Merge pull request #884 from chkr1011/feature-isconnected

Added check if the server is started or not.

Build/MQTTnet.nuspec

@@ -26,6 +26,7 @@
 * [Server] Added interceptor for unsubscriptions.
 * [Server] Removed exceptions when user properties are set with MQTT protocol version 3.1
 * [Server] Added custom session items to the client status.
+* [Server] Added option to check whether the server is already started properly or not.
 * [MQTTnet.AspNetCore] improved compatibility with AspNetCore 3.1
 * [MQTTnet.Server] Added interceptor for unsubscriptions.
     </releaseNotes>

Source/MQTTnet/Server/IMqttServer.cs

@@ -27,5 +27,7 @@ namespace MQTTnet.Server
 
         Task StartAsync(IMqttServerOptions options);
         Task StopAsync();
+
+        bool IsStarted { get; }
     }
 }

Source/MQTTnet/Server/MqttServer.cs

@@ -190,6 +190,8 @@ namespace MQTTnet.Server
             return _retainedMessagesManager?.ClearMessagesAsync();
         }
 
+        public bool IsStarted => _cancellationTokenSource != null;
+
         private Task OnHandleClient(IMqttChannelAdapter channelAdapter)
         {
             return _clientSessionsManager.HandleClientConnectionAsync(channelAdapter);