# Yahoo! UI Library

### connection 2.4.1

Yahoo! UI Library > connection > connection.js (source view)

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    /**
     * The Connection Manager provides a simplified interface to the XMLHttpRequest
     * object.  It handles cross-browser instantiantion of XMLHttpRequest, negotiates the
     * interactive states and server response, returning the results to a pre-defined
     * callback you create.
     *
     * @namespace YAHOO.util
     * @module connection
     * @requires yahoo
     * @requires event
     */

    /**
     * The Connection Manager singleton provides methods for creating and managing
     * asynchronous transactions.
     *
     * @class Connect
     */

    YAHOO.util.Connect =
    {
      /**
       * @description Array of MSFT ActiveX ids for XMLHttpRequest.
       * @property _msxml_progid
       * @private
       * @static
       * @type array
       */
    	_msxml_progid:[
    		'MSXML2.XMLHTTP.3.0',
    		'MSXML2.XMLHTTP',
    		'Microsoft.XMLHTTP'
    		],

      /**
       * @description Object literal of HTTP header(s)
       * @property _http_header
       * @private
       * @static
       * @type object
       */
    	_http_headers:{},

      /**
       * @description Determines if HTTP headers are set.
       * @property _has_http_headers
       * @private
       * @static
       * @type boolean
       */
    	_has_http_headers:false,

     /**
      * @description Determines if a default header of
      * Content-Type of 'application/x-www-form-urlencoded'
      * will be added to any client HTTP headers sent for POST
      * transactions.
      * @property _use_default_post_header
      * @private
      * @static
      * @type boolean
      */
        _use_default_post_header:true,

     /**
      * @description Determines if a default header of
      * Content-Type of 'application/x-www-form-urlencoded'
      * will be added to client HTTP headers sent for POST
      * transactions.
      * @property _default_post_header
      * @private
      * @static
      * @type boolean
      */
        _default_post_header:'application/x-www-form-urlencoded; charset=UTF-8',

     /**
      * @description Determines if a default header of
      * 'X-Requested-With: XMLHttpRequest'
      * will be added to each transaction.
      * @property _use_default_xhr_header
      * @private
      * @static
      * @type boolean
      */
        _use_default_xhr_header:true,

     /**
      * @description The default header value for the label
      * "X-Requested-With".  This is sent with each
      * transaction, by default, to identify the
      * request as being made by YUI Connection Manager.
      * @property _default_xhr_header
      * @private
      * @static
      * @type boolean
      */
        _default_xhr_header:'XMLHttpRequest',

     /**
      * @description Determines if custom, default headers
      * are set for each transaction.
      * @property _has_default_header
      * @private
      * @static
      * @type boolean
      */
        _has_default_headers:true,

     /**
      * @description Determines if custom, default headers
      * are set for each transaction.
      * @property _has_default_header
      * @private
      * @static
      * @type boolean
      */
        _default_headers:{},

     /**
      * @description Property modified by setForm() to determine if the data
      * should be submitted as an HTML form.
      * @property _isFormSubmit
      * @private
      * @static
      * @type boolean
      */
        _isFormSubmit:false,

     /**
      * @description Property modified by setForm() to determine if a file(s)
      * upload is expected.
      * @property _isFileUpload
      * @private
      * @static
      * @type boolean
      */
        _isFileUpload:false,

     /**
      * @description Property modified by setForm() to set a reference to the HTML
      * form node if the desired action is file upload.
      * @property _formNode
      * @private
      * @static
      * @type object
      */
        _formNode:null,

     /**
      * @description Property modified by setForm() to set the HTML form data
      * for each transaction.
      * @property _sFormData
      * @private
      * @static
      * @type string
      */
        _sFormData:null,

     /**
      * @description Collection of polling references to the polling mechanism in handleReadyState.
      * @property _poll
      * @private
      * @static
      * @type object
      */
        _poll:{},

     /**
      * @description Queue of timeout values for each transaction callback with a defined timeout value.
      * @property _timeOut
      * @private
      * @static
      * @type object
      */
        _timeOut:{},

      /**
       * @description The polling frequency, in milliseconds, for HandleReadyState.
       * when attempting to determine a transaction's XHR readyState.
       * The default is 50 milliseconds.
       * @property _polling_interval
       * @private
       * @static
       * @type int
       */
         _polling_interval:50,

      /**
       * @description A transaction counter that increments the transaction id for each transaction.
       * @property _transaction_id
       * @private
       * @static
       * @type int
       */
         _transaction_id:0,

      /**
       * @description Tracks the name-value pair of the "clicked" submit button if multiple submit
       * buttons are present in an HTML form; and, if YAHOO.util.Event is available.
       * @property _submitElementValue
       * @private
       * @static
       * @type string
       */
    	 _submitElementValue:null,

