urllib3 test_delayed_body_read_timeout_with

The Fix

pip install urllib3==1.25.9

Based on closed urllib3/urllib3 issue #1883 · PR/commit linked

Production note: Watch p95/p99 latency and retry volume; timeouts can turn into retry storms and duplicate side-effects.

Jump to Verify Open PR/Commit

@@ -300,5 +300,8 @@ In chronological order:
   * Fix for connection not being released on HTTP redirect and response not preloaded
 
+* [Bastiaan Bakker] <https://github.com/bastiaanb>
+  * Support for logging session keys via environment variable ``SSLKEYLOGFILE`` (Python 3.8+)
+

repro.py

2020-05-31T04:32:39.1658820Z ________ TestSocketClosing.test_delayed_body_read_timeout_with_preload _________
2020-05-31T04:32:39.1659980Z Traceback (most recent call last):
2020-05-31T04:32:39.1663620Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/connection.py", line 159, in _new_conn
2020-05-31T04:32:39.1664020Z     (self._dns_host, self.port), self.timeout, **extra_kw
2020-05-31T04:32:39.1665550Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/util/connection.py", line 84, in create_connection
2020-05-31T04:32:39.1665760Z     raise err
2020-05-31T04:32:39.1666450Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/util/connection.py", line 74, in create_connection
2020-05-31T04:32:39.1666640Z     sock.connect(sa)
2020-05-31T04:32:39.1666770Z ConnectionRefusedError: [Errno 61] Connection refused
2020-05-31T04:32:39.1666830Z 
2020-05-31T04:32:39.1666950Z During handling of the above exception, another exception occurred:
2020-05-31T04:32:39.1667010Z 
2020-05-31T04:32:39.1667140Z Traceback (most recent call last):
2020-05-31T04:32:39.1667370Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/test/with_dummyserver/test_socketlevel.py", line 570, in test_delayed_body_read_timeout_with_preload
2020-05-31T04:32:39.1667540Z     pool.urlopen("GET", "/", retries=False, timeout=timeout)
2020-05-31T04:32:39.1668150Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/connectionpool.py", line 727, in urlopen
2020-05-31T04:32:39.1668340Z     method, url, error=e, _pool=self, _stacktrace=sys.exc_info()[2]
2020-05-31T04:32:39.1668950Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/util/retry.py", line 400, in increment
2020-05-31T04:32:39.1669170Z     raise six.reraise(type(error), error, _stacktrace)
2020-05-31T04:32:39.1669840Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/packages/six.py", line 735, in reraise
2020-05-31T04:32:39.1669990Z     raise value
2020-05-31T04:32:39.1670620Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/connectionpool.py", line 677, in urlopen
2020-05-31T04:32:39.1670770Z     chunked=chunked,
2020-05-31T04:32:39.1671360Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/connectionpool.py", line 392, in _make_request
2020-05-31T04:32:39.1671540Z     conn.request(method, url, **httplib_request_kw)
2020-05-31T04:32:39.1671720Z   File "/Users/runner/hostedtoolcache/Python/3.7.7/x64/lib/python3.7/http/client.py", line 1252, in request
2020-05-31T04:32:39.1671870Z     self._send_request(method, url, body, headers, encode_chunked)
2020-05-31T04:32:39.1672060Z   File "/Users/runner/hostedtoolcache/Python/3.7.7/x64/lib/python3.7/http/client.py", line 1298, in _send_request
2020-05-31T04:32:39.1672200Z     self.endheaders(body, encode_chunked=encode_chunked)
2020-05-31T04:32:39.1672390Z   File "/Users/runner/hostedtoolcache/Python/3.7.7/x64/lib/python3.7/http/client.py", line 1247, in endheaders
2020-05-31T04:32:39.1672510Z     self._send_output(message_body, encode_chunked=encode_chunked)
2020-05-31T04:32:39.1673070Z   File "/Users/runner/hostedtoolcache/Python/3.7.7/x64/lib/python3.7/http/client.py", line 1026, in _send_output
2020-05-31T04:
... (truncated) ...

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\npip install urllib3==1.25.9\nWhen NOT to use: This fix should not be applied if the flaky behavior is due to actual network issues.\n\n

Why This Fix Works in Production

Trigger: ConnectionRefusedError: [Errno 61] Connection refused
Mechanism: The flaky test 'test_delayed_body_read_timeout_with_preload' is caused by intermittent connection issues during testing
Why the fix works: The issue regarding the flaky test 'test_delayed_body_read_timeout_with_preload' has been noted, but no specific fix was implemented in a PR that closes the issue. (first fixed release: 1.25.9).

Production impact:

If left unfixed, tail latency can spike under load and surface as timeouts/retries (amplifying incident impact).

Why This Breaks in Prod

Shows up under Python 3.7 in real deployments (not just unit tests).
The flaky test 'test_delayed_body_read_timeout_with_preload' is caused by intermittent connection issues during testing
Surfaces as: ConnectionRefusedError: [Errno 61] Connection refused

Proof / Evidence

GitHub issue: #1883
Fix PR: https://github.com/urllib3/urllib3/pull/1867
First fixed release: 1.25.9
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.70
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.46

Discussion

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

Jump to Sources Open on GitHub

“I haven't seen this test being as flaky lately (at least any more than any other timeout test?) so I'm going to close this. Let…”

@sethmlarson · 2022-02-10 · source

“I think it's still flaky but this issue isn't helping.”

