[Catalyst] Detecting if a user aborted a (long) download

[Carl Johnstone]

Here's a worst-case scenario you send it to IE and somewhere along the 
line it picks up a Vary header.

IE won't store anything in it's cache with a Vary header - not even 
downloaded files. So it downloads the file then deletes it.

You can't save it elsewhere or retrieve it!

http://support.microsoft.com/?kbid=824847

(By the way it exhibits the same behaviour if you send proper no-cache 
headers.)

So as far as the server is concerned, your logs are concerned, and 
anything else you are concerned that file has been delivered to the 
client successfully. As far as the user is concerned you may as well not 
have bothered as the browser's eaten the download.

Carl