Fix packet identifier which is sent from the server.

Frameworks/MQTTnet.NetStandard/Adapter/MqttChannelAdapter.cs

@@ -138,7 +138,7 @@ namespace MQTTnet.Adapter
             }
 
             var body = header.BodyLength <= ReadBufferSize ? new MemoryStream(header.BodyLength) : new MemoryStream();
-            
+
             var buffer = new byte[ReadBufferSize];
             while (body.Length < header.BodyLength)
             {
@@ -149,7 +149,7 @@ namespace MQTTnet.Adapter
                 }
 
                 var readBytesCount = await stream.ReadAsync(buffer, 0, bytesLeft, cancellationToken).ConfigureAwait(false);
-                
+
                 // Check if the client closed the connection before sending the full body.
                 if (readBytesCount == 0)
                 {
@@ -162,7 +162,7 @@ namespace MQTTnet.Adapter
             }
 
             body.Seek(0L, SeekOrigin.Begin);
-            
+
             return new ReceivedMqttPacket(header, body);
         }
 
@@ -190,7 +190,7 @@ namespace MQTTnet.Adapter
             }
             catch (COMException comException)
             {
-                if ((uint) comException.HResult == ErrorOperationAborted)
+                if ((uint)comException.HResult == ErrorOperationAborted)
                 {
                     throw new OperationCanceledException();
                 }

Frameworks/MQTTnet.NetStandard/Adapter/MqttChannelAdapterExtensions.cs

@@ -1,17 +0,0 @@
-using System;
-using System.Threading;
-using System.Threading.Tasks;
-using MQTTnet.Packets;
-
-namespace MQTTnet.Adapter
-{
-    public static class MqttChannelAdapterExtensions
-    {
-        public static Task SendPacketsAsync(this IMqttChannelAdapter adapter, TimeSpan timeout, CancellationToken cancellationToken, params MqttBasePacket[] packets)
-        {
-            if (adapter == null) throw new ArgumentNullException(nameof(adapter));
-
-            return adapter.SendPacketsAsync(timeout, cancellationToken, packets);
-        }
-    }
-}

Frameworks/MQTTnet.NetStandard/Packets/IMqttPacketWithIdentifier.cs

@@ -2,6 +2,6 @@
 {
     public interface IMqttPacketWithIdentifier
     {
-        ushort PacketIdentifier { get; set; }
+        ushort? PacketIdentifier { get; set; }
     }
 }

Frameworks/MQTTnet.NetStandard/Packets/MqttBasePublishPacket.cs

@@ -2,6 +2,6 @@
 {
     public class MqttBasePublishPacket : MqttBasePacket, IMqttPacketWithIdentifier
     {
-        public ushort PacketIdentifier { get; set; }
+        public ushort? PacketIdentifier { get; set; }
     }
 }

Frameworks/MQTTnet.NetStandard/Packets/MqttPacketExtensions.cs

@@ -1,26 +0,0 @@
-using System;
-
-namespace MQTTnet.Packets
-{
-    public static class MqttPacketExtensions
-    {
-        public static TResponsePacket CreateResponse<TResponsePacket>(this MqttBasePacket packet)
-        {
-            if (packet == null) throw new ArgumentNullException(nameof(packet));
-
-            var responsePacket = Activator.CreateInstance<TResponsePacket>();
-
-            if (responsePacket is IMqttPacketWithIdentifier responsePacketWithIdentifier)
-            {
-                if (!(packet is IMqttPacketWithIdentifier requestPacketWithIdentifier))
-                {
-                    throw new InvalidOperationException("Response packet has PacketIdentifier but request packet does not.");
-                }
-
-                responsePacketWithIdentifier.PacketIdentifier = requestPacketWithIdentifier.PacketIdentifier;
-            }
-
-            return responsePacket;
-        }
-    }
-}

