Cross-Domain AJAX calls using PHP

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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:

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
When the request is received by transport.php, it uses cURL to make a call to the page mentioned in action.
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.
After the response is received, transport.php echoes it. So, you have what you need!

Download

transport.php
Cross-Domain AJAX call transporter.
Downloaded: 1464 times

Comments and suggestions are most welcomed

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Filed under Javascript, PHP, Programming, Web Development by Emran Hasan on March 6, 2008 at 2:09 am. Bookmark the Permalink. Subscribe to the Comment RSS. Post a comment or leave a trackback: Trackback URL.

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Loïc Hoguin 7 months ago 1 point
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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.

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http://wee.extend.ws

H2 7 months ago 1 point
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Does it also support POST simulation?

Good Work Batman!

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http://hasin.wordpress.com

Md Emran Hasan (phpfour) 7 months ago 1 point
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@H2: Of course. Thanks !

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1 /people/phpfour/ /people/phpfour/following/ http://www.phpfour.com 500059546 in/phpfour phpfour phpfour ehasan phpfour

Saidur Rahman 7 months ago 1 point
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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 */ });

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http://saidur.wordpress.com

zack 7 months ago 1 point
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I think that Loic Hoguin's recommendation is accurate.
No comment ?

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Md Emran Hasan (phpfour) 7 months ago 1 point
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@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 !

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Loïc Hoguin 7 months ago 1 point
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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.

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http://wee.extend.ws

Md Emran Hasan (phpfour) 7 months ago 1 point
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@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.

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SuNcO 6 months ago 1 point
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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 );

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François Labarde 6 months ago 1 point
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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)

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Kelvin 5 months ago 1 point
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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.

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Rene Veerman 2 weeks ago 1 point
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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?

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http://mediabeez.ws