Add Unit Tests

Fixes https://github.com/dotnet/MQTTnet/issues/1765.

.github/workflows/ReleaseNotes.md

@@ -1,13 +1,4 @@
-* [Core] Add validation of maximum string lengths (#1718).
+* [Client] Fixed _PlatformNotSupportedException_ when using Blazor (#1755, thanks to @Nickztar).
-* [Core] Added .NET 4.8 builds (#1729).
+* [Server] Fixed _NullReferenceException_ in retained messages management (#1762, thanks to @logicaloud).
-* [Core] Exposed more details of DISCONNECT packet in log (#1729).
+* [Server] Exposed new option which allows disabling packet fragmentation (#1753).
-* [Core] Fixed _ArgumentNullException_ in _ConvertPayloadToString_ (#1745, thanks to @ramonsmits).
+* [Server] Expired sessions will no longer be used when a client connects (#1756).
-* [Client] Added overloads for setting packet payload and will payload (#1720).
-* [Client] The proper connect result is now exposed in the _Disconnected_ event when authentication fails (#1139).
-* [Client] Exposed _UseDefaultCredentials_ and more for Web Socket options and proxy options (#1734, thanks to @impworks).
-* [Client] Exposed more TLS options (#1729).
-* [Client] Fixed wrong return code conversion (#1729).
-* [Client] Added an option to avoid throwing an exception when the server returned a proper non success (but valid) response (#1681).
-* [Server] Improved performance by changing internal locking strategy for subscriptions (#1716, thanks to @zeheng).
-* [Server] Fixed exceptions when clients are connecting and disconnecting very fast while accessing the client status for connection validation (#1742).
-* [Server] Exposed more properties in _ClientConnectedEventArgs_ (#1738).

Samples/Client/Client_Subscribe_Samples.cs

@@ -6,6 +6,7 @@
 // ReSharper disable UnusedMember.Global
 // ReSharper disable InconsistentNaming
 
+using MQTTnet;
 using MQTTnet.Client;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;

Samples/Server/Server_Retained_Messages_Samples.cs

@@ -7,6 +7,8 @@
 // ReSharper disable InconsistentNaming
 
 using System.Text.Json;
+using MQTTnet.Packets;
+using MQTTnet.Protocol;
 
 namespace MQTTnet.Samples.Server;
 
@@ -32,7 +34,10 @@ public static class Server_Retained_Messages_Samples
             {
                 try
                 {
-                    eventArgs.LoadedRetainedMessages = await JsonSerializer.DeserializeAsync<List<MqttApplicationMessage>>(File.OpenRead(storePath));
+                    var models = await JsonSerializer.DeserializeAsync<List<MqttRetainedMessageModel>>(File.OpenRead(storePath)) ?? new List<MqttRetainedMessageModel>();
+                    var retainedMessages = models.Select(m => m.ToApplicationMessage()).ToList();
+
+                    eventArgs.LoadedRetainedMessages = retainedMessages;
                     Console.WriteLine("Retained messages loaded.");
                 }
                 catch (FileNotFoundException)
@@ -56,7 +61,9 @@ public static class Server_Retained_Messages_Samples
                     // used to write all retained messages to dedicated files etc. Then all files must be loaded and a full list
                     // of retained messages must be provided in the loaded event.
 
-                    var buffer = JsonSerializer.SerializeToUtf8Bytes(eventArgs.StoredRetainedMessages);
+                    var models = eventArgs.StoredRetainedMessages.Select(MqttRetainedMessageModel.Create);
+
+                    var buffer = JsonSerializer.SerializeToUtf8Bytes(models);
                     await File.WriteAllBytesAsync(storePath, buffer);
                     Console.WriteLine("Retained messages saved.");
                 }
@@ -79,4 +86,59 @@ public static class Server_Retained_Messages_Samples
             Console.ReadLine();
         }
     }
+
+    sealed class MqttRetainedMessageModel
+    {
+        public string? ContentType { get; set; }
+        public byte[]? CorrelationData { get; set; }
+        public byte[]? Payload { get; set; }
+        public MqttPayloadFormatIndicator PayloadFormatIndicator { get; set; }
+        public MqttQualityOfServiceLevel QualityOfServiceLevel { get; set; }
+        public string? ResponseTopic { get; set; }
+        public string? Topic { get; set; }
+        public List<MqttUserProperty>? UserProperties { get; set; }
+
+        public static MqttRetainedMessageModel Create(MqttApplicationMessage message)
+        {
+            if (message == null)
+            {
+                throw new ArgumentNullException(nameof(message));
+            }
+
+            return new MqttRetainedMessageModel
+            {
+                Topic = message.Topic,
+
+                // Create a copy of the buffer from the payload segment because 
+                // it cannot be serialized and deserialized with the JSON serializer.
+                Payload = message.PayloadSegment.ToArray(),
+                UserProperties = message.UserProperties,
+                ResponseTopic = message.ResponseTopic,
+                CorrelationData = message.CorrelationData,
+                ContentType = message.ContentType,
+                PayloadFormatIndicator = message.PayloadFormatIndicator,
+                QualityOfServiceLevel = message.QualityOfServiceLevel
+
+                // Other properties like "Retain" are not if interest in the storage.
+                // That's why a custom model makes sense.
+            };
+        }
+
+        public MqttApplicationMessage ToApplicationMessage()
+        {
+            return new MqttApplicationMessage
+            {
+                Topic = Topic,
+                PayloadSegment = new ArraySegment<byte>(Payload ?? Array.Empty<byte>()),
+                PayloadFormatIndicator = PayloadFormatIndicator,
+                ResponseTopic = ResponseTopic,
+                CorrelationData = CorrelationData,
+                ContentType = ContentType,
+                UserProperties = UserProperties,
+                QualityOfServiceLevel = QualityOfServiceLevel,
+                Dup = false,
+                Retain = true
+            };
+        }
+    }
 }

Source/MQTTnet.Extensions.Rpc/MqttRpcClient.cs

@@ -69,6 +69,11 @@ namespace MQTTnet.Extensions.Rpc
                 throw new ArgumentNullException(nameof(methodName));
             }
 
