web-socket/node_modules/mqtt/lib/client.js

'use strict'

/**
 * Module dependencies
 */
var events = require('events')
var Store = require('./store')
var eos = require('end-of-stream')
var mqttPacket = require('mqtt-packet')
var Writable = require('readable-stream').Writable
var inherits = require('inherits')
var reInterval = require('reinterval')
var validations = require('./validations')
var xtend = require('xtend')
var setImmediate = global.setImmediate || function (callback) {
  // works in node v0.8
  process.nextTick(callback)
}
var defaultConnectOptions = {
  keepalive: 60,
  reschedulePings: true,
  protocolId: 'MQTT',
  protocolVersion: 4,
  reconnectPeriod: 1000,
  connectTimeout: 30 * 1000,
  clean: true,
  resubscribe: true
}

function defaultId () {
  return 'mqttjs_' + Math.random().toString(16).substr(2, 8)
}

function sendPacket (client, packet, cb) {
  client.emit('packetsend', packet)

  var result = mqttPacket.writeToStream(packet, client.stream)

  if (!result && cb) {
    client.stream.once('drain', cb)
  } else if (cb) {
    cb()
  }
}

function flush (queue) {
  if (queue) {
    Object.keys(queue).forEach(function (messageId) {
      if (typeof queue[messageId] === 'function') {
        queue[messageId](new Error('Connection closed'))
        delete queue[messageId]
      }
    })
  }
}

function storeAndSend (client, packet, cb) {
  client.outgoingStore.put(packet, function storedPacket (err) {
    if (err) {
      return cb && cb(err)
    }
    sendPacket(client, packet, cb)
  })
}

function nop () {}

/**
 * MqttClient constructor
 *
 * @param {Stream} stream - stream
 * @param {Object} [options] - connection options
 * (see Connection#connect)
 */
function MqttClient (streamBuilder, options) {
  var k
  var that = this

  if (!(this instanceof MqttClient)) {
    return new MqttClient(streamBuilder, options)
  }

  this.options = options || {}

  // Defaults
  for (k in defaultConnectOptions) {
    if (typeof this.options[k] === 'undefined') {
      this.options[k] = defaultConnectOptions[k]
    } else {
      this.options[k] = options[k]
    }
  }

  this.options.clientId = (typeof this.options.clientId === 'string') ? this.options.clientId : defaultId()

  this.streamBuilder = streamBuilder

  // Inflight message storages
  this.outgoingStore = this.options.outgoingStore || new Store()
  this.incomingStore = this.options.incomingStore || new Store()

  // Should QoS zero messages be queued when the connection is broken?
  this.queueQoSZero = this.options.queueQoSZero === undefined ? true : this.options.queueQoSZero

  // map of subscribed topics to support reconnection
  this._resubscribeTopics = {}

  // map of a subscribe messageId and a topic
  this.messageIdToTopic = {}

  // Ping timer, setup in _setupPingTimer
  this.pingTimer = null
  // Is the client connected?
  this.connected = false
  // Are we disconnecting?
  this.disconnecting = false
  // Packet queue
  this.queue = []
  // connack timer
  this.connackTimer = null
  // Reconnect timer
  this.reconnectTimer = null
  // MessageIDs starting with 1
  this.nextId = Math.floor(Math.random() * 65535)

  // Inflight callbacks
  this.outgoing = {}

  // Mark connected on connect
  this.on('connect', function () {
    if (this.disconnected) {
      return
    }

    this.connected = true
    var outStore = null
    outStore = this.outgoingStore.createStream()

    // Control of stored messages
    outStore.once('readable', function () {
      function storeDeliver () {
        var packet = outStore.read(1)
        var cb

        if (!packet) {
          return
        }

        // Avoid unnecessary stream read operations when disconnected
        if (!that.disconnecting && !that.reconnectTimer && that.options.reconnectPeriod > 0) {
          outStore.read(0)
          cb = that.outgoing[packet.messageId]
          that.outgoing[packet.messageId] = function (err, status) {
            // Ensure that the original callback passed in to publish gets invoked
            if (cb) {
              cb(err, status)
            }

            storeDeliver()
          }
          that._sendPacket(packet)
        } else if (outStore.destroy) {
          outStore.destroy()
        }
      }
      storeDeliver()
    }).on('error', this.emit.bind(this, 'error'))
  })

