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Editing: _compression.py
"""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
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