      /**
       * @description Determines whether YAHOO.util.Event is available and returns true or false.
       * If true, an event listener is bound at the document level to trap click events that
       * resolve to a target type of "Submit".  This listener will enable setForm() to determine
       * the clicked "Submit" value in a multi-Submit button, HTML form.
       * @property _hasSubmitListener
       * @private
       * @static
       */
    	 _hasSubmitListener:(function()
    	 {
    		if(YAHOO.util.Event){
    			YAHOO.util.Event.addListener(
    				document,
    				'click',
    				function(e){
    					var obj = YAHOO.util.Event.getTarget(e);
    					if(obj.type == 'submit'){
    						YAHOO.util.Connect._submitElementValue = encodeURIComponent(obj.name) + "=" + encodeURIComponent(obj.value);
    					}
    				});
    			return true;
    	    }
    	    return false;
    	 })(),

      /**
       * @description Custom event that fires at the start of a transaction
       * @property startEvent
       * @private
       * @static
       * @type CustomEvent
       */
    	startEvent: new YAHOO.util.CustomEvent('start'),

      /**
       * @description Custom event that fires when a transaction response has completed.
       * @property completeEvent
       * @private
       * @static
       * @type CustomEvent
       */
    	completeEvent: new YAHOO.util.CustomEvent('complete'),

      /**
       * @description Custom event that fires when handleTransactionResponse() determines a
       * response in the HTTP 2xx range.
       * @property successEvent
       * @private
       * @static
       * @type CustomEvent
       */
    	successEvent: new YAHOO.util.CustomEvent('success'),

      /**
       * @description Custom event that fires when handleTransactionResponse() determines a
       * response in the HTTP 4xx/5xx range.
       * @property failureEvent
       * @private
       * @static
       * @type CustomEvent
       */
    	failureEvent: new YAHOO.util.CustomEvent('failure'),

      /**
       * @description Custom event that fires when handleTransactionResponse() determines a
       * response in the HTTP 4xx/5xx range.
       * @property failureEvent
       * @private
       * @static
       * @type CustomEvent
       */
    	uploadEvent: new YAHOO.util.CustomEvent('upload'),

      /**
       * @description Custom event that fires when a transaction is successfully aborted.
       * @property abortEvent
       * @private
       * @static
       * @type CustomEvent
       */
    	abortEvent: new YAHOO.util.CustomEvent('abort'),

      /**
       * @description A reference table that maps callback custom events members to its specific
       * event name.
       * @property _customEvents
       * @private
       * @static
       * @type object
       */
    	_customEvents:
    	{
    		onStart:['startEvent', 'start'],
    		onComplete:['completeEvent', 'complete'],
    		onSuccess:['successEvent', 'success'],
    		onFailure:['failureEvent', 'failure'],
    		onUpload:['uploadEvent', 'upload'],
    		onAbort:['abortEvent', 'abort']
    	},

      /**
       * @description Member to add an ActiveX id to the existing xml_progid array.
       * In the event(unlikely) a new ActiveX id is introduced, it can be added
       * without internal code modifications.
       * @method setProgId
       * @public
       * @static
       * @param {string} id The ActiveX id to be added to initialize the XHR object.
       * @return void
       */
    	setProgId:function(id)
    	{
    		this._msxml_progid.unshift(id);
    		YAHOO.log('ActiveX Program Id  ' + id + ' added to _msxml_progid.', 'info', 'Connection');
    	},

      /**
       * @description Member to enable or disable the default POST header.
       * @method setDefaultPostHeader
       * @public
       * @static
       * @param {boolean} b Set and use default header - true or false .
       * @return void
       */
    	setDefaultPostHeader:function(b)
    	{
    		this._use_default_post_header = b;
    		YAHOO.log('Use default POST header set to  ' + b, 'info', 'Connection');
    	},

      /**
       * @description Member to enable or disable the default POST header.
       * @method setDefaultXhrHeader
       * @public
       * @static
       * @param {boolean} b Set and use default header - true or false .
       * @return void
       */
    	setDefaultXhrHeader:function(b)
    	{
    		this._use_default_xhr_header = b;
    		YAHOO.log('Use default transaction header set to  ' + b, 'info', 'Connection');
    	},

      /**
       * @description Member to modify the default polling interval.
       * @method setPollingInterval
       * @public
       * @static
       * @param {int} i The polling interval in milliseconds.
       * @return void
       */
    	setPollingInterval:function(i)
    	{
    		if(typeof i == 'number' && isFinite(i)){
    			this._polling_interval = i;
    			YAHOO.log('Default polling interval set to ' + i +'ms', 'info', 'Connection');
    		}
    	},

      /**
       * @description Instantiates a XMLHttpRequest object and returns an object with two properties:
       * the XMLHttpRequest instance and the transaction id.
       * @method createXhrObject
       * @private
       * @static
       * @param {int} transactionId Property containing the transaction id for this transaction.
       * @return object
       */
    	createXhrObject:function(transactionId)
    	{
    		var obj,http;
    		try
    		{
    			// Instantiates XMLHttpRequest in non-IE browsers and assigns to http.
    			http = new XMLHttpRequest();
    			//  Object literal with http and tId properties
    			obj = { conn:http, tId:transactionId };
    			YAHOO.log('XHR object created for transaction ' + transactionId, 'info', 'Connection');
    		}
    		catch(e)
    		{
    			for(var i=0; i<this._msxml_progid.length; ++i){
    				try
    				{
    					// Instantiates XMLHttpRequest for IE and assign to http.
    					http = new ActiveXObject(this._msxml_progid[i]);
    					//  Object literal with conn and tId properties
    					obj = { conn:http, tId:transactionId };
    					YAHOO.log('ActiveX XHR object created for transaction ' + transactionId, 'info', 'Connection');
    					break;
    				}
    				catch(e){}
    			}
    		}
    		finally
    		{
    			return obj;
    		}
    	},

