如何检测用户何时成功完成在php中下载文件

我有一个处理文件下载请求的php页面。我需要能够检测文件何时成功下载。如何才能做到这一点？也许有一些方法可以检测到这个客户端然后向服务器发送确认。

I've got a php page which handles requets for file downloads. I need to be able to detect when a file has been downloaded successfully. How can this be done? Perhaps there's some means of detecting this client-side then sending a confirmation down to the server.

谢谢。

编辑：
通过句柄，我的意思是该页面的行为是这样的：

By handle, I mean that the page is doing something like this:

$file = '/var/www/html/file-to-download.xyz';
  header('Content-Type: application/octet-stream');
  header('Content-Length: ' . filesize($file));
  header('Content-Disposition: attachment; filename=' . basename($file));
  readfile($file);