1，在 .vue 文件中引入 mqttws31.js 文件（mqttws31.js 文件代码在本页底部）

import '@/utils/mqttws31'

2，在 .vue 文件中添加代码

export default {
  data() {
    return {
      client: new Paho.MQTT.Client('192.168.11.248', 9001, ''), // 第三个参数是clientID可以为空
      topic: 'mqtt' // 订阅的主题
    };
  },
  methods: {
    onConnectionLost: function (responseObject) {
      if (responseObject.errorCode !== 0) {
        console.log('onConnectionLost:' + responseObject.errorMessage);
        console.log('连接已断开');
      }
    },
    onMessageArrived: function(message) {
      console.log("收到消息:"+message.payloadString);
    },
    onConnect: function() {
      console.log('onConnected');
      this.client.subscribe(this.topic); // 订阅主题
    }
  },
  created: function() {
    this.client.connect({onSuccess: this.onConnect}); // 连接服务器并注册连接成功处理事件
    this.client.onConnectionLost = this.onConnectionLost; // 注册连接断开处理事件
    this.client.onMessageArrived = this.onMessageArrived; // 注册消息接收处理事件
    // this.client.disconnect(); // 断开连接
  }
};

mqttws31.js 文件代码如下：

/* eslint-disable */
/*******************************************************************************
 * Copyright (c) 2013 IBM Corp.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * and Eclipse Distribution License v1.0 which accompany this distribution. 
 *
 * The Eclipse Public License is available at 
 *    http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at 
 *   http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *    Andrew Banks - initial API and implementation and initial documentation
 *******************************************************************************/


// Only expose a single object name in the global namespace.
// Everything must go through this module. Global Paho.MQTT module
// only has a single public function, client, which returns
// a Paho.MQTT client object given connection details.

/**
 * Send and receive messages using web browsers.
 * <p> 
 * This programming interface lets a JavaScript client application use the MQTT V3.1 or
 * V3.1.1 protocol to connect to an MQTT-supporting messaging server.
 *  
 * The function supported includes:
 * <ol>
 * <li>Connecting to and disconnecting from a server. The server is identified by its host name and port number. 
 * <li>Specifying options that relate to the communications link with the server, 
 * for example the frequency of keep-alive heartbeats, and whether SSL/TLS is required.
 * <li>Subscribing to and receiving messages from MQTT Topics.
 * <li>Publishing messages to MQTT Topics.
 * </ol>
 * <p>
 * The API consists of two main objects:
 * <dl>
 * <dt><b>{@link Paho.MQTT.Client}</b></dt>
 * <dd>This contains methods that provide the functionality of the API,
 * including provision of callbacks that notify the application when a message
 * arrives from or is delivered to the messaging server,
 * or when the status of its connection to the messaging server changes.</dd>
 * <dt><b>{@link Paho.MQTT.Message}</b></dt>
 * <dd>This encapsulates the payload of the message along with various attributes
 * associated with its delivery, in particular the destination to which it has
 * been (or is about to be) sent.</dd>
 * </dl> 
 * <p>
 * The programming interface validates parameters passed to it, and will throw
 * an Error containing an error message intended for developer use, if it detects
 * an error with any parameter.
 * <p>
 * Example:
 * 
 * <code><pre>
client = new Paho.MQTT.Client(location.hostname, Number(location.port), "clientId");
client.onConnectionLost = onConnectionLost;
client.onMessageArrived = onMessageArrived;
client.connect({onSuccess:onConnect});

function onConnect() {
  // Once a connection has been made, make a subscription and send a message.
  console.log("onConnect");
  client.subscribe("/World");
  message = new Paho.MQTT.Message("Hello");
  message.destinationName = "/World";
  client.send(message); 
};
function onConnectionLost(responseObject) {
  if (responseObject.errorCode !== 0)
    console.log("onConnectionLost:"+responseObject.errorMessage);
};
function onMessageArrived(message) {
  console.log("onMessageArrived:"+message.payloadString);
  client.disconnect(); 
};  
 * </pre></code>
 * @namespace Paho.MQTT 
 */

if (typeof Paho === "undefined") {
    Paho = {};
}

Paho.MQTT = (function (global) {

    // Private variables below, these are only visible inside the function closure
    // which is used to define the module. 

    var version = "@VERSION@";
    var buildLevel = "@BUILDLEVEL@";

    /** 
     * Unique message type identifiers, with associated
     * associated integer values.
     * @private 
     */
    var MESSAGE_TYPE = {
        CONNECT: 1, 
        CONNACK: 2, 
        PUBLISH: 3,
        PUBACK: 4,
        PUBREC: 5, 
        PUBREL: 6,
        PUBCOMP: 7,
        SUBSCRIBE: 8,
        SUBACK: 9,
        UNSUBSCRIBE: 10,
        UNSUBACK: 11,
        PINGREQ: 12,
        PINGRESP: 13,
        DISCONNECT: 14
    };

    // Collection of utility methods used to simplify module code 
    // and promote the DRY pattern.  

    /**
     * Validate an object's parameter names to ensure they 
     * match a list of expected variables name for this option
     * type. Used to ensure option object passed into the API don't
     * contain erroneous parameters.
     * @param {Object} obj - User options object
     * @param {Object} keys - valid keys and types that may exist in obj. 
     * @throws {Error} Invalid option parameter found. 
     * @private 
     */
    var validate = function(obj, keys) {
        for (var key in obj) {
            if (obj.hasOwnProperty(key)) {              
                if (keys.hasOwnProperty(key)) {
                    if (typeof obj[key] !== keys[key])
                       throw new Error(format(ERROR.INVALID_TYPE, [typeof obj[key], key]));
                } else {    
                    var errorStr = "Unknown property, " + key + ". Valid properties are:";
                    for (var key in keys)
                        if (keys.hasOwnProperty(key))
                            errorStr = errorStr+" "+key;
                    throw new Error(errorStr);
                }
            }
        }
    };

    /**
     * Return a new function which runs the user function bound
     * to a fixed scope. 
     * @param {function} User function
     * @param {object} Function scope  
     * @return {function} User function bound to another scope
     * @private 
     */
    var scope = function (f, scope) {
        return function () {
            return f.apply(scope, arguments);
        };
    };

    /** 
     * Unique message type identifiers, with associated
     * associated integer values.
     * @private 
     */
    var ERROR = {
        OK: {code:0, text:"AMQJSC0000I OK."},
        CONNECT_TIMEOUT: {code:1, text:"AMQJSC0001E Connect timed out."},
        SUBSCRIBE_TIMEOUT: {code:2, text:"AMQJS0002E Subscribe timed out."}, 
        UNSUBSCRIBE_TIMEOUT: {code:3, text:"AMQJS0003E Unsubscribe timed out."},
        PING_TIMEOUT: {code:4, text:"AMQJS0004E Ping timed out."},
        INTERNAL_ERROR: {code:5, text:"AMQJS0005E Internal error. Error Message: {0}, Stack trace: {1}"},
        CONNACK_RETURNCODE: {code:6, text:"AMQJS0006E Bad Connack return code:{0} {1}."},
        SOCKET_ERROR: {code:7, text:"AMQJS0007E Socket error:{0}."},
        SOCKET_CLOSE: {code:8, text:"AMQJS0008I Socket closed."},
        MALFORMED_UTF: {code:9, text:"AMQJS0009E Malformed UTF data:{0} {1} {2}."},
        UNSUPPORTED: {code:10, text:"AMQJS0010E {0} is not supported by this browser."},
        INVALID_STATE: {code:11, text:"AMQJS0011E Invalid state {0}."},
        INVALID_TYPE: {code:12, text:"AMQJS0012E Invalid type {0} for {1}."},
        INVALID_ARGUMENT: {code:13, text:"AMQJS0013E Invalid argument {0} for {1}."},
        UNSUPPORTED_OPERATION: {code:14, text:"AMQJS0014E Unsupported operation."},
        INVALID_STORED_DATA: {code:15, text:"AMQJS0015E Invalid data in local storage key={0} value={1}."},
        INVALID_MQTT_MESSAGE_TYPE: {code:16, text:"AMQJS0016E Invalid MQTT message type {0}."},
        MALFORMED_UNICODE: {code:17, text:"AMQJS0017E Malformed Unicode string:{0} {1}."},
    };

    /** CONNACK RC Meaning. */
    var CONNACK_RC = {
        0:"Connection Accepted",
        1:"Connection Refused: unacceptable protocol version",
        2:"Connection Refused: identifier rejected",
        3:"Connection Refused: server unavailable",
        4:"Connection Refused: bad user name or password",
        5:"Connection Refused: not authorized"
    };

    /**
     * Format an error message text.
     * @private
     * @param {error} ERROR.KEY value above.
     * @param {substitutions} [array] substituted into the text.
     * @return the text with the substitutions made.
     */
    var format = function(error, substitutions) {
        var text = error.text;
        if (substitutions) {
          var field,start;
          for (var i=0; i<substitutions.length; i++) {
            field = "{"+i+"}";
            start = text.indexOf(field);
            if(start > 0) {
                var part1 = text.substring(0,start);
                var part2 = text.substring(start+field.length);
                text = part1+substitutions[i]+part2;
            }
          }
        }
        return text;
    };

    //MQTT protocol and version          6    M    Q    I    s    d    p    3
    var MqttProtoIdentifierv3 = [0x00,0x06,0x4d,0x51,0x49,0x73,0x64,0x70,0x03];
    //MQTT proto/version for 311         4    M    Q    T    T    4
    var MqttProtoIdentifierv4 = [0x00,0x04,0x4d,0x51,0x54,0x54,0x04];

    /**
     * Construct an MQTT wire protocol message.
     * @param type MQTT packet type.
     * @param options optional wire message attributes.
     * 
     * Optional properties
     * 
     * messageIdentifier: message ID in the range [0..65535]
     * payloadMessage:  Application Message - PUBLISH only
     * connectStrings:  array of 0 or more Strings to be put into the CONNECT payload
     * topics:          array of strings (SUBSCRIBE, UNSUBSCRIBE)
     * requestQoS:      array of QoS values [0..2]
     *  
     * "Flag" properties 
     * cleanSession:    true if present / false if absent (CONNECT)
     * willMessage:     true if present / false if absent (CONNECT)
     * isRetained:      true if present / false if absent (CONNECT)
     * userName:        true if present / false if absent (CONNECT)
     * password:        true if present / false if absent (CONNECT)
     * keepAliveInterval:   integer [0..65535]  (CONNECT)
     *
     * @private
     * @ignore
     */
    var WireMessage = function (type, options) {    
        this.type = type;
        for (var name in options) {
            if (options.hasOwnProperty(name)) {
                this[name] = options[name];
            }
        }
    };

