Mini Shell
"""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 struct, sys, time, os
import zlib
import builtins
import io
__all__ = ["GzipFile", "open", "compress", "decompress"]
FTEXT, FHCRC, FEXTRA, FNAME, FCOMMENT = 1, 2, 4, 8, 16
READ, WRITE = 1, 2
def open(filename, mode="rb", compresslevel=9,
encoding=None, errors=None, newline=None):
"""Open a gzip-compressed file in binary or text mode.
The filename argument can be an actual filename (a str or bytes object), or
an existing file object to read from or write to.
The mode argument can be "r", "rb", "w", "wb", "x", "xb", "a" or "ab" for
binary mode, or "rt", "wt", "xt" or "at" for text mode. The default mode is
"rb", and the default compresslevel is 9.
For binary mode, this function is equivalent to the GzipFile constructor:
GzipFile(filename, mode, compresslevel). In this case, the encoding, errors
and newline arguments must not be provided.
For text mode, a GzipFile object is created, and wrapped in an
io.TextIOWrapper instance with the specified encoding, error handling
behavior, and line ending(s).
"""
if "t" in mode:
if "b" in mode:
raise ValueError("Invalid mode: %r" % (mode,))
else:
if encoding is not None:
raise ValueError("Argument 'encoding' not supported in binary mode")
if errors is not None:
raise ValueError("Argument 'errors' not supported in binary mode")
if newline is not None:
raise ValueError("Argument 'newline' not supported in binary mode")
gz_mode = mode.replace("t", "")
if isinstance(filename, (str, bytes)):
binary_file = GzipFile(filename, gz_mode, compresslevel)
elif hasattr(filename, "read") or hasattr(filename, "write"):
binary_file = GzipFile(None, gz_mode, compresslevel, filename)
else:
raise TypeError("filename must be a str or bytes object, or a file")
if "t" in mode:
return io.TextIOWrapper(binary_file, encoding, errors, newline)
else:
return binary_file
def write32u(output, value):
# The L format writes the bit pattern correctly whether signed
# or unsigned.
output.write(struct.pack("<L", value))
class _PaddedFile:
"""Minimal read-only file object that prepends a string to the contents
of an actual file. Shouldn't be used outside of gzip.py, as it lacks
essential functionality."""
def __init__(self, f, prepend=b''):
self._buffer = prepend
self._length = len(prepend)
self.file = f
self._read = 0
def read(self, size):
if self._read is None:
return self.file.read(size)
if self._read + size <= self._length:
read = self._read
self._read += size
return self._buffer[read:self._read]
else:
read = self._read
self._read = None
return self._buffer[read:] + \
self.file.read(size-self._length+read)
def prepend(self, prepend=b'', readprevious=False):
if self._read is None:
self._buffer = prepend
elif readprevious and len(prepend) <= self._read:
self._read -= len(prepend)
return
else:
self._buffer = self._buffer[self._read:] + prepend
self._length = len(self._buffer)
self._read = 0
def unused(self):
if self._read is None:
return b''
return self._buffer[self._read:]
def seek(self, offset, whence=0):
# This is only ever called with offset=whence=0
if whence == 1 and self._read is not None:
if 0 <= offset + self._read <= self._length:
self._read += offset
return
else:
offset += self._length - self._read
self._read = None
self._buffer = None
return self.file.seek(offset, whence)
def __getattr__(self, name):
return getattr(self.file, name)
class GzipFile(io.BufferedIOBase):
"""The GzipFile class simulates most of the methods of a file object with
the exception of the readinto() and truncate() methods.
This class only supports opening files in binary mode. If you need to open a
compressed file in text mode, use the gzip.open() function.
"""
myfileobj = None
max_read_chunk = 10 * 1024 * 1024 # 10Mb
def __init__(self, filename=None, mode=None,
compresslevel=9, fileobj=None, mtime=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, an io.BytesIO 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', 'wb', 'x', or
'xb' depending on whether the file will be read or written. The default
is the mode of fileobj if discernible; otherwise, the default is 'rb'.
A mode of 'r' is equivalent to one of 'rb', and similarly for 'w' and
'wb', 'a' and 'ab', and 'x' and 'xb'.
The compresslevel argument is an integer from 0 to 9 controlling the
level of compression; 1 is fastest and produces the least compression,
and 9 is slowest and produces the most compression. 0 is no compression
at all. The default is 9.
