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#
# gzread.py - python gzip input wrapper
#
# Jakub Jelinek <jakub@redhat.com>
#
# Copyright 2001 Red Hat, Inc.
#
# This software may be freely redistributed under the terms of the GNU
# library public license.
#
# You should have received a copy of the GNU Library Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
#
import string
import zlib
import __builtin__
# implements a python function that reads and writes a gzipped file
# 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
FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16
def read32(buf):
v = ord(buf[0])
v = v + (ord(buf[1]) << 8)
v = v + (ord(buf[2]) << 16)
v = v + (ord(buf[3]) << 24)
return v
def open(filename, fileobj=None):
return GzipFile(filename, fileobj)
class GzipFile:
myfileobj = None
def __init__(self, filename=None, fileobj=None):
if fileobj is None:
fileobj = self.myfileobj = __builtin__.open(filename, 'r')
self._init_read()
self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
self.fileobj = fileobj
self.compressed = 1
self._read_gzip_header()
def _init_read(self):
self.crc = zlib.crc32("")
self.size = 0
self.extrabuf = ""
self.extrasize = 0
self.lastbuf = ""
def _read_gzip_header(self):
magic = self.fileobj.read(2)
if magic != '\037\213':
self._unread(magic)
self.compressed = 0
return
method = ord( self.fileobj.read(1) )
if method != 8:
raise RuntimeError, '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 read(self,size=None):
if self.extrasize <= 0 and self.fileobj is None:
return ''
if not self.compressed:
chunk = ''
if size and self.extrasize >= size:
chunk = self.extrabuf[:size]
self.extrabuf = self.extrabuf[size:]
self.extrasize = self.extrasize - size
return chunk
if self.extrasize:
chunk = self.extrabuf
if size:
size = size - self.extrasize
self.extrasize = 0
self.extrabuf = ''
if not size:
return chunk + self.fileobj.read()
else:
return chunk + self.fileobj.read(size)
readsize = 1024
if not size: # 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:
pass
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):
try:
buf = self.fileobj.read(size)
except AttributeError:
raise EOFError, "Reached EOF"
if buf == "":
uncompress = self.decompress.flush()
if uncompress == "":
self._read_eof()
self.fileobj = None
raise EOFError, 'Reached EOF'
else:
xlen = len(buf)
if xlen >= 8:
xoff = 0
boff = xlen - 8
else:
xoff = 8 - xlen
boff = 0
self.lastbuf = self.lastbuf[:xoff] + buf[boff:]
uncompress = self.decompress.decompress(buf)
self.crc = zlib.crc32(uncompress, self.crc)
self.extrabuf = self.extrabuf + uncompress
self.extrasize = self.extrasize + len(uncompress)
self.size = self.size + len(uncompress)
def _read_eof(self):
crc32 = read32(self.lastbuf[:4])
isize = read32(self.lastbuf[4:8])
if crc32 != self.crc:
raise IOError, 'CRC check failed'
elif isize != self.size:
raise IOError, 'Incorrect length of data produced'
def close(self):
self.fileobj = None
if self.myfileobj:
self.myfileobj.close()
self.myfileobj = None
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])
self._unread(c[i+1:])
return string.join(bufs, '')
bufs.append(c)
readsize = readsize * 2
return None
def readlines(self):
buf = self.read()
return string.split(buf, '\n')
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