arduino-mosquitto-basic-example.ino

#define DEBUG

#ifdef DEBUG
    // https://forum.arduino.cc/index.php?topic=46900.0
    #define DEBUG_PRINT(str) Serial.println(str);
    #define DEBUG_PRINT2(str1, str2) Serial.print(str1); Serial.println(str2);
#else
    #define DEBUG_PRINT(str)
    #define DEBUG_PRINT2(str1, str2)
#endif

#include <UIPEthernet.h>
#include <PubSubClient.h>
#include "include/DebugUtils.h"

#define MQTT_CLIENT_ID   "arduino-client" // replace with desired client name
#define MQTT_SERVER      "mqtt-server.com" // replace with MQTT server or port
#define MQTT_SERVERPORT  1883U // mqtt port
#define MQTT_USERNAME    "my-username" // replace with real username
#define MQTT_PASSWORD    "some-long-password" // replace with real password
#define MQTT_REQUEST_TOPIC  "/request/" // topic via which responses are sent
#define MQTT_RESPONSE_TOPIC "/response/" // topic which we subscribe to for requests

EthernetClient ethClient;
PubSubClient mqttClient;

void setup() {

#ifdef DEBUG
    Serial.begin(9600);
#endif

  DEBUG_PRINT("\n[setup started]");

  initNetworking();
  initMqtt();
}

/** sets up the MQTT client */
void initMqtt() {
  mqttClient.setClient(ethClient);
  mqttClient.setServer(MQTT_SERVER, MQTT_SERVERPORT);
  mqttClient.setCallback(mqttMessageHandler);
}

/** Sets up the network layer */
void initNetworking() {
  // ethernet mac address - must be unique on your network
  uint8_t  mymac[6] = { 0x74,0x69,0x69,0x2D,0x30,0x31 };

  if(Ethernet.begin(mymac)) {
    DEBUG_PRINT(F("=> DHCP lease issued"));
    DEBUG_PRINT2(F("   IP: "), Ethernet.localIP());
    DEBUG_PRINT2(F("   GW: "), Ethernet.gatewayIP());
    DEBUG_PRINT2(F("   DNS:"), Ethernet.dnsServerIP());
  } else {
    DEBUG_PRINT(F("=> failed to get DHCP lease"));
  }

  // Allow the hardware to sort itself out
  delay(1500);
}

void loop() {
  if (!mqttClient.connected()) {
    mqttReconnect();
  }

  mqttClient.loop();
}

/** connects to MQTT server */
void mqttReconnect() {
  if(mqttClient.connect(MQTT_CLIENT_ID, MQTT_USERNAME, MQTT_PASSWORD)) {

    DEBUG_PRINT("\n=> MQTT connected");
    DEBUG_PRINT2("\n=> subscribed to ", MQTT_REQUEST_TOPIC);
    mqttClient.subscribe(MQTT_REQUEST_TOPIC);

    if(mqttClient.publish(MQTT_RESPONSE_TOPIC, "Hello world! I'm listening...")) {
      DEBUG_PRINT("\n=> MQTT successfull publish");
    } else {
      DEBUG_PRINT("\n=> MQTT publish failed");
    }
  } else {
    DEBUG_PRINT("\n=> MQTT connection failed");
  }
}

/** Handles messages received via MQTT */
void mqttMessageHandler(char* topic, byte* payload, unsigned int length) {
  char buff[length+1];

  memcpy(buff, payload, length);
  buff[length] = 0; // string terminator

  DEBUG_PRINT2("\n=> MQTT message received in topic", topic);
  DEBUG_PRINT2("\n   message=", buff);
  
  mqttClient.publish(MQTT_RESPONSE_TOPIC, "Thank you for your message!");
}