[wrangler] Log ProxyWorker request error details at debug level - #15207

exKAZUu · 2026-08-15T13:28:31Z

Since #15252, a failed request proxied to the local Worker is logged and wrangler dev keeps running. That log shows only the error message, though, such as Network connection lost.. The stack and cause chain, which are the only clues to why the connection failed, aren't logged even with --log-level debug.

This PR:

logs the rehydrated error (stack and cause chain) at debug level in DevEnv's handler for Error inside ProxyWorker, the same way the other non-fatal ProxyController errors are logged;
removes the fallback to cause.cause.message, left over from before [wrangler] Preserve serialized error details in castErrorCause #14906. castErrorCause now preserves the message itself, and .cause holds the real underlying cause, so the fallback could report the wrong message.

Tests
- Tests included/updated
- Automated tests not possible - manual testing has been completed as follows:
- Additional testing not necessary because:
Public documentation
- Cloudflare docs PR(s):
- Documentation not necessary because: only debug-level log output changes; no public API or configuration changes.

changeset-bot · 2026-08-15T13:28:36Z

🦋 Changeset detected

Latest commit: 294f30a

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

This PR includes changesets to release 3 packages

Name	Type
wrangler	Patch
@cloudflare/vite-plugin	Patch
@cloudflare/vitest-plugin	Patch

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workers-devprod · 2026-08-15T13:28:56Z

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.changeset/tidy-pandas-smile.md: [@cloudflare/wrangler]
packages/wrangler/src/tests/api/startDevWorker/ProxyController.test.ts: [@cloudflare/wrangler]
packages/wrangler/src/api/startDevWorker/ProxyController.ts: [@cloudflare/wrangler]

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pkg-pr-new · 2026-08-15T13:32:05Z

@cloudflare/autoconfig

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/autoconfig@15207

@cloudflare/build-output-utils

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/build-output-utils@15207

@cloudflare/codemods

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/codemods@15207

@cloudflare/config

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/config@15207

@cloudflare/containers-shared

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/containers-shared@15207

create-cloudflare

npm i https://pkg.pr.new/cloudflare/workers-sdk/create-cloudflare@15207

@cloudflare/deploy-helpers

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/deploy-helpers@15207

@cloudflare/kv-asset-handler

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/kv-asset-handler@15207

miniflare

npm i https://pkg.pr.new/cloudflare/workers-sdk/miniflare@15207

@cloudflare/pages-functions

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/pages-functions@15207

@cloudflare/pages-shared

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/pages-shared@15207

@cloudflare/runtime-types

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/runtime-types@15207

@cloudflare/unenv-preset

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/unenv-preset@15207

@cloudflare/vite-plugin

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/vite-plugin@15207

@cloudflare/vitest-plugin

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/vitest-plugin@15207

@cloudflare/workers-auth

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/workers-auth@15207

@cloudflare/workers-editor-shared

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/workers-editor-shared@15207

@cloudflare/workers-utils

npm i https://pkg.pr.new/cloudflare/workers-sdk/@cloudflare/workers-utils@15207

wrangler

npm i https://pkg.pr.new/cloudflare/workers-sdk/wrangler@15207

commit: 294f30a

The e2e job died mid-run and passed on a re-run. It was not flaky infrastructure and it was not the OOM killer: `wrangler dev` exits on a SINGLE failed proxied request, and reports it as `✘ [ERROR]` with an empty message. Wrangler forwards every request through its own ProxyWorker. When that inner fetch rejects, the ProxyWorker reports it to the ProxyController, `DevEnv.handleErrorEvent` finds no matching non-fatal case and re-emits it as a top-level `error`; the dev command is `await events.once(devEnv, "teardown")`, and Node's `events.once` rejects on `error`, so the command throws and the process exits 1. The cause crossed a Worker boundary, so it is a plain object rather than an Error, and `castErrorCause` wraps it in `new Error()` -- message "". Hence a fatal exit that names nothing. The rejection is `Network connection lost.`, raised when a client disconnects while its request body is still uploading. Playwright does that every time it closes a page with a form POST in flight. Confirmed by reduction: five aborted uploads against a bare Worker kill wrangler 4.121.0 with the exact CI signature, and survive it patched. So the failure was one browser-side race taking down the server for the rest of the suite -- seventy `ERR_CONNECTION_REFUSED` failures, three attempts each, none of them naming the event. Patch wrangler with upstream's own fix (cloudflare/workers-sdk#15207, issue #15203): report the failed request and keep serving. Two call sites, because wrangler bundles the ProxyController twice. Remove the patch when a release carries the fix -- a version bump that leaves it here fails the install rather than applying quietly. `patches/**` joins the js paths filter: a patched dependency is application behaviour, and editing it must run the suite that proves it. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

