cnpython/Lib/_compression.py at cnpython · lp9102/cnpython · GitHub

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"""Internal classes used by the gzip, lzma and bz2 modules"""

import io

BUFFER_SIZE = io.DEFAULT_BUFFER_SIZE # Compressed data read chunk size

class BaseStream(io.BufferedIOBase):

"""Mode-checking helper functions."""

def _check_not_closed(self):

if self.closed:

raise ValueError("I/O operation on closed file")

def _check_can_read(self):

if not self.readable():

raise io.UnsupportedOperation("File not open for reading")

def _check_can_write(self):

if not self.writable():

raise io.UnsupportedOperation("File not open for writing")

def _check_can_seek(self):

if not self.readable():

raise io.UnsupportedOperation("Seeking is only supported "

"on files open for reading")

if not self.seekable():

raise io.UnsupportedOperation("The underlying file object "

"does not support seeking")

class DecompressReader(io.RawIOBase):

"""Adapts the decompressor API to a RawIOBase reader API"""

def readable(self):

return True

def __init__(self, fp, decomp_factory, trailing_error=(), **decomp_args):

self._fp = fp

self._eof = False

self._pos = 0 # Current offset in decompressed stream

# Set to size of decompressed stream once it is known, for SEEK_END

self._size = -1

# Save the decompressor factory and arguments.

# If the file contains multiple compressed streams, each

# stream will need a separate decompressor object. A new decompressor

# object is also needed when implementing a backwards seek().

self._decomp_factory = decomp_factory

self._decomp_args = decomp_args

self._decompressor = self._decomp_factory(**self._decomp_args)

# Exception class to catch from decompressor signifying invalid

# trailing data to ignore

self._trailing_error = trailing_error

def close(self):

self._decompressor = None

return super().close()

def seekable(self):

return self._fp.seekable()

def readinto(self, b):

with memoryview(b) as view, view.cast("B") as byte_view:

data = self.read(len(byte_view))

byte_view[:len(data)] = data

return len(data)

def read(self, size=-1):

if size < 0:

return self.readall()

if not size or self._eof:

return b""

data = None # Default if EOF is encountered

# Depending on the input data, our call to the decompressor may not

# return any data. In this case, try again after reading another block.

while True:

if self._decompressor.eof:

rawblock = (self._decompressor.unused_data or

self._fp.read(BUFFER_SIZE))

if not rawblock:

break

# Continue to next stream.

self._decompressor = self._decomp_factory(

**self._decomp_args)

try:

data = self._decompressor.decompress(rawblock, size)

except self._trailing_error:

# Trailing data isn't a valid compressed stream; ignore it.

break

else:

if self._decompressor.needs_input:

rawblock = self._fp.read(BUFFER_SIZE)

if not rawblock:

raise EOFError("Compressed file ended before the "

"end-of-stream marker was reached")

else:

rawblock = b""

data = self._decompressor.decompress(rawblock, size)

if data:

break

if not data:

self._eof = True

self._size = self._pos

return b""

self._pos += len(data)

return data

# Rewind the file to the beginning of the data stream.

def _rewind(self):

self._fp.seek(0)

self._eof = False

self._pos = 0

self._decompressor = self._decomp_factory(**self._decomp_args)

def seek(self, offset, whence=io.SEEK_SET):

# Recalculate offset as an absolute file position.

if whence == io.SEEK_SET:

pass

elif whence == io.SEEK_CUR:

offset = self._pos + offset

elif whence == io.SEEK_END:

# Seeking relative to EOF - we need to know the file's size.

if self._size < 0:

while self.read(io.DEFAULT_BUFFER_SIZE):

pass

offset = self._size + offset

else:

raise ValueError("Invalid value for whence: {}".format(whence))

# Make it so that offset is the number of bytes to skip forward.

if offset < self._pos:

self._rewind()

else:

offset -= self._pos

# Read and discard data until we reach the desired position.

while offset > 0:

data = self.read(min(io.DEFAULT_BUFFER_SIZE, offset))

if not data:

break

offset -= len(data)

return self._pos

def tell(self):

"""Return the current file position."""

return self._pos

cnpython/Lib/_compression.py at cnpython · lp9102/cnpython · GitHub

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