Bencode (pronounced like B encode) is the encoding used by the peer-to-peer file sharing system BitTorrent for storing and transmitting loosely structured data.
It supports four different types of values: byte strings, integers, lists, and dictionaries (associative arrays).
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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.
Oh, and it doesn't guarantee that your message will fit in a single line. JSON can be encoded to a line.