135 lines
4.3 KiB
Python
Executable File
135 lines
4.3 KiB
Python
Executable File
#!/usr/bin/env python3
|
|
# Demo program for zlib; it compresses or decompresses files, but *doesn't*
|
|
# delete the original. This doesn't support all of gzip's options.
|
|
#
|
|
# The 'gzip' module in the standard library provides a more complete
|
|
# implementation of gzip-format files.
|
|
|
|
import zlib, sys, os
|
|
|
|
FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16
|
|
|
|
def write32(output, value):
|
|
output.write(bytes([value & 255])) ; value=value // 256
|
|
output.write(bytes([value & 255])) ; value=value // 256
|
|
output.write(bytes([value & 255])) ; value=value // 256
|
|
output.write(bytes([value & 255]))
|
|
|
|
def read32(input):
|
|
v = ord(input.read(1))
|
|
v += (ord(input.read(1)) << 8 )
|
|
v += (ord(input.read(1)) << 16)
|
|
v += (ord(input.read(1)) << 24)
|
|
return v
|
|
|
|
def compress(filename, input, output):
|
|
output.write(b'\037\213\010') # Write the header, ...
|
|
output.write(bytes([FNAME])) # ... flag byte ...
|
|
|
|
statval = os.stat(filename) # ... modification time ...
|
|
mtime = statval[8]
|
|
write32(output, mtime)
|
|
output.write(b'\002') # ... slowest compression alg. ...
|
|
output.write(b'\377') # ... OS (=unknown) ...
|
|
bfilename = os.fsencode(filename)
|
|
output.write(bfilename + b'\000') # ... original filename ...
|
|
|
|
crcval = zlib.crc32(b'')
|
|
compobj = zlib.compressobj(9, zlib.DEFLATED, -zlib.MAX_WBITS,
|
|
zlib.DEF_MEM_LEVEL, 0)
|
|
while True:
|
|
data = input.read(1024)
|
|
if data == b'':
|
|
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.
|
|
|
|
def decompress(input, output):
|
|
magic = input.read(2)
|
|
if magic != b'\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 += 256*ord(input.read(1))
|
|
input.read(xlen)
|
|
if flag & FNAME:
|
|
# Read and discard a null-terminated string containing the filename
|
|
while True:
|
|
s = input.read(1)
|
|
if s == b'\0': break
|
|
if flag & FCOMMENT:
|
|
# Read and discard a null-terminated string containing a comment
|
|
while True:
|
|
s = input.read(1)
|
|
if s == b'\0': break
|
|
if flag & FHCRC:
|
|
input.read(2) # Read & discard the 16-bit header CRC
|
|
|
|
decompobj = zlib.decompressobj(-zlib.MAX_WBITS)
|
|
crcval = zlib.crc32(b'')
|
|
length = 0
|
|
while True:
|
|
data = input.read(1024)
|
|
if data == b"":
|
|
break
|
|
decompdata = decompobj.decompress(data)
|
|
output.write(decompdata)
|
|
length += len(decompdata)
|
|
crcval = zlib.crc32(decompdata, crcval)
|
|
|
|
decompdata = decompobj.flush()
|
|
output.write(decompdata)
|
|
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')
|
|
|
|
def main():
|
|
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]
|
|
if filename.endswith('.gz'):
|
|
compressing = False
|
|
outputname = filename[:-3]
|
|
else:
|
|
compressing = True
|
|
outputname = filename + '.gz'
|
|
|
|
input = open(filename, 'rb')
|
|
output = open(outputname, 'wb')
|
|
|
|
if compressing:
|
|
compress(filename, input, output)
|
|
else:
|
|
decompress(input, output)
|
|
|
|
input.close()
|
|
output.close()
|
|
|
|
if __name__ == '__main__':
|
|
main()
|