Implement persence API in websocket transport

src/Microsoft.Azure.SignalR.AspNet/ServerConnections/ServiceConnectionManager.cs

@@ -168,4 +168,9 @@ private IEnumerable<IServiceConnectionContainer> GetConnections()
             }
         }
     }
+
+    public IAsyncEnumerable<GroupMember> ListConnectionsInGroupAsync(string groupName, int? top)
+    {
+        throw new NotSupportedException();
+    }
 }

src/Microsoft.Azure.SignalR.Common/Interfaces/IPresenceManager.cs

@@ -0,0 +1,15 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System.Collections.Generic;
+using Microsoft.Azure.SignalR.Protocol;
+
+namespace Microsoft.Azure.SignalR;
+
+/// <summary>
+/// Manager for presence operations.
+/// </summary>
+internal interface IPresenceManager
+{
+    IAsyncEnumerable<GroupMember> ListConnectionsInGroupAsync(string groupName, int? top);
+}

src/Microsoft.Azure.SignalR.Common/Interfaces/IServiceConnectionContainer.cs

@@ -6,7 +6,7 @@
 
 namespace Microsoft.Azure.SignalR;
 
-internal interface IServiceConnectionContainer : IServiceConnectionManager, IDisposable
+internal interface IServiceConnectionContainer : IServiceConnectionManager, IPresenceManager, IDisposable
 {
     ServiceConnectionStatus Status { get; }
 

src/Microsoft.Azure.SignalR.Common/ServiceConnections/MultiEndpointMessageWriter.cs

@@ -16,7 +16,7 @@ namespace Microsoft.Azure.SignalR;
 /// <summary>
 /// A service connection container which sends message to multiple service endpoints.
 /// </summary>
-internal class MultiEndpointMessageWriter : IServiceMessageWriter
+internal class MultiEndpointMessageWriter : IServiceMessageWriter, IPresenceManager
 {
     private readonly ILogger _logger;
 
@@ -55,8 +55,8 @@ public Task WriteAsync(ServiceMessage serviceMessage)
 
     public Task<bool> WriteAckableMessageAsync(ServiceMessage serviceMessage, CancellationToken cancellationToken = default)
     {
-        if (serviceMessage is CheckConnectionExistenceWithAckMessage 
-            || serviceMessage is JoinGroupWithAckMessage 
+        if (serviceMessage is CheckConnectionExistenceWithAckMessage
+            || serviceMessage is JoinGroupWithAckMessage
             || serviceMessage is LeaveGroupWithAckMessage)
         {
             return WriteSingleResultAckableMessage(serviceMessage, cancellationToken);
@@ -172,6 +172,32 @@ private async Task WriteSingleEndpointMessageAsync(HubServiceEndpoint endpoint,
         }
     }
 
+    public async IAsyncEnumerable<GroupMember> ListConnectionsInGroupAsync(string groupName, int? top)
+    {
+        if (TargetEndpoints.Length == 0)
+        {
+            Log.NoEndpointRouted(_logger, nameof(GroupMemberQueryMessage));
+            yield break;
+        }
+        foreach (var endpoint in TargetEndpoints)
+        {
+            IAsyncEnumerable<GroupMember> enumerable;
+            try
+            {
+                enumerable = endpoint.ConnectionContainer.ListConnectionsInGroupAsync(groupName, top);
+            }
+            catch (ServiceConnectionNotActiveException)
+            {
+                Log.FailedWritingMessageToEndpoint(_logger, nameof(GroupMemberQueryMessage), null, endpoint.ToString());
+                continue;
+            }
+            await foreach (var member in enumerable)
+            {
+                yield return member;
+            }
+        }
+    }
+
     internal static class Log
     {
         public const string FailedWritingMessageToEndpointTemplate = "{0} message {1} is not sent to endpoint {2} because all connections to this endpoint are offline.";

src/Microsoft.Azure.SignalR.Common/ServiceConnections/MultiEndpointServiceConnectionContainer.cs

@@ -150,6 +150,14 @@ public Task<bool> WriteAckableMessageAsync(ServiceMessage serviceMessage, Cancel
         return CreateMessageWriter(serviceMessage).WriteAckableMessageAsync(serviceMessage, cancellationToken);
     }
 
+
+    public IAsyncEnumerable<GroupMember> ListConnectionsInGroupAsync(string groupName, int? top)
+    {
+        var targetEndpoints = _routerEndpoints.needRouter ? _router.GetEndpointsForGroup(groupName, _routerEndpoints.endpoints) : _routerEndpoints.endpoints;
+        var messageWriter = new MultiEndpointMessageWriter(targetEndpoints?.ToList(), _loggerFactory);
+        return messageWriter.ListConnectionsInGroupAsync(groupName, top);
+    }
+
     public Task StartGetServersPing()
     {
         return Task.WhenAll(_routerEndpoints.endpoints.Select(c => c.ConnectionContainer.StartGetServersPing()));

src/Microsoft.Azure.SignalR.Common/ServiceConnections/ServiceConnectionContainerBase.cs

