How to check if the MQTT connection is still active?

Question

I am wondering if there is a way to check and see if the MQTT connection is still active.

The reason for this is that I am having trouble with the connection dropping after a short while and not seeming to reconnect.

/*
 ArduinoMqttClient - WiFi Simple Sender
 This example connects to a MQTT broker and publishes a message to
 a topic once a second.
 The circuit:
 - Arduino MKR 1000, MKR 1010 or Uno WiFi Rev2 board
 This example code is in the public domain.
*/
#include <ArduinoMqttClient.h>
#include <MKRGSM.h>
#include "arduino_secrets.h"
// Please enter your sensitive data in the Secret tab or arduino_secrets.h
// PIN Number
const char PINNUMBER[] = SECRET_PINNUMBER;
// APN data
const char GPRS_APN[] = SECRET_GPRS_APN;
const char GPRS_LOGIN[] = SECRET_GPRS_LOGIN;
const char GPRS_PASSWORD[] = SECRET_GPRS_PASSWORD;
GSMClient client;
GPRS gprs;
GSM gsmAccess;
MqttClient mqttClient(client);
const char broker[] = "*****";
int port = 1883;
const char topic[] = "Tempdata";
const long interval = 500000;
unsigned long previousMillis = 0;
float SERIESRESISTOR = 9.87;
float TEMPERATURENOMINAL = 25.0;
float BCOEFFICIENT = 3540.0;
float thermistor = 0.0;
float THERMISTORNOMINAL = 10;
int count = 0;
void setup() {
 // Initialize serial and wait for port to open:
 Serial.begin(9600);
 Serial.println("Starting Arduino web client.");
 // connection state
 bool connected = false;
 // After starting the modem with GSM.begin()
 // attach the shield to the GPRS network with the APN, login and password
 while (!connected) {
 if ((gsmAccess.begin(PINNUMBER) == GSM_READY) &&
 (gprs.attachGPRS(GPRS_APN, GPRS_LOGIN, GPRS_PASSWORD) == GPRS_READY)) {
 connected = true;
 } else {
 Serial.println("Not connected");
 delay(1000);
 }
 }
 Serial.println("You're connected to the network");
 Serial.println();
 // You can provide a unique client ID, if not set the library uses Arduino-millis()
 // Each client must have a unique client ID
 mqttClient.setId("pump-house-gsm");
 // You can provide a username and password for authentication
 //mqttClient.setUsernamePassword("****", "****");
 Serial.print("Attempting to connect to the MQTT broker: ");
 Serial.println(broker);
 if (!mqttClient.connect(broker, port)) {
 Serial.print("MQTT connection failed! Error code = ");
 Serial.println(mqttClient.connectError());
 while (1);
 }
 Serial.println("You're connected to the MQTT broker!");
 Serial.println();
 // set analog resulotion to 12
 analogReadResolution(12);
}
void loop() {
 // call poll() regularly to allow the library to send MQTT keep alives which
 // avoids being disconnected by the broker
 mqttClient.poll();
 // to avoid having delays in loop, we'll use the strategy from BlinkWithoutDelay
 // see: File -> Examples -> 02.Digital -> BlinkWithoutDelay for more info
 unsigned long currentMillis = millis();
 if (currentMillis - previousMillis >= interval) {
 /*Read analog outputof NTC module,
 i.e the voltage across the thermistor */
 float average = ((float)analogRead(A0) / 4095.0) * 3.3;
 average = (average * SERIESRESISTOR) / (3.3 - average);
 float steinhart;
 steinhart = average / THERMISTORNOMINAL; // (R/Ro)
 steinhart = log(steinhart); // ln(R/Ro)
 steinhart /= BCOEFFICIENT; // 1/B * ln(R/Ro)
 steinhart += 1.0 / (TEMPERATURENOMINAL + 273.15); // + (1/To)
 steinhart = 1.0 / steinhart; // Invert
 steinhart -= 273.15; // convert absolute temp to C
 // save the last time a message was sent
 previousMillis = currentMillis;
 // Keep track of times a message was sent
 // this is to reconnect every hour.
 count = count + 1;
 // send message, the Print interface can be used to set the message contents
 mqttClient.beginMessage(topic);
 mqttClient.print("The temperature is ");
 mqttClient.print(steinhart);
 mqttClient.endMessage();
 }
}

Maybe endMessage, beginMessage, or poll has a return that says it has failed to send a message?

I've looked at endMessage and beginMessage and it does not seem like it to me, but poll is much more complicated and I can't really tell.

Answer 1

I found the solution with the connected function included in the ArduinoMqttClient (found it browsing the library code).

Here is a code snippet showing what I added:

...
...
if (currentMillis - previousMillis >= interval) {
 if (!mqttClient.connected()) {
 if (mqttClient.connect(broker, port)) {
 Serial.println("reconnected");
 }
 }
 /*Read analog outputof NTC module,
 i.e the voltage across the thermistor */
 float average = ((float)analogRead(A0) / 4095.0) * 3.3;
...
...

It is working so far!