Better handling for joining channels with only ID

osu.Game/Online/API/Requests/GetChannelRequest.cs

@@ -0,0 +1,19 @@
+// 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 osu.Game.Online.API.Requests.Responses;
+
+namespace osu.Game.Online.API.Requests
+{
+    public class GetChannelRequest : APIRequest<GetChannelResponse>
+    {
+        private readonly long channelId;
+
+        public GetChannelRequest(long channelId)
+        {
+            this.channelId = channelId;
+        }
+
+        protected override string Target => $"chat/channels/{channelId}";
+    }
+}

osu.Game/Online/API/Requests/Responses/GetChannelResponse.cs

@@ -0,0 +1,19 @@
+// 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.Collections.Generic;
+using Newtonsoft.Json;
+using osu.Game.Online.Chat;
+
+namespace osu.Game.Online.API.Requests.Responses
+{
+    [JsonObject(MemberSerialization.OptIn)]
+    public class GetChannelResponse
+    {
+        [JsonProperty(@"channel")]
+        public Channel Channel { get; set; } = null!;
+
+        [JsonProperty(@"users")]
+        public List<APIUser> Users { get; set; } = null!;
+    }
+}

osu.Game/Online/Chat/ChannelManager.cs

@@ -88,15 +88,14 @@ namespace osu.Game.Online.Chat
         {
             connector.ChannelJoined += ch => Schedule(() =>
             {
-                var localChannel = getChannel(ch);
+                if (ch.Joined.Value)
-
+                    JoinChannel(ch);
-                if (localChannel != ch)
+                else
                 {
-                    localChannel.Joined.Value = true;
+                    var req = new GetChannelRequest(ch.Id);
-                    localChannel.Id = ch.Id;
+                    req.Success += response => JoinChannel(response.Channel);
+                    api.Queue(req);
                 }
-
-                joinChannel(localChannel);
             });
 
             connector.ChannelParted += ch => Schedule(() => LeaveChannel(getChannel(ch)));
@@ -421,20 +420,7 @@ namespace osu.Game.Online.Chat
         {
             Channel found = null;
 
-            bool lookupCondition(Channel ch)
+            bool lookupCondition(Channel ch) => lookup.Id > 0 ? ch.Id == lookup.Id : ch.Name == lookup.Name;
-            {
-                // If both channels have an id, use that.
-                if (lookup.Id > 0 && ch.Id > 0)
-                    return ch.Id == lookup.Id;
-
-                // In the case that the local echo is received in a new channel (i.e. one that does not yet have an ID),
-                // then we need to check for any existing channel with the message containing the same message matched by UUID.
-                if (lookup.Messages.Count > 0 && ch.Messages.Any(m => m.Uuid == lookup.Messages.Last().Uuid))
-                    return true;
-
-                // As a last resort, fallback to matching by name.
-                return lookup.Name == ch.Name;
-            }
 
             var available = AvailableChannels.FirstOrDefault(lookupCondition);
             if (available != null)

osu.Game/Online/Notifications/NotificationsClient.cs

@@ -46,7 +46,10 @@ namespace osu.Game.Online.Notifications
                 if (updates?.Presence != null)
                 {
                     foreach (var channel in updates.Presence)
+                    {
+                        channel.Joined.Value = true;
                         HandleJoinedChannel(channel);
+                    }
 
                     //todo: handle left channels
 
@@ -59,12 +62,7 @@ namespace osu.Game.Online.Notifications
             return fetchReq;
         }
 
-        protected void HandleJoinedChannel(Channel channel)
+        protected void HandleJoinedChannel(Channel channel) => ChannelJoined?.Invoke(channel);
-        {
-            // we received this from the server so should mark the channel already joined.
-            channel.Joined.Value = true;
-            ChannelJoined?.Invoke(channel);
-        }
 
         protected void HandleChannelParted(Channel channel) => ChannelParted?.Invoke(channel);
 

osu.Game/Online/Notifications/WebSocket/WebSocketNotificationsClient.cs

@@ -119,6 +119,7 @@ namespace osu.Game.Online.Notifications.WebSocket
                     Channel? joinedChannel = JsonConvert.DeserializeObject<Channel>(message.Data.ToString());
                     Debug.Assert(joinedChannel != null);
 
+                    joinedChannel.Joined.Value = true;
                     HandleJoinedChannel(joinedChannel);
                     break;
 
@@ -138,7 +139,7 @@ namespace osu.Game.Online.Notifications.WebSocket
                     Debug.Assert(messageData != null);
 
                     foreach (var msg in messageData.Messages)
-                        HandleJoinedChannel(new Channel(msg.Sender) { Id = msg.ChannelId, Messages = { msg } });
+                        HandleJoinedChannel(new Channel { Id = msg.ChannelId });
 
                     HandleMessages(messageData.Messages);
                     break;