Websocket server without Phoenix

Jim · December 12, 2017, 2:40pm

Hi All…

I’m working on an embedded project that will collect data from a system of sensors, do some minimal processing and, among other things, stream data to a number of devices including phones, tablets and laptops. For this last requirement I was thinking WiFi and websockets. What I don’t need, however, is an entire framework.

I was reading about this:

But I’m wondering, could that be enough to implement websocket connectivity to a number of clients? It could work as peer to peer. At the device end (my device) I was thinking there would be a process to handle each connected client and each of these would periodically push data through the socket.

I’m just trying to avoid extra complexity and bloat.

Suggestions are appreciated, thank you.

idi527 · December 12, 2017, 3:44pm

Why do you need websockets? I think of them as “tcp for browsers.” Wouldn’t something like mqtt or plain tcp suit your needs better?

Jim · December 12, 2017, 5:11pm

Hm, I’m not sure. The clients are going to be single page web apps. The thought was to stream JSON data in via websocket and render it.

idi527 · December 12, 2017, 5:14pm

Ah, ok. This bit got me confused

number of devices including phones, tablets and laptops

Thought you would use their native tcp/ip stack.

You can use cowboy without phoenix. It has enough functionality to serve as a websocket server.

Jim · December 12, 2017, 7:04pm

That does seem to be what I need, thanks!

entone · December 13, 2017, 5:16pm

Cowboy has websocket support built in, and you can use Plug to make a clean interface. I’ve still yet to jump into Phoenix and this works great for me.

Here’ some sample code, https://github.com/NationalAssociationOfRealtors/BoothNanoleaf/blob/master/lib/booth_nanoleaf/application.ex

github.com

NationalAssociationOfRealtors/BoothNanoleaf/blob/master/lib/booth_nanoleaf/websocket_handler.ex

defmodule BoothNanoleaf.WebSocketHandler do
  require Logger
  @behaviour :cowboy_websocket_handler
  @timeout 60000

  defmodule EventHandler do
    use GenEvent
    require Logger

    def handle_event(%IEQGateway.IEQStation.State{id: :"IEQStation-38"} = device, parent) do
      send(parent, device)
      {:ok, parent}
    end

    def handle_event(_device, parent) do
      {:ok, parent}
    end

    def terminate(reason, parent) do
      Logger.info "IEQ Sensor EventHandler Terminating: #{inspect reason}"

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Jim · December 13, 2017, 5:30pm

Excellent thank you! I got Cowboy working last night, websockets are next on the list.