AppPkg/Applications/Python/Python-2.7.2/Demo/zlib/minigzip.py

   1 #!/usr/bin/env python
   2 # Demo program for zlib; it compresses or decompresses files, but *doesn't*
   3 # delete the original.  This doesn't support all of gzip's options.
   4 #
   5 # The 'gzip' module in the standard library provides a more complete
   6 # implementation of gzip-format files.
   7
   8 import zlib, sys, os
   9
  10 FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16
  11
  12 def write32(output, value):
  13     output.write(chr(value & 255)) ; value=value // 256
  14     output.write(chr(value & 255)) ; value=value // 256
  15     output.write(chr(value & 255)) ; value=value // 256
  16     output.write(chr(value & 255))
  17
  18 def read32(input):
  19     v = ord(input.read(1))
  20     v += (ord(input.read(1)) << 8 )
  21     v += (ord(input.read(1)) << 16)
  22     v += (ord(input.read(1)) << 24)
  23     return v
  24
  25 def compress (filename, input, output):
  26     output.write('\037\213\010')        # Write the header, ...
  27     output.write(chr(FNAME))            # ... flag byte ...
  28
  29     statval = os.stat(filename)           # ... modification time ...
  30     mtime = statval[8]
  31     write32(output, mtime)
  32     output.write('\002')                # ... slowest compression alg. ...
  33     output.write('\377')                # ... OS (=unknown) ...
  34     output.write(filename+'\000')       # ... original filename ...
  35
  36     crcval = zlib.crc32("")
  37     compobj = zlib.compressobj(9, zlib.DEFLATED, -zlib.MAX_WBITS,
  38                              zlib.DEF_MEM_LEVEL, 0)
  39     while True:
  40         data = input.read(1024)
  41         if data == "":
  42             break
  43         crcval = zlib.crc32(data, crcval)
  44         output.write(compobj.compress(data))
  45     output.write(compobj.flush())
  46     write32(output, crcval)             # ... the CRC ...
  47     write32(output, statval[6])         # and the file size.
  48
  49 def decompress (input, output):
  50     magic = input.read(2)
  51     if magic != '\037\213':
  52         print 'Not a gzipped file'
  53         sys.exit(0)
  54     if ord(input.read(1)) != 8:
  55         print 'Unknown compression method'
  56         sys.exit(0)
  57     flag = ord(input.read(1))
  58     input.read(4+1+1)                   # Discard modification time,
  59                                         # extra flags, and OS byte.
  60     if flag & FEXTRA:
  61         # Read & discard the extra field, if present
  62         xlen = ord(input.read(1))
  63         xlen += 256*ord(input.read(1))
  64         input.read(xlen)
  65     if flag & FNAME:
  66         # Read and discard a null-terminated string containing the filename
  67         while True:
  68             s = input.read(1)
  69             if s == '\0': break
  70     if flag & FCOMMENT:
  71         # Read and discard a null-terminated string containing a comment
  72         while True:
  73             s=input.read(1)
  74             if s=='\0': break
  75     if flag & FHCRC:
  76         input.read(2)                   # Read & discard the 16-bit header CRC
  77
  78     decompobj = zlib.decompressobj(-zlib.MAX_WBITS)
  79     crcval = zlib.crc32("")
  80     length = 0
  81     while True:
  82         data=input.read(1024)
  83         if data == "":
  84             break
  85         decompdata = decompobj.decompress(data)
  86         output.write(decompdata)
  87         length += len(decompdata)
  88         crcval = zlib.crc32(decompdata, crcval)
  89
  90     decompdata = decompobj.flush()
  91     output.write(decompdata)
  92     length += len(decompdata)
  93     crcval = zlib.crc32(decompdata, crcval)
  94
  95     # We've read to the end of the file, so we have to rewind in order
  96     # to reread the 8 bytes containing the CRC and the file size.  The
  97     # decompressor is smart and knows when to stop, so feeding it
  98     # extra data is harmless.
  99     input.seek(-8, 2)
 100     crc32 = read32(input)
 101     isize = read32(input)
 102     if crc32 != crcval:
 103         print 'CRC check failed.'
 104     if isize != length:
 105         print 'Incorrect length of data produced'
 106
 107 def main():
 108     if len(sys.argv)!=2:
 109         print 'Usage: minigzip.py <filename>'
 110         print '  The file will be compressed or decompressed.'
 111         sys.exit(0)
 112
 113     filename = sys.argv[1]
 114     if filename.endswith('.gz'):
 115         compressing = False
 116         outputname = filename[:-3]
 117     else:
 118         compressing = True
 119         outputname = filename + '.gz'
 120
 121     input = open(filename, 'rb')
 122     output = open(outputname, 'wb')
 123
 124     if compressing:
 125         compress(filename, input, output)
 126     else:
 127         decompress(input, output)
 128
 129     input.close()
 130     output.close()
 131
 132 if __name__ == '__main__':
 133     main()