echo_server.ex

defmodule EchoServer do
  def accept(port) do
    {:ok, sock} = :gen_tcp.listen(port, [:binary, packet: :line, active: false, reuseaddr: true])
    loop_accept(sock)
  end
  
  defp loop_accept(sock) do
    {:ok, client} = :gen_tcp.accept(sock)
    serve(client)
    loop_accept(sock)
  end

  defp serve(sock) do
    sock
    |> read_line()
    |> write_line_with_hello(sock)

    serve(sock)
  end

  defp read_line(sock) do
    {:ok, line} = :gen_tcp.recv(sock, 0)
    line
  end

  defp write_line_with_hello(line, sock) do
    write_line("Hai! " <> line, sock)
  end

  defp write_line(line, sock) do
    :gen_tcp.send(sock, line)
  end
end

EchoServer.accept(4040)