Binary encoding of OUCH messages in Elixir

README.md

Reuse logic in Elixir

Here are commons ways to reuse logic in Elixir:

1a. Move Function to other module (guards, pattern-matching) 1b. Protocol - Polymorphism

2. Behaviour Dynamic-func - with def method_name(implemetation, args)

encode_decode.ex

# See: http://www.nasdaqtrader.com/content/technicalsupport/specifications/tradingproducts/ouch4.2.pdf
# See: https://hexdocs.pm/elixir/Kernel.SpecialForms.html#%3C%3C%3E%3E/1-modifiers
# See: https://hexdocs.pm/elixir/Kernel.SpecialForms.html#%3C%3C%3E%3E/1-options

alias Decimal, as: D

symbol = "BTC_IDR"
shares = 5000
price = "1.3"

# Encode
p = D.new(price) |> D.round(4) |> D.mult(10000) |> D.to_integer()
message = <<shares::big-integer-4*8, String.pad_trailing(symbol, 8)::binary-8, p::big-integer-32>>

# Decode
<<shares2::big-integer-size(4)-unit(8), symbol2::binary-8, p2::big-integer-32>> = message
{:ok, p2} = D.cast(p2)
price2 = p2 |> D.div(10000) |> D.to_string()
{shares2, symbol2, price2}

# Pattern-match
<<coinSymbol::binary-size(s), "_IDR" >> = symbol2

protocols.ex

defprotocol Ouch42Binary do
  @doc "Serialize "
  def marshal?(struct)
  
  def unmarshal?(binary)
end