Check if URL is a torrent in C# .NET

Question

What's the best way for me to take url like: http://foobar.com/foo.torrent and check if that really is a torrent, not a html page or something else funny. Suggestions? Thank you :)

Answer 1

To check the type of a resource without downloading it, use a HEAD request:

WebRequest request= WebRequest.Create("http://foobar.com/foo.torrent");
request.Method= "HEAD";
WebResponse response= request.GetResponse();
if (response.Headers.Get("Content-Type")=="application/x-bittorrent") {
    ...

However, the type application/x-bittorrent might not be set up in some servers, so it's possible you might get application/octet-stream instead, or even text/plain if you are unlucky. If you need to account for this, about all you could do would be to fetch the file with a normal GET request, and see if you can decode it.

The BitTorrent file format is based around a format called ‘bencode’. Here's a .NET library that claims to handle it. You can guess any file that's valid bencode is a torrent file, but if you want to make sure you can look at the mapping it decodes to and check for the info and announce properties.

Answer 2

The only way to know if it's really a torrent file is to download it and check if it's a torrent file.