echo_server.ex

# 比較用
# https://elixir-lang.org/getting-started/mix-otp/task-and-gen-tcp.html
defmodule KVServer do
  require Logger

  @doc """
  Starts accepting connections on the given `port`.
  """
  def accept(port) do
    {:ok, socket} = :gen_tcp.listen(port,
                      [:binary, packet: :line, active: false, reuseaddr: true])
    Logger.info "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)
    :ok = :gen_tcp.controlling_process(client, pid)
    loop_acceptor(socket)
  end

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

    serve(socket)
  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

echo_server.rb

# https://elixir-lang.org/getting-started/mix-otp/task-and-gen-tcp.html にある
# Elixir製のEchoサーバーをRubyのRactorを使って書いてみるとこうなるかなという想像。
#
# https://docs.ruby-lang.org/ja/latest/class/TCPServer.html
# にあるTCPServerの例も参考にした。

require "socket"

class EchoServer
  def init(port)
    @port = port
  end

  def accept()
    socket = TCPServer.open(@port)
    addr = socket.addr
    addr.shift
    printf("server is on %s\n", addr.join(":"))
    loop_acceptor(socket)
  end

  private
  def loop_acceptor(socket)
    loop do
      client = socket.accept
      # もしEchoServerをシャットダウンするときに子の接続が全部なくなるまで待つならractorを配列で保持しておかないといけないな
      Ractor.new client do |c|
        # Ractor#receive しない限りエラーが親に影響を及ぼさないのでエラーハンドリングしなくてもいいや
        serve(c)
      end
      # :gen_tcp.controlling_process(client, pid)
      # は下記のとおりErlangVM特有の話だと思うのでRubyでは考慮しなくていいや
      # This makes the child process the “controlling process” of the client socket.
      # If we didn’t do this, the acceptor would bring down all the clients if it crashed
      # because sockets would be tied to the process that accepted them (which is the default behaviour).
    end
  end

  def serve(socket)
    loop do
      s.write(s.gets)
    end
  end
end

EchoServer.new(8080).accept()