A complete BitTorrent client implementation in C++20 with multi-peer downloading, SHA-1 verification, and cross-platform support.

Click above → VS Code opens in browser → Run: ./run.sh docker

Two ways to run:

1. Docker (instant, works anywhere)
2. Local Build (for development)

Works on any system with Docker installed.

git clone https://github.com/tanmaygithub04/Bit-Torrent.git
cd Bit-Torrent

./run.sh docker

That's it! The script will:

• Build the Docker image automatically
• Download a sample torrent file
• Show real-time progress
• Save the file to downloads/ directory

For development and customization.

Ubuntu/Debian:

sudo apt-get update
sudo apt-get install build-essential libboost-all-dev libssl-dev cmake

macOS:

brew install boost openssl cmake

git clone https://github.com/tanmaygithub04/Bit-Torrent.git
cd Bit-Torrent
./run.sh build

The script will compile and test automatically.

Bit-Torrent/
├── src/
│   ├── core/
│   │   ├── DownloadManager.cpp     # Orchestrates downloads
│   │   ├── DownloadManager.h
│   │   ├── peer.cpp                # Peer communication
│   │   ├── peer.h
│   │   ├── torrent.cpp             # Torrent metadata parsing
│   │   ├── torrent.h
│   │   ├── tracker.cpp             # Tracker communication
│   │   └── tracker.h
│   ├── utils/
│   │   ├── bencode.cpp             # Bencode parsing
│   │   ├── bencode.h
│   │   ├── error.h                 # Error handling
│   │   ├── hash.cpp                # SHA-1 hashing
│   │   ├── hash.h
│   │   └── terminal_ui.h           # UI utilities
│   └── Main.cpp                    # Entry point
├── torrents/
│   └── sample.torrent              # Sample torrent file
├── downloads/                      # Downloaded files appear here
├── README.md                       # Project documentation
├── run.sh                          # Simple runner script

┌─────────────────────────────────────────────────────────────┐
│                        Main Application                     │
└─────────────────────────┬───────────────────────────────────┘
                          │
┌─────────────────────────▼───────────────────────────────────┐
│                   Download Manager                          │
│  • Orchestrates download process                            │
│  • Manages piece verification                               │
│  • Handles file assembly                                    │
└─────────────────────────┬───────────────────────────────────┘
                          │
         ┌────────────────┼────────────────┐
         │                │                │
┌────────▼────────┐  ┌────▼────────┐  ┌───-▼─────────┐
│  Torrent Parser │  │   Tracker   │  │  Peer Manager│
│  • Metadata     │  │  • Get peers│  │  • Handshake │
│  • Bencode      │  │  • Announce │  │  • Messages  │
│  • Info hash    │  │  • HTTP     │  │  • Downloads │
└─────────────────┘  └─────────────┘  └──────────────┘

1. Block-Based Piece Downloading✅: Downloads pieces in 16 KiB blocks by sending REQUEST messages and assembling the corresponding PIECE messages.

2. Piece Integrity Verification✅: Computes the SHA-1 hash of each downloaded piece and compares it against the expected hash from the torrent metadata to ensure file integrity.

3. File Assembly✅: Once all pieces are successfully downloaded and verified, the client assembles them into the final output file.

4. Peer Connection & Handshake✅: Uses Boost.Asio to resolve peer addresses, establish TCP connections, and perform the BitTorrent handshake.

5. Torrent Metadata Parsing✅: Extracts essential information (info_hash, piece length, total file length, concatenated SHA-1 hashes) from torrent files.

6. Bencode Decoding✅: Implements bencode parsing utilities to correctly read and interpret torrent metadata.

7. Modular Architecture✅: Refactored from a monolithic implementation into separate, maintainable components (TorrentMetadata, Peer, and DownloadManager) to improve clarity and scalability.

Assumptions 📌 This is a simple Bit torrent client without Piece Selection , or Tracker Implementation , or any Choking Algorithm so might not work for all torrent files The client assumes the .torrent file is valid and well-formed. Peers listed in the torrent metadata are available and active. The download directory (src/downloads/) exists before running the program.

• Make it compatibility with standard multi file torrents
• Can go in direction of video downloading/streaming or in the direction of implementing advanced algorithms
• Multithreaded piece downloading
• DHT (Distributed Hash Table) support
• Magnet link support
• Web UI interface
• Bandwidth throttling

• Monolithic Code Structure Initially, all functionality was implemented in a single file, making the code hard to maintain. This necessitated refactoring into modular components. Linker and Undefined Symbols

• Some functions were declared but not defined or had signature mismatches, leading to linker errors. URL Encoding and Conversion Errors

• Improper encoding of binary data (like the info hash) resulted in conversion errors such as “stoul: no conversion.” UTF‑8 Validation Issues

• The tracker’s compact peer data wasn’t valid UTF‑8, which broke JSON parsing until UTF‑8 validation was disabled. File Path and Directory Problems

• Incorrect relative paths (e.g., using "../downloads/sample.txt" instead of the correct path) and missing directories led to file-opening errors. Piece Assembly Errors

• Using vector insertion to assemble piece data appended blocks rather than placing them at the correct offsets, causing hash mismatches. State Management for Peer Communication

• Waiting for an UNCHOKE message on every piece download—even when the peer was already unchoked—resulted in failed downloads. Segmentation Faults & Memory Issues

• Mismanagement of memory and null pointer dereferences caused segmentation faults during handshake and piece download. And Many more 😅

If you want to contribute:

• Fork the repo
• Create a feature branch
• Make changes and submit a PR 🚀

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