docs: def WriteFileFooter(self):
      """Writes file footer (finishes the file)."""
  
      if self.cur_file_size != self.cur_info.size:
        raise IOError("Incorrect file size: st_size=%d, but written %d bytes." %
                      (self.cur_info.size, self.cur_file_size))
  
      # TODO(user):pytype: BLOCKSIZE/NUL constants are not visible to type
      # checker.
      # pytype: disable=module-attr
      blocks, remainder = divmod(self.cur_file_size, tarfile.BLOCKSIZE)
      if remainder > 0:
        self._tar_fd.fileobj.write(tarfile.NUL * (tarfile.BLOCKSIZE - remainder))
        blocks += 1
      self._tar_fd.offset += blocks * tarfile.BLOCKSIZE
      # pytype: enable=module-attr
  
      self._ResetState()
  
      return self._stream.GetValueAndReset()