Restricting file downloads

Question

I'm currently creating a website for a client that will basically involve selling various files. This is obviously a really common thing to do, which is making me feel kind of foolish for not thinking of a method for doing it.

Once the purchase has been made the customer should be taken to a page containing the download link, as well as receiving emails that contain a download link and an email with information about an account that will be created for them (they will also be able to download from their account's control panel). What I'm trying to figure out is how I can hide/obscure the file's location on my server so that one person who buys it can't simply copy and paste the direct link to the file elsewhere. Even if I make the request to download a file a link of the format http://example.com/blah/download/454643, a URL which does not correspond to the actual location of the file, I think it might still be possible to locate the file on the server? I don't really understand too much about how permissions work on my server, which is why I ask. Thanks in advance :)

Answer 1

You basically don't give the users the direct URL to the file. Server based permissions have nothing to do here.

Say you have the required file(s) saved in /data/files/file.pdf (good practice to store files out of your web root). You can provide the users a link to download which looks something like /download.php?auth=32

When a user clicks the link, download.php will check if the session/cookie is authenticated and if the download id is valid (in case you have time based download expiry) Then download.php will read the required file from its location and send it to the browser with appropriate headers to force download.