Use event pattern correctly for incoming server connections.

Frameworks/MQTTnet.NetStandard/Implementations/MqttServerAdapter.cs

@@ -20,15 +20,11 @@ namespace MQTTnet.Implementations
         private Socket _tlsEndpointSocket;
         private X509Certificate2 _tlsCertificate;
 
-        private bool _isRunning;
-
-        public event Action<IMqttCommunicationAdapter> ClientAccepted;
+        public event EventHandler<MqttServerAdapterClientAcceptedEventArgs> ClientAccepted;
 
         public Task StartAsync(MqttServerOptions options)
         {
-            if (_isRunning) throw new InvalidOperationException("Server is already started.");
-
-            _isRunning = true;
+            if (_cancellationTokenSource != null) throw new InvalidOperationException("Server is already started.");
 
             _cancellationTokenSource = new CancellationTokenSource();
 
@@ -49,6 +45,10 @@ namespace MQTTnet.Implementations
                 }
 
                 _tlsCertificate = new X509Certificate2(options.TlsEndpointOptions.Certificate);
+                if (!_tlsCertificate.HasPrivateKey)
+                {
+                    throw new InvalidOperationException("The certificate for TLS encryption must contain the private key.");
+                }
 
                 _tlsEndpointSocket = new Socket(SocketType.Stream, ProtocolType.Tcp);
                 _tlsEndpointSocket.Bind(new IPEndPoint(IPAddress.Any, options.GetTlsEndpointPort()));
@@ -62,8 +62,6 @@ namespace MQTTnet.Implementations
 
         public Task StopAsync()
         {
-            _isRunning = false;
-
             _cancellationTokenSource?.Cancel(false);
             _cancellationTokenSource?.Dispose();
             _cancellationTokenSource = null;
@@ -71,6 +69,8 @@ namespace MQTTnet.Implementations
             _defaultEndpointSocket?.Dispose();
             _defaultEndpointSocket = null;
 
+            _tlsCertificate = null;
+            
             _tlsEndpointSocket?.Dispose();
             _tlsEndpointSocket = null;
 
@@ -88,14 +88,14 @@ namespace MQTTnet.Implementations
             {
                 try
                 {
-//todo: else branch can be used with min dependency NET46
+                    //todo: else branch can be used with min dependency NET46
 #if NET45
                     var clientSocket = await Task.Factory.FromAsync(_defaultEndpointSocket.BeginAccept, _defaultEndpointSocket.EndAccept, null).ConfigureAwait(false);
 #else
                     var clientSocket = await _defaultEndpointSocket.AcceptAsync().ConfigureAwait(false);
 #endif
                     var clientAdapter = new MqttChannelCommunicationAdapter(new MqttTcpChannel(clientSocket, null), new MqttPacketSerializer());
-                    ClientAccepted?.Invoke(clientAdapter);
+                    ClientAccepted?.Invoke(this, new MqttServerAdapterClientAcceptedEventArgs(clientAdapter));
                 }
                 catch (Exception exception)
                 {
@@ -123,7 +123,7 @@ namespace MQTTnet.Implementations
                     await sslStream.AuthenticateAsServerAsync(_tlsCertificate, false, SslProtocols.Tls12, false).ConfigureAwait(false);
 
                     var clientAdapter = new MqttChannelCommunicationAdapter(new MqttTcpChannel(clientSocket, sslStream), new MqttPacketSerializer());
-                    ClientAccepted?.Invoke(clientAdapter);
+                    ClientAccepted?.Invoke(this, new MqttServerAdapterClientAcceptedEventArgs(clientAdapter));
                 }
                 catch (Exception exception)
                 {

Frameworks/MQTTnet.UniversalWindows/Implementations/MqttServerAdapter.cs

@@ -12,18 +12,14 @@ namespace MQTTnet.Implementations
     {
         private StreamSocketListener _defaultEndpointSocket;
 
-        private bool _isRunning;
-
-        public event Action<IMqttCommunicationAdapter> ClientAccepted;
+        public event EventHandler<MqttServerAdapterClientAcceptedEventArgs> ClientAccepted;
 
         public async Task StartAsync(MqttServerOptions options)
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
-            if (_isRunning) throw new InvalidOperationException("Server is already started.");
-
-            _isRunning = true;
-
+            if (_defaultEndpointSocket != null) throw new InvalidOperationException("Server is already started.");
+            
             if (options.DefaultEndpointOptions.IsEnabled)
             {
                 _defaultEndpointSocket = new StreamSocketListener();
@@ -39,8 +35,6 @@ namespace MQTTnet.Implementations
 
         public Task StopAsync()
         {
-            _isRunning = false;
-
             _defaultEndpointSocket?.Dispose();
             _defaultEndpointSocket = null;
 
@@ -57,7 +51,7 @@ namespace MQTTnet.Implementations
             try
             {
                 var clientAdapter = new MqttChannelCommunicationAdapter(new MqttTcpChannel(args.Socket), new MqttPacketSerializer());
-                ClientAccepted?.Invoke(clientAdapter);
+                ClientAccepted?.Invoke(this, new MqttServerAdapterClientAcceptedEventArgs(clientAdapter));
             }
             catch (Exception exception)
             {