  // Mark disconnected on stream close
  this.on('close', function () {
    this.connected = false
    clearTimeout(this.connackTimer)
  })

  // Setup ping timer
  this.on('connect', this._setupPingTimer)

  // Send queued packets
  this.on('connect', function () {
    var queue = this.queue

    function deliver () {
      var entry = queue.shift()
      var packet = null

      if (!entry) {
        return
      }

      packet = entry.packet

      that._sendPacket(
        packet,
        function (err) {
          if (entry.cb) {
            entry.cb(err)
          }
          deliver()
        }
      )
    }

    deliver()
  })

  var firstConnection = true
  // resubscribe
  this.on('connect', function () {
    if (!firstConnection &&
        this.options.clean &&
        Object.keys(this._resubscribeTopics).length > 0) {
      if (this.options.resubscribe) {
        this._resubscribeTopics.resubscribe = true
        this.subscribe(this._resubscribeTopics)
      } else {
        this._resubscribeTopics = {}
      }
    }

    firstConnection = false
  })

  // Clear ping timer
  this.on('close', function () {
    if (that.pingTimer !== null) {
      that.pingTimer.clear()
      that.pingTimer = null
    }
  })

  // Setup reconnect timer on disconnect
  this.on('close', this._setupReconnect)

  events.EventEmitter.call(this)

  this._setupStream()
}
inherits(MqttClient, events.EventEmitter)

/**
 * setup the event handlers in the inner stream.
 *
 * @api private
 */
MqttClient.prototype._setupStream = function () {
  var connectPacket
  var that = this
  var writable = new Writable()
  var parser = mqttPacket.parser(this.options)
  var completeParse = null
  var packets = []

  this._clearReconnect()

  this.stream = this.streamBuilder(this)

  parser.on('packet', function (packet) {
    packets.push(packet)
  })

  function nextTickWork () {
    process.nextTick(work)
  }

  function work () {
    var packet = packets.shift()
    var done = completeParse

    if (packet) {
      that._handlePacket(packet, nextTickWork)
    } else {
      completeParse = null
      done()
    }
  }

  writable._write = function (buf, enc, done) {
    completeParse = done
    parser.parse(buf)
    work()
  }

  this.stream.pipe(writable)

  // Suppress connection errors
  this.stream.on('error', nop)

  // Echo stream close
  eos(this.stream, this.emit.bind(this, 'close'))

  // Send a connect packet
  connectPacket = Object.create(this.options)
  connectPacket.cmd = 'connect'
  // avoid message queue
  sendPacket(this, connectPacket)

  // Echo connection errors
  parser.on('error', this.emit.bind(this, 'error'))

  // many drain listeners are needed for qos 1 callbacks if the connection is intermittent
  this.stream.setMaxListeners(1000)

  clearTimeout(this.connackTimer)
  this.connackTimer = setTimeout(function () {
    that._cleanUp(true)
  }, this.options.connectTimeout)
}

MqttClient.prototype._handlePacket = function (packet, done) {
  this.emit('packetreceive', packet)

  switch (packet.cmd) {
    case 'publish':
      this._handlePublish(packet, done)
      break
    case 'puback':
    case 'pubrec':
    case 'pubcomp':
    case 'suback':
    case 'unsuback':
      this._handleAck(packet)
      done()
      break
    case 'pubrel':
      this._handlePubrel(packet, done)
      break
    case 'connack':
      this._handleConnack(packet)
      done()
      break
    case 'pingresp':
      this._handlePingresp(packet)
      done()
      break
    default:
      // do nothing
      // maybe we should do an error handling
      // or just log it
      break
  }
}

MqttClient.prototype._checkDisconnecting = function (callback) {
  if (this.disconnecting) {
    if (callback) {
      callback(new Error('client disconnecting'))
    } else {
      this.emit('error', new Error('client disconnecting'))
    }
  }
  return this.disconnecting
}

/**
 * publish - publish <message> to <topic>
 *
 * @param {String} topic - topic to publish to
 * @param {String, Buffer} message - message to publish
 * @param {Object} [opts] - publish options, includes:
 *    {Number} qos - qos level to publish on
 *    {Boolean} retain - whether or not to retain the message
 *    {Boolean} dup - whether or not mark a message as duplicate
 * @param {Function} [callback] - function(err){}
 *    called when publish succeeds or fails
 * @returns {MqttClient} this - for chaining
 * @api public
 *
 * @example client.publish('topic', 'message');
 * @example
 *     client.publish('topic', 'message', {qos: 1, retain: true, dup: true});
 * @example client.publish('topic', 'message', console.log);
 */
MqttClient.prototype.publish = function (topic, message, opts, callback) {
  var packet

