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

Here is sample code of what I have done for something quite similar:

// $mimeType is the mime type of the file
header('Content-type: ' . $mimeType);
// this will get the size of the file
// (helps for giving the size to the browser so a percent complete can be shown)
header('Content-length: ' . (string) (filesize($path)));
// disposition is either attachment (for binary files that can't be read by the browser) 
// or inline (for files that can be read by the browser
// some times you have play with this to get working so users get the download window in all browsers
// original filename is the name you want to users to see 
// (shouldn't have any special characters as you can end up with weird issues)
header('Content-Disposition: ' . $disposition . '; filename=' . $originalFilename);
// the next 2 lines try to help the browser understand that the file can't be cached
// and should be downloaded (not viewed)
header('Pragma: Public');
header('Cache-control: private');
// this will output the file to browser
readfile($path);

You can of course add to this any login checking and logging to ensure it isn't downloaded too many times.

Also, as said earlier, ensure you put the file outside (or above) the web server document root so people can't figure out the path. Or you could even put a password on the directory so only internal people could access the file list more easily, but wouldn't recommend this. (Only do this if you can put something outside the doc root.)

Answer 2

You can have the URL be an authorization code for the buyer. You get her to log in again, check which file the code is for, then pipe the file to her. Here is an exemple of PHP code from osCommerce (I wrote that a long time ago).

// Now send the file with header() magic
  header("Expires: Mon, 26 Nov 1962 00:00:00 GMT");
  header("Last-Modified: " . gmdate("D,d M Y H:i:s") . " GMT");
  header("Cache-Control: no-cache, must-revalidate");
  header("Pragma: no-cache");
  header("Content-Type: Application/octet-stream");
  header("Content-disposition: attachment; filename=" . $downloads['orders_products_filename']);

  if (DOWNLOAD_BY_REDIRECT == 'true') {
// This will work only on Unix/Linux hosts
    tep_unlink_temp_dir(DIR_FS_DOWNLOAD_PUBLIC);
    $tempdir = tep_random_name();
    umask(0000);
    mkdir(DIR_FS_DOWNLOAD_PUBLIC . $tempdir, 0777);
    symlink(DIR_FS_DOWNLOAD . $downloads['orders_products_filename'], DIR_FS_DOWNLOAD_PUBLIC . $tempdir . '/' . $downloads['orders_products_filename']);
    if (file_exists(DIR_FS_DOWNLOAD_PUBLIC . $tempdir . '/' . $downloads['orders_products_filename'])) {
      tep_redirect(tep_href_link(DIR_WS_DOWNLOAD_PUBLIC . $tempdir . '/' . $downloads['orders_products_filename']));
    }
  }