Add extension methods for server.

Source/MQTTnet/Server/MqttServerExtensions.cs

@@ -10,6 +10,70 @@ namespace MQTTnet.Server
 {
     public static class MqttServerExtensions
     {
+        public static IMqttServer UseClientConnectedHandler(this IMqttServer server, Func<MqttServerClientConnectedEventArgs, Task> handler)
+        {
+            if (server == null) throw new ArgumentNullException(nameof(server));
+
+            if (handler == null)
+            {
+                return server.UseClientConnectedHandler((IMqttServerClientConnectedHandler)null);
+            }
+
+            return server.UseClientConnectedHandler(new MqttServerClientConnectedHandlerDelegate(handler));
+        }
+
+        public static IMqttServer UseClientConnectedHandler(this IMqttServer server, Action<MqttServerClientConnectedEventArgs> handler)
+        {
+            if (server == null) throw new ArgumentNullException(nameof(server));
+
+            if (handler == null)
+            {
+                return server.UseClientConnectedHandler((IMqttServerClientConnectedHandler)null);
+            }
+
+            return server.UseClientConnectedHandler(new MqttServerClientConnectedHandlerDelegate(handler));
+        }
+
+        public static IMqttServer UseClientConnectedHandler(this IMqttServer server, IMqttServerClientConnectedHandler handler)
+        {
+            if (server == null) throw new ArgumentNullException(nameof(server));
+
+            server.ClientConnectedHandler = handler;
+            return server;
+        }
+
+        public static IMqttServer UseClientDisconnectedHandler(this IMqttServer server, Func<MqttServerClientDisconnectedEventArgs, Task> handler)
+        {
+            if (server == null) throw new ArgumentNullException(nameof(server));
+
+            if (handler == null)
+            {
+                return server.UseClientDisconnectedHandler((IMqttServerClientDisconnectedHandler)null);
+            }
+
+            return server.UseClientDisconnectedHandler(new MqttServerClientDisconnectedHandlerDelegate(handler));
+        }
+
+        public static IMqttServer UseClientDisconnectedHandler(this IMqttServer server, Action<MqttServerClientDisconnectedEventArgs> handler)
+        {
+            if (server == null) throw new ArgumentNullException(nameof(server));
+
+            if (handler == null)
+            {
+                return server.UseClientDisconnectedHandler((IMqttServerClientDisconnectedHandler)null);
+            }
+
+            return server.UseClientDisconnectedHandler(new MqttServerClientDisconnectedHandlerDelegate(handler));
+        }
+
+        public static IMqttServer UseClientDisconnectedHandler(this IMqttServer server, IMqttServerClientDisconnectedHandler handler)
+        {
+            if (server == null) throw new ArgumentNullException(nameof(server));
+
+            server.ClientDisconnectedHandler = handler;
+            return server;
+        }
+
         public static IMqttServer UseApplicationMessageReceivedHandler(this IMqttServer server, Func<MqttApplicationMessageReceivedEventArgs, Task> handler)
         {
             if (server == null) throw new ArgumentNullException(nameof(server));