gen_tcp and GenServer example in Elixir (1.5.2)

a-usage.md

gen_tcp and GenServer example in Elixir (1.5.2)

Usage

server.ex

Server.start

Test the server

telnet 127.0.0.1 8000
> Hello World

client.ex

Server.start

In another terminal

{:ok, pid} = Client.start
Client.send_message(pid, "Hello World")

b-client.ex

defmodule Client do
  require Logger
  use GenServer

  @ip {127, 0, 0, 1}
  @port 8000

  def send_message(pid, message) do
    GenServer.cast(pid, {:message, message})
  end

  def start do
    GenServer.start(__MODULE__, %{socket: nil})
  end

  def init(state) do
    send(self(), :connect)
    {:ok, state}
  end

  def handle_info(:connect, state) do
    Logger.info "Connecting to #{:inet.ntoa(@ip)}:#{@port}"

    case :gen_tcp.connect(@ip, @port, [:binary, active: true]) do
      {:ok, socket} ->
        {:noreply, %{state | socket: socket}}
      {:error, reason} ->
        disconnect(state, reason)
    end
  end

  def handle_info({:tcp, _, data}, state) do
    Logger.info "Received #{data}"

    {:noreply, state}
  end

  def handle_info({:tcp_closed, _}, state), do: {:stop, :normal, state}
  def handle_info({:tcp_error, _}, state), do: {:stop, :normal, state}

  def handle_cast({:message, message}, %{socket: socket} = state) do
    Logger.info "Sending #{message}"

    :ok = :gen_tcp.send(socket, message)
    {:noreply, state}
  end

  def disconnect(state, reason) do
    Logger.info "Disconnected: #{reason}"
    {:stop, :normal, state}
  end
end

c-server.ex

defmodule Server do
  require Logger
  use GenServer

  @port 8000

  def start do
    GenServer.start(__MODULE__, %{socket: nil})
  end

  def init(state) do
    {:ok, socket} = :gen_tcp.listen(@port, [:binary, active: true])
    send(self(), :accept)

    Logger.info "Accepting connection on port #{@port}..."
    {:ok, %{state | socket: socket}}
  end

  def handle_info(:accept, %{socket: socket} = state) do
    {:ok, _} = :gen_tcp.accept(socket)

    Logger.info "Client connected"
    {:noreply, state}
  end

  def handle_info({:tcp, socket, data}, state) do
    Logger.info "Received #{data}"
    Logger.info "Sending it back"

    :ok = :gen_tcp.send(socket, data)

    {:noreply, state}
  end

  def handle_info({:tcp_closed, _}, state), do: {:stop, :normal, state}
  def handle_info({:tcp_error, _}, state), do: {:stop, :normal, state}
end

Thanks, that's really helpful!

@hryniuk
Your welcome. I am surprised this code is still useful

I got the same situation with one of my gists and I thought it would be good to say "thank you" :)

I've just started with Elixir and I was trying to do the client part. I did a loop with :gen_tcp.recv and wanted to switch to "active" socket, but around 95% of guides I've found were only about writing tcp servers. This code is exactly what I needed, thank you again for sharing. I'd definitely need a while to figure this out on my own.

@hryniuk Thanks for saying thanks 👍