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

serhiy-storchaka · May 22, 2026 · May 19, 2025 · May 19, 2025 · May 19, 2025 · May 21, 2025
commit 64681af6c69ec52a76ef64877ae56851ccab5f8e
diff --git a/Doc/library/gzip.rst b/Doc/library/gzip.rst
@@ -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*.
+   Use *mtime* = ``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.
 
    See below for the :attr:`mtime` attribute that is set when decompressing.
 

diff --git a/Lib/gzip.py b/Lib/gzip.py
@@ -297,6 +297,8 @@ 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'

diff --git a/Lib/test/test_gzip.py b/Lib/test/test_gzip.py
@@ -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
@@ -351,6 +352,27 @@ def test_mtime(self):
             self.assertEqual(dataRead, data1)
             self.assertEqual(fRead.mtime, mtime)
 
+    def test_mtime_out_of_range(self):
+        # exception should be raised when mtime<0 or mtime>=2**32 and is
+        # explicitly specified
+        with self.assertRaises(Exception):
+            with gzip.GzipFile(self.filename, 'w', mtime=-1) as fWrite:
+                pass
+        with self.assertRaises(Exception):
+            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