Simplest plug based http sever

hello.exs

# run with $ elixir --no-halt hello.exs
Mix.install([{:plug_cowboy, "~> 2.0"}])

defmodule HWPlug.Plug do
  import Plug.Conn

  def init(options), do: options

  def call(conn, _opts) do
    conn
    |> put_resp_content_type("text/plain")
    |> send_resp(200, "Hello World!\n")
  end
end

Plug.Adapters.Cowboy.http(HWPlug.Plug, [])