    WireMessage.prototype.encode = function() {
        // Compute the first byte of the fixed header
        var first = ((this.type & 0x0f) << 4);

        /*
         * Now calculate the length of the variable header + payload by adding up the lengths
         * of all the component parts
         */

        var remLength = 0;
        var topicStrLength = [];
        var destinationNameLength = 0;

        // if the message contains a messageIdentifier then we need two bytes for that
        if (this.messageIdentifier != undefined)
            remLength += 2;

        switch(this.type) {
            // If this a Connect then we need to include 12 bytes for its header
            case MESSAGE_TYPE.CONNECT:
                switch(this.mqttVersion) {
                    case 3:
                        remLength += MqttProtoIdentifierv3.length + 3;
                        break;
                    case 4:
                        remLength += MqttProtoIdentifierv4.length + 3;
                        break;
                }

                remLength += UTF8Length(this.clientId) + 2;
                if (this.willMessage != undefined) {
                    remLength += UTF8Length(this.willMessage.destinationName) + 2;
                    // Will message is always a string, sent as UTF-8 characters with a preceding length.
                    var willMessagePayloadBytes = this.willMessage.payloadBytes;
                    if (!(willMessagePayloadBytes instanceof Uint8Array))
                        willMessagePayloadBytes = new Uint8Array(payloadBytes);
                    remLength += willMessagePayloadBytes.byteLength +2;
                }
                if (this.userName != undefined)
                    remLength += UTF8Length(this.userName) + 2; 
                if (this.password != undefined)
                    remLength += UTF8Length(this.password) + 2;
            break;

            // Subscribe, Unsubscribe can both contain topic strings
            case MESSAGE_TYPE.SUBSCRIBE:                
                first |= 0x02; // Qos = 1;
                for ( var i = 0; i < this.topics.length; i++) {
                    topicStrLength[i] = UTF8Length(this.topics[i]);
                    remLength += topicStrLength[i] + 2;
                }
                remLength += this.requestedQos.length; // 1 byte for each topic's Qos
                // QoS on Subscribe only
                break;

            case MESSAGE_TYPE.UNSUBSCRIBE:
                first |= 0x02; // Qos = 1;
                for ( var i = 0; i < this.topics.length; i++) {
                    topicStrLength[i] = UTF8Length(this.topics[i]);
                    remLength += topicStrLength[i] + 2;
                }
                break;

            case MESSAGE_TYPE.PUBREL:
                first |= 0x02; // Qos = 1;
                break;

            case MESSAGE_TYPE.PUBLISH:
                if (this.payloadMessage.duplicate) first |= 0x08;
                first  = first |= (this.payloadMessage.qos << 1);
                if (this.payloadMessage.retained) first |= 0x01;
                destinationNameLength = UTF8Length(this.payloadMessage.destinationName);
                remLength += destinationNameLength + 2;    
                var payloadBytes = this.payloadMessage.payloadBytes;
                remLength += payloadBytes.byteLength;  
                if (payloadBytes instanceof ArrayBuffer)
                    payloadBytes = new Uint8Array(payloadBytes);
                else if (!(payloadBytes instanceof Uint8Array))
                    payloadBytes = new Uint8Array(payloadBytes.buffer);
                break;

            case MESSAGE_TYPE.DISCONNECT:
                break;

            default:
        }

        // Now we can allocate a buffer for the message

        var mbi = encodeMBI(remLength);  // Convert the length to MQTT MBI format
        var pos = mbi.length + 1;        // Offset of start of variable header
        var buffer = new ArrayBuffer(remLength + pos);
        var byteStream = new Uint8Array(buffer);    // view it as a sequence of bytes

        //Write the fixed header into the buffer
        byteStream[0] = first;
        byteStream.set(mbi,1);

        // If this is a PUBLISH then the variable header starts with a topic
        if (this.type == MESSAGE_TYPE.PUBLISH)
            pos = writeString(this.payloadMessage.destinationName, destinationNameLength, byteStream, pos);
        // If this is a CONNECT then the variable header contains the protocol name/version, flags and keepalive time

        else if (this.type == MESSAGE_TYPE.CONNECT) {
            switch (this.mqttVersion) {
                case 3:
                    byteStream.set(MqttProtoIdentifierv3, pos);
                    pos += MqttProtoIdentifierv3.length;
                    break;
                case 4:
                    byteStream.set(MqttProtoIdentifierv4, pos);
                    pos += MqttProtoIdentifierv4.length;
                    break;
            }
            var connectFlags = 0;
            if (this.cleanSession) 
                connectFlags = 0x02;
            if (this.willMessage != undefined ) {
                connectFlags |= 0x04;
                connectFlags |= (this.willMessage.qos<<3);
                if (this.willMessage.retained) {
                    connectFlags |= 0x20;
                }
            }
            if (this.userName != undefined)
                connectFlags |= 0x80;
            if (this.password != undefined)
                connectFlags |= 0x40;
            byteStream[pos++] = connectFlags; 
            pos = writeUint16 (this.keepAliveInterval, byteStream, pos);
        }

        // Output the messageIdentifier - if there is one
        if (this.messageIdentifier != undefined)
            pos = writeUint16 (this.messageIdentifier, byteStream, pos);

        switch(this.type) {
            case MESSAGE_TYPE.CONNECT:
                pos = writeString(this.clientId, UTF8Length(this.clientId), byteStream, pos); 
                if (this.willMessage != undefined) {
                    pos = writeString(this.willMessage.destinationName, UTF8Length(this.willMessage.destinationName), byteStream, pos);
                    pos = writeUint16(willMessagePayloadBytes.byteLength, byteStream, pos);
                    byteStream.set(willMessagePayloadBytes, pos);
                    pos += willMessagePayloadBytes.byteLength;

                }
            if (this.userName != undefined)
                pos = writeString(this.userName, UTF8Length(this.userName), byteStream, pos);
            if (this.password != undefined) 
                pos = writeString(this.password, UTF8Length(this.password), byteStream, pos);
            break;

            case MESSAGE_TYPE.PUBLISH:  
                // PUBLISH has a text or binary payload, if text do not add a 2 byte length field, just the UTF characters. 
                byteStream.set(payloadBytes, pos);

                break;

//          case MESSAGE_TYPE.PUBREC:   
//          case MESSAGE_TYPE.PUBREL:   
//          case MESSAGE_TYPE.PUBCOMP:  
//              break;

            case MESSAGE_TYPE.SUBSCRIBE:
                // SUBSCRIBE has a list of topic strings and request QoS
                for (var i=0; i<this.topics.length; i++) {
                    pos = writeString(this.topics[i], topicStrLength[i], byteStream, pos);
                    byteStream[pos++] = this.requestedQos[i];
                }
                break;

            case MESSAGE_TYPE.UNSUBSCRIBE:  
                // UNSUBSCRIBE has a list of topic strings
                for (var i=0; i<this.topics.length; i++)
                    pos = writeString(this.topics[i], topicStrLength[i], byteStream, pos);
                break;

            default:
                // Do nothing.
        }

        return buffer;
    };

    function decodeMessage(input,pos) {
        var startingPos = pos;
        var first = input[pos];
        var type = first >> 4;
        var messageInfo = first &= 0x0f;
        pos += 1;


        // Decode the remaining length (MBI format)

        var digit;
        var remLength = 0;
        var multiplier = 1;
        do {
            if (pos == input.length) {
                return [null,startingPos];
            }
            digit = input[pos++];
            remLength += ((digit & 0x7F) * multiplier);
            multiplier *= 128;
        } while ((digit & 0x80) != 0);

        var endPos = pos+remLength;
        if (endPos > input.length) {
            return [null,startingPos];
        }

        var wireMessage = new WireMessage(type);
        switch(type) {
            case MESSAGE_TYPE.CONNACK:
                var connectAcknowledgeFlags = input[pos++];
                if (connectAcknowledgeFlags & 0x01)
                    wireMessage.sessionPresent = true;
                wireMessage.returnCode = input[pos++];
                break;

            case MESSAGE_TYPE.PUBLISH:              
                var qos = (messageInfo >> 1) & 0x03;

                var len = readUint16(input, pos);
                pos += 2;
                var topicName = parseUTF8(input, pos, len);
                pos += len;
                // If QoS 1 or 2 there will be a messageIdentifier
                if (qos > 0) {
                    wireMessage.messageIdentifier = readUint16(input, pos);
                    pos += 2;
                }

                var message = new Paho.MQTT.Message(input.subarray(pos, endPos));
                if ((messageInfo & 0x01) == 0x01) 
                    message.retained = true;
                if ((messageInfo & 0x08) == 0x08)
                    message.duplicate =  true;
                message.qos = qos;
                message.destinationName = topicName;
                wireMessage.payloadMessage = message;   
                break;

            case  MESSAGE_TYPE.PUBACK:
            case  MESSAGE_TYPE.PUBREC:      
            case  MESSAGE_TYPE.PUBREL:    
            case  MESSAGE_TYPE.PUBCOMP:
            case  MESSAGE_TYPE.UNSUBACK:                
                wireMessage.messageIdentifier = readUint16(input, pos);
                break;

            case  MESSAGE_TYPE.SUBACK:
                wireMessage.messageIdentifier = readUint16(input, pos);
                pos += 2;
                wireMessage.returnCode = input.subarray(pos, endPos);   
                break;

            default:
        }

        return [wireMessage,endPos];    
    }

    function writeUint16(input, buffer, offset) {
        buffer[offset++] = input >> 8;      //MSB
        buffer[offset++] = input % 256;     //LSB 
        return offset;
    }   

    function writeString(input, utf8Length, buffer, offset) {
        offset = writeUint16(utf8Length, buffer, offset);
        stringToUTF8(input, buffer, offset);
        return offset + utf8Length;
    }   

    function readUint16(buffer, offset) {
        return 256*buffer[offset] + buffer[offset+1];
    }   

