CI_Config::site_url PHP Method

    public function site_url($uri = '', $protocol = NULL)
    {
        $base_url = $this->slash_item('base_url');
        if (isset($protocol)) {
            // For protocol-relative links
            if ($protocol === '') {
                $base_url = substr($base_url, strpos($base_url, '//'));
            } else {
                $base_url = $protocol . substr($base_url, strpos($base_url, '://'));
            }
        }
        if (empty($uri)) {
            return $base_url . $this->item('index_page');
        }
        $uri = $this->_uri_string($uri);
        if ($this->item('enable_query_strings') === FALSE) {
            $suffix = isset($this->config['url_suffix']) ? $this->config['url_suffix'] : '';
            if ($suffix !== '') {
                if (($offset = strpos($uri, '?')) !== FALSE) {
                    $uri = substr($uri, 0, $offset) . $suffix . substr($uri, $offset);
                } else {
                    $uri .= $suffix;
                }
            }
            return $base_url . $this->slash_item('index_page') . $uri;
        } elseif (strpos($uri, '?') === FALSE) {
            $uri = '?' . $uri;
        }
        return $base_url . $this->item('index_page') . $uri;
    }

 public function site_url($uri = '', $force_secure = FALSE)
 {
     //	Prepare the URI as normal
     $_uri = parent::site_url($uri);
     // --------------------------------------------------------------------------
     //	If forcing secure just return now
     if ($force_secure) {
         return preg_replace('#^' . BASE_URL . '#', SECURE_BASE_URL, $_uri);
     }
     // --------------------------------------------------------------------------
     //	If SSL routing is enabled then parse the URL
     if (APP_SSL_ROUTING) {
         $_prefix = 'https://';
         $this->load('routes_ssl');
         // --------------------------------------------------------------------------
         //	Fetch SSL routes
         if (!$this->routes_ssl) {
             $this->routes_ssl = $this->item('routes_ssl');
             if (!$this->routes_ssl) {
                 $this->routes_ssl = array();
             }
         }
         // --------------------------------------------------------------------------
         //	Analyse target URL, if it matches a route then change it to be an https URL
         $_is_secure_route = FALSE;
         foreach ($this->routes_ssl as $route) {
             //	Swap out the pseudo regex's
             $route = str_replace(':any', '.*', $route);
             $route = str_replace(':num', '[0-9]*', $route);
             //	See if any of the routes match, if they do halt the loop.
             //	We need to do an optional prefix for the hosts
             if (BASE_URL !== SECURE_BASE_URL) {
                 $_pattern = '#^(' . preg_quote(BASE_URL, '#') . '|' . preg_quote(SECURE_BASE_URL, '#') . ')?' . $route . '#';
             } else {
                 $_pattern = '#^(' . preg_quote(BASE_URL, '#') . ')?' . $route . '#';
             }
             if (preg_match($_pattern, $_uri)) {
                 $_is_secure_route = TRUE;
                 break;
             }
         }
         // --------------------------------------------------------------------------
         //	If there was a match replace http:// with https://; also replace any
         //	calls for anything to the assets folder or the favicon (so secure content
         //	is shown).
         //	HTTPS is considered on if the domain matches that given in SECURE_BASE_URL
         //	or if the page is being served through HTTPS
         if (isset($_SERVER)) {
             $_page_is_secure = page_is_secure();
             if ($_is_secure_route || $_page_is_secure && preg_match('#^' . BASE_URL . 'assets.*#', $_uri) || $_page_is_secure && preg_match('#^' . NAILS_ASSETS_URL . '.*#', $_uri) || $_page_is_secure && preg_match('#^' . BASE_URL . 'favicon\\.ico#', $_uri)) {
                 //	SSL is off and there was a match, turn SSL on
                 $_uri = preg_replace('#^' . BASE_URL . '#', SECURE_BASE_URL, $_uri);
             }
         }
     }
     // --------------------------------------------------------------------------
     //	Spit back our result
     return $_uri;
 }