1  ---
 2  tags:
 3    - bittorrent
 4  related-to:
 5    - "[[Learn BitTorrent]]"
 6    - "[[Advertising BitTorrent content on Codex]]"
 7  ---
 8  #bittorrent 
 9  
10  | related-to | [[Learn BitTorrent]], [[Advertising BitTorrent content on Codex]] |
11  | ---------- | ----------------------------------------------------------------- |
12  
13  Called `torrent` files.
14  
15  Although we are using trackerless torrents, still the information contained in torrent files is indispensable and will be provided by the peers using number of extension mechanism. We talk more about it in [[Advertising BitTorrent content on Codex]].
16  
17  ## BitTorrent v1
18  
19  Files are split into fixed-size *pieces* of the same length except for maybe the last one that may be truncated. *Almost always* power of two, most commonly 2^18 = 256 KiB (older versions prior to v 3.2 used 2^20 = 1 MiB as default). For directories, the files are concatenated in the order in which they appear in the file list (see the `files` key in the `info` dictionary below).
20  
21  Metainfo files, or `.torrent` files are **bencoded** dictionaries with the following keys:
22  
23  - announce - the url of the tracker
24  - info - maps to a dictionaries with the following keys:
25  	- name - suggested name to save a file or dictionary - purely advisory
26  	- piece length - number of bytes each *piece* is split info
27  
28  ### BitTorrent  v2
29  
30  Here the `info` dictionary, has the following keys:
31  
32  - `announce` - the url of the tracker
33  - `info`
34  	- `file tree` - a three structure describing each file position in the file tree
35  		- `length`
36  		- `pieces root` - Merkle tree toor for the given file
37  	- `piece length` - as in v1, number of bytes each *piece* is split info
38  	- `meta version` - set to `2`
39  	- `name` - as in v1 above
40   - `piece layers` - dictionary with entries for each file larger than one piece: key being the corresponding `pieces root` and value being string being a concatenation of piece layer hashes for that file.
41  
42  We have extensive examples showing how the torrent files are constructed. They can be found under the following url: [https://link.excalidraw.com/readonly/c9z3gLsV1qkTSQJUxEXk](https://link.excalidraw.com/readonly/c9z3gLsV1qkTSQJUxEXk)