Requests urllib3 exceptions passing through requests API

The Fix

pip install requests==2.27.0

Based on closed psf/requests issue #1572 · 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

@@ -19,6 +19,7 @@
                     prepend_scheme_if_needed, get_auth_from_url, urldefragauth)
 from .structures import CaseInsensitiveDict
+from .packages.urllib3.exceptions import ClosedPoolError
 from .packages.urllib3.exceptions import ConnectTimeoutError
 from .packages.urllib3.exceptions import HTTPError as _HTTPError

repro.py

......
  File "C:\Python27\lib\site-packages\requests\sessions.py", line 347, in get
    return self.request('GET', url, **kwargs)
  File "C:\Python27\lib\site-packages\requests\sessions.py", line 335, in request
    resp = self.send(prep, **send_kwargs)
  File "C:\Python27\lib\site-packages\requests\sessions.py", line 438, in send
    r = adapter.send(request, **kwargs)
  File "C:\Python27\lib\site-packages\requests\adapters.py", line 292, in send
    timeout=timeout
  File "C:\Python27\lib\site-packages\requests\packages\urllib3\connectionpool.py", line 423, in url
open
    conn = self._get_conn(timeout=pool_timeout)
  File "C:\Python27\lib\site-packages\requests\packages\urllib3\connectionpool.py", line 224, in _ge
t_conn
    raise ClosedPoolError(self, "Pool is closed.")
ClosedPoolError: HTTPConnectionPool(host='......', port=80): Pool is closed.

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 requests==2.27.0\nWhen NOT to use: This fix should not be applied if the application relies on raw urllib3 exceptions.\n\n

Why This Fix Works in Production

Mechanism: ClosedPoolError from urllib3 was not being caught and wrapped in requests
Why the fix works: Catches and wraps the ClosedPoolError exception from urllib3, preventing it from leaking through the requests API. (first fixed release: 2.27.0).

Production impact:

If left unfixed, this can cause silent data inconsistencies that propagate (bad cache entries, incorrect downstream decisions).

Why This Breaks in Prod

Shows up under Python 2.7 in real deployments (not just unit tests).
ClosedPoolError from urllib3 was not being caught and wrapped in requests
Surfaces as: ......

Proof / Evidence

GitHub issue: #1572
Fix PR: https://github.com/psf/requests/pull/2674
First fixed release: 2.27.0
Reproduced locally: No (not executed)
Last verified: 2026-02-07
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.21

Discussion

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

Jump to Sources Open on GitHub

“I also got urllib3 exceptions passing through when use Session in several threads, trace:”

@zbb42 · 2013-09-06 · source

“I definitely agree with you and would agree that these should be wrapped. Could you give us stack-traces so we can find where they're bleeding…”

@sigmavirus24 · 2013-09-03 · source

“Sorry I don't have stack traces readily available :/”

@sylvinus · 2013-09-03 · source

“No worries”

@sigmavirus24 · 2013-09-03 · source

Error Message

Stack trace

error.txt

Error Message
-------------
......
  File "C:\Python27\lib\site-packages\requests\sessions.py", line 347, in get
    return self.request('GET', url, **kwargs)
  File "C:\Python27\lib\site-packages\requests\sessions.py", line 335, in request
    resp = self.send(prep, **send_kwargs)
  File "C:\Python27\lib\site-packages\requests\sessions.py", line 438, in send
    r = adapter.send(request, **kwargs)
  File "C:\Python27\lib\site-packages\requests\adapters.py", line 292, in send
    timeout=timeout
  File "C:\Python27\lib\site-packages\requests\packages\urllib3\connectionpool.py", line 423, in url
open
    conn = self._get_conn(timeout=pool_timeout)
  File "C:\Python27\lib\site-packages\requests\packages\urllib3\connectionpool.py", line 224, in _ge
t_conn
    raise ClosedPoolError(self, "Pool is closed.")
ClosedPoolError: HTTPConnectionPool(host='......', port=80): Pool is closed.

