Elixir Module to parse UDHCPD Lease Files

parse_udhcpd.exs

defmodule ParseUdhcpd do
  def find_leases(interface \\ "eth0") do
    udhcpd_lease_bytes =
      "/tmp/vintage_net/udhcpd.#{interface}.leases"
      |> File.read!()

    <<written_at::signed-integer-64, leases_bytes::bits >> = udhcpd_lease_bytes

    parse_leases(leases_bytes, [])
  end

  def parse_leases("", leases) do
    leases
  end
  def parse_leases(udhcpd_lease_bytes, leases) do
    <<expires::signed-integer-32,
      ip::4-bytes,
      mac::6-bytes,
      hostname::20-bytes,
      pad::2-bytes,
      udhcpd_leases_rest::bits >> = udhcpd_lease_bytes

      lease = %{
        expires: expires,
        ip: ip |> :erlang.binary_to_list() |> :erlang.list_to_tuple(),
        hostname: String.trim(hostname,"\0")
      }
      udhcpd_leases_rest
      |> parse_leases(leases++[lease])
  end
end