+            if (!_mqttClient.IsConnected)
+            {
+                throw new MqttClientDisconnectedException(null);
+            }
+
             var context = new TopicGenerationContext(_mqttClient, _options, methodName, qualityOfServiceLevel);
             var topicNames = _options.TopicGenerationStrategy.CreateRpcTopics(context);
 

Source/MQTTnet.Tests/Clients/MqttClient/MqttClient_Connection_Tests.cs

@@ -9,6 +9,7 @@ using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Client;
 using MQTTnet.Exceptions;
+using MQTTnet.Extensions.Rpc;
 using MQTTnet.Formatter;
 using MQTTnet.Internal;
 using MQTTnet.Packets;
@@ -20,6 +21,38 @@ namespace MQTTnet.Tests.Clients.MqttClient
     [TestClass]
     public sealed class MqttClient_Connection_Tests : BaseTestClass
     {
+        [TestMethod]
+        public async Task Connect_Disconnect_Connect()
+        {
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                await testEnvironment.StartServer();
+
+                var clientOptions = testEnvironment.CreateDefaultClientOptions();
+                var client = testEnvironment.CreateClient();
+
+                await client.ConnectAsync(clientOptions);
+                await client.DisconnectAsync();
+                await client.ConnectAsync(clientOptions);
+            }
+        }
+
+        [TestMethod]
+        [ExpectedException(typeof(InvalidOperationException))]
+        public async Task Connect_Multiple_Times_Should_Fail()
+        {
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                await testEnvironment.StartServer();
+
+                var clientOptions = testEnvironment.CreateDefaultClientOptions();
+                var client = testEnvironment.CreateClient();
+
+                await client.ConnectAsync(clientOptions);
+                await client.ConnectAsync(clientOptions);
+            }
+        }
+
         [TestMethod]
         [ExpectedException(typeof(MqttCommunicationException))]
         public async Task Connect_To_Invalid_Server_Port_Not_Opened()
@@ -196,5 +229,17 @@ namespace MQTTnet.Tests.Clients.MqttClient
                 Assert.AreEqual(response.UserProperties[0].Value, "Value");
             }
         }
+
+        [TestMethod]
+        [ExpectedException(typeof(MqttClientDisconnectedException))]
+        public async Task Rpc_Client_Not_Connected()
+        {
+            var factory = new MqttFactory();
+            using (var client = factory.CreateMqttClient())
+            {
+                var rpcClient = factory.CreateMqttRpcClient(client);
+                await rpcClient.ExecuteAsync("aaa", new byte[] { 1, 2, 3 }, MqttQualityOfServiceLevel.AtLeastOnce);
+            }
+        }
     }
 }

Source/MQTTnet.Tests/Clients/MqttClient/MqttClient_Publish_Tests.cs

@@ -0,0 +1,59 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Client;
+using MQTTnet.Protocol;
+using MQTTnet.Server;
+
+namespace MQTTnet.Tests.Clients.MqttClient
+{
+    [TestClass]
+    public sealed class MqttClient_Publish_Tests : BaseTestClass
+    {
+        [TestMethod]
+        public async Task Acknowledge_After_Disconnect_Should_Fail()
+        {
+            using (var testEnvironment = CreateTestEnvironment())
+            {
+                var server = await testEnvironment.StartServer();
+
+                var client = await testEnvironment.ConnectClient();
+                await client.SubscribeAsync("TEST", MqttQualityOfServiceLevel.AtLeastOnce);
+
+                var flag = false;
+                
+                client.ApplicationMessageReceivedAsync += async args =>
+                {
+                    try
+                    {
+                        args.AutoAcknowledge = false;
+                        
+                        await client.DisconnectAsync();
+                        await args.AcknowledgeAsync();
+
+                        flag = true;
+                    }
+                    catch (Exception exception)
+                    {
+                        
+                    }
+                };
+
+                await server.InjectApplicationMessageAsync(
+                    new MqttApplicationMessage
+                    {
+                        Topic = "TEST"
+                    });
+
+                SpinWait.SpinUntil(() => flag, TimeSpan.FromSeconds(10));
+                
+                Assert.IsTrue(flag);
+            }
+        }
+    }
+}

Source/MQTTnet.Tests/Clients/MqttClient/MqttClient_Tests.cs

@@ -70,37 +70,7 @@ namespace MQTTnet.Tests.Clients.MqttClient
             }
         }
        
-        [TestMethod]
-        public async Task Connect_Disconnect_Connect()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                await testEnvironment.StartServer();
 
-                var clientOptions = testEnvironment.CreateDefaultClientOptions();
-                var client = testEnvironment.CreateClient();
-
-                await client.ConnectAsync(clientOptions);
-                await client.DisconnectAsync();
-                await client.ConnectAsync(clientOptions);
-            }
-        }
-        
-        [TestMethod]
-        [ExpectedException(typeof(InvalidOperationException))]
-        public async Task Connect_Multiple_Times_Should_Fail()
-        {
-            using (var testEnvironment = CreateTestEnvironment())
-            {
-                await testEnvironment.StartServer();
-
-                var clientOptions = testEnvironment.CreateDefaultClientOptions();
-                var client = testEnvironment.CreateClient();
-
-                await client.ConnectAsync(clientOptions);
-                await client.ConnectAsync(clientOptions);
-            }
-        }
 
         [TestMethod]
         public async Task Disconnect_Event_Contains_Exception()

Source/MQTTnet.Tests/Clients/MqttClientOptionsBuilder_Tests.cs

@@ -10,7 +10,7 @@ using MQTTnet.Client;
 namespace MQTTnet.Tests.Clients
 {
     [TestClass]
-    public class MqttClientOptionsBuilder_Tests
+    public sealed class MqttClientOptionsBuilder_Tests
     {
         [TestMethod]
         public void WithConnectionUri_Credential_Test()

