zipfile library will raise uncaught oserror when reading length incorrect zip file

BPO	46931
Files	damaged.zip: use notepad to open and deleted some contents of the zip file

^{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 2022-03-05.17:37:33.918>
labels = ['type-bug', 'library', '3.10']
title = 'zipfile library will raise uncaught oserror when reading length incorrect zip file'
updated_at = <Date 2022-03-05.17:37:33.918>
user = 'https://bugs.python.org/ultimalium'

bugs.python.org fields:

activity = <Date 2022-03-05.17:37:33.918>
actor = 'ultimalium'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2022-03-05.17:37:33.918>
creator = 'ultimalium'
dependencies = []
files = ['50658']
hgrepos = []
issue_num = 46931
keywords = []
message_count = 1.0
messages = ['414590']
nosy_count = 1.0
nosy_names = ['ultimalium']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue46931'
versions = ['Python 3.10']

Linked PRs

gh-91087: Reject negative local file header offsets in zipfile #158913

I intentionally made some corrupted zip archive files for testing.
If some contents were removed from the archive instead of changing the bits. when trying to read such files, the zipfile will raise an uncaught OSError, instead of a badzipfile error as expected.

os is windows 10 x64 not sure if this also happens on the UNIX system or it's intended to be happen.

code:

import zipfile
with zipfile.ZipFile(r'damaged.zip') as dmg:
    dmg.testzip()

result:
OSError
[Errno 22] Invalid argument
File "test.py", line 20, in <module>
file = dmg.testzip()

has this been fixed in newer versions of python? I'm getting the same error while trying to unpack a .bz2 archive on python 3.8.5, while python 3.11's zipfile returns BadZipFile exception, as expected.

Well, testzip() only catches BadZipFile. It does not catch the compression errors and OSError. This is not clearly documented, and would perhaps be worth to catch the compression errors. This OSError was caused by seek() with negative argument, which is a zipfile integrity error. Should it catch all OSErrors or only handle this particular case (offset can be checked before calling seek())?

You can easy reimplement this method in your code with larger flexibility. But it seems that some people found it useful.

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zipfile library will raise uncaught oserror when reading length incorrect zip file #91087

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zipfile library will raise uncaught oserror when reading length incorrect zip file #91087

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ultimalium commented on Mar 5, 2022

MrSeemsGood commented on Oct 25, 2023

serhiy-storchaka commented on May 18, 2026

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