Create Your First Connected Light using Arduino Yun

#include <SPI.h>
#include <YunClient.h>
#include <PubSubClient.h>
/* ------------------ */
/* SKETCH CREDENTIALS */
/* ------------------ */
char* deviceId     = "<DEVICE-ID>";             // * set your device id (will be the MQTT client username)
char* deviceSecret = "<DEVICE-SECRET>";         // * set your device secret (will be the MQTT client password)
char* outTopic     = "devices/<DEVICE-ID>/set"; // * MQTT channel where physical updates are published
char* inTopic      = "devices/<DEVICE-ID>/get"; // * MQTT channel where lelylan updates are received
char* clientId     = "<CLIENT-ID>";             // * set a random string (max 23 chars, will be the MQTT client id)
/* ------------ */
/* SKETCH LOGIC */
/* ------------ */
/* Server settings */
byte server[] = { 96, 126, 109, 170 }; // MQTT server address
/* Sample payload published to lelylan */
/* The id is the status property id of the basic light /*
/* http://lelylan.github.io/types-dashboard-ng/#/types/518be107ef539711af000001/ */ 
char* payloadOn  = "{\"properties\":[{\"id\":\"518be5a700045e1521000001\",\"value\":\"on\"}]}";
char* payloadOff = "{\"properties\":[{\"id\":\"518be5a700045e1521000001\",\"value\":\"off\"}]}";
/* Yun configuration */
byte mac[] = { 0xA0, 0xA0, 0xBA, 0xAC, 0xAE, 0x12 };
YunClient yun;
/* MQTT communication */
void callback(char* topic, byte* payload, unsigned int length); // subscription callback
PubSubClient client(server, 1883, callback, yun);         // mqtt client
/* Pins configuration */
int inPin = 3; // button
int outPin = 13; // led
/* Button and led logics */
int state = HIGH;     // current state of the output pin
int reading;          // current reading from the input pin
int previous = LOW;   // previous reading from the input pin
long time = 0;        // the last time the output pin was toggled
long debounce = 200;  // the debounce time, increase if the output flickers
/* arduino setup */
void setup() {
  Serial.begin(9600);
  delay(500);
  Serial.println("Start initialization of Yun...");
  Bridge.begin();
  Serial.println("Bridge finished setup");
  Serial.println("Starting connection to lelylan...");
  lelylanConnection();      // MQTT server connection
  pinMode(inPin, INPUT);    // button pin setup
  pinMode(outPin, OUTPUT);  // led pin setup
}
/* arduino loop */
void loop() {
  lelylanConnection();
  char* value;
  reading = digitalRead(inPin);  // read the button state
  // if the input just went from LOW and HIGH and we've waited long enough to ignore
  // any noise on the circuit, toggle the output pin and remember the time
  if (reading == HIGH && previous == LOW && millis() - time > debounce) {
    if (state == LOW) {
      Serial.println("[PHYSICAL] Led turned on");
      lelylanPublish("on");
      state = HIGH;
    } else {
      Serial.println("[PHYSICAL] Led turned off");
      lelylanPublish("off");
      state = LOW;
    }
    time = millis();
  }
  // effectively update the light status
  digitalWrite(outPin, state);
  previous = reading;
}
/* MQTT server connection */
void lelylanConnection() {
  // add reconnection logics
  if (!client.connected()) {
    // connection to MQTT server
    if (client.connect(clientId, deviceId, deviceSecret)) {
      Serial.println("[PHYSICAL] Successfully connected with MQTT");
      lelylanSubscribe(); // topic subscription
    }
  }
  client.loop();
}
/* MQTT publish */
void lelylanPublish(char* value) {
  if (value == "on")
    client.publish(outTopic, payloadOn); // light on
  else
    client.publish(outTopic, payloadOff); // light off
}
/* MQTT subscribe */
void lelylanSubscribe() {
  client.subscribe(inTopic);
}
/* Receive Lelylan message and confirm the physical change */
void callback(char* topic, byte* payload, unsigned int length) {
  // copu the payload content into a char*
  char* json;
  json = (char*) malloc(length + 1);
  memcpy(json, payload, length);
  json[length] = '\0';
  // update the physical status and confirm the executed update
  if (String(payloadOn) == String(json)) {
    Serial.println("[LELYLAN] Led turned on");
    lelylanPublish("on");
    state = HIGH;
  } else {
    Serial.println("[LELYLAN] Led turned off");
    lelylanPublish("off");
    state = LOW;
  }
  digitalWrite(outPin, state);
  free(json);
}