      /**
       * @description This method is called by asyncRequest to create a
       * valid connection object for the transaction.  It also passes a
       * transaction id and increments the transaction id counter.
       * @method getConnectionObject
       * @private
       * @static
       * @return {object}
       */
    	getConnectionObject:function(isFileUpload)
    	{
    		var o;
    		var tId = this._transaction_id;

    		try
    		{
    			if(!isFileUpload){
    				o = this.createXhrObject(tId);
    			}
    			else{
    				o = {};
    				o.tId = tId;
    				o.isUpload = true;
    			}

    			if(o){
    				this._transaction_id++;
    			}
    		}
    		catch(e){}
    		finally
    		{
    			return o;
    		}
    	},

      /**
       * @description Method for initiating an asynchronous request via the XHR object.
       * @method asyncRequest
       * @public
       * @static
       * @param {string} method HTTP transaction method
       * @param {string} uri Fully qualified path of resource
       * @param {callback} callback User-defined callback function or object
       * @param {string} postData POST body
       * @return {object} Returns the connection object
       */
    	asyncRequest:function(method, uri, callback, postData)
    	{
    		var o = (this._isFileUpload)?this.getConnectionObject(true):this.getConnectionObject();

    		if(!o){
    			YAHOO.log('Unable to create connection object.', 'error', 'Connection');
    			return null;
    		}
    		else{

    			// Intialize any transaction-specific custom events, if provided.
    			if(callback && callback.customevents){
    				this.initCustomEvents(o, callback);
    			}

    			if(this._isFormSubmit){
    				if(this._isFileUpload){
    					this.uploadFile(o, callback, uri, postData);
    					return o;
    				}

    				// If the specified HTTP method is GET, setForm() will return an
    				// encoded string that is concatenated to the uri to
    				// create a querystring.
    				if(method.toUpperCase() == 'GET'){
    					if(this._sFormData.length !== 0){
    						// If the URI already contains a querystring, append an ampersand
    						// and then concatenate _sFormData to the URI.
    						uri += ((uri.indexOf('?') == -1)?'?':'&') + this._sFormData;
    					}
    					else{
    						uri += "?" + this._sFormData;
    					}
    				}
    				else if(method.toUpperCase() == 'POST'){
    					// If POST data exist in addition to the HTML form data,
    					// it will be concatenated to the form data.
    					postData = postData?this._sFormData + "&" + postData:this._sFormData;
    				}
    			}

    			o.conn.open(method, uri, true);
    			//this.processTransactionHeaders(o);

    			// Each transaction will automatically include a custom header of
    			// "X-Requested-With: XMLHttpRequest" to identify the request as
    			// having originated from Connection Manager.
    			if(this._use_default_xhr_header){
    				if(!this._default_headers['X-Requested-With']){
    					this.initHeader('X-Requested-With', this._default_xhr_header, true);
    					YAHOO.log('Initialize transaction header X-Request-Header to XMLHttpRequest.', 'info', 'Connection');
    				}
    			}

    			if(this._isFormSubmit || (postData && this._use_default_post_header)){
    				this.initHeader('Content-Type', this._default_post_header);
    				YAHOO.log('Initialize header Content-Type to application/x-www-form-urlencoded for POST transaction.', 'info', 'Connection');
    				if(this._isFormSubmit){
    					this.resetFormState();
    				}
    			}

    			if(this._has_default_headers || this._has_http_headers){
    				this.setHeader(o);
    			}

    			this.handleReadyState(o, callback);
    			o.conn.send(postData || null);

    			// Fire global custom event -- startEvent
    			this.startEvent.fire(o);

    			if(o.startEvent){
    				// Fire transaction custom event -- startEvent
    				o.startEvent.fire(o);
    			}

    			return o;
    		}
    	},

      /**
       * @description This method creates and subscribes custom events,
       * specific to each transaction
       * @method initCustomEvents
       * @private
       * @static
       * @param {object} o The connection object
       * @param {callback} callback The user-defined callback object
       * @return {void}
       */
    	initCustomEvents:function(o, callback)
    	{
    		// Enumerate through callback.customevents members and bind/subscribe
    		// events that match in the _customEvents table.
    		for(var prop in callback.customevents){
    			if(this._customEvents[prop][0]){
    				// Create the custom event
    				o[this._customEvents[prop][0]] = new YAHOO.util.CustomEvent(this._customEvents[prop][1], (callback.scope)?callback.scope:null);
    				YAHOO.log('Transaction-specific Custom Event ' + o[this._customEvents[prop][1]] + ' created.', 'info', 'Connection');

    				// Subscribe the custom event
    				o[this._customEvents[prop][0]].subscribe(callback.customevents[prop]);
    				YAHOO.log('Transaction-specific Custom Event ' + o[this._customEvents[prop][1]] + ' subscribed.', 'info', 'Connection');
    			}
    		}
    	},

