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

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import io

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BUFFER_SIZE = io.DEFAULT_BUFFER_SIZE # Compressed data read chunk size

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class BaseStream(io.BufferedIOBase):

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

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def _check_not_closed(self):

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if self.closed:

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

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def _check_can_read(self):

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if not self.readable():

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

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def _check_can_write(self):

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if not self.writable():

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

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def _check_can_seek(self):

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if not self.readable():

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raise io.UnsupportedOperation("Seeking is only supported "

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"on files open for reading")

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if not self.seekable():

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raise io.UnsupportedOperation("The underlying file object "

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"does not support seeking")

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class DecompressReader(io.RawIOBase):

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

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def readable(self):

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return True

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

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self._fp = fp

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self._eof = False

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self._pos = 0 # Current offset in decompressed stream

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

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self._size = -1

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# Save the decompressor factory and arguments.

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# If the file contains multiple compressed streams, each

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

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

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self._decomp_factory = decomp_factory

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self._decomp_args = decomp_args

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

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# Exception class to catch from decompressor signifying invalid

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# trailing data to ignore

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self._trailing_error = trailing_error

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def close(self):

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self._decompressor = None

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return super().close()

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def seekable(self):

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return self._fp.seekable()

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def readinto(self, b):

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

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data = self.read(len(byte_view))

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byte_view[:len(data)] = data

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return len(data)

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def read(self, size=-1):

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if size < 0:

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return self.readall()

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if not size or self._eof:

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return b""

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data = None # Default if EOF is encountered

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

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

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while True:

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if self._decompressor.eof:

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rawblock = (self._decompressor.unused_data or

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self._fp.read(BUFFER_SIZE))

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if not rawblock:

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break

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# Continue to next stream.

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self._decompressor = self._decomp_factory(

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**self._decomp_args)

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try:

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

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except self._trailing_error:

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

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break

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else:

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if self._decompressor.needs_input:

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rawblock = self._fp.read(BUFFER_SIZE)

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if not rawblock:

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raise EOFError("Compressed file ended before the "

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"end-of-stream marker was reached")

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else:

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rawblock = b""

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

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if data:

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break

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if not data:

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self._eof = True

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self._size = self._pos

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return b""

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self._pos += len(data)

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return data

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

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def _rewind(self):

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self._fp.seek(0)

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self._eof = False

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self._pos = 0

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

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

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# Recalculate offset as an absolute file position.

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if whence == io.SEEK_SET:

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pass

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elif whence == io.SEEK_CUR:

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offset = self._pos + offset

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elif whence == io.SEEK_END:

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

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if self._size < 0:

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while self.read(io.DEFAULT_BUFFER_SIZE):

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pass

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offset = self._size + offset

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else:

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

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

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if offset < self._pos:

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self._rewind()

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else:

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offset -= self._pos

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

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while offset > 0:

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

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if not data:

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break

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offset -= len(data)

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return self._pos

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def tell(self):

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

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return self._pos

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