Frameworks/MQTTnet.NetStandard/Packets/MqttSubAckPacket.cs

@@ -6,7 +6,7 @@ namespace MQTTnet.Packets
 {
     public sealed class MqttSubAckPacket : MqttBasePacket, IMqttPacketWithIdentifier
     {
-        public ushort PacketIdentifier { get; set; }
+        public ushort? PacketIdentifier { get; set; }
 
         public IList<MqttSubscribeReturnCode> SubscribeReturnCodes { get; } = new List<MqttSubscribeReturnCode>();
 

Frameworks/MQTTnet.NetStandard/Packets/MqttSubscribePacket.cs

@@ -5,7 +5,7 @@ namespace MQTTnet.Packets
 {
     public sealed class MqttSubscribePacket : MqttBasePacket, IMqttPacketWithIdentifier
     {
-        public ushort PacketIdentifier { get; set; }
+        public ushort? PacketIdentifier { get; set; }
 
         public IList<TopicFilter> TopicFilters { get; set; } = new List<TopicFilter>();
 

Frameworks/MQTTnet.NetStandard/Packets/MqttUnsubAckPacket.cs

@@ -2,7 +2,7 @@
 {
     public sealed class MqttUnsubAckPacket : MqttBasePacket, IMqttPacketWithIdentifier
     {
-        public ushort PacketIdentifier { get; set; }
+        public ushort? PacketIdentifier { get; set; }
 
         public override string ToString()
         {

Frameworks/MQTTnet.NetStandard/Packets/MqttUnsubscribe.cs

@@ -4,7 +4,7 @@ namespace MQTTnet.Packets
 {
     public sealed class MqttUnsubscribePacket : MqttBasePacket, IMqttPacketWithIdentifier
     {
-        public ushort PacketIdentifier { get; set; }
+        public ushort? PacketIdentifier { get; set; }
 
         public IList<string> TopicFilters { get; set; } = new List<string>();
 

Frameworks/MQTTnet.NetStandard/Serializer/MqttPacketSerializer.cs

@@ -397,7 +397,12 @@ namespace MQTTnet.Serializer
 
         private static byte Serialize(MqttPubRelPacket packet, MqttPacketWriter writer)
         {
-            writer.Write(packet.PacketIdentifier);
+            if (!packet.PacketIdentifier.HasValue)
+            {
+                throw new MqttProtocolViolationException("PubRel packet has no packet identifier.");
+            }
+
+            writer.Write(packet.PacketIdentifier.Value);
 
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.PubRel, 0x02);
         }
@@ -410,7 +415,12 @@ namespace MQTTnet.Serializer
 
             if (packet.QualityOfServiceLevel > MqttQualityOfServiceLevel.AtMostOnce)
             {
-                writer.Write(packet.PacketIdentifier);
+                if (!packet.PacketIdentifier.HasValue)
+                {
+                    throw new MqttProtocolViolationException("Publish packet has no packet identifier.");
+                }
+
+                writer.Write(packet.PacketIdentifier.Value);
             }
             else
             {
@@ -444,21 +454,36 @@ namespace MQTTnet.Serializer
 
         private static byte Serialize(MqttPubAckPacket packet, MqttPacketWriter writer)
         {
-            writer.Write(packet.PacketIdentifier);
+            if (!packet.PacketIdentifier.HasValue)
+            {
+                throw new MqttProtocolViolationException("PubAck packet has no packet identifier.");
+            }
+
+            writer.Write(packet.PacketIdentifier.Value);
 
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.PubAck);
         }
 
         private static byte Serialize(MqttPubRecPacket packet, MqttPacketWriter writer)
         {
-            writer.Write(packet.PacketIdentifier);
+            if (!packet.PacketIdentifier.HasValue)
+            {
+                throw new MqttProtocolViolationException("PubRec packet has no packet identifier.");
+            }
+
+            writer.Write(packet.PacketIdentifier.Value);
 
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.PubRec);
         }
 
         private static byte Serialize(MqttPubCompPacket packet, MqttPacketWriter writer)
         {
-            writer.Write(packet.PacketIdentifier);
+            if (!packet.PacketIdentifier.HasValue)
+            {
+                throw new MqttProtocolViolationