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gh-133998: Fix gzip file creation when time is out of range #134278

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gh-133998: Fix gzip file creation when time is out of range #134278

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gh-133998: Fix gzip file creation when time is out of range
adang1345 May 19, 2025
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📜🤖 Added by blurb_it.
blurb-it[bot] May 19, 2025
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Remove extra newline
adang1345 May 19, 2025
e701310
Address review comments regarding documentation
adang1345 May 21, 2025
90a881b
Keep docstring in line with documentation
adang1345 May 21, 2025
9638ca0
Improve error message when mtime is out of range
adang1345 May 21, 2025
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Re-format changelog message
adang1345 May 21, 2025
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9 changes: 6 additions & 3 deletions Doc/library/gzip.rst
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Expand Up @@ -101,9 +101,12 @@ The module defines the following items:
is no compression. The default is ``9``.

The optional *mtime* argument is the timestamp requested by gzip. The time
is in Unix format, i.e., seconds since 00:00:00 UTC, January 1, 1970.
If *mtime* is omitted or ``None``, the current time is used. Use *mtime* = 0
to generate a compressed stream that does not depend on creation time.
is in Unix format, i.e., seconds since 00:00:00 UTC, January 1, 1970. Set
*mtime* to ``0`` to generate a compressed stream that does not depend on
creation time. If *mtime* is omitted or ``None``, the current time is used;
however, if the current time is outside the range 00:00:00 UTC, January 1,
1970 through 06:28:15 UTC, February 7, 2106, then the value ``0`` is used
instead.

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The docs are slightly wrong now that GzipFile.__init__ will raise a ValueError if the specified value is out of range.
I know you've documented it in the docstring for __init__, but I think it's worth clarifying here since we're already in the area.

See below for the :attr:`mtime` attribute that is set when decompressing.

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12 changes: 10 additions & 2 deletions Lib/gzip.py
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Expand Up @@ -188,8 +188,11 @@ def __init__(self, filename=None, mode=None,

The optional mtime argument is the timestamp requested by gzip. The time
is in Unix format, i.e., seconds since 00:00:00 UTC, January 1, 1970.
If mtime is omitted or None, the current time is used. Use mtime = 0
to generate a compressed stream that does not depend on creation time.
Set mtime to 0 to generate a compressed stream that does not depend on
creation time. If mtime is omitted or None, the current time is used;
however, if the current time is outside the range 00:00:00 UTC, January
1, 1970 through 06:28:15 UTC, February 7, 2106, then the value 0 is used
instead.
Comment on lines +191 to +195
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Ditto, see previous comment


"""

Expand All @@ -203,6 +206,9 @@ def __init__(self, filename=None, mode=None,
if mode and 'b' not in mode:
mode += 'b'

if mtime is not None and (mtime < 0 or mtime >= 2**32):
raise ValueError(f'mtime must be in the range 0 through {2**32-1}')

try:
if fileobj is None:
fileobj = self.myfileobj = builtins.open(filename, mode or 'rb')
Expand Down Expand Up @@ -297,6 +303,8 @@ def _write_gzip_header(self, compresslevel):
mtime = self._write_mtime
if mtime is None:
mtime = time.time()
if mtime < 0 or mtime >= 2**32:
mtime = 0
write32u(self.fileobj, int(mtime))
if compresslevel == _COMPRESS_LEVEL_BEST:
xfl = b'\002'
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21 changes: 21 additions & 0 deletions Lib/test/test_gzip.py
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@
import unittest
import warnings
from subprocess import PIPE, Popen
from unittest import mock
from test.support import catch_unraisable_exception
from test.support import import_helper
from test.support import os_helper
Expand Down Expand Up @@ -351,6 +352,26 @@ def test_mtime(self):
self.assertEqual(dataRead, data1)
self.assertEqual(fRead.mtime, mtime)

def test_mtime_out_of_range(self):
# ValueError should be raised when mtime<0 or mtime>=2**32 and is
# explicitly specified
with self.assertRaises(ValueError):
with gzip.GzipFile(self.filename, 'w', mtime=-1) as fWrite:
pass
with self.assertRaises(ValueError):
with gzip.GzipFile(self.filename, 'w', mtime=2**32) as fWrite:
pass

# mtime should be set to 0 when time.time() is out of range and mtime is
# not explicitly given
for mtime in (-1, 2**32):
with mock.patch('time.time', return_value=float(mtime)):
with gzip.GzipFile(self.filename, 'w') as fWrite:
fWrite.write(data1)
with gzip.GzipFile(self.filename) as fRead:
fRead.read()
self.assertEqual(fRead.mtime, 0)

def test_metadata(self):
mtime = 123456789

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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2025-05-19-20-29-35.gh-issue-133998.KmElUw.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix ``struct.error`` exception when creating a file with ``gzip.GzipFile()`` if the system time is outside the range 00:00:00 UTC, January 1, 1970 through 06:28:15 UTC, February 7, 2106.
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I think this should also be tweaked since the behaviour of providing an out-of-range mtime has changed

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