<?

class proxy_detector {

	/**
	* CONSTRUCTOR
	*	Set defaults...
	*/
	function proxy_detector(){
		$this->config = array();
		$this->lastLog = "";

        //set default headers
		$this->scan_headers = array(
			'HTTP_VIA',
			'HTTP_X_FORWARDED_FOR',
			'HTTP_FORWARDED_FOR',
			'HTTP_X_FORWARDED',
			'HTTP_FORWARDED',
			'HTTP_CLIENT_IP',
			'HTTP_FORWARDED_FOR_IP',
			'VIA',
			'X_FORWARDED_FOR',
			'FORWARDED_FOR',
			'X_FORWARDED',
			'FORWARDED',
			'CLIENT_IP',
			'FORWARDED_FOR_IP',
			'HTTP_PROXY_CONNECTION'
		);
	}


	/**
	* VOID setHeader( STRING $trigger )
	*	Set new header trigger...
	*/
	function setHeader($trigger){
		$this->scan_headers[] = $trigger;
	}


	/**
	* ARRAY $triggers = getHeaders( VOID )
	*	Get all triggers in one array
	*/
	function getHeaders(){
    	return $this->scan_headers;
	}


	/**
	* VOID setConfig( STRING $key,  STRING $value)
	*	Set config line...
	*/
	function setConfig($key,$value){
		$this->config[$key] = $value;
	}


	/**
	* MIXED $config = getConfig( [STRING $key] )
	*	Get all config in one array, or only one config value as a string.
	*/
	function getConfig($key=''){
    	if($key)
    		return $this->config[$key];
    	else
    		return $this->config;
	}


	/**
	* STRING $log = getLog( VOID )
	*	Get last logged information. Only works AFTER calling detect()!
	*/
	function getLog(){
		return $this->lastLog;
	}


	/**
	* BOOL $proxy = detect( VOID )
	*	Start detection and return true if a proxy server is detected...
	*/
	function detect(){
		$log = "";

		//scan all headers
		foreach($this->scan_headers as $i){
			//proxy detected? lets log...
			if($_SERVER[$i])
				$log.= "trigger $i: ".$_SERVER[$i]."\n";
		}

    	//let's do something...
		if($log){
			$log = $this->lastLog = date("Y-m-d H:i:s")."\nDetected proxy server: ".gethostbyaddr($_SERVER['REMOTE_ADDR'])." ({$_SERVER['REMOTE_ADDR']})\n".$log;

			//mail message
            if($this->getConfig('MAIL_ALERT_TO'))
				mail($this->getConfig('MAIL_ALERT_TO'),"Proxy detected at {$_SERVER['REQUEST_URI']}",$log);

			//write to file
			$f = $this->getConfig('LOG_FILE');
            if($f){
				if(is_writable($f)){
					$fp = fopen($f,'a');
					fwrite($fp,"$log\n");
					fclose($fp);
            	}else{
					die("<strong>Fatal Error:</strong> Couldn't write to file: '<strong>$f</strong>'<br>Please check if the path exists and is writable for the webserver or php...");
            	}
            }

			//done
			return true;
		}

		//nope, no proxy was logged...
		return false;
	}
}

?>

<?

//include detector class, assuming it's in the same directory as this file...
include_once(dirname(__FILE__)."/proxy_detector.class.php");

//init class
$proxy = new proxy_detector();

//set optional extra triggers, no need to... I think I've got all of them covered in the class...
// $proxy->setTrigger('HTTP_SOME_HEADER_1');
// $proxy->setTrigger('HTTP_SOME_HEADER_2');

//set optional config
// $proxy->setConfig('MAIL_ALERT_TO','me@daantje.nl');
// $proxy->setConfig('LOG_FILE','/home/daantje/public_html/proxy/proxy_detector.log');

//start detect
if($proxy->detect()){

    //returned true, lets die...
	echo "<h1>Proxy detected</h1>";
	echo "Please disable your proxy server in your browser preferences or internet settings, and try again.<br><br>";

	//parse logged info
	echo nl2br($proxy->getLog());

    //some credits...
	echo "<hr><strong>proxy detector v0.1</strong> - ©2006 <a href=\"http://www.daantje.nl\" target=\"_blank\">daantje.nl</a>";

	//and do nothing anymore! (but not in my example)
	//exit();
}

//else, proceed as normal, put your code here...
?>