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bpo-39121: write gzip header OS information #17682

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bpo-39121: write gzip header OS information #17682

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16 changes: 15 additions & 1 deletion Lib/gzip.py
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,15 @@

READ, WRITE = 1, 2

# OS field values as specified in RFC 1952
_OS_CODES = {
'unix': b'\x03',
'ntfs': b'\x0b',
'unknown': b'\xff'
}
_OS_UNIX = ('linux', 'freebsd', 'netbsd', 'openbsd', 'darwin', 'sunos', 'aix')
_OS_NTFS = ('win32')

_COMPRESS_LEVEL_FAST = 1
_COMPRESS_LEVEL_TRADEOFF = 6
_COMPRESS_LEVEL_BEST = 9
Expand Down Expand Up @@ -264,7 +273,12 @@ def _write_gzip_header(self, compresslevel):
else:
xfl = b'\000'
self.fileobj.write(xfl)
self.fileobj.write(b'\377')
if sys.platform.startswith(_OS_UNIX):
self.fileobj.write(_OS_CODES['unix'])
elif sys.platform.startswith(_OS_NTFS):
self.fileobj.write(_OS_CODES['ntfs'])
else:
self.fileobj.write(_OS_CODES['unknown'])
if fname:
self.fileobj.write(fname + b'\000')

Expand Down
9 changes: 7 additions & 2 deletions Lib/test/test_gzip.py
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Expand Up @@ -315,7 +315,12 @@ def test_mtime(self):

def test_metadata(self):
mtime = 123456789

if sys.platform.startswith(gzip._OS_UNIX):
os_code = gzip._OS_CODES['unix']
elif sys.platform.startswith(gzip._OS_NTFS):
os_code = gzip._OS_CODES['ntfs']
else:
os_code = gzip._OS_CODES['unknown']
with gzip.GzipFile(self.filename, 'w', mtime = mtime) as fWrite:
fWrite.write(data1)

Expand All @@ -338,7 +343,7 @@ def test_metadata(self):
self.assertEqual(xflByte, b'\x02') # maximum compression

osByte = fRead.read(1)
self.assertEqual(osByte, b'\xff') # OS "unknown" (OS-independent)
self.assertEqual(osByte, os_code) # gzip OS code

# Since the FNAME flag is set, the zero-terminated filename follows.
# RFC 1952 specifies that this is the name of the input file, if any.
Expand Down
1 change: 1 addition & 0 deletions Misc/ACKS
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Expand Up @@ -1072,6 +1072,7 @@ Grzegorz Makarewicz
David Malcolm
Greg Malcolm
William Mallard
Robert Mandic
Ken Manheimer
Vladimir Marangozov
Colin Marc
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2019-12-23-03-21-38.bpo-39121.HgPaAz.rst
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@@ -0,0 +1,2 @@
Writing gzip files sets 10th byte of the gzip header (the OS information)
based on :attr:`sys.platform` Patch by Robert Mandic.