Web Server with Elixir

http_server.ex

defmodule HTTPServer do
  @moduledoc """
  Este módulo é responsável por estabelecer uma conexão de servidor TCP
  para suportar requisições HTTP.

  Função principal: `start/1`
  """

  defmodule Conn do
    @moduledoc """
    Estrutura de conexão que será usada para gerenciar nosso socket TCP.
    """

    defstruct [:socket, :raw, :response]
  end

  @doc """
  Inicia uma conexão TCP na porta indicada.

  Esse socket espera receber chamadas HTTP num endpoint de health check.
  Demais endpoints retornam 404.
  """
  @spec start(integer()) :: {:ok, any()}
  def start(port) do
    IO.puts("[*:#{port}] Web Server started!")
    with {:ok, socket} <- :gen_tcp.listen(port, [:binary, active: false]),
         {:ok, client} <- :gen_tcp.accept(socket) do
      client
      |> receive_data()
      |> build_http_response()
      |> respond()
    end
  end

  defp receive_data(socket) do
    with {:ok, data} <- :gen_tcp.recv(socket, 0) do
      IO.puts("received: #{data}")

      %Conn{socket: socket, raw: data}
    end
  end

  defp build_http_response(%Conn{socket: socket, raw: raw}) do
    result =
      case String.contains?(raw, "GET /health") do
        true ->
          %{status: 200, body: "Up and running"}

        false ->
          %{status: 404, body: "Not found"}
      end

    response = "HTTP/1.1 #{result.status} OK\nContent-Type: text/plain\nContent-Length: #{String.length(result.body)}\n\n#{result.body}"

    %Conn{socket: socket, response: response}
  end

  defp respond(%Conn{socket: socket, response: response}) do
    :gen_tcp.send(socket, response)
  end
end

HTTPServer.start(8000)