code: def handle_unsuback(self):
          
          self.logger.info("UNSUBACK received")
  
          ret, mid = self.in_packet.read_uint16()
  
          if ret != NC.ERR_SUCCESS:
              return ret
  
          evt = event.EventUnsuback(mid)
          self.push_event(evt)
  
          return NC.ERR_SUCCESS
docs: Handle incoming UNSUBACK packet.