Fix handling of local echo deduplication

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

@@ -28,6 +28,7 @@ namespace osu.Game.Online.API.Requests
             req.AddParameter(@"target_id", user.Id.ToString());
             req.AddParameter(@"message", message.Content);
             req.AddParameter(@"is_action", message.IsAction.ToString().ToLowerInvariant());
+            req.AddParameter(@"uuid", message.Uuid);
             return req;
         }
 

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

@@ -25,6 +25,7 @@ namespace osu.Game.Online.API.Requests
             req.Method = HttpMethod.Post;
             req.AddParameter(@"is_action", Message.IsAction.ToString().ToLowerInvariant());
             req.AddParameter(@"message", Message.Content);
+            req.AddParameter(@"uuid", Message.Uuid);
 
             return req;
         }

osu.Game/Online/Chat/Channel.cs

@@ -134,6 +134,14 @@ namespace osu.Game.Online.Chat
         /// <param name="messages"></param>
         public void AddNewMessages(params Message[] messages)
         {
+            foreach (var m in messages)
+            {
+                LocalEchoMessage localEcho = pendingMessages.FirstOrDefault(local => local.Uuid == m.Uuid);
+
+                if (localEcho != null)
+                    ReplaceMessage(localEcho, m);
+            }
+
             messages = messages.Except(Messages).ToArray();
 
             if (messages.Length == 0) return;

osu.Game/Online/Chat/ChannelManager.cs

@@ -85,8 +85,21 @@ namespace osu.Game.Online.Chat
         [BackgroundDependencyLoader]
         private void load()
         {
-            connector.ChannelJoined += ch => Schedule(() => joinChannel(ch));
+            connector.ChannelJoined += ch => Schedule(() =>
+            {
+                var localChannel = getChannel(ch);
+
+                if (localChannel != ch)
+                {
+                    localChannel.Joined.Value = true;
+                    localChannel.Id = ch.Id;
+                }
+
+                joinChannel(localChannel);
+            });
+
             connector.NewMessages += msgs => Schedule(() => addMessages(msgs));
+
             connector.PresenceReceived += () => Schedule(() =>
             {
                 if (!channelsInitialised)
@@ -189,7 +202,8 @@ namespace osu.Game.Online.Chat
                     Timestamp = DateTimeOffset.Now,
                     ChannelId = target.Id,
                     IsAction = isAction,
-                    Content = text
+                    Content = text,
+                    Uuid = Guid.NewGuid().ToString()
                 };
 
                 target.AddLocalEcho(message);
@@ -199,13 +213,7 @@ namespace osu.Game.Online.Chat
                 {
                     var createNewPrivateMessageRequest = new CreateNewPrivateMessageRequest(target.Users.First(), message);
 
-                    createNewPrivateMessageRequest.Success += createRes =>
+                    createNewPrivateMessageRequest.Success += _ => dequeueAndRun();
-                    {
-                        target.Id = createRes.ChannelID;
-                        target.ReplaceMessage(message, createRes.Message);
-                        dequeueAndRun();
-                    };
-
                     createNewPrivateMessageRequest.Failure += exception =>
                     {
                         handlePostException(exception);
@@ -219,12 +227,7 @@ namespace osu.Game.Online.Chat
 
                 var req = new PostMessageRequest(message);
 
-                req.Success += m =>
+                req.Success += m => dequeueAndRun();
-                {
-                    target.ReplaceMessage(message, m);
-                    dequeueAndRun();
-                };
-
                 req.Failure += exception =>
                 {
                     handlePostException(exception);
@@ -403,7 +406,20 @@ namespace osu.Game.Online.Chat
         {
             Channel found = null;
 
-            bool lookupCondition(Channel ch) => lookup.Id > 0 ? ch.Id == lookup.Id : lookup.Name == ch.Name;
+            bool lookupCondition(Channel ch)
+            {
+                // 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/Chat/Message.cs

@@ -37,6 +37,12 @@ namespace osu.Game.Online.Chat
             set => Sender = new APIUser { Id = value };
         }
 
+        /// <summary>
+        /// A unique identifier for this message. Sent to and from osu!web to use for deduplication.
+        /// </summary>
+        [JsonProperty(@"uuid")]
+        public string Uuid { get; set; } = string.Empty;
+
         [JsonConstructor]
         public Message()
         {

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

@@ -2,9 +2,7 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
-using System.Collections.Generic;
 using System.Diagnostics;
-using System.Linq;
 using System.Net.WebSockets;
 using System.Text;
 using System.Threading;
@@ -126,12 +124,10 @@ namespace osu.Game.Online.Notifications.WebSocket
                     NewChatMessageData? messageData = JsonConvert.DeserializeObject<NewChatMessageData>(message.Data.ToString());
                     Debug.Assert(messageData != null);
 
-                    List<Message> messages = messageData.Messages.Where(m => m.Sender.OnlineID != api.LocalUser.Value.OnlineID).ToList();
+                    foreach (var msg in messageData.Messages)
+                        HandleJoinedChannel(new Channel(msg.Sender) { Id = msg.ChannelId, Messages = { msg } });
 
-                    foreach (var msg in messages)
+                    HandleMessages(messageData.Messages);
-                        HandleJoinedChannel(new Channel(msg.Sender) { Id = msg.ChannelId });
-
-                    HandleMessages(messages);
                     break;
             }