Demo of Ragnar (http://www.nuget.org/packages/ragnar)

Ragnar

// Ragnar is available on NuGet: http://www.nuget.org/packages/ragnar
// The source code is available on GitHub: https://github.com/libragnar/ragnar

using System;
using System.IO;
using System.Linq;
using System.Threading;

namespace Ragnar.SampleClient
{
    public class Program
    {
        public static void Main(string[] args)
        {
            Console.Title = "Ragnar demo";
            Console.Clear();
            Console.CursorVisible = false;

            // Create a new session.
            using (var session = new Session())
            {
                // Create the torrent settings that will keep
                // all there is to know about the torrent we will be downloading.
                var torrentSettings = new AddTorrentParams
                {
                    SavePath = "C:\\Downloads",
                    TorrentInfo = new TorrentInfo(args[0])
                };

                // Load session state.
                // The session state contains DHT state and such,
                // which will make the application faster to start next time.
                LoadSessionState(session);

                // Load torrent state.
                // The torrent state keeps track of what pieces that
                // are already downloaded. We do not need to do this,
                // but it will keep Ragnar from having to calculate hashes.
                LoadTorrentState(torrentSettings);

                // Start the session by listening on ports
                // in the range 6881-6889.
                session.ListenOn(6881, 6889);

                // Get the torrent handle by adding the torrent to the session.
                var torrentHandle = session.AddTorrent(torrentSettings);

                // Wait for Ctrl+C to be pressed.
                WaitForKeyPress(torrentHandle);

                // Pause the session.
                session.Pause();

                // Save torrent state.
                SaveTorrentState(torrentHandle, session);
                // Save session state
                SaveSessionState(session);
            }
        }

        private static void WaitForKeyPress(TorrentHandle torrentHandle)
        {
            var waitHandle = new ManualResetEvent(false);
            Console.CancelKeyPress += (sender, args) => waitHandle.Set();

            long tick = 0;
            while (!waitHandle.WaitOne(0))
            {
                // Query the status until we're not downloading anymore.
                var status = torrentHandle.QueryStatus();
                if (status.IsSeeding)
                {
                    break;
                }

                // Output some information to the console.
                Console.SetCursorPosition(0, 1);
                Console.Write("                                                        ");
                Console.SetCursorPosition(0, 1);
                Console.Write("Status: {0} {1}", status.State.ToString(), tick%2 == 0 ? "-" : "|");
                Console.SetCursorPosition(0, 2);
                Console.WriteLine("Progress: {0}%", status.Progress*100);

                // Wait 300 ms.
                waitHandle.WaitOne(300);
                tick++;
            }
        }

        private static void LoadSessionState(Session session)
        {
            if (File.Exists(".ses_state"))
            {
                Console.WriteLine("Loading state");
                session.LoadState(File.ReadAllBytes(".ses_state"));
            }
        }

        private static void SaveSessionState(Session session)
        {
            Console.WriteLine("Saving state.");
            File.WriteAllBytes(".ses_state", session.SaveState());
        }

        private static void LoadTorrentState(AddTorrentParams p)
        {
            if (File.Exists(Path.Combine(".resume", p.TorrentInfo.Name + ".fastresume")))
            {
                Console.WriteLine("Loading fast resume data");
                p.ResumeData = File.ReadAllBytes(Path.Combine(".resume", p.TorrentInfo.Name + ".fastresume"));
            }
        }

        private static void SaveTorrentState(TorrentHandle torrentHandle, Session session)
        {
            if (torrentHandle.NeedSaveResumeData())
            {
                Console.WriteLine("Saving resume data");
                torrentHandle.SaveResumeData();
                var savedFastResume = false;

                while (!savedFastResume)
                {
                    var alerts = session.Alerts.PopAll();
                    if (alerts == null || !alerts.Any()) continue;

                    foreach (var alert in alerts)
                    {
                        if (alert is SaveResumeDataAlert)
                        {
                            var saveResumeAlert = (SaveResumeDataAlert) alert;

                            if (!Directory.Exists(".resume")) Directory.CreateDirectory(".resume");

                            var status = saveResumeAlert.Handle.QueryStatus();
                            File.WriteAllBytes(
                                Path.Combine(".resume", status.Name + ".fastresume"),
                                saveResumeAlert.ResumeData);

                            Console.WriteLine("Resume data saved");

                            savedFastResume = true;

                            break;
                        }
                    }
                }
            }
        }
    }
}