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"""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 distributed with the zlib module
import __builtin__
import struct
import sys
import time
import zlib
__all__ = ["GzipFile", "open"]
READ, WRITE = 1, 2
def U32(i):
"""Return i as an unsigned integer, assuming it fits in 32 bits.
If it's >= 2GB when viewed as a 32-bit unsigned int, return a long.
if i < 0:
i += 1L << 32
return i
def LOWU32(i):
"""Return the low-order 32 bits of an int, as a non-negative int."""
return i & 0xFFFFFFFFL
def write32(output, value):
output.write(struct.pack("<l", value))
def write32u(output, value):
# The L format writes the bit pattern correctly whether signed
# or unsigned.
output.write(struct.pack("<L", value))
def read32(input):
i =
val = 0
if len(i) > 0:
#print 'cool with len %d' % (len(i))
val = struct.unpack("<l", i)[0]
return val
def open(filename, mode="rb", compresslevel=9):
"""Shorthand for GzipFile(filename, mode, compresslevel).
The filename argument is required; mode defaults to 'rb'
and compresslevel defaults to 9.
return GzipFile(filename, mode, compresslevel)
class GzipFile:
"""The GzipFile class simulates most of the methods of a file object with
the exception of the readinto() and truncate() methods.
myfileobj = None
max_read_chunk = 10 * 1024 * 1024 # 10Mb
def __init__(self, filename=None, mode=None,
compresslevel=9, fileobj=None):
"""Constructor for the GzipFile class.
At least one of fileobj and filename must be given a
non-trivial value.
The new class instance is based on fileobj, which can be a regular
file, a StringIO object, or any other object which simulates a file.
It defaults to None, in which case filename is opened to provide
a file object.
When fileobj is not None, the filename argument is only used to be
included in the gzip file header, which may includes the original
filename of the uncompressed file. It defaults to the filename of
fileobj, if discernible; otherwise, it defaults to the empty string,
and in this case the original filename is not included in the header.
The mode argument can be any of 'r', 'rb', 'a', 'ab', 'w', or 'wb',
depending on whether the file will be read or written. The default
is the mode of fileobj if discernible; otherwise, the default is 'rb'.
Be aware that only the 'rb', 'ab', and 'wb' values should be used
for cross-platform portability.
The compresslevel argument is an integer from 1 to 9 controlling the
level of compression; 1 is fastest and produces the least compression,
and 9 is slowest and produces the most compression. The default is 9.
# guarantee the file is opened in binary mode on platforms
# that care about that sort of thing
if mode and 'b' not in mode:
mode += 'b'
if fileobj is None:
fileobj = self.myfileobj =, mode or 'rb')
if filename is None:
if hasattr(fileobj, 'name'): filename =
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 = True
self.extrabuf = ""
self.extrasize = 0
self.filename = filename
# Starts small, scales exponentially
self.min_readsize = 100
elif mode[0:1] == 'w' or mode[0:1] == 'a':
self.mode = WRITE
self.compress = zlib.compressobj(compresslevel,
- zlib.MAX_WBITS,
raise IOError, "Mode " + mode + " not supported"
self.fileobj = fileobj
self.offset = 0
if self.mode == WRITE:
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
write32u(self.fileobj, long(time.time()))
if fname:
self.fileobj.write(fname + '\000')
def _init_read(self):
self.crc = zlib.crc32("")
self.size = 0
def _read_gzip_header(self):
magic =
if len(magic) < 2:
raise EOFError, 'end of file'
if magic != '\037\213':
raise IOError, 'Not a gzipped file'
method = ord(
if method != 8:
raise IOError, 'Unknown compression method'
flag = ord(
# modtime =
# extraflag =
# os =
if flag & FEXTRA:
# Read & discard the extra field, if present
xlen = ord(
xlen = xlen + 256 * ord(
if flag & FNAME:
# Read and discard a null-terminated string containing the filename
while True:
s =
if not s or s == '\000':
if flag & FCOMMENT:
# Read and discard a null-terminated string containing a comment
while True:
s =
if not s or s == '\000':
if flag & FHCRC: # Read & discard the 16-bit header CRC
def write(self, data):
if self.mode != WRITE:
import errno
raise IOError(errno.EBADF, "write() on read-only GzipFile object")
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.offset += len(data)
def read(self, size= -1):
if self.mode != READ:
import errno
raise IOError(errno.EBADF, "read() on write-only GzipFile object")
if self.extrasize <= 0 and self.fileobj is None:
return ''
readsize = 1024
if size < 0: # get the whole thing
while True:
readsize = min(self.max_read_chunk, readsize * 2)
except EOFError:
size = self.extrasize
else: # just get some more of it
while size > self.extrasize:
readsize = min(self.max_read_chunk, 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
self.offset += size
return chunk
def _unread(self, buf):
self.extrabuf = buf + self.extrabuf
self.extrasize = len(buf) + self.extrasize
self.offset -= len(buf)
