ValueError is now raised if mtime is a naive datetime object

Author: gchqdev227

Doc/library/gzip.rst

@@ -107,7 +107,8 @@ The module defines the following items:
 
    .. versionchanged:: next
       The *mtime* parameter can now be a :class:`~datetime.datetime` object as well
-      as a :class:`float`.
+      as a :class:`float`. If not :ref:`timezone aware <datetime-naive-aware>` then a
+      :class:`ValueError` will be raised.
 
    See below for the :attr:`mtime` attribute that is set when decompressing.
 
@@ -215,7 +216,8 @@ The module defines the following items:
 
    .. versionchanged:: next
       The *mtime* parameter can now be a :class:`~datetime.datetime` object as well
-      as a :class:`float`.
+      as a :class:`float`. If not :ref:`timezone aware <datetime-naive-aware>` then a
+      :class:`ValueError` will be raised.
 
 .. function:: decompress(data)
 

Lib/gzip.py

@@ -281,6 +281,8 @@ def _write_gzip_header(self, compresslevel):
         if mtime is None:
             mtime = time.time()
         elif isinstance(mtime, datetime):
+            if mtime.tzinfo is None:
+                raise ValueError("Refusing to write naive datetime to Gzip header")
             mtime = mtime.timestamp()
         write32u(self.fileobj, int(mtime))
         if compresslevel == _COMPRESS_LEVEL_BEST:
@@ -596,6 +598,8 @@ def compress(data, compresslevel=_COMPRESS_LEVEL_BEST, *, mtime=0):
     if mtime is None:
         mtime = time.time()
     elif isinstance(mtime, datetime):
+        if mtime.tzinfo is None:
+            raise ValueError("Refusing to write naive datetime to Gzip header")
         mtime = mtime.timestamp()
     # Reuse gzip header created by zlib, replace mtime and OS byte for
     # consistency.

Lib/test/test_gzip.py

@@ -328,6 +328,13 @@ def test_mtime_as_datetime(self):
             self.assertEqual(dataRead, data1)
             self.assertEqual(fRead.mtime, int(mtime.timestamp()))
 
+    def test_mtime_as_datetime_no_timezone(self):
+        mtime = datetime(1973, 11, 29, 21, 33, 9)
+        self.assertIsNone(mtime.tzinfo)
+        with self.assertRaises(ValueError):
+            with gzip.GzipFile(self.filename, 'w', mtime = mtime) as fWrite:
+                fWrite.write(data1)
+
     def test_metadata(self):
         mtime = 123456789
 
@@ -736,6 +743,15 @@ def test_compress_mtime_as_datetime(self):
                         f.read(1) # to set mtime attribute
                         self.assertEqual(f.mtime, int(mtime.timestamp()))
 
+    def test_compress_mtime_as_datetime_no_timezone(self):
+        mtime = datetime(1973, 11, 29, 21, 33, 9)
+        self.assertIsNone(mtime.tzinfo)
+        for data in [data1, data2]:
+            for args in [(), (1,), (6,), (9,)]:
+                with self.subTest(data=data, args=args):
+                    with self.assertRaises(ValueError):
+                        gzip.compress(data, *args, mtime=mtime)
+
     def test_compress_mtime_default(self):
         # test for gh-125260
         datac = gzip.compress(data1, mtime=0)