Scope of this blog

To be able to understand what a torrent file does. What does contents inside torrent file do.

How you download a torrent.

Say you were to download arch linux from the provided torrent file on the archlinux website. You would

1. Download the file from the website
2. load the file onto a torrent client like deluge/transmission/uTorrent etc and it begins downloading.

Observing a torrent file

Let’s disect the Arch Linux Iso and open the file.

The file looks alot gibberish but you can see some ascii charecters like d,i,i with numbers next to them and maybe some urls.

this encoding of a file is called bencoding and it is a representation of a object similar to how yaml/json works.

now that we know that it is bencoded, we should know how bencoding works.

Working of bencoding

Opening torrent file in a bencoding viewer tool

this tool helps us open a bencoded file and let’s see it in JSON format.

Let’s see the file in JSON which is more human readable format for an object.

{
   "comment": "Arch Linux 2023.11.01 <https://archlinux.org>",
   "created by": "mktorrent 1.1",
   "creation date": 1698821953,
   "info": {
      "length": 846540800,
      "name": "archlinux-2023.11.01-x86_64.iso",
      "piece length": 524288,
      "pieces": "<hex>27 51 12 5C 1A DB 1B......Ommited for ease.....</hex>"
   },
   "url-list": [
      "https://mirror.aarnet.edu.au/pub/archlinux/iso/2023.11.01/",
      "https://mirrors.rit.edu/archlinux/iso/2023.11.01/",
      "https://ftp.ek-cer.hu/pub/mirrors/ftp.archlinux.org/iso/2023.11.01/",
      "https://ftp.heanet.ie/mirrors/ftp.archlinux.org/iso/2023.11.01/",
      "https://mirror.puzzle.ch/archlinux/iso/2023.11.01/",
      "https://mirror.csclub.uwaterloo.ca/archlinux/iso/2023.11.01/",
      .
      .
      .
      // Omitted for ease
      .
      .
      .
   ]
}