Bento

Bento is a new Bencoding library for Elixir focusing on incredibly fast speed without sacrificing simplicity, completeness, or correctness.

It takes inspiration from Poison, a pure-Elixir JSON library, and uses several techniques found there to achieve this speed:

• Extensive sub-binary matching
• A hand-rolled parser using several techniques known to benefit HiPE for native compilation
• IO list encoding
• Single-pass decoding

Additionally, and unlike some other Elixir bencoding libraries, Bento will also reject all malformed input. This guarantees you're working with a well-formed bencoded file.

Preliminary benchmarking shows that Bento performs over 2x faster when encoding, and at least as fast when decoding, compared to other existing Elixir libraries.

Installation

Bento is available in Hex. The package can be installed by:

1. Add bento to your list of dependencies in mix.exs:

   {:bento, "~> 0.9"}

2. Update your dependencies.

   $ mix deps.get

Usage

Encoding an Elixir data type:

iex> Bento.encode([1, "two", [3]])
{:ok, "li1e3:twoli3eee"}
iex> Bento.encode!(%{"foo" => ["bar", "baz"], "qux" => "norf"})
"d3:fool3:bar3:baze3:qux4:norfe"

Decoding a bencoded string:

iex> Bento.decode("li1e3:twoli3eee")
{:ok, [1, "two", [3]]}
iex> Bento.decode!("d3:fool3:bar3:baze3:qux4:norfe")
%{"foo" => ["bar", "baz"], "qux" => "norf"}

Bento is also metainfo-aware and comes with a .torrent decoder out of the box:

iex> File.read!("test/_data/ubuntu-14.04.4-desktop-amd64.iso.torrent") |> Bento.torrent!()
%Bento.Metainfo.Torrent{announce: "http://torrent.ubuntu.com:6969/announce",
 "announce-list": [["http://torrent.ubuntu.com:6969/announce"],
  ["http://ipv6.torrent.ubuntu.com:6969/announce"]],
 comment: "Ubuntu CD releases.ubuntu.com", "created by": nil,
 "creation date": 1455826371, encoding: nil,
 info: %Bento.Metainfo.SingleFile{length: 1069547520, md5sum: nil,
  name: "ubuntu-14.04.4-desktop-amd64.iso", "piece length": 524288,
  pieces: <<109, 235, 143, 234, 36, 25, 142, 36, 20, 3, 227, 227, 134, 136, 205, 130, 176, ...>>,
  private: nil}}

Since Bento uses Poison's Decoder module for .torrent(), this means it also supports decoding bencoded data into any struct you choose, like so:

defmodule Name do
  defstruct [:family, :given]
end
iex> Bento.decode!("d6:family4:Folz5:given6:Rodneye", as: %Name{})
%Name{family: "Folz", given: "Rodney"}

Benchmarking

$ MIX_ENV=bench mix bench

We currently benchmark against: Bento (this project), bencode, Bencodex, bencoder, and bencoded.

We are aware of, but unable to benchmark against: exbencode (build errors), and elixir_bencode (module name conflicts with Bencode).

PRs that add libraries to the benchmarks are greatly appreciated!

License

See LICENSE.