PHP: get client IP

function getClientIP() {
    $ipaddress = '';
    
    if (isset($_SERVER['HTTP_CLIENT_IP'])) {
        $ipaddress = $_SERVER['HTTP_CLIENT_IP'];
    } else if(isset($_SERVER['HTTP_X_FORWARDED_FOR'])) {
        $ipaddress = $_SERVER['HTTP_X_FORWARDED_FOR'];
    } else if(isset($_SERVER['HTTP_X_FORWARDED'])) {
        $ipaddress = $_SERVER['HTTP_X_FORWARDED'];
    } else if(isset($_SERVER['HTTP_FORWARDED_FOR'])) {
        $ipaddress = $_SERVER['HTTP_FORWARDED_FOR'];
    } else if(isset($_SERVER['HTTP_FORWARDED'])) {
        $ipaddress = $_SERVER['HTTP_FORWARDED'];
    } else if(isset($_SERVER['REMOTE_ADDR'])) {
        $ipaddress = $_SERVER['REMOTE_ADDR'];
    } else {
        $ipaddress = 'UNKNOWN';
    }

    return $ipaddress;
}