MQTT is lightweight pub/sub messaging protocol for IoT/M2M. MQTT target is large scale pub/sub system, used on Facebook Messenger and others(not for the message queue like a RabbitMQ/AMQP…etc).  MQTT for Arduino is already developed as pubsubclient, but Arduino like open source system “Spark.io” don’t have MQTT library.  So I made MQTT for Spark.io based on pubsubclient. Thanks for knolleary.

MQTT for Spark.

#include "MQTT.h"

void callback(char* topic, byte* payload, unsigned int length);
MQTT client("server_name", 1883, callback);

// recieve message
void callback(char* topic, byte* payload, unsigned int length) {
    char p[length + 1];
    memcpy(p, payload, length);
    p[length] = NULL;
    String message(p);

    if (message.equals("RED"))    
        RGB.color(255, 0, 0);
    else if (message.equals("GREEN"))    
        RGB.color(0, 255, 0);
    else if (message.equals("BLUE"))    
        RGB.color(0, 0, 255);
    else    
        RGB.color(255, 255, 255);
    delay(1000);
}


void setup() {
    RGB.control(true);
    
    // connect to the MQTT server
    client.connect("sparkclient");

    // publish/subscribe
    if (client.isConnected()) {
        client.publish("outTopic","hello world");
        client.subscribe("inTopic");
    }
}

void loop() {
    if (client.isConnected())
        client.loop();
}