* [Server] Added support for complex client IDs.

* [Server] Fixed an issue with not correctly removed old client sessions.
* [Server] Several minor performance improvements.
* [Server] An existing client session is no longer closed if a new client connection is invalid.
* [Client] Added support for sending "CleanSession" flag.

MQTTnet.Core/Client/MqttClientOptions.cs

@@ -14,6 +14,8 @@ namespace MQTTnet.Core.Client
 
         public string ClientId { get; set; } = Guid.NewGuid().ToString().Replace("-", string.Empty);
 
+        public bool CleanSession { get; set; } = true;
+
         public TimeSpan KeepAlivePeriod { get; set; } = TimeSpan.FromSeconds(5);
 
         public TimeSpan DefaultCommunicationTimeout { get; set; } = TimeSpan.FromSeconds(10);