ztoriansimonson/ztor
A (partial) bittorrent client in zig
README
ZTOR
Zig BitTorrent Client
A small but slightly more than non-trivial program written in Zig.
This was mostly an experiment in using zig with a c event-loop library and callback-based appraoch. A number of useful zig features, such as errors, can't be used due to the C abi boundary being pervasive.
I do not recommend using this code as a good example as there are no tests and currently I've thrown a lot of it together in one place. But if it helps then go for it.
The torrent file is for the debian net install image which was used because A. debian has seeders so we probably don't have to worry about being choked all the time, and B. it's a single file torrent so no need to deal with directories and multiple files.
Build
This program depends on a number of modules and builds both http_parser and libuv.
git clone --recursive https://github.com/iansimonson/ztor.git
cd ztor
zig build
Plan
Connect to tracker and download peer info
Parse .torrent into tree
Find announce url
Connect and download peer list
Establish connections to peers
Construct peer connection info per peer
Only download on unchoke
Use uv_get_handle rather than the members
Support for N .torrent files at once
Don't shutdown after a file is done downloading
Implement upload and answering requests
Send have messages to all peers on download
If have send piece on request
provide mechanism to get non-owning immutable slice to piece
Setup server for incoming connections
Upload throttled amount of data
Send bitfield on new incoming connections
Add invalid threshold
After x amount of invalid pieces close connection to peer
Throttle data speeds
Token Bucket?
Upload throttle
Download throttle
Setup imgui (or similar) for handling torrents in GUI mode
Additional TODO:
Build libuv in build.zig
Move from libuv to native zig async/await
Abstract away libuv
Support non-compact peer list
Confirm peer_ids
Support uTP protocol rather than using TCP
Support UDP tracker protocol (BEP 015)
SSL/TLS support?
Watch a folder for .torrent files
Other BEPs?
Make the Torrent Lexer work with Reader/Writer
Relevant links
Prior to this I only knew how torrents worked conceptually. How to implement a torrent downloader was way outside what I knew. The following are relevant links when learning: