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import time
import string
import zlib
import StringIO
# 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 sequential 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
READ, WRITE = 1, 2
def write32(output, value):
t = divmod(value, 256)
b1 = chr(t[1])
t = divmod(t[0], 256)
b2 = chr(t[1])
t = divmod(t[0], 256)
b3 = chr(t[1])
t = divmod(t[0], 256)
b4 = chr(t[1])
buf = b1 + b2 + b3 + b4
output.write(buf)
def read32(input):
buf = input.read(4)
v = ord(buf[0])
v = v + (ord(buf[1]) << 8)
v = v + (ord(buf[2]) << 16)
v = v + (ord(buf[3]) << 24)
return v
written = []
_py_open = open
def open(filename, mode, compresslevel=9):
return GzipFile(filename, mode, compresslevel)
class GzipFile:
def __init__(self, filename, mode='r', compresslevel=9):
if mode == 'r' or mode == 'rb':
self.mode = READ
self._init_read()
self.filename = filename
self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
elif mode == 'w' or mode == 'wb':
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 = _py_open(self.filename,mode)
if self.mode == WRITE:
self._write_gzip_header()
elif self.mode == READ:
self._read_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
self.fileobj.write(chr(FNAME))
write32(self.fileobj, int(time.time()))
self.fileobj.write('\002')
self.fileobj.write('\377')
self.fileobj.write(self.filename[:-3] + '\000')
def _init_read(self):
self.crc = zlib.crc32("")
self.size = 0
self.extrabuf = ""
self.extrasize = 0
def _read_gzip_header(self):
magic = self.fileobj.read(2)
if magic != '\037\213':
raise RuntimeError, 'Not a gzipped file'
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 s=='\000': break
if flag & FCOMMENT:
# Read and discard a null-terminated string containing a comment
while (1):
s=self.fileobj.read(1)
if s=='\000': break
if flag & FHCRC:
self.fileobj.read(2) # Read & discard the 16-bit header CRC
def write(self,data):
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=None):
if self.extrasize <= 0 and self.fileobj.closed:
return ''
if not size:
# get the whole thing
try:
while 1:
self._read()
except EOFError:
size = self.extrasize
else:
# just get some more of it
try:
while size > self.extrasize:
self._read()
except EOFError:
pass
chunk = self.extrabuf[:size]
self.extrabuf = self.extrabuf[size:]
self.extrasize = self.extrasize - size
return chunk
def _read(self):
buf = self.fileobj.read(1024)
if buf == "":
uncompress = self.decompress.flush()
if uncompress == "":
self._read_eof()
self.fileobj.close()
raise EOFError, 'Reached EOF'
else:
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):
# Andrew writes:
## 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.
self.fileobj.seek(-8, 2)
crc32 = read32(self.fileobj)
isize = read32(self.fileobj)
if crc32 != self.crc:
self.error = "CRC check failed"
elif isize != self.size:
self.error = "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.close()
elif self.mode == READ:
self.fileobj.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):
# should I bother with this
raise RuntimeError, "not implemented"
def readlines(self):
# should I bother with this
raise RuntimeError, "not implemented"
class StringIOgz(GzipFile):
"""A StringIO substitute that reads/writes gzipped buffers."""
def __init__(self, buf=None, filename="StringIOgz"):
"""Read/write mode depends on first argument.
If __init__ is passed a buffer, it will treat that as the
gzipped data and set up the StringIO for reading. Without the
initial argument, it will assume a new file for writing.
The filename argument is written in the header of buffers
opened for writing. Not sure that this is useful, but the
GzipFile code expects *some* filename."""
if buf:
self.mode = READ
self._init_read()
self.filename = filename
self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
self.fileobj = StringIO.StringIO(buf)
else:
self.mode = WRITE
self._init_write(filename)
self.compress = zlib.compressobj(compresslevel,
zlib.DEFLATED,
-zlib.MAX_WBITS,
zlib.DEF_MEM_LEVEL,
0)
self.fileobj = StringIO.StringIO()
if self.mode == WRITE:
self._write_gzip_header()
elif self.mode == READ:
self._read_gzip_header()
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