code: def read_length_block(fp, fmt='I', padding=1):
      
      length = read_fmt(fmt, fp)[0]
      data = fp.read(length)
      assert len(data) == length, (len(data), length)
      read_padding(fp, length, padding)
      return data
docs: Read a block of data with a length marker at the beginning.
  
      :param fp: file-like
      :param fmt: format of the length marker
      :return: bytes object