Understanding HTTP Redirection in Font

Creating Code 39 Full ASCII in Font Understanding HTTP Redirection

HTTP redirection is a handshaking protocol. The client makes a request, and the server receives and processes the request. If the server indicates a redirection is in order, then an HTTP status code in the 300 range is returned. Upon receiving the 300-range status code, the client inspects the response and can take action by loading the redirected URL.

The following is an example HTTP conversation that performs an HTTP redirection. As usual, a client makes an HTTP request: GET /resource/ HTTP/1.1 Accept: */* Accept-Language: en Accept-Encoding: gzip, deflate User-Agent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en) AppleWebKit/412.6.2 (KHTML, like Gecko) Safari/412.2.2 Connection: keep-alive Host: 192.168.1.242:8100 The URL /resource is recognized by the HTTP server as a generic URL that will redirect to a specific URL when called. The HTTP server responds with an HTTP 302 to indicate a redirection, as illustrated by the following HTTP response: HTTP/1.1 302 Found Date: Tues, 05 Sep 2005 16:29:04 GMT Server: Apache/2.0.53 (Ubuntu) PHP/4.3.10-10ubuntu4 Location: /resource/joesmith Content-Length: 346 Keep-Alive: timeout=15, max=100 Connection: Keep-Alive Content-Type: text/html; charset=iso-8859-1 In the example, the specific URL sent to the client is defined as /resource/joesmith. When either a Web browser or an XMLHttpRequest object receives a redirect, the client will recognize the redirect and attempt to retrieve the contents of the redirected URL, as illustrated by the following final request: GET /resource/joesmith HTTP/1.1 Accept: */* Accept-Language: en Accept-Encoding: gzip, deflate User-Agent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en) AppleWebKit/412.6.2 (KHTML, like Gecko) Safari/412.2.2 Connection: keep-alive Host: 192.168.1.242:8100 An HTTP redirection, whether executed by the Web browser or XMLHttpRequest, can be executed only if the redirection follows the same origin policy. If a redirection to another domain is attempted with XMLHttpRequest, the results vary. For example, Microsoft Internet Explorer returns a status code of 0 and no further data. Mozilla-based browsers return the status code 302 and the redirected URL. Although using HTTP redirection can be effective, it can also be problematic from an Ajax perspective. When using the XMLHttpRequest object and calling a URL that generates a redirection, the redirected URL will be loaded automatically. This is bad because the script needs to know what the redirected URL is, but the XMLHttpRequest object doesn t give that URL. Therefore, in the context of this recipe, you cannot use a 300-range HTTP status code.

It would seem that the original idea of retrieving the unique URL in the body of the action URL response is the only solution, but never fear. Another solution does exist, and it s compliant with the HTTP protocol. The HTTP status code 201 corresponds to a response where the server has created another URL that can be found in the Location HTTP header. This logic corresponds closely to what the role of the action URL is with respect to the unique URL. When the server responds with an HTTP status 201, the browser or XMLHttpRequest instance doesn t perform a redirect automatically. It s up to the code or browser to take action on the response. You can use the following JavaScript class to retrieve the unique URL from the action URL. Source: /client/scripts/jaxson/communications.js function UniqueURL( url) { this.asynchronous = null; this.baseURL = url; this.uniqueURL = null; this.haveIt = function() { } } UniqueURL.prototype.getIt = function() { var instance = this; this.asynchronous = FactoryHttp.getAsynchronous(); this.asynchronous.settings = { onComplete : function(xmlhttp) { if( xmlhttp.status == 201) { instance.uniqueURL = xmlhttp.getResponseHeader( "Location"); instance.haveIt(); } } } this.asynchronous.get(this.baseURL); } UniqueURL.prototype.postIt = function( inpData) { var instance = this; this.asynchronous = FactoryHttp.getAsynchronous(); this.asynchronous.settings = { onComplete : function(xmlhttp) { if( xmlhttp.status == 201) { instance.uniqueURL = xmlhttp.getResponseHeader( "Location"); instance.haveIt(); } } } this.asynchronous.post(this.baseURL, inpData); }