File Explorer

1"""Internal classes used by the gzip, lzma and bz2 modules"""2 3import io4 5 6BUFFER_SIZE = io.DEFAULT_BUFFER_SIZE  # Compressed data read chunk size7 8 9class BaseStream(io.BufferedIOBase):10    """Mode-checking helper functions."""11 12    def _check_not_closed(self):13        if self.closed:14            raise ValueError("I/O operation on closed file")15 16    def _check_can_read(self):17        if not self.readable():18            raise io.UnsupportedOperation("File not open for reading")19 20    def _check_can_write(self):21        if not self.writable():22            raise io.UnsupportedOperation("File not open for writing")23 24    def _check_can_seek(self):25        if not self.readable():26            raise io.UnsupportedOperation("Seeking is only supported "27                                          "on files open for reading")28        if not self.seekable():29            raise io.UnsupportedOperation("The underlying file object "30                                          "does not support seeking")31 32 33class DecompressReader(io.RawIOBase):34    """Adapts the decompressor API to a RawIOBase reader API"""35 36    def readable(self):37        return True38 39    def __init__(self, fp, decomp_factory, trailing_error=(), **decomp_args):40        self._fp = fp41        self._eof = False42        self._pos = 0  # Current offset in decompressed stream43 44        # Set to size of decompressed stream once it is known, for SEEK_END45        self._size = -146 47        # Save the decompressor factory and arguments.48        # If the file contains multiple compressed streams, each49        # stream will need a separate decompressor object. A new decompressor50        # object is also needed when implementing a backwards seek().51        self._decomp_factory = decomp_factory52        self._decomp_args = decomp_args53        self._decompressor = self._decomp_factory(**self._decomp_args)54 55        # Exception class to catch from decompressor signifying invalid56        # trailing data to ignore57        self._trailing_error = trailing_error58 59    def close(self):60        self._decompressor = None61        return super().close()62 63    def seekable(self):64        return self._fp.seekable()65 66    def readinto(self, b):67        with memoryview(b) as view, view.cast("B") as byte_view:68            data = self.read(len(byte_view))69            byte_view[:len(data)] = data70        return len(data)71 72    def read(self, size=-1):73        if size < 0:74            return self.readall()75 76        if not size or self._eof:77            return b""78        data = None  # Default if EOF is encountered79        # Depending on the input data, our call to the decompressor may not80        # return any data. In this case, try again after reading another block.81        while True:82            if self._decompressor.eof:83                rawblock = (self._decompressor.unused_data or84                            self._fp.read(BUFFER_SIZE))85                if not rawblock:86                    break87                # Continue to next stream.88                self._decompressor = self._decomp_factory(89                    **self._decomp_args)90                try:91                    data = self._decompressor.decompress(rawblock, size)92                except self._trailing_error:93                    # Trailing data isn't a valid compressed stream; ignore it.94                    break95            else:96                if self._decompressor.needs_input:97                    rawblock = self._fp.read(BUFFER_SIZE)98                    if not rawblock:99                        raise EOFError("Compressed file ended before the "100                                       "end-of-stream marker was reached")101                else:102                    rawblock = b""103                data = self._decompressor.decompress(rawblock, size)104            if data:105                break106        if not data:107            self._eof = True108            self._size = self._pos109            return b""110        self._pos += len(data)111        return data112 113    # Rewind the file to the beginning of the data stream.114    def _rewind(self):115        self._fp.seek(0)116        self._eof = False117        self._pos = 0118        self._decompressor = self._decomp_factory(**self._decomp_args)119 120    def seek(self, offset, whence=io.SEEK_SET):121        # Recalculate offset as an absolute file position.122        if whence == io.SEEK_SET:123            pass124        elif whence == io.SEEK_CUR:125            offset = self._pos + offset126        elif whence == io.SEEK_END:127            # Seeking relative to EOF - we need to know the file's size.128            if self._size < 0:129                while self.read(io.DEFAULT_BUFFER_SIZE):130                    pass131            offset = self._size + offset132        else:133            raise ValueError("Invalid value for whence: {}".format(whence))134 135        # Make it so that offset is the number of bytes to skip forward.136        if offset < self._pos:137            self._rewind()138        else:139            offset -= self._pos140 141        # Read and discard data until we reach the desired position.142        while offset > 0:143            data = self.read(min(io.DEFAULT_BUFFER_SIZE, offset))144            if not data:145                break146            offset -= len(data)147 148        return self._pos149 150    def tell(self):151        """Return the current file position."""152        return self._pos153