event_source.ex

def index(conn, %{"event" => "true"}) do                                                                       
  conn = conn                                                                                                  
          |> put_resp_content_type("text/event-stream")                                                        
          |> send_chunked(200)                                                                                 
  {:ok, conn} = chunk(conn, ["data: ", JSON.encode!(Thermostat.Data.get()), "\n\n"])                           
  Phoenix.Topic.subscribe self, "data"                                                                         
  data_updated(conn)                                                                                           
end 

defp data_updated(conn) do                                                                                     
  receive do                                                                                                   
    { :update, data } ->                                                                                       
      IO.puts "GOT DATA"                                                                                       
      {:ok, conn} = chunk(conn, ["data: ", JSON.encode!(data), "\n\n"])                                        
    _ ->                                                                                                       
  end                                                                                                          
  data_updated(conn)                                                                                           
end