kv_server.ex

defmodule KVServer do
  use Application

  def start(_type, _args) do
    import Supervisor.Spec

    children = [
      supervisor(Task.Supervisor, [[name: KVServer.TaskSupervisor]]),
      worker(Task, [KVServer, :accept, [4040]])
    ]

    opts = [strategy: :one_for_one, name: KVServer.Supervisor]
    Supervisor.start_link(children, opts)
  end

  def accept(port) do
    {:ok, socket} =:gen_tcp.listen(port, [:binary, packet: :line, active: false])
    IO.puts "Accepting connections on port #{port}"
    loop_acceptor(socket)
  end

  defp loop_acceptor(socket) do
    {:ok, client} = :gen_tcp.accept(socket)
    {:ok, pid} = Task.Supervisor.start_child(KVServer.TaskSupervisor, fn -> serve(client) end)
    :gen_tcp.controlling_process(client, pid)

    # deliberately fail after 10 sec
    :timer.sleep(10_000)
    1 = 2

    loop_acceptor(socket)
  end

  defp serve(client) do
    client
    |> read_line()
    |> write_line(client)

    serve(client)
  end

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

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

end