    /**
     * Encodes an MQTT Multi-Byte Integer
     * @private 
     */
    function encodeMBI(number) {
        var output = new Array(1);
        var numBytes = 0;

        do {
            var digit = number % 128;
            number = number >> 7;
            if (number > 0) {
                digit |= 0x80;
            }
            output[numBytes++] = digit;
        } while ( (number > 0) && (numBytes<4) );

        return output;
    }

    /**
     * Takes a String and calculates its length in bytes when encoded in UTF8.
     * @private
     */
    function UTF8Length(input) {
        var output = 0;
        for (var i = 0; i<input.length; i++) 
        {
            var charCode = input.charCodeAt(i);
                if (charCode > 0x7FF)
                   {
                      // Surrogate pair means its a 4 byte character
                      if (0xD800 <= charCode && charCode <= 0xDBFF)
                        {
                          i++;
                          output++;
                        }
                   output +=3;
                   }
            else if (charCode > 0x7F)
                output +=2;
            else
                output++;
        } 
        return output;
    }

    /**
     * Takes a String and writes it into an array as UTF8 encoded bytes.
     * @private
     */
    function stringToUTF8(input, output, start) {
        var pos = start;
        for (var i = 0; i<input.length; i++) {
            var charCode = input.charCodeAt(i);

            // Check for a surrogate pair.
            if (0xD800 <= charCode && charCode <= 0xDBFF) {
                var lowCharCode = input.charCodeAt(++i);
                if (isNaN(lowCharCode)) {
                    throw new Error(format(ERROR.MALFORMED_UNICODE, [charCode, lowCharCode]));
                }
                charCode = ((charCode - 0xD800)<<10) + (lowCharCode - 0xDC00) + 0x10000;

            }

            if (charCode <= 0x7F) {
                output[pos++] = charCode;
            } else if (charCode <= 0x7FF) {
                output[pos++] = charCode>>6  & 0x1F | 0xC0;
                output[pos++] = charCode     & 0x3F | 0x80;
            } else if (charCode <= 0xFFFF) {                        
                output[pos++] = charCode>>12 & 0x0F | 0xE0;
                output[pos++] = charCode>>6  & 0x3F | 0x80;   
                output[pos++] = charCode     & 0x3F | 0x80;   
            } else {
                output[pos++] = charCode>>18 & 0x07 | 0xF0;
                output[pos++] = charCode>>12 & 0x3F | 0x80;
                output[pos++] = charCode>>6  & 0x3F | 0x80;
                output[pos++] = charCode     & 0x3F | 0x80;
            }
        }
        return output;
    }

    function parseUTF8(input, offset, length) {
        var output = "";
        var utf16;
        var pos = offset;

        while (pos < offset+length)
        {
            var byte1 = input[pos++];
            if (byte1 < 128)
                utf16 = byte1;
            else 
            {
                var byte2 = input[pos++]-128;
                if (byte2 < 0) 
                    throw new Error(format(ERROR.MALFORMED_UTF, [byte1.toString(16), byte2.toString(16),""]));
                if (byte1 < 0xE0)             // 2 byte character
                    utf16 = 64*(byte1-0xC0) + byte2;
                else 
                { 
                    var byte3 = input[pos++]-128;
                    if (byte3 < 0) 
                        throw new Error(format(ERROR.MALFORMED_UTF, [byte1.toString(16), byte2.toString(16), byte3.toString(16)]));
                    if (byte1 < 0xF0)        // 3 byte character
                        utf16 = 4096*(byte1-0xE0) + 64*byte2 + byte3;
                                else
                                {
                                   var byte4 = input[pos++]-128;
                                   if (byte4 < 0) 
                        throw new Error(format(ERROR.MALFORMED_UTF, [byte1.toString(16), byte2.toString(16), byte3.toString(16), byte4.toString(16)]));
                                   if (byte1 < 0xF8)        // 4 byte character 
                                           utf16 = 262144*(byte1-0xF0) + 4096*byte2 + 64*byte3 + byte4;
                       else                     // longer encodings are not supported  
                        throw new Error(format(ERROR.MALFORMED_UTF, [byte1.toString(16), byte2.toString(16), byte3.toString(16), byte4.toString(16)]));
                                }
                }
            }  

                if (utf16 > 0xFFFF)   // 4 byte character - express as a surrogate pair
                  {
                     utf16 -= 0x10000;
                     output += String.fromCharCode(0xD800 + (utf16 >> 10)); // lead character
                     utf16 = 0xDC00 + (utf16 & 0x3FF);  // trail character
                  }
            output += String.fromCharCode(utf16);
        }
        return output;
    }

    /** 
     * Repeat keepalive requests, monitor responses.
     * @ignore
     */
    var Pinger = function(client, window, keepAliveInterval) { 
        this._client = client;          
        this._window = window;
        this._keepAliveInterval = keepAliveInterval*1000;       
        this.isReset = false;

        var pingReq = new WireMessage(MESSAGE_TYPE.PINGREQ).encode(); 

        var doTimeout = function (pinger) {
            return function () {
                return doPing.apply(pinger);
            };
        };

        /** @ignore */
        var doPing = function() { 
            if (!this.isReset) {
                this._client._trace("Pinger.doPing", "Timed out");
                this._client._disconnected( ERROR.PING_TIMEOUT.code , format(ERROR.PING_TIMEOUT));
            } else {
                this.isReset = false;
                this._client._trace("Pinger.doPing", "send PINGREQ");
                this._client.socket.send(pingReq); 
                this.timeout = this._window.setTimeout(doTimeout(this), this._keepAliveInterval);
            }
        };

        this.reset = function() {
            this.isReset = true;
            this._window.clearTimeout(this.timeout);
            if (this._keepAliveInterval > 0)
                this.timeout = setTimeout(doTimeout(this), this._keepAliveInterval);
        };

        this.cancel = function() {
            this._window.clearTimeout(this.timeout);
        }
     }; 

    /**
     * Monitor request completion.
     * @ignore
     */
    var Timeout = function(client, window, timeoutSeconds, action, args) {
        this._window = window;
        if (!timeoutSeconds)
            timeoutSeconds = 30;

        var doTimeout = function (action, client, args) {
            return function () {
                return action.apply(client, args);
            };
        };
        this.timeout = setTimeout(doTimeout(action, client, args), timeoutSeconds * 1000);

        this.cancel = function() {
            this._window.clearTimeout(this.timeout);
        }
    }; 

    /*
     * Internal implementation of the Websockets MQTT V3.1 client.
     * 
     * @name Paho.MQTT.ClientImpl @constructor 
     * @param {String} host the DNS nameof the webSocket host. 
     * @param {Number} port the port number for that host.
     * @param {String} clientId the MQ client identifier.
     */
    var ClientImpl = function (uri, host, port, path, clientId) {
        // Check dependencies are satisfied in this browser.
        if (!("WebSocket" in global && global["WebSocket"] !== null)) {
            throw new Error(format(ERROR.UNSUPPORTED, ["WebSocket"]));
        }
        if (!("localStorage" in global && global["localStorage"] !== null)) {
            throw new Error(format(ERROR.UNSUPPORTED, ["localStorage"]));
        }
        if (!("ArrayBuffer" in global && global["ArrayBuffer"] !== null)) {
            throw new Error(format(ERROR.UNSUPPORTED, ["ArrayBuffer"]));
        }
        this._trace("Paho.MQTT.Client", uri, host, port, path, clientId);

        this.host = host;
        this.port = port;
        this.path = path;
        this.uri = uri;
        this.clientId = clientId;

        // Local storagekeys are qualified with the following string.
        // The conditional inclusion of path in the key is for backward
        // compatibility to when the path was not configurable and assumed to
        // be /mqtt
        this._localKey=host+":"+port+(path!="/mqtt"?":"+path:"")+":"+clientId+":";

        // Create private instance-only message queue
        // Internal queue of messages to be sent, in sending order. 
        this._msg_queue = [];

        // Messages we have sent and are expecting a response for, indexed by their respective message ids. 
        this._sentMessages = {};

        // Messages we have received and acknowleged and are expecting a confirm message for
        // indexed by their respective message ids. 
        this._receivedMessages = {};

        // Internal list of callbacks to be executed when messages
        // have been successfully sent over web socket, e.g. disconnect
        // when it doesn't have to wait for ACK, just message is dispatched.
        this._notify_msg_sent = {};

        // Unique identifier for SEND messages, incrementing
        // counter as messages are sent.
        this._message_identifier = 1;

        // Used to determine the transmission sequence of stored sent messages.
        this._sequence = 0;


        // Load the local state, if any, from the saved version, only restore state relevant to this client.    
        for (var key in localStorage)
            if (   key.indexOf("Sent:"+this._localKey) == 0             
                || key.indexOf("Received:"+this._localKey) == 0)
            this.restore(key);
    };

    // Messaging Client public instance members. 
    ClientImpl.prototype.host;
    ClientImpl.prototype.port;
    ClientImpl.prototype.path;
    ClientImpl.prototype.uri;
    ClientImpl.prototype.clientId;

    // Messaging Client private instance members.
    ClientImpl.prototype.socket;
    /* true once we have received an acknowledgement to a CONNECT packet. */
    ClientImpl.prototype.connected = false;
    /* The largest message identifier allowed, may not be larger than 2**16 but 
     * if set smaller reduces the maximum number of outbound messages allowed.
     */ 
    ClientImpl.prototype.maxMessageIdentifier = 65536;
    ClientImpl.prototype.connectOptions;
    ClientImpl.prototype.hostIndex;
    ClientImpl.prototype.onConnectionLost;
    ClientImpl.prototype.onMessageDelivered;
    ClientImpl.prototype.onMessageArrived;
    ClientImpl.prototype.traceFunction;
    ClientImpl.prototype._msg_queue = null;
    ClientImpl.prototype._connectTimeout;
    /* The sendPinger monitors how long we allow before we send data to prove to the server that we are alive. */
    ClientImpl.prototype.sendPinger = null;
    /* The receivePinger monitors how long we allow before we require evidence that the server is alive. */
    ClientImpl.prototype.receivePinger = null;

    ClientImpl.prototype.receiveBuffer = null;

    ClientImpl.prototype._traceBuffer = null;
    ClientImpl.prototype._MAX_TRACE_ENTRIES = 100;

    ClientImpl.prototype.connect = function (connectOptions) {
        var connectOptionsMasked = this._traceMask(connectOptions, "password"); 
        this._trace("Client.connect", connectOptionsMasked, this.socket, this.connected);

        if (this.connected) 
            throw new Error(format(ERROR.INVALID_STATE, ["already connected"]));
        if (this.socket)
            throw new Error(format(ERROR.INVALID_STATE, ["already connected"]));

        this.connectOptions = connectOptions;

        if (connectOptions.uris) {
            this.hostIndex = 0;
            this._doConnect(connectOptions.uris[0]);  
        } else {
            this._doConnect(this.uri);          
        }

