Checking in zlib demo.

Demo/zlib/minigzip.py

+#!/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()
+

Demo/zlib/zlibdemo.py

+#!/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)
+