How to restrict what files a desktop app can download from an online server

Question

The closest example I can think of is iTunes. I'm thinking about a system where a server stores loads of files, and each user only has access to those they have paid for. Using a desktop app, they can download these to their local PC where they are stored as regular files.

How might one approach this? I can see a couple of possible options, and have some initial thoughts, but would welcome feedback on these or other ideas. If you post your preferred design, people can vote on them!

1)Use HTTP requests, and the response is the file data. Then a simple servlet (or similar) can act as a control on which files are downloaded. PROs: easy to do CONs: seems a little hacky, how would you display a progress bar?

2)Use sockets, and a custom server app which pipes data to the server PROs: Perhaps more performant (?), can send data in nice sized chunks CONs: A little more work on the client side, quite a bit more to write a custom server-side app that runs 24/7

Thanks in advance. Someone please edit my tags, I can't think of the right ones!

Answer 1

As said, FTP is what you need. To control per user, per file permissions you can create one system user and then you can apply filesystem level ACLs. Then, a FTP server like PureFTPd will let you login with system accounts with the specified permissions.

Answer 2

Use HTTP requests, and the response is the file data. Then a simple servlet (or similar) can act as a control on which files are downloaded. PROs: easy to do CONs: seems a little hacky, how would you display a progress bar?

I don't see why this is hacky? Your App would authenticate using the user's user name and password (if you want it to work like iTunes) and fetch files according to permission level. A progress bar is easy to do because you will get the content-length header in the response. It's a more flexible approach than FTP - but if FTP already does everything you need, go for that.