Implement client-side disconnection flow

osu.Game/Online/HubClientConnector.cs

@@ -102,6 +102,8 @@ namespace osu.Game.Online
             return Task.FromResult((PersistentEndpointClient)new HubClient(newConnection));
         }
 
+        Task IHubClientConnector.Disconnect() => base.Disconnect();
+
         protected override string ClientName { get; }
     }
 }

osu.Game/Online/IHubClientConnector.cs

@@ -30,6 +30,11 @@ namespace osu.Game.Online
         /// </summary>
         public Action<HubConnection>? ConfigureConnection { get; set; }
 
+        /// <summary>
+        /// Forcefully disconnects the client from the server.
+        /// </summary>
+        Task Disconnect();
+
         /// <summary>
         /// Reconnect if already connected.
         /// </summary>

osu.Game/Online/IStatefulUserHubClient.cs

@@ -0,0 +1,18 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Threading.Tasks;
+
+namespace osu.Game.Online
+{
+    /// <summary>
+    /// Common interface for clients of "stateful user hubs", i.e. server-side hubs
+    /// that preserve user state.
+    /// In the case of such hubs, concurrency constraints are enforced (only one client
+    /// can be connected at a time).
+    /// </summary>
+    public interface IStatefulUserHubClient
+    {
+        Task DisconnectRequested();
+    }
+}

osu.Game/Online/Multiplayer/IMultiplayerClient.cs

@@ -13,7 +13,7 @@ namespace osu.Game.Online.Multiplayer
     /// <summary>
     /// An interface defining a multiplayer client instance.
     /// </summary>
-    public interface IMultiplayerClient
+    public interface IMultiplayerClient : IStatefulUserHubClient
     {
         /// <summary>
         /// Signals that the room has changed state.

osu.Game/Online/Multiplayer/MultiplayerClient.cs

@@ -357,6 +357,8 @@ namespace osu.Game.Online.Multiplayer
 
         public abstract Task ChangeBeatmapAvailability(BeatmapAvailability newBeatmapAvailability);
 
+        public abstract Task DisconnectInternal();
+
         /// <summary>
         /// Change the local user's mods in the currently joined room.
         /// </summary>
@@ -876,5 +878,11 @@ namespace osu.Game.Online.Multiplayer
 
             return tcs.Task;
         }
+
+        Task IStatefulUserHubClient.DisconnectRequested()
+        {
+            Schedule(() => DisconnectInternal());
+            return Task.CompletedTask;
+        }
     }
 }

osu.Game/Online/Multiplayer/OnlineMultiplayerClient.cs

@@ -68,6 +68,7 @@ namespace osu.Game.Online.Multiplayer
                     connection.On<MultiplayerPlaylistItem>(nameof(IMultiplayerClient.PlaylistItemAdded), ((IMultiplayerClient)this).PlaylistItemAdded);
                     connection.On<long>(nameof(IMultiplayerClient.PlaylistItemRemoved), ((IMultiplayerClient)this).PlaylistItemRemoved);
                     connection.On<MultiplayerPlaylistItem>(nameof(IMultiplayerClient.PlaylistItemChanged), ((IMultiplayerClient)this).PlaylistItemChanged);
+                    connection.On(nameof(IStatefulUserHubClient.DisconnectRequested), ((IMultiplayerClient)this).DisconnectRequested);
                 };
 
                 IsConnected.BindTo(connector.IsConnected);
@@ -255,6 +256,14 @@ namespace osu.Game.Online.Multiplayer
             return connection.InvokeAsync(nameof(IMultiplayerServer.RemovePlaylistItem), playlistItemId);
         }
 
+        public override Task DisconnectInternal()
+        {
+            if (connector == null)
+                return Task.CompletedTask;
+
+            return connector.Disconnect();
+        }
+
         protected override void Dispose(bool isDisposing)
         {
             base.Dispose(isDisposing);

osu.Game/Online/PersistentEndpointClientConnector.cs

@@ -159,6 +159,8 @@ namespace osu.Game.Online
                 await Task.Run(connect, default).ConfigureAwait(false);
         }
 
