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[3.13] gh-112346: Always set OS byte to 255, simpler gzip.compress function. (GH-120486) (#120563)

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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.
(cherry picked from commit 08d09cf5ba)

Co-authored-by: Ruben Vorderman <r.h.p.vorderman@lumc.nl>
This commit is contained in:
Miss Islington (bot) 2024-06-15 21:10:50 +02:00 • committed by GitHub
parent 3a9f438c92
commit a19bb261a3
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4 changed files with 26 additions and 34 deletions
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38
Lib/gzip.py
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@ -580,27 +580,6 @@ class _GzipReader(_compression.DecompressReader):
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):