Source/MQTTnet.Tests/Extension_Tests.cs

@@ -1,98 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-using System.Linq;
-using System.Threading;
-using System.Threading.Tasks;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using MQTTnet.Exceptions;
-using MQTTnet.Internal;
-
-namespace MQTTnet.Tests
-{
-    [TestClass]
-    public class Extension_Tests
-    {
-        [ExpectedException(typeof(MqttCommunicationTimedOutException))]
-        [TestMethod]
-        public async Task TimeoutAfter()
-        {
-            await MqttTaskTimeout.WaitAsync(ct => Task.Delay(TimeSpan.FromMilliseconds(500), ct),
-                TimeSpan.FromMilliseconds(100), CancellationToken.None);
-        }
-
-        [ExpectedException(typeof(MqttCommunicationTimedOutException))]
-        [TestMethod]
-        public async Task TimeoutAfterWithResult()
-        {
-            await MqttTaskTimeout.WaitAsync(
-                ct => Task.Delay(TimeSpan.FromMilliseconds(500), ct).ContinueWith(t => 5, ct),
-                TimeSpan.FromMilliseconds(100), CancellationToken.None);
-        }
-        
-        [TestMethod]
-        public async Task TimeoutAfterWithInnerException()
-        {
-            try
-            {
-                await MqttTaskTimeout.WaitAsync(ct => Task.Run(() =>
-                {
-                    var iis = new int[0];
-                    iis[1] = 0;
-                }, ct), TimeSpan.FromSeconds(1), CancellationToken.None);
-
-                Assert.Fail();
-            }
-            catch (Exception e)
-            {
-                Assert.IsTrue(e is IndexOutOfRangeException);
-            }
-        }
-
-        [TestMethod]
-        public async Task TimeoutAfterWithInnerExceptionWithResult()
-        {
-            try
-            {
-                await MqttTaskTimeout.WaitAsync(ct => Task.Run(() =>
-                {
-                    var iis = new int[0];
-                    iis[1] = 0;
-                    return iis[0];
-                }, ct), TimeSpan.FromSeconds(1), CancellationToken.None);
-
-                Assert.Fail();
-            }
-            catch (Exception e)
-            {
-                Assert.IsTrue(e is IndexOutOfRangeException);
-            }
-        }
-
-        [TestMethod]
-        public async Task TimeoutAfterMemoryUsage()
-        {
-            var initialMemory = GC.GetTotalMemory(true);
-
-            var tasks = Enumerable.Range(0, 100000)
-                .Select(i =>
-                {
-                    return MqttTaskTimeout.WaitAsync(ct => Task.Delay(TimeSpan.FromMilliseconds(1), ct),
-                        TimeSpan.FromMinutes(1), CancellationToken.None);
-                });
-
-            await Task.WhenAll(tasks);
-            AssertIsLess(initialMemory + 2_000_000, GC.GetTotalMemory(true));
-        }
-
-        static void AssertIsLess(long bound, long actual)
-        {
-            if (bound < actual)
-            {
-                Assert.Fail($"value must be less than {bound:N0} but is {actual:N0}");
-            }
-        }
-    }
-}

Source/MQTTnet.Tests/Mockups/TestEnvironment.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
@@ -24,10 +25,9 @@ namespace MQTTnet.Tests.Mockups
     public sealed class TestEnvironment : IDisposable
     {
         readonly List<string> _clientErrors = new List<string>();
-        readonly List<IMqttClient> _clients = new List<IMqttClient>();
+        readonly ConcurrentBag<IMqttClient> _clients = new ConcurrentBag<IMqttClient>();
-
         readonly List<Exception> _exceptions = new List<Exception>();
-        readonly List<ILowLevelMqttClient> _lowLevelClients = new List<ILowLevelMqttClient>();
+        readonly ConcurrentBag<ILowLevelMqttClient> _lowLevelClients = new ConcurrentBag<ILowLevelMqttClient>();
         readonly MqttProtocolVersion _protocolVersion;
         readonly List<string> _serverErrors = new List<string>();
 
@@ -65,9 +65,12 @@ namespace MQTTnet.Tests.Mockups
 
                 if (e.LogMessage.Level == MqttNetLogLevel.Error)
                 {
-                    lock (_clientErrors)
+                    if (!IgnoreClientLogErrors)
                     {
-                        _clientErrors.Add(e.LogMessage.ToString());
+                        lock (_clientErrors)
+                        {
+                            _clientErrors.Add(e.LogMessage.ToString());
+                        }
                     }
                 }
             };
@@ -212,30 +215,27 @@ namespace MQTTnet.Tests.Mockups
 
         public IMqttClient CreateClient()
         {
-            lock (_clients)
+            var logger = EnableLogger ? (IMqttNetLogger)ClientLogger : MqttNetNullLogger.Instance;
+            
+            var client = Factory.CreateMqttClient(logger);
+            client.ConnectingAsync += e =>
             {
-                var logger = EnableLogger ? (IMqttNetLogger)ClientLogger : new MqttNetNullLogger();
+                if (TestContext != null)
-
-                var client = Factory.CreateMqttClient(logger);
-                _clients.Add(client);
-
-                client.ConnectingAsync += e =>
                 {
-                    if (TestContext != null)
+                    var clientOptions = e.ClientOptions;
+                    var existingClientId = clientOptions.ClientId;
+                    if (existingClientId != null && !existingClientId.StartsWith(TestContext.TestName))
                     {
-                        var clientOptions = e.ClientOptions;
+                        clientOptions.ClientId = TestContext.TestName + "_" + existingClientId;
-                        var existingClientId = clientOptions.ClientId;
-                        if (existingClientId != null && !existingClientId.StartsWith(TestContext.TestName))
-                        {
-                            clientOptions.ClientId = TestContext.TestName + "_" + existingClientId;
-                        }
                     }
+                }
 
-                    return CompletedTask.Instance;
+                return CompletedTask.Instance;
-                };
+            };
             
-                return client;
+            _clients.Add(client);
-            }
+            
+            return client;
         }
 
         public MqttClientOptions CreateDefaultClientOptions()
@@ -250,13 +250,10 @@ namespace MQTTnet.Tests.Mockups
 
         public ILowLevelMqttClient CreateLowLevelClient()
         {
-            lock (_clients)
+            var client = Factory.CreateLowLevelMqttClient(ClientLogger);
-            {
+            _lowLevelClients.Add(client);
-                var client = Factory.CreateLowLevelMqttClient(ClientLogger);
-                _lowLevelClients.Add(client);
 
