BitTorrent Client

A lightweight BitTorrent client implemented in JavaScript.
This project demonstrates the core functionalities of the BitTorrent protocol, enabling peer-to-peer file sharing in a decentralized network.

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🧠 Overview

The BitTorrent protocol is a peer-to-peer (P2P) file-sharing system that allows users to download and distribute files efficiently without relying on a central server.

This client implements the fundamental features of the protocol, including:

• Tracker Communication: Finding peers with the desired file.
• Peer-to-Peer Networking: Exchanging pieces of the file with other peers.
• Piece Management: Downloading and assembling file pieces efficiently.
• File Writing: Saving the downloaded file to the local filesystem.

This project is a practical example of networking, concurrency, and protocol implementation in JavaScript.

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⚙️ Features

• Connects to both HTTP and UDP trackers.
• Maintains a queue of pieces to download from multiple peers concurrently.
• Handles downloading, assembling, and writing file pieces.
• Supports basic message handling between peers.
• Modular design with separate modules for pieces, queue management, downloading, torrent parsing, tracker communication, and utility functions.

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📁 Project Structure

BitTorrent-Client/
├── src/
│   ├── pieces.js           # Piece management and bitfield handling
│   ├── Queue.js            # Queue system for pieces to download
│   ├── download.js         # Handles piece downloading from peers
│   ├── message.js          # Peer message creation and parsing
│   ├── torrent-parser.js   # Parses .torrent files
│   ├── tracker.js          # Tracker communication (HTTP/UDP)
│   └── utils.js            # Utility functions (hashing, conversions, etc.)
├── index.js                # Main entry point for the client
├── add-udp-tracker.js      # Adds UDP tracker support
├── print-trackers.js       # Prints tracker info for a torrent
├── package.json            # Project metadata and dependencies
├── .gitignore              # Git ignore file

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🚀 Installation

1. Clone the repository:

git clone https://github.com/Akrishna4/BitTorrent-Client.git
cd BitTorrent-Client

2. Install dependencies:

npm install

3. Run the client:

node index.js <path-to-torrent-file>

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📄 Usage

1. Obtain a .torrent file from a trusted source.

2. Place the .torrent file in the project directory.

3. Run the client using the above command.

4. The client will:

   • Parse the torrent file
   • Connect to the tracker
   • Find peers and start downloading pieces
   • Reassemble pieces into the full file

• add-udp-tracker.js: Adds support for discovering peers via UDP trackers.
• print-trackers.js: Prints all tracker URLs from a given .torrent file.

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🛠️ How It Works

1. Torrent Parser (torrent-parser.js)

• Reads metadata from .torrent files
• Extracts file info, piece hashes, and tracker URLs

2. Tracker (tracker.js)

• Connects to trackers via HTTP/UDP
• Retrieves a list of peers

3. Piece Management (pieces.js)

• Keeps track of downloaded and missing pieces
• Validates piece integrity using SHA-1 hash

4. Queue (Queue.js)

• Manages download order for pieces
• Optimizes concurrent downloading

5. Downloader (download.js)

• Requests pieces from multiple peers simultaneously
• Handles reassembly into the original file

6. Messaging (message.js)

• Implements peer messaging protocol
• Handles handshakes, requests, and piece transfers

7. Utilities (utils.js)

• Common helper functions like hashing, buffer conversions, etc.

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📸 Architecture Diagram (ASCII)

[Torrent Parser] --> [Tracker] --> [Peers]
                          |
                          v
                     [Queue System]
                          |
                          v
                   [Piece Downloader]
                          |
                          v
                    [Piece Management]
                          |
                          v
                       [File Writer]

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📚 Resources

• BitTorrent Protocol Specification
• Understanding the BitTorrent Protocol
• Implementing a BitTorrent Client in JavaScript

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