Fix beatmap getting nulled due to failing web request

osu.Game/Online/Multiplayer/MultiplayerClient.cs

@@ -9,7 +9,9 @@ using System.Threading.Tasks;
 using Microsoft.AspNetCore.SignalR.Client;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
+using osu.Game.Beatmaps;
 using osu.Game.Online.API;
+using osu.Game.Online.API.Requests;
 using osu.Game.Online.Rooms;
 
 namespace osu.Game.Online.Multiplayer
@@ -121,6 +123,29 @@ namespace osu.Game.Online.Multiplayer
             return connection.InvokeAsync(nameof(IMultiplayerServer.StartMatch));
         }
 
+        protected override Task<BeatmapSetInfo> GetOnlineBeatmapSet(int beatmapId, CancellationToken cancellationToken = default)
+        {
+            var tcs = new TaskCompletionSource<BeatmapSetInfo>();
+            var req = new GetBeatmapSetRequest(beatmapId, BeatmapSetLookupType.BeatmapId);
+
+            req.Success += res =>
+            {
+                if (cancellationToken.IsCancellationRequested)
+                {
+                    tcs.SetCanceled();
+                    return;
+                }
+
+                tcs.SetResult(res.ToBeatmapSet(Rulesets));
+            };
+
+            req.Failure += e => tcs.SetException(e);
+
+            API.Queue(req);
+
+            return tcs.Task;
+        }
+
         protected override void Dispose(bool isDisposing)
         {
             base.Dispose(isDisposing);

osu.Game/Online/Multiplayer/StatefulMultiplayerClient.cs

@@ -17,8 +17,6 @@ using osu.Framework.Logging;
 using osu.Game.Beatmaps;
 using osu.Game.Database;
 using osu.Game.Online.API;
-using osu.Game.Online.API.Requests;
-using osu.Game.Online.API.Requests.Responses;
 using osu.Game.Online.Rooms;
 using osu.Game.Online.Rooms.RoomStatuses;
 using osu.Game.Rulesets;
@@ -71,7 +69,7 @@ namespace osu.Game.Online.Multiplayer
         /// <summary>
         /// The <see cref="MultiplayerRoomUser"/> corresponding to the local player, if available.
         /// </summary>
-        public MultiplayerRoomUser? LocalUser => Room?.Users.SingleOrDefault(u => u.User?.Id == api.LocalUser.Value.Id);
+        public MultiplayerRoomUser? LocalUser => Room?.Users.SingleOrDefault(u => u.User?.Id == API.LocalUser.Value.Id);
 
         /// <summary>
         /// Whether the <see cref="LocalUser"/> is the host in <see cref="Room"/>.
@@ -85,15 +83,15 @@ namespace osu.Game.Online.Multiplayer
             }
         }
 
+        [Resolved]
+        protected IAPIProvider API { get; private set; } = null!;
+
+        [Resolved]
+        protected RulesetStore Rulesets { get; private set; } = null!;
+
         [Resolved]
         private UserLookupCache userLookupCache { get; set; } = null!;
 
-        [Resolved]
-        private IAPIProvider api { get; set; } = null!;
-
-        [Resolved]
-        private RulesetStore rulesets { get; set; } = null!;
-
         // Only exists for compatibility with old osu-server-spectator build.
         // Todo: Can be removed on 2021/02/26.
         private long defaultPlaylistItemId;
@@ -515,30 +513,26 @@ namespace osu.Game.Online.Multiplayer
 
             RoomUpdated?.Invoke();
 
-            var req = new GetBeatmapSetRequest(settings.BeatmapID, BeatmapSetLookupType.BeatmapId);
+            GetOnlineBeatmapSet(settings.BeatmapID, cancellationToken).ContinueWith(set => Schedule(() =>
-            req.Success += res =>
             {
                 if (cancellationToken.IsCancellationRequested)
                     return;
 
-                updatePlaylist(settings, res);
+                updatePlaylist(settings, set.Result);
-            };
+            }), TaskContinuationOptions.OnlyOnRanToCompletion);
-
-            api.Queue(req);
         }, cancellationToken);
 
-        private void updatePlaylist(MultiplayerRoomSettings settings, APIBeatmapSet onlineSet)
+        private void updatePlaylist(MultiplayerRoomSettings settings, BeatmapSetInfo beatmapSet)
         {
             if (Room == null || !Room.Settings.Equals(settings))
                 return;
 
             Debug.Assert(apiRoom != null);
 
-            var beatmapSet = onlineSet.ToBeatmapSet(rulesets);
             var beatmap = beatmapSet.Beatmaps.Single(b => b.OnlineBeatmapID == settings.BeatmapID);
             beatmap.MD5Hash = settings.BeatmapChecksum;
 
-            var ruleset = rulesets.GetRuleset(settings.RulesetID).CreateInstance();
+            var ruleset = Rulesets.GetRuleset(settings.RulesetID).CreateInstance();
             var mods = settings.RequiredMods.Select(m => m.ToMod(ruleset));
             var allowedMods = settings.AllowedMods.Select(m => m.ToMod(ruleset));
 
@@ -568,6 +562,14 @@ namespace osu.Game.Online.Multiplayer
             }
         }
 
+        /// <summary>
+        /// Retrieves a <see cref="BeatmapSetInfo"/> from an online source.
+        /// </summary>
+        /// <param name="beatmapId">The beatmap set ID.</param>
+        /// <param name="cancellationToken">A token to cancel the request.</param>
+        /// <returns>The <see cref="BeatmapSetInfo"/> retrieval task.</returns>
+        protected abstract Task<BeatmapSetInfo> GetOnlineBeatmapSet(int beatmapId, CancellationToken cancellationToken = default);
+
         /// <summary>
         /// For the provided user ID, update whether the user is included in <see cref="CurrentMatchPlayingUserIds"/>.
         /// </summary>

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

@@ -3,12 +3,15 @@
 
 #nullable enable
 
+using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
+using osu.Game.Beatmaps;
 using osu.Game.Online.API;
 using osu.Game.Online.Multiplayer;
 using osu.Game.Online.Rooms;
@@ -28,6 +31,9 @@ namespace osu.Game.Tests.Visual.Multiplayer
         [Resolved]
         private Room apiRoom { get; set; } = null!;
 
+        [Resolved]
+        private BeatmapManager beatmaps { get; set; } = null!;
+
         public void Connect() => isConnected.Value = true;
 
         public void Disconnect() => isConnected.Value = false;
@@ -168,5 +174,19 @@ namespace osu.Game.Tests.Visual.Multiplayer
 
             return ((IMultiplayerClient)this).LoadRequested();
         }
+
+        protected override Task<BeatmapSetInfo> GetOnlineBeatmapSet(int beatmapId, CancellationToken cancellationToken = default)
+        {
+            Debug.Assert(Room != null);
+            Debug.Assert(apiRoom != null);
+
+            var set = apiRoom.Playlist.FirstOrDefault(p => p.BeatmapID == beatmapId)?.Beatmap.Value.BeatmapSet
+                      ?? beatmaps.QueryBeatmap(b => b.OnlineBeatmapID == beatmapId)?.BeatmapSet;
+
+            if (set == null)
+                throw new InvalidOperationException("Beatmap not found.");
+
+            return Task.FromResult(set);
+        }
     }
 }