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

[June157]

What versions & operating system are you using?

  System:
    OS: Linux 6.8 Ubuntu 24.04.4 LTS 24.04.4 LTS (Noble Numbat)
    CPU: (6) x64 AMD EPYC-Milan Processor
    Memory: 13.01 GB / 15.61 GB
    Container: Yes
    Shell: 5.2.21 - /bin/bash
  Binaries:
    Node: 22.23.2 - /usr/bin/node
    npm: 10.9.8 - /usr/bin/npm
    pnpm: 9.0.0 - /usr/bin/pnpm
  npmPackages:
    wrangler: ^4.123.0 => 4.123.0

(workerd 1.20260811.1 and miniflare 5.20260811.1-alpha come in as wrangler's dependencies.)

Please provide a link to a minimal reproduction

https://gist.github.com/June157/7dd408450d8c153b47986a8c3325132c

(5 files: worker.mjs, wrangler.json, hammer.mjs, index.html → put under public/, and a README with the two commands.)

Describe the Bug

With Static Assets configured (assets.directory), wrangler dev exits — not just returns an error — after a few dozen POST requests that carry a body and target a path where an asset exists. The assets layer answers those requests with 405 itself (they never reach the user Worker), and after some number of them the ProxyWorker dies. The same POSTs without a body are fine indefinitely, and the same Worker without assets is fine indefinitely.

Client-side symptom: 405 … 405 → one or two HTTP 500 → socket hang up / ECONNRESET → ECONNREFUSED for everything after. wrangler dev prints an empty ✘ [ERROR] and exits.

Production Workers with the same code do not exhibit this.

Minimal reproduction (also in the gist)

worker.mjs — its content barely matters; the crashing requests never reach it:

export default {
  fetch(request) {
    if (request.method === "POST") return new Response("Forbidden", { status: 403 });
    return new Response("ok");
  },
};

wrangler.json:

{ "name": "repro", "main": "worker.mjs", "compatibility_date": "2026-08-13",
  "assets": { "directory": "./public", "binding": "ASSETS" } }

public/index.html: any file (so that / is an asset path).

npx wrangler dev -c wrangler.json --port 8788
# in another shell — 300 POSTs with a small form body, 3 concurrent:
node --input-type=module -e '
const N=300,C=3,B="http://127.0.0.1:8788";let i=0,ok=0,fail=0;
const one=()=>fetch(B+"/",{method:"POST",body:"a=b",headers:{"content-type":"application/x-www-form-urlencoded"}});
await Promise.all(Array.from({length:C},async()=>{while(i<N){i++;try{const r=await one();if(r.status>=500)throw 0;ok++}catch{fail++}}}));
console.log({ok,fail});'

Observed: e.g. { ok: 107, fail: 193 }; afterwards curl http://127.0.0.1:8788/ → connection refused. Successful responses are 405 (from the assets layer, not from the Worker).

Expected: 300 × 405 (or the request forwarded to the Worker), and wrangler dev stays up.

What I varied (300 requests each, 2–3 runs each)

Variation	Result
Same config, POST / without body	✅ 300 × 405, alive
Same config, POST /api/x (no asset there) with body → reaches Worker → 403	✅ 300 × 403, alive
Same config, POST / with body, concurrency 1	❌ dies (first failure at request 9)
No assets in config, POST / with body → 403 from Worker	✅ alive
+ compatibility_flags: ["nodejs_compat"]	no change either way
+ assets.html_handling: "drop-trailing-slash"	no change
+ public/_headers or public/_redirects	no change
Worker drains the body (await request.text()) before responding	irrelevant — request doesn't reach the Worker

So the necessary conditions I could isolate are: assets configured + POST with a body + path resolves to an asset (assets layer answers 405).

Where I hit it (possibly related, not reduced)

In an Astro site on @astrojs/cloudflare, the same crash signature also occurs on POST /api/contact (an SSR route, not an asset) when the request has a form body and no Origin header — Astro's CSRF middleware answers 403 without reading the body. The identical request with an Origin header (handler reads the body, answers 400) never crashes, and the same request without a body never crashes. I could not reduce that variant to a bare Worker: a bare Worker returning 403 to the same request on a non-asset path stays up. I mention it because it may be the same underlying stream-handling issue reached by a different route; happy to provide the Astro repro if useful.

Guess at the mechanism (unverified)

With assets, requests pass through an asset router before the user Worker. When the router itself answers (405 for POST-to-asset) while a request body is still in flight, the abandoned body stream seems to surface as Network connection lost inside the ProxyWorker and is treated as fatal for the whole dev server rather than for that one request.

Please provide any relevant error logs

Debug log (~/.config/.wrangler/logs/wrangler-*.log) at the moment of the crash:

Error in ProxyController: Error inside ProxyWorker
 Error
    at castErrorCause (…/wrangler/wrangler-dist/cli.js:179580:20)
    at ProxyController2.emitErrorEvent (…/wrangler/wrangler-dist/cli.js:280188:20)
    at ProxyController2.onProxyWorkerMessage (…/wrangler/wrangler-dist/cli.js:280065:18)
    at PROXY_CONTROLLER (…/wrangler/wrangler-dist/cli.js:279792:24)
    at process.processTicksAndRejections (node:internal/process/task_queues:103:5)
    at async #handleLoopbackCustomFetchService (…/miniflare/dist/src/index.js:111517:22)
    at async #handleLoopback (…/miniflare/dist/src/index.js:111748:20) {
  cause: {
    name: 'Error',
    message: 'Network connection lost.',
    stack: 'Error: Network connection lost.'
  }
}

The user Worker's runtime WebSocket had opened ~2 s earlier; there is nothing between Runtime.enable and this error in the debug log.