+        protected Task Disconnect() => disconnect(true);
+
         private async Task disconnect(bool takeLock)
         {
             cancelExistingConnect();

osu.Game/Online/Spectator/ISpectatorClient.cs

@@ -8,7 +8,7 @@ namespace osu.Game.Online.Spectator
     /// <summary>
     /// An interface defining a spectator client instance.
     /// </summary>
-    public interface ISpectatorClient
+    public interface ISpectatorClient : IStatefulUserHubClient
     {
         /// <summary>
         /// Signals that a user has begun a new play session.

osu.Game/Online/Spectator/OnlineSpectatorClient.cs

@@ -42,6 +42,7 @@ namespace osu.Game.Online.Spectator
                     connection.On<int, FrameDataBundle>(nameof(ISpectatorClient.UserSentFrames), ((ISpectatorClient)this).UserSentFrames);
                     connection.On<int, SpectatorState>(nameof(ISpectatorClient.UserFinishedPlaying), ((ISpectatorClient)this).UserFinishedPlaying);
                     connection.On<int, long>(nameof(ISpectatorClient.UserScoreProcessed), ((ISpectatorClient)this).UserScoreProcessed);
+                    connection.On(nameof(IStatefulUserHubClient.DisconnectRequested), ((IStatefulUserHubClient)this).DisconnectRequested);
                 };
 
                 IsConnected.BindTo(connector.IsConnected);
@@ -113,5 +114,13 @@ namespace osu.Game.Online.Spectator
 
             return connection.InvokeAsync(nameof(ISpectatorServer.EndWatchingUser), userId);
         }
+
+        protected override Task DisconnectInternal()
+        {
+            if (connector == null)
+                return Task.CompletedTask;
+
+            return connector.Disconnect();
+        }
     }
 }

osu.Game/Online/Spectator/SpectatorClient.cs

@@ -174,6 +174,12 @@ namespace osu.Game.Online.Spectator
             return Task.CompletedTask;
         }
 
+        Task IStatefulUserHubClient.DisconnectRequested()
+        {
+            Schedule(() => DisconnectInternal());
+            return Task.CompletedTask;
+        }
+
         public void BeginPlaying(long? scoreToken, GameplayState state, Score score)
         {
             // This schedule is only here to match the one below in `EndPlaying`.
@@ -291,6 +297,8 @@ namespace osu.Game.Online.Spectator
 
         protected abstract Task StopWatchingUserInternal(int userId);
 
+        protected abstract Task DisconnectInternal();
+
         protected override void Update()
         {
             base.Update();

osu.Game/Tests/Visual/Multiplayer/TestMultiplayerClient.cs

@@ -658,5 +658,11 @@ namespace osu.Game.Tests.Visual.Multiplayer
             PlayedAt = item.PlayedAt,
             StarRating = item.Beatmap.StarRating,
         };
+
+        public override Task DisconnectInternal()
+        {
+            isConnected.Value = false;
+            return Task.CompletedTask;
+        }
     }
 }

osu.Game/Tests/Visual/Spectator/TestSpectatorClient.cs

@@ -33,7 +33,8 @@ namespace osu.Game.Tests.Visual.Spectator
 
         public int FrameSendAttempts { get; private set; }
 
-        public override IBindable<bool> IsConnected { get; } = new Bindable<bool>(true);
+        public override IBindable<bool> IsConnected => isConnected;
+        private readonly BindableBool isConnected = new BindableBool(true);
 
         public IReadOnlyDictionary<int, ReplayFrame> LastReceivedUserFrames => lastReceivedUserFrames;
 
@@ -179,5 +180,11 @@ namespace osu.Game.Tests.Visual.Spectator
                 State = SpectatedUserState.Playing
             });
         }
+
+        protected override Task DisconnectInternal()
+        {
+            isConnected.Value = false;
+            return Task.CompletedTask;
+        }
     }
 }