The mtime argument is an optional numeric timestamp to be written
to the stream when compressing. All gzip compressed streams
are required to contain a timestamp. If omitted or None, the
current time is used. This module ignores the timestamp when
decompressing; however, some programs, such as gunzip, make use
of it. The format of the timestamp is the same as that of the
return value of time.time() and of the st_mtime member of the
object returned by os.stat().
"""
if mode and ('t' in mode or 'U' in mode):
raise ValueError("Invalid mode: {!r}".format(mode))
if mode and 'b' not in mode:
mode += 'b'
if fileobj is None:
fileobj = self.myfileobj = builtins.open(filename, mode or 'rb')
if filename is None:
filename = getattr(fileobj, 'name', '')
if not isinstance(filename, (str, bytes)):
filename = ''
if mode is None:
mode = getattr(fileobj, 'mode', 'rb')
if mode.startswith('r'):
self.mode = READ
# Set flag indicating start of a new member
self._new_member = True
# Buffer data read from gzip file. extrastart is offset in
# stream where buffer starts. extrasize is number of
# bytes remaining in buffer from current stream position.
self.extrabuf = b""
self.extrasize = 0
self.extrastart = 0
self.name = filename
# Starts small, scales exponentially
self.min_readsize = 100
fileobj = _PaddedFile(fileobj)
elif mode.startswith(('w', 'a', 'x')):
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("Invalid mode: {!r}".format(mode))
self.fileobj = fileobj
self.offset = 0
self.mtime = mtime
if self.mode == WRITE:
self._write_gzip_header()
@property
def filename(self):
import warnings
warnings.warn("use the name attribute", DeprecationWarning, 2)
if self.mode == WRITE and self.name[-3:] != ".gz":
return self.name + ".gz"
return self.name
def __repr__(self):
fileobj = self.fileobj
if isinstance(fileobj, _PaddedFile):
fileobj = fileobj.file
s = repr(fileobj)
return '<gzip ' + s[1:-1] + ' ' + hex(id(self)) + '>'
def _check_closed(self):
"""Raises a ValueError if the underlying file object has been closed.
"""
if self.closed:
raise ValueError('I/O operation on closed file.')
def _init_write(self, filename):
self.name = filename
self.crc = zlib.crc32(b"") & 0xffffffff
self.size = 0
self.writebuf = []
self.bufsize = 0
def _write_gzip_header(self):
self.fileobj.write(b'\037\213') # magic header
self.fileobj.write(b'\010') # compression method
try:
# RFC 1952 requires the FNAME field to be Latin-1. Do not
# include filenames that cannot be represented that way.
fname = os.path.basename(self.name)
if not isinstance(fname, bytes):
fname = fname.encode('latin-1')
if fname.endswith(b'.gz'):
fname = fname[:-3]
except UnicodeEncodeError:
fname = b''
flags = 0
if fname:
flags = FNAME
self.fileobj.write(chr(flags).encode('latin-1'))
mtime = self.mtime
if mtime is None:
mtime = time.time()
write32u(self.fileobj, int(mtime))
self.fileobj.write(b'\002')
self.fileobj.write(b'\377')
if fname:
self.fileobj.write(fname + b'\000')
def _init_read(self):
self.crc = zlib.crc32(b"") & 0xffffffff
self.size = 0
def _read_exact(self, n):
data = self.fileobj.read(n)
while len(data) < n:
b = self.fileobj.read(n - len(data))
if not b:
raise EOFError("Compressed file ended before the "
"end-of-stream marker was reached")
data += b
return data
def _read_gzip_header(self):
magic = self.fileobj.read(2)
if magic == b'':
return False
if magic != b'\037\213':
raise OSError('Not a gzipped file')
method, flag, self.mtime = struct.unpack("<BBIxx", self._read_exact(8))
if method != 8:
raise OSError('Unknown compression method')
if flag & FEXTRA:
# Read & discard the extra field, if present
extra_len, = struct.unpack("<H", self._read_exact(2))
self._read_exact(extra_len)
if flag & FNAME:
# Read and discard a null-terminated string containing the filename
while True:
s = self.fileobj.read(1)
if not s or s==b'\000':
break
if flag & FCOMMENT:
# Read and discard a null-terminated string containing a comment
while True:
s = self.fileobj.read(1)
if not s or s==b'\000':
break
if flag & FHCRC:
self._read_exact(2) # Read & discard the 16-bit header CRC
unused = self.fileobj.unused()
if unused:
uncompress = self.decompress.decompress(unused)
self._add_read_data(uncompress)
return True
def write(self,data):
self._check_closed()
if self.mode != WRITE:
import errno
raise OSError(errno.EBADF, "write() on read-only GzipFile object")
if self.fileobj is None:
raise ValueError("write() on closed GzipFile object")
