Re: zlib and zip files
- From: Jan Prochazka <jena.forum@xxxxxxxxxx>
- Date: Fri, 14 Apr 2006 17:14:55 +0200
Michael Ekstrand napsal(a):
Jan Prochazka wrote:Yes, zipfile can read zip format, but i need to read nad write big files to zip archive, and zipfile.ZipFile object can only write or read strings stored in memory. (i need the ZipFile.read() method to return file-like object, not string). also any variant of write method don't accpet file-like object
Hi,
I need to decompress zip archive. I wrote a parser of zip file, i obtain
the compressed data, but when i call zlib.decompress(data) on them,
it throws this error:
decbuf = decompressor.decompress(compressed_data)
error: Error -3 while decompressing: unknown compression method
I try to compress by zlib the same data which are in that file, the
result was 6 bytes bigger, '\x78\xda' on begin and '\xc9\x1f\x87\x0b' on end
when i tried to put this extending data to zlib decompressor, it
decompress some files of zip archive, but it fails, when i try to
decompress 100MB file from archive
could you help, please?
The zlib module is for reading and writing the gzip compression format, used by the gzip program; it is not the same as a zip archive a la PKZip. The zipfile module will let you read and write zip archives.
- Michael
The gzip compressor and decompressor can work on the fly , but the format that it produces is a bit other than the format of compressed data zipfile (but it differs only in 6 bytes described, so i think, it shoud by possible to create and parse zipfile only using zlib module).
Here is my module for parsing zip files:
import struct, zlib
class ZipHeaderEntry:
name = ''
offset = 0
uncomlen = 0
comlen = 0
class ZipStream:
entries = []
fd = None # file like object
def __init__(self, fd):
self.fd = fd
self.entries = []
class ZipWriteStream(ZipStream):
pass
class ZipReadStream(ZipStream):
cbytesleft = 0
ubytesleft = 0
dec = None # decompress object
decbuf = None
writed_footer = False
def __init__(self, fd):
ZipStream.__init__(self, fd)
self.read_directory()
def open_entry(self, entry):
self.fd.seek(entry.offset) self.dec = zlib.decompressobj()
self.ubytesleft = entry.uncomlen
self.cbytesleft = entry.comlen
print 'ubytes=', self.ubytesleft, 'cbytes=', self.cbytesleft
self.read_header()
self.dec.decompress('\x78\xda', 0) # patch bytes on the begin of compressed buffer
self.decbuf = ''
self.writed_footer = False
def decompress_next(self):
assert len(self.decbuf) == 0
rbytes = 0x1000
if rbytes > self.cbytesleft: rbytes = self.cbytesleft
udata = self.fd.read(rbytes)
self.cbytesleft -= rbytes
self.decbuf = self.dec.decompress(udata)
if self.cbytesleft == 0 and not self.writed_footer:
self.decbuf += self.dec.decompress('\xc9\x1f\x87\x0b') # patch bytes on the end of compressed buffer
self.writed_footer = True
def read(self, bytes = None):
if bytes is None: bytes = self.ubytesleft
if bytes > self.ubytesleft: bytes = self.ubytesleft
res = ''
while bytes > 0:
s = self.decbuf[:bytes]
self.decbuf = self.decbuf[bytes:]
self.ubytesleft -= len(s)
res += s
bytes -= len(s)
if bytes > 0:
self.decompress_next()
return res
def open_file(self, filename):
for entry in self.entries:
if entry.name.upper() == filename.upper():
return self.open_entry(entry)
raise Exception('File not found in archive: %s' % filename)
def read_header(self):
hdr = self.fd.read(0x1E)
hdrvalues = struct.unpack('=ccccHHHHHLLLHH', hdr)
sigp, sigk, sig3, sig4, ver, flag, method, tm, dt, crc, uncsize, comsize, fnlen, extlen = hdrvalues
assert sigp == 'P' and sigk == 'K' and sig3 == '\x03' and sig4 == '\x04'
name = self.fd.read(fnlen)
extra = self.fd.read(extlen)
print name
def read_directory(self):
self.fd.seek(0, 2)
size = self.fd.tell()
dpos = 0x1000
if dpos > size: dpos = size
self.fd.seek(-dpos, 1)
enddata = self.fd.read()
index = enddata.find('PK\x05\x06')
assert index >= 0
enddata = enddata[index: index + 0x16]
sig, ndisk, ndiskc, entriesdisk, entries, dirsize, dirofs, comlen = struct.unpack('=LHHHHLLH', enddata)
self.fd.seek(dirofs)
for i in xrange(entries):
cdirdata = self.fd.read(0x2E)
hdrvalues = struct.unpack('=LBBBBHHHHLLLHHHHHLL', cdirdata)
(sig, vermade, hosts, verex, osver, flag, method, dt, tm, crc,
csize, uncsize, fnlen, extlen, comlen, disknum, fileattr, extattr, fileofs) = hdrvalues
name = self.fd.read(fnlen)
extra = self.fd.read(extlen)
comment = self.fd.read(comlen)
entry = ZipHeaderEntry()
entry.name = name
entry.offset = fileofs
entry.uncomlen = uncsize
entry.comlen = csize
self.entries.append(entry)
.
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