sse_router.ex

defmodule MyApp.SSERouter do
  use Plug.Router

  @event_delay 2000

  plug(:match)
  plug(:dispatch)

  defp send_chunk(conn) do
    :timer.sleep(@event_delay)

    {:ok, conn} = chunk(conn, "event: first\n")
    {:ok, conn} = chunk(conn, "data: here we go!\n")
    {:ok, conn} = chunk(conn, "\n")

    send_chunk(conn, 1)
  end

  defp send_chunk(conn, value) do
    :timer.sleep(@event_delay)

    {:ok, conn} = chunk(conn, "event: number\n")
    {:ok, conn} = chunk(conn, "data: " <> Integer.to_string(value) <> "\n")
    {:ok, conn} = chunk(conn, "\n")

    send_chunk(conn, value + 1)
  end

  get "/sse" do
    conn
    |> put_resp_content_type("text/event-stream")
    |> put_resp_header("connection", "keep-alive")
    |> put_resp_header("cache-control", "no-cache")
    |> send_chunked(200)
    |> send_chunk
  end

  get "/foo" do
    send_resp(conn, 200, "ok!")
  end

  match _ do
    send_resp(conn, 404, "oops")
  end
end