deduplicate redis hub lifetime group msges

Author: datwelk

src/SignalR/server/Core/src/DefaultHubLifetimeManager.cs

@@ -225,6 +225,8 @@ public override Task SendGroupAsync(string groupName, string methodName, object?
     public override Task SendGroupsAsync(IReadOnlyList<string> groupNames, string methodName, object?[] args, CancellationToken cancellationToken = default)
     {
         // Each task represents the list of tasks for each of the writes within a group
+        List<Task>? tasks = new List<Task>();
+
         var connections = new ConcurrentDictionary<string, HubConnectionContext>();
 
         foreach (var groupName in groupNames)
@@ -246,7 +248,12 @@ public override Task SendGroupsAsync(IReadOnlyList<string> groupNames, string me
 
         foreach (var connection in connections)
         {
-            SendConnectionAsync(connection.Key, methodName, args, cancellationToken);
+            tasks.Add(SendConnectionAsync(connection.Key, methodName, args, cancellationToken));
+        }
+
+        if (tasks != null)
+        {
+            return Task.WhenAll(tasks);
         }
 
         return Task.CompletedTask;

src/SignalR/server/StackExchangeRedis/src/Internal/RedisSubscriptionManager.cs

@@ -63,4 +63,14 @@ public async Task RemoveSubscriptionAsync(string id, HubConnectionContext connec
             _lock.Release();
         }
     }
+
+    public HubConnectionStore? GetStore(string id)
+    {
+        if (_subscriptions.TryGetValue(id, out var store))
+        {
+            return store;
+        }
+
+        return null;
+    }
 }

src/SignalR/server/StackExchangeRedis/src/RedisHubLifetimeManager.cs

@@ -259,15 +259,29 @@ public override Task SendGroupsAsync(IReadOnlyList<string> groupNames, string me
         ArgumentNullException.ThrowIfNull(groupNames);
         var publishTasks = new List<Task>(groupNames.Count);
         var payload = _protocol.WriteInvocation(methodName, args);
+        var connections = new HashSet<string>();
 
         foreach (var groupName in groupNames)
         {
             if (!string.IsNullOrEmpty(groupName))
             {
-                publishTasks.Add(PublishAsync(_channels.Group(groupName), payload));
+                var connectionStore = _groups.GetStore(groupName);
+                if (connectionStore != null)
+                {
+                    foreach (var connection in connectionStore)
+                    {
+                        connections.Add(connection.ConnectionId);
+                    }
+                }
             }
         }
 
+        // Send to unique connections
+        foreach (var connectionId in connections)
+        {
+            publishTasks.Add(PublishAsync(_channels.Connection(connectionId), payload));
+        }
+
         return Task.WhenAll(publishTasks);
     }