# Convert data type if called by io.BufferedWriter.
if isinstance(data, memoryview):
data = data.tobytes()
if len(data) > 0:
self.fileobj.write(self.compress.compress(data))
self.size += len(data)
self.crc = zlib.crc32(data, self.crc) & 0xffffffff
self.offset += len(data)
return len(data)
def read(self, size=-1):
self._check_closed()
if self.mode != READ:
import errno
raise OSError(errno.EBADF, "read() on write-only GzipFile object")
if self.extrasize <= 0 and self.fileobj is None:
return b''
readsize = 1024
if size < 0: # get the whole thing
while self._read(readsize):
readsize = min(self.max_read_chunk, readsize * 2)
size = self.extrasize
else: # just get some more of it
while size > self.extrasize:
if not self._read(readsize):
if size > self.extrasize:
size = self.extrasize
break
readsize = min(self.max_read_chunk, readsize * 2)
offset = self.offset - self.extrastart
chunk = self.extrabuf[offset: offset + size]
self.extrasize = self.extrasize - size
self.offset += size
return chunk
def read1(self, size=-1):
self._check_closed()
if self.mode != READ:
import errno
raise OSError(errno.EBADF, "read1() on write-only GzipFile object")
if self.extrasize <= 0 and self.fileobj is None:
return b''
# For certain input data, a single call to _read() may not return
# any data. In this case, retry until we get some data or reach EOF.
while self.extrasize <= 0 and self._read():
pass
if size < 0 or size > self.extrasize:
size = self.extrasize
offset = self.offset - self.extrastart
chunk = self.extrabuf[offset: offset + size]
self.extrasize -= size
self.offset += size
return chunk
def peek(self, n):
if self.mode != READ:
import errno
raise OSError(errno.EBADF, "peek() on write-only GzipFile object")
# Do not return ridiculously small buffers, for one common idiom
# is to call peek(1) and expect more bytes in return.
if n < 100:
n = 100
if self.extrasize == 0:
if self.fileobj is None:
return b''
# Ensure that we don't return b"" if we haven't reached EOF.
# 1024 is the same buffering heuristic used in read()
while self.extrasize == 0 and self._read(max(n, 1024)):
pass
offset = self.offset - self.extrastart
remaining = self.extrasize
assert remaining == len(self.extrabuf) - offset
return self.extrabuf[offset:offset + n]
def _unread(self, buf):
self.extrasize = len(buf) + self.extrasize
self.offset -= len(buf)
def _read(self, size=1024):
if self.fileobj is None:
return False
if self._new_member:
# If the _new_member flag is set, we have to
# jump to the next member, if there is one.
self._init_read()
if not self._read_gzip_header():
return False
self.decompress = zlib.decompressobj(-zlib.MAX_WBITS)
self._new_member = False
# 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 == b"":
uncompress = self.decompress.flush()
# Prepend the already read bytes to the fileobj to they can be
# seen by _read_eof()
self.fileobj.prepend(self.decompress.unused_data, True)
self._read_eof()
self._add_read_data( uncompress )
return False
uncompress = self.decompress.decompress(buf)
self._add_read_data( uncompress )
if self.decompress.unused_data != b"":
# 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.
# Prepend the already read bytes to the fileobj to they can be
# seen by _read_eof() and _read_gzip_header()
self.fileobj.prepend(self.decompress.unused_data, True)
# 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 = True
return True
def _add_read_data(self, data):
self.crc = zlib.crc32(data, self.crc) & 0xffffffff
offset = self.offset - self.extrastart
self.extrabuf = self.extrabuf[offset:] + data
self.extrasize = self.extrasize + len(data)
self.extrastart = self.offset
self.size = self.size + len(data)
def _read_eof(self):
# We've read to the end of the file
# 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.
crc32, isize = struct.unpack("<II", self._read_exact(8))
if crc32 != self.crc:
raise OSError("CRC check failed %s != %s" % (hex(crc32),
hex(self.crc)))
elif isize != (self.size & 0xffffffff):
raise OSError("Incorrect length of data produced")
