def message_received(&callback)
      if block_given?
        @message_received_callbacks << callback
      else
        @message_received_callbacks.each { |c| c.call }
        if @check_interval > 0
          now = Time.now
          if (now - @last_received) > MIN_RESTART_INACTIVITY_TIMER_INTERVAL
            @last_received = now
            restart_inactivity_timer
          end
        end
      end
      true
    end
def message_received(&callback)
      if block_given?
        @message_received_callbacks << callback
      else
        @message_received_callbacks.each { |c| c.call }
        if @check_interval > 0
          now = Time.now
          if (now - @last_received) > MIN_RESTART_INACTIVITY_TIMER_INTERVAL
            @last_received = now
            restart_inactivity_timer
          end
        end
      end
      true
    end
Update the time this agent last received a request or response message
 and restart the inactivity timer thus deferring the next connectivity check
 Also forward this message receipt notification to any callbacks that have registered

 === Block
 Optional block without parameters that is activated when a message is received

 === Return
 true:: Always return true