httpx ResourceWarning: unclosed transport

The Fix

Upgrade to version 0.7.2 or later.

Based on closed encode/httpx issue #825 · 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

@@ -1,9 +1,17 @@
 import mimetypes
 import os
+import re
 import typing
 from io import BytesIO

repro.py

$ cat reproducer.py 
import asyncio

import httpx

async def mdk():
    async with httpx.AsyncClient() as client:
        r = await client.get('https://www.example.org/')
    print(r.text)

asyncio.run(mdk())
 
$ python reproducer.py 
TRACE [2020-02-26 09:37:29] httpx._config - load_ssl_context verify=True cert=None trust_env=True http2=False
TRACE [2020-02-26 09:37:29] httpx._config - load_verify_locations cafile=/home/mdk/clones/python/docsbuild-scripts/.venv/lib/python3.8/site-packages/certifi/cacert.pem
TRACE [2020-02-26 09:37:29] httpx._dispatch.connection_pool - acquire_connection origin=Origin(scheme='https' host='www.example.org' port=443)
TRACE [2020-02-26 09:37:29] httpx._dispatch.connection_pool - new_connection connection=HTTPConnection(origin=Origin(scheme='https' host='www.example.org' port=443))
TRACE [2020-02-26 09:37:29] httpx._dispatch.connection - start_connect tcp host='www.example.org' port=443 timeout=Timeout(timeout=5.0)
TRACE [2020-02-26 09:37:29] httpx._dispatch.connection - connected http_version='HTTP/1.1'
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - send_headers method='GET' target='/' headers=Headers({'host': 'www.example.org', 'user-agent': 'python-httpx/0.11.1', 'accept': '*/*', 'accept-encoding': 'gzip, deflate', 'connection': 'keep-alive'})
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - send_data data=Data(<0 bytes>)
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - receive_event event=NEED_DATA
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - receive_event event=Response(status_code=200, headers=[(b'content-encoding', b'gzip'), (b'accept-ranges', b'bytes'), (b'age', b'499617'), (b'cache-control', b'max-age=604800'), (b'content-type', b'text/html; charset=UTF-8'), (b'date', b'Wed, 26 Feb 2020 08:37:29 GMT'), (b'etag', b'"3147526947"'), (b'expires', b'Wed, 04 Mar 2020 08:37:29 GMT'), (b'last-modified', b'Thu, 17 Oct 2019 07:18:26 GMT'), (b'server', b'ECS (bsa/EB17)'), (b'vary', b'Accept-Encoding'), (b'x-cache', b'HIT'), (b'content-length', b'648')], http_version=b'1.1', reason=b'OK')
DEBUG [2020-02-26 09:37:29] httpx._client - HTTP Request: GET https://www.example.org/ "HTTP/1.1 200 OK"
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - receive_event event=Data(<648 bytes>)
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - receive_event event=EndOfMessage(headers=[])
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - response_closed our_state=DONE their_state=DONE
TRACE [2020-02-26 09:37:29] httpx._dispatch.connection_pool - release_connection connection=HTTPConnection(origin=Origin(scheme='https' host='www.example.org' port=443))
TRACE [2020-02-26 09:37:29] httpx._dispatch.connection - close_connection
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - send_event event=ConnectionClosed()
<!doctype html>
[... redacted (useless html) ...]

/home/mdk/.local/lib/python3.8/asyncio/selector_events.py:694: ResourceWarning: unclosed transport <_SelectorSocketTransport fd=6>
  _warn(f"unclosed transport {self!r}", ResourceWarning, source=self)
Object allocated at (most recent call last):
  File "reproducer.py", lineno 10
    asyncio.run(mdk())
  File "/home/mdk/.local/lib/python3.8/asyncio/runners.py", lineno 43
    return loop.run_until_complete(main)
  File "/home/mdk/.local/lib/python3.8/asyncio/base_events.py", lineno 603
    self.run_forever()
  File "/home/mdk/.local/lib/python3.8/asyncio/base_events.py", lineno 570
    self._run_once()
  File "/home/mdk/.local/lib/python3.8/asyncio/base_events.py", lineno 1859
    handle._run()
  File "/home/mdk/.local/lib/python3.8/asyncio/
... (truncated) ...