  // .publish(topic, payload, cb);
  if (typeof opts === 'function') {
    callback = opts
    opts = null
  }

  // default opts
  var defaultOpts = {qos: 0, retain: false, dup: false}
  opts = xtend(defaultOpts, opts)

  if (this._checkDisconnecting(callback)) {
    return this
  }

  packet = {
    cmd: 'publish',
    topic: topic,
    payload: message,
    qos: opts.qos,
    retain: opts.retain,
    messageId: this._nextId(),
    dup: opts.dup
  }

  switch (opts.qos) {
    case 1:
    case 2:

      // Add to callbacks
      this.outgoing[packet.messageId] = callback || nop
      this._sendPacket(packet)
      break
    default:
      this._sendPacket(packet, callback)
      break
  }

  return this
}

/**
 * subscribe - subscribe to <topic>
 *
 * @param {String, Array, Object} topic - topic(s) to subscribe to, supports objects in the form {'topic': qos}
 * @param {Object} [opts] - optional subscription options, includes:
 *    {Number} qos - subscribe qos level
 * @param {Function} [callback] - function(err, granted){} where:
 *    {Error} err - subscription error (none at the moment!)
 *    {Array} granted - array of {topic: 't', qos: 0}
 * @returns {MqttClient} this - for chaining
 * @api public
 * @example client.subscribe('topic');
 * @example client.subscribe('topic', {qos: 1});
 * @example client.subscribe({'topic': 0, 'topic2': 1}, console.log);
 * @example client.subscribe('topic', console.log);
 */
MqttClient.prototype.subscribe = function () {
  var packet
  var args = Array.prototype.slice.call(arguments)
  var subs = []
  var obj = args.shift()
  var resubscribe = obj.resubscribe
  var callback = args.pop() || nop
  var opts = args.pop()
  var invalidTopic
  var that = this

  delete obj.resubscribe

  if (typeof obj === 'string') {
    obj = [obj]
  }

  if (typeof callback !== 'function') {
    opts = callback
    callback = nop
  }

  invalidTopic = validations.validateTopics(obj)
  if (invalidTopic !== null) {
    setImmediate(callback, new Error('Invalid topic ' + invalidTopic))
    return this
  }

  if (this._checkDisconnecting(callback)) {
    return this
  }

  var defaultOpts = { qos: 0 }
  opts = xtend(defaultOpts, opts)

  if (Array.isArray(obj)) {
    obj.forEach(function (topic) {
      if (that._resubscribeTopics[topic] < opts.qos ||
          !that._resubscribeTopics.hasOwnProperty(topic) ||
          resubscribe) {
        subs.push({
          topic: topic,
          qos: opts.qos
        })
      }
    })
  } else {
    Object
      .keys(obj)
      .forEach(function (k) {
        if (that._resubscribeTopics[k] < obj[k] ||
            !that._resubscribeTopics.hasOwnProperty(k) ||
            resubscribe) {
          subs.push({
            topic: k,
            qos: obj[k]
          })
        }
      })
  }

  packet = {
    cmd: 'subscribe',
    subscriptions: subs,
    qos: 1,
    retain: false,
    dup: false,
    messageId: this._nextId()
  }

  if (!subs.length) {
    callback(null, [])
    return
  }

  // subscriptions to resubscribe to in case of disconnect
  if (this.options.resubscribe) {
    var topics = []
    subs.forEach(function (sub) {
      if (that.options.reconnectPeriod > 0) {
        that._resubscribeTopics[sub.topic] = sub.qos
        topics.push(sub.topic)
      }
    })
    that.messageIdToTopic[packet.messageId] = topics
  }

  this.outgoing[packet.messageId] = function (err, packet) {
    if (!err) {
      var granted = packet.granted
      for (var i = 0; i < granted.length; i += 1) {
        subs[i].qos = granted[i]
      }
    }

    callback(err, subs)
  }

  this._sendPacket(packet)