      /**
       * @description This method serves as a timer that polls the XHR object's readyState
       * property during a transaction, instead of binding a callback to the
       * onreadystatechange event.  Upon readyState 4, handleTransactionResponse
       * will process the response, and the timer will be cleared.
       * @method handleReadyState
       * @private
       * @static
       * @param {object} o The connection object
       * @param {callback} callback The user-defined callback object
       * @return {void}
       */

        handleReadyState:function(o, callback)

        {
    		var oConn = this;

    		if(callback && callback.timeout){
    			this._timeOut[o.tId] = window.setTimeout(function(){ oConn.abort(o, callback, true); }, callback.timeout);
    		}

    		this._poll[o.tId] = window.setInterval(
    			function(){
    				if(o.conn && o.conn.readyState === 4){

    					// Clear the polling interval for the transaction
    					// and remove the reference from _poll.
    					window.clearInterval(oConn._poll[o.tId]);
    					delete oConn._poll[o.tId];

    					if(callback && callback.timeout){
    						window.clearTimeout(oConn._timeOut[o.tId]);
    						delete oConn._timeOut[o.tId];
    					}

    					// Fire global custom event -- completeEvent
    					oConn.completeEvent.fire(o);

    					if(o.completeEvent){
    						// Fire transaction custom event -- completeEvent
    						o.completeEvent.fire(o);
    					}

    					oConn.handleTransactionResponse(o, callback);
    				}
    			}
    		,this._polling_interval);
        },

      /**
       * @description This method attempts to interpret the server response and
       * determine whether the transaction was successful, or if an error or
       * exception was encountered.
       * @method handleTransactionResponse
       * @private
       * @static
       * @param {object} o The connection object
       * @param {object} callback The user-defined callback object
       * @param {boolean} isAbort Determines if the transaction was terminated via abort().
       * @return {void}
       */
        handleTransactionResponse:function(o, callback, isAbort)
        {
    		// If no valid callback is provided, then do not process any callback handling.
    		if(!callback){
    			this.releaseObject(o);
    			YAHOO.log('No callback object to process. Transaction complete.', 'info', 'Connection');
    			return;
    		}

    		var httpStatus, responseObject;

    		try
    		{
    			if(o.conn.status !== undefined && o.conn.status !== 0){
    				httpStatus = o.conn.status;
    			}
    			else{
    				httpStatus = 13030;
    			}
    		}
    		catch(e){

    			 // 13030 is the custom code to indicate the condition -- in Mozilla/FF --
    			 // when the o object's status and statusText properties are
    			 // unavailable, and a query attempt throws an exception.
    			httpStatus = 13030;
    		}

    		if(httpStatus >= 200 && httpStatus < 300 || httpStatus === 1223){
    			responseObject = this.createResponseObject(o, callback.argument);
    			if(callback.success){
    				if(!callback.scope){
    					callback.success(responseObject);
    					YAHOO.log('Success callback. HTTP code is ' + httpStatus, 'info', 'Connection');
    				}
    				else{
    					// If a scope property is defined, the callback will be fired from
    					// the context of the object.
    					callback.success.apply(callback.scope, [responseObject]);
    					YAHOO.log('Success callback with scope. HTTP code is ' + httpStatus, 'info', 'Connection');
    				}
    			}

    			// Fire global custom event -- successEvent
    			this.successEvent.fire(responseObject);

    			if(o.successEvent){
    				// Fire transaction custom event -- successEvent
    				o.successEvent.fire(responseObject);
    			}
    		}
    		else{
    			switch(httpStatus){
    				// The following cases are wininet.dll error codes that may be encountered.
    				case 12002: // Server timeout
    				case 12029: // 12029 to 12031 correspond to dropped connections.
    				case 12030:
    				case 12031:
    				case 12152: // Connection closed by server.
    				case 13030: // See above comments for variable status.
    					responseObject = this.createExceptionObject(o.tId, callback.argument, (isAbort?isAbort:false));
    					if(callback.failure){
    						if(!callback.scope){
    							callback.failure(responseObject);
    							YAHOO.log('Failure callback. Exception detected. Status code is ' + httpStatus, 'warn', 'Connection');
    						}
    						else{
    							callback.failure.apply(callback.scope, [responseObject]);
    							YAHOO.log('Failure callback with scope. Exception detected. Status code is ' + httpStatus, 'warn', 'Connection');
    						}
    					}
    					break;
    				default:
    					responseObject = this.createResponseObject(o, callback.argument);
    					if(callback.failure){
    						if(!callback.scope){
    							callback.failure(responseObject);
    							YAHOO.log('Failure callback. HTTP status code is ' + httpStatus, 'warn', 'Connection');
    						}
    						else{
    							callback.failure.apply(callback.scope, [responseObject]);
    							YAHOO.log('Failure callback with scope. HTTP status code is ' + httpStatus, 'warn', 'Connection');
    						}
    					}
    			}

    			// Fire global custom event -- failureEvent
    			this.failureEvent.fire(responseObject);

    			if(o.failureEvent){
    				// Fire transaction custom event -- failureEvent
    				o.failureEvent.fire(responseObject);
    			}

