Check if URL is a torrent in C# .NET

Question

Hi! 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

Read the torrent file specification, then write a C# app to download the contents of the URL and see if it meets the rules in the specification.

Answer 2

Probably best to download and validate it and/ or check the content type is application/x-bittorrent.

Answer 3

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

Answer 4

If you are willing to learn some c++ you could make a external call to the libtorrent library with a P/Invoke I am shure it has a way to validate files.

Answer 5

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 6

In additon to the good answer bobince provided, you could also have a look at the monotorrent open source c# implementation. They download the whole .torrent file and parse the bencode afterwards (cf.: http://anonsvn.mono-project.com/viewvc/trunk/bitsharp/src/MonoTorrent/MonoTorrent.Common/Torrent.cs lines 611ff)

Answer 7

I would use the MonoTorrent library. Specifically, you could use the static method

Torrent.TryLoad(Uri url, string location, out Torrent torrent)

which will return a boolean value indicating whether the url parameter points to a valid torrent file.