# Gzip files can be padded with zeroes and still have archives.
# Consume all zero bytes and set the file position to the first
# non-zero byte. See http://www.gzip.org/#faq8
c = b"\x00"
while c == b"\x00":
c = self.fileobj.read(1)
if c:
self.fileobj.prepend(c, True)
@property
def closed(self):
return self.fileobj is None
def close(self):
fileobj = self.fileobj
if fileobj is None:
return
self.fileobj = None
try:
if self.mode == WRITE:
fileobj.write(self.compress.flush())
write32u(fileobj, self.crc)
# self.size may exceed 2GB, or even 4GB
write32u(fileobj, self.size & 0xffffffff)
finally:
myfileobj = self.myfileobj
if myfileobj:
self.myfileobj = None
myfileobj.close()
def flush(self,zlib_mode=zlib.Z_SYNC_FLUSH):
self._check_closed()
if self.mode == WRITE:
# Ensure the compressor's buffer is flushed
self.fileobj.write(self.compress.flush(zlib_mode))
self.fileobj.flush()
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 rewind(self):
'''Return the uncompressed stream file position indicator to the
beginning of the file'''
if self.mode != READ:
raise OSError("Can't rewind in write mode")
self.fileobj.seek(0)
self._new_member = True
self.extrabuf = b""
self.extrasize = 0
self.extrastart = 0
self.offset = 0
def readable(self):
return self.mode == READ
def writable(self):
return self.mode == WRITE
def seekable(self):
return True
def seek(self, offset, whence=0):
if whence:
if whence == 1:
offset = self.offset + offset
else:
raise ValueError('Seek from end not supported')
if self.mode == WRITE:
if offset < self.offset:
raise OSError('Negative seek in write mode')
count = offset - self.offset
chunk = bytes(1024)
for i in range(count // 1024):
self.write(chunk)
self.write(bytes(count % 1024))
elif self.mode == READ:
if offset < self.offset:
# for negative seek, rewind and do positive seek
self.rewind()
count = offset - self.offset
for i in range(count // 1024):
self.read(1024)
self.read(count % 1024)
return self.offset
def readline(self, size=-1):
if size < 0:
# Shortcut common case - newline found in buffer.
offset = self.offset - self.extrastart
i = self.extrabuf.find(b'\n', offset) + 1
if i > 0:
self.extrasize -= i - offset
self.offset += i - offset
return self.extrabuf[offset: i]
size = sys.maxsize
readsize = self.min_readsize
else:
readsize = size
bufs = []
while size != 0:
c = self.read(readsize)
i = c.find(b'\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 == b'':
bufs.append(c[:i + 1]) # Add portion of last chunk
self._unread(c[i + 1:]) # Push back rest of chunk
break
# Append chunk to list, decrease 'size',
bufs.append(c)
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 b''.join(bufs) # Return resulting line
def compress(data, compresslevel=9):
"""Compress data in one shot and return the compressed string.
Optional argument is the compression level, in range of 0-9.
"""
buf = io.BytesIO()
with GzipFile(fileobj=buf, mode='wb', compresslevel=compresslevel) as f:
f.write(data)
return buf.getvalue()
def decompress(data):
"""Decompress a gzip compressed string in one shot.
Return the decompressed string.
"""
with GzipFile(fileobj=io.BytesIO(data)) as f:
return f.read()
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.buffer)
g = sys.stdout.buffer
else:
if arg[-3:] != ".gz":
print("filename doesn't end in .gz:", repr(arg))
continue
f = open(arg, "rb")
g = builtins.open(arg[:-3], "wb")
else:
if arg == "-":
f = sys.stdin.buffer
g = GzipFile(filename="", mode="wb", fileobj=sys.stdout.buffer)
else:
f = builtins.open(arg, "rb")
g = open(arg + ".gz", "wb")
while True:
chunk = f.read(1024)
if not chunk:
break
g.write(chunk)
if g is not sys.stdout.buffer:
g.close()
if f is not sys.stdin.buffer:
f.close()
if __name__ == '__main__':
_test()
Zerion Mini Shell 1.0