🧩 BitTorrent Client (Go)

Overview

This project is a lightweight BitTorrent client implemented in Go. It can download files from peers using a .torrent file — demonstrating how the BitTorrent protocol works under the hood: parsing torrent metadata, connecting to peers, and downloading verified pieces.

The goal is educational clarity and simplicity rather than a full-featured production client.

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✨ Features

• Parses .torrent files
• Connects to peers discovered via tracker
• Downloads file pieces concurrently
• Verifies each piece using SHA-1 hashes
• Assembles the complete file from verified pieces
• Simple, minimal entry point with no CLI flags

🚀 Getting Started

1. Prerequisites

• Go 1.23+
• Internet connection
• A valid .torrent file

2. Clone the Repository

git clone https://github.com/onahvictor/torrent-client.git
cd torrent-client

3. Build the Binary

go build -o torrent-client ./cmd

4. Run the Client

The client takes two arguments:

1. Path to the .torrent file
2. Output directory for the downloaded file

Example:

./torrent-client ./testdata/example.torrent ./downloads

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⚙️ How It Works

1. Open the torrent file

   • Reads and parses the .torrent metadata (announce URL, info hash, piece hashes, etc.).

2. Announce to tracker

   • Contacts the tracker to get a list of available peers.

3. Handshake with peers

   • Performs the BitTorrent handshake to confirm they share the same torrent.

4. Download pieces

   • Requests and downloads file pieces concurrently from multiple peers.

5. Verify and assemble

   • Verifies each piece using SHA-1 hash and assembles the final file once all pieces are complete.

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📦 Example Output

Opening torrent file: example.torrent
Connecting to tracker...
Found 8 peers
Downloading piece 4/256
Piece 4 verified ✅
Download complete: ./downloads/example.iso

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🧠 Key Concepts

Concept	Description
Torrent file	A metadata file describing the files and trackers for the torrent
Tracker	A server that helps peers discover each other
Peer	Another client sharing the same torrent
Piece	A fixed-size chunk of the full file
Info hash	Unique identifier for the torrent content

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🧩 Future Improvements

• Add support for flags (e.g., -torrent, -out)
• Add DHT and magnet link support
• Implement upload (seeding)
• Handle multi-file torrents
• Improve download progress display