-                return client;
+            return client;
-            }
         }
 
         public MqttServer CreateServer(MqttServerOptions options)
@@ -383,13 +380,16 @@ namespace MQTTnet.Tests.Mockups
                 }
             }
 
-            lock (_clientErrors)
+            if (!IgnoreClientLogErrors)
             {
-                if (!IgnoreClientLogErrors && _clientErrors.Count > 0)
+                lock (_clientErrors)
                 {
-                    var message = $"Client(s) had {_clientErrors.Count} errors (${string.Join(Environment.NewLine, _clientErrors)})";
+                    if (_clientErrors.Count > 0)
-                    Console.WriteLine(message);
+                    {
-                    throw new Exception(message);
+                        var message = $"Client(s) had {_clientErrors.Count} errors (${string.Join(Environment.NewLine, _clientErrors)})";
+                        Console.WriteLine(message);
+                        throw new Exception(message);
+                    }
                 }
             }
         }

Source/MQTTnet.Tests/Server/General.cs

@@ -598,8 +598,7 @@ namespace MQTTnet.Tests.Server
                 // c
                 var c1 = await testEnvironment.ConnectClient(clientOptionsBuilder);
 
-                await Task.Delay(500);
+                await LongTestDelay();
-
                 var flow = string.Join(string.Empty, events);
                 Assert.AreEqual("c", flow);
 
@@ -607,10 +606,8 @@ namespace MQTTnet.Tests.Server
                 // Connect client with same client ID. Should disconnect existing client.
                 var c2 = await testEnvironment.ConnectClient(clientOptionsBuilder);
 
-                await Task.Delay(500);
+                await LongTestDelay();
-
                 flow = string.Join(string.Empty, events);
-
                 Assert.AreEqual("cdc", flow);
 
                 c2.ApplicationMessageReceivedAsync += e =>
@@ -628,8 +625,7 @@ namespace MQTTnet.Tests.Server
                 // r
                 await c2.PublishStringAsync("topic");
 
-                await Task.Delay(500);
+                await LongTestDelay();
-
                 flow = string.Join(string.Empty, events);
                 Assert.AreEqual("cdcr", flow);
 
@@ -639,16 +635,17 @@ namespace MQTTnet.Tests.Server
                 await c1.TryDisconnectAsync();
                 Assert.AreEqual(false, c1.IsConnected);
 
-                await Task.Delay(500);
+                await LongTestDelay();
 
                 // d
                 Assert.AreEqual(true, c2.IsConnected);
                 await c2.DisconnectAsync();
 
-                await Task.Delay(500);
+                await LongTestDelay();
 
                 await server.StopAsync();
 
+                await LongTestDelay();
                 flow = string.Join(string.Empty, events);
                 Assert.AreEqual("cdcrd", flow);
             }
@@ -852,11 +849,11 @@ namespace MQTTnet.Tests.Server
                     return CompletedTask.Instance;
                 };
 
-                await Task.Delay(100);
+                // Stopping the server should disconnect the connection with the client
-
+                // which, it turn, will fire the disconnected event at the client.
                 await server.StopAsync();
 
-                await Task.Delay(100);
+                await LongTestDelay();
 
                 Assert.AreEqual(1, disconnectCalled);
             }

Source/MQTTnet.Tests/Server/MqttRetainedMessageManager_Tests.cs

@@ -0,0 +1,25 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace MQTTnet.Tests.Server
+{
+    [TestClass]
+    public sealed class MqttRetainedMessageManager_Tests
+    {
+        [TestMethod]
+        public async Task MqttRetainedMessageManager_GetUndefinedTopic()
+        {
+            var logger = new Mockups.TestLogger();
+            var eventContainer = new MQTTnet.Server.MqttServerEventContainer();
+            var retainedMessagesManager = new MQTTnet.Server.MqttRetainedMessagesManager(eventContainer, logger);
+            var task = retainedMessagesManager.GetMessage("undefined");
+            Assert.IsNotNull(task, "Task should not be null");
+            var result = await task;
+            Assert.IsNull(result, "Null result expected");
+        }
+    }
+}

Source/MQTTnet.Tests/Server/MqttSubscriptionsManager_Tests.cs

@@ -221,7 +221,10 @@ namespace MQTTnet.Tests.Server
             var eventContainer = new MqttServerEventContainer();
             var clientSessionManager = new MqttClientSessionsManager(options, retainedMessagesManager, eventContainer, logger);
 
-            var session = new MqttSession("", false, new ConcurrentDictionary<object, object>(), options, eventContainer, retainedMessagesManager, clientSessionManager);
+            var session = new MqttSession(new MqttConnectPacket
+            {
+                ClientId = ""
+            }, new ConcurrentDictionary<object, object>(), options, eventContainer, retainedMessagesManager, clientSessionManager);
 
             _subscriptionsManager = new MqttClientSubscriptionsManager(session, new MqttServerEventContainer(), retainedMessagesManager, clientSessionManager);
         }

Source/MQTTnet.Tests/Server/Session_Tests.cs

@@ -70,6 +70,28 @@ namespace MQTTnet.Tests.Server
             }
         }
 
+        [TestMethod]
+        public async Task Do_Not_Use_Expired_Session()
+        {
+            using (var testEnvironment = CreateTestEnvironment(MqttProtocolVersion.V500))
+            {
+                await testEnvironment.StartServer(o => o.WithPersistentSessions());
+
+                var c1 = await testEnvironment.ConnectClient(o => o.WithClientId("Client1").WithCleanSession(false).WithSessionExpiryInterval(3));
+
+                // Kill the client connection and ensure that the session will stay there but is expired after 3 seconds!
+                c1.Dispose();
+
+                await Task.Delay(TimeSpan.FromSeconds(6));
+
+                c1 = testEnvironment.CreateClient();
+                var options = testEnvironment.CreateDefaultClientOptionsBuilder().WithClientId("Client1").WithCleanSession(false).WithSessionExpiryInterval(3).Build();
+
+                var connectResult = await c1.ConnectAsync(options);
+                Assert.AreEqual(false, connectResult.IsSessionPresent);
+            }
+        }
+
         [TestMethod]
         public async Task Fire_Deleted_Event()
         {
@@ -134,16 +156,12 @@ namespace MQTTnet.Tests.Server
 
                 await testEnvironment.StartServer();
 
