Send shutdown messages to users when signaltower shuts down

lib/signal_tower.ex

@@ -10,11 +10,6 @@ defmodule SignalTower do
     |> start_supervisor()
   end
 
-  @impl Application
-  def stop(_state) do
-    :ok
-  end
-
   defp start_cowboy() do
     {port, _} = Integer.parse(System.get_env("SIGNALTOWER_PORT") || "4233")
 
@@ -45,4 +40,16 @@ defmodule SignalTower do
     Logger.info("SignalTower started")
     ret
   end
+
+  @impl Application
+  def stop(_) do
+    DynamicSupervisor.which_children()
+    |> Enum.map(fn
+      {:undefined, pid, :worker, _} when is_pid(pid) ->
+        send(pid, :shutdown)
+
+      _ ->
+        :ok
+    end)
+  end
 end

lib/signal_tower/websocket_handler.ex

@@ -67,6 +67,11 @@ defmodule SignalTower.WebsocketHandler do
     {:reply, {:text, internal_to_json(msg)}, state}
   end
 
+  @impl :cowboy_websocket
+  def websocket_info(:shutdown, state) do
+    {:reply, {:text, internal_to_json(%{event: "shutdown"})}, state}
+  end
+
   @impl :cowboy_websocket
   def websocket_info(msg, state) do
     Logger.warn("Unknown info message: #{inspect(msg)}")