python · rhpvorderman · Jan 16, 2024 · Jan 16, 2024 · Jan 16, 2024 · Jan 16, 2024
diff --git a/Doc/library/gzip.rst b/Doc/library/gzip.rst
@@ -188,17 +188,15 @@ The module defines the following items:
 
    Compress the *data*, returning a :class:`bytes` object containing
    the compressed data.  *compresslevel* and *mtime* have the same meaning as in
-   the :class:`GzipFile` constructor above. When *mtime* is set to ``0``, this
-   function is equivalent to :func:`zlib.compress` with *wbits* set to ``31``.
-   The zlib function is faster.
+   the :class:`GzipFile` constructor above.
+   :func:`zlib.compress` with *wbits* set to ``31`` is faster.
 
    .. versionadded:: 3.2
    .. versionchanged:: 3.8
       Added the *mtime* parameter for reproducible output.
    .. versionchanged:: 3.11
       Speed is improved by compressing all data at once instead of in a
-      streamed fashion. Calls with *mtime* set to ``0`` are delegated to
-      :func:`zlib.compress` for better speed.
+      streamed fashion.
 
 .. function:: decompress(data)
 

diff --git a/Lib/gzip.py b/Lib/gzip.py
@@ -608,10 +608,6 @@ def compress(data, compresslevel=_COMPRESS_LEVEL_BEST, *, mtime=None):
     mtime can be used to set the modification time. The modification time is
     set to the current time by default.
     """
-    if mtime == 0:
-        # Use zlib as it creates the header with 0 mtime by default.
-        # This is faster and with less overhead.
-        return zlib.compress(data, level=compresslevel, wbits=31)
     header = _create_simple_gzip_header(compresslevel, mtime)
     trailer = struct.pack("<LL", zlib.crc32(data), (len(data) & 0xffffffff))
     # Wbits=-15 creates a raw deflate block.

diff --git a/Lib/test/test_gzip.py b/Lib/test/test_gzip.py
@@ -714,14 +714,25 @@ def test_compress_mtime(self):
                         self.assertEqual(f.mtime, mtime)
 
     def test_compress_correct_level(self):
-        # gzip.compress calls with mtime == 0 take a different code path.
         for mtime in (0, 42):
             with self.subTest(mtime=mtime):
                 nocompress = gzip.compress(data1, compresslevel=0, mtime=mtime)
-                yescompress = gzip.compress(data1, compresslevel=1, mtime=mtime)
+                yescompress = gzip.compress(data1, compresslevel=1,
+                                                 mtime=mtime)
                 self.assertIn(data1, nocompress)
                 self.assertNotIn(data1, yescompress)
 
+    def test_issue112346(self):
+        # The OS byte should be 255, this should not change between Python versions.
+        for mtime in (0, 42):
+            with self.subTest(mtime=mtime):
+                compress = gzip.compress(data1, compresslevel=1, mtime=mtime)
+                self.assertEqual(
+                    struct.unpack("<IxB", compress[4:10]),
+                    (mtime, 255),
+                    "Gzip header does not properly set either mtime or OS byte."
+                )
+
     def test_decompress(self):
         for data in (data1, data2):
             buf = io.BytesIO()

diff --git a/Misc/NEWS.d/next/Library/2024-06-12-10-00-31.gh-issue-90425.5CfkKG.rst b/Misc/NEWS.d/next/Library/2024-06-12-10-00-31.gh-issue-90425.5CfkKG.rst
@@ -0,0 +1,2 @@
+The OS byte in gzip headers is now always set to 255 when using
+gzip.compress.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		The OS byte in gzip headers is now always set to 255 when using
		gzip.compress.