    		}

    		this.releaseObject(o);
    		responseObject = null;
        },

      /**
       * @description This method evaluates the server response, creates and returns the results via
       * its properties.  Success and failure cases will differ in the response
       * object's property values.
       * @method createResponseObject
       * @private
       * @static
       * @param {object} o The connection object
       * @param {callbackArg} callbackArg The user-defined argument or arguments to be passed to the callback
       * @return {object}
       */
        createResponseObject:function(o, callbackArg)
        {
    		var obj = {};
    		var headerObj = {};

    		try
    		{
    			var headerStr = o.conn.getAllResponseHeaders();
    			var header = headerStr.split('\n');
    			for(var i=0; i<header.length; i++){
    				var delimitPos = header[i].indexOf(':');
    				if(delimitPos != -1){
    					headerObj[header[i].substring(0,delimitPos)] = header[i].substring(delimitPos+2);
    				}
    			}
    		}
    		catch(e){}

    		obj.tId = o.tId;
    		// Normalize IE's response to HTTP 204 when Win error 1223.
    		obj.status = (o.conn.status == 1223)?204:o.conn.status;
    		// Normalize IE's statusText to "No Content" instead of "Unknown".
    		obj.statusText = (o.conn.status == 1223)?"No Content":o.conn.statusText;
    		obj.getResponseHeader = headerObj;
    		obj.getAllResponseHeaders = headerStr;
    		obj.responseText = o.conn.responseText;
    		obj.responseXML = o.conn.responseXML;

    		if(typeof callbackArg !== undefined){
    			obj.argument = callbackArg;
    		}

    		return obj;
        },

      /**
       * @description If a transaction cannot be completed due to dropped or closed connections,
       * there may be not be enough information to build a full response object.
       * The failure callback will be fired and this specific condition can be identified
       * by a status property value of 0.
       *
       * If an abort was successful, the status property will report a value of -1.
       *
       * @method createExceptionObject
       * @private
       * @static
       * @param {int} tId The Transaction Id
       * @param {callbackArg} callbackArg The user-defined argument or arguments to be passed to the callback
       * @param {boolean} isAbort Determines if the exception case is caused by a transaction abort
       * @return {object}
       */
        createExceptionObject:function(tId, callbackArg, isAbort)
        {
    		var COMM_CODE = 0;
    		var COMM_ERROR = 'communication failure';
    		var ABORT_CODE = -1;
    		var ABORT_ERROR = 'transaction aborted';

    		var obj = {};

    		obj.tId = tId;
    		if(isAbort){
    			obj.status = ABORT_CODE;
    			obj.statusText = ABORT_ERROR;
    		}
    		else{
    			obj.status = COMM_CODE;
    			obj.statusText = COMM_ERROR;
    		}

    		if(callbackArg){
    			obj.argument = callbackArg;
    		}

    		return obj;
        },

      /**
       * @description Method that initializes the custom HTTP headers for the each transaction.
       * @method initHeader
       * @public
       * @static
       * @param {string} label The HTTP header label
       * @param {string} value The HTTP header value
       * @param {string} isDefault Determines if the specific header is a default header
       * automatically sent with each transaction.
       * @return {void}
       */
    	initHeader:function(label,value,isDefault)
    	{
    		var headerObj = (isDefault)?this._default_headers:this._http_headers;

    		if(headerObj[label] === undefined){
    			headerObj[label] = value;
    		}
    		else{
    			// Concatenate multiple values, comma-delimited,
    			// for the same header label,
    			headerObj[label] =  value + "," + headerObj[label];
    		}

    		if(isDefault){
    			this._has_default_headers = true;
    		}
    		else{
    			this._has_http_headers = true;
    		}
    	},

      /**
       * @description Accessor that sets the HTTP headers for each transaction.
       * @method setHeader
       * @private
       * @static
       * @param {object} o The connection object for the transaction.
       * @return {void}
       */
    	setHeader:function(o)
    	{
    		if(this._has_default_headers){
    			for(var prop in this._default_headers){
    				if(YAHOO.lang.hasOwnProperty(this._default_headers, prop)){
    					o.conn.setRequestHeader(prop, this._default_headers[prop]);
    					YAHOO.log('Default HTTP header ' + prop + ' set with value of ' + this._default_headers[prop], 'info', 'Connection');
    				}
    			}
    		}

    		if(this._has_http_headers){
    			for(var prop in this._http_headers){
    				if(YAHOO.lang.hasOwnProperty(this._http_headers, prop)){
    					o.conn.setRequestHeader(prop, this._http_headers[prop]);
    					YAHOO.log('HTTP header ' + prop + ' set with value of ' + this._http_headers[prop], 'info', 'Connection');
    				}
    			}
    			delete this._http_headers;

    			this._http_headers = {};
    			this._has_http_headers = false;
    		}
    	},

      /**
       * @description Resets the default HTTP headers object
       * @method resetDefaultHeaders
       * @public
       * @static
       * @return {void}
       */
    	resetDefaultHeaders:function(){
    		delete this._default_headers;
    		this._default_headers = {};
    		this._has_default_headers = false;
    	},