-                var options = new MqttClientOptionsBuilder().WithClientId("1").WithTimeout(TimeSpan.FromSeconds(1)).WithProtocolVersion(protocolVersion);
+                var options = new MqttClientOptionsBuilder().WithClientId("1").WithTimeout(TimeSpan.FromSeconds(10)).WithProtocolVersion(protocolVersion);
 
                 var hasReceive = false;
-
                 void OnReceive()
                 {
-                    if (!hasReceive)
+                    hasReceive = true;
-                    {
-                        hasReceive = true;
-                    }
                 }
 
                 // Try to connect 50 clients at the same time.
@@ -356,7 +374,7 @@ namespace MQTTnet.Tests.Server
                     return CompletedTask.Instance;
                 };
 
-                using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(5)))
+                using (var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(30)))
                 {
                     await client.SubscribeAsync("aaa", MqttQualityOfServiceLevel.AtMostOnce, timeout.Token).ConfigureAwait(false);
                 }

Source/MQTTnet.Tests/Server/Subscription_TopicHash_Tests.cs

@@ -557,7 +557,7 @@ namespace MQTTnet.Tests.Server
             var eventContainer = new MqttServerEventContainer();
             var retainedMessagesManager = new MqttRetainedMessagesManager(eventContainer, logger);
             var sessionManager = new MqttClientSessionsManager(serverOptions, retainedMessagesManager, eventContainer, logger);
-            _clientSession = new MqttSession(clientId, false, new Dictionary<object, object>(), serverOptions, eventContainer, retainedMessagesManager, sessionManager);
+            _clientSession = new MqttSession(new MqttConnectPacket{ ClientId = clientId }, new Dictionary<object, object>(), serverOptions, eventContainer, retainedMessagesManager, sessionManager);
 
             List<string> topicsToSubscribe;
 

Source/MQTTnet/Client/MqttClient.cs

@@ -442,10 +442,18 @@ namespace MQTTnet.Client
                 {
                     result = MqttClientResultFactory.ConnectResult.Create(connAckPacket, _adapter.PacketFormatterAdapter.ProtocolVersion);
                 }
-                else
+                else if (receivedPacket is MqttAuthPacket)
                 {
                     throw new NotSupportedException("Extended authentication handler is not yet supported");
                 }
+                else if (receivedPacket == null)
+                {
+                    throw new MqttCommunicationException("Connection closed.");
+                }
+                else
+                {
+                    throw new InvalidOperationException($"Received an unexpected MQTT packet ({receivedPacket}).");
+                }
             }
             catch (Exception exception)
             {
@@ -547,7 +555,7 @@ namespace MQTTnet.Client
 
             try
             {
-                _packetDispatcher.Dispose(new MqttClientDisconnectedException(exception));
+                _packetDispatcher?.Dispose(new MqttClientDisconnectedException(exception));
 
                 var receiverTask = _packetReceiverTask.WaitAsync(sender, _logger);
                 var publishPacketReceiverTask = _publishPacketReceiverTask.WaitAsync(sender, _logger);
@@ -873,6 +881,7 @@ namespace MQTTnet.Client
 
             _lastPacketSentTimestamp = DateTime.UtcNow;
 
+            //ThrowIfNotConnected();
             return _adapter.SendPacketAsync(packet, cancellationToken);
         }
 

Source/MQTTnet/Client/Receiving/MqttApplicationMessageReceivedEventArgs.cs

@@ -77,7 +77,7 @@ namespace MQTTnet.Client
 
         internal MqttPublishPacket PublishPacket { get; set; }
 
-        public Task AcknowledgeAsync(CancellationToken cancellationToken)
+        public Task AcknowledgeAsync(CancellationToken cancellationToken = default)
         {
             if (_acknowledgeHandler == null)
             {

Source/MQTTnet/Implementations/MqttTcpServerListener.cs

@@ -231,6 +231,7 @@ namespace MQTTnet.Implementations
                     
                     using (var clientAdapter = new MqttChannelAdapter(tcpChannel, packetFormatterAdapter, _rootLogger))
                     {
+                        clientAdapter.AllowPacketFragmentation = _options.AllowPacketFragmentation;
                         await clientHandler(clientAdapter).ConfigureAwait(false);
                     }
                 }
@@ -255,6 +256,7 @@ namespace MQTTnet.Implementations
             {
                 try
                 {
+                    // ReSharper disable once MethodHasAsyncOverload
                     stream?.Dispose();
                     clientSocket?.Dispose();
                 }

Source/MQTTnet/Implementations/MqttWebSocketChannel.cs

@@ -221,11 +221,23 @@ namespace MQTTnet.Implementations
 
 #if !NETSTANDARD1_3
 #if !WINDOWS_UWP
-            clientWebSocket.Options.UseDefaultCredentials = _options.UseDefaultCredentials;
+            // Only set the value if it is actually true. This property is not supported on all platforms
+            // and will throw a _PlatformNotSupported_ (i.e. WASM) exception when being used regardless of the actual value.
+            if (_options.UseDefaultCredentials)
+            {
+                clientWebSocket.Options.UseDefaultCredentials = _options.UseDefaultCredentials;
+            }
+
+            if (_options.KeepAliveInterval != WebSocket.DefaultKeepAliveInterval)
+            {
+                clientWebSocket.Options.KeepAliveInterval = _options.KeepAliveInterval;
+            }
 #endif
-            clientWebSocket.Options.KeepAliveInterval = _options.KeepAliveInterval;
 #endif
-            clientWebSocket.Options.Credentials = _options.Credentials;
+            if (_options.Credentials != null)
+            {
+                clientWebSocket.Options.Credentials = _options.Credentials;
+            }
             
             var certificateValidationHandler = _options.TlsOptions?.CertificateValidationHandler;
             if (certificateValidationHandler != null)

