<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_content_body(self, message_uuid, body_size):
 """Get Content Body using RPC requests. :param str uuid_body: Rpc Identifier. :param int body_size: Content Size. :rtype: str """

        body = bytes()
        while len(body) < body_size:
            body_piece = self._channel.rpc.get_request(message_uuid, raw=True,
                                                       multiple=True)
            if not body_piece.value:
                break
            body += body_piece.value
        return body