    };

    ClientImpl.prototype.subscribe = function (filter, subscribeOptions) {
        this._trace("Client.subscribe", filter, subscribeOptions);

        if (!this.connected)
            throw new Error(format(ERROR.INVALID_STATE, ["not connected"]));

        var wireMessage = new WireMessage(MESSAGE_TYPE.SUBSCRIBE);
        wireMessage.topics=[filter];
        if (subscribeOptions.qos != undefined)
            wireMessage.requestedQos = [subscribeOptions.qos];
        else 
            wireMessage.requestedQos = [0];

        if (subscribeOptions.onSuccess) {
            wireMessage.onSuccess = function(grantedQos) {subscribeOptions.onSuccess({invocationContext:subscribeOptions.invocationContext,grantedQos:grantedQos});};
        }

        if (subscribeOptions.onFailure) {
            wireMessage.onFailure = function(errorCode) {subscribeOptions.onFailure({invocationContext:subscribeOptions.invocationContext,errorCode:errorCode});};
        }

        if (subscribeOptions.timeout) {
            wireMessage.timeOut = new Timeout(this, window, subscribeOptions.timeout, subscribeOptions.onFailure
                    , [{invocationContext:subscribeOptions.invocationContext, 
                        errorCode:ERROR.SUBSCRIBE_TIMEOUT.code, 
                        errorMessage:format(ERROR.SUBSCRIBE_TIMEOUT)}]);
        }

        // All subscriptions return a SUBACK. 
        this._requires_ack(wireMessage);
        this._schedule_message(wireMessage);
    };

    /** @ignore */
    ClientImpl.prototype.unsubscribe = function(filter, unsubscribeOptions) {  
        this._trace("Client.unsubscribe", filter, unsubscribeOptions);

        if (!this.connected)
           throw new Error(format(ERROR.INVALID_STATE, ["not connected"]));

        var wireMessage = new WireMessage(MESSAGE_TYPE.UNSUBSCRIBE);
        wireMessage.topics = [filter];

        if (unsubscribeOptions.onSuccess) {
            wireMessage.callback = function() {unsubscribeOptions.onSuccess({invocationContext:unsubscribeOptions.invocationContext});};
        }
        if (unsubscribeOptions.timeout) {
            wireMessage.timeOut = new Timeout(this, window, unsubscribeOptions.timeout, unsubscribeOptions.onFailure
                    , [{invocationContext:unsubscribeOptions.invocationContext,
                        errorCode:ERROR.UNSUBSCRIBE_TIMEOUT.code,
                        errorMessage:format(ERROR.UNSUBSCRIBE_TIMEOUT)}]);
        }

        // All unsubscribes return a SUBACK.         
        this._requires_ack(wireMessage);
        this._schedule_message(wireMessage);
    };

    ClientImpl.prototype.send = function (message) {
        this._trace("Client.send", message);

        if (!this.connected)
           throw new Error(format(ERROR.INVALID_STATE, ["not connected"]));

        wireMessage = new WireMessage(MESSAGE_TYPE.PUBLISH);
        wireMessage.payloadMessage = message;

        if (message.qos > 0)
            this._requires_ack(wireMessage);
        else if (this.onMessageDelivered)
            this._notify_msg_sent[wireMessage] = this.onMessageDelivered(wireMessage.payloadMessage);
        this._schedule_message(wireMessage);
    };

    ClientImpl.prototype.disconnect = function () {
        this._trace("Client.disconnect");

        if (!this.socket)
            throw new Error(format(ERROR.INVALID_STATE, ["not connecting or connected"]));

        wireMessage = new WireMessage(MESSAGE_TYPE.DISCONNECT);

        // Run the disconnected call back as soon as the message has been sent,
        // in case of a failure later on in the disconnect processing.
        // as a consequence, the _disconected call back may be run several times.
        this._notify_msg_sent[wireMessage] = scope(this._disconnected, this);

        this._schedule_message(wireMessage);
    };

    ClientImpl.prototype.getTraceLog = function () {
        if ( this._traceBuffer !== null ) {
            this._trace("Client.getTraceLog", new Date());
            this._trace("Client.getTraceLog in flight messages", this._sentMessages.length);
            for (var key in this._sentMessages)
                this._trace("_sentMessages ",key, this._sentMessages[key]);
            for (var key in this._receivedMessages)
                this._trace("_receivedMessages ",key, this._receivedMessages[key]);

            return this._traceBuffer;
        }
    };

    ClientImpl.prototype.startTrace = function () {
        if ( this._traceBuffer === null ) {
            this._traceBuffer = [];
        }
        this._trace("Client.startTrace", new Date(), version);
    };

    ClientImpl.prototype.stopTrace = function () {
        delete this._traceBuffer;
    };

    ClientImpl.prototype._doConnect = function (wsurl) {            
        // When the socket is open, this client will send the CONNECT WireMessage using the saved parameters. 
        if (this.connectOptions.useSSL) {
            var uriParts = wsurl.split(":");
            uriParts[0] = "wss";
            wsurl = uriParts.join(":");
        }
        this.connected = false;
        if (this.connectOptions.mqttVersion < 4) {
            this.socket = new WebSocket(wsurl, ["mqttv3.1"]);
        } else {
            this.socket = new WebSocket(wsurl, ["mqtt"]);
        }
        this.socket.binaryType = 'arraybuffer';

        this.socket.onopen = scope(this._on_socket_open, this);
        this.socket.onmessage = scope(this._on_socket_message, this);
        this.socket.onerror = scope(this._on_socket_error, this);
        this.socket.onclose = scope(this._on_socket_close, this);

        this.sendPinger = new Pinger(this, window, this.connectOptions.keepAliveInterval);
        this.receivePinger = new Pinger(this, window, this.connectOptions.keepAliveInterval);

        this._connectTimeout = new Timeout(this, window, this.connectOptions.timeout, this._disconnected,  [ERROR.CONNECT_TIMEOUT.code, format(ERROR.CONNECT_TIMEOUT)]);
    };


    // Schedule a new message to be sent over the WebSockets
    // connection. CONNECT messages cause WebSocket connection
    // to be started. All other messages are queued internally
    // until this has happened. When WS connection starts, process
    // all outstanding messages. 
    ClientImpl.prototype._schedule_message = function (message) {
        this._msg_queue.push(message);
        // Process outstanding messages in the queue if we have an  open socket, and have received CONNACK. 
        if (this.connected) {
            this._process_queue();
        }
    };

    ClientImpl.prototype.store = function(prefix, wireMessage) {
        var storedMessage = {type:wireMessage.type, messageIdentifier:wireMessage.messageIdentifier, version:1};

        switch(wireMessage.type) {
          case MESSAGE_TYPE.PUBLISH:
              if(wireMessage.pubRecReceived)
                  storedMessage.pubRecReceived = true;

              // Convert the payload to a hex string.
              storedMessage.payloadMessage = {};
              var hex = "";
              var messageBytes = wireMessage.payloadMessage.payloadBytes;
              for (var i=0; i<messageBytes.length; i++) {
                if (messageBytes[i] <= 0xF)
                  hex = hex+"0"+messageBytes[i].toString(16);
                else 
                  hex = hex+messageBytes[i].toString(16);
              }
              storedMessage.payloadMessage.payloadHex = hex;

              storedMessage.payloadMessage.qos = wireMessage.payloadMessage.qos;
              storedMessage.payloadMessage.destinationName = wireMessage.payloadMessage.destinationName;
              if (wireMessage.payloadMessage.duplicate) 
                  storedMessage.payloadMessage.duplicate = true;
              if (wireMessage.payloadMessage.retained) 
                  storedMessage.payloadMessage.retained = true;    

              // Add a sequence number to sent messages.
              if ( prefix.indexOf("Sent:") == 0 ) {
                  if ( wireMessage.sequence === undefined )
                      wireMessage.sequence = ++this._sequence;
                  storedMessage.sequence = wireMessage.sequence;
              }
              break;    

            default:
                throw Error(format(ERROR.INVALID_STORED_DATA, [key, storedMessage]));
        }
        localStorage.setItem(prefix+this._localKey+wireMessage.messageIdentifier, JSON.stringify(storedMessage));
    };

    ClientImpl.prototype.restore = function(key) {      
        var value = localStorage.getItem(key);
        var storedMessage = JSON.parse(value);

        var wireMessage = new WireMessage(storedMessage.type, storedMessage);

        switch(storedMessage.type) {
          case MESSAGE_TYPE.PUBLISH:
              // Replace the payload message with a Message object.
              var hex = storedMessage.payloadMessage.payloadHex;
              var buffer = new ArrayBuffer((hex.length)/2);
              var byteStream = new Uint8Array(buffer); 
              var i = 0;
              while (hex.length >= 2) { 
                  var x = parseInt(hex.substring(0, 2), 16);
                  hex = hex.substring(2, hex.length);
                  byteStream[i++] = x;
              }
              var payloadMessage = new Paho.MQTT.Message(byteStream);

              payloadMessage.qos = storedMessage.payloadMessage.qos;
              payloadMessage.destinationName = storedMessage.payloadMessage.destinationName;
              if (storedMessage.payloadMessage.duplicate) 
                  payloadMessage.duplicate = true;
              if (storedMessage.payloadMessage.retained) 
                  payloadMessage.retained = true;    
              wireMessage.payloadMessage = payloadMessage;

              break;    

            default:
              throw Error(format(ERROR.INVALID_STORED_DATA, [key, value]));
        }

        if (key.indexOf("Sent:"+this._localKey) == 0) {
            wireMessage.payloadMessage.duplicate = true;
            this._sentMessages[wireMessage.messageIdentifier] = wireMessage;                
        } else if (key.indexOf("Received:"+this._localKey) == 0) {
            this._receivedMessages[wireMessage.messageIdentifier] = wireMessage;
        }
    };

    ClientImpl.prototype._process_queue = function () {
        var message = null;
        // Process messages in order they were added
        var fifo = this._msg_queue.reverse();

        // Send all queued messages down socket connection
        while ((message = fifo.pop())) {
            this._socket_send(message);
            // Notify listeners that message was successfully sent
            if (this._notify_msg_sent[message]) {
                this._notify_msg_sent[message]();
                delete this._notify_msg_sent[message];
            }
        }
    };

