"""Functions that read and write gzipped files.
The user of the file doesn't have to worry about the compression,
but random access is not allowed."""
# based on Andrew Kuchling's minigzip.py distributed with the zlib module
import time
import string
import zlib
import struct
import __builtin__
FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16
READ, WRITE = 1, 2
def write32(output, value):
output.write(struct.pack("<l", value))
def write32u(output, value):
output.write(struct.pack("<L", value))
def read32(input):
return struct.unpack("<l", input.read(4))[0]
def open(filename, mode="rb", compresslevel=9):
return GzipFile(filename, mode, compresslevel)
class GzipFile:
myfileobj = None
def __init__(self, filename=None, mode=None,
compresslevel=9, fileobj=None):
if fileobj is None:
fileobj = self.myfileobj = __builtin__.open(filename, mode or 'rb')
if filename is None:
if hasattr(fileobj, 'name'): filename = fileobj.name
else: filename = ''
if mode is None:
if hasattr(fileobj, 'mode'): mode = fileobj.mode
else: mode = 'rb'
if mode[0:1] == 'r':
self.mode = READ
# Set flag indicating start of a new member
self._new_member = 1
self.extrabuf = ""
self.extrasize = 0
self.filename = filename
elif mode[0:1] == 'w' or mode[0:1] == 'a':
self.mode = WRITE
self._init_write(filename)
self.compress = zlib.compressobj(compresslevel,
zlib.DEFLATED,
-zlib.MAX_WBITS,
zlib.DEF_MEM_LEVEL,
0)
else:
raise ValueError, "Mode " + mode + " not supported"
self.fileobj = fileobj
if self.mode == WRITE:
self._write_gzip_header()
def __repr__(self):
s = repr(self.fileobj)
return '<gzip ' + s[1:-1] + ' ' + hex(id(self)) + '>'
def _init_write(self, filename):
if filename[-3:] != '.gz':
filename = filename + '.gz'
self.filename = filename
self.crc = zlib.crc32("")
self.size = 0
self.writebuf = []
self.bufsize = 0
def _write_gzip_header(self):
self.fileobj.write('\037\213') # magic header
self.fileobj.write('\010') # compression method
fname = self.filename[:-3]
flags = 0
if fname:
flags = FNAME
self.fileobj.write(chr(flags))
write32u(self.fileobj, long(time.time()))
self.fileobj.write('\002')
self.fileobj.write('\377')
if fname:
self.fileobj.write(fname + '\000')
def _init_read(self):
self.crc = zlib.crc32("")
self.size = 0
def _read_gzip_header(self):
magic = self.fileobj.read(2)
if magic != '\037\213':
raise IOError, 'Not a gzipped file'
method = ord( self.fileobj.read(1) )
if method != 8:
raise IOError, 'Unknown compression method'
flag = ord( self.fileobj.read(1) )
# modtime = self.fileobj.read(4)
# extraflag = self.fileobj.read(1)
# os = self.fileobj.read(1)
self.fileobj.read(6)
if flag & FEXTRA:
# Read & discard the extra field, if present
xlen=ord(self.fileobj.read(1))
xlen=xlen+256*ord(self.fileobj.read(1))
self.fileobj.read(xlen)
if flag & FNAME:
# Read and discard a null-terminated string containing the filename
while (1):
s=self.fileobj.read(1)
if not s or s=='\000': break
if flag & FCOMMENT:
# Read and discard a null-terminated string containing a comment
while (1):
s=self.fileobj.read(1)
if not s or s=='\000': break
if flag & FHCRC:
self.fileobj.read(2) # Read & discard the 16-bit header CRC
def write(self,data):
if self.fileobj is None:
raise ValueError, "write() on closed GzipFile object"
if len(data) > 0:
self.size = self.size + len(data)
self.crc = zlib.crc32(data, self.crc)
self.fileobj.write( self.compress.compress(data) )
def writelines(self,lines):
self.write(string.join(lines))
def read(self, size=-1):
if self.extrasize <= 0 and self.fileobj is None:
return ''
readsize = 1024
if size < 0: # get the whole thing
try:
while 1:
self._read(readsize)
readsize = readsize * 2
except EOFError:
size = self.extrasize
else: # just get some more of it
try:
while size > self.extrasize:
self._read(readsize)
readsize = readsize * 2
except EOFError:
if size > self.extrasize:
size = self.extrasize
chunk = self.extrabuf[:size]
self.extrabuf = self.extrabuf[size:]
self.extrasize = self.extrasize - size
return chunk
def _unread(self, buf):
self.extrabuf = buf + self.extrabuf
self.extrasize = len(buf) + self.extrasize
def _read(self, size=1024):
if self.fileobj is None: raise EOFError, "Reached EOF"
if self._new_member:
