Cross-Domain AJAX calls using PHP

icon1 Posted by Emran Hasan in Javascript, PHP, Programming, Web Development on 03 6th, 2008 | Comments

AJAX has become the core component of many web applications around us. And its fairly easy to handle AJAX now a days, with the help of various javascript libraries (ex: jQuery, Prototype, Mootools, YUI, etc). But there is one security issue that web browsers impose in doing AJAX calls - they don’t let you do AJAX calls in web servers different than yours. That means, if your script is in www.mydomain.com and you’re trying to do AJAX call to www.anotherdomain.com/get.php, then the browser will through error like: “Error: uncaught exception: Permission denied to call method XMLHttpRequest.open”.

Now, there are a number of solutions to this problem. Instead of explaining them all to you, lemme provide you the simplest one: using a PHP transport file. If you already know the thing and just need the script, download from here.

Others, let’s see an example implementation first.

Example use

   1: xmlHttp.onreadystatechange=function()
   2: {
   3:     if(xmlHttp.readyState==4)
   4:     {
   5:         alert(xmlHttp.responseText);
   6:     }
   7: }
   8:  
   9: xmlHttp.open("GET", 'http://myserver.com/transport.php?action=' + 
  10:                     urlencode('different-server.com/return_call.php') +
  11:                     '&method=get&data1=101&data2=pass', true );
  12:  
  13: xmlHttp.send(null);

Now, lets see how it works:

  1. The script makes an AJAX call to the myserver.com/transport.php with a few parameters:
    • action = the target URL you need to fetch, from a different domain
    • method = the HTTP method (post/get)
    • data1, data2 = sample parameters for using as either query-string or POST fields
  2. When the request is received by transport.php, it uses cURL to make a call to the page mentioned in action.
  3. Based on the method, it either makes a GET request or a POST request. In both cases, it sends the extra parameters that are sent.
  4. After the response is received, transport.php echoes it. So, you have what you need!

Download

transport.php
Cross-Domain AJAX call transporter.
Downloaded: 3185 times

Comments and suggestions are most welcomed :)

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  • Please please please add some caching mechanism to your script. You do not want to allow some kiddie to flood another website using your script. Even 1-minute cache is enough, but just don't call this website everytime like this. Not only will it be slow but the other site owner might get angry at you.
  • H2
    Does it also support POST simulation?

    Good Work Batman!
  • @H2: Of course. Thanks !
  • This is a nice tutorial with explanation. Well I want t o show if you want to use jquery (http://jquery.com/).

    If you want to get json data , then you can easily use getJSON.

    $.getJSON("http://api.flickr.com/services/feeds/photos_public.gne?tags=cat&tagmode=any&format=json&jsoncallback=?",
    function(data){
    $.each(data.items, function(i,item){
    $("").attr("src", item.media.m).appendTo("#images");
    });
    });

    Or if you don’t want to get other type of data like XML or other type, then you have to use cURL in PHP:

    $.ajax({
    type: "GET",
    url : ”http://myserver.com/transport.php?action=’ +
    urlencode(‘different-server.com/return_call.php’) +
    ‘&method=get&data1=101&data2=pass”,
    success: function(serverResponse)
    /*parse serverResponse data */
    });
  • zack
    I think that Loic Hoguin's recommendation is accurate.
    No comment ?
  • @Loic Hoguin: I completely agree with you that this script shouldn't allow other person from web to misuse it for their own use.

    But I would suggest using $_SERVER['REMOTE_ADDR'] to block request from scripts other than the server I'm invoking it from.

    The reason I think that way is, in the project I used it, the other server was also mine and I needed to communicate between them. As the output was quite dynamic, caching couldn't be done.

    But then again, if needed, caching can be added easily. I will be uploading one with caching later tonight.

    Thanks everybody for commenting !
  • Indeed, filtering using REMOTE_ADDR is the best if both servers are yours.

    What's important to note, too, is that if curl_exec can't fetch the data for some reasons it will return false. That means that your script will echo nothing. People using it should take care on the javascript side to check the data they get and if it's empty display an error.
  • @Loic Hoguin: Yes, you're right. Also, to be safe, using a http wraper class supporting both cURL and fsockopen (like mine one) can be suggested to avoid problem.
  • SuNcO
    On the transport file you can't get the action because is named url

    You must change that line :

    $action = $_REQUEST['url'];

    To :

    $action = $_REQUEST['action'];

    Or change this :

    xmlHttp.open(“GET”, ‘http://myserver.com/transport.php?action=’ + 10: urlencode(‘different-server.com/return_call.php’) + 11: ‘&method=get&data1=101&data2=pass’, true );

    With this :

    xmlHttp.open(“GET”, ‘http://myserver.com/transport.php?url=’ + 10: urlencode(‘different-server.com/return_call.php’) + 11: ‘&method=get&data1=101&data2=pass’, true );
  • François Labarde
    there's a typo:

    you wrote this:
    if ($key != 'url' || $key != 'method')

    while you obviously meant this:
    if ($key != 'url' && $key != 'method')


    (since ($key != 'url' || $key != 'method') is always true)
  • Kelvin
    I have tried this proxy approach, but neither Firefox nor IE 6 will allow me to call a php page with XMLHttpRequest. Of course, it won't allow me to call webservice cross-domain either.
    Thanks.
  • Hi, i've tried using your script and on my homeserver it runs fine but on my shared hoster it hangs at curl_exec().
    Is there anything you know of that causes this freezing/hanging?
  • Nice to know that.
    Thank you
  • Nick Syed
    I am using the following code, I get an error saying Object Not Found, can you please help ?

    <html>
    <body>

    <script type="text/javascript">

    function ajaxFunction()

    {

    xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
    xmlHttp.onreadystatechange=function()
    {
    if(xmlHttp.readyState==4)
    {
    document.myForm.time.value=xmlHttp.responseText;
    }
    }
    xmlHttp.open("GET","transport.php?action="+urlencode("http://www.netshelter.net/time.php"),true);
    xmlHttp.send(null);

    }

    </script>

    <form name="myForm">
    Name: <input type="text" onkeyup="ajaxFunction();" name="username" />
    Time: <input type="text" name="time" />
    </form>

    </body>
    </html>
  • Hi, thanx a lot for the code!!

    I've made the following solution with Jquery + PHP:

    $.get("http://mydomain.com/transport.php?action=<? echo urlencode('http://www.anotherdomain.com'); ?>&method=get&var1=variable1&var2=variable2&var3=variable3",
    function(serverResponse) {
    alert(serverResponse);
    }
    );

    And I had to change the transport.php on the line 18 to: $action = $_REQUEST['action'];

    It worked very well!!

    Thx again
  • Piro
    My target page has '?page=x' to get the different contents according to x.
    In this case, this script ignores '?page=x' and it results in getting the default contents.

    Could you please give me some hints how to fix this problem.

    Thank you!
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