Checking in zlib demo.
This commit is contained in:
Guido van Rossum
parent
68bdad1015
commit
5416a0d97c
|
|
@ -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()
|
||||
|
||||
|
|
@ -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)
|
||||
|
||||
Loading…
Reference in New Issue