proxying responses

page_controller.ex

defmodule PhoenixTest.PageController do
  use PhoenixTest.Web, :controller

  def index(conn, _params) do
    render conn, "index.html"
  end

  def proxy(conn, params) do
    query_string = conn.query_string
    path = Enum.join(params["path"], "/")
    path = path <> case query_string do
                    "" -> ""
                    _ -> "?" <> query_string
                  end

    headers = for {k, v} <- conn.req_headers do
      {String.to_charlist(k), String.to_charlist(v)}
    end

    {:ok, {{status_code, _}, response_headers, body}} = :lhttpc.request(
      'http://localhost:8090/#{path}', :get, headers, "", :infinity,
      [{:partial_download, [{:window_size, 10}, {:part_size, 10000}]}])

    response_headers = for {k, v} <- response_headers,
      k != 'Transfer-Encoding' do {k, v} end

    resp_body_function = fn socket, transport ->
      stream_body(body, socket, transport)
    end

    {adapter, payload} = conn.adapter
    {:ok, payload} = :cowboy_req.reply(status_code, response_headers, :cowboy_req.set_resp_body_fun(resp_body_function, payload))
    %{conn | adapter: { adapter, payload }, resp_body: nil, state: :sent}
  end

  defp stream_body(body, socket, transport) do
    case :lhttpc.get_body_part(body) do
      {:ok, chunk} when is_binary(chunk) ->
        transport.send(socket, chunk)
        stream_body(body, socket, transport)

      {:ok, {:http_eob, _}} -> nil

      {:error, err} -> raise err
    end
  end
end