# If the _new_member flag is set, we have to
#
# First, check if we're at the end of the file;
# if so, it's time to stop; no more members to read.
pos = self.fileobj.tell() # Save current position
self.fileobj.seek(0, 2) # Seek to end of file
if pos == self.fileobj.tell():
self.fileobj = None
raise EOFError, "Reached EOF"
else:
self.fileobj.seek( pos ) # Return to original position
self._init_read()
self._read_gzip_header()
self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
self._new_member = 0
# Read a chunk of data from the file
buf = self.fileobj.read(size)
# If the EOF has been reached, flush the decompression object
# and mark this object as finished.
if buf == "":
uncompress = self.decompress.flush()
self._read_eof()
self.fileobj = None
self._add_read_data( uncompress )
raise EOFError, 'Reached EOF'
uncompress = self.decompress.decompress(buf)
self._add_read_data( uncompress )
if self.decompress.unused_data != "":
# Ending case: we've come to the end of a member in the file,
# so seek back to the start of the unused data, finish up
# this member, and read a new gzip header.
# (The number of bytes to seek back is the length of the unused
# data, minus 8 because _read_eof() will rewind a further 8 bytes)
self.fileobj.seek( -len(self.decompress.unused_data)+8, 1)
# Check the CRC and file size, and set the flag so we read
# a new member on the next call
self._read_eof()
self._new_member = 1
def _add_read_data(self, data):
self.crc = zlib.crc32(data, self.crc)
self.extrabuf = self.extrabuf + data
self.extrasize = self.extrasize + len(data)
self.size = self.size + len(data)
def _read_eof(self):
# 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.
# We check the that the computed CRC and size of the
# uncompressed data matches the stored values.
self.fileobj.seek(-8, 1)
crc32 = read32(self.fileobj)
isize = read32(self.fileobj)
if crc32%0x100000000L != self.crc%0x100000000L:
raise ValueError, "CRC check failed"
elif isize != self.size:
raise ValueError, "Incorrect length of data produced"
def close(self):
if self.mode == WRITE:
self.fileobj.write(self.compress.flush())
write32(self.fileobj, self.crc)
write32(self.fileobj, self.size)
self.fileobj = None
elif self.mode == READ:
self.fileobj = None
if self.myfileobj:
self.myfileobj.close()
self.myfileobj = None
def __del__(self):
if (self.myfileobj is not None or
self.fileobj is not None):
self.close()
def flush(self):
self.fileobj.flush()
def seek(self):
raise IOError, 'Random access not allowed in gzip files'
def tell(self):
raise IOError, 'I won\'t tell() you for gzip files'
def isatty(self):
return 0
def readline(self):
bufs = []
readsize = 100
while 1:
c = self.read(readsize)
i = string.find(c, '\n')
if i >= 0 or c == '':
bufs.append(c[:i+1])
self._unread(c[i+1:])
return string.join(bufs, '')
bufs.append(c)
readsize = readsize * 2
def readlines(self, ignored=None):
buf = self.read()
lines = string.split(buf, '\n')
for i in range(len(lines)-1):
lines[i] = lines[i] + '\n'
if lines and not lines[-1]:
del lines[-1]
return lines
def writelines(self, L):
for line in L:
self.write(line)
def _test():
# Act like gzip; with -d, act like gunzip.
# The input file is not deleted, however, nor are any other gzip
# options or features supported.
import sys
args = sys.argv[1:]
decompress = args and args[0] == "-d"
if decompress:
args = args[1:]
if not args:
args = ["-"]
for arg in args:
if decompress:
if arg == "-":
f = GzipFile(filename="", mode="rb", fileobj=sys.stdin)
g = sys.stdout
else:
if arg[-3:] != ".gz":
print "filename doesn't end in .gz:", `arg`
continue
f = open(arg, "rb")
g = __builtin__.open(arg[:-3], "wb")
else:
if arg == "-":
f = sys.stdin
g = GzipFile(filename="", mode="wb", fileobj=sys.stdout)
else:
f = __builtin__.open(arg, "rb")
g = open(arg + ".gz", "wb")
while 1:
chunk = f.read(1024)
if not chunk:
break
g.write(chunk)
if g is not sys.stdout:
g.close()
if f is not sys.stdin:
f.close()
if __name__ == '__main__':
_test()
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