Torque

A minimal (standard & UNIX libraries only!) Bittorrent client implementation in C. Download .torrent files with one terminal command.

Motivation

This program is being developed as a side-project of mine to explore networking & memory management in C. It is by no means production ready and only meant as an educational tool.

It includes:

• The world's worst Bencode parser.
• A low level networking api that can send & receive data from TCP sockets.
• A partial HTTP 1.0 implementation.
• A multi-threaded torrent part downloader & validator.
• A CLI argument parser.

I have tried to keep the source code as clean and minimal as possible so it should be quite readable for anyone who wants to take a look at the code. I am also planning on making a blog post write-up once the project is finished.

Development status

• Bencode parser
  • Parsing of bencode strings, ints
  • Parsing of bencode dicts, lists, simple bencode files
  • Parsing of .torrent files
• TCP client
  • Implement connect, close, send receive functions
  • Able to ping-pong a echo server
• HTTP client
  • DNS lookup to get server IPs from hostnames
  • HTTP GET Able to get HTTP 200 HTML data from example.com Query parameters unsupported for now
  • HTTP POST
• Core torrent stuff
  • Parse a torrent file and extract the info hashes
  • Connect to a tracker, retrieve list of peers
  • Downloading from peers
    • Complete Bittorrent handshake
    • Parse downloadable data from peer using bitfields
    • Pipelining
    • Assemble file and validate using the hash
• Cleanup
  • CLI interface with help command
  • Unit tests & better error handling
  • Improve readme

Resources

• I am following this great article by Jesse Li who did something similar in Go.
• Initial inspiration for this project came from a Rust video by Jon Gjengset: implementing a bittorrent client using the (paid) Build your own BitTorrent course at codecrafters.io
• SHA1 implementation copied from Steve Reid

Usage

A CLI interface is planned but not available yet.

Building & Contributing

Only buildable on linux systems due to reliance on standard C UNIX networking api's. No build system required, Build manually using the build.sh bash script. Please don't submit issues / merge requests while still in development.