php download file code

 public function down()
    {
        header('content-type:application:json;charset=utf8');
        header('Access-Control-Allow-Origin:https://coucouchina.com');
        header('Access-Control-Allow-Methods:POST');
        header('Access-Control-Allow-Headers:x-requested-with,content-type');
        header("Content-type:text/html;charset=utf-8");// $file_name="cookie.jpg";
        $file_name = "apple-app-site-association";//用以解决中文不能显示出来的问题
        $file_name = iconv("utf-8", "gb2312", $file_name);        $file_sub_path = $_SERVER['DOCUMENT_ROOT'] . "/";        
        $file_path = $file_sub_path . $file_name;//首先要判断给定的文件存在与否
        if (!file_exists($file_path)) {            echo "没有该文件文件";            return;
        }        $fp = fopen($file_path, "r");        $file_size = filesize($file_path);//下载文件需要用到的头
        Header("Content-type: application/octet-stream");
        Header("Accept-Ranges: bytes");
        Header("Accept-Length:" . $file_size);
        Header("Content-Disposition: attachment; filename=" . $file_name);        $buffer = 1024;        $file_count = 0;//向浏览器返回数据
        while (!feof($fp) && $file_count < $file_size) {            
        $file_con = fread($fp, $buffer);            
        $file_count += $buffer;            
        echo $file_con;
        }
        fclose($fp);
    }