timeout option of socket.create_connection is not respected

[devl00p]

BPO	46625
Nosy	@devl00p

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2022-02-03.14:18:19.228>
labels = ['type-bug', '3.9', 'expert-IO']
title = 'timeout option of socket.create_connection is not respected'
updated_at = <Date 2022-02-03.14:18:19.228>
user = 'https://github.com/devl00p'

bugs.python.org fields:

activity = <Date 2022-02-03.14:18:19.228>
actor = 'Nicolas SURRIBAS'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['IO']
creation = <Date 2022-02-03.14:18:19.228>
creator = 'Nicolas SURRIBAS'
dependencies = []
files = []
hgrepos = []
issue_num = 46625
keywords = []
message_count = 1.0
messages = ['412443']
nosy_count = 1.0
nosy_names = ['Nicolas SURRIBAS']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue46625'
versions = ['Python 3.9']

[devl00p]

When passing to socket.create_connection a timeout option above (approximately) 127 seconds, the timeout is not respected.

Code to reproduce the issue :

import socket
from time import monotonic

print(socket.getdefaulttimeout())
start = monotonic()
try:
    socket.create_connection(("1.1.1.1", 21), 300)
except Exception as exception:
    print(exception)

print(monotonic() - start)

Output at execution:

None
[Errno 110] Connection timed out
129.3075186319984

Expected behavior would be that the "Connection timed out" exception is raised after 300 seconds, as given in argument, not 129.

Observed with Python 3.9.1

[mmmarcos]

This is most likely related to the OS timeout.

See socket - Timeouts and the connect method:

However, the system network stack may also return a connection timeout error
of its own regardless of any Python socket timeout setting.

On Linux the default timeout usually correspond to retrying for ~127s. Look for tcp_syn_retries on tcp(7) man page.

[morrissimo]

Seeing similar behavior: if I set a much lower timeout, socket.create_connection is still ignoring it. Doesn't matter if the lower timeout is provided via socket.setdefaulttimeout or as the timeout= kwarg in the call to create_connection().

I'm assuming this is a "me" problem in that I'm not fully understanding the nuance of the socket lib, the low-level networking OS behavior, or both - but as I also am unsure how to deal with this behavior, figured I'd drop a note here just in case 🤷

Observed in python 3.8.17 on python docker 3.8-buster (amd64)