如何使用CURL获取文件扩展名

Question

So, I've got to download a file to do a verification, I must check if the downloaded file is an XML or an ZIP.

I have the following code:

$url = $return->DocXMLLink; //link to download the file
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_FAILONERROR, true);

$response = curl_exec($ch);
//by here I may get the file extension and do something

Thanks in advance