Add AbortLoad() method to abort gameplay loads

osu.Game/Online/Multiplayer/IMultiplayerRoomServer.cs

@@ -77,6 +77,11 @@ namespace osu.Game.Online.Multiplayer
         /// <exception cref="InvalidStateException">If an attempt to start the game occurs when the game's (or users') state disallows it.</exception>
         Task StartMatch();
 
+        /// <summary>
+        /// Aborts an ongoing gameplay load.
+        /// </summary>
+        Task AbortLoad();
+
         /// <summary>
         /// Adds an item to the playlist.
         /// </summary>

osu.Game/Online/Multiplayer/MultiplayerClient.cs

@@ -333,6 +333,8 @@ namespace osu.Game.Online.Multiplayer
 
         public abstract Task StartMatch();
 
+        public abstract Task AbortLoad();
+
         public abstract Task AddPlaylistItem(MultiplayerPlaylistItem item);
 
         public abstract Task EditPlaylistItem(MultiplayerPlaylistItem item);

osu.Game/Online/Multiplayer/OnlineMultiplayerClient.cs

@@ -154,6 +154,14 @@ namespace osu.Game.Online.Multiplayer
             return connection.InvokeAsync(nameof(IMultiplayerServer.StartMatch));
         }
 
+        public override Task AbortLoad()
+        {
+            if (!IsConnected.Value)
+                return Task.CompletedTask;
+
+            return connection.InvokeAsync(nameof(IMultiplayerServer.AbortLoad));
+        }
+
         public override Task AddPlaylistItem(MultiplayerPlaylistItem item)
         {
             if (!IsConnected.Value)

osu.Game/Screens/OnlinePlay/Multiplayer/Multiplayer.cs

@@ -1,6 +1,7 @@
 // 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.Diagnostics;
 using osu.Framework.Allocation;
 using osu.Framework.Screens;
 using osu.Game.Online.Multiplayer;
@@ -18,8 +19,24 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
         {
             base.OnResuming(last);
 
-            if (client.Room != null && client.LocalUser?.State != MultiplayerUserState.Spectating)
+            if (client.Room == null)
-                client.ChangeState(MultiplayerUserState.Idle);
+                return;
+
+            Debug.Assert(client.LocalUser != null);
+
+            switch (client.LocalUser.State)
+            {
+                case MultiplayerUserState.Spectating:
+                    break;
+
+                case MultiplayerUserState.WaitingForLoad:
+                    client.AbortLoad();
+                    break;
+
+                default:
+                    client.ChangeState(MultiplayerUserState.Idle);
+                    break;
+            }
         }
 
         protected override string ScreenTitle => "Multiplayer";

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

@@ -242,6 +242,11 @@ namespace osu.Game.Tests.Visual.Multiplayer
 
         public override Task ChangeState(MultiplayerUserState newState)
         {
+            Debug.Assert(Room != null);
+
+            if (newState == MultiplayerUserState.Idle && LocalUser?.State == MultiplayerUserState.WaitingForLoad)
+                return Task.CompletedTask;
+
             ChangeUserState(api.LocalUser.Value.Id, newState);
             return Task.CompletedTask;
         }
@@ -303,6 +308,16 @@ namespace osu.Game.Tests.Visual.Multiplayer
             return ((IMultiplayerClient)this).LoadRequested();
         }
 
+        public override Task AbortLoad()
+        {
+            Debug.Assert(Room != null);
+            Debug.Assert(LocalUser != null);
+
+            ChangeUserState(LocalUser.UserID, MultiplayerUserState.Idle);
+
+            return Task.CompletedTask;
+        }
+
         public async Task AddUserPlaylistItem(int userId, MultiplayerPlaylistItem item)
         {
             Debug.Assert(Room != null);