Monday, 6 June 2011

Proxy to read information


In a situation where Flash needs to get information from another server, normally a text based information, like XML, there are security issues that need to be overcomed.

If you try to load a URLRequest using a URLLoader object, it will run normally locally, but if you publish it on the net, it won't work. That's because on network the Flash player request a security file to catch the information, from the server it wants to access.

That file is called crossdomain.xml (Maybe I'll do a article about this later), which has to be on the root of the accessed server.

But what if you don't have privileged access to the server and the administrator doesn't want to put that file for you? Probably yesterday I could ask that, but at the time it would involve a lot of people and too much time spent.

So I had to come up with an alternative solution. That solution is by making this request through a PHP (or ASP) script. In my case I'm more comfortable with PHP, and that's what I'm presenting.

It works this way:
1- Flash will make the request, including the url that it wants to access to the PHP file;
2- The PHP file will ask the url given for the information we want to read;
3- Once it gets to the PHP, it will return the information to the Flash.

The PHP won't ask for any crossdomain.xml, so is like someone making the request directly through the address bar of the browser. I read also that there maybe some servers that prevent this mechanism to work, but usually, no. In this case, there's no chance (not that I know of) to get the data unless you can get a privilege to that.

I know that Adobe has a web page with several proxy script for PHP and ASP, but yesterday I couldn't find it, but another did... and I think it's a much better script that the one of Adobe.

So here it is. This code is in

Just copy and paste to a PHP file. Call it "proxy.php" for example.

$post_data = $HTTP_RAW_POST_DATA;

$header[] = "Content-type: text/xml";
$header[] = "Content-length: ".strlen($post_data);

$ch = curl_init( $_GET['url'] ); 
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_TIMEOUT, 10);
curl_setopt($ch, CURLOPT_HTTPHEADER, $header);

if ( strlen($post_data)>0 ){
    curl_setopt($ch, CURLOPT_POST, 1);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $post_data);

$response = curl_exec($ch);     
$response_headers = curl_getinfo($ch);     

if (curl_errno($ch)) {
    print curl_error($ch);
} else {
    header( 'Content-type: ' . $response_headers['content-type']);
    print $response;


On the Flash side, just make the call has you would normally, like this:

var xmlLoader:URLLoader = new URLLoader();

var xmlData:XML = new XML();




In the last line please regard "proxy.php?url=" followed by the url of the data you want to fetch.

After all this it worked very well. I thisnk this also insures that the data will be forced to refresh. I don't know if is that some servers I use, but it seems that sometimes cleaning the browser cache it's not enough to refresh data, being requested the normal way.