PHP: como obter o endereço IP real do cliente

function get_client_ip() {
 
    // Default to REMOTE_ADDR
    $ip = $_SERVER['REMOTE_ADDR'];
 
    $proxy_headers = array(
        'HTTP_CF_CONNECTING_IP', // CloudFlare
        'HTTP_INCAP_CLIENT_IP', // Incapsula
        'HTTP_X_SUCURI_CLIENTIP', // Sucuri
        'HTTP_X_FORWARDED_FOR', // Any Proxy
    );
 
    // Check for alternate headers indicating a forwarded IP address
    foreach ( $proxy_headers as $proxy_header ) {
        if ( isset( $_SERVER[ $proxy_header ] ) ) {
            $forwarded_ips = explode( ',', $_SERVER[ $proxy_header ] );
            $forwarded_ip = array_shift( $forwarded_ips );
            if ( $forwarded_ip ) {
                $ip = $forwarded_ip;
                break;
            }
        }
    }
 
    return $ip;
}