torrent_client

A concurrent bit torrent downloader written in Crystal!

Background and design

This application is a Crystal port of Jesse Li's golang client. I recommend Jesse's companion article on how bit torrent works, which served as an inspiration for this project.

This project is meant for didactic purposes, and aims to illustrate differences in design choices and performance between Crystal and Go. The client can only download files, at the moment, but I'm planning on extending the functionality to support uploads, too.

Installation

shards install # install dependencies
crystal build -Dpreview_mt src/torrent_client.cr # compile with multi-threading support

Usage

CRYSTAL_WORKERS=<n-workers>  ./torrent_client <torrent_path> [options]

Options:

  -r, --replay                     Will replay events from the previous run. [type:Bool] [default:false]
  -o <destination_path>, --output=<destination_path>
                                    Download destination [type:String]
  -m <minimal|ncurses|web>, --mode=<minimal|ncurses|web>
                                    UI mode [type:String] [default:"minimal"]
  --help                           Show this help.

Arguments:

  01. torrent_path      The torrent file you want to download. [type:String]

Examples

CRYSTAL_WORKERS=8  ./torrent_client ./spec/testdata/debian.iso.torrent -o ./data/debian.iso
# sample output
Downloading debian-10.2.0-amd64-netinst.iso: 2 pieces of 1340 completed (8 peers)

CRYSTAL_WORKERS=8  ./torrent_client ./spec/testdata/debian.iso.torrent -m web

CRYSTAL_WORKERS=8  ./torrent_client ./spec/testdata/debian.iso.torrent -m ncurses
# sample output
Downloading debian-10.2.0-amd64-netinst.iso: 8 pieces of 1340 completed (9 peers)
┌────────────────┬─────────────┬───────┬────────────┐
│ Peer           │ Status      │ Piece │ Downloaded │
├────────────────┼─────────────┼───────┼────────────┤
│ 163.172.10.185 │ downloading │ 15    │ 2          │
│ 163.172.43.117 │ finished    │ 7     │ 2          │
│ 185.45.195.169 │ downloading │ 10    │ 1          │
│ 176.9.45.212   │ downloading │ 12    │ 1          │
│ 78.62.187.199  │ downloading │ 4     │ 0          │
│ 185.148.3.52   │ downloading │ 13    │ 1          │
│ 84.2.20.22     │ downloading │ 14    │ 1          │
│ 91.239.69.64   │ downloading │ 9     │ 0          │
│ 203.220.135.51 │ downloading │ 11    │ 0          │
└────────────────┴─────────────┴───────┴────────────┘

Prometheus integration

The application exposes prometheus metrics at localhost:5000/metrics. See the crometheus documentation for further information.

Development

Replaying

To make local testing of UI and metrics collection simpler, you can start by downloading a file, e.g.

crystal src/torrent_client.cr ./spec/testdata/debian-10.2.0-amd64-netinst.iso.torrent

and then replay the download on the following runs.

crystal src/torrent_client.cr --replay

A replay does not initiate any connection to peers, but simply replays the events stored in history.log - you'll see this file popping up in the project root folder after the first download.

Running the specs

crystal specs

Contributing

1. Fork it (https://github.com/lbarasti/torrent_client/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• lbarasti - creator and maintainer