  return this
}

/**
 * unsubscribe - unsubscribe from topic(s)
 *
 * @param {String, Array} topic - topics to unsubscribe from
 * @param {Function} [callback] - callback fired on unsuback
 * @returns {MqttClient} this - for chaining
 * @api public
 * @example client.unsubscribe('topic');
 * @example client.unsubscribe('topic', console.log);
 */
MqttClient.prototype.unsubscribe = function (topic, callback) {
  var packet = {
    cmd: 'unsubscribe',
    qos: 1,
    messageId: this._nextId()
  }
  var that = this

  callback = callback || nop

  if (this._checkDisconnecting(callback)) {
    return this
  }

  if (typeof topic === 'string') {
    packet.unsubscriptions = [topic]
  } else if (typeof topic === 'object' && topic.length) {
    packet.unsubscriptions = topic
  }

  if (this.options.resubscribe) {
    packet.unsubscriptions.forEach(function (topic) {
      delete that._resubscribeTopics[topic]
    })
  }

  this.outgoing[packet.messageId] = callback

  this._sendPacket(packet)

  return this
}

/**
 * end - close connection
 *
 * @returns {MqttClient} this - for chaining
 * @param {Boolean} force - do not wait for all in-flight messages to be acked
 * @param {Function} cb - called when the client has been closed
 *
 * @api public
 */
MqttClient.prototype.end = function (force, cb) {
  var that = this

  if (typeof force === 'function') {
    cb = force
    force = false
  }

  function closeStores () {
    that.disconnected = true
    that.incomingStore.close(function () {
      that.outgoingStore.close(function () {
        if (cb) {
          cb.apply(null, arguments)
        }
        that.emit('end')
      })
    })
    if (that._deferredReconnect) {
      that._deferredReconnect()
    }
  }

  function finish () {
    // defer closesStores of an I/O cycle,
    // just to make sure things are
    // ok for websockets
    that._cleanUp(force, setImmediate.bind(null, closeStores))
  }

  if (this.disconnecting) {
    return this
  }

  this._clearReconnect()

  this.disconnecting = true

  if (!force && Object.keys(this.outgoing).length > 0) {
    // wait 10ms, just to be sure we received all of it
    this.once('outgoingEmpty', setTimeout.bind(null, finish, 10))
  } else {
    finish()
  }

  return this
}

/**
 * removeOutgoingMessage - remove a message in outgoing store
 * the outgoing callback will be called withe Error('Message removed') if the message is removed
 *
 * @param {Number} mid - messageId to remove message
 * @returns {MqttClient} this - for chaining
 * @api public
 *
 * @example client.removeOutgoingMessage(client.getLastMessageId());
 */
MqttClient.prototype.removeOutgoingMessage = function (mid) {
  var cb = this.outgoing[mid]
  delete this.outgoing[mid]
  this.outgoingStore.del({messageId: mid}, function () {
    cb(new Error('Message removed'))
  })
  return this
}

/**
 * reconnect - connect again using the same options as connect()
 *
 * @param {Object} [opts] - optional reconnect options, includes:
 *    {Store} incomingStore - a store for the incoming packets
 *    {Store} outgoingStore - a store for the outgoing packets
 *    if opts is not given, current stores are used
 * @returns {MqttClient} this - for chaining
 *
 * @api public
 */
MqttClient.prototype.reconnect = function (opts) {
  var that = this
  var f = function () {
    if (opts) {
      that.options.incomingStore = opts.incomingStore
      that.options.outgoingStore = opts.outgoingStore
    } else {
      that.options.incomingStore = null
      that.options.outgoingStore = null
    }
    that.incomingStore = that.options.incomingStore || new Store()
    that.outgoingStore = that.options.outgoingStore || new Store()
    that.disconnecting = false
    that.disconnected = false
    that._deferredReconnect = null
    that._reconnect()
  }

  if (this.disconnecting && !this.disconnected) {
    this._deferredReconnect = f
  } else {
    f()
  }
  return this
}

/**
 * _reconnect - implement reconnection
 * @api privateish
 */
MqttClient.prototype._reconnect = function () {
  this.emit('reconnect')
  this._setupStream()
}

/**
 * _setupReconnect - setup reconnect timer
 */
MqttClient.prototype._setupReconnect = function () {
  var that = this

  if (!that.disconnecting && !that.reconnectTimer && (that.options.reconnectPeriod > 0)) {
    if (!this.reconnecting) {
      this.emit('offline')
      this.reconnecting = true
    }
    that.reconnectTimer = setInterval(function () {
      that._reconnect()
    }, that.options.reconnectPeriod)
  }
}

