BitTorrent Client

This BitTorrent client is a simple tool designed to download files using .torrent files. It has limited functionality, with specific constraints and features outlined below.

Features

• Supports .torrent files: This client works exclusively with .torrent files and does not support magnet links.
• Supports HTTP trackers: Only HTTP trackers are supported. There is no support for UDP trackers.
• Single-file torrents only: Multi-file torrents are not supported.
• Leech-only mode: This client downloads files but does not upload pieces back to the network.
• No DHT support: The client does not support the Distributed Hash Table (DHT) protocol.

Usage

Below are the example commands and their descriptions:

Decode

Decode bencoded data using the decode command:

./bittorrent.sh decode <bencoded_data>

Examples:

./bittorrent.sh decode 5:hello

Output:

"hello"

./bittorrent.sh decode i52e

Output:

52

./bittorrent.sh decode l5:helloi52ee

Output:

["hello", 52]

./bittorrent.sh decode d3:foo3:bar5:helloi52ee

Output:

{"foo": "bar", "hello": 52}

Torrent Info

Get information about a torrent file using the info command:

./bittorrent.sh info <file.torrent>

Example:

./bittorrent.sh info torrents/sample.torrent

Output:

Tracker URL: http://bittorrent-test-tracker.codecrafters.io/announce
Length: 92063
Info Hash: d69f91e6b2ae4c542468d1073a71d4ea13879a7f
Piece Length: 32768
Piece Hashes:
e876f67a2a8886e8f36b136726c30fa29703022d
6e2275e604a0766656736e81ff10b55204ad8d35
f00d937a0213df1982bc8d097227ad9e909acc17

List Peers

List peers available for a torrent using the peers command:

./bittorrent.sh peers <file.torrent>

Example:

./bittorrent.sh peers torrents/sample.torrent

Output:

178.62.82.89:51470
165.232.33.77:51467
178.62.85.20:51489

Handshake

Initiate a handshake with a peer using the handshake command:

./bittorrent.sh handshake <file.torrent> <peer_ip>:<peer_port>

Example:

./bittorrent.sh handshake torrents/sample.torrent 178.62.82.89:51470

Output:

Peer ID: 0102030405060708090a0b0c0d0e0f1011121314

Download Piece

Download a specific piece of the file using the download_piece command:

./bittorrent.sh download_piece -o <output_path> <file.torrent> <piece_index>

Example:

./bittorrent.sh download_piece -o /Users/william/Documents/bittorrent/tmp/test-piece-0 torrents/sample.torrent 0

Output:

Piece 0 downloaded to /tmp/test-piece-0.

Download File

Download the entire file using the download command:

./bittorrent.sh download -o <output_path> <file.torrent>

Examples:

./bittorrent.sh download -o /Users/william/Documents/bittorrent/tmp/sample.txt torrents/sample.torrent

./bittorrent.sh download -o /Users/william/Documents/bittorrent/tmp/codercat.gif torrents/codercat.gif.torrent

./bittorrent.sh download -o /Users/william/Documents/bittorrent/tmp/congratulations.gif torrents/congratulations.gif.torrent

./bittorrent.sh download -o /Users/william/Documents/bittorrent/tmp/debian.iso torrents/debian.torrent

./bittorrent.sh download -o /Users/william/Documents/bittorrent/tmp/itsworking.gif torrents/itsworking.gif.torrent

Limitations

• No support for magnet links: Ensure you have a valid .torrent file.
• HTTP trackers only: Make sure the tracker URL is an HTTP link; UDP trackers are not supported.
• Single-file torrents: Multi-file torrents are not supported, so use only single-file torrents.
• Leech-only client: This client does not upload pieces, so it will not contribute to the sharing process.
• No DHT support: The Distributed Hash Table (DHT) protocol is not implemented.

Planned Features

We are planning to implement the following features in future updates:

• Seeding: Ability to upload pieces to contribute to the network.
• Multi-torrent support: Download multiple torrents simultaneously.
• DHT protocol: Support for the Distributed Hash Table protocol to enhance peer discovery.

Installation

Ensure you have the necessary permissions to run the script and place it in a directory included in your system's PATH.

chmod +x bittorrent.sh