BitTorrent Client (C#)

A modern, feature-rich BitTorrent client built with C# and WPF, implementing the full BitTorrent protocol specification.

Key Technologies

• C# 11 / .NET 8.0 — Core language and runtime
• WPF — Desktop UI framework (Windows only)
• MVVM — UI architecture pattern
• System.Net.Sockets — TCP networking for peer/tracker communication
• System.Net.Http — HTTP/HTTPS tracker requests
• System.IO — File and stream management
• System.Threading — Async operations and concurrency
• Custom Bencode Parser — For .torrent files and tracker responses
• Custom Peer Wire Protocol Implementation — For BitTorrent peer messaging
• AI/Heuristic Peer Selection — Adaptive, extensible peer ranking
• Logging — To file and console for debugging and troubleshooting
• StealthMode — Privacy features, peer ID masking, and tracker request obfuscation

Features

• Full BitTorrent Protocol Support: Complete implementation of BEP 3 (BitTorrent Protocol)
• Torrent File Parsing: Parse and load .torrent files with metadata extraction
• Tracker Communication: HTTP/HTTPS tracker support with peer discovery
• Peer Wire Protocol: Full peer-to-peer communication with piece management
• Modern WPF UI: Clean, intuitive interface with real-time progress tracking
• Console Mode: Command-line interface for testing and automation
• File Management: Support for both single and multi-file torrents
• Piece Verification: SHA1 hash verification for data integrity
• Progress Tracking: Real-time download progress, speed, and ETA
• Peer Management: Connection management and peer statistics

Requirements

• .NET 8.0 SDK or later
• Windows 10/11 (for WPF UI)
• Visual Studio 2022 or later (recommended)

Quick Start

1. Clone and Build

git clone <repository-url>
cd BitTorrent-Client

2. Build the Project

Using PowerShell (recommended):

.\build.ps1

Using Batch file:

build.bat

Using dotnet CLI:

dotnet restore
dotnet build --configuration Release

3. Run the Application

WPF Mode (GUI):

dotnet run --project BitTorrentClient

Console Mode (for testing):

dotnet run --project BitTorrentClient -- --console

Usage

WPF Interface

1. Add Torrent: Click "Add Torrent" and select a .torrent file
2. Select Download Location: Choose where to save the files
3. Start Download: Click "Start" to begin downloading
4. Monitor Progress: View real-time progress, speed, and peer information
5. Control Downloads: Use Start/Stop/Pause/Remove buttons to manage torrents

Console Mode

The console mode provides a simple interface for testing:

1. Enter the path to a .torrent file
2. Specify the download directory
3. Monitor real-time progress in the console
4. Press any key to stop the download

Architecture

Core Components

• TorrentParser.cs: Parses .torrent files and extracts metadata
• BencodeParser.cs: Handles Bencode encoding/decoding (BEP 3)
• TrackerClient.cs: Communicates with BitTorrent trackers
• PeerConnection.cs: Manages peer-to-peer connections
• PieceManager.cs: Handles piece verification and file assembly
• TorrentDownloader.cs: Orchestrates the entire download process

UI Components

• MainWindow.xaml: Main application window
• TorrentViewModel.cs: MVVM view model for torrent management
• App.xaml: Application entry point

🧠 Intelligent Peer Selection (AI Module)

The client includes an AI-powered peer selection module (Core/AI/IntelligentPeerSelector.cs) that optimizes which peers to connect to and request pieces from. This module:

• Scores and ranks peers based on download speed, reliability, response time, and piece success rate.
• Promotes or demotes peers dynamically, blacklisting unreliable ones and prioritizing high-performing peers.
• Adapts peer selection in real time to maximize download speed and reliability.
• Extensible for future ML integration (e.g., reinforcement learning for peer selection).

This intelligent selection helps the client avoid slow or malicious peers and improves overall torrent performance.