      /**
       * @description This method assembles the form label and value pairs and
       * constructs an encoded string.
       * asyncRequest() will automatically initialize the transaction with a
       * a HTTP header Content-Type of application/x-www-form-urlencoded.
       * @method setForm
       * @public
       * @static
       * @param {string || object} form id or name attribute, or form object.
       * @param {boolean} optional enable file upload.
       * @param {boolean} optional enable file upload over SSL in IE only.
       * @return {string} string of the HTML form field name and value pairs..
       */
    	setForm:function(formId, isUpload, secureUri)
    	{
    		this.resetFormState();
    		var oForm;
    		if(typeof formId == 'string'){
    			// Determine if the argument is a form id or a form name.
    			// Note form name usage is deprecated by supported
    			// here for legacy reasons.
    			oForm = (document.getElementById(formId) || document.forms[formId]);
    		}
    		else if(typeof formId == 'object'){
    			// Treat argument as an HTML form object.
    			oForm = formId;
    		}
    		else{
    			YAHOO.log('Unable to create form object ' + formId, 'warn', 'Connection');
    			return;
    		}

    		// If the isUpload argument is true, setForm will call createFrame to initialize
    		// an iframe as the form target.
    		//
    		// The argument secureURI is also required by IE in SSL environments
    		// where the secureURI string is a fully qualified HTTP path, used to set the source
    		// of the iframe, to a stub resource in the same domain.
    		if(isUpload){

    			// Create iframe in preparation for file upload.
    			var io = this.createFrame(secureUri?secureUri:null);
    			// Set form reference and file upload properties to true.
    			this._isFormSubmit = true;
    			this._isFileUpload = true;
    			this._formNode = oForm;

    			return;

    		}

    		var oElement, oName, oValue, oDisabled;
    		var hasSubmit = false;

    		// Iterate over the form elements collection to construct the
    		// label-value pairs.
    		for (var i=0; i<oForm.elements.length; i++){
    			oElement = oForm.elements[i];
    			oDisabled = oForm.elements[i].disabled;
    			oName = oForm.elements[i].name;
    			oValue = oForm.elements[i].value;

    			// Do not submit fields that are disabled or
    			// do not have a name attribute value.
    			if(!oDisabled && oName)
    			{
    				switch(oElement.type)
    				{
    					case 'select-one':
    					case 'select-multiple':
    						for(var j=0; j<oElement.options.length; j++){
    							if(oElement.options[j].selected){
    								if(window.ActiveXObject){
    									this._sFormData += encodeURIComponent(oName) + '=' + encodeURIComponent(oElement.options[j].attributes['value'].specified?oElement.options[j].value:oElement.options[j].text) + '&';
    								}
    								else{
    									this._sFormData += encodeURIComponent(oName) + '=' + encodeURIComponent(oElement.options[j].hasAttribute('value')?oElement.options[j].value:oElement.options[j].text) + '&';
    								}
    							}
    						}
    						break;
    					case 'radio':
    					case 'checkbox':
    						if(oElement.checked){
    							this._sFormData += encodeURIComponent(oName) + '=' + encodeURIComponent(oValue) + '&';
    						}
    						break;
    					case 'file':
    						// stub case as XMLHttpRequest will only send the file path as a string.
    					case undefined:
    						// stub case for fieldset element which returns undefined.
    					case 'reset':
    						// stub case for input type reset button.
    					case 'button':
    						// stub case for input type button elements.
    						break;
    					case 'submit':
    						if(hasSubmit === false){
    							if(this._hasSubmitListener && this._submitElementValue){
    								this._sFormData += this._submitElementValue + '&';
    							}
    							else{
    								this._sFormData += encodeURIComponent(oName) + '=' + encodeURIComponent(oValue) + '&';
    							}

    							hasSubmit = true;
    						}
    						break;
    					default:
    						this._sFormData += encodeURIComponent(oName) + '=' + encodeURIComponent(oValue) + '&';
    				}
    			}
    		}

    		this._isFormSubmit = true;
    		this._sFormData = this._sFormData.substr(0, this._sFormData.length - 1);

    		YAHOO.log('Form initialized for transaction. HTML form POST message is: ' + this._sFormData, 'info', 'Connection');

    		return this._sFormData;
    	},

      /**
       * @description Resets HTML form properties when an HTML form or HTML form
       * with file upload transaction is sent.
       * @method resetFormState
       * @private
       * @static
       * @return {void}
       */
    	resetFormState:function(){
    		this._isFormSubmit = false;
    		this._isFileUpload = false;
    		this._formNode = null;
    		this._sFormData = "";
    	},

      /**
       * @description Creates an iframe to be used for form file uploads.  It is remove from the
       * document upon completion of the upload transaction.
       * @method createFrame
       * @private
       * @static
       * @param {string} optional qualified path of iframe resource for SSL in IE.
       * @return {void}
       */
    	createFrame:function(secureUri){

    		// IE does not allow the setting of id and name attributes as object
    		// properties via createElement().  A different iframe creation
    		// pattern is required for IE.
    		var frameId = 'yuiIO' + this._transaction_id;
    		var io;
    		if(window.ActiveXObject){
    			io = document.createElement('<iframe id="' + frameId + '" name="' + frameId + '" />');

