Bencoding, pronounced "B-encoding", is the encoding used by BitTorrent.
Introduction
Bencoding, pronounced "B-encoding", is the encoding used by BitTorrent, a peer-to-peer file sharing protocol. It supports the encoding of byte strings, integers, lists, and dictionaries (key-value pairs).
From Wikipedia (http://en.wikipedia.org/w/index.php?title=Bencode&oldid=644035222):
Bencode uses ASCII characters as delimiters and digits.
- An integer is encoded as
i<integer encoded in base ten ASCII>e. Leading zeros are not allowed (although the number zero is still
represented as "0"). Negative values are encoded by prefixing the
number with a minus sign. The number 42 would thus be encoded as
i42e, 0 asi0e, and -42 asi-42e. Negative zero is not permitted.- A byte string (a sequence of bytes, not necessarily characters) is encoded as
<length>:<contents>. The length is encoded in base 10,
like integers, but must be non-negative (zero is allowed); the
contents are just the bytes that make up the string. The string
"spam" would be encoded as4:spam. The specification does not deal
with encoding of characters outside the ASCII set; to mitigate this,
some BitTorrent applications explicitly communicate the encoding
(most commonly UTF-8) in various non-standard ways. This is identical to how netstrings work, except that netstrings additionally append a
comma suffix after the byte sequence.- A list of values is encoded as
l<contents>e. The contents consist of the bencoded elements of the list, in order, concatenated. A list consisting of the string "spam" and the number 42 would be encoded as:l4:spami42ee. Note the absence of separators between elements.- A dictionary is encoded as
d<contents>e. The elements of the dictionary are encoded each key immediately followed by its value.
All keys must be byte strings and must appear in lexicographical
order. A dictionary that associates the values 42 and "spam" with the keys "foo" and "bar", respectively (in other words,{"bar": "spam", "foo": 42}), would be encoded as follows:d3:bar4:spam3:fooi42ee. (This might be easier to read by inserting some spaces:d 3:bar 4:spam 3:foo i42e e.)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.
