possibly fixed timing issue in test

Frameworks/MQTTnet.AspnetCore/MqttHostedServer.cs

@@ -11,8 +11,14 @@ namespace MQTTnet.AspNetCore
 {
     public class MqttHostedServer : MqttServer, IHostedService
     {
-        public MqttHostedServer(IOptions<MqttServerOptions> options, IEnumerable<IMqttServerAdapter> adapters, ILogger<MqttServer> logger, MqttClientSessionsManager clientSessionsManager) 
+        public MqttHostedServer(
-            : base(options, adapters, logger, clientSessionsManager)
+            IOptions<MqttServerOptions> options,
+            IEnumerable<IMqttServerAdapter> adapters,
+            ILogger<MqttServer> logger, 
+            MqttClientSessionsManager clientSessionsManager,
+            IMqttClientRetainedMessageManager clientRetainedMessageManager
+            ) 
+            : base(options, adapters, logger, clientSessionsManager, clientRetainedMessageManager)
         {
         }
 

Frameworks/MQTTnet.NetStandard/MqttFactory.cs

@@ -99,7 +99,9 @@ namespace MQTTnet
                 clientSessionsManager,
                 _serviceProvider.GetRequiredService<MqttClientSubscriptionsManager>(),
                 _serviceProvider.GetRequiredService<ILogger<MqttClientSession>>(),
-                _serviceProvider.GetRequiredService<ILogger<MqttClientPendingMessagesQueue>>());
+                _serviceProvider.GetRequiredService<ILogger<MqttClientPendingMessagesQueue>>(),
+                _serviceProvider.GetRequiredService<IMqttClientRetainedMessageManager>()
+                );
         }
 
         public IMqttClient CreateMqttClient()

Frameworks/MQTTnet.NetStandard/ServiceCollectionExtensions.cs

@@ -33,9 +33,9 @@ namespace MQTTnet
             services.AddTransient<IMqttServerAdapter, MqttServerAdapter>();
             services.AddTransient<IMqttPacketSerializer, MqttPacketSerializer>();
 
-            services.AddTransient<MqttClientSessionsManager>();
+            services.AddSingleton<MqttClientSessionsManager>();
             services.AddTransient<MqttClientSubscriptionsManager>();
-            services.AddTransient<MqttClientRetainedMessagesManager>();
+            services.AddSingleton<IMqttClientRetainedMessageManager, MqttClientRetainedMessagesManager>();
             return services;
         }
 

MQTTnet.Core/Server/IMqttClientRetainedMessageManager.cs

@@ -0,0 +1,15 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using MQTTnet.Core.Packets;
+
+namespace MQTTnet.Core.Server
+{
+    public interface IMqttClientRetainedMessageManager
+    {
+        Task LoadMessagesAsync();
+
+        Task HandleMessageAsync(string clientId, MqttApplicationMessage applicationMessage);
+
+        List<MqttApplicationMessage> GetMessages(MqttSubscribePacket subscribePacket);
+    }
+}

MQTTnet.Core/Server/MqttClientRetainedMessagesManager.cs

@@ -8,7 +8,7 @@ using Microsoft.Extensions.Options;
 
 namespace MQTTnet.Core.Server
 {
-    public sealed class MqttClientRetainedMessagesManager
+    public sealed class MqttClientRetainedMessagesManager : IMqttClientRetainedMessageManager
     {
         private readonly Dictionary<string, MqttApplicationMessage> _retainedMessages = new Dictionary<string, MqttApplicationMessage>();
         private readonly ILogger<MqttClientRetainedMessagesManager> _logger;

MQTTnet.Core/Server/MqttClientSession.cs

@@ -15,6 +15,7 @@ namespace MQTTnet.Core.Server
 {
     public sealed class MqttClientSession : IDisposable
     {
+        private readonly IMqttClientRetainedMessageManager _clientRetainedMessageManager;
         private readonly HashSet<ushort> _unacknowledgedPublishPackets = new HashSet<ushort>();
 
         private readonly MqttClientSubscriptionsManager _subscriptionsManager;
@@ -33,10 +34,12 @@ namespace MQTTnet.Core.Server
             MqttClientSessionsManager sessionsManager,
             MqttClientSubscriptionsManager subscriptionsManager,
             ILogger<MqttClientSession> logger, 
-            ILogger<MqttClientPendingMessagesQueue> messageQueueLogger)
+            ILogger<MqttClientPendingMessagesQueue> messageQueueLogger,
+            IMqttClientRetainedMessageManager clientRetainedMessageManager)
         {
+            _clientRetainedMessageManager = clientRetainedMessageManager ?? throw new ArgumentNullException(nameof(clientRetainedMessageManager));
             _sessionsManager = sessionsManager ?? throw new ArgumentNullException(nameof(sessionsManager));
-            _subscriptionsManager = subscriptionsManager ?? throw new ArgumentNullException(nameof(sessionsManager));
+            _subscriptionsManager = subscriptionsManager ?? throw new ArgumentNullException(nameof(subscriptionsManager));
             _logger = logger ?? throw new ArgumentNullException(nameof(logger));
 
             ClientId = clientId;
@@ -206,7 +209,7 @@ namespace MQTTnet.Core.Server
 
         private void EnqueueRetainedMessages(MqttSubscribePacket subscribePacket)
         {
-            var retainedMessages = _sessionsManager.RetainedMessagesManager.GetMessages(subscribePacket);
+            var retainedMessages = _clientRetainedMessageManager.GetMessages(subscribePacket);
             foreach (var publishPacket in retainedMessages)
             {
                 EnqueuePublishPacket(publishPacket.ToPublishPacket());
@@ -227,7 +230,7 @@ namespace MQTTnet.Core.Server
 
             if (applicationMessage.Retain)
             {
-                await _sessionsManager.RetainedMessagesManager.HandleMessageAsync(ClientId, applicationMessage);
+                await _clientRetainedMessageManager.HandleMessageAsync(ClientId, applicationMessage);
             }
 
             switch (applicationMessage.QualityOfServiceLevel)