    			// IE will throw a security exception in an SSL environment if the
    			// iframe source is undefined.
    			if(typeof secureUri == 'boolean'){
    				io.src = 'javascript:false';
    			}
    			else if(typeof secureURI == 'string'){
    				// Deprecated
    				io.src = secureUri;
    			}
    		}
    		else{
    			io = document.createElement('iframe');
    			io.id = frameId;
    			io.name = frameId;
    		}

    		io.style.position = 'absolute';
    		io.style.top = '-1000px';
    		io.style.left = '-1000px';

    		document.body.appendChild(io);
    		YAHOO.log('File upload iframe created. Id is:' + frameId, 'info', 'Connection');
    	},

      /**
       * @description Parses the POST data and creates hidden form elements
       * for each key-value, and appends them to the HTML form object.
       * @method appendPostData
       * @private
       * @static
       * @param {string} postData The HTTP POST data
       * @return {array} formElements Collection of hidden fields.
       */
    	appendPostData:function(postData)
    	{
    		var formElements = [];
    		var postMessage = postData.split('&');
    		for(var i=0; i < postMessage.length; i++){
    			var delimitPos = postMessage[i].indexOf('=');
    			if(delimitPos != -1){
    				formElements[i] = document.createElement('input');
    				formElements[i].type = 'hidden';
    				formElements[i].name = postMessage[i].substring(0,delimitPos);
    				formElements[i].value = postMessage[i].substring(delimitPos+1);
    				this._formNode.appendChild(formElements[i]);
    			}
    		}

    		return formElements;
    	},

      /**
       * @description Uploads HTML form, inclusive of files/attachments, using the
       * iframe created in createFrame to facilitate the transaction.
       * @method uploadFile
       * @private
       * @static
       * @param {int} id The transaction id.
       * @param {object} callback User-defined callback object.
       * @param {string} uri Fully qualified path of resource.
       * @param {string} postData POST data to be submitted in addition to HTML form.
       * @return {void}
       */
    	uploadFile:function(o, callback, uri, postData){

    		// Each iframe has an id prefix of "yuiIO" followed
    		// by the unique transaction id.
    		var frameId = 'yuiIO' + o.tId;
    		var uploadEncoding = 'multipart/form-data';
    		var io = document.getElementById(frameId);
    		var oConn = this;

    		// Track original HTML form attribute values.
    		var rawFormAttributes =
    		{
    			action:this._formNode.getAttribute('action'),
    			method:this._formNode.getAttribute('method'),
    			target:this._formNode.getAttribute('target')
    		};

    		// Initialize the HTML form properties in case they are
    		// not defined in the HTML form.
    		this._formNode.setAttribute('action', uri);
    		this._formNode.setAttribute('method', 'POST');
    		this._formNode.setAttribute('target', frameId);

    		if(this._formNode.encoding){
    			// IE does not respect property enctype for HTML forms.
    			// Instead it uses the property - "encoding".
    			this._formNode.setAttribute('encoding', uploadEncoding);
    		}
    		else{
    			this._formNode.setAttribute('enctype', uploadEncoding);
    		}

    		if(postData){
    			var oElements = this.appendPostData(postData);
    		}

    		// Start file upload.
    		this._formNode.submit();

    		// Fire global custom event -- startEvent
    		this.startEvent.fire(o);

    		if(o.startEvent){
    			// Fire transaction custom event -- startEvent
    			o.startEvent.fire(o);
    		}

    		// Start polling if a callback is present and the timeout
    		// property has been defined.
    		if(callback && callback.timeout){
    			this._timeOut[o.tId] = window.setTimeout(function(){ oConn.abort(o, callback, true); }, callback.timeout);
    		}

    		// Remove HTML elements created by appendPostData
    		if(oElements && oElements.length > 0){
    			for(var i=0; i < oElements.length; i++){
    				this._formNode.removeChild(oElements[i]);
    			}
    		}

    		// Restore HTML form attributes to their original
    		// values prior to file upload.
    		for(var prop in rawFormAttributes){
    			if(YAHOO.lang.hasOwnProperty(rawFormAttributes, prop)){
    				if(rawFormAttributes[prop]){
    					this._formNode.setAttribute(prop, rawFormAttributes[prop]);
    				}
    				else{
    					this._formNode.removeAttribute(prop);
    				}
    			}
    		}

    		// Reset HTML form state properties.
    		this.resetFormState();

    		// Create the upload callback handler that fires when the iframe
    		// receives the load event.  Subsequently, the event handler is detached
    		// and the iframe removed from the document.
    		var uploadCallback = function()
    		{
    			if(callback && callback.timeout){
    				window.clearTimeout(oConn._timeOut[o.tId]);
    				delete oConn._timeOut[o.tId];
    			}

