Ensure single subscription (#56)

lib/jellyfish_web/server_socket.ex

@@ -25,6 +25,7 @@ defmodule JellyfishWeb.ServerSocket do
   alias Jellyfish.ServerMessage.SubscribeResponse.{RoomNotFound, RoomsState, RoomState}
 
   @heartbeat_interval 30_000
+  @valid_subscribe_topics [:server_notification, :metrics]
 
   @impl true
   def child_spec(_opts), do: :ignore
@@ -38,7 +39,14 @@ defmodule JellyfishWeb.ServerSocket do
 
   @impl true
   def init(state) do
-    {:ok, Map.put(state, :authenticated?, false)}
+    state =
+      state
+      |> Map.merge(%{
+        authenticated?: false,
+        subscriptions: MapSet.new()
+      })
+
+    {:ok, state}
   end
 
   @impl true
@@ -84,7 +92,7 @@ defmodule JellyfishWeb.ServerSocket do
   def handle_in({encoded_message, [opcode: :binary]}, state) do
     with %ServerMessage{content: {:subscribe_request, request}} <-
            ServerMessage.decode(encoded_message),
-         {:ok, response} <- handle_subscribe(request) do
+         {:ok, response, state} <- handle_subscribe(request, state) do
       reply =
         %ServerMessage{
           content: {:subscribe_response, response}
@@ -116,29 +124,33 @@ defmodule JellyfishWeb.ServerSocket do
     {:stop, :closed, {1003, "operation not allowed"}, state}
   end
 
-  defp handle_subscribe(%SubscribeRequest{
-         id: id,
-         event_type:
-           {:server_notification,
-            %SubscribeRequest.ServerNotification{room_id: {_variant, option}}}
-       }) do
-    :ok = Phoenix.PubSub.subscribe(Jellyfish.PubSub, "server_notification")
+  defp handle_subscribe(
+         %SubscribeRequest{
+           id: id,
+           event_type: {topic, event_type}
+         },
+         state
+       )
+       when topic in @valid_subscribe_topics do
+    unless MapSet.member?(state.subscriptions, topic) do
+      :ok = Phoenix.PubSub.subscribe(Jellyfish.PubSub, Atom.to_string(topic))
+    end
 
-    room_state = get_room_state(option)
+    state = update_in(state.subscriptions, &MapSet.put(&1, topic))
 
-    {:ok, %SubscribeResponse{id: id, content: room_state}}
-  end
+    content =
+      case event_type do
+        %SubscribeRequest.ServerNotification{room_id: {_variant, option}} ->
+          get_room_state(option)
 
-  defp handle_subscribe(%SubscribeRequest{
-         id: id,
-         event_type: {:metrics, %SubscribeRequest.Metrics{}}
-       }) do
-    :ok = Phoenix.PubSub.subscribe(Jellyfish.PubSub, "metrics")
+        %SubscribeRequest.Metrics{} ->
+          nil
+      end
 
-    {:ok, %SubscribeResponse{id: id}}
+    {:ok, %SubscribeResponse{id: id, content: content}, state}
   end
 
-  defp handle_subscribe(request), do: {:error, request}
+  defp handle_subscribe(request, _state), do: {:error, request}
 
   @impl true
   def handle_info(:send_ping, state) do