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