cpython/Lib/gzip.py

344 lines
11 KiB
Python
Raw Normal View History

"""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]
1999-04-05 15:37:59 -03:00
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):
try:
if (self.myfileobj is None and
self.fileobj is None):
return
except AttributeError:
return
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()