    /**
     * Expect an ACK response for this message. Add message to the set of in progress
     * messages and set an unused identifier in this message.
     * @ignore
     */
    ClientImpl.prototype._requires_ack = function (wireMessage) {
        var messageCount = Object.keys(this._sentMessages).length;
        if (messageCount > this.maxMessageIdentifier)
            throw Error ("Too many messages:"+messageCount);

        while(this._sentMessages[this._message_identifier] !== undefined) {
            this._message_identifier++;
        }
        wireMessage.messageIdentifier = this._message_identifier;
        this._sentMessages[wireMessage.messageIdentifier] = wireMessage;
        if (wireMessage.type === MESSAGE_TYPE.PUBLISH) {
            this.store("Sent:", wireMessage);
        }
        if (this._message_identifier === this.maxMessageIdentifier) {
            this._message_identifier = 1;
        }
    };

    /** 
     * Called when the underlying websocket has been opened.
     * @ignore
     */
    ClientImpl.prototype._on_socket_open = function () {      
        // Create the CONNECT message object.
        var wireMessage = new WireMessage(MESSAGE_TYPE.CONNECT, this.connectOptions); 
        wireMessage.clientId = this.clientId;
        this._socket_send(wireMessage);
    };

    /** 
     * Called when the underlying websocket has received a complete packet.
     * @ignore
     */
    ClientImpl.prototype._on_socket_message = function (event) {
        this._trace("Client._on_socket_message", event.data);
        // Reset the receive ping timer, we now have evidence the server is alive.
        this.receivePinger.reset();
        var messages = this._deframeMessages(event.data);
        for (var i = 0; i < messages.length; i+=1) {
            this._handleMessage(messages[i]);
        }
    };

    ClientImpl.prototype._deframeMessages = function(data) {
        var byteArray = new Uint8Array(data);
        if (this.receiveBuffer) {
            var newData = new Uint8Array(this.receiveBuffer.length+byteArray.length);
            newData.set(this.receiveBuffer);
            newData.set(byteArray,this.receiveBuffer.length);
            byteArray = newData;
            delete this.receiveBuffer;
        }
        try {
            var offset = 0;
            var messages = [];
            while(offset < byteArray.length) {
                var result = decodeMessage(byteArray,offset);
                var wireMessage = result[0];
                offset = result[1];
                if (wireMessage !== null) {
                    messages.push(wireMessage);
                } else {
                    break;
                }
            }
            if (offset < byteArray.length) {
                this.receiveBuffer = byteArray.subarray(offset);
            }
        } catch (error) {
            this._disconnected(ERROR.INTERNAL_ERROR.code , format(ERROR.INTERNAL_ERROR, [error.message,error.stack.toString()]));
            return;
        }
        return messages;
    };

    ClientImpl.prototype._handleMessage = function(wireMessage) {

        this._trace("Client._handleMessage", wireMessage);

        try {
            switch(wireMessage.type) {
            case MESSAGE_TYPE.CONNACK:
                this._connectTimeout.cancel();

                // If we have started using clean session then clear up the local state.
                if (this.connectOptions.cleanSession) {
                    for (var key in this._sentMessages) {               
                        var sentMessage = this._sentMessages[key];
                        localStorage.removeItem("Sent:"+this._localKey+sentMessage.messageIdentifier);
                    }
                    this._sentMessages = {};

                    for (var key in this._receivedMessages) {
                        var receivedMessage = this._receivedMessages[key];
                        localStorage.removeItem("Received:"+this._localKey+receivedMessage.messageIdentifier);
                    }
                    this._receivedMessages = {};
                }
                // Client connected and ready for business.
                if (wireMessage.returnCode === 0) {
                    this.connected = true;
                    // Jump to the end of the list of uris and stop looking for a good host.
                    if (this.connectOptions.uris)
                        this.hostIndex = this.connectOptions.uris.length;
                } else {
                    this._disconnected(ERROR.CONNACK_RETURNCODE.code , format(ERROR.CONNACK_RETURNCODE, [wireMessage.returnCode, CONNACK_RC[wireMessage.returnCode]]));
                    break;
                }

                // Resend messages.
                var sequencedMessages = [];
                for (var msgId in this._sentMessages) {
                    if (this._sentMessages.hasOwnProperty(msgId))
                        sequencedMessages.push(this._sentMessages[msgId]);
                }

                // Sort sentMessages into the original sent order.
                var sequencedMessages = sequencedMessages.sort(function(a,b) {return a.sequence - b.sequence;} );
                for (var i=0, len=sequencedMessages.length; i<len; i++) {
                    var sentMessage = sequencedMessages[i];
                    if (sentMessage.type == MESSAGE_TYPE.PUBLISH && sentMessage.pubRecReceived) {
                        var pubRelMessage = new WireMessage(MESSAGE_TYPE.PUBREL, {messageIdentifier:sentMessage.messageIdentifier});
                        this._schedule_message(pubRelMessage);
                    } else {
                        this._schedule_message(sentMessage);
                    }
                }

                // Execute the connectOptions.onSuccess callback if there is one.
                if (this.connectOptions.onSuccess) {
                    this.connectOptions.onSuccess({invocationContext:this.connectOptions.invocationContext});
                }

                // Process all queued messages now that the connection is established. 
                this._process_queue();
                break;

            case MESSAGE_TYPE.PUBLISH:
                this._receivePublish(wireMessage);
                break;

            case MESSAGE_TYPE.PUBACK:
                var sentMessage = this._sentMessages[wireMessage.messageIdentifier];
                 // If this is a re flow of a PUBACK after we have restarted receivedMessage will not exist.
                if (sentMessage) {
                    delete this._sentMessages[wireMessage.messageIdentifier];
                    localStorage.removeItem("Sent:"+this._localKey+wireMessage.messageIdentifier);
                    if (this.onMessageDelivered)
                        this.onMessageDelivered(sentMessage.payloadMessage);
                }
                break;

            case MESSAGE_TYPE.PUBREC:
                var sentMessage = this._sentMessages[wireMessage.messageIdentifier];
                // If this is a re flow of a PUBREC after we have restarted receivedMessage will not exist.
                if (sentMessage) {
                    sentMessage.pubRecReceived = true;
                    var pubRelMessage = new WireMessage(MESSAGE_TYPE.PUBREL, {messageIdentifier:wireMessage.messageIdentifier});
                    this.store("Sent:", sentMessage);
                    this._schedule_message(pubRelMessage);
                }
                break;

            case MESSAGE_TYPE.PUBREL:
                var receivedMessage = this._receivedMessages[wireMessage.messageIdentifier];
                localStorage.removeItem("Received:"+this._localKey+wireMessage.messageIdentifier);
                // If this is a re flow of a PUBREL after we have restarted receivedMessage will not exist.
                if (receivedMessage) {
                    this._receiveMessage(receivedMessage);
                    delete this._receivedMessages[wireMessage.messageIdentifier];
                }
                // Always flow PubComp, we may have previously flowed PubComp but the server lost it and restarted.
                var pubCompMessage = new WireMessage(MESSAGE_TYPE.PUBCOMP, {messageIdentifier:wireMessage.messageIdentifier});
                this._schedule_message(pubCompMessage);                    
                break;

            case MESSAGE_TYPE.PUBCOMP: 
                var sentMessage = this._sentMessages[wireMessage.messageIdentifier];
                delete this._sentMessages[wireMessage.messageIdentifier];
                localStorage.removeItem("Sent:"+this._localKey+wireMessage.messageIdentifier);
                if (this.onMessageDelivered)
                    this.onMessageDelivered(sentMessage.payloadMessage);
                break;

            case MESSAGE_TYPE.SUBACK:
                var sentMessage = this._sentMessages[wireMessage.messageIdentifier];
                if (sentMessage) {
                    if(sentMessage.timeOut)
                        sentMessage.timeOut.cancel();
                    wireMessage.returnCode.indexOf = Array.prototype.indexOf;
                    if (wireMessage.returnCode.indexOf(0x80) !== -1) {
                        if (sentMessage.onFailure) {
                            sentMessage.onFailure(wireMessage.returnCode);
                        } 
                    } else if (sentMessage.onSuccess) {
                        sentMessage.onSuccess(wireMessage.returnCode);
                    }
                    delete this._sentMessages[wireMessage.messageIdentifier];
                }
                break;

            case MESSAGE_TYPE.UNSUBACK:
                var sentMessage = this._sentMessages[wireMessage.messageIdentifier];
                if (sentMessage) { 
                    if (sentMessage.timeOut)
                        sentMessage.timeOut.cancel();
                    if (sentMessage.callback) {
                        sentMessage.callback();
                    }
                    delete this._sentMessages[wireMessage.messageIdentifier];
                }

                break;

            case MESSAGE_TYPE.PINGRESP:
                /* The sendPinger or receivePinger may have sent a ping, the receivePinger has already been reset. */
                this.sendPinger.reset();
                break;

            case MESSAGE_TYPE.DISCONNECT:
                // Clients do not expect to receive disconnect packets.
                this._disconnected(ERROR.INVALID_MQTT_MESSAGE_TYPE.code , format(ERROR.INVALID_MQTT_MESSAGE_TYPE, [wireMessage.type]));
                break;

            default:
                this._disconnected(ERROR.INVALID_MQTT_MESSAGE_TYPE.code , format(ERROR.INVALID_MQTT_MESSAGE_TYPE, [wireMessage.type]));
            }
        } catch (error) {
            this._disconnected(ERROR.INTERNAL_ERROR.code , format(ERROR.INTERNAL_ERROR, [error.message,error.stack.toString()]));

        }
    };

    /** @ignore */
    ClientImpl.prototype._on_socket_error = function (error) {
        this._disconnected(ERROR.SOCKET_ERROR.code , format(ERROR.SOCKET_ERROR, [error.data]));
    };

    /** @ignore */
    ClientImpl.prototype._on_socket_close = function () {
        this._disconnected(ERROR.SOCKET_CLOSE.code , format(ERROR.SOCKET_CLOSE));
    };

    /** @ignore */
    ClientImpl.prototype._socket_send = function (wireMessage) {

        if (wireMessage.type == 1) {
            var wireMessageMasked = this._traceMask(wireMessage, "password"); 
            this._trace("Client._socket_send", wireMessageMasked);
        }
        else this._trace("Client._socket_send", wireMessage);

        this.socket.send(wireMessage.encode());
        /* We have proved to the server we are alive. */
        this.sendPinger.reset();
    };

