简单灵活的 PHP页面跳转函数

<?
        function Location($url = null){        
                $location = null;
                if ( !$url) {
                        $url =  $_SERVER['PHP_SELF'];
                }
                elseif ( substr($url,,) == '?' ) {
                        $url = $_SERVER['PHP_SELF'] . $url;
                }
                if ( substr($url,,) === 'http://' or substr($url,,) === 'https://' ) {
                        $location = $url;
                }
                else {
                        $port = null;
                        if ( $_SERVER['SERVER_PORT'] ==  ) {
                                $protocol = 'https://';
                        }        
                        else {
                                $protocol = 'http://';
                                $checkPoint=explode(":",$_SERVER['HTTP_HOST']);
                                 if (count($checkPoint)==) {
                                         $port = ':'.$_SERVER['SERVER_PORT'];        
                                 }                                
                        }
                        $dir = dirname($_SERVER['SCRIPT_NAME']);
                        if ( $dir === "/" ) {
                                $dir = "";
                        }
                        if ( substr($url,,) === './' ) {
                                if ( $dir ) {
                                        $location = $protocol . $_SERVER['HTTP_HOST'] . $port . '/' . $dir        . '/' . basename($url);
                                }
                                else {
                                        $location = $protocol . $_SERVER['HTTP_HOST'] . $port . '/' . basename($url);
                                }
                        }
                        elseif ( substr($url,,) === "/" ) {
                                $location = $protocol . $_SERVER['HTTP_HOST'] . $port . $url;
                        }
                        else {
                                $location = $protocol . $_SERVER['HTTP_HOST'] . $port . $dir . '/' . $url;
                        }
                }
                header("Location: $location");
                exit();

        }?>// 跳转到百度首页 
Location('http://www.baidu.com');