verify

Re-run: ipython

fix.md

Option A — Upgrade to fixed release\nUpgrade to version 0.7.2 or later.\nWhen NOT to use: Do not use if it changes public behavior or if the failure cannot be reproduced.\n\n

Why This Fix Works in Production

Trigger: $ ipython
Mechanism: Fixed multipart header params encoding, resolving issues with non-ASCII letters in multipart/form-data requests.
Why the fix works: Fixed multipart header params encoding, resolving issues with non-ASCII letters in multipart/form-data requests. (first fixed release: 0.7.2).

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

Shows up under Python 3.8.0 in real deployments (not just unit tests).
Surfaces as: $ ipython

Proof / Evidence

GitHub issue: #825
Fix PR: https://github.com/encode/httpcore/pull/167
First fixed release: 0.7.2
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.26

Discussion

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

Jump to Sources Open on GitHub

“I'm changing the title appropriately, as the "An open stream ..." has been fixed in Python 3.8.1, this discussion is about the ResourceWarning.”

@JulienPalard · 2020-02-26 · confirmation · source

“Raised https://bugs.python.org/issue39758”

@lovelydinosaur · 2020-02-26 · source

“Tried with HTTPX_LOG_LEVE=trace because tracemalloc don't tells me much, and Python 3.8.2:”

@JulienPalard · 2020-02-26 · source

“So this is related to https://github.com/encode/httpx/issues/634, _backends/asyncio.py, SocketStream's close method: Obviously adding a await self.stream_writer.wait_closed() fixes #825 probably while reopening #634 So I'm going to…”

@JulienPalard · 2020-02-26 · source

Failure Signature (Search String)

$ ipython

Error Message

Stack trace

error.txt

Error Message
-------------
$ ipython
Python 3.8.0 (default, Dec 12 2019, 09:56:28) 
Type 'copyright', 'credits' or 'license' for more information
IPython 7.12.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: import httpx                                                                                                                                           

In [2]: async with httpx.AsyncClient() as client: 
   ...:     r = await client.get('https://www.example.org/')                                                                                                   

In [3]: r                                                                                                                                                      
Out[3]: <Response [200 OK]>

In [4]:                                                                                                                                                        
Do you really want to exit ([y]/n)? 
An open stream object is being garbage collected; call "stream.close()" explicitly.
source_traceback: Object created at (most recent call last):
[...]
  File "/home/mdk/.local/lib/python3.8/asyncio/base_events.py", line 595, in run_until_complete
    self.run_forever()
  File "/home/mdk/.local/lib/python3.8/asyncio/base_events.py", line 563, in run_forever
    self._run_once()
  File "/home/mdk/.local/lib/python3.8/asyncio/base_events.py", line 183
... (truncated) ...

Minimal Reproduction

repro.py

$ cat reproducer.py 
import asyncio

import httpx

async def mdk():
    async with httpx.AsyncClient() as client:
        r = await client.get('https://www.example.org/')
    print(r.text)

asyncio.run(mdk())
 
