Add new server option to disable/enable persistent sessions.

Frameworks/MQTTnet.NetStandard/Server/IMqttServerOptions.cs

@@ -5,6 +5,9 @@ namespace MQTTnet.Server
     public interface IMqttServerOptions
     {
         int ConnectionBacklog { get; }
+
+        bool EnablePersistentSessions { get; }
+
         int MaxPendingMessagesPerClient { get; }
         MqttPendingMessagesOverflowStrategy PendingMessagesOverflowStrategy { get; }
 

Frameworks/MQTTnet.NetStandard/Server/MqttClientSessionsManager.cs

@@ -107,6 +107,11 @@ namespace MQTTnet.Server
                     _logger.Error(exception, exception.Message);
                 }
 
+                if (!_options.EnablePersistentSessions)
+                {
+                    await DeleteSessionAsync(clientId).ConfigureAwait(false);
+                }
+
                 Server.OnClientDisconnected(new ConnectedMqttClient
                 {
                     ClientId = clientId,
@@ -224,6 +229,20 @@ namespace MQTTnet.Server
             return context.ReturnCode;
         }
 
+        private async Task DeleteSessionAsync(string clientId)
+        {
+            await _sessionsLock.EnterAsync(CancellationToken.None);
+            try
+            {
+                _sessions.Remove(clientId);
+                _logger.Verbose("Session for client '{0}' deleted.", clientId);
+            }
+            finally
+            {
+                _sessionsLock.Exit();
+            }
+        }
+
         private async Task<GetOrCreateClientSessionResult> PrepareClientSessionAsync(MqttConnectPacket connectPacket)
         {
             await _sessionsLock.EnterAsync(CancellationToken.None).ConfigureAwait(false);

Frameworks/MQTTnet.NetStandard/Server/MqttServerOptions.cs

@@ -8,10 +8,11 @@ namespace MQTTnet.Server
 
         public MqttServerTlsEndpointOptions TlsEndpointOptions { get; } = new MqttServerTlsEndpointOptions();
 
+        public bool EnablePersistentSessions { get; set; }
+
         public int ConnectionBacklog { get; set; } = 10;
 
         public int MaxPendingMessagesPerClient { get; set; } = 250;
-
         public MqttPendingMessagesOverflowStrategy PendingMessagesOverflowStrategy { get; set; } = MqttPendingMessagesOverflowStrategy.DropOldestQueuedMessage;
 
         public TimeSpan DefaultCommunicationTimeout { get; set; } = TimeSpan.FromSeconds(15);

Frameworks/MQTTnet.NetStandard/Server/MqttServerOptionsBuilder.cs

@@ -103,6 +103,12 @@ namespace MQTTnet.Server
             return this;
         }
 
+        public MqttServerOptionsBuilder WithPersistentSessions()
+        {
+            _options.EnablePersistentSessions = true;
+            return this;
+        }
+
         public IMqttServerOptions Build()
         {
             return _options;