starlette Disconnect event not received when using

The Fix

Upgrade to version 0.21.0 or later.

Based on closed Kludex/starlette issue #1247 · 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%.

Jump to Verify Open PR/Commit

@@ -391,3 +391,34 @@ def test_streaming_response_known_size(test_client_factory):
     response = client.get("/")
     assert response.headers["content-length"] == "10"
+
+
[email protected]

repro.py

import requests

def test_server():
    response = requests.post('http://localhost:8000/', stream=True)
    print('response.status', response.status)
    response.close()

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\nUpgrade to version 0.21.0 or later.\nWhen NOT to use: This fix is not applicable if using non-streaming responses or different testing frameworks.\n\n

Why This Fix Works in Production

Trigger: In other words, remove anything that doesn't make the bug go away.
Mechanism: Added a test to check that StreamingResponse will interrupt its streaming when the client disconnects.
Why the fix works: Added a test to check that StreamingResponse will interrupt its streaming when the client disconnects. (first fixed release: 0.21.0).

Production impact:

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): In other words, remove anything that doesn't make the bug go away.

Proof / Evidence

GitHub issue: #1247
Fix PR: https://github.com/encode/starlette/pull/1727
First fixed release: 0.21.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.65

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“We should take care of this for https://github.com/encode/starlette/issues/652 , I guess.”

@Kludex · 2021-11-27 · source

“I think this will always be a limitation of the TestClient. I think we should add a test case, and maybe add a few lines…”

@Kludex · 2022-05-09 · source

“A way to test an ASGI application with http.disconnect without the TestClient: https://github.com/encode/starlette/pull/1727”

@Kludex · 2022-08-17 · source

Failure Signature (Search String)

In other words, remove anything that doesn't make the bug go away.
<!-- Any tracebacks, screenshots, etc. that can help understanding the problem.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
In other words, remove anything that doesn't make the bug go away.
<!-- Any tracebacks, screenshots, etc. that can help understanding the problem.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
In other words, remove anything that doesn't make the bug go away.
<!-- Any tracebacks, screenshots, etc. that can help understanding the problem.

Minimal Reproduction

repro.py

import requests

def test_server():
    response = requests.post('http://localhost:8000/', stream=True)
    print('response.status', response.status)
    response.close()

What Broke

Tests fail to receive disconnect events, leading to incomplete testing of streaming functionality.

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

Upgrade to version 0.21.0 or later.

When NOT to use: This fix is not applicable if using non-streaming responses or different testing frameworks.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/encode/starlette/pull/1727

First fixed release: 0.21.0

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

This fix is not applicable if using non-streaming responses or different testing frameworks.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Add a TLS smoke test that performs a real handshake in CI (include CA bundle validation and hostname checks).
Alert on handshake failures by error string and endpoint to catch cert/CA changes quickly.

Version Compatibility Table

Version	Status
0.21.0	Fixed

Related Issues

No related fixes found.

Cluster: starlette:configuration-error All hubs All clusters

Related clusters: Data consistency SSL handshake Other

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

starlette Disconnect event not received when using TestClient (Fix)