Keepalive timer on mqtt of nodemcu (esp8266) is not responding

Question

Dears, I am trying to use mqtt on esp8266 build on nodemcu. I am currently using a custom build (https://nodemcu-build.com/index.php)

modules used: adc,enduser_setup,file,gpio,http,mqtt,net,node,ow,pwm,tmr,uart,wifi

version:powered by Lua 5.1.4 on SDK 1.5.1(e67da894)

function connect_to_mqtt_broker()


    print("Connecting to broker...")
    m:connect(BROKER, PORT, 0, 1, function(client) 
                                    print("connected") 
                                    print("["..tmr.time().."(s)] - Client connected to broker: "..BROKER)
                                    m:subscribe(SUB_TOPIC,0, function(conn) 
                                        print("Subscribed to "..SUB_TOPIC.." topic")
                                        led(0,204,0,150) 
                                    end)
                                    m:publish(PUB_TOPIC,"Hello from: "..node.chipid()..RESTART_REASON,0,0, function(conn) 
                                        print("sent")
                                    end)
                                  end, 
                                  function(client, reason) 
                                    print("failed reason: "..reason)
                                  end)

end

---

---MQTT client---
print("--------------> Create mqtt clinet")
--set up MQTT client
-- init mqtt client with keepalive timer 120sec
m = mqtt.Client("ESP"..node.chipid(), KEEP_ALIVE_TMR, USER, PASSWORD)
m:lwt(PUB_TOPIC, "offline", 0, 0)
m:on("offline", function(conn) 
        print("["..tmr.time().."(s)] - Mqtt client gone offline")

end)
m:on("message", function(conn, topic, data) 
        --receive_data(data, topic)
        print("Data received: "..data) 
        led(200,50,50,30)
        receive_data(data, topic)
        led(0,204,0,150)
end)

So at the initialization of the of the program I am calling connect_to_mqtt_broker(), which is working perfectly and I can subscribe and publish to topics.

The problem is that the keepalive timer is not correct. Let me explain that with an example. I set KEEP_ALIVE_TMR = 120s and after the esp8266 connected successfully to mqtt broker I disabled the wifi on my router and start counting seconds. According to KEEP_ALIVE_TMR the offline event:

m:on("offline", function(conn) 
        print("["..tmr.time().."(s)] - Mqtt client gone offline")

end)

should fire exactly 120 seconds from the moment I have disable WiFi, but for some unknown reason this won't happen. Usually the event fires up about 10-15 minutes later. I am struggling to understand the reason of this delay with no success. Do you have any ideas why this strange thing happens?

Answer 1

I've also faced with the same issue when autoreconnect flag was set. This flag breaks the run of offline event of connection between broker.

Try it without setting autoreconnect, whose default is 0 :

m:connect(BROKER, PORT, 0, function(client) 

Answer 2

If you do your testing by turning your mqtt broker on/off, and it works. But not by switching your wifi connections, then it is the nodemcu's mqtt library problem.

I believe that there is no such mqtt offline/disconnect event on wifi disconnection. Here it is the workaround by add connection's watchdog.

tmr.alarm(1, 3000, 1, function()
  if wifi.sta.getip() == nil then
   --mark as mqtt restart needed
   restart = true
 else
   -- wifi reconnect detected then restart mqtt connections
   if restart == true then
     --reset flag, clean object, init for a new one
     restart = false
     m = nil
     mqtt_init()
     connect()
   end
 end
end)

Here it is the full code example