@pquentin · 2022-02-10 · source

Failure Signature (Search String)

ConnectionRefusedError: [Errno 61] Connection refused

Error Message

Stack trace

error.txt

Error Message
-------------
ConnectionRefusedError: [Errno 61] Connection refused

Minimal Reproduction

repro.py

2020-05-31T04:32:39.1658820Z ________ TestSocketClosing.test_delayed_body_read_timeout_with_preload _________
2020-05-31T04:32:39.1659980Z Traceback (most recent call last):
2020-05-31T04:32:39.1663620Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/connection.py", line 159, in _new_conn
2020-05-31T04:32:39.1664020Z     (self._dns_host, self.port), self.timeout, **extra_kw
2020-05-31T04:32:39.1665550Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/util/connection.py", line 84, in create_connection
2020-05-31T04:32:39.1665760Z     raise err
2020-05-31T04:32:39.1666450Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/util/connection.py", line 74, in create_connection
2020-05-31T04:32:39.1666640Z     sock.connect(sa)
2020-05-31T04:32:39.1666770Z ConnectionRefusedError: [Errno 61] Connection refused
2020-05-31T04:32:39.1666830Z 
2020-05-31T04:32:39.1666950Z During handling of the above exception, another exception occurred:
2020-05-31T04:32:39.1667010Z 
2020-05-31T04:32:39.1667140Z Traceback (most recent call last):
2020-05-31T04:32:39.1667370Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/test/with_dummyserver/test_socketlevel.py", line 570, in test_delayed_body_read_timeout_with_preload
2020-05-31T04:32:39.1667540Z     pool.urlopen("GET", "/", retries=False, timeout=timeout)
2020-05-31T04:32:39.1668150Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/connectionpool.py", line 727, in urlopen
2020-05-31T04:32:39.1668340Z     method, url, error=e, _pool=self, _stacktrace=sys.exc_info()[2]
2020-05-31T04:32:39.1668950Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/util/retry.py", line 400, in increment
2020-05-31T04:32:39.1669170Z     raise six.reraise(type(error), error, _stacktrace)
2020-05-31T04:32:39.1669840Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/packages/six.py", line 735, in reraise
2020-05-31T04:32:39.1669990Z     raise value
2020-05-31T04:32:39.1670620Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/connectionpool.py", line 677, in urlopen
2020-05-31T04:32:39.1670770Z     chunked=chunked,
2020-05-31T04:32:39.1671360Z   File "/Users/runner/runners/2.263.0/work/urllib3/urllib3/.nox/test-3-7/lib/python3.7/site-packages/urllib3/connectionpool.py", line 392, in _make_request
2020-05-31T04:32:39.1671540Z     conn.request(method, url, **httplib_request_kw)
2020-05-31T04:32:39.1671720Z   File "/Users/runner/hostedtoolcache/Python/3.7.7/x64/lib/python3.7/http/client.py", line 1252, in request
2020-05-31T04:32:39.1671870Z     self._send_request(method, url, body, headers, encode_chunked)
2020-05-31T04:32:39.1672060Z   File "/Users/runner/hostedtoolcache/Python/3.7.7/x64/lib/python3.7/http/client.py", line 1298, in _send_request
2020-05-31T04:32:39.1672200Z     self.endheaders(body, encode_chunked=encode_chunked)
2020-05-31T04:32:39.1672390Z   File "/Users/runner/hostedtoolcache/Python/3.7.7/x64/lib/python3.7/http/client.py", line 1247, in endheaders
2020-05-31T04:32:39.1672510Z     self._send_output(message_body, encode_chunked=encode_chunked)
2020-05-31T04:32:39.1673070Z   File "/Users/runner/hostedtoolcache/Python/3.7.7/x64/lib/python3.7/http/client.py", line 1026, in _send_output
2020-05-31T04:
... (truncated) ...

Environment

Python: 3.7

What Broke

Intermittent test failures leading to unreliable CI results and potential delays in development.

Why It Broke

The flaky test 'test_delayed_body_read_timeout_with_preload' is caused by intermittent connection issues during testing

Fix Options (Details)

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

pip install urllib3==1.25.9

When NOT to use: This fix should not be applied if the flaky behavior is due to actual network issues.

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

Fix reference: https://github.com/urllib3/urllib3/pull/1867

First fixed release: 1.25.9

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

When NOT to Use This Fix

This fix should not be applied if the flaky behavior is due to actual network issues.

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 CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
Upgrade behind a canary and run integration tests against the canary before 100% rollout.
Track RSS + object counts after deployments; alert on monotonic growth and GC pressure.
Add a long-running test that repeats the failing call path and asserts stable memory.

Version Compatibility Table

Version	Status
1.25.9	Fixed

Related Issues

No related fixes found.

Cluster: urllib3:timeout urllib3 hub urllib3 best practices All hubs All clusters

Related clusters: Configuration error Data consistency SSL handshake

Sources

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

urllib3 test_delayed_body_read_timeout_with_preload is flaky (Fix)