/**
 * _clearReconnect - clear the reconnect timer
 */
MqttClient.prototype._clearReconnect = function () {
  if (this.reconnectTimer) {
    clearInterval(this.reconnectTimer)
    this.reconnectTimer = null
  }
}

/**
 * _cleanUp - clean up on connection end
 * @api private
 */
MqttClient.prototype._cleanUp = function (forced, done) {
  if (done) {
    this.stream.on('close', done)
  }

  if (forced) {
    if ((this.options.reconnectPeriod === 0) && this.options.clean) {
      flush(this.outgoing)
    }
    this.stream.destroy()
  } else {
    this._sendPacket(
      { cmd: 'disconnect' },
      setImmediate.bind(
        null,
        this.stream.end.bind(this.stream)
      )
    )
  }

  if (!this.disconnecting) {
    this._clearReconnect()
    this._setupReconnect()
  }

  if (this.pingTimer !== null) {
    this.pingTimer.clear()
    this.pingTimer = null
  }

  if (done && !this.connected) {
    this.stream.removeListener('close', done)
    done()
  }
}

/**
 * _sendPacket - send or queue a packet
 * @param {String} type - packet type (see `protocol`)
 * @param {Object} packet - packet options
 * @param {Function} cb - callback when the packet is sent
 * @api private
 */
MqttClient.prototype._sendPacket = function (packet, cb) {
  if (!this.connected) {
    if (((packet.qos || 0) === 0 && this.queueQoSZero) || packet.cmd !== 'publish') {
      this.queue.push({ packet: packet, cb: cb })
    } else if (packet.qos > 0) {
      cb = this.outgoing[packet.messageId]
      this.outgoingStore.put(packet, function (err) {
        if (err) {
          return cb && cb(err)
        }
      })
    } else if (cb) {
      cb(new Error('No connection to broker'))
    }

    return
  }

  // When sending a packet, reschedule the ping timer
  this._shiftPingInterval()

  if (packet.cmd !== 'publish') {
    sendPacket(this, packet, cb)
    return
  }

  switch (packet.qos) {
    case 2:
    case 1:
      storeAndSend(this, packet, cb)
      break
    /**
     * no need of case here since it will be caught by default
     * and jshint comply that before default it must be a break
     * anyway it will result in -1 evaluation
     */
    case 0:
      /* falls through */
    default:
      sendPacket(this, packet, cb)
      break
  }
}

/**
 * _setupPingTimer - setup the ping timer
 *
 * @api private
 */
MqttClient.prototype._setupPingTimer = function () {
  var that = this

  if (!this.pingTimer && this.options.keepalive) {
    this.pingResp = true
    this.pingTimer = reInterval(function () {
      that._checkPing()
    }, this.options.keepalive * 1000)
  }
}

/**
 * _shiftPingInterval - reschedule the ping interval
 *
 * @api private
 */
MqttClient.prototype._shiftPingInterval = function () {
  if (this.pingTimer && this.options.keepalive && this.options.reschedulePings) {
    this.pingTimer.reschedule(this.options.keepalive * 1000)
  }
}
/**
 * _checkPing - check if a pingresp has come back, and ping the server again
 *
 * @api private
 */
MqttClient.prototype._checkPing = function () {
  if (this.pingResp) {
    this.pingResp = false
    this._sendPacket({ cmd: 'pingreq' })
  } else {
    // do a forced cleanup since socket will be in bad shape
    this._cleanUp(true)
  }
}

/**
 * _handlePingresp - handle a pingresp
 *
 * @api private
 */
MqttClient.prototype._handlePingresp = function () {
  this.pingResp = true
}

/**
 * _handleConnack
 *
 * @param {Object} packet
 * @api private
 */

MqttClient.prototype._handleConnack = function (packet) {
  var rc = packet.returnCode
  var errors = [
    '',
    'Unacceptable protocol version',
    'Identifier rejected',
    'Server unavailable',
    'Bad username or password',
    'Not authorized'
  ]

  clearTimeout(this.connackTimer)

  if (rc === 0) {
    this.reconnecting = false
    this.emit('connect', packet)
  } else if (rc > 0) {
    var err = new Error('Connection refused: ' + errors[rc])
    err.code = rc
    this.emit('error', err)
  }
}

