ExRLP

Elixir implementation of Ethereum’s RLP (Recursive Length Prefix) encoding

The encoding’s specification can be found in the yellow paper or in the ethereum wiki

Installation

The easiest way to add ExRLP to your project is by using Mix.

Add :ex_rlp as a dependency to your project’s mix.exs:

defp deps do
  [
    {:ex_rlp, "~> 0.1.0"}
  ]
end

And run:

$ mix deps.get

Basic Usage

Use ExRLP.encode/1 method to encode an item to RLP representation. An item can be nonnegative integer, binary or list. List can contain integers, binaries or lists.

  ## Examples
  
      iex(1)> "dog" |> ExRLP.encode(encoding: :hex)
      "83646f67"

      iex(2)> "dog" |> ExRLP.encode(encoding: :binary)
      <<0x83, 0x64, 0x6f, 0x67>>

      iex(3)> 1000 |> ExRLP.encode(encoding: :hex)
      "8203e8"

      # Default encoding is binary
      iex(3)> 1000 |> ExRLP.encode
      <<0x82, 0x03, 0xe8>>

      iex(4)> [ [ [], [] ], [] ] |> ExRLP.encode(encoding: :hex)
      "c4c2c0c0c0"

Use ExRLP.decode/1 method to decode a rlp encoded data. All items except lists are decoded as binaries so additional deserialization is needed if initially an item of another type was encoded.

  ## Examples
  
      iex(1)> "83646f67" |> ExRLP.decode(:binary, encoding: :hex)
      "dog"

      iex(2)> "8203e8" |> ExRLP.decode(:binary, encoding: :hex) |> :binary.decode_unsigned
      1000

      iex(3)> "c4c2c0c0c0" |> ExRLP.decode(:binary, encoding: :hex)
      [[[], []], []]

More examples can be found in test files.

Protocols

You can define protocols for encoding/decoding custom data types.

Custom protocols for Map have already been implemented in ExRLP:

defimpl ExRLP.Encoder, for: Map do
  alias ExRLP.Encode

  def encode(map, _) do
    map
    |> Map.keys
    |> Enum.reduce([], fn(key, acc) ->
      value = Map.get(map, key)

      acc ++ [value]
    end)
    |> Encode.encode
  end
end

defimpl ExRLP.Decoder, for: BitString do
  alias ExRLP.Decode

  def decode(value, :map, options) do
    keys =
      options
      |> Keyword.fetch!(:keys)
      |> Enum.sort

    value
    |> Decode.decode
    |> Enum.with_index
    |> Enum.reduce(%{}, fn({value, index}, acc) ->
      key = keys |> Enum.at(index)

      acc |> Map.put(key, value)
    end)

    ...
  end
end

So now it’s possible to encode/decode maps:

iex(1)> %{name: "Vitalik", surname: "Buterin"} |> ExRLP.encode(encoding: :hex)
"d087566974616c696b874275746572696e"

iex(2)> "d087566974616c696b874275746572696e" |> ExRLP.decode(:map, keys: [:surname, :name], encoding: :hex)
%{name: "Vitalik", surname: "Buterin"}

Contributing

1. Fork it!
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

Author

Ayrat Badykov (@ayrat555)

License

ExRLP is released under the MIT License. See the LICENSE file for further details.