I am trying to design a system for something like this with ASP.net/C#.
The users pay for downloading some content (files- mp3s/PDFs,doc etc).I should be able to track the number of bytes downloaded by the user. If the number of bytes downloaded match the number of bytes on the server, I should set a flag in DB (telling that the download was successful and prevent them from downloading the file again/asking them to pay for the download again). If the download was incomplete, they should be able to download the file again without paying for it again(since the flag will not be set).
Is there any way to keep track of the number of bytes successfully downloaded by the client ?
Also when I see a file size in my WinXP machine, I see two sizes(size,size on disk). Which one should I consider ? And will it differ from one OS to another ?
you can create an asp.net handler that serves the file ( for asp.net mvc u can do a result action instead ... this is what I'm using). Make sure it supports resumable downloads.
from the you can track the bytes served.
Ps. this incurs a performance overhead vs. letting IIS serve it
update 1: I used something pretty similar to this http://dotnetslackers.com/articles/aspnet/Range-Specific-Requests-in-ASP-NET.aspx ... and the article has a pretty clear explanation on what's inside it. You probably can use that one as is, see the example in that post.