The e2e job died mid-run and passed on a re-run. It was not flaky infrastructure and it was not the OOM killer: `wrangler dev` exits on a SINGLE failed proxied request, and reports it as `✘ [ERROR]` with an empty message. Wrangler forwards every request through its own ProxyWorker. When that inner fetch rejects, the ProxyWorker reports it to the ProxyController, `DevEnv.handleErrorEvent` finds no matching non-fatal case and re-emits it as a top-level `error`; the dev command is `await events.once(devEnv, "teardown")`, and Node's `events.once` rejects on `error`, so the command throws and the process exits 1. The cause crossed a Worker boundary, so it is a plain object rather than an Error, and `castErrorCause` wraps it in `new Error()` -- message "". Hence a fatal exit that names nothing. The rejection is `Network connection lost.`, raised when a client disconnects while its request body is still uploading. Playwright does that every time it closes a page with a form POST in flight. Confirmed by reduction: five aborted uploads against a bare Worker kill wrangler 4.121.0 with the exact CI signature, and survive it patched. So the failure was one browser-side race taking down the server for the rest of the suite -- seventy `ERR_CONNECTION_REFUSED` failures, three attempts each, none of them naming the event. Patch wrangler with upstream's own fix (cloudflare/workers-sdk#15207, issue #15203): report the failed request and keep serving. Two call sites, because wrangler bundles the ProxyController twice. Remove the patch when a release carries the fix -- a version bump that leaves it here fails the install rather than applying quietly. `patches/**` joins the js paths filter: a patched dependency is application behaviour, and editing it must run the suite that proves it. Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

anthonywu · 2026-08-20T17:55:28Z

+💯 priority to fix. This is blocking us in development. In the meantime, we're using the patch.

workers-devprod · 2026-08-27T02:37:26Z

Codeowners approval required for this PR:

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.changeset/tidy-pandas-smile.md: [@cloudflare/wrangler]
packages/wrangler/src/tests/api/startDevWorker/ProxyController.test.ts: [@cloudflare/wrangler]
packages/wrangler/src/api/startDevWorker/ProxyController.ts: [@cloudflare/wrangler]

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workers-devprod · 2026-09-02T05:17:00Z

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.changeset/tidy-pandas-smile.md: [@cloudflare/wrangler]
packages/wrangler/src/tests/api/startDevWorker/ProxyController.test.ts: [@cloudflare/wrangler]
packages/wrangler/src/api/startDevWorker/ProxyController.ts: [@cloudflare/wrangler]

…est-errors # Conflicts: # .changeset/tidy-pandas-smile.md

workers-devprod · 2026-09-15T15:35:20Z

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.changeset/steady-proxy-requests.md: [@cloudflare/wrangler]
packages/wrangler/src/tests/api/startDevWorker/DevEnv.test.ts: [@cloudflare/wrangler]
packages/wrangler/src/api/startDevWorker/DevEnv.ts: [@cloudflare/wrangler]

… of main

…est-errors

GregoryCollett · 2026-09-17T12:31:26Z

The improvement here seems extremely sensible. I can definitely get behind this!

workers-devprod · 2026-09-21T13:36:13Z

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fix(wrangler): keep request-scoped proxy errors non-fatal

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exKAZUu requested a review from workers-devprod as a code owner August 15, 2026 13:28

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workers-devprod requested review from a team and emily-shen and removed request for a team August 15, 2026 13:28

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exKAZUu added 2 commits August 16, 2026 16:47

Merge branch 'main' into fix-proxy-worker-request-errors

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yashau mentioned this pull request Aug 19, 2026

fix(ci): stop one aborted upload from killing wrangler dev yashau/prick#20

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yashau mentioned this pull request Aug 19, 2026

wrangler dev exits with "Error inside ProxyWorker / Network connection lost" on POST requests with a body when assets is configured #15203

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exKAZUu and others added 3 commits September 3, 2026 21:07

Skip logging ProxyWorker request errors after teardown

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Merge branch 'main' into fix-proxy-worker-request-errors

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Merge branch 'main' into fix-proxy-worker-request-errors

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Keep ProxyWorker error stack and cause reachable at debug level

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exKAZUu added 2 commits September 16, 2026 00:31

Merge remote-tracking branch 'origin/main' into fix-proxy-worker-requ…

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…est-errors # Conflicts: # .changeset/tidy-pandas-smile.md

Update JSON-channel ProxyWorker error test for logged request errors

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Narrow ProxyWorker request error handling to debug diagnostics on top…

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… of main

exKAZUu changed the title ~~[wrangler] Keep request-scoped proxy errors non-fatal~~ [wrangler] Log ProxyWorker request error details at debug level Sep 15, 2026

Merge remote-tracking branch 'origin/main' into fix-proxy-worker-requ…

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exKAZUu added 2 commits September 18, 2026 10:05

Merge branch 'main' into fix-proxy-worker-request-errors

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Merge branch 'main' into fix-proxy-worker-request-errors

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Merge branch 'main' into fix-proxy-worker-request-errors

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cjol approved these changes Sep 22, 2026

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Merge branch 'main' into fix-proxy-worker-request-errors

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cjol merged commit 805af2f into cloudflare:main Sep 25, 2026
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workers-devprod mentioned this pull request Sep 25, 2026

Version Packages #15867

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