Add a class to nav menu items depending on URL

/*
From:
http://www.rarescosma.com/2010/11/add-a-class-to-wp_nav_menu-items-with-urls-included-in-the-current-url/
*/

add_filter( 'nav_menu_css_class', 'add_parent_url_menu_class', 10, 2 );

function add_parent_url_menu_class( $classes = array(), $item = false ) {
    // Get current URL
    $current_url = current_url();

    // Get homepage URL
    $homepage_url = trailingslashit( get_bloginfo( 'url' ) );

    // Exclude 404 and homepage
    if( is_404() or $item->url == $homepage_url ) return $classes;

    if ( strstr( $current_url, $item->url) ) {
        // Add the 'parent_url' class
        $classes[] = 'parent_url';
    }

    return $classes;
}

function current_url() {
    // Protocol
    $url = ( 'on' == $_SERVER['HTTPS'] ) ? 'https://' : 'http://';

    $url .= $_SERVER['SERVER_NAME'];

    // Port
    $url .= ( '80' == $_SERVER['SERVER_PORT'] ) ? '' : ':' . $_SERVER['SERVER_PORT'];

    $url .= $_SERVER['REQUEST_URI'];

    return trailingslashit( $url );
}