Protocol Implementation

Supported Features

• ✅ BEP 3: BitTorrent Protocol
• ✅ Bencode: Data serialization format
• ✅ Peer Wire Protocol: Message types and handshaking
• ✅ Tracker Protocol: HTTP/HTTPS tracker communication
• ✅ Piece Management: Download, verification, and assembly
• ✅ Choking Algorithm: Basic peer selection
• 🔄 Magnet Links: Planned (BEP 9)
• 🔄 DHT: Planned (BEP 5)

Message Types

• choke (0): Peer is choking the client
• unchoke (1): Peer is unchoking the client
• interested (2): Client is interested in peer
• not_interested (3): Client is not interested in peer
• have (4): Peer has a piece
• bitfield (5): Peer's piece availability
• request (6): Request a piece block
• piece (7): Piece block data
• cancel (8): Cancel a request

Development

Project Structure

BitTorrentClient/
├── Core/                    # Core protocol implementation
│   ├── TorrentParser.cs     # Torrent file parsing
│   ├── TrackerClient.cs     # Tracker communication
│   ├── PeerConnection.cs    # Peer wire protocol
│   ├── PieceManager.cs      # Piece management
│   └── Downloader.cs        # Main download orchestrator
├── ViewModels/              # MVVM view models
│   └── TorrentViewModel.cs  # Torrent management
├── Tests/                   # Unit tests
│   └── TorrentParserTests.cs
├── MainWindow.xaml          # Main UI
├── App.xaml                 # Application entry
└── Program.cs               # Program entry point

Building from Source

1. Install Prerequisites:

   • .NET 8.0 SDK
   • Visual Studio 2022 (optional)

2. Clone Repository:

   git clone <repository-url>
   cd BitTorrent-Client

3. Restore Dependencies:

   dotnet restore

4. Build Project:

   dotnet build --configuration Release

5. Run Tests:

   dotnet test

Adding Features

The project is designed with extensibility in mind:

• New Protocol Features: Add to the Core namespace
• UI Enhancements: Modify WPF files in the root
• Additional Formats: Extend the parser classes

Testing

Unit Tests

Run the test suite:

dotnet test

Manual Testing

1. Console Mode: Test core functionality

   dotnet run --project BitTorrentClient -- --console

2. WPF Mode: Test user interface

   dotnet run --project BitTorrentClient

Test Torrents

For testing, you can use:

• Ubuntu ISO torrents (legal and reliable)
• Open source software distributions
• Public domain content

Troubleshooting

Common Issues

1. Build Errors:

   • Ensure .NET 8.0 SDK is installed
   • Run dotnet restore before building
   • Check for missing dependencies

2. Network Issues:

   • Verify firewall settings
   • Check port 6881 availability
   • Ensure tracker URLs are accessible

3. Permission Errors:

   • Run as administrator if needed
   • Check download directory permissions

Debug Mode

Enable detailed logging:

dotnet run --project BitTorrentClient --configuration Debug

Default Port

• The client listens on port 6882 by default (previously 6881). You can change this in TorrentDownloader and StealthMode if needed.

Logging

• The client writes debug logs to debug.log in the working directory and also outputs logs to the console.
• If you do not see the log file, check the console output or search your user folder for debug.log.
• Log messages include [DEBUG], [PEER], and [DOWNLOADER] for detailed protocol and connection information.

Troubleshooting Peer Connections

If you see Connected Peers: 0/0 and no download progress:

• Check the console for [PEER] and [DOWNLOADER] log messages.
• Make sure your firewall allows inbound and outbound connections on port 6882.
• Try a different torrent with a healthy swarm.
• If all peer connections time out, the tracker may be returning stale or unreachable peers.
• The log file may not update if the app is run from a different working directory. Try searching your user folder for debug.log.

Known Issues

• Some ISPs block BitTorrent ports (6881-6889). Try changing the port if you have connectivity issues.
• The log file may not update if the app is run from a different working directory.
• The client currently does not support DHT or magnet links (planned features).

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Add tests for new functionality
5. Submit a pull request

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgments

• BitTorrent Protocol Specification (BEP 3)
• .NET Community for excellent tooling
• Open source community for inspiration

Roadmap

• Magnet link support (BEP 9)
• Distributed Hash Table (BEP 5)
• Peer Exchange (BEP 11)
• IPv6 support
• Bandwidth limiting
• Encryption (BEP 7)
• Web seed support (BEP 19)
• Cross-platform UI (Avalonia)