Have you seen this blog post?

It’s my goto binary pattern matching blog post.

In this case parsing these messages is ultra easy:

def parse(<<destination_address,
            destination_bus,
            source_address,
            source_bus,
            length,
            pid,
            ext,
            function,
            data::binary-size(length),
            checksum::32>>
) do
  if valid_checksum?(<<destination_address,
            destination_bus,
            source_address,
            source_bus,
            length,
            pid,
            ext,
            function,
            data::binary>>) do
    {:ok, %{
      destination_address: destination_address,
      destination_bus: destination_bus,
      source_address: source_address,
      source_bus: source_bus,
      pid: pid,
      ext: ext,
      function: function,
      data: data
    }}
  else
    {:error, :invalid_checksum}
  end
end

Unfortunately, the spec didn’t specified which CRC16 they meant so I cannot provide that one.

Shows a nice way by using Mixin module. Highly recommend this talk