SpawnDev.WebTorrent 2.0.0

SpawnDev.WebTorrent

Pure C# BitTorrent/WebTorrent client and server. No JavaScript dependencies. Runs on desktop (.NET) and browser (Blazor WASM). 452+ tests. 15 BEPs implemented.

Features

• Pure C# — No JavaScript interop, no Node.js, no npm. 100% .NET.
• Desktop + Browser — Same library, same API. WPF, console, Blazor WebAssembly.
• DI Singleton Services — WebTorrentClient and ServiceWorkerStreamHandler implement IAsyncBackgroundService. Register once, start with the app, inject anywhere.
• Real WebRTC P2P — Browser (SpawnDev.BlazorJS) and desktop (SIPSorcery) peers interop seamlessly via the same tracker.
• 15 BEPs — Full wire protocol, DHT, Fast Extension, ut_metadata, ut_pex, private torrents, magnet file selection, and more.
• 3 Tracker Types — WebSocket (browser+desktop), HTTP/HTTPS, UDP (desktop).
• Web Seed Download — HTTP range requests with multi-file piece assembly (BEP 17/19).
• Persistent Storage — Torrents and pieces persist in OPFS (browser) or filesystem (desktop). Survive page reloads. Resume downloading automatically.
• Media Streaming with Seeking — Service worker intercepts video/audio range requests and serves pieces on demand. file.StreamURL, file.StreamTo(elem), file.CreateReadStream(). True seeking — pieces download as the video plays.
• Service Worker — webtorrent-sw.js ships with the library. Handles Cross-Origin-Isolation headers, Blazor loading, and torrent streaming via MessageChannel. One <script> tag and your app streams.
• System.IO.Stream — file.CreateReadStream() returns a seekable .NET Stream backed by torrent pieces. Use with any API that takes a Stream.
• Random-Access Streaming — Read any byte range from a torrent file as it downloads. Pieces download on demand. Perfect for ML model weight streaming.
• Seeding — Upload pieces to requesting peers with configurable rate limiting.
• Speed Tracking — Real-time download/upload bytes/sec per torrent.
• AI Agent Communication — BEP 46 DHT mutable items with real ECDSA-P256 signing via SpawnDev.BlazorJS.Cryptography. AgentChannel pub/sub for shared AI state.
• HuggingFace Integration — Optional server extension that proxies HuggingFace model CDN with local caching and automatic torrent generation.
• .torrent Creation — Create and parse .torrent files. Complete Bencode encoder/decoder.
• 452+ Unit Tests — Every BEP tested, ECDSA crypto verified in browser, service worker streaming verified end-to-end, security tests for signature verification.

Packages

Quick Start — Blazor WebAssembly (DI)

// Program.cs
using SpawnDev.AsyncFileSystem;
using SpawnDev.AsyncFileSystem.BrowserWASM;
using SpawnDev.BlazorJS;
using SpawnDev.BlazorJS.Cryptography;
using SpawnDev.WebTorrent;

var builder = WebAssemblyHostBuilder.CreateDefault(args);
builder.Services.AddBlazorJSRuntime();

// Cross-platform crypto for BEP 46 signing
if (OperatingSystem.IsBrowser())
    builder.Services.AddSingleton<IPortableCrypto, BrowserWASMCrypto>();
else
    builder.Services.AddSingleton<IPortableCrypto, DotNetCrypto>();

// Persistent file system (OPFS in browser)
builder.Services.AddSingleton<IAsyncFS, AsyncFSFileSystemDirectoryHandle>();

// WebTorrent services — start with the app via IAsyncBackgroundService
builder.Services.AddSingleton<ServiceWorkerStreamHandler>();
builder.Services.AddSingleton<WebTorrentClient>();

await builder.Build().BlazorJSRunAsync();

<script src="webtorrent-sw.js"></script>

// Any page or service — inject the singleton
@inject WebTorrentClient Client

// Download a torrent
var torrent = await Client.AddAsync("magnet:?xt=urn:btih:...");

// Stream a video with seeking
var url = torrent.Files[0].StreamURL;
// <video src="@url" controls></video>

// Or set directly on an element
torrent.Files[0].StreamTo(videoElement);

// Get a .NET Stream
using var stream = torrent.Files[0].CreateReadStream();
var buffer = new byte[4096];
var bytesRead = await stream.ReadAsync(buffer);
stream.Position = 1000000; // seek
bytesRead = await stream.ReadAsync(buffer);

// Seed data
var seeded = await Client.SeedAsync(myBytes, "model.onnx");
Console.WriteLine(seeded.MagnetURI);

Torrents persist across page reloads — pieces stored in OPFS, metadata restored on startup.

File API

Feature parity with the WebTorrent JS File API:

Service Worker — Media Streaming with Seeking

webtorrent-sw.js ships with the NuGet package and deploys to your app root automatically. It:

1. Registers itself as a service worker
2. Adds Cross-Origin-Isolation headers (COOP/COEP) for SharedArrayBuffer
3. Waits for the SW to be ready, then loads Blazor
4. Intercepts /webtorrent/{infoHash}/{fileIndex} requests
5. Forwards range requests to the ServiceWorkerStreamHandler singleton via MessageChannel
6. Streams piece data back as a ReadableStream with proper 206 Partial Content headers

Health check: fetch /webtorrent-sw-check to verify the SW is active.

Quick Start — Server

using SpawnDev.WebTorrent.Server;

var tracker = new TorrentTracker();
var webSeed = new WebSeedServer("seed-data");

var app = WebApplication.CreateBuilder(args).Build();
app.UseWebSockets();
app.MapWebTorrentServer(tracker, webSeed);
app.Run();

Quick Start — HuggingFace Proxy

using SpawnDev.WebTorrent.Server.HuggingFace;

var proxy = new HuggingFaceProxy(new HuggingFaceProxyOptions
{
    CacheDirectory = "hf-cache",
});
app.MapHuggingFaceProxy(proxy);

// Clients access: https://your-server/hf/{repoId}/{filePath}
// Auto-caches from HuggingFace CDN on first request
// Generates .torrent files for P2P distribution

Demo Apps

Both demos connect to the same trackers and can P2P with each other.

BEP Support

15 BitTorrent Enhancement Proposals implemented:

See Docs/bep-support.md for full details.

Why This Exists

AI models are big. CDNs can't scale when every user downloads the same 2GB model. SpawnDev.WebTorrent turns every browser into a peer — the more users, the faster delivery. Built for SpawnDev.ILGPU.ML, the GPU-accelerated ML library for Blazor WebAssembly.

Architecture

Browser Client                    Desktop Client
+---------------+                 +------------------+
| WebTorrent    |                 | WebTorrent       |
| Client        |                 | Client           |
|               |                 |                  |
| WebRTC (P2P)<-+------+-------->+ SIPSorcery (P2P) |
| BlazorJS      |      |         | RTCPeerConnection|
|               |      |         |                  |
| OPFS Storage  |      |         | FileChunkStore   |
+---------------+      |         +------------------+
        |               |                |
        v               v                v
+-------------------------------------------+
| hub.spawndev.com                          |
| TorrentTracker (WebSocket signaling)      |
| WebSeedServer (HTTP range fallback)       |
| HuggingFaceProxy (model CDN cache)        |
+-------------------------------------------+

Documentation

Credits

Built by Todd Tanner (@LostBeard) and the SpawnDev team.

License

MIT