PHP下载文件 <a>标签

$filename = "http://www.xxxx.com/images/xiaoxiangmuban.jpg";
            $fb = @fopen($filename, "rb+");
            if($fb){
                $fileinfo = pathinfo($filename);
                header('Content-type: application/x-'.$fileinfo['extension']);
                header('Content-Transfer-Encoding:binary');  //二进制
                header('Content-Disposition: attachment; filename='.$fileinfo['basename']);
                header('Content-Length: '.filesize($filename));
                ob_clean ();        
                flush ();
                readfile($filename);
                fclose($fb);
                exit();
            }else{
                die("文件不存在");
            }

之前搞了比较久，突然发现代码上部分写了一个header("Content-type:text/html;charset=gbk"),然后后来在大神的执导下用了一个ob_clean()和flush()，然后可以成功下载。