The Fix
Modifies the WebSocketResponse.close() method to wait for a close message within its timeout window, preventing spurious abnormal closure reports.
Based on closed aio-libs/aiohttp issue #9506 · PR/commit linked
Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.
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+Fixed :py:meth:`WebSocketResponse.close() <aiohttp.web.WebSocketResponse.close>` to discard non-close messages within its timeout window after sending close -- by :user:`lenard-mosys`.
diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index 3940c2693b7..5d5f922e6fb 100644
Option A — Apply the official fix\nModifies the WebSocketResponse.close() method to wait for a close message within its timeout window, preventing spurious abnormal closure reports.\nWhen NOT to use: This fix should not be used if the application requires immediate closure without waiting for a close message.\n\n
Why This Fix Works in Production
- Trigger: WebSocketResponse.close() should wait for a close frame in its timeout window
- Mechanism: Modifies the WebSocketResponse.close() method to wait for a close message within its timeout window, preventing spurious abnormal closure reports.
- If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.
Why This Breaks in Prod
- Production symptom (often without a traceback): WebSocketResponse.close() should wait for a close frame in its timeout window
Proof / Evidence
- GitHub issue: #9506
- Fix PR: https://github.com/aio-libs/aiohttp/pull/9508
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.70
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.67
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“Yeah' that doesn't sound right. Feel free to make a PR, or maybe @bdraco might be interested in this one.”
“fixed via https://github.com/aio-libs/aiohttp/pull/9508”
Failure Signature (Search String)
- WebSocketResponse.close() should wait for a close frame in its timeout window
- During the timeout wait for a close message, and discard messages that arrive before that. Only report an abnormal closure if that close message never arrives.
Copy-friendly signature
Failure Signature
-----------------
WebSocketResponse.close() should wait for a close frame in its timeout window
During the timeout wait for a close message, and discard messages that arrive before that. Only report an abnormal closure if that close message never arrives.
Error Message
Signature-only (no traceback captured)
Error Message
-------------
WebSocketResponse.close() should wait for a close frame in its timeout window
During the timeout wait for a close message, and discard messages that arrive before that. Only report an abnormal closure if that close message never arrives.
What Broke
Abnormal closure reports occur when non-close messages are received after sending a close message.
Fix Options (Details)
Option A — Apply the official fix
Modifies the WebSocketResponse.close() method to wait for a close message within its timeout window, preventing spurious abnormal closure reports.
Fix reference: https://github.com/aio-libs/aiohttp/pull/9508
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- This fix should not be used if the application requires immediate closure without waiting for a close message.
Did This Fix Work in Your Case?
Quick signal helps us prioritize which fixes to verify and improve.
Prevention
- Make timeouts explicit and test them (unit + integration) to avoid silent behavior changes.
- Instrument retries (attempt count + reason) and alert on spikes to catch dependency slowdowns.
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.