    /** @ignore */
    ClientImpl.prototype._receivePublish = function (wireMessage) {
        switch(wireMessage.payloadMessage.qos) {
            case "undefined":
            case 0:
                this._receiveMessage(wireMessage);
                break;

            case 1:
                var pubAckMessage = new WireMessage(MESSAGE_TYPE.PUBACK, {messageIdentifier:wireMessage.messageIdentifier});
                this._schedule_message(pubAckMessage);
                this._receiveMessage(wireMessage);
                break;

            case 2:
                this._receivedMessages[wireMessage.messageIdentifier] = wireMessage;
                this.store("Received:", wireMessage);
                var pubRecMessage = new WireMessage(MESSAGE_TYPE.PUBREC, {messageIdentifier:wireMessage.messageIdentifier});
                this._schedule_message(pubRecMessage);

                break;

            default:
                throw Error("Invaild qos="+wireMmessage.payloadMessage.qos);
        }
    };

    /** @ignore */
    ClientImpl.prototype._receiveMessage = function (wireMessage) {
        if (this.onMessageArrived) {
            this.onMessageArrived(wireMessage.payloadMessage);
        }
    };

    /**
     * Client has disconnected either at its own request or because the server
     * or network disconnected it. Remove all non-durable state.
     * @param {errorCode} [number] the error number.
     * @param {errorText} [string] the error text.
     * @ignore
     */
    ClientImpl.prototype._disconnected = function (errorCode, errorText) {
        this._trace("Client._disconnected", errorCode, errorText);

        this.sendPinger.cancel();
        this.receivePinger.cancel();
        if (this._connectTimeout)
            this._connectTimeout.cancel();
        // Clear message buffers.
        this._msg_queue = [];
        this._notify_msg_sent = {};

        if (this.socket) {
            // Cancel all socket callbacks so that they cannot be driven again by this socket.
            this.socket.onopen = null;
            this.socket.onmessage = null;
            this.socket.onerror = null;
            this.socket.onclose = null;
            if (this.socket.readyState === 1)
                this.socket.close();
            delete this.socket;           
        }

        if (this.connectOptions.uris && this.hostIndex < this.connectOptions.uris.length-1) {
            // Try the next host.
            this.hostIndex++;
            this._doConnect(this.connectOptions.uris[this.hostIndex]);

        } else {

            if (errorCode === undefined) {
                errorCode = ERROR.OK.code;
                errorText = format(ERROR.OK);
            }

            // Run any application callbacks last as they may attempt to reconnect and hence create a new socket.
            if (this.connected) {
                this.connected = false;
                // Execute the connectionLostCallback if there is one, and we were connected.       
                if (this.onConnectionLost)
                    this.onConnectionLost({errorCode:errorCode, errorMessage:errorText});       
            } else {
                // Otherwise we never had a connection, so indicate that the connect has failed.
                if (this.connectOptions.mqttVersion === 4 && this.connectOptions.mqttVersionExplicit === false) {
                    this._trace("Failed to connect V4, dropping back to V3");
                    this.connectOptions.mqttVersion = 3;
                    if (this.connectOptions.uris) {
                        this.hostIndex = 0;
                        this._doConnect(this.connectOptions.uris[0]);  
                    } else {
                        this._doConnect(this.uri);
                    }   
                } else if(this.connectOptions.onFailure) {
                    this.connectOptions.onFailure({invocationContext:this.connectOptions.invocationContext, errorCode:errorCode, errorMessage:errorText});
                }
            }
        }
    };

    /** @ignore */
    ClientImpl.prototype._trace = function () {
        // Pass trace message back to client's callback function
        if (this.traceFunction) {
            for (var i in arguments)
            {   
                if (typeof arguments[i] !== "undefined")
                    arguments[i] = JSON.stringify(arguments[i]);
            }
            var record = Array.prototype.slice.call(arguments).join("");
            this.traceFunction ({severity: "Debug", message: record });
        }

        //buffer style trace
        if ( this._traceBuffer !== null ) {  
            for (var i = 0, max = arguments.length; i < max; i++) {
                if ( this._traceBuffer.length == this._MAX_TRACE_ENTRIES ) {    
                    this._traceBuffer.shift();              
                }
                if (i === 0) this._traceBuffer.push(arguments[i]);
                else if (typeof arguments[i] === "undefined" ) this._traceBuffer.push(arguments[i]);
                else this._traceBuffer.push("  "+JSON.stringify(arguments[i]));
            }
        }
    };

    /** @ignore */
    ClientImpl.prototype._traceMask = function (traceObject, masked) {
        var traceObjectMasked = {};
        for (var attr in traceObject) {
            if (traceObject.hasOwnProperty(attr)) {
                if (attr == masked) 
                    traceObjectMasked[attr] = "******";
                else
                    traceObjectMasked[attr] = traceObject[attr];
            } 
        }
        return traceObjectMasked;
    };

    // ------------------------------------------------------------------------
    // Public Programming interface.
    // ------------------------------------------------------------------------

    /** 
     * The JavaScript application communicates to the server using a {@link Paho.MQTT.Client} object. 
     * <p>
     * Most applications will create just one Client object and then call its connect() method,
     * however applications can create more than one Client object if they wish. 
     * In this case the combination of host, port and clientId attributes must be different for each Client object.
     * <p>
     * The send, subscribe and unsubscribe methods are implemented as asynchronous JavaScript methods 
     * (even though the underlying protocol exchange might be synchronous in nature). 
     * This means they signal their completion by calling back to the application, 
     * via Success or Failure callback functions provided by the application on the method in question. 
     * Such callbacks are called at most once per method invocation and do not persist beyond the lifetime 
     * of the script that made the invocation.
     * <p>
     * In contrast there are some callback functions, most notably <i>onMessageArrived</i>, 
     * that are defined on the {@link Paho.MQTT.Client} object.  
     * These may get called multiple times, and aren't directly related to specific method invocations made by the client. 
     *
     * @name Paho.MQTT.Client    
     * 
     * @constructor
     *  
     * @param {string} host - the address of the messaging server, as a fully qualified WebSocket URI, as a DNS name or dotted decimal IP address.
     * @param {number} port - the port number to connect to - only required if host is not a URI
     * @param {string} path - the path on the host to connect to - only used if host is not a URI. Default: '/mqtt'.
     * @param {string} clientId - the Messaging client identifier, between 1 and 23 characters in length.
     * 
     * @property {string} host - <i>read only</i> the server's DNS hostname or dotted decimal IP address.
     * @property {number} port - <i>read only</i> the server's port.
     * @property {string} path - <i>read only</i> the server's path.
     * @property {string} clientId - <i>read only</i> used when connecting to the server.
     * @property {function} onConnectionLost - called when a connection has been lost. 
     *                            after a connect() method has succeeded.
     *                            Establish the call back used when a connection has been lost. The connection may be
     *                            lost because the client initiates a disconnect or because the server or network 
     *                            cause the client to be disconnected. The disconnect call back may be called without 
     *                            the connectionComplete call back being invoked if, for example the client fails to 
     *                            connect.
     *                            A single response object parameter is passed to the onConnectionLost callback containing the following fields:
     *                            <ol>   
     *                            <li>errorCode
     *                            <li>errorMessage       
     *                            </ol>
     * @property {function} onMessageDelivered called when a message has been delivered. 
     *                            All processing that this Client will ever do has been completed. So, for example,
     *                            in the case of a Qos=2 message sent by this client, the PubComp flow has been received from the server
     *                            and the message has been removed from persistent storage before this callback is invoked. 
     *                            Parameters passed to the onMessageDelivered callback are:
     *                            <ol>   
     *                            <li>{@link Paho.MQTT.Message} that was delivered.
     *                            </ol>    
     * @property {function} onMessageArrived called when a message has arrived in this Paho.MQTT.client. 
     *                            Parameters passed to the onMessageArrived callback are:
     *                            <ol>   
     *                            <li>{@link Paho.MQTT.Message} that has arrived.
     *                            </ol>    
     */
    var Client = function (host, port, path, clientId) {

        var uri;

        if (typeof host !== "string")
            throw new Error(format(ERROR.INVALID_TYPE, [typeof host, "host"]));

        if (arguments.length == 2) {
            // host: must be full ws:// uri
            // port: clientId
            clientId = port;
            uri = host;
            var match = uri.match(/^(wss?):\/\/((\[(.+)\])|([^\/]+?))(:(\d+))?(\/.*)$/);
            if (match) {
                host = match[4]||match[2];
                port = parseInt(match[7]);
                path = match[8];
            } else {
                throw new Error(format(ERROR.INVALID_ARGUMENT,[host,"host"]));
            }
        } else {
            if (arguments.length == 3) {
                clientId = path;
                path = "/mqtt";
            }
            if (typeof port !== "number" || port < 0)
                throw new Error(format(ERROR.INVALID_TYPE, [typeof port, "port"]));
            if (typeof path !== "string")
                throw new Error(format(ERROR.INVALID_TYPE, [typeof path, "path"]));

            var ipv6AddSBracket = (host.indexOf(":") != -1 && host.slice(0,1) != "[" && host.slice(-1) != "]");
            uri = "ws://"+(ipv6AddSBracket?"["+host+"]":host)+":"+port+path;
        }

        var clientIdLength = 0;
        for (var i = 0; i<clientId.length; i++) {
            var charCode = clientId.charCodeAt(i);                   
            if (0xD800 <= charCode && charCode <= 0xDBFF)  {                
                 i++; // Surrogate pair.
            }              
            clientIdLength++;
        }           
        if (typeof clientId !== "string" || clientIdLength > 65535)
            throw new Error(format(ERROR.INVALID_ARGUMENT, [clientId, "clientId"])); 

        var client = new ClientImpl(uri, host, port, path, clientId);
        this._getHost =  function() { return host; };
        this._setHost = function() { throw new Error(format(ERROR.UNSUPPORTED_OPERATION)); };

        this._getPort = function() { return port; };
        this._setPort = function() { throw new Error(format(ERROR.UNSUPPORTED_OPERATION)); };

        this._getPath = function() { return path; };
        this._setPath = function() { throw new Error(format(ERROR.UNSUPPORTED_OPERATION)); };

        this._getURI = function() { return uri; };
        this._setURI = function() { throw new Error(format(ERROR.UNSUPPORTED_OPERATION)); };

        this._getClientId = function() { return client.clientId; };
        this._setClientId = function() { throw new Error(format(ERROR.UNSUPPORTED_OPERATION)); };

        this._getOnConnectionLost = function() { return client.onConnectionLost; };
        this._setOnConnectionLost = function(newOnConnectionLost) { 
            if (typeof newOnConnectionLost === "function")
                client.onConnectionLost = newOnConnectionLost;
            else 
                throw new Error(format(ERROR.INVALID_TYPE, [typeof newOnConnectionLost, "onConnectionLost"]));
        };

        this._getOnMessageDelivered = function() { return client.onMessageDelivered; };
        this._setOnMessageDelivered = function(newOnMessageDelivered) { 
            if (typeof newOnMessageDelivered === "function")
                client.onMessageDelivered = newOnMessageDelivered;
            else 
                throw new Error(format(ERROR.INVALID_TYPE, [typeof newOnMessageDelivered, "onMessageDelivered"]));
        };

        this._getOnMessageArrived = function() { return client.onMessageArrived; };
        this._setOnMessageArrived = function(newOnMessageArrived) { 
            if (typeof newOnMessageArrived === "function")
                client.onMessageArrived = newOnMessageArrived;
            else 
                throw new Error(format(ERROR.INVALID_TYPE, [typeof newOnMessageArrived, "onMessageArrived"]));
        };

        this._getTrace = function() { return client.traceFunction; };
        this._setTrace = function(trace) {
            if(typeof trace === "function"){
                client.traceFunction = trace;
            }else{
                throw new Error(format(ERROR.INVALID_TYPE, [typeof trace, "onTrace"]));
            }
        };

