how to know when download is finished

Question

Hi I\'m creating online shop. In this shope people online must be buy files with zip extension. They pay with their credit cards or other methods get key and download produc

Answer 1

you can use custom file server that works on either http or ftp and have it send a notification once the client received the last file fragment.

all other options are problematic; the client might download the file using a download manager,so you cannot even register for any browser event, if there was any.