat(deps): bump [@sentry/webpack-plugin](https://github.com/sentry/webpack-plugin) from 4.3.0 to 4.6.1 ([#18272](getsentry/sentry-javascript#18272)) - feat(nextjs): Add cloudflare `waitUntil` detection ([#18336](getsentry/sentry-javascript#18336)) - feat(node): Add LangChain v1 support ([#18306](getsentry/sentry-javascript#18306)) - feat(remix): Add parameterized transaction naming for routes ([#17951](getsentry/sentry-javascript#17951)) - fix(cloudflare): Keep http root span alive until streaming responses are consumed ([#18087](getsentry/sentry-javascript#18087)) - fix(cloudflare): Wait for async events to finish ([#18334](getsentry/sentry-javascript#18334)) - fix(core): `continueTrace` doesn't propagate given trace ID if active span exists ([#18328](getsentry/sentry-javascript#18328)) - fix(node-core): Handle custom scope in log messages without parameters ([#18322](getsentry/sentry-javascript#18322)) - fix(opentelemetry): Ensure Sentry spans don't leak when tracing is disabled ([#18337](getsentry/sentry-javascript#18337)) - fix(react-router): Use underscores in trace origin values ([#18351](getsentry/sentry-javascript#18351)) - chore(tanstackstart-react): Export custom inits from tanstackstart-react ([#18369](getsentry/sentry-javascript#18369)) - chore(tanstackstart-react)!: Remove empty placeholder implementations ([#18338](getsentry/sentry-javascript#18338)) <details> <summary><strong>Internal Changes</strong></summary> - chore: Allow URLs as issue ([#18372](getsentry/sentry-javascript#18372)) - chore(changelog): Add entry for [#18304](getsentry/sentry-javascript#18304) ([#18329](getsentry/sentry-javascript#18329)) - chore(ci): Add action to track all PRs as issues ([#18363](getsentry/sentry-javascript#18363)) - chore(github): Adjust `BUGBOT.md` rules to flag invalid op and origin values during review ([#18352](getsentry/sentry-javascript#18352)) - ci: Add action to create issue on gitflow merge conflicts ([#18319](getsentry/sentry-javascript#18319)) - ci(deps): bump actions/checkout from 5 to 6 ([#18268](getsentry/sentry-javascript#18268)) - ci(deps): bump peter-evans/create-pull-request from 7.0.8 to 7.0.9 ([#18361](getsentry/sentry-javascript#18361)) - test(cloudflare): Add typechecks for cloudflare-worker e2e test ([#18321](getsentry/sentry-javascript#18321)) </details> #### Bundle size 📦 | Path | Size | | ----------------------------------------------------------------------------------------------------- | --------- | | [@sentry/browser](https://github.com/sentry/browser) | 24.22 KB | | [@sentry/browser](https://github.com/sentry/browser) - with treeshaking flags | 22.76 KB | | [@sentry/browser](https://github.com/sentry/browser) (incl. Tracing) | 40.57 KB | | [@sentry/browser](https://github.com/sentry/browser) (incl. Tracing, Profiling) | 45.05 KB | | [@sentry/browser](https://github.com/sentry/browser) (incl. Tracing, Replay) | 78.08 KB | | [@sentry/browser](https://github.com/sentry/browser) (incl. Tracing, Replay) - with treeshaking flags | 68.05 KB | | [@sentry/browser](https://github.com/sentry/browser) (incl. Tracing, Replay with Canvas) | 82.65 KB | | [@sentry/browser](https://github.com/sentry/browser) (incl. Tracing, Replay, Feedback) | 94.61 KB | | [@sentry/browser](https://github.com/sentry/browser) (incl. Feedback) | 40.51 KB | | [@sentry/browser](https://github.com/sentry/browser) (incl. sendFeedback) | 28.8 KB | | [@sentry/browser](https://github.com/sentry/browser) (incl. FeedbackAsync) | 33.66 KB | | [@sentry/react](https://github.com/sentry/react) | 25.9 KB | | [@sentry/react](https://github.com/sentry/react) (incl. Tracing) | 42.72 KB | | [@sentry/vue](https://github.com/sentry/vue) | 28.56 KB | | [@sentry/vue](https://github.com/sentry/vue) (incl. Tracing) | 42.32 KB | | [@sentry/svelte](https://github.com/sentry/svelte) | 24.24 KB | | CDN Bundle | 26.57 KB | | CDN Bundle (incl. Tracing) | 41.22 KB | | CDN Bundle (incl. Tracing, Replay) | 76.9 KB | | CDN Bundle (incl. Tracing, Replay, Feedback) | 82.23 KB | | CDN Bundle - uncompressed | 78.09 KB | | CDN Bundle (incl. Tracing) - uncompressed | 122.4 KB | | CDN Bundle (incl. Tracing, Replay) - uncompressed | 235.71 KB | | CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed | 248.17 KB | | [@sentry/nextjs](https://github.com/sentry/nextjs) (client) | 44.88 KB | | [@sentry/sveltekit](https://github.com/sentry/sveltekit) (client) | 40.92 KB | | [@sentry/node-core](https://github.com/sentry/node-core) | 50.06 KB | | [@sentry/node](https://github.com/sentry/node) | 155.7 KB | | [@sentry/node](https://github.com/sentry/node) - without tracing | 90.67 KB | | [@sentry/aws-serverless](https://github.com/sentry/aws-serverless) | 105.61 KB | </details> --- ### Configuration 📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined). 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about this update again. --- - [ ] If you want to rebase/retry this PR, check this box --- This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).  Reviewed-on: https://git.foxden.network/foxCaves/foxCaves/pulls/12 Co-authored-by: Renovate <[email protected]> Co-committed-by: Renovate <[email protected]>