Source/MQTTnet/Internal/MqttTaskTimeout.cs

@@ -1,38 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for more information.
-
-using System;
-using System.Threading;
-using System.Threading.Tasks;
-using MQTTnet.Exceptions;
-
-namespace MQTTnet.Internal
-{
-    public static class MqttTaskTimeout
-    {
-        public static async Task WaitAsync(Func<CancellationToken, Task> action, TimeSpan timeout, CancellationToken cancellationToken)
-        {
-            if (action == null) throw new ArgumentNullException(nameof(action));
-
-            using (var timeoutCts = new CancellationTokenSource(timeout))
-            using (var linkedCts = CancellationTokenSource.CreateLinkedTokenSource(timeoutCts.Token, cancellationToken))
-            {
-                try
-                {
-                    await action(linkedCts.Token).ConfigureAwait(false);
-                }
-                catch (OperationCanceledException exception)
-                {
-                    var timeoutReached = timeoutCts.IsCancellationRequested && !cancellationToken.IsCancellationRequested;
-                    if (timeoutReached)
-                    {
-                        throw new MqttCommunicationTimedOutException(exception);
-                    }
-
-                    throw;
-                }
-            }
-        }
-    }
-}

Source/MQTTnet/Server/Internal/MqttClient.cs

@@ -104,6 +104,8 @@ namespace MQTTnet.Server
             {
                 IsRunning = false;
                 
+                Session.DisconnectedTimestamp = DateTime.UtcNow;
+
                 _cancellationToken?.TryCancel();
                 _cancellationToken?.Dispose();
                 _cancellationToken = null;

Source/MQTTnet/Server/Internal/MqttClientSessionsManager.cs

@@ -34,7 +34,7 @@ namespace MQTTnet.Server
 
         // The _sessions dictionary contains all session, the _subscriberSessions hash set contains subscriber sessions only.
         // See the MqttSubscription object for a detailed explanation.
-        readonly Dictionary<string, MqttSession> _sessions = new Dictionary<string, MqttSession>(4096);
+        readonly MqttSessionsStorage _sessionsStorage = new MqttSessionsStorage();
 
         readonly ReaderWriterLockSlim _sessionsManagementLock = new ReaderWriterLockSlim();
         readonly HashSet<MqttSession> _subscriberSessions = new HashSet<MqttSession>();
@@ -78,21 +78,16 @@ namespace MQTTnet.Server
             _logger.Verbose("Deleting session for client '{0}'.", clientId);
 
             MqttClient connection;
-
             lock (_clients)
             {
                 _clients.TryGetValue(clientId, out connection);
             }
 
             MqttSession session;
-
             _sessionsManagementLock.EnterWriteLock();
             try
             {
-                _sessions.TryGetValue(clientId, out session);
+                if (_sessionsStorage.TryRemoveSession(clientId, out session))
-                _sessions.Remove(clientId);
-
-                if (session != null)
                 {
                     _subscriberSessions.Remove(session);
                 }
@@ -111,7 +106,7 @@ namespace MQTTnet.Server
             }
             catch (Exception exception)
             {
-                _logger.Error(exception, $"Error while deleting session '{clientId}'.");
+                _logger.Error(exception, "Error while deleting session '{0}'", clientId);
             }
 
             try
@@ -124,12 +119,12 @@ namespace MQTTnet.Server
             }
             catch (Exception exception)
             {
-                _logger.Error(exception, $"Error while executing session deleted event for session '{clientId}'.");
+                _logger.Error(exception, "Error while executing session deleted event for session '{0}'", clientId);
             }
 
             session?.Dispose();
 
-            _logger.Verbose("Session for client '{0}' deleted.", clientId);
+            _logger.Verbose("Session of client '{0}' deleted", clientId);
         }
 
         public async Task<DispatchApplicationMessageResult> DispatchApplicationMessage(
@@ -269,20 +264,14 @@ namespace MQTTnet.Server
             _sessionsManagementLock.EnterWriteLock();
             try
             {
-                foreach (var sessionItem in _sessions)
+                _sessionsStorage.Dispose();
-                {
-                    sessionItem.Value.Dispose();
-                }
             }
             finally
             {
                 _sessionsManagementLock.ExitWriteLock();
             }
 
-            if (_sessionsManagementLock != null)
+            _sessionsManagementLock?.Dispose();
-            {
-                _sessionsManagementLock.Dispose();
-            }
         }
 
         public MqttClient GetClient(string id)
@@ -333,9 +322,9 @@ namespace MQTTnet.Server
             _sessionsManagementLock.EnterReadLock();
             try
             {
-                foreach (var sessionItem in _sessions)
+                foreach (var session in _sessionsStorage.ReadAllSessions())
                 {
-                    var sessionStatus = new MqttSessionStatus(sessionItem.Value);
+                    var sessionStatus = new MqttSessionStatus(session);
                     result.Add(sessionStatus);
                 }
             }
@@ -484,7 +473,7 @@ namespace MQTTnet.Server
         {
             if (!_options.EnablePersistentSessions)
             {
-                _sessions.Clear();
+                _sessionsStorage.Clear();
             }
         }
 
@@ -584,32 +573,34 @@ namespace MQTTnet.Server
                     MqttSession session;
 
                     // Create a new session (if required).
-                    if (!_sessions.TryGetValue(connectPacket.ClientId, out oldSession))
+                    if (!_sessionsStorage.TryGetSession(connectPacket.ClientId, out oldSession))
                     {
-                        session = CreateSession(connectPacket.ClientId, validatingConnectionEventArgs.SessionItems, sessionShouldPersist);
+                        session = CreateSession(connectPacket, validatingConnectionEventArgs, sessionShouldPersist);
                     }
                     else
                     {
                         if (connectPacket.CleanSession)
                         {
-                            _logger.Verbose("Deleting existing session of client '{0}' due to clean start.", connectPacket.ClientId);
+                            _logger.Verbose("Deleting existing session of client '{0}' due to clean start", connectPacket.ClientId);
                             _subscriberSessions.Remove(oldSession);
-                            session = CreateSession(connectPacket.ClientId, validatingConnectionEventArgs.SessionItems, sessionShouldPersist);
+                            session = CreateSession(connectPacket, validatingConnectionEventArgs, sessionShouldPersist);
                         }
                         else
                         {
-                            _logger.Verbose("Reusing existing session of client '{0}'.", connectPacket.ClientId);
+                            _logger.Verbose("Reusing existing session of client '{0}'", connectPacket.ClientId);
                             session = oldSession;
                             oldSession = null;
 
