drop observers who have left

game.go

@@ -46,6 +46,11 @@ func applyAction(g *game.Match, a action) error {
 	}
 }
 
+type observer struct {
+	conn *websocket.Conn
+	ctx  context.Context
+}
+
 // gameActor is an actor that updates a game's state and relays changes to all
 // observers.
 func gameActor(ctx context.Context, g *game.Match, dealer, chall person, join <-chan person) {
@@ -53,7 +58,7 @@ func gameActor(ctx context.Context, g *game.Match, dealer, chall person, join <-
 	// definitely expired.
 	ctx, stop := context.WithTimeoutCause(ctx, 4*time.Hour, errMatchExpired)
 	defer stop()
-	var obs []person
+	var obs []observer
 	actions := make(chan action, 2)
 	go playerActor(ctx, dealer, actions)
 	go playerActor(ctx, chall, actions)
@@ -72,10 +77,8 @@ func gameActor(ctx context.Context, g *game.Match, dealer, chall person, join <-
 				go p.conn.Close(websocket.StatusNormalClosure, "looks like you dropped")
 				continue
 			}
-			obs = append(obs, p)
+			q := p.conn.CloseRead(ctx)
-			// TODO(zeph): CloseRead returns a context we can use to drop the
+			obs = append(obs, observer{conn: p.conn, ctx: q})
-			// observer when they disconnect
-			p.conn.CloseRead(ctx)
 		case a := <-actions:
 			slog.DebugContext(ctx, "got action", "from", a.Player, "action", a.Action)
 			err := applyAction(g, a)
@@ -102,6 +105,13 @@ func gameActor(ctx context.Context, g *game.Match, dealer, chall person, join <-
 				slog.ErrorContext(ctx, "action caused a mystery error", "from", a.Player, "action", a.Action, "err", err.Error())
 			}
 		}
+		// Clear observers who have left.
+		for k := len(obs) - 1; k >= 0; k-- {
+			if obs[k].ctx.Err() != nil {
+				obs[k], obs[len(obs)-1] = obs[len(obs)-1], observer{}
+				obs = obs[:len(obs)-1]
+			}
+		}
 	}
 }
 
@@ -127,7 +137,7 @@ func playerActor(ctx context.Context, p person, actions chan<- action) {
 	}
 }
 
-func broadcast(ctx context.Context, g *game.Match, dealer, chall person, obs []person) {
+func broadcast(ctx context.Context, g *game.Match, dealer, chall person, obs []observer) {
 	// TODO(zeph): this probably should return an error or some other signal
 	// if a player drops so that the actor knows to quit
 	if err := wsjson.Write(ctx, dealer.conn, g.DTO(dealer.id)); err != nil {
@@ -138,14 +148,18 @@ func broadcast(ctx context.Context, g *game.Match, dealer, chall person, obs []p
 		// TODO(zeph): concede, but we need to be careful not to recurse
 		slog.DebugContext(ctx, "lost challenger", "player", chall.id, "err", err.Error())
 	}
+	if len(obs) == 0 {
+		return
+	}
+	d := g.DTO(player.ID{})
 	for _, p := range obs {
-		if err := wsjson.Write(ctx, p.conn, g.DTO(p.id)); err != nil {
+		if err := wsjson.Write(ctx, p.conn, &d); err != nil {
-			slog.DebugContext(ctx, "lost observer", "player", p.id, "err", err.Error())
+			slog.DebugContext(ctx, "lost observer", "err", err.Error())
 		}
 	}
 }
 
-func gameOver(ctx context.Context, dealer, chall person, obs []person) {
+func gameOver(ctx context.Context, dealer, chall person, obs []observer) {
 	// TODO(zeph): need to communicate to the server that these have gone away
 	go dealer.conn.Close(websocket.StatusNormalClosure, "match ended")
 	go chall.conn.Close(websocket.StatusNormalClosure, "match ended")