https://github.com/python/cpython/commit/08d09cf5ba041c9c5c3860200b56bab66fd44a23
commit: 08d09cf5ba041c9c5c3860200b56bab66fd44a23
branch: main
author: Ruben Vorderman <[email protected]>
committer: gpshead <[email protected]>
date: 2024-06-15T18:46:39Z
summary:
gh-112346: Always set OS byte to 255, simpler gzip.compress function.
(GH-120486)
This matches the output behavior in 3.10 and earlier; the optimization in 3.11
allowed the zlib library's "os" value to be filled in instead in the
circumstance when mtime was 0. this keeps things consistent.
files:
A Misc/NEWS.d/next/Library/2024-06-12-10-00-31.gh-issue-90425.5CfkKG.rst
M Doc/library/gzip.rst
M Lib/gzip.py
M Lib/test/test_gzip.py
diff --git a/Doc/library/gzip.rst b/Doc/library/gzip.rst
index 965da5981f6dbc..152cba4f653cb4 100644
--- a/Doc/library/gzip.rst
+++ b/Doc/library/gzip.rst
@@ -188,9 +188,7 @@ 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.
.. versionadded:: 3.2
.. versionchanged:: 3.8
@@ -200,6 +198,10 @@ The module defines the following items:
streamed fashion. Calls with *mtime* set to ``0`` are delegated to
:func:`zlib.compress` for better speed.
+ .. versionchanged:: 3.13
+ The gzip header OS byte is guaranteed to be set to 255 when this function
+ is used as was the case in 3.10 and earlier.
+
.. function:: decompress(data)
Decompress the *data*, returning a :class:`bytes` object containing the
diff --git a/Lib/gzip.py b/Lib/gzip.py
index 0d19c84c59cfa7..ba753ce3050dd8 100644
--- a/Lib/gzip.py
+++ b/Lib/gzip.py
@@ -580,27 +580,6 @@ def _rewind(self):
self._new_member = True
-def _create_simple_gzip_header(compresslevel: int,
- mtime = None) -> bytes:
- """
- Write a simple gzip header with no extra fields.
- :param compresslevel: Compresslevel used to determine the xfl bytes.
- :param mtime: The mtime (must support conversion to a 32-bit integer).
- :return: A bytes object representing the gzip header.
- """
- if mtime is None:
- mtime = time.time()
- if compresslevel == _COMPRESS_LEVEL_BEST:
- xfl = 2
- elif compresslevel == _COMPRESS_LEVEL_FAST:
- xfl = 4
- else:
- xfl = 0
- # Pack ID1 and ID2 magic bytes, method (8=deflate), header flags (no extra
- # fields added to header), mtime, xfl and os (255 for unknown OS).
- return struct.pack("<BBBBLBB", 0x1f, 0x8b, 8, 0, int(mtime), xfl, 255)
-
-
def compress(data, compresslevel=_COMPRESS_LEVEL_BEST, *, mtime=None):
"""Compress data in one shot and return the compressed string.
@@ -608,15 +587,14 @@ 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.
- return (header + zlib.compress(data, level=compresslevel, wbits=-15) +
- trailer)
+ # Wbits=31 automatically includes a gzip header and trailer.
+ gzip_data = zlib.compress(data, level=compresslevel, wbits=31)
+ if mtime is None:
+ mtime = time.time()
+ # Reuse gzip header created by zlib, replace mtime and OS byte for
+ # consistency.
+ header = struct.pack("<4sLBB", gzip_data, int(mtime), gzip_data[8], 255)
+ return header + gzip_data[10:]
def decompress(data):
diff --git a/Lib/test/test_gzip.py b/Lib/test/test_gzip.py
index cf801278da9e9b..ae384c3849d49e 100644
--- a/Lib/test/test_gzip.py
+++ b/Lib/test/test_gzip.py
@@ -714,7 +714,6 @@ 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)
@@ -722,6 +721,17 @@ def test_compress_correct_level(self):
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
new file mode 100644
index 00000000000000..d152af49287a0b
--- /dev/null
+++ 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
+:func:`gzip.compress`.
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