MQTTnet.Core/Adapter/IMqttServerAdapter.cs

@@ -6,7 +6,7 @@ namespace MQTTnet.Core.Adapter
 {
     public interface IMqttServerAdapter
     {
-        event Action<IMqttCommunicationAdapter> ClientAccepted;
+        event EventHandler<MqttServerAdapterClientAcceptedEventArgs> ClientAccepted;
 
         Task StartAsync(MqttServerOptions options);
         Task StopAsync();

MQTTnet.Core/Adapter/MqttServerAdapterClientAcceptedEventArgs.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace MQTTnet.Core.Adapter
+{
+    public class MqttServerAdapterClientAcceptedEventArgs : EventArgs
+    {
+        public MqttServerAdapterClientAcceptedEventArgs(IMqttCommunicationAdapter client)
+        {
+            Client = client ?? throw new ArgumentNullException(nameof(client));
+        }
+
+        public IMqttCommunicationAdapter Client { get; }
+    }
+}

MQTTnet.Core/Server/MqttClientConnectedEventArgs.cs

@@ -1,7 +1,6 @@
-using MQTTnet.Core.Server;
-using System;
+using System;
 
-namespace MQTTnet.Core.Adapter
+namespace MQTTnet.Core.Server
 {
     public class MqttClientConnectedEventArgs : EventArgs
     {

MQTTnet.Core/Server/MqttClientDisconnectedEventArgs.cs

@@ -1,7 +1,6 @@
-using MQTTnet.Core.Server;
-using System;
+using System;
 
-namespace MQTTnet.Core.Adapter
+namespace MQTTnet.Core.Server
 {
     public class MqttClientDisconnectedEventArgs : EventArgs
     {

MQTTnet.Core/Server/MqttServer.cs

@@ -77,9 +77,9 @@ namespace MQTTnet.Core.Server
             MqttNetTrace.Information(nameof(MqttServer), "Stopped.");
         }
 
-        private void OnClientAccepted(IMqttCommunicationAdapter adapter)
+        private void OnClientAccepted(object sender, MqttServerAdapterClientAcceptedEventArgs eventArgs)
         {
-            Task.Run(() =>_clientSessionsManager.RunClientSessionAsync(adapter), _cancellationTokenSource.Token);
+            Task.Run(() =>_clientSessionsManager.RunClientSessionAsync(eventArgs.Client), _cancellationTokenSource.Token);
         }
 
         private void OnClientConnected(object sender, MqttClientConnectedEventArgs eventArgs)

MQTTnet.sln

@@ -1,7 +1,7 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio 15
-VisualStudioVersion = 15.0.26730.16
+VisualStudioVersion = 15.0.27004.2002
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Core.Tests", "Tests\MQTTnet.Core.Tests\MQTTnet.Core.Tests.csproj", "{A7FF0C91-25DE-4BA6-B39E-F54E8DADF1CC}"
 EndProject

Tests/MQTTnet.Core.Tests/TestMqttServerAdapter.cs

@@ -8,7 +8,7 @@ namespace MQTTnet.Core.Tests
 {
     public class TestMqttServerAdapter : IMqttServerAdapter
     {
-        public event Action<IMqttCommunicationAdapter> ClientAccepted;
+        public event EventHandler<MqttServerAdapterClientAcceptedEventArgs> ClientAccepted;
 
         public async Task<MqttClient> ConnectTestClient(IMqttServer server, string clientId, MqttApplicationMessage willMessage = null)
         {
@@ -47,7 +47,7 @@ namespace MQTTnet.Core.Tests
 
         private void FireClientAcceptedEvent(IMqttCommunicationAdapter adapter)
         {
-            ClientAccepted?.Invoke(adapter);
+            ClientAccepted?.Invoke(this, new MqttServerAdapterClientAcceptedEventArgs(adapter));
         }
 
         public Task StartAsync(MqttServerOptions options)

Tests/MQTTnet.TestApp.NetCore/Program.cs

@@ -6,6 +6,7 @@ using MQTTnet.Core.Protocol;
 using MQTTnet.Core.Server;
 using System;
 using System.Collections.Generic;
+using System.Security.Cryptography.X509Certificates;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
@@ -42,7 +43,7 @@ namespace MQTTnet.TestApp.NetCore
         {
             MqttNetTrace.TraceMessagePublished += (s, e) =>
             {
-                Console.WriteLine($">> [{e.ThreadId}] [{e.Source}] [{e.Level}]: {e.Message}");
+                Console.WriteLine($">> [{DateTime.Now:O}] [{e.ThreadId}] [{e.Source}] [{e.Level}]: {e.Message}");
                 if (e.Exception != null)
                 {
                     Console.WriteLine(e.Exception);
@@ -156,6 +157,9 @@ namespace MQTTnet.TestApp.NetCore
                     }
                 };
 
+                var certificate = new X509Certificate(@"C:\certs\test\test.cer", "");
+                options.TlsEndpointOptions.Certificate = certificate.Export(X509ContentType.Cert);
+
                 var mqttServer = new MqttServerFactory().CreateMqttServer(options);
                 mqttServer.StartAsync();