Example of websocket handler

application_router.ex

defmodule ApplicationRouter do
  use Dynamo.Router

  prepare do
    conn.fetch([:params])
  end

  post "/publish" do
    room_id = conn.params[:room_id]
    data = conn.params[:data]
    if room_id && data do
      Chaussette.Pubsub.publish(room_id, data)
      conn.resp 200, "Message sent."
    else
      conn.resp 406, "Not Acceptable"
    end
  end

  websocket "/web-socket", using: Chaussette.WebsocketHandler
end

updater.coffee

class Updater
  constructor: (options) ->
    {roomId, websocketUrl} = options
    @setup("#{websocketUrl}?room_id=#{roomId}")

  setup: (url) ->
    @ws = new WebSocket(url)
    @ws.onmessage = (evt) => @onMessage JSON.parse(evt.data)

  destroy: ->
    @ws?.close()

  onMessage: (data) ->
    console.log "received message:", data
    # update something using data content
    # ...

@App.Updater = Updater

websocket_handler.ex

defmodule Chaussette.WebsocketHandler do
  @behaviour :cowboy_websocket_handler

  alias Chaussette.Pubsub

  def websocket_init(_transport_name, req, [ conn: conn ]) do
    room_id = conn.params[:room_id]
    if room_id, do: Pubsub.register(room_id, self)
    { :ok, req, [ room: room_id ] }
  end

  def websocket_handle( { :text, message }, req, state) do
    { :reply, {:text, message }, req, state }
  end
  def websocket_handle(_data, req, state), do: { :ok, req, state}

  def websocket_info({ :pubsub_message, message }, req, state) do
    { :reply, { :text, message }, req, state }
  end
  def websocket_info(_data, req, state), do: { :ok, req, state }

  def websocket_terminate(_reason, _req, state) do
    [ room: room ] = state
    Pubsub.unregister(room, self)
    :ok
  end
end