Request source server domain via cURL in PHP

I have 2 web servers, Server A & Server B. Both running PHP5 + Apache + Ubuntu environment.

Server A sends a request via cURL in PHP to Server B. I would like to get the source server domain of the request. As far as I know, $_SERVER['REMOTE_ADDR'] can get the IP of the source server (Server A). If I want to get the domain of Server A, how can I get it?

p.s. Server A hosts multiple domains, thus reverse IP resolve does not work in this case.

Here are the codes :

$data = array('user' => $user, 'pass' => $pass);

$ch = curl_init();
curl_setopt开发者_JAVA技巧($ch, CURLOPT_URL, 'http://ServerB/handler.php');
curl_setopt($ch, CURLOPT_PORT, 80);
curl_setopt($ch, CURLOPT_VERBOSE, 0); 
curl_setopt($ch, CURLOPT_HEADER, 0); 
curl_setopt($ch, CURLOPT_POST, 1); 
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false); 
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); 
curl_setopt($ch, CURLOPT_POSTFIELDS, $data); 

$ans_xml = curl_exec($ch);

<?  
$data = array('user' => $user, 'pass' => $pass, 'appid' => 'pukeko');
$domain = $_SERVER["SERVER_NAME"]; // user the super global $_SERVER["SERVER_NAME"] or set it  manually to, ex: http://www.myserver.com 

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, 'http://ServerB/handler.php');
curl_setopt($ch, CURLOPT_PORT, 80);
curl_setopt($ch, CURLOPT_VERBOSE, 0); 
curl_setopt($ch, CURLOPT_HEADER, 0); 
curl_setopt($ch, CURLOPT_POST, 1); 
curl_setopt($ch, CURLOPT_REFERER, $domain); // USE CURLOPT_REFERER to set the referer 
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false); 
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); 
curl_setopt($ch, CURLOPT_POSTFIELDS, $data); 

$ans_xml = curl_exec($ch);
?> 

<?
// ServerB - http://ServerB/handler.php
$referer = $_SERVER['HTTP_REFERER'];  // http://www.myserver.com 
?>

The super global $_SERVER["SERVER_NAME"] will only work if you call scriptA via apache, ex: "wget http://serverA/scritptA.php"

UPDATE:

You can also send $domain = $_SERVER["SERVER_NAME"] in your post data:

$domain = $_SERVER["SERVER_NAME"]
$data = array('user' => $user, 'pass' => $pass, 'appid' => 'pukeko', 'icomefrom' => $domain);

and in http://ServerB/handler.php get it with:

$icomefrom = $_POST['icomefrom'];

This way you don't have to worry with fake referers.

As stats Pelshoff in his comment above, you should use custom HTTP header:

Custom HTTP headers : naming conventions