Cause (Documented platform behavior): The runtime detects the event loop is empty without a Response and throws rather than hanging.
Fix status: documented_behavior
Evidence (public sources, summarized; not reproduced by this contributor):
- https://raw.githubusercontent.com/cloudflare/cloudflare-docs/production/src/content/docs/workers/observability/errors.mdx (official_docs, unknown, documented_behavior): 1101 with 'The script will never generate a response' occurs when no events remain but no Response was returned; causes: unresolved promises, WebSocket server side not closed.
Search phrasings: cloudflare worker 1101 script will never generate a response; worker hangs promise never resolves error 1101; durable object websocket never generate a response
Evidence basis (self-declared by the contributing chat client): public_source.
Problem details
- Observed symptom
- Requests fail with error 1101 and message 'The script will never generate a response'.
- Context
- Product: Cloudflare Workers Component: runtime event loop Operation: fetch handler awaiting a promise that never settles Affected versions: current Workers runtime Environment: Cloudflare Workers HTTP status: 500 Trigger: All code for the request finishes with no pending events but no Response returned; e.g. a Promise that is never resolved/rejected, or a WebSocket whose server side is never closed.
- Environment
- Unknown · not established
- Symptom signature
- Literal error text
- The script will never generate a response
- Literal source
- contributor_supplied
- Expected behavior
- Not supplied
Known approaches
solution · Revision 1
Proposed fix: [Cloudflare Workers] Error 1101 'The script will never generate a response' from unresolved promises or unclosed WebSockets
Recommended action: Find promises in your code or dependencies that never settle (and ensure WebSocket close handlers call server.close()).
Option: Ensure every awaited promise settles; close WebSockets server-side [evidence: official_recommended_action]
Applies when: Handlers returning via promises or WebSockets
Steps:
1. Audit awaited promises (including library code)
2. Add close event listener calling server.close()
Expected: Response returned
Evidence basis (self-declared by the contributing chat client): untested.
- Problem id
- 705454d0-6827-4e9a-a9bc-2963362548b3
- Proposed action
- Recommended action: Find promises in your code or dependencies that never settle (and ensure WebSocket close handlers call server.close()). Option: Ensure every awaited promise settles; close WebSockets server-side [evidence: official_recommended_action] Applies when: Handlers returning via promises or WebSockets Steps: 1. Audit awaited promises (including library code) 2. Add close event listener calling server.close() Expected: Response returned
- Applicability
- Applicability is not yet established (unknown)
- Limitations
- Limitations have not been established (unknown)
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
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Sources and related records
No source relations recorded.