# ExRLP [](https://circleci.com/gh/exthereum/ex_rlp)
Elixir implementation of Ethereum's RLP (Recursive Length Prefix) encoding
The encoding's specification can be found in [the yellow paper](http://yellowpaper.io/) or in the [ethereum wiki](https://github.com/ethereum/wiki/wiki/RLP)
## Installation
The easiest way to add ExRLP to your project is by [using Mix](http://elixir-lang.org/getting-started/mix-otp/introduction-to-mix.html).
Add `:ex_rlp` as a dependency to your project's `mix.exs`:
```elixir
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.
```elixir
## 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.
```elixir
## 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:
```elixir
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:
```elixir
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!](https://github.com/exthereum/ex_rlp/fork)
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.