MQTTnet.Core/Server/MqttClientSessionsManager.cs

@@ -24,12 +24,10 @@ namespace MQTTnet.Core.Server
         public MqttClientSessionsManager(
             IOptions<MqttServerOptions> options, 
             ILogger<MqttClientSessionsManager> logger,
-            MqttClientRetainedMessagesManager retainedMessagesManager, 
             IMqttClientSesssionFactory clientSesssionFactory)
         {
             _logger = logger ?? throw new ArgumentNullException(nameof(logger));
             _options = options.Value ?? throw new ArgumentNullException(nameof(options));
-            RetainedMessagesManager = retainedMessagesManager ?? throw new ArgumentNullException(nameof(options));
             _clientSesssionFactory = clientSesssionFactory ?? throw new ArgumentNullException(nameof(clientSesssionFactory));
         }
 
@@ -37,8 +35,6 @@ namespace MQTTnet.Core.Server
         public event EventHandler<MqttClientDisconnectedEventArgs> ClientDisconnected;
         public event EventHandler<MqttApplicationMessageReceivedEventArgs> ApplicationMessageReceived;
 
-        public MqttClientRetainedMessagesManager RetainedMessagesManager { get; }
-
         public async Task RunClientSessionAsync(IMqttCommunicationAdapter clientAdapter, CancellationToken cancellationToken)
         {
             var clientId = string.Empty;

MQTTnet.Core/Server/MqttServer.cs

@@ -6,11 +6,13 @@ using MQTTnet.Core.Adapter;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
 using System.Linq;
+using Microsoft.Extensions.DependencyInjection;
 
 namespace MQTTnet.Core.Server
 {
     public class MqttServer : IMqttServer
     {
+        private readonly IMqttClientRetainedMessageManager _clientRetainedMessageManager;
         private readonly ILogger<MqttServer> _logger;
         private readonly MqttClientSessionsManager _clientSessionsManager;
         private readonly ICollection<IMqttServerAdapter> _adapters;
@@ -18,11 +20,18 @@ namespace MQTTnet.Core.Server
 
         private CancellationTokenSource _cancellationTokenSource;
 
-        public MqttServer(IOptions<MqttServerOptions> options, IEnumerable<IMqttServerAdapter> adapters, ILogger<MqttServer> logger, MqttClientSessionsManager clientSessionsManager)
+        public MqttServer(
+            IOptions<MqttServerOptions> options, 
+            IEnumerable<IMqttServerAdapter> adapters,
+            ILogger<MqttServer> logger,
+            MqttClientSessionsManager clientSessionsManager,
+            IMqttClientRetainedMessageManager clientRetainedMessageManager
+            )
         {
             _options = options.Value ?? throw new ArgumentNullException(nameof(options));
             _logger = logger ?? throw new ArgumentNullException(nameof(logger));
             _clientSessionsManager = clientSessionsManager ?? throw new ArgumentNullException(nameof(clientSessionsManager));
+            _clientRetainedMessageManager = clientRetainedMessageManager ?? throw new ArgumentNullException(nameof(clientRetainedMessageManager));
 
             if (adapters == null)
             {
@@ -79,7 +88,7 @@ namespace MQTTnet.Core.Server
 
             _cancellationTokenSource = new CancellationTokenSource();
 
-            await _clientSessionsManager.RetainedMessagesManager.LoadMessagesAsync();
+            await _clientRetainedMessageManager.LoadMessagesAsync();
 
             foreach (var adapter in _adapters)
             {

Tests/MQTTnet.Core.Tests/MqttServerTests.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
@@ -8,6 +9,7 @@ using MQTTnet.Core.Client;
 using MQTTnet.Core.Protocol;
 using MQTTnet.Core.Server;
 using Microsoft.Extensions.DependencyInjection;
+using MQTTnet.Core.Packets;
 
 namespace MQTTnet.Core.Tests
 {
@@ -210,6 +212,7 @@ namespace MQTTnet.Core.Tests
                 .BuildServiceProvider();
 
             var s = new MqttFactory(services).CreateMqttServer();
+            var retainMessagemanager = services.GetRequiredService<IMqttClientRetainedMessageManager>();
 
             var receivedMessagesCount = 0;
             try
@@ -220,6 +223,20 @@ namespace MQTTnet.Core.Tests
                 await c1.PublishAsync(new MqttApplicationMessageBuilder().WithTopic("retained").WithPayload(new byte[3]).WithRetainFlag().Build());
                 await c1.DisconnectAsync();
 
+                var subscribe = new MqttSubscribePacket()
+                {
+                    TopicFilters = new List<TopicFilter>()
+                    {
+                        new TopicFilter("retained", MqttQualityOfServiceLevel.AtMostOnce)
+                    }
+                };
+
+                //make shure the retainedMessageManagerreceived the package
+                while (retainMessagemanager.GetMessages(subscribe).Any())
+                {
+                    await Task.Delay(TimeSpan.FromMilliseconds(10));
+                }
+
                 var c2 = await serverAdapter.ConnectTestClient(s, "c2");
                 c2.ApplicationMessageReceived += (_, __) => receivedMessagesCount++;
                 await c2.SubscribeAsync(new TopicFilter("retained", MqttQualityOfServiceLevel.AtMostOnce));