var fs = require('fs');

// function to create file from base64 encoded string
function base64_decode(base64str, file) {
    // create buffer object from base64 encoded string, it is important to tell the constructor that the string is base64 encoded
    var bitmap = new Buffer(base64str, 'base64');
    // write buffer to file
    fs.writeFileSync(file, bitmap);
}

var mqtt = require('mqtt');

var options = {
  username: 'JackRoboticS',
  password:'tlXrjyglDSg69lQxaENkqTX5I6SsBC0ZFSSbBFS8',
  port: 1883,
  host: 'service.anto.io',
  clientId: 'JackRoboticS_API'+Math.random()
};
var client = mqtt.connect(options);
client.on('connect', function () {
 client.subscribe('channel/JackRoboticS/image/image'); // < เลือก subscribe ข้อมูลจาก mqtt
});
client.on('message', function (topic, message) {
 var MSG = message.toString();
 base64_decode(MSG, 'savefilename.png'); //< บันทึกไฟล์ลง disk
});