        /** 
         * Connect this Messaging client to its server. 
         * 
         * @name Paho.MQTT.Client#connect
         * @function
         * @param {Object} connectOptions - attributes used with the connection. 
         * @param {number} connectOptions.timeout - If the connect has not succeeded within this 
         *                    number of seconds, it is deemed to have failed.
         *                    The default is 30 seconds.
         * @param {string} connectOptions.userName - Authentication username for this connection.
         * @param {string} connectOptions.password - Authentication password for this connection.
         * @param {Paho.MQTT.Message} connectOptions.willMessage - sent by the server when the client
         *                    disconnects abnormally.
         * @param {Number} connectOptions.keepAliveInterval - the server disconnects this client if
         *                    there is no activity for this number of seconds.
         *                    The default value of 60 seconds is assumed if not set.
         * @param {boolean} connectOptions.cleanSession - if true(default) the client and server 
         *                    persistent state is deleted on successful connect.
         * @param {boolean} connectOptions.useSSL - if present and true, use an SSL Websocket connection.
         * @param {object} connectOptions.invocationContext - passed to the onSuccess callback or onFailure callback.
         * @param {function} connectOptions.onSuccess - called when the connect acknowledgement 
         *                    has been received from the server.
         * A single response object parameter is passed to the onSuccess callback containing the following fields:
         * <ol>
         * <li>invocationContext as passed in to the onSuccess method in the connectOptions.       
         * </ol>
         * @config {function} [onFailure] called when the connect request has failed or timed out.
         * A single response object parameter is passed to the onFailure callback containing the following fields:
         * <ol>
         * <li>invocationContext as passed in to the onFailure method in the connectOptions.       
         * <li>errorCode a number indicating the nature of the error.
         * <li>errorMessage text describing the error.      
         * </ol>
         * @config {Array} [hosts] If present this contains either a set of hostnames or fully qualified
         * WebSocket URIs (ws://example.com:1883/mqtt), that are tried in order in place 
         * of the host and port paramater on the construtor. The hosts are tried one at at time in order until
         * one of then succeeds.
         * @config {Array} [ports] If present the set of ports matching the hosts. If hosts contains URIs, this property
         * is not used.
         * @throws {InvalidState} if the client is not in disconnected state. The client must have received connectionLost
         * or disconnected before calling connect for a second or subsequent time.
         */
        this.connect = function (connectOptions) {
            connectOptions = connectOptions || {} ;
            validate(connectOptions,  {timeout:"number",
                                       userName:"string", 
                                       password:"string", 
                                       willMessage:"object", 
                                       keepAliveInterval:"number", 
                                       cleanSession:"boolean", 
                                       useSSL:"boolean",
                                       invocationContext:"object", 
                                       onSuccess:"function", 
                                       onFailure:"function",
                                       hosts:"object",
                                       ports:"object",
                                       mqttVersion:"number"});

            // If no keep alive interval is set, assume 60 seconds.
            if (connectOptions.keepAliveInterval === undefined)
                connectOptions.keepAliveInterval = 60;

            if (connectOptions.mqttVersion > 4 || connectOptions.mqttVersion < 3) {
                throw new Error(format(ERROR.INVALID_ARGUMENT, [connectOptions.mqttVersion, "connectOptions.mqttVersion"]));
            }

            if (connectOptions.mqttVersion === undefined) {
                connectOptions.mqttVersionExplicit = false;
                connectOptions.mqttVersion = 4;
            } else {
                connectOptions.mqttVersionExplicit = true;
            }

            //Check that if password is set, so is username
            if (connectOptions.password === undefined && connectOptions.userName !== undefined)
                throw new Error(format(ERROR.INVALID_ARGUMENT, [connectOptions.password, "connectOptions.password"]));

            if (connectOptions.willMessage) {
                if (!(connectOptions.willMessage instanceof Message))
                    throw new Error(format(ERROR.INVALID_TYPE, [connectOptions.willMessage, "connectOptions.willMessage"]));
                // The will message must have a payload that can be represented as a string.
                // Cause the willMessage to throw an exception if this is not the case.
                connectOptions.willMessage.stringPayload;

                if (typeof connectOptions.willMessage.destinationName === "undefined")
                    throw new Error(format(ERROR.INVALID_TYPE, [typeof connectOptions.willMessage.destinationName, "connectOptions.willMessage.destinationName"]));
            }
            if (typeof connectOptions.cleanSession === "undefined")
                connectOptions.cleanSession = true;
            if (connectOptions.hosts) {

                if (!(connectOptions.hosts instanceof Array) )
                    throw new Error(format(ERROR.INVALID_ARGUMENT, [connectOptions.hosts, "connectOptions.hosts"]));
                if (connectOptions.hosts.length <1 )
                    throw new Error(format(ERROR.INVALID_ARGUMENT, [connectOptions.hosts, "connectOptions.hosts"]));

                var usingURIs = false;
                for (var i = 0; i<connectOptions.hosts.length; i++) {
                    if (typeof connectOptions.hosts[i] !== "string")
                        throw new Error(format(ERROR.INVALID_TYPE, [typeof connectOptions.hosts[i], "connectOptions.hosts["+i+"]"]));
                    if (/^(wss?):\/\/((\[(.+)\])|([^\/]+?))(:(\d+))?(\/.*)$/.test(connectOptions.hosts[i])) {
                        if (i == 0) {
                            usingURIs = true;
                        } else if (!usingURIs) {
                            throw new Error(format(ERROR.INVALID_ARGUMENT, [connectOptions.hosts[i], "connectOptions.hosts["+i+"]"]));
                        }
                    } else if (usingURIs) {
                        throw new Error(format(ERROR.INVALID_ARGUMENT, [connectOptions.hosts[i], "connectOptions.hosts["+i+"]"]));
                    }
                }

                if (!usingURIs) {
                    if (!connectOptions.ports)
                        throw new Error(format(ERROR.INVALID_ARGUMENT, [connectOptions.ports, "connectOptions.ports"]));
                    if (!(connectOptions.ports instanceof Array) )
                        throw new Error(format(ERROR.INVALID_ARGUMENT, [connectOptions.ports, "connectOptions.ports"]));
                    if (connectOptions.hosts.length != connectOptions.ports.length)
                        throw new Error(format(ERROR.INVALID_ARGUMENT, [connectOptions.ports, "connectOptions.ports"]));

                    connectOptions.uris = [];

                    for (var i = 0; i<connectOptions.hosts.length; i++) {
                        if (typeof connectOptions.ports[i] !== "number" || connectOptions.ports[i] < 0)
                            throw new Error(format(ERROR.INVALID_TYPE, [typeof connectOptions.ports[i], "connectOptions.ports["+i+"]"]));
                        var host = connectOptions.hosts[i];
                        var port = connectOptions.ports[i];

                        var ipv6 = (host.indexOf(":") != -1);
                        uri = "ws://"+(ipv6?"["+host+"]":host)+":"+port+path;
                        connectOptions.uris.push(uri);
                    }
                } else {
                    connectOptions.uris = connectOptions.hosts;
                }
            }

            client.connect(connectOptions);
        };

        /** 
         * Subscribe for messages, request receipt of a copy of messages sent to the destinations described by the filter.
         * 
         * @name Paho.MQTT.Client#subscribe
         * @function
         * @param {string} filter describing the destinations to receive messages from.
         * <br>
         * @param {object} subscribeOptions - used to control the subscription
         *
         * @param {number} subscribeOptions.qos - the maiximum qos of any publications sent 
         *                                  as a result of making this subscription.
         * @param {object} subscribeOptions.invocationContext - passed to the onSuccess callback 
         *                                  or onFailure callback.
         * @param {function} subscribeOptions.onSuccess - called when the subscribe acknowledgement
         *                                  has been received from the server.
         *                                  A single response object parameter is passed to the onSuccess callback containing the following fields:
         *                                  <ol>
         *                                  <li>invocationContext if set in the subscribeOptions.       
         *                                  </ol>
         * @param {function} subscribeOptions.onFailure - called when the subscribe request has failed or timed out.
         *                                  A single response object parameter is passed to the onFailure callback containing the following fields:
         *                                  <ol>
         *                                  <li>invocationContext - if set in the subscribeOptions.       
         *                                  <li>errorCode - a number indicating the nature of the error.
         *                                  <li>errorMessage - text describing the error.      
         *                                  </ol>
         * @param {number} subscribeOptions.timeout - which, if present, determines the number of
         *                                  seconds after which the onFailure calback is called.
         *                                  The presence of a timeout does not prevent the onSuccess
         *                                  callback from being called when the subscribe completes.         
         * @throws {InvalidState} if the client is not in connected state.
         */
        this.subscribe = function (filter, subscribeOptions) {
            if (typeof filter !== "string")
                throw new Error("Invalid argument:"+filter);
            subscribeOptions = subscribeOptions || {} ;
            validate(subscribeOptions,  {qos:"number", 
                                         invocationContext:"object", 
                                         onSuccess:"function", 
                                         onFailure:"function",
                                         timeout:"number"
                                        });
            if (subscribeOptions.timeout && !subscribeOptions.onFailure)
                throw new Error("subscribeOptions.timeout specified with no onFailure callback.");
            if (typeof subscribeOptions.qos !== "undefined" 
                && !(subscribeOptions.qos === 0 || subscribeOptions.qos === 1 || subscribeOptions.qos === 2 ))
                throw new Error(format(ERROR.INVALID_ARGUMENT, [subscribeOptions.qos, "subscribeOptions.qos"]));
            client.subscribe(filter, subscribeOptions);
        };

