A simple script that publishes that it is online when it starts and publishes that it is offline when it quits. Using mqttjs.

README.md

purpose

Lively.js is a simple illustration of using MQTT as a device presence indicator

installation

1. git clone git://gist.github.com/1832048.git lively
2. cd lively
3. npm install .
4. node lively.js ...

functionality

1. Connects to broker with a will topic set to --topic and will payload set to --not-present
2. Publishes --present to --topic
3. Pings until dead
4. Once dead, publishes --not-present to --topic or relies on the broker to do so.

lively.js

var mqtt = require('mqttjs')
  , optimist = require('optimist');

var argv = optimist
    .usage('lively - a script that makes itself look alive\nnode lively.js -t <topic> -h <host> -p <port>')
          
    .options('t', {
      demand: true
    , describe: 'Topic to publish status messages on'
    , alias: 'topic'
    })
    .options('h', {
      demand: true
    , describe: 'Broker to publish status messages on'
    , alias: 'host'
    })
    .options('c', {
      demand: true
    , describe: 'The ID of the lively client'
    , alias: 'id'
    })
    .options('k', {
      default: 1000
    , describe: 'Keepalive period'
    , alias: 'keepalive'
    })
    .options('p', {
      default: 1883
    , describe: 'Broker port'
    , alias: 'port'
    })
    .options('present', {
      default: '1'
    , describe: 'The \'present\' message to publish to the broker'
   })
    .options('not-present', {
      default: '0'
    , describe: 'The \'not present\' message to publish to the broker'
    })
    .argv;

var host = argv.h
  , topic = argv.t
  , cid = argv.c
  , keepalive = argv.k
  , pr = argv['present']
  , np = argv['not-present']
  , port = argv.p;

console.dir(argv);

function statusPacket(status) {
  return {
    topic: topic
  , payload: status
  , retain: true
  }
}

var client = mqtt.createClient(port, host, function(err, client) {
  if (err) { console.log(err); process.exit(1); }
  client.connect({client: cid, will: statusPacket(np), keepalive: keepalive});
  client.on('connack', function(packet) {
    if (packet.returnCode !== 0) return console.log('Bad code');
    client.publish(statusPacket(pr));
  });
  client.on('pingresp', function(packet) {
    console.log('Ping resp received');
  });
  client.interval = setInterval(function() {
    client.pingreq();
  }, keepalive);
});

function handleSignal(signal) {
  process.on(signal, function() {
    clearInterval(client.interval);
    client.publish(statusPacket(np));
    client.disconnect();
  });
}

handleSignal('SIGHUP');
handleSignal('SIGINT');
handleSignal('SIGQUIT');
handleSignal('SIGTERM');

package.json

{
  "author": "Adam Rudd <adam.rudd@uqconnect.edu.au>",
  "name": "lively",
  "description": "A simple script that publishes that it is online when it starts and publishes that it is offline when it quits. Using mqttjs.",
  "version": "0.0.1",
  "repository": {
    "type": "git",
    "url": "git://gist.github.com/1832048.git"
  },
  "main": "lively.js",
  "engines": {
    "node": "~0.6.5"
  },
  "dependencies": {
    "mqttjs": ">0.1.3",
    "optimist": ">=0.3.1"
  },
  "devDependencies": {},
  "optionalDependencies": {}
}