feat(multiplayer): cap websocket connections per player

server/api/events.go

@@ -19,12 +19,13 @@ import (
 )
 
 const (
-	webSocketGUID          = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
-	maxWebSocketFrame      = 64 << 10
-	eventQueueCapacity     = 32
-	webSocketIdleLimit     = 2 * time.Minute
-	webSocketMessageLimit  = 120
-	webSocketMessageWindow = time.Minute
+	webSocketGUID                = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
+	maxWebSocketFrame            = 64 << 10
+	eventQueueCapacity           = 32
+	webSocketIdleLimit           = 2 * time.Minute
+	webSocketMessageLimit        = 120
+	webSocketMessageWindow       = time.Minute
+	maxEventConnectionsPerPlayer = 2
 )
 
 // ControlPlaneEvent is the server-to-client envelope defined by the v1
@@ -56,8 +57,18 @@ func newEventHub() *eventHub {
 }
 
 func (h *eventHub) subscribe(playerID string) *eventSubscriber {
-	subscriber := &eventSubscriber{playerID: playerID, queue: make(chan []byte, eventQueueCapacity)}
 	h.mu.Lock()
+	connections := 0
+	for subscriber := range h.subscribers {
+		if subscriber.playerID == playerID {
+			connections++
+		}
+	}
+	if connections >= maxEventConnectionsPerPlayer {
+		h.mu.Unlock()
+		return nil
+	}
+	subscriber := &eventSubscriber{playerID: playerID, queue: make(chan []byte, eventQueueCapacity)}
 	h.subscribers[subscriber] = struct{}{}
 	h.mu.Unlock()
 	return subscriber
@@ -168,6 +179,9 @@ func (s *Service) controlPlaneEvent(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	subscriber := s.getEventHub().subscribe(playerID)
+	if subscriber == nil {
+		return
+	}
 	defer s.getEventHub().unsubscribe(subscriber)
 
 	var writeMu sync.Mutex

server/api/events_connection_test.go

@@ -0,0 +1,22 @@
+package api
+
+import "testing"
+
+func TestEventHubCapsConnectionsPerPlayerAndReleasesCapacity(t *testing.T) {
+	hub := newEventHub()
+	first := hub.subscribe("player-1")
+	second := hub.subscribe("player-1")
+	if first == nil || second == nil {
+		t.Fatal("connection within per-player cap was rejected")
+	}
+	if third := hub.subscribe("player-1"); third != nil {
+		t.Fatal("connection over per-player cap was accepted")
+	}
+	hub.unsubscribe(first)
+	if third := hub.subscribe("player-1"); third == nil {
+		t.Fatal("released connection capacity was not reusable")
+	} else {
+		hub.unsubscribe(third)
+	}
+	hub.unsubscribe(second)
+}