code: def _get_file_size(self):
          
          file_size = retry(self._retry_count)(_get_content_length)(
              self._session, self.url, self._timeout
          )
          file_size = int(file_size)
          if file_size == 0:
              with io.open(self._file_path, 'a', encoding='utf-8'):
                  pass
          return file_size
docs: Fetches file size by reading the Content-Length header
          for the resource.
          :return: File size.