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# $Id: gzip.py 23 2006-11-08 15:45:33Z dugsong $
"""GNU zip."""
import struct, zlib
import dpkt
# RFC 1952
GZIP_MAGIC = '\x1f\x8b'
# Compression methods
GZIP_MSTORED = 0
GZIP_MCOMPRESS = 1
GZIP_MPACKED = 2
GZIP_MLZHED = 3
GZIP_MDEFLATE = 8
# Flags
GZIP_FTEXT = 0x01
GZIP_FHCRC = 0x02
GZIP_FEXTRA = 0x04
GZIP_FNAME = 0x08
GZIP_FCOMMENT = 0x10
GZIP_FENCRYPT = 0x20
GZIP_FRESERVED = 0xC0
# OS
GZIP_OS_MSDOS = 0
GZIP_OS_AMIGA = 1
GZIP_OS_VMS = 2
GZIP_OS_UNIX = 3
GZIP_OS_VMCMS = 4
GZIP_OS_ATARI = 5
GZIP_OS_OS2 = 6
GZIP_OS_MACOS = 7
GZIP_OS_ZSYSTEM = 8
GZIP_OS_CPM = 9
GZIP_OS_TOPS20 = 10
GZIP_OS_WIN32 = 11
GZIP_OS_QDOS = 12
GZIP_OS_RISCOS = 13
GZIP_OS_UNKNOWN = 255
GZIP_FENCRYPT_LEN = 12
class GzipExtra(dpkt.Packet):
__hdr__ = (
('id', '2s', ''),
('len', 'H', 0)
)
class Gzip(dpkt.Packet):
__hdr__ = (
('magic', '2s', GZIP_MAGIC),
('method', 'B', GZIP_MDEFLATE),
('flags', 'B', 0),
('mtime', 'I', 0),
('xflags', 'B', 0),
('os', 'B', GZIP_OS_UNIX),
('extra', '0s', ''), # XXX - GZIP_FEXTRA
('filename', '0s', ''), # XXX - GZIP_FNAME
('comment', '0s', '') # XXX - GZIP_FCOMMENT
)
def unpack(self, buf):
super(Gzip, self).unpack(buf)
if self.flags & GZIP_FEXTRA:
n = struct.unpack(self.data[:2], '>H')[0]
self.extra = GzipExtra(self.data[2:2+n])
self.data = self.data[2+n:]
if self.flags & GZIP_FNAME:
n = self.data.find('\x00')
self.filename = self.data[:n]
self.data = self.data[n + 1:]
if self.flags & GZIP_FCOMMENT:
n = self.data.find('\x00')
self.comment = self.data[:n]
self.data = self.data[n + 1:]
if self.flags & GZIP_FENCRYPT:
self.data = self.data[GZIP_FENCRYPT_LEN:] # XXX - skip
if self.flags & GZIP_FHCRC:
self.data = self.data[2:] # XXX - skip
def pack_hdr(self):
l = []
if self.extra:
self.flags |= GZIP_FEXTRA
s = str(self.extra)
l.append(struct.pack('>H', len(s)))
l.append(s)
if self.filename:
self.flags |= GZIP_FNAME
l.append(self.filename)
l.append('\x00')
if self.comment:
self.flags |= GZIP_FCOMMENT
l.append(self.comment)
l.append('\x00')
l.insert(0, super(Gzip, self).pack_hdr())
return ''.join(l)
def compress(self):
"""Compress self.data."""
c = zlib.compressobj(9, zlib.DEFLATED, -zlib.MAX_WBITS,
zlib.DEF_MEM_LEVEL, 0)
self.data = c.compress(self.data)
def decompress(self):
"""Return decompressed payload."""
d = zlib.decompressobj(-zlib.MAX_WBITS)
return d.decompress(self.data)
if __name__ == '__main__':
import sys
gz = Gzip(open(sys.argv[1]).read())
print `gz`, `gz.decompress()`
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