Merge pull request #993 from chkr1011/client-disconnected-handler

Tried to add a MqttServerOptions fluent method for the client disconn…

Source/MQTTnet/Server/IMqttServerOptions.cs

@@ -27,5 +27,7 @@ namespace MQTTnet.Server
         IMqttRetainedMessagesManager RetainedMessagesManager { get; }
 
         IMqttServerApplicationMessageInterceptor UndeliveredMessageInterceptor { get; set; }
+
+        IMqttServerClientDisconnectedHandler ClientDisconnectedInterceptor { get; set; }
     }
 }

Source/MQTTnet/Server/MqttServerOptions.cs

@@ -33,5 +33,7 @@ namespace MQTTnet.Server
         public IMqttRetainedMessagesManager RetainedMessagesManager { get; set; } = new MqttRetainedMessagesManager();
 
         public IMqttServerApplicationMessageInterceptor UndeliveredMessageInterceptor { get; set; }
+
+        public IMqttServerClientDisconnectedHandler ClientDisconnectedInterceptor { get; set; }
     }
 }

Source/MQTTnet/Server/MqttServerOptionsBuilder.cs

@@ -163,6 +163,18 @@ namespace MQTTnet.Server
             return this;
         }
 
+        public MqttServerOptionsBuilder WithDisconnectedInterceptor(IMqttServerClientDisconnectedHandler value)
+        {
+            _options.ClientDisconnectedInterceptor = value;
+            return this;
+        }
+
+        public MqttServerOptionsBuilder WithDisconnectedInterceptor(Action<MqttServerClientDisconnectedEventArgs> value)
+        {
+            _options.ClientDisconnectedInterceptor = new MqttServerClientDisconnectedHandlerDelegate(value);
+            return this;
+        }
+
         public MqttServerOptionsBuilder WithApplicationMessageInterceptor(IMqttServerApplicationMessageInterceptor value)
         {
             _options.ApplicationMessageInterceptor = value;