ESP32 MQTT PubSub Client

esp32_mqtt_client.ino

#include <Wifi.h>
#include <PubSubClient.h>

#ifndef STASSID
#define STASSID ""
#define STAPSK  ""
#endif

const char* ssid     = STASSID;
const char* password = STAPSK;
const int LED = 2;

// Broker
const char* mqtt_server = "";

WiFiClient wifiClient;
PubSubClient client(wifiClient);

void setup() {
  setup_wifi();
  client.setServer(mqtt_server, 1883);
  client.setCallback(callback);

  pinMode(LED, OUTPUT);

}

void setup_wifi() {
  Serial.begin(115200);

  // We start by connecting to a WiFi network

  Serial.println();
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);

  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}

void callback(char* topic, byte* message, unsigned int length) {
  Serial.print("Message arrived on topic: ");
  Serial.print(topic);
  Serial.print(". Message: ");
  String msg;

  for (int i = 0; i < length; i++) {
    Serial.print((char)message[i]);
    msg += (char)message[i];
  }
  Serial.println();

  if (String(topic) == "temptron/output") {
    Serial.print("Changing output to ");
    if (msg == "on") {
      Serial.println("on");
      digitalWrite(LED, HIGH);
    }
    else if (msg == "off") {
      Serial.println("off");
      digitalWrite(LED, LOW);
    }
  }

}

void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Attempt to connect
    String clientId = "ESP8266Client-";
    clientId += String(random(0xffff), HEX);
    if (client.connect(clientId.c_str())) {
      Serial.println("connected");
      // Subscribe
      client.subscribe("temptron/output");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

void loop() {
  if (!client.connected()) {
    reconnect();
  }
  client.loop();
}