BitTorrentTrackerExtensions - Describes the various extensions of the Tracker protocol that are in use.
Conventions
In this document, a number of conventions are used in an attempt to present information in a concise and unambiguous fashion.
- peer v/s client: In this document, a peer is any BitTorrent client participating in a download. The client is also a peer, however it is the BitTorrent client that is running on the local machine. Reader of this specification may choose to think of themselves as the client which connects to numerous peers.
- piece v/s block: In this document, a piece refers to a portion of the downloaded data that is described in the metainfo file, which can be verified by a SHA1 hash. A block is a portion of data that a client may request from a peer. Two or more blocks make up a whole piece, which may then be verified.
- defacto standard: Large blocks of text in italics indicates a practice so common in various client implementations of BitTorrent that it is considered a defacto standard.
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bencoding
Bencoding is a way to specify and organize data in a terse format. It supports the following types: byte strings, integers, lists, and dictionaries.
byte strings
Byte strings are encoded as follows: <string length encoded in base ten ASCII>:<string data>
Note that there is no constant beginning delimiter, and no ending delimiter.
Example: 4:spam represents the string "spam"
integers
Integers are encoded as follows: i<integer encoded in base ten ASCII>e
The initial i and trailing e are beginning and ending delimiters.
You can have negative numbers such as i-3e. You cannot prefix the number with a zero such as i04e. However, i0e is valid.
Example i3e represents the integer "3"
lists
Lists are encoded as follows: l<bencoded values>e
The initial l and trailing e are beginning and ending delimiters.
Lists may contain any bencoded type, including integers, strings, dictionaries, and other lists.
Example: l4:spam4:eggse represents the list of two strings: ["spam", "eggs"]
dictionaries
Dictionaries are encoded as follows: d<bencoded string><bencoded element>e
The initial d and trailing e are the beginning and ending delimiters.
Note that the keys must be bencoded strings. The values may be any bencoded type, including integers, strings, lists, and other dictionaries. Keys must be strings and appear in sorted order (sorted as raw strings, not alphanumerics).
Example: d3:cow3:moo4:spam4:eggse represents the dictionary { "cow" => "moo", "spam" => "eggs" }