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
  File "/home/krat/Projects/Grubhub/source/Pit/pit/web.py", line 52, in request
    response = session.request(method, url, **kw)
  File "/home/krat/.virtualenvs/grubhub/local/lib/python2.7/site-packages/requests/sessions.py", line 357, in request
    resp = self.send(prep, **send_kwargs)
  File "/home/krat/.virtualenvs/grubhub/local/lib/python2.7/site-packages/requests/sessions.py", line 460, in send
    r = adapter.send(request, **kwargs)
  File "/home/krat/.virtualenvs/grubhub/local/lib/python2.7/site-packages/requests/adapters.py", line 367, in send
    r.content
  File "/home/krat/.virtualenvs/grubhub/local/lib/python2.7/site-packages/requests/models.py", line 633, in content
    self._content = bytes().join(self.iter_content(CONTENT_CHUNK_SIZE)) or bytes()
  File "/home/krat/.virtualenvs/grubhub/local/lib/python2.7/site-packages/requests/models.py", line 572, in generate
    decode_content=True):
  File "/home/krat/.virtualenvs/grubhub/local/lib/python2.7/site-packages/requests/packages/urllib3/response.py", line 225, in stream
    data = self.read(amt=amt, decode_content=decode_content)
  File "/home/krat/.virtualenvs/grubhub/local/lib/python2.7/site-packages/requests/packages/urllib3/response.py", line 193, in read
    e)
DecodeError: ('Received response with content-encoding: gzip, but failed to decode it.', error('Error -3 while deco
... (truncated) ...

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
  File "/home/oliver/wc/trunk/mtmCore/python/asagent/samplers/net/web.py", line 255, in process_url
    resp = self.request(self.params.httpverb, url, data=data)
  File "/home/oliver/wc/trunk/mtmCore/python/asagent/samplers/net/web.py", line 320, in request
    verb, url, data=data))
  File "abilisoft/requests/opt/abilisoft.com/thirdparty/requests/lib/python2.7/site-packages/requests/sessions.py", line 286, in prepare_request
  File "abilisoft/requests/opt/abilisoft.com/thirdparty/requests/lib/python2.7/site-packages/requests/models.py", line 286, in prepare
  File "abilisoft/requests/opt/abilisoft.com/thirdparty/requests/lib/python2.7/site-packages/requests/models.py", line 333, in prepare_url
  File "abilisoft/requests/opt/abilisoft.com/thirdparty/requests/lib/python2.7/site-packages/requests/packages/urllib3/util.py", line 397, in parse_url
LocationParseError: Failed to parse: Failed to parse: fe80::5054:ff:fe5a:fc0

Minimal Reproduction

repro.py

......
  File "C:\Python27\lib\site-packages\requests\sessions.py", line 347, in get
    return self.request('GET', url, **kwargs)
  File "C:\Python27\lib\site-packages\requests\sessions.py", line 335, in request
    resp = self.send(prep, **send_kwargs)
  File "C:\Python27\lib\site-packages\requests\sessions.py", line 438, in send
    r = adapter.send(request, **kwargs)
  File "C:\Python27\lib\site-packages\requests\adapters.py", line 292, in send
    timeout=timeout
  File "C:\Python27\lib\site-packages\requests\packages\urllib3\connectionpool.py", line 423, in url
open
    conn = self._get_conn(timeout=pool_timeout)
  File "C:\Python27\lib\site-packages\requests\packages\urllib3\connectionpool.py", line 224, in _ge
t_conn
    raise ClosedPoolError(self, "Pool is closed.")
ClosedPoolError: HTTPConnectionPool(host='......', port=80): Pool is closed.

Environment

Python: 2.7

What Broke

Users experienced unhandled urllib3 exceptions causing application crashes.

Why It Broke

ClosedPoolError from urllib3 was not being caught and wrapped in requests

Fix Options (Details)

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

pip install requests==2.27.0

When NOT to use: This fix should not be applied if the application relies on raw urllib3 exceptions.

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

Fix reference: https://github.com/psf/requests/pull/2674

First fixed release: 2.27.0

Last verified: 2026-02-07. Validate in your environment.

When NOT to Use This Fix

This fix should not be applied if the application relies on raw urllib3 exceptions.

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

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.
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.

Version Compatibility Table

Version	Status
2.27.0	Fixed

Related Issues

No related fixes found.

Cluster: requests:data-consistency Requests hub Requests best practices All hubs All clusters

Related clusters: Configuration error SSL handshake Other

Sources

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

Requests urllib3 exceptions passing through requests API (Fix)

The Fix

Why This Fix Works in Production

Why This Breaks in Prod

Proof / Evidence

Discussion

Error Message

Minimal Reproduction

Environment

What Broke

Why It Broke

Fix Options (Details)

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

Get updates

When NOT to Use This Fix

Verify Fix

Did This Fix Work in Your Case?

Prevention

Version Compatibility Table

Related Issues

Sources