错误：请求的资源上没有“Access-Control-Allow-Origin”标头

Question

I have two systems helpdesk.ops.something.in and dev1.ops.something.in

I have a file fetchP.php in helpdesk.ops whose code goes something like this:

<?php
header('Access-Control-Allow-Origin: *');
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>
<script type="text/javascript">
    function someFunc(item) {
        $.ajax({method:"GET", 
        url:"http://dev1.ops.something.in/wallet/createurl.php?phone="+item, 
        success:function(response){
            console.log(response);
        }
        });
    };
</script>';
<?php
echo '<div id="callToWallet" class="sample-button" onclick="someFunc(911234567890);"><a href="#"> Click here</a></div>';

which is doing a GET request to a file createurl.php present in the dev1.ops, which goes something like this:

<?php
header('Access-Control-Allow-Origin: *');?>
<script>response.addHeader("Access-Control-Allow-Origin", "*");</script>
<?php 
// the rest of the code
?>

But on executing, the GET request is not successful, and I am getting error:

XMLHttpRequest cannot load http://dev1.ops.something.in/wallet/createurl.php?phone=911234567890. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://helpdesk.ops.something.in' is therefore not allowed access. The response had HTTP status code 500.

What am I missing?

Answer 1

Even with the Access-Control-Allow-Origin header set, a XMLHttpRequest cannot request ressources on domains that are different from the one of your current domain (this is due to the same-origin policy).

One way you could try to get around it is to use JSONP. Here's a simple and rudimentary example:

fetchP.php (Ajax call):

function someFunc(item) {
    $.ajax({
        method: "GET",
        data: { phone: item },
        url: "http://localhost:2512/createurl.php", 
        success: function(response){
            console.log(response);
        },
        dataType: "jsonp",
    });
};

createurl.php:

<?php
  header('Access-Control-Allow-Origin: *');

  $data = ["foo" => "bar", "bar" => "baz"];
  $json = json_encode($data);

  $functionName = $_GET['callback'];

  echo "$functionName($json);";
?>

Example output of the createurl.php on an ajax request:

jQuery2130388456100365147_1447744407137({"foo":"bar","bar":"baz"});

jQuery then executes the defined function and calls the defined success method on the given parameters (JSON in this case).