Torrent file

Check
Filename extension	.torrent
Internet media type	c706de10d03b7d5c5007692e89418f20e192973d
File formats category -   edit

Torrent file
File formats category -   edit

A torrent file (.torrent file, BitTorrent metainfo file) is required by a BitTorrent client to initiate file transfer using the BitTorrent protocol.

bencoding

bencoding is a way to store some data structures in the torrent file format.

Strings

Strings are stored as <length of string>:<string>:

<span class="c-key">4:<span class="c-string">wiki

Integers

Integers are stored as i<integer>e:

<span class="c-key">i<span class="c-number">90<span class="c-key">e

List

Lists are stored as l[value 1][value2][value3][...]e. For example, {spam, eggs, cheeseburger} is stored as:

<span class="c-key">l4:<span class="c-string">spam<span class="c-key">4:<span class="c-string">eggs<span class="c-key">12:<span class="c-string">cheeseburger<span class="c-key">e

Dictionary

Dictionaries are stored as d[key1][value1][key2][value2][...]e. Keys and values appear alternately. Keys must be strings and must be ordered alphabetically. For example, {apple-red, lemon-yellow, violet-blue, banana-yellow} is stored as:

<span class="c-key">d5:<span class="c-string">apple<span class="c-key">3:<span class="c-string">red<span class="c-key">6:<span class="c-string">banana<span class="c-key">6:<span class="c-string">yellow<span class="c-key">5:<span class="c-string">lemon<span class="c-key">6:<span class="c-string">yellow<span class="c-key">6:<span class="c-string">violet<span class="c-key">4:<span class="c-string">blue<span class="c-key">e

Specification

Data in a torrent file is bencoded as a dictionary, with no other header. The top-level dictionary has the following keys:

Key	Type	Description
info	dictionary	File information for the torrent.
announce	string	The URL of the tracker for the torrent. For example, <span class="c-key">29:<span class="c-string">http://tracker.example.com:80
announce-list	list	A listing of the URLs of alternate trackers for the torrent. The URLs are divided into groups (each is a list), trackers in each group may be shuffled, and groups are processed in the order they appear. Optional.
creation date	integer	The creation date and time, expressed as the number of seconds since January 1, 1970 12:00. Optional.
comment	string	Any user comment for the torrent. Optional.
created by	string	Application-generated string that may include its name, version, etc. Optional.

File information (info)

The info key corresponds to the files in the torrent. There are two-forms: a single-file format that contains only a single file, and a multi-file format that may contain multiple files and directories. The info key itself corresponds to another (essentially "nested") dictionary with the keys as follows:

Common file keys

Key	Type	Description
piece length	integer	The number of bytes in each piece. Files in a torrents are divided into "pieces" with a specific length.
pieces	string	A (byte) string consisting of the concatenation of all 20-byte SHA1 hash values, one per piece.

Single-file format keys

Key	Type	Description
name	string	The proposed filename of the file.
length	integer	The length of the file, in bytes.

Multi-file format keys

Key	Type	Description
name	string	The proposed name of directory to store the files.
files	list (of dictionary)	A list of dictionaries, one dictionary for each file in the torrent, which is described in the next table.

A dictionary in the file list corresponds to one file and contains the following:

Key	Type	Description
length	integer	The length of the file, in bytes.
path	list (of string)	A list of strings representing the relative path to the file. For example, <span class="c-key">l6:<span class="c-string">source<span class="c-key">3:<span class="c-string">bin<span class="c-key">8:<span class="c-string">test.exe<span class="c-key">e corresponds to the path "<directory name>\source\bin\test.exe".

References

• BitTorrent Specification
• Unofficial BitTorrent Specification at theory.org