    			// Fire global custom event -- completeEvent
    			oConn.completeEvent.fire(o);

    			if(o.completeEvent){
    				// Fire transaction custom event -- completeEvent
    				o.completeEvent.fire(o);
    			}

    			var obj = {};
    			obj.tId = o.tId;
    			obj.argument = callback.argument;

    			try
    			{
    				// responseText and responseXML will be populated with the same data from the iframe.
    				// Since the HTTP headers cannot be read from the iframe
    				obj.responseText = io.contentWindow.document.body?io.contentWindow.document.body.innerHTML:io.contentWindow.document.documentElement.textContent;
    				obj.responseXML = io.contentWindow.document.XMLDocument?io.contentWindow.document.XMLDocument:io.contentWindow.document;
    			}
    			catch(e){}

    			if(callback && callback.upload){
    				if(!callback.scope){
    					callback.upload(obj);
    					YAHOO.log('Upload callback.', 'info', 'Connection');
    				}
    				else{
    					callback.upload.apply(callback.scope, [obj]);
    					YAHOO.log('Upload callback with scope.', 'info', 'Connection');
    				}
    			}

    			// Fire global custom event -- completeEvent
    			oConn.uploadEvent.fire(obj);

    			if(o.uploadEvent){
    				// Fire transaction custom event -- completeEvent
    				o.uploadEvent.fire(obj);
    			}

    			if(YAHOO.util.Event){
    				YAHOO.util.Event.removeListener(io, "load", uploadCallback);
    			}
    			else if(window.detachEvent){
    				io.detachEvent('onload', uploadCallback);
    			}
    			else{
    				io.removeEventListener('load', uploadCallback, false);
    			}
    			setTimeout(
    				function(){
    					document.body.removeChild(io);
    					oConn.releaseObject(o);
    					YAHOO.log('File upload iframe destroyed. Id is:' + frameId, 'info', 'Connection');
    				}, 100);
    		};

    		// Bind the onload handler to the iframe to detect the file upload response.
    		if(YAHOO.util.Event){
    			YAHOO.util.Event.addListener(io, "load", uploadCallback);
    		}
    		else if(window.attachEvent){
    			io.attachEvent('onload', uploadCallback);
    		}
    		else{
    			io.addEventListener('load', uploadCallback, false);
    		}
    	},

      /**
       * @description Method to terminate a transaction, if it has not reached readyState 4.
       * @method abort
       * @public
       * @static
       * @param {object} o The connection object returned by asyncRequest.
       * @param {object} callback  User-defined callback object.
       * @param {string} isTimeout boolean to indicate if abort resulted from a callback timeout.
       * @return {boolean}
       */
    	abort:function(o, callback, isTimeout)
    	{
    		var abortStatus;

    		if(o.conn){
    			if(this.isCallInProgress(o)){
    				// Issue abort request
    				o.conn.abort();

    				window.clearInterval(this._poll[o.tId]);
    				delete this._poll[o.tId];

    				if(isTimeout){
    					window.clearTimeout(this._timeOut[o.tId]);
    					delete this._timeOut[o.tId];
    				}

    				abortStatus = true;
    			}
    		}
    		else if(o.isUpload === true){
    			var frameId = 'yuiIO' + o.tId;
    			var io = document.getElementById(frameId);

    			if(io){
    				// Destroy the iframe facilitating the transaction.
    				document.body.removeChild(io);
    				YAHOO.log('File upload iframe destroyed. Id is:' + frameId, 'info', 'Connection');

    				if(isTimeout){
    					window.clearTimeout(this._timeOut[o.tId]);
    					delete this._timeOut[o.tId];
    				}

    				abortStatus = true;
    			}
    		}
    		else{
    			abortStatus = false;
    		}

    		if(abortStatus === true){
    			// Fire global custom event -- abortEvent
    			this.abortEvent.fire(o);

    			if(o.abortEvent){
    				// Fire transaction custom event -- abortEvent
    				o.abortEvent.fire(o);
    			}

    			this.handleTransactionResponse(o, callback, true);
    			YAHOO.log('Transaction ' + o.tId + ' aborted.', 'info', 'Connection');
    		}
    		else{
    			YAHOO.log('Transaction ' + o.tId + ' abort call failed.  Connection object no longer exists.', 'warn', 'Connection');
    		}

    		return abortStatus;
    	},

      /**
       * Public method to check if the transaction is still being processed.
       *
       * @method isCallInProgress
       * @public
       * @static
       * @param {object} o The connection object returned by asyncRequest
       * @return {boolean}
       */
    	isCallInProgress:function(o)
    	{
    		// if the XHR object assigned to the transaction has not been dereferenced,
    		// then check its readyState status.  Otherwise, return false.
    		if(o && o.conn){
    			return o.conn.readyState !== 4 && o.conn.readyState !== 0;
    		}
    		else if(o && o.isUpload === true){
    			var frameId = 'yuiIO' + o.tId;
    			return document.getElementById(frameId)?true:false;
    		}
    		else{
    			return false;
    		}
    	},

      /**
       * @description Dereference the XHR instance and the connection object after the transaction is completed.
       * @method releaseObject
       * @private
       * @static
       * @param {object} o The connection object
       * @return {void}
       */
    	releaseObject:function(o)
    	{
    		//dereference the XHR instance.
    		if(o.conn){
    			o.conn = null;
    		}
    		YAHOO.log('Connection object for transaction ' + o.tId + ' destroyed.', 'info', 'Connection');
    		//dereference the connection object.
    		o = null;
    	}
    };

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