                             // Session persistence could change for MQTT 5 clients that reconnect with different SessionExpiryInterval
                             session.IsPersistent = sessionShouldPersist;
-                            connAckPacket.IsSessionPresent = true;
+                            session.DisconnectedTimestamp = null;
                             session.Recover();
+                            
+                            connAckPacket.IsSessionPresent = true;
                         }
                     }
 
-                    _sessions[connectPacket.ClientId] = session;
+                    _sessionsStorage.UpdateSession(connectPacket.ClientId, session);
                     
                     // Create a new client (always required).
                     lock (_clients)
@@ -656,11 +647,14 @@ namespace MQTTnet.Server
             return client;
         }
 
-        MqttSession CreateSession(string clientId, IDictionary sessionItems, bool isPersistent)
+        MqttSession CreateSession(MqttConnectPacket connectPacket, ValidatingConnectionEventArgs validatingConnectionEventArgs, bool isPersistent)
         {
-            _logger.Verbose("Created new session for client '{0}'.", clientId);
+            _logger.Verbose("Created new session for client '{0}'", connectPacket.ClientId);
 
-            return new MqttSession(clientId, isPersistent, sessionItems, _options, _eventContainer, _retainedMessagesManager, this);
+            return new MqttSession(connectPacket, validatingConnectionEventArgs.SessionItems, _options, _eventContainer, _retainedMessagesManager, this)
+            {
+                IsPersistent = isPersistent
+            };
         }
 
         async Task FireApplicationMessageNotConsumedEvent(MqttApplicationMessage applicationMessage, string senderId)
@@ -679,7 +673,7 @@ namespace MQTTnet.Server
             _sessionsManagementLock.EnterReadLock();
             try
             {
-                if (!_sessions.TryGetValue(clientId, out var session))
+                if (!_sessionsStorage.TryGetSession(clientId, out var session))
                 {
                     throw new InvalidOperationException($"Client session '{clientId}' is unknown.");
                 }

Source/MQTTnet/Server/Internal/MqttClientSubscriptionsManager.cs

@@ -162,10 +162,7 @@ namespace MQTTnet.Server
 
         public void Dispose()
         {
-            if (_subscriptionsLock != null)
+            _subscriptionsLock?.Dispose();
-            {
-                _subscriptionsLock.Dispose();
-            }
         }
 
         public async Task<SubscribeResult> Subscribe(MqttSubscribePacket subscribePacket, CancellationToken cancellationToken)

Source/MQTTnet/Server/Internal/MqttRetainedMessagesManager.cs

@@ -134,9 +134,9 @@ namespace MQTTnet.Server
                 {
                     return Task.FromResult(message);
                 }
-
-                return null;
             }
+
+            return Task.FromResult<MqttApplicationMessage>(null);
         }
 
         public async Task ClearMessages()

Source/MQTTnet/Server/Internal/MqttSession.cs

@@ -21,6 +21,7 @@ namespace MQTTnet.Server
         readonly MqttPacketBus _packetBus = new MqttPacketBus();
         readonly MqttPacketIdentifierProvider _packetIdentifierProvider = new MqttPacketIdentifierProvider();
 
+        readonly MqttConnectPacket _connectPacket;
         readonly MqttServerOptions _serverOptions;
         readonly MqttClientSubscriptionsManager _subscriptionsManager;
 
@@ -31,18 +32,16 @@ namespace MQTTnet.Server
         HashSet<string> _subscribedTopics;
 
         public MqttSession(
-            string clientId,
+            MqttConnectPacket connectPacket,
-            bool isPersistent,
             IDictionary items,
             MqttServerOptions serverOptions,
             MqttServerEventContainer eventContainer,
             MqttRetainedMessagesManager retainedMessagesManager,
             MqttClientSessionsManager clientSessionsManager)
         {
-            Id = clientId ?? throw new ArgumentNullException(nameof(clientId));
-            IsPersistent = isPersistent;
             Items = items ?? throw new ArgumentNullException(nameof(items));
 
+            _connectPacket = connectPacket ?? throw new ArgumentNullException(nameof(connectPacket));
             _serverOptions = serverOptions ?? throw new ArgumentNullException(nameof(serverOptions));
             _clientSessionsManager = clientSessionsManager ?? throw new ArgumentNullException(nameof(clientSessionsManager));
 
@@ -51,9 +50,13 @@ namespace MQTTnet.Server
 
         public DateTime CreatedTimestamp { get; } = DateTime.UtcNow;
         
+        public DateTime? DisconnectedTimestamp { get; set; }
+
         public bool HasSubscribedTopics => _subscribedTopics != null && _subscribedTopics.Count > 0;
 
-        public string Id { get; }
+        public uint ExpiryInterval => _connectPacket.SessionExpiryInterval;
+        
+        public string Id => _connectPacket.ClientId;
 
         /// <summary>
         ///     Session should persist if CleanSession was set to false (Mqtt3) or if SessionExpiryInterval != 0 (Mqtt5)