        /**
         * Unsubscribe for messages, stop receiving messages sent to destinations described by the filter.
         * 
         * @name Paho.MQTT.Client#unsubscribe
         * @function
         * @param {string} filter - describing the destinations to receive messages from.
         * @param {object} unsubscribeOptions - used to control the subscription
         * @param {object} unsubscribeOptions.invocationContext - passed to the onSuccess callback 
                                              or onFailure callback.
         * @param {function} unsubscribeOptions.onSuccess - called when the unsubscribe acknowledgement has been received from the server.
         *                                    A single response object parameter is passed to the 
         *                                    onSuccess callback containing the following fields:
         *                                    <ol>
         *                                    <li>invocationContext - if set in the unsubscribeOptions.     
         *                                    </ol>
         * @param {function} unsubscribeOptions.onFailure called when the unsubscribe request has failed or timed out.
         *                                    A single response object parameter is passed to the onFailure callback containing the following fields:
         *                                    <ol>
         *                                    <li>invocationContext - if set in the unsubscribeOptions.       
         *                                    <li>errorCode - a number indicating the nature of the error.
         *                                    <li>errorMessage - text describing the error.      
         *                                    </ol>
         * @param {number} unsubscribeOptions.timeout - which, if present, determines the number of seconds
         *                                    after which the onFailure callback is called. The presence of
         *                                    a timeout does not prevent the onSuccess callback from being
         *                                    called when the unsubscribe completes
         * @throws {InvalidState} if the client is not in connected state.
         */
        this.unsubscribe = function (filter, unsubscribeOptions) {
            if (typeof filter !== "string")
                throw new Error("Invalid argument:"+filter);
            unsubscribeOptions = unsubscribeOptions || {} ;
            validate(unsubscribeOptions,  {invocationContext:"object", 
                                           onSuccess:"function", 
                                           onFailure:"function",
                                           timeout:"number"
                                          });
            if (unsubscribeOptions.timeout && !unsubscribeOptions.onFailure)
                throw new Error("unsubscribeOptions.timeout specified with no onFailure callback.");
            client.unsubscribe(filter, unsubscribeOptions);
        };

        /**
         * Send a message to the consumers of the destination in the Message.
         * 
         * @name Paho.MQTT.Client#send
         * @function 
         * @param {string|Paho.MQTT.Message} topic - <b>mandatory</b> The name of the destination to which the message is to be sent. 
         *                     - If it is the only parameter, used as Paho.MQTT.Message object.
         * @param {String|ArrayBuffer} payload - The message data to be sent. 
         * @param {number} qos The Quality of Service used to deliver the message.
         *      <dl>
         *          <dt>0 Best effort (default).
         *              <dt>1 At least once.
         *              <dt>2 Exactly once.     
         *      </dl>
         * @param {Boolean} retained If true, the message is to be retained by the server and delivered 
         *                     to both current and future subscriptions.
         *                     If false the server only delivers the message to current subscribers, this is the default for new Messages. 
         *                     A received message has the retained boolean set to true if the message was published 
         *                     with the retained boolean set to true
         *                     and the subscrption was made after the message has been published. 
         * @throws {InvalidState} if the client is not connected.
         */   
        this.send = function (topic,payload,qos,retained) {   
            var message ;  

            if(arguments.length == 0){
                throw new Error("Invalid argument."+"length");

            }else if(arguments.length == 1) {

                if (!(topic instanceof Message) && (typeof topic !== "string"))
                    throw new Error("Invalid argument:"+ typeof topic);

                message = topic;
                if (typeof message.destinationName === "undefined")
                    throw new Error(format(ERROR.INVALID_ARGUMENT,[message.destinationName,"Message.destinationName"]));
                client.send(message); 

            }else {
                //parameter checking in Message object 
                message = new Message(payload);
                message.destinationName = topic;
                if(arguments.length >= 3)
                    message.qos = qos;
                if(arguments.length >= 4)
                    message.retained = retained;
                client.send(message); 
            }
        };

        /** 
         * Normal disconnect of this Messaging client from its server.
         * 
         * @name Paho.MQTT.Client#disconnect
         * @function
         * @throws {InvalidState} if the client is already disconnected.     
         */
        this.disconnect = function () {
            client.disconnect();
        };

        /** 
         * Get the contents of the trace log.
         * 
         * @name Paho.MQTT.Client#getTraceLog
         * @function
         * @return {Object[]} tracebuffer containing the time ordered trace records.
         */
        this.getTraceLog = function () {
            return client.getTraceLog();
        };

        /** 
         * Start tracing.
         * 
         * @name Paho.MQTT.Client#startTrace
         * @function
         */
        this.startTrace = function () {
            client.startTrace();
        };

        /** 
         * Stop tracing.
         * 
         * @name Paho.MQTT.Client#stopTrace
         * @function
         */
        this.stopTrace = function () {
            client.stopTrace();
        };

        this.isConnected = function() {
            return client.connected;
        };
    };

    Client.prototype = {
        get host() { return this._getHost(); },
        set host(newHost) { this._setHost(newHost); },

        get port() { return this._getPort(); },
        set port(newPort) { this._setPort(newPort); },

        get path() { return this._getPath(); },
        set path(newPath) { this._setPath(newPath); },

        get clientId() { return this._getClientId(); },
        set clientId(newClientId) { this._setClientId(newClientId); },

        get onConnectionLost() { return this._getOnConnectionLost(); },
        set onConnectionLost(newOnConnectionLost) { this._setOnConnectionLost(newOnConnectionLost); },

        get onMessageDelivered() { return this._getOnMessageDelivered(); },
        set onMessageDelivered(newOnMessageDelivered) { this._setOnMessageDelivered(newOnMessageDelivered); },

        get onMessageArrived() { return this._getOnMessageArrived(); },
        set onMessageArrived(newOnMessageArrived) { this._setOnMessageArrived(newOnMessageArrived); },

        get trace() { return this._getTrace(); },
        set trace(newTraceFunction) { this._setTrace(newTraceFunction); }   

    };

    /** 
     * An application message, sent or received.
     * <p>
     * All attributes may be null, which implies the default values.
     * 
     * @name Paho.MQTT.Message
     * @constructor
     * @param {String|ArrayBuffer} payload The message data to be sent.
     * <p>
     * @property {string} payloadString <i>read only</i> The payload as a string if the payload consists of valid UTF-8 characters.
     * @property {ArrayBuffer} payloadBytes <i>read only</i> The payload as an ArrayBuffer.
     * <p>
     * @property {string} destinationName <b>mandatory</b> The name of the destination to which the message is to be sent
     *                    (for messages about to be sent) or the name of the destination from which the message has been received.
     *                    (for messages received by the onMessage function).
     * <p>
     * @property {number} qos The Quality of Service used to deliver the message.
     * <dl>
     *     <dt>0 Best effort (default).
     *     <dt>1 At least once.
     *     <dt>2 Exactly once.     
     * </dl>
     * <p>
     * @property {Boolean} retained If true, the message is to be retained by the server and delivered 
     *                     to both current and future subscriptions.
     *                     If false the server only delivers the message to current subscribers, this is the default for new Messages. 
     *                     A received message has the retained boolean set to true if the message was published 
     *                     with the retained boolean set to true
     *                     and the subscrption was made after the message has been published. 
     * <p>
     * @property {Boolean} duplicate <i>read only</i> If true, this message might be a duplicate of one which has already been received. 
     *                     This is only set on messages received from the server.
     *                     
     */
    var Message = function (newPayload) {  
        var payload;
        if (   typeof newPayload === "string" 
            || newPayload instanceof ArrayBuffer
            || newPayload instanceof Int8Array
            || newPayload instanceof Uint8Array
            || newPayload instanceof Int16Array
            || newPayload instanceof Uint16Array
            || newPayload instanceof Int32Array
            || newPayload instanceof Uint32Array
            || newPayload instanceof Float32Array
            || newPayload instanceof Float64Array
           ) {
            payload = newPayload;
        } else {
            throw (format(ERROR.INVALID_ARGUMENT, [newPayload, "newPayload"]));
        }

        this._getPayloadString = function () {
            if (typeof payload === "string")
                return payload;
            else
                return parseUTF8(payload, 0, payload.length); 
        };

        this._getPayloadBytes = function() {
            if (typeof payload === "string") {
                var buffer = new ArrayBuffer(UTF8Length(payload));
                var byteStream = new Uint8Array(buffer); 
                stringToUTF8(payload, byteStream, 0);

                return byteStream;
            } else {
                return payload;
            }
        };

        var destinationName = undefined;
        this._getDestinationName = function() { return destinationName; };
        this._setDestinationName = function(newDestinationName) { 
            if (typeof newDestinationName === "string")
                destinationName = newDestinationName;
            else 
                throw new Error(format(ERROR.INVALID_ARGUMENT, [newDestinationName, "newDestinationName"]));
        };

        var qos = 0;
        this._getQos = function() { return qos; };
        this._setQos = function(newQos) { 
            if (newQos === 0 || newQos === 1 || newQos === 2 )
                qos = newQos;
            else 
                throw new Error("Invalid argument:"+newQos);
        };

        var retained = false;
        this._getRetained = function() { return retained; };
        this._setRetained = function(newRetained) { 
            if (typeof newRetained === "boolean")
                retained = newRetained;
            else 
                throw new Error(format(ERROR.INVALID_ARGUMENT, [newRetained, "newRetained"]));
        };

        var duplicate = false;
        this._getDuplicate = function() { return duplicate; };
        this._setDuplicate = function(newDuplicate) { duplicate = newDuplicate; };
    };

    Message.prototype = {
        get payloadString() { return this._getPayloadString(); },
        get payloadBytes() { return this._getPayloadBytes(); },

        get destinationName() { return this._getDestinationName(); },
        set destinationName(newDestinationName) { this._setDestinationName(newDestinationName); },

        get qos() { return this._getQos(); },
        set qos(newQos) { this._setQos(newQos); },

        get retained() { return this._getRetained(); },
        set retained(newRetained) { this._setRetained(newRetained); },

        get duplicate() { return this._getDuplicate(); },
        set duplicate(newDuplicate) { this._setDuplicate(newDuplicate); }
    };

    // Module contents.
    return {
        Client: Client,
        Message: Message
    };
})(window);