BitTorrent Client in Go

A lightweight BitTorrent client implementation written in Go that can download files from torrent networks.

Features

• Parse .torrent files using bencode encoding
• Connect to tracker servers to discover peers
• Establish peer connections with BitTorrent handshake protocol
• Download pieces in parallel from multiple peers
• Verify piece integrity using SHA-1 hashes
• Handle BitTorrent protocol messages (choke, unchoke, interested, have, bitfield, request, piece)
• Concurrent download workers for efficient file retrieval

Installation

# Clone the repository
git clone https://github.com/ProgrammedByHussain/bittorrent-go.git
cd bittorrent-go

# Install dependencies
go mod download

Usage

go run . <torrent-file> <output-file>

Example:

go run . ubuntu.torrent ubuntu.iso

Project Structure

.
├── bitfield/          # Bitfield operations for tracking piece availability
├── client/            # TCP client for peer connections
├── handshake/         # BitTorrent handshake protocol implementation
├── message/           # Protocol message encoding/decoding
├── p2p/               # Peer-to-peer download orchestration
├── peers/             # Peer data structures and parsing
├── torrentfile/       # Torrent file parsing and tracker communication
└── main.go            # Entry point

How It Works

1. Parse Torrent File: Reads and decodes the .torrent file to extract metadata including tracker URL, piece hashes, and file information
2. Request Peers: Contacts the tracker server to get a list of peers sharing the file
3. Establish Connections: Performs handshakes with available peers
4. Download Pieces: Spawns concurrent workers to download file pieces from multiple peers
5. Verify Integrity: Validates each downloaded piece against its SHA-1 hash
6. Assemble File: Combines verified pieces into the complete file

Technical Details

• Piece Size: Standard 262 KB pieces with configurable block size (16 KB)
• Concurrency: Multiple goroutines handle parallel downloads from different peers
• Protocol: Implements core BitTorrent protocol v1.0 messages
• Timeout Handling: 3-second handshake timeout, 30-second piece download timeout

Dependencies

• github.com/jackpal/bencode-go - Bencode encoding/decoding

Requirements

• Go 1.25.1 or higher

License

This project is for educational purposes.