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
# jump to the next member, if there is one.
# 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, 2) # Seek to end of file
if pos == self.fileobj.tell():
raise EOFError, "Reached EOF"
else: # Return to original position
self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
self._new_member = False
# Read a chunk of data from the file
buf =
# If the EOF has been reached, flush the decompression object
# and mark this object as finished.
if buf == "":
uncompress = self.decompress.flush()
raise EOFError, 'Reached EOF'
uncompress = self.decompress.decompress(buf)
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) + 8, 1)
# Check the CRC and file size, and set the flag so we read
# a new member on the next call
self._new_member = True
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. Note that the size
# stored is the true file size mod 2**32., 1)
crc32 = read32(self.fileobj)
isize = U32(read32(self.fileobj)) # may exceed 2GB
if U32(crc32) != U32(self.crc):
pass #print 'IOError, "CRC check failed"'
#raise IOError, "CRC check failed"
elif isize != LOWU32(self.size):
raise IOError, "Incorrect length of data produced"
def close(self):
if self.mode == WRITE:
# The native zlib crc is an unsigned 32-bit integer, but
# the Python wrapper implicitly casts that to a signed C
# long. So, on a 32-bit box self.crc may "look negative",
# while the same crc on a 64-bit box may "look positive".
# To avoid irksome warnings from the `struct` module, force
# it to look positive on all boxes.
write32u(self.fileobj, LOWU32(self.crc))
# self.size may exceed 2GB, or even 4GB
write32u(self.fileobj, LOWU32(self.size))
self.fileobj = None
elif self.mode == READ:
self.fileobj = None
if self.myfileobj:
self.myfileobj = None
def __del__(self):
if (self.myfileobj is None and
self.fileobj is None):
except AttributeError:
def flush(self, zlib_mode=zlib.Z_SYNC_FLUSH):
if self.mode == WRITE:
# Ensure the compressor's buffer is flushed
def fileno(self):
"""Invoke the underlying file object's fileno() method.
This will raise AttributeError if the underlying file object
doesn't support fileno().
return self.fileobj.fileno()
def isatty(self):
return False
def tell(self):
return self.offset
def rewind(self):
'''Return the uncompressed stream file position indicator to the
beginning of the file'''
if self.mode != READ:
raise IOError("Can't rewind in write mode")
self._new_member = True
self.extrabuf = ""
self.extrasize = 0
self.offset = 0
def seek(self, offset):
if self.mode == WRITE:
if offset < self.offset:
raise IOError('Negative seek in write mode')
count = offset - self.offset
for i in range(count // 1024):
self.write(1024 * '\0')
self.write((count % 1024) * '\0')
elif self.mode == READ:
if offset < self.offset:
# for negative seek, rewind and do positive seek
count = offset - self.offset
for i in range(count // 1024): % 1024)
def readline(self, size= -1):
if size < 0:
size = sys.maxint
readsize = self.min_readsize
readsize = size
bufs = []
while size != 0:
c =
i = c.find('\n')
# We set i=size to break out of the loop under two
# conditions: 1) there's no newline, and the chunk is
# larger than size, or 2) there is a newline, but the
# resulting line would be longer than 'size'.
if (size <= i) or (i == -1 and len(c) > size):
i = size - 1
if i >= 0 or c == '':
bufs.append(c[:i + 1]) # Add portion of last chunk
self._unread(c[i + 1:]) # Push back rest of chunk
# Append chunk to list, decrease 'size',
size = size - len(c)
readsize = min(size, readsize * 2)
if readsize > self.min_readsize:
self.min_readsize = min(readsize, self.min_readsize * 2, 512)
return ''.join(bufs) # Return resulting line
def readlines(self, sizehint=0):
# Negative numbers result in reading all the lines
if sizehint <= 0:
sizehint = sys.maxint
L = []
while sizehint > 0:
line = self.readline()
if line == "":
sizehint = sizehint - len(line)
return L
def writelines(self, L):
for line in L:
def __iter__(self):
return self
def next(self):
line = self.readline()
if line:
return line
raise StopIteration
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.
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
if arg[-3:] != ".gz":
print "filename doesn't end in .gz:", repr(arg)
f = open(arg, "rb")
g =[:-3], "wb")
if arg == "-":
f = sys.stdin
g = GzipFile(filename="", mode="wb", fileobj=sys.stdout)
f =, "rb")
g = open(arg + ".gz", "wb")
while True:
chunk =
if not chunk:
if g is not sys.stdout:
if f is not sys.stdin:
if __name__ == '__main__':