def get_meta_data(self, request_adu):
return {<EOL>'<STR_LIT>': struct.unpack('<STR_LIT>', request_adu[:<NUM_LIT:1>])[<NUM_LIT:0>],<EOL>}<EOL>
Extract MBAP header from request adu and return it. The dict has
        4 keys: transaction_id, protocol_id, length and unit_id.

        :param request_adu: A bytearray containing request ADU.
        :return: Dict with meta data of request.