$ python reproducer.py 
TRACE [2020-02-26 09:37:29] httpx._config - load_ssl_context verify=True cert=None trust_env=True http2=False
TRACE [2020-02-26 09:37:29] httpx._config - load_verify_locations cafile=/home/mdk/clones/python/docsbuild-scripts/.venv/lib/python3.8/site-packages/certifi/cacert.pem
TRACE [2020-02-26 09:37:29] httpx._dispatch.connection_pool - acquire_connection origin=Origin(scheme='https' host='www.example.org' port=443)
TRACE [2020-02-26 09:37:29] httpx._dispatch.connection_pool - new_connection connection=HTTPConnection(origin=Origin(scheme='https' host='www.example.org' port=443))
TRACE [2020-02-26 09:37:29] httpx._dispatch.connection - start_connect tcp host='www.example.org' port=443 timeout=Timeout(timeout=5.0)
TRACE [2020-02-26 09:37:29] httpx._dispatch.connection - connected http_version='HTTP/1.1'
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - send_headers method='GET' target='/' headers=Headers({'host': 'www.example.org', 'user-agent': 'python-httpx/0.11.1', 'accept': '*/*', 'accept-encoding': 'gzip, deflate', 'connection': 'keep-alive'})
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - send_data data=Data(<0 bytes>)
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - receive_event event=NEED_DATA
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - receive_event event=Response(status_code=200, headers=[(b'content-encoding', b'gzip'), (b'accept-ranges', b'bytes'), (b'age', b'499617'), (b'cache-control', b'max-age=604800'), (b'content-type', b'text/html; charset=UTF-8'), (b'date', b'Wed, 26 Feb 2020 08:37:29 GMT'), (b'etag', b'"3147526947"'), (b'expires', b'Wed, 04 Mar 2020 08:37:29 GMT'), (b'last-modified', b'Thu, 17 Oct 2019 07:18:26 GMT'), (b'server', b'ECS (bsa/EB17)'), (b'vary', b'Accept-Encoding'), (b'x-cache', b'HIT'), (b'content-length', b'648')], http_version=b'1.1', reason=b'OK')
DEBUG [2020-02-26 09:37:29] httpx._client - HTTP Request: GET https://www.example.org/ "HTTP/1.1 200 OK"
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - receive_event event=Data(<648 bytes>)
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - receive_event event=EndOfMessage(headers=[])
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - response_closed our_state=DONE their_state=DONE
TRACE [2020-02-26 09:37:29] httpx._dispatch.connection_pool - release_connection connection=HTTPConnection(origin=Origin(scheme='https' host='www.example.org' port=443))
TRACE [2020-02-26 09:37:29] httpx._dispatch.connection - close_connection
TRACE [2020-02-26 09:37:29] httpx._dispatch.http11 - send_event event=ConnectionClosed()
<!doctype html>
[... redacted (useless html) ...]

/home/mdk/.local/lib/python3.8/asyncio/selector_events.py:694: ResourceWarning: unclosed transport <_SelectorSocketTransport fd=6>
  _warn(f"unclosed transport {self!r}", ResourceWarning, source=self)
Object allocated at (most recent call last):
  File "reproducer.py", lineno 10
    asyncio.run(mdk())
  File "/home/mdk/.local/lib/python3.8/asyncio/runners.py", lineno 43
    return loop.run_until_complete(main)
  File "/home/mdk/.local/lib/python3.8/asyncio/base_events.py", lineno 603
    self.run_forever()
  File "/home/mdk/.local/lib/python3.8/asyncio/base_events.py", lineno 570
    self._run_once()
  File "/home/mdk/.local/lib/python3.8/asyncio/base_events.py", lineno 1859
    handle._run()
  File "/home/mdk/.local/lib/python3.8/asyncio/
... (truncated) ...

Environment

Python: 3.8.0
httpx: 0.11.1

What Broke

Users experience ResourceWarning due to unclosed transport leading to potential memory leaks.

Fix Options (Details)

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

Upgrade to version 0.7.2 or later.

When NOT to use: Do not use if it changes public behavior or if the failure cannot be reproduced.

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

Fix reference: https://github.com/encode/httpcore/pull/167

First fixed release: 0.7.2

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

When NOT to Use This Fix

Do not use if it changes public behavior or if the failure cannot be reproduced.

Verify Fix

verify

Re-run: ipython

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.
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
0.7.2	Fixed

Related Issues

No related fixes found.

Cluster: httpx:configuration-error All hubs All clusters

Related clusters: Data consistency Other Timeout

Sources

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

httpx ResourceWarning: unclosed transport <_SelectorSocketTransport fd=6> (asyncio only) (Fix)