请教thinkphp如何实现弹窗下载?

header("Pragma: public");
header("Cache-control: max-age=".$expire);

//header('Cache-Control: no-store, no-cache, must-revalidate');
header("Expires: " . gmdate("D, d M Y H:i:s",time()+$expire) . "GMT");
header("Last-Modified: " . gmdate("D, d M Y H:i:s",time()) . "GMT");
header("Content-Disposition: attachment; filename=".$showname);
header("Content-Length: ".$length);
header("Content-type: ".$type);
header('Content-Encoding: none');
header("Content-Transfer-Encoding: binary" );
if($content == '' ) {
readfile($filename);
}else {
echo($content);
}
exit();

这是http里面的一段代码，可是我用它只能读出到浏览器中。请问有什么方法点击链接如“下载”便出现一个弹框然后自己输入保存名字存起来呢？