Fix MQTT 3.1.1 session persistence when CleanSession=1 (#1294)

Source/MQTTnet/Server/Internal/MqttClientSession.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using MQTTnet.Server.Status;
 
@@ -8,24 +8,34 @@ namespace MQTTnet.Server.Internal
     {
         readonly DateTime _createdTimestamp = DateTime.UtcNow;
 
+        /// <summary>
+        /// Session should persist if CleanSession was set to false (Mqtt3) or if SessionExpiryInterval != 0 (Mqtt5)
+        /// </summary>
+        readonly bool _isPersistent;
+
         public MqttClientSession(
             string clientId,
             IDictionary<object, object> items,
             MqttServerEventDispatcher eventDispatcher,
             IMqttServerOptions serverOptions,
-            IMqttRetainedMessagesManager retainedMessagesManager)
+            IMqttRetainedMessagesManager retainedMessagesManager,
+            bool isPersistent
+            )
         {
             ClientId = clientId ?? throw new ArgumentNullException(nameof(clientId));
             Items = items ?? throw new ArgumentNullException(nameof(items));
 
             SubscriptionsManager = new MqttClientSubscriptionsManager(this, serverOptions, eventDispatcher, retainedMessagesManager);
             ApplicationMessagesQueue = new MqttClientSessionApplicationMessagesQueue(serverOptions);
+            _isPersistent = isPersistent;
         }
 
         public string ClientId { get; }
 
         public bool IsCleanSession { get; set; } = true;
 
+        public bool IsPersistent => _isPersistent;
+
         public MqttApplicationMessage WillMessage { get; set; }
 
         public MqttClientSubscriptionsManager SubscriptionsManager { get; }

Source/MQTTnet/Server/Internal/MqttClientSessionsManager.cs

@@ -126,7 +126,7 @@ namespace MQTTnet.Server.Internal
 
                 // Pass connAckPacket so that IsSessionPresent flag can be set if the client session already exists
                 clientConnection = await CreateClientConnection(connectPacket, connAckPacket, channelAdapter,
-                    connectionValidatorContext.SessionItems).ConfigureAwait(false);
+                    connectionValidatorContext).ConfigureAwait(false);
 
                 await channelAdapter.SendPacketAsync(connAckPacket, cancellationToken).ConfigureAwait(false);
 
@@ -156,7 +156,7 @@ namespace MQTTnet.Server.Internal
                                 _clientConnections.Remove(clientConnection.ClientId);
                             }
 
-                            if (!_options.EnablePersistentSessions)
+                            if ((!_options.EnablePersistentSessions) || (!clientConnection.Session.IsPersistent))
                             {
                                 await DeleteSessionAsync(clientConnection.ClientId).ConfigureAwait(false);
                             }
@@ -491,10 +491,35 @@ namespace MQTTnet.Server.Internal
             MqttConnectPacket connectPacket,
             MqttConnAckPacket connAckPacket,
             IMqttChannelAdapter channelAdapter,
-            IDictionary<object, object> sessionItems)
+            MqttConnectionValidatorContext context)
         {
             MqttClientConnection connection;
 
+            bool sessionShouldPersist;
+
+            if (context.ProtocolVersion == MqttProtocolVersion.V500)
+            {
+                // MQTT 5.0 section 3.1.2.11.2
+                // The Client and Server MUST store the Session State after the Network Connection is closed if the Session Expiry Interval is greater than 0 [MQTT-3.1.2-23].
+                //
+                // A Client that only wants to process messages while connected will set the Clean Start to 1 and set the Session Expiry Interval to 0.
+                // It will not receive Application Messages published before it connected and has to subscribe afresh to any topics that it is interested
+                // in each time it connects.
+
+                // Persist if SessionExpiryInterval != 0, but may start with a clean session
+                sessionShouldPersist = context.SessionExpiryInterval != 0;
+            }
+            else
+            {
+                // MQTT 3.1.1 section 3.1.2.4: persist only if 'not CleanSession'
+                //
+                // If CleanSession is set to 1, the Client and Server MUST discard any previous Session and start a new one.
+                // This Session lasts as long as the Network Connection. State data associated with this Session MUST NOT be
+                // reused in any subsequent Session [MQTT-3.1.2-6].
+
+                sessionShouldPersist = !connectPacket.CleanSession;
+            }
+
             using (await _createConnectionSyncRoot.WaitAsync(CancellationToken.None).ConfigureAwait(false))
             {
                 MqttClientSession session;
@@ -503,14 +528,14 @@ namespace MQTTnet.Server.Internal
                     if (!_clientSessions.TryGetValue(connectPacket.ClientId, out session))
                     {
                         _logger.Verbose("Created a new session for client '{0}'.", connectPacket.ClientId);
-                        session = CreateSession(connectPacket.ClientId, sessionItems);
+                        session = CreateSession(connectPacket.ClientId, context.SessionItems, sessionShouldPersist);
                     }
                     else
                     {
                         if (connectPacket.CleanSession)
                         {
                             _logger.Verbose("Deleting existing session of client '{0}'.", connectPacket.ClientId);
-                            session = CreateSession(connectPacket.ClientId, sessionItems);
+                            session = CreateSession(connectPacket.ClientId, context.SessionItems, sessionShouldPersist);
                         }
                         else
                         {
@@ -604,14 +629,16 @@ namespace MQTTnet.Server.Internal
                 _rootLogger);
         }
 
-        MqttClientSession CreateSession(string clientId, IDictionary<object, object> sessionItems)
+        MqttClientSession CreateSession(string clientId, IDictionary<object, object> sessionItems, bool isPersistent)
         {
             return new MqttClientSession(
                 clientId,
                 sessionItems,
                 _eventDispatcher,
                 _options,
-                _retainedMessagesManager);
+                _retainedMessagesManager,
+                isPersistent
+                );
         }
     }
 }