/Demo/zlib/minigzip.py
http://unladen-swallow.googlecode.com/ · Python · 133 lines · 102 code · 17 blank · 14 comment · 22 complexity · 4fd9d813d490c0e9e8b3cc7acb71da2c MD5 · raw file
- #!/usr/bin/env python
- # Demo program for zlib; it compresses or decompresses files, but *doesn't*
- # delete the original. This doesn't support all of gzip's options.
- #
- # The 'gzip' module in the standard library provides a more complete
- # implementation of gzip-format files.
- import zlib, sys, os
- FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16
- def write32(output, value):
- output.write(chr(value & 255)) ; value=value // 256
- output.write(chr(value & 255)) ; value=value // 256
- output.write(chr(value & 255)) ; value=value // 256
- output.write(chr(value & 255))
- def read32(input):
- v = ord(input.read(1))
- v += (ord(input.read(1)) << 8 )
- v += (ord(input.read(1)) << 16)
- v += (ord(input.read(1)) << 24)
- return v
- def compress (filename, input, output):
- output.write('\037\213\010') # Write the header, ...
- output.write(chr(FNAME)) # ... flag byte ...
- statval = os.stat(filename) # ... modification time ...
- mtime = statval[8]
- write32(output, mtime)
- output.write('\002') # ... slowest compression alg. ...
- output.write('\377') # ... OS (=unknown) ...
- output.write(filename+'\000') # ... original filename ...
- crcval = zlib.crc32("")
- compobj = zlib.compressobj(9, zlib.DEFLATED, -zlib.MAX_WBITS,
- zlib.DEF_MEM_LEVEL, 0)
- while True:
- data = input.read(1024)
- if data == "":
- break
- crcval = zlib.crc32(data, crcval)
- output.write(compobj.compress(data))
- output.write(compobj.flush())
- write32(output, crcval) # ... the CRC ...
- write32(output, statval[6]) # and the file size.
- def decompress (input, output):
- magic = input.read(2)
- if magic != '\037\213':
- print 'Not a gzipped file'
- sys.exit(0)
- if ord(input.read(1)) != 8:
- print 'Unknown compression method'
- sys.exit(0)
- flag = ord(input.read(1))
- input.read(4+1+1) # Discard modification time,
- # extra flags, and OS byte.
- if flag & FEXTRA:
- # Read & discard the extra field, if present
- xlen = ord(input.read(1))
- xlen += 256*ord(input.read(1))
- input.read(xlen)
- if flag & FNAME:
- # Read and discard a null-terminated string containing the filename
- while True:
- s = input.read(1)
- if s == '\0': break
- if flag & FCOMMENT:
- # Read and discard a null-terminated string containing a comment
- while True:
- s=input.read(1)
- if s=='\0': break
- if flag & FHCRC:
- input.read(2) # Read & discard the 16-bit header CRC
- decompobj = zlib.decompressobj(-zlib.MAX_WBITS)
- crcval = zlib.crc32("")
- length = 0
- while True:
- data=input.read(1024)
- if data == "":
- break
- decompdata = decompobj.decompress(data)
- output.write(decompdata)
- length += len(decompdata)
- crcval = zlib.crc32(decompdata, crcval)
- decompdata = decompobj.flush()
- output.write(decompdata)
- length += len(decompdata)
- crcval = zlib.crc32(decompdata, crcval)
- # We've read to the end of the file, so we have to rewind in order
- # to reread the 8 bytes containing the CRC and the file size. The
- # decompressor is smart and knows when to stop, so feeding it
- # extra data is harmless.
- input.seek(-8, 2)
- crc32 = read32(input)
- isize = read32(input)
- if crc32 != crcval:
- print 'CRC check failed.'
- if isize != length:
- print 'Incorrect length of data produced'
- def main():
- if len(sys.argv)!=2:
- print 'Usage: minigzip.py <filename>'
- print ' The file will be compressed or decompressed.'
- sys.exit(0)
- filename = sys.argv[1]
- if filename.endswith('.gz'):
- compressing = False
- outputname = filename[:-3]
- else:
- compressing = True
- outputname = filename + '.gz'
- input = open(filename, 'rb')
- output = open(outputname, 'wb')
- if compressing:
- compress(filename, input, output)
- else:
- decompress(input, output)
- input.close()
- output.close()
- if __name__ == '__main__':
- main()