@@ -221,7 +221,7 @@ public virtual Task HandlePingAsync(PingMessage pingMessage)
 
     public void HandleAck(AckMessage ackMessage)
     {
-        _ackHandler.TriggerAck(ackMessage.AckId, (AckStatus)ackMessage.Status);
+        _ackHandler.TriggerAck(ackMessage.AckId, (AckStatus)ackMessage.Status, ackMessage.Payload);
     }
 
     public virtual Task WriteAsync(ServiceMessage serviceMessage)
@@ -249,6 +249,53 @@ public async Task<bool> WriteAckableMessageAsync(ServiceMessage serviceMessage,
         return AckHandler.HandleAckStatus(ackableMessage, status);
     }
 
+    public async IAsyncEnumerable<GroupMember> ListConnectionsInGroupAsync(string groupName, int? top)
+    {
+        var currentCount = 0;
+        do
+        {
+            if (top != null)
+            {
+                top -= currentCount;
+            }
+            var message = new GroupMemberQueryMessage() { GroupName = groupName, Top = top };
+            var response = await InvokeAsync<GroupMemberQueryResponse>(message);
+            foreach (var member in response.Members)
+            {
+                yield return member;
+                currentCount++;
+                if (top != null && currentCount >= top || response.ContinuationToken == null)
+                {
+                    yield break;
+                }
+            }
+            message.ContinuationToken = response.ContinuationToken;
+        } while (true);
+    }
+
+    /// <summary>
+    /// <see cref="WriteAckableMessageAsync(ServiceMessage, CancellationToken)"/> only checks <see cref="AckMessage.Status"/> as the response, 
+    /// while this method checks <see cref="AckMessage.Payload"/> and deserialize it to <typeparamref name="T"/>.
+    /// </summary>
+    private async Task<T> InvokeAsync<T>(ServiceMessage serviceMessage, CancellationToken cancellationToken = default) where T : notnull, new()
+    {
+        if (serviceMessage is not IAckableMessage ackableMessage)
+        {
+            throw new ArgumentException($"{nameof(serviceMessage)} is not {nameof(IAckableMessage)}");
+        }
+
+        var task = _ackHandler.CreateSingleAck<T>(out var id, null, cancellationToken);
+        ackableMessage.AckId = id;
+
+        // Sending regular messages completes as soon as the data leaves the outbound pipe,
+        // whereas ackable ones complete upon full roundtrip of the message and the ack (or timeout).
+        // Therefore sending them over different connections creates a possibility for processing them out of original order.
+        // By sending both message types over the same connection we ensure that they are sent (and processed) in their original order.
+        await WriteMessageAsync(serviceMessage);
+
+        return await task;
+    }
+
     public virtual Task OfflineAsync(GracefulShutdownMode mode, CancellationToken token)
     {
         _terminated = true;

src/Microsoft.Azure.SignalR.Common/Utilities/AckHandler.cs

@@ -50,16 +50,16 @@ public Task<AckStatus> CreateSingleAck(out int id, TimeSpan? ackTimeout = defaul
             return info.Task;
         }
 
-        public Task<T> CreateSingleAck<T>(out int id, TimeSpan? ackTimeout = default, CancellationToken cancellationToken = default) where T : IMessagePackSerializable, new()
+        public Task<T> CreateSingleAck<T>(out int id, TimeSpan? ackTimeout = default, CancellationToken cancellationToken = default) where T : notnull, new()
         {
             id = NextId();
             if (_disposed)
             {
                 return Task.FromResult(new T());
             }
-            var info = (IAckInfo<IMessagePackSerializable>)_acks.GetOrAdd(id, _ => new SinglePayloadAck<T>(ackTimeout ?? _defaultAckTimeout));
+            var info = (SinglePayloadAck<T>)_acks.GetOrAdd(id, _ => new SinglePayloadAck<T>(ackTimeout ?? _defaultAckTimeout));
             cancellationToken.Register(info.Cancel);
-            return info.Task.ContinueWith(task => (T)task.Result);
+            return info.Task.ContinueWith(task => task.Result);
         }
 
         public static bool HandleAckStatus(IAckableMessage message, AckStatus status)
@@ -210,7 +210,7 @@ public override bool Ack(AckStatus status, ReadOnlySequence<byte>? payload = nul
                 _tcs.TrySetResult(status);
         }
 
-        private sealed class SinglePayloadAck<T> : SingleAckInfo<IMessagePackSerializable> where T : IMessagePackSerializable, new()
+        private sealed class SinglePayloadAck<T> : SingleAckInfo<T> where T : notnull, new()
         {
             public SinglePayloadAck(TimeSpan timeout) : base(timeout) { }
             public override bool Ack(AckStatus status, ReadOnlySequence<byte>? payload = null)

test/Microsoft.Azure.SignalR.Tests.Common/TestClasses/TestServiceConnectionContainer.cs

@@ -109,4 +109,9 @@ public Task CloseClientConnections(CancellationToken token)
     {
         throw new NotImplementedException();
     }
+
+    public IAsyncEnumerable<GroupMember> ListConnectionsInGroupAsync(string groupName, int? top)
+    {
+        throw new NotImplementedException();
+    }
 }