    /**
     * @author Don Griffin
     *
     * Simulates an XMLHttpRequest object's methods and properties but is backed by a
     * {@link Ext.ux.ajax.Simlet} instance that provides the data.
     */
    Ext.define('Ext.ux.ajax.SimXhr', {
        readyState: 0,

        mgr: null,
        simlet: null,

        constructor: function (config) {
            var me = this;

            Ext.apply(me, config);
            me.requestHeaders = {};
        },

        abort: function () {
            var me = this;

            if (me.timer) {
                clearTimeout(me.timer);
                me.timer = null;
            }
            me.aborted = true;
        },

        getAllResponseHeaders: function () {
            var headers = [];
            Ext.Object.each(this.responseHeaders, function (name, value) {
                headers.push(name + ': ' + value);
            });
            return headers.join('\x0d\x0a');
        },

        getResponseHeader: function (header) {
            var headers = this.responseHeaders;
            return (headers && headers[header]) || null;
        },

        open: function (method, url, async, user, password) {
            var me = this;
            me.method = method;
            me.url = url;
            me.async = async !== false;
            me.user = user;
            me.password = password;

            me.setReadyState(1);
        },

        overrideMimeType: function (mimeType) {
            this.mimeType = mimeType;
        },

        schedule: function () {
            var me = this;
            me.timer = setTimeout(function () {
                me.onTick();
            }, me.mgr.delay);
        },

        send: function (body) {
            var me = this;

            me.body = body;

            if (me.async) {
                me.schedule();
            } else {
                me.onComplete();
            }
        },

        setReadyState: function (state) {
            var me = this;
            if (me.readyState != state) {
                me.readyState = state;
                me.onreadystatechange();
            }
        },

        setRequestHeader: function (header, value) {
            this.requestHeaders[header] = value;
        },

        // handlers

        onreadystatechange: Ext.emptyFn,

        onComplete: function () {
            var me = this,
                callback;

            me.readyState = 4;
            Ext.apply(me, me.simlet.exec(me));

            callback = me.jsonpCallback;
            if (callback) {
                var text = callback + '(' + me.responseText + ')';
                eval(text);
            }
        },

        onTick: function () {
            var me = this;

            me.timer = null;
            me.onComplete();
            me.onreadystatechange && me.onreadystatechange();
        }
    });