/*    Copyright 2006 Christian Gross http://www.devspace.com    From the book Ajax Patterns and Best Practices   Licensed under the Apache License, Version 2.0 (the "License");   you may not use this file except in compliance with the License.   You may obtain a copy of the License at       http://www.apache.org/licenses/LICENSE-2.0   Unless required by applicable law or agreed to in writing, software   distributed under the License is distributed on an "AS IS" BASIS,   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.   See the License for the specific language governing permissions and   limitations under the License.*/var CacheController = {    _cache : new Array(),    prefetch : function( url) { },    didNotFindETagError : function( url) { },        getCachedURL : function( url) {        var func = function( status, statusText, responseText, responseXML) { }        CacheController.getURL( url, func, true);    },            getURL : function( url, complete, calledFromCache) {        var asynchronous = new Asynchronous();        asynchronous.openCallback = function( xmlhttp) {            var obj = CacheController._cache[ url];            if( obj != null) {                xmlhttp.setRequestHeader( "If-None-Match", obj.ETag);            }        }        asynchronous.userComplete = complete;        asynchronous.complete = function( status, statusText, responseText, responseXML) {            if( status == 200) {                try {                    var foundetag = this._xmlhttp.getResponseHeader( "ETag");                    if( foundetag != null) {                        CacheController._cache[ url] = {                            ETag : foundetag,                            Status : status,                            StatusText : statusText,                            ResponseText : responseText,                            ResponseXML : responseXML                        };                    }                    else {                        CacheController.didNotFindETagError( url);                    }                }                catch( exception) {                    CacheController.didNotFindETagError( url);                }                this.userComplete( status, statusText, responseText, responseXML);            }            else if( status == 304) {                var obj = CacheController._cache[ url];                if( obj != null) {                    this.userComplete( 304, obj.StatusText,                         obj.ResponseText, obj.ResponseXML);                }                else {                    throw new Error( "Server indicated that this data is in the cache, but it does not seem to be");                }            }            else {                this.userComplete( status, statusText, responseText, responseXML);            }        }        asynchronous.get( url);        if( calledFromCache != true) {            CacheController.prefetch( url);        }    }}