Why is $_POST array empty in PHP after an a request with post data

I make a post request to the the page getremote.php with post data but the $_POST array seems to be empty. Would be grateful if anyone can tell me what I've done wrong.

The javascript code to make the request is

var postdata = "Content-Type: application/x-www-form-urlencoded\n\nedits=" + this.createEditXMLtext(this.editXMLstruct);
 var xmlhttp;
 if (window.XMLHttpRequest)
   {// code for IE7+, Firefox, Chrome, Opera, Safari
   xmlhttp=new XMLHttpRequest();
   }
 else
   {// code for IE6, IE5
   xmlhttp=new ActiveXObject("Micros开发者_JAVA百科oft.XMLHTTP");
   }
  dispmes("processing edits");
 xmlhttp.open("POST",userProfile.homeurl + "?remoteurl=" + userProfile.homeurl + "&cmdeditprofile&password=password",false);

 xmlhttp.send(postdata);

 var response = xmlhttp.responseXML;

where this.createEditXMLtext(this.editXMLstruct) simply creates a string

I haven't had this problem before and don't seem to have the same solution as other people who have posted similar problems. The php code at userProfile.homeurl + " is

header("Content-type: text/xml");
 $query = '';                  
    foreach( $_POST as $key => $value ){ 
  $query .= "$key=$value&";
 }
 echo do_post_request($_GET['remoteurl'] . $qstring,$query);

but the string $query is always empty - I checked it by adding echo $query to the bottom of the file

The value you pass to send() should be the entire post body, and you've included a header in it. When that body reaches PHP, it will fail to parse it as encoded form data.

Instead, set the data type by calling setRequestHeader()

 //create the postdata, taking care over the encoding
 var postdata = "edits=" + encodeURI(this.createEditXMLtext(this.editXMLstruct));

 //let server know the encoding we used for the request body
 xmlhttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");

 //and here we go 
 xmlhttp.send(postdata);

I've never seen it done this way, try setting your header separately from the POST body via XMLHttpRequest.setRequestHeader(), like this:

var postdata = "edits=" + this.createEditXMLtext(this.editXMLstruct);
var xmlhttp;
if (window.XMLHttpRequest) { // code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp = new XMLHttpRequest();
} else { // code for IE6, IE5
  xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded")
dispmes("processing edits");
xmlhttp.open("POST", userProfile.homeurl + "?remoteurl=" + userProfile.homeurl + "&cmdeditprofile&password=password",false);
xmlhttp.send(postdata);
var response = xmlhttp.responseXML;