Source/MQTTnet/Server/Internal/MqttSessionsStorage.cs

@@ -0,0 +1,93 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Linq;
+
+namespace MQTTnet.Server
+{
+    public sealed class MqttSessionsStorage
+    {
+        readonly Dictionary<string, MqttSession> _sessions = new Dictionary<string, MqttSession>(4096);
+
+        public void Clear()
+        {
+            // Make sure that the sessions are also getting disposed!
+            // This object can be reused after disposing.
+            Dispose();
+        }
+
+        public void Dispose()
+        {
+            foreach (var sessionItem in _sessions)
+            {
+                sessionItem.Value.Dispose();
+            }
+
+            _sessions.Clear();
+        }
+
+        public IReadOnlyCollection<MqttSession> ReadAllSessions()
+        {
+            return new ReadOnlyCollection<MqttSession>(_sessions.Values.ToList());
+        }
+
+        public bool TryGetSession(string id, out MqttSession session)
+        {
+            if (id == null)
+            {
+                throw new ArgumentNullException(nameof(id));
+            }
+
+            if (!_sessions.TryGetValue(id, out session))
+            {
+                return false;
+            }
+
+            // If the Session Expiry Interval is 0xFFFFFFFF (UINT_MAX), the Session does not expire.
+            if (session.ExpiryInterval > 0 && session.ExpiryInterval != uint.MaxValue)
+            {
+                if (session.DisconnectedTimestamp.HasValue)
+                {
+                    if (DateTime.UtcNow > session.DisconnectedTimestamp.Value.AddSeconds(session.ExpiryInterval))
+                    {
+                        TryRemoveSession(id, out var oldSession);
+                        oldSession?.Dispose();
+                        return false;
+                    }
+                }
+            }
+
+            return true;
+        }
+
+        public bool TryRemoveSession(string id, out MqttSession session)
+        {
+            if (id == null)
+            {
+                throw new ArgumentNullException(nameof(id));
+            }
+
+            if (_sessions.TryGetValue(id, out session))
+            {
+                _sessions.Remove(id);
+                return true;
+            }
+
+            return false;
+        }
+
+        public void UpdateSession(string id, MqttSession session)
+        {
+            if (id == null)
+            {
+                throw new ArgumentNullException(nameof(id));
+            }
+
+            _sessions[id] = session;
+        }
+    }
+}

Source/MQTTnet/Server/MqttServer.cs

@@ -229,7 +229,13 @@ namespace MQTTnet.Server
             return _clientSessionsManager.GetSessionsStatus();
         }
 
+        [Obsolete("Use InjectApplicationMessageAsync instead.")]
         public Task InjectApplicationMessage(InjectedMqttApplicationMessage injectedApplicationMessage, CancellationToken cancellationToken = default)
+        {
+            return InjectApplicationMessageAsync(injectedApplicationMessage, cancellationToken);
+        }
+        
+        public Task InjectApplicationMessageAsync(InjectedMqttApplicationMessage injectedApplicationMessage, CancellationToken cancellationToken = default)
         {
             if (injectedApplicationMessage == null)
             {

Source/MQTTnet/Server/MqttServerExtensions.cs

@@ -13,12 +13,38 @@ namespace MQTTnet.Server
 {
     public static class MqttServerExtensions
     {
+        [Obsolete("Use InjectApplicationMessageAsync instead.")]
         public static Task InjectApplicationMessage(
             this MqttServer server,
             string topic,
             string payload = null,
             MqttQualityOfServiceLevel qualityOfServiceLevel = MqttQualityOfServiceLevel.AtMostOnce,
             bool retain = false)
+        {
+            return InjectApplicationMessageAsync(server, topic, payload, qualityOfServiceLevel, retain);
+        }
+
+        public static Task InjectApplicationMessageAsync(this MqttServer server, MqttApplicationMessage applicationMessage)
+        {
+            if (server == null)
+            {
+                throw new ArgumentNullException(nameof(server));
+            }
+
+            if (applicationMessage == null)
+            {
+                throw new ArgumentNullException(nameof(applicationMessage));
+            }
+
+            return server.InjectApplicationMessageAsync(new InjectedMqttApplicationMessage(applicationMessage));
+        }
+
+        public static Task InjectApplicationMessageAsync(
+            this MqttServer server,
+            string topic,
+            string payload = null,
+            MqttQualityOfServiceLevel qualityOfServiceLevel = MqttQualityOfServiceLevel.AtMostOnce,
+            bool retain = false)
         {
             if (server == null)
             {
@@ -36,7 +62,7 @@ namespace MQTTnet.Server
                 payloadBuffer = Encoding.UTF8.GetBytes(stringPayload);
             }
 
-            return server.InjectApplicationMessage(
+            return server.InjectApplicationMessageAsync(
                 new InjectedMqttApplicationMessage(
                     new MqttApplicationMessage
                     {

Source/MQTTnet/Server/Options/MqttServerOptionsBuilder.cs

@@ -131,6 +131,18 @@ namespace MQTTnet.Server
             return this;
         }
 
+        /// <summary>
+        ///     Usually the MQTT packets can be send partially to improve memory allocations.
+        ///     This is done by using multiple TCP packets or WebSocket frames etc.
+        ///     Unfortunately not all clients do support this and will close the connection when receiving partial packets.
+        /// </summary>
+        public MqttServerOptionsBuilder WithoutPacketFragmentation()
+        {
+            _options.DefaultEndpointOptions.AllowPacketFragmentation = false;
+            _options.TlsEndpointOptions.AllowPacketFragmentation = false;
+            return this;
+        }
+
         public MqttServerOptionsBuilder WithPersistentSessions(bool value = true)
         {
             _options.EnablePersistentSessions = value;

Source/MQTTnet/Server/Options/MqttServerTcpEndpointBaseOptions.cs

@@ -23,6 +23,14 @@ namespace MQTTnet.Server
         /// </summary>
         public bool? KeepAlive { get; set; }
 
+        /// <summary>
+        ///     Usually the MQTT packets can be send partially. This is done by using multiple TCP packets
+        ///     or WebSocket frames etc. Unfortunately not all clients do support this feature and
+        ///     will close the connection when receiving such packets. If such clients are connecting to this
+        ///     server the flag must be set to _false_.
+        /// </summary>
+        public bool AllowPacketFragmentation { get; set; } = true;
+
         /// <summary>
         ///     Gets or sets the TCP keep alive interval.
         ///     The value _null_ indicates that the OS and framework defaults should be used.

Source/MQTTnet/Server/Status/MqttSessionStatus.cs

@@ -21,6 +21,10 @@ namespace MQTTnet.Server
 
         public DateTime CreatedTimestamp => _session.CreatedTimestamp;
 
+        public DateTime? DisconnectedTimestamp => _session.DisconnectedTimestamp;
+
+        public uint ExpiryInterval => _session.ExpiryInterval;
+
         public string Id => _session.Id;
 
         public IDictionary Items => _session.Items;