php下载zip格式文件打开zip文件报错?报错

php下载zip格式文件打开zip文件报错“这个压缩文件格式错误”

 $filename=iconv('utf-8','gb2312',$filename);
            //处理中文文件名
            header("Cache-Control: public");
            header("Content-Description: File Transfer");
            header("Pragma: public");
            header("Expires: 0");
            header("Content-type: application/octet-stream");
            header('Content-disposition: attachment; filename='.basename($filename)); //文件名
            header("Accept-Ranges: bytes");
            header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
            header("Content-Type: application/zip"); //zip格式的
            header("Content-Transfer-Encoding: binary"); //告诉浏览器，这是二进制文件
            header('Content-Length: '. filesize($filename)); //告诉浏览器，文件大小

            ob_clean();
            flush();
            readfile($filename);
//            unlink($filename);

虽然可以通过zip修复可以打开 但是体验不友好，求大佬指点