/**
 * _handlePublish
 *
 * @param {Object} packet
 * @api private
 */
/*
those late 2 case should be rewrite to comply with coding style:

case 1:
case 0:
  // do not wait sending a puback
  // no callback passed
  if (1 === qos) {
    this._sendPacket({
      cmd: 'puback',
      messageId: mid
    });
  }
  // emit the message event for both qos 1 and 0
  this.emit('message', topic, message, packet);
  this.handleMessage(packet, done);
  break;
default:
  // do nothing but every switch mus have a default
  // log or throw an error about unknown qos
  break;

for now i just suppressed the warnings
*/
MqttClient.prototype._handlePublish = function (packet, done) {
  var topic = packet.topic.toString()
  var message = packet.payload
  var qos = packet.qos
  var mid = packet.messageId
  var that = this

  switch (qos) {
    case 2:
      this.incomingStore.put(packet, function () {
        that._sendPacket({cmd: 'pubrec', messageId: mid}, done)
      })
      break
    case 1:
      // emit the message event
      this.emit('message', topic, message, packet)
      this.handleMessage(packet, function (err) {
        if (err) {
          return done && done(err)
        }
        // send 'puback' if the above 'handleMessage' method executed
        // successfully.
        that._sendPacket({cmd: 'puback', messageId: mid}, done)
      })
      break
    case 0:
      // emit the message event
      this.emit('message', topic, message, packet)
      this.handleMessage(packet, done)
      break
    default:
      // do nothing
      // log or throw an error about unknown qos
      break
  }
}

/**
 * Handle messages with backpressure support, one at a time.
 * Override at will.
 *
 * @param Packet packet the packet
 * @param Function callback call when finished
 * @api public
 */
MqttClient.prototype.handleMessage = function (packet, callback) {
  callback()
}

/**
 * _handleAck
 *
 * @param {Object} packet
 * @api private
 */

MqttClient.prototype._handleAck = function (packet) {
  /* eslint no-fallthrough: "off" */
  var mid = packet.messageId
  var type = packet.cmd
  var response = null
  var cb = this.outgoing[mid]
  var that = this

  if (!cb) {
    // Server sent an ack in error, ignore it.
    return
  }

  // Process
  switch (type) {
    case 'pubcomp':
      // same thing as puback for QoS 2
    case 'puback':
      // Callback - we're done
      delete this.outgoing[mid]
      this.outgoingStore.del(packet, cb)
      break
    case 'pubrec':
      response = {
        cmd: 'pubrel',
        qos: 2,
        messageId: mid
      }

      this._sendPacket(response)
      break
    case 'suback':
      delete this.outgoing[mid]
      if (packet.granted.length === 1 && (packet.granted[0] & 0x80) !== 0) {
        // suback with Failure status
        var topics = this.messageIdToTopic[mid]
        if (topics) {
          topics.forEach(function (topic) {
            delete that._resubscribeTopics[topic]
          })
        }
      }
      cb(null, packet)
      break
    case 'unsuback':
      delete this.outgoing[mid]
      cb(null)
      break
    default:
      that.emit('error', new Error('unrecognized packet type'))
  }

  if (this.disconnecting &&
      Object.keys(this.outgoing).length === 0) {
    this.emit('outgoingEmpty')
  }
}

/**
 * _handlePubrel
 *
 * @param {Object} packet
 * @api private
 */
MqttClient.prototype._handlePubrel = function (packet, callback) {
  var mid = packet.messageId
  var that = this

  var comp = {cmd: 'pubcomp', messageId: mid}

  that.incomingStore.get(packet, function (err, pub) {
    if (!err && pub.cmd !== 'pubrel') {
      that.emit('message', pub.topic, pub.payload, pub)
      that.incomingStore.put(packet)
      that.handleMessage(pub, function (err) {
        if (err) {
          return callback && callback(err)
        }
        that._sendPacket(comp, callback)
      })
    } else {
      that._sendPacket(comp, callback)
    }
  })
}

/**
 * _nextId
 */
MqttClient.prototype._nextId = function () {
  var id = this.nextId++
  // Ensure 16 bit unsigned int:
  if (id === 65535) {
    this.nextId = 1
  }
  return id
}

/**
 * getLastMessageId
 */
MqttClient.prototype.getLastMessageId = function () {
  return (this.nextId === 1) ? 65535 : (this.nextId - 1)
}

module.exports = MqttClient