From 74b001e4e429e16cc5cee22b528983b85274ebd7 Mon Sep 17 00:00:00 2001
From: Marius Melzer <marius@rasumi.net>
Date: Fri, 29 May 2020 01:40:58 +0200
Subject: [PATCH] Send shutdown messages to users when signaltower shuts down

---
 lib/signal_tower.ex                   | 17 ++++++++++++-----
 lib/signal_tower/websocket_handler.ex |  5 +++++
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/lib/signal_tower.ex b/lib/signal_tower.ex
index 0c67b57..da03a5d 100644
--- a/lib/signal_tower.ex
+++ b/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
diff --git a/lib/signal_tower/websocket_handler.ex b/lib/signal_tower/websocket_handler.ex
index bac62be..3196ce2 100644
--- a/lib/signal_tower/websocket_handler.ex
+++ b/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)}")