CustomTransportProtocol

Example: Custom Transport Prococol

This example demonstrates how to create a custom Transport protocol.

Summary

The custom FileTransportProtocol sends data between peers by writing each packet as a file in a specified directory. The remote peer watches the directory for new files.

The custom transport protocol is used by registering it in the DI container:

// Simplified for brevity. See Program.cs for the full code.

var client = new TorrentClientBuilder()
    .ConfigureServices(services =>
    {
        services.AddSingleton<ITransportProtocol>(s => new FileTransportProtocol(...));
    })
    .AddBitTorrentApplicationProtocol()
    .AddDefaultPipeline()
    .Build();

The program sets up two peers - one seeder and one downloader with a torrent consisting of the single file TorrentContent.txt. The program completes once the downloader has downloaded the torrent.

A file-based tracker is used, where peers announce by placing a file containing their peer ID into a known directory.

File Transport Structure

The directory structure is as follows (all relative to the working directory):

• seeder - contains the torrent data to be sent to the downloader by the seeder
• downloader - the downloader will download the torrent into this directory
• transport - directory used by the FileTransportProtocol
  • announce - peers announce to the file-based tracker by placing the file {PeerId}.txt containing their peer ID into this directory
  • {PeerA}/{PeerB} - contains the data sent from PeerB to PeerA

After running the example you should see that downloader/TorrentContent.txt contains the data downloaded from the seeder:

Torrent content here!

You can also see each packet transmitted between the seeder and downloader by looking at the files on disk in the transport directory. The directory names are padded with trailing Xs to make them 20 characters long (the length of a BitTorrent Peer ID).

transport/DOWNLOADERXXXXXXXXXX/SEEDERXXXXXXXXXXXXXX$ ll 

# Files sent from Seeder -> Downloader

File_000.bin # BitTorrent connection header
File_001.bin # Bitfield message
File_002.bin # Unchoke message
File_003.bin # Piece message conntaining the torrent data