Provide single-file websocket example about plug HOT 3 CLOSED

Mix.install([
  {:bandit, ">= 0.0.0"},
  {:websock_adapter, ">= 0.0.0"}
])

defmodule EchoServer do
  def init(args) do
    {:ok, []}
  end

  def handle_in({"ping", [opcode: :text]}, state) do
    {:reply, :ok, {:text, "pong"}, state}
  end

  def terminate(:timeout, state) do
    {:ok, state}
  end
end

defmodule Router do
  use Plug.Router
  plug(Plug.Logger)
  plug(:match)
  plug(:dispatch)

  get "/" do
    response = """
    Use the JavaScript console to interact using websockets

    sock  = new WebSocket("ws://localhost:4000/websocket")
    sock.addEventListener("message", console.log)
    sock.addEventListener("open", () => sock.send("ping"))
    """
    send_resp(conn, 200, response)
  end

  get "/websocket" do
    conn
    |> WebSockAdapter.upgrade(EchoServer, [], timeout: 60_000)
    |> halt()
  end

  match _ do
    send_resp(conn, 404, "not found")
  end
end

bandit = {Bandit, plug: Router, scheme: :http, port: 4000}
require Logger
Logger.info("starting #{inspect(bandit)}")
{:ok, _} = Supervisor.start_link([bandit], strategy: :one_for_one)

# unless running from IEx, sleep idenfinitely so we can serve requests
unless IEx.started?() do
  Process.sleep(:infinity)
end