diff options
Diffstat (limited to 'Demo')
| -rwxr-xr-x | Demo/zlib/minigzip.py | 107 | ||||
| -rwxr-xr-x | Demo/zlib/zlibdemo.py | 36 |
2 files changed, 143 insertions, 0 deletions
diff --git a/Demo/zlib/minigzip.py b/Demo/zlib/minigzip.py new file mode 100755 index 0000000..0bfe355 --- /dev/null +++ b/Demo/zlib/minigzip.py @@ -0,0 +1,107 @@ +#!/usr/local/bin/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. + +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=v+ (ord(input.read(1))<<8 ) + v=v+ (ord(input.read(1))<<16) + v=v+ (ord(input.read(1))<<24) + return v + +import zlib, sys +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] +compressing=1 ; outputname=filename+'.gz' +if filename[-3:]=='.gz': + compressing=0 ; outputname=filename[:-3] +input=open(filename) ; output=open(outputname, 'w') + +if compressing: + output.write('\037\213\010') # Write the header, ... + output.write(chr(FNAME)) # ... flag byte ... + + import os # ... modification time ... + statval=os.stat(filename) + 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 (1): + 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. + +else: + 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=xlen+256*ord(input.read(1)) + input.read(xlen) + if flag & FNAME: + # Read and discard a null-terminated string containing the filename + while (1): + s=input.read(1) + if s=='\000': break + if flag & FCOMMENT: + # Read and discard a null-terminated string containing a comment + while (1): + s=input.read(1) + if s=='\000': 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 (1): + data=input.read(1024) + if data=="": break + decompdata=decompobj.decompress(data) + print len(decompdata) + output.write(decompdata) ; length=length+len(decompdata) + crcval=zlib.crc32(decompdata, crcval) + decompdata=decompobj.flush() + output.write(decompdata) ; length=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' + +input.close() ; output.close() + diff --git a/Demo/zlib/zlibdemo.py b/Demo/zlib/zlibdemo.py new file mode 100755 index 0000000..fff1750 --- /dev/null +++ b/Demo/zlib/zlibdemo.py @@ -0,0 +1,36 @@ +#!/usr/local/bin/python + +import zlib, sys +if len(sys.argv)>1: filename=sys.argv[1] +else: filename='zlibdemo.py' +print 'Reading', filename +f=open(filename, 'r') # Get the data to compress +s=f.read() +f.close() + +# First, we'll compress the string in one step +comptext=zlib.compress(s, 1) +decomp=zlib.decompress(comptext) + +print '1-step compression: (level 1)' +print ' Original:', len(s), 'Compressed:', len(comptext), +print 'Uncompressed:', len(decomp) + +# Now, let's compress the string in stages; set chunk to work in smaller steps + +chunk=256 +compressor=zlib.compressobj(9) +decompressor=zlib.decompressobj() +comptext=decomp='' +for i in range(0, len(s), chunk): + comptext=comptext+compressor.compress(s[i:i+chunk]) +comptext=comptext+compressor.flush() # Don't forget to call flush()!! + +for i in range(0, len(comptext), chunk): + decomp=decomp+decompressor.decompress(comptext[i:i+chunk]) +decomp=decomp+decompressor.flush() + +print 'Progressive compression (level 9):' +print ' Original:', len(s), 'Compressed:', len(comptext), +print 'Uncompressed:', len(decomp) + |