PHP POST variable not defined when using Chrome + XHR

Question

This question is nearly identical to the year-old unanswered question:

HTTP-POST XHR not working in chrome.

I was hoping to find a solution and can offer more details than the original question.

Background

I have a sever-side php script that is supposed to take POST data from a form or XHR request. When I test the site using a form for submission, it works in Chrome and IE9. However, when I generate the request using XHR, the php POST variable is undefined when using Chrome on the client side. This behavior is inconsistent: about 1 in 20 tries, the php does accept the data.

I have checked the php://input stream and see that the post data is being sent to server in all cases; and note that a small few of the HTTP headers ($_SERVER) are different between test cases.

Code

Server side:

<?php
   echo file_get_contents("php://input") . "\n";
   print_r($_SERVER);
   print_r($_POST);
?>

Client side form version (Chrome and IE9 both work)

<form action="scriptName.php" method="post">
      Field: <input type="text" name="myField"><br>
      <input type="submit" value="Submit">
</form>

Client side XHR version (IE9 always works, Chrome works about 5% of time)

<script>
function postToURL(url,data)
{
  // Typical XHLHttpRequest declarations are removed for brevity
  //  - checks browser type and declares xmlhttp accordingly
  //  - defines a onreadystatechange handle

    xmlhttp.open("POST",url,false);
    xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    xmlhttp.send(data);
}
</script>
...
<form>
<button type="button" onClick="postToURL('scriptname.php','myField=test');">
Test
</button>
</form>

Output

In all cases the request body data (php://input) returns the same value. The headers are mostly the same, but Chrome adds an [HTTP_PRAGMA] => no-cache in XHR mode

The $_POST variable is defined as [myField] => test except in the Chrome + XHR case.

Questions

Where is the problem likely occurring? Is there something wrong with the HTTP headers possibly, or should I be looking server-side. Any ideas?

Answer 1

Place this code in the first line of your page

<?php ob_start(); error_reporting(E_ALL & ~E_NOTICE & ~8192); ?>
<!-- Ignore Errors , Header Sent Report -->

and this code in the last line of your page

<!-- Ignore Header Sent Error -->
<?php ob_flush(); ?>
<!-- Ignore Header Sent Error -->

i hope that helps you