<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _build_message_body(self, body_size):
 """Build the Message body from the inbound queue. :rtype: str """

        body = bytes()
        while len(body) < body_size:
            if not self._inbound:
                self.check_for_errors()
                sleep(IDLE_WAIT)
                continue
            body_piece = self._inbound.pop(0)
            if not body_piece.value:
                break
            body += body_piece.value
        return body