Bencode

Bencode (pronounced like B encode) is the encoding used by the peer-to-peer file sharing system for storing and transmitting loosely structured data.

It supports four different types of values:

Bencoding is most commonly used in torrent files. These metadata files are simply bencoded dictionaries.

While less efficient than a pure binary encoding, bencoding is simple and (because numbers are encoded as text in decimal notation) is unaffected by endianness, which is important for a cross-platform application like BitTorrent. It is also fairly flexible, as long as applications ignore unexpected dictionary keys, so that new ones can be added without creating incompatibilities.

Bencode uses ASCII characters as delimiters and digits.

There are no restrictions on what kind of values may be stored in lists and dictionaries; they may (and usually do) contain other lists and dictionaries. This allows for arbitrarily complex data structures to be encoded.

Bencode is a very specialized kind of binary coding with some unique properties:

However, this uniqueness can cause some problems:

...
Wikipedia