RulaKhaled added 3 commits October 31, 2025 13:59

try to override p-map till react router esolves this issue

2b3eaf1

fix(cloudflare): Keep root span alive until streaming responses are c…

0842114

…onsumed

Merge branch 'develop' into fix-streaming

7a570db

RulaKhaled force-pushed the fix-streaming branch from e7d2476 to b9d02cf Compare November 4, 2025 13:17

quick refactor

eb7a5c1

RulaKhaled force-pushed the fix-streaming branch from 2875b4f to eb7a5c1 Compare November 4, 2025 14:29

RulaKhaled added 3 commits November 4, 2025 15:53

test buffered without timeout

ae8e345

remove timeout

62a1b2c

give this a shot

ca4bafa

RulaKhaled force-pushed the fix-streaming branch from febee8b to fadd2eb Compare November 20, 2025 16:47

revert and fix tests

31ecf58

RulaKhaled force-pushed the fix-streaming branch from d729aae to 31ecf58 Compare November 21, 2025 10:59

fix test

17a03a7

RulaKhaled requested review from AbhiPrasad and Lms24 and removed request for Lms24 November 21, 2025 12:49

RulaKhaled changed the title ~~WIP fix(cloudflare): Keep http root span alive until streaming responses are consumed~~ fix(cloudflare): Keep http root span alive until streaming responses are consumed Nov 21, 2025

RulaKhaled marked this pull request as ready for review November 21, 2025 12:50

sentry bot reviewed Nov 21, 2025

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Lms24 reviewed Nov 28, 2025

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RulaKhaled added 3 commits November 28, 2025 14:41

remove res from classify fn, quick refactor

1f75f5c

Merge branch 'develop' into fix-streaming

0686eaa

lint

a5e65f3

RulaKhaled requested a review from Lms24 November 28, 2025 14:43

Lms24 approved these changes Nov 28, 2025

View reviewed changes

RulaKhaled merged commit 2f8a039 into develop Dec 1, 2025
49 checks passed

RulaKhaled deleted the fix-streaming branch December 1, 2025 10:25

Uh oh!

fix(cloudflare): Keep http root span alive until streaming responses are consumed #18087

fix(cloudflare): Keep http root span alive until streaming responses are consumed #18087

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node-overhead report 🧳

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RulaKhaled commented Nov 4, 2025 •

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