[workers-devprod]

Note

This is an automated, advisory triage report generated by workers-devprod. It is not an official maintainer response — a maintainer will follow up.

🤖 Automated triage report

Issue Triage: #15203

Summary

With Static Assets configured, wrangler dev crashes and exits after a few dozen POST requests that carry a body and target a path where an asset exists (the assets layer replies 405, then the ProxyWorker dies).

Classification

• Type: Bug
• Component: packages/wrangler (Workers Assets + local dev ProxyWorker; possibly packages/miniflare)
• Severity: High
• Has Reproduction: Yes (with link)
• Quality: Complete

Findings

• Created: not reliably extractable from context.json (single-line file truncated by tooling)
• Author: June157
• Version: wrangler 4.123.0 (workerd 1.20260811.1, miniflare 5.20260811.1-alpha)
• Labels: not reliably extractable from context.json
• Comments: not reliably extractable from context.json

Analysis

• Tooling / local-dev bug, not runtime. The reporter explicitly notes production Workers with the same code do not exhibit the crash, and the crash is in the ProxyWorker / wrangler dev process — this is a workers-sdk tooling issue, not a workerd runtime issue. Belongs in packages/wrangler (Workers Assets path) and possibly packages/miniflare.
• Well-scoped reproduction. The report isolates the trigger precisely: POST + request body + a path where a static asset exists → the assets layer answers 405 before reaching the user Worker; after a few dozen such requests the dev process exits. Two clean control cases are provided (POST without a body is fine; the same Worker without assets is fine), which strongly points at the assets layer's handling of unconsumed request bodies for 405 responses.
• Crash severity. The symptom is a full process exit (✘ [ERROR] printed empty, then ECONNREFUSED for everything after), not just an error response. A crash of wrangler dev degrades the local development experience significantly for anyone using Static Assets, though it requires a specific request pattern.
• Good repro artifact. A public gist with 5 files (worker.mjs, wrangler.json, hammer.mjs, index.html, README) and exact commands is provided, plus full version/OS output. This meets the bug template requirements.
• Likely root cause hypothesis (for maintainers). The 405 short-circuit in the assets layer appears not to drain/consume the POST body, leaving the request stream in a state that eventually exhausts a resource / breaks the connection pipeline in the ProxyWorker. The "with body vs without body" contrast is the key signal.

Recommendation

Status: NEEDS VERIFICATION

Reasoning: This is a complete, well-isolated bug report with a minimal reproduction, version info, and OS details. It describes a hard crash of wrangler dev specific to Static Assets handling of POST-with-body requests. A maintainer should reproduce it against the latest wrangler to confirm and locate the fix in the assets/ProxyWorker code.

Action: Run the provided gist reproduction (hammer.mjs against wrangler dev with assets.directory set) on the latest wrangler to confirm the crash. Investigate how the Workers Assets layer handles unconsumed request bodies when short-circuiting with 405 in the dev ProxyWorker (and whether miniflare is involved). If confirmed, apply bug and the relevant component labels.

Suggested Labels: none (component/type labels omitted — cannot confirm exact repo label names from the truncated context.json)

Suggested Comment

Thanks for the detailed report and the reproduction — the "POST with a body to an asset path returns 405, then wrangler dev exits after a few dozen requests" breakdown is really helpful, and the with-body / without-body and with-assets / without-assets contrasts narrow this down nicely.

This looks like a local dev (ProxyWorker / Workers Assets) issue rather than a runtime one, which matches your note that production is unaffected. We'll try to reproduce with your gist on the latest version and investigate how the assets layer handles the request body when it short-circuits with a 405. If you have a chance, could you confirm whether the crash still reproduces on the very latest wrangler release?

Structured summary (JSON)

{
  "issueNumber": 15203,
  "title": "wrangler dev exits after repeated POST-with-body requests to asset paths when Static Assets are configured",
  "githubUrl": "https://github.com/cloudflare/workers-sdk/issues/15203",
  "recommendation": "NEEDS VERIFICATION",
  "difficulty": "medium",
  "reasoning": "Complete, well-isolated bug report with a minimal reproduction and version info describing a hard crash of wrangler dev specific to the Static Assets layer handling POST-with-body requests. It needs a maintainer to reproduce and locate the fix in the assets/ProxyWorker code.",
  "suggestedAction": "Run the provided gist reproduction on the latest wrangler to confirm the crash, then investigate how the Workers Assets layer handles unconsumed request bodies when short-circuiting with 405 in the dev ProxyWorker.",
  "hasSuggestedComment": true,
  "suggestedLabels": []
}

[workers-devprod]

• Reproduction: ✅ Successfully reproduced. wrangler dev with assets configured crashed after ~281 POST requests with body to / (asset path), printing empty ✘ [ERROR] and exiting; 19 of 300 concurrent requests failed. Baseline without assets handled all 300 requests fine with no crash.