[Zope] How to create an accurate download counter?

I need to keep a record of files downloaded from my website using zope. It is easy enough to add a counter and update my database – I already have this working – but how can I tell if the download has succeeded or if it has been aborted? I only want to keep a record of complete downloads only, if possible. Regards, Julian Gollop Codo Technologies ltd. www.codotech.com www.lasersquadnemesis.com