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Python 3.14.0a2 should have raised exception when a socket is already in used, shouldn't it? #127319

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rayluo opened this issue Nov 27, 2024 · 4 comments
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Python 3.14.0a2 should have raised exception when a socket is already in used, shouldn't it? #127319

rayluo opened this issue Nov 27, 2024 · 4 comments
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3.14 bugs and security fixes stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error

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@rayluo
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rayluo commented Nov 27, 2024 •
edited by bedevere-app bot
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Bug report

Bug description:

In earlier versions of Python all the way to 3.13, it would not allow a server to listen on a port that has already been used, and rightfully so.

$ python -m http.server 8000
Serving HTTP on 0.0.0.0 port 8000 (http://0.0.0.0:8000/) ...

# Trying to start the second server on the same port
$ python -m http.server 8000
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/usr/lib/python3.11/http/server.py", line 1309, in <module>
    test(
  File "/usr/lib/python3.11/http/server.py", line 1256, in test
    with ServerClass(addr, HandlerClass) as httpd:
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/socketserver.py", line 456, in __init__
    self.server_bind()
  File "/usr/lib/python3.11/http/server.py", line 1303, in server_bind
    return super().server_bind()
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/http/server.py", line 136, in server_bind
    socketserver.TCPServer.server_bind(self)
  File "/usr/lib/python3.11/socketserver.py", line 472, in server_bind
    self.socket.bind(self.server_address)
OSError: [Errno 98] Address already in use

But in Python 3.14.0a2, the second command would also start a server without exception. Is that expected?

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs
@rayluo rayluo added the type-bug An unexpected behavior, bug, or error label Nov 27, 2024
@skirpichev skirpichev added the stdlib Python modules in the Lib dir label Nov 27, 2024
@skirpichev
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I confirm this in the main. It seems, for two processes, the last started process - serves requests. If it's terminated - works the first.

At least, seems as a documentation issue for me (nothing in news).

@oskar-skog
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I believe it's caused by this commit:
192d17c

See also comment: #120485 (comment)
Maybe allow_reuse_port should default to False?

@AlexWaygood AlexWaygood added the 3.14 bugs and security fixes label Nov 27, 2024
@rayluo
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rayluo commented Nov 27, 2024

I confirm this in the main. It seems, for two processes, the last started process - serves requests. If it's terminated - works the first.

At least, seems as a documentation issue for me (nothing in news).

Based on #120485 (comment) (thanks for the finding, @oskar-skog ), "the kernel may dispatch the request to different server process randomly", which is concerning.

Maybe allow_reuse_port should default to False?

+1

@rayluo rayluo mentioned this issue Nov 27, 2024
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@github-actions github-actions bot mentioned this issue Dec 1, 2024
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@musicinmybrain
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I can still reproduce this (and AzureAD/microsoft-authentication-library-for-python#768) on Python 3.14.0b2. Is there any plan to change this behavior before the 3.14.0 final release?

jeremycline added a commit to jeremycline/cpython that referenced this issue Jun 11, 2025
@jeremycline
pythongh-127319: Disable port reuse on HTTP, XMLRPC, and logging TCP …
7397ff3 
…servers

Prior to issue python#120485 these servers did not allow port reuse, which
makes sense as the behavior of port reuse is surprising if you're not
expecting it. It's unclear to me why these services were switched to
allow port reuse, but I believe the desired behavior (unless subclasses
opt in) is to not allow port reuse.

See also: https://bugzilla.redhat.com/show_bug.cgi?id=2323170
@bedevere-app bedevere-app bot mentioned this issue Jun 11, 2025
Merged
vsajip pushed a commit that referenced this issue Jun 15, 2025
@jeremycline
gh-127319: Disable port reuse on HTTP, XMLRPC, and logging TCP servers (
2bd3895 
GH-135405)

Prior to issue #120485 these servers did not allow port reuse, which
makes sense as the behavior of port reuse is surprising if you're not
expecting it. It's unclear to me why these services were switched to
allow port reuse, but I believe the desired behavior (unless subclasses
opt in) is to not allow port reuse.

See also: https://bugzilla.redhat.com/show_bug.cgi?id=2323170
@sourcery-ai sourcery-ai bot mentioned this issue Jun 15, 2025
Merged
miss-islington pushed a commit to miss-islington/cpython that referenced this issue Jun 15, 2025
@jeremycline @miss-islington
pythongh-127319: Disable port reuse on HTTP, XMLRPC, and logging TCP …
cac8fbd 
…servers (pythonGH-135405)

Prior to issue pythonGH-120485 these servers did not allow port reuse, which
makes sense as the behavior of port reuse is surprising if you're not
expecting it. It's unclear to me why these services were switched to
allow port reuse, but I believe the desired behavior (unless subclasses
opt in) is to not allow port reuse.

See also: https://bugzilla.redhat.com/show_bug.cgi?id=2323170
(cherry picked from commit 2bd3895)

Co-authored-by: Jeremy Cline <jeremycline@linux.microsoft.com>
@bedevere-app bedevere-app bot mentioned this issue Jun 15, 2025
Merged
shuimu5418 pushed a commit to shuimu5418/cpython001 that referenced this issue Jun 16, 2025
@jeremycline @shuimu5418
pythongh-127319: Disable port reuse on HTTP, XMLRPC, and logging TCP …
67c853f 
…servers (pythonGH-135405)

Prior to issue python#120485 these servers did not allow port reuse, which
makes sense as the behavior of port reuse is surprising if you're not
expecting it. It's unclear to me why these services were switched to
allow port reuse, but I believe the desired behavior (unless subclasses
opt in) is to not allow port reuse.

See also: https://bugzilla.redhat.com/show_bug.cgi?id=2323170
vsajip pushed a commit that referenced this issue Jun 16, 2025
@miss-islington
[3.14] gh-127319: Disable port reuse on HTTP, XMLRPC, and logging TCP…
43bf8b3 
… servers (GH-135405) (GH-135538)

(cherry picked from commit 2bd3895)
@vsajip vsajip closed this as completed Jun 16, 2025
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@vsajip @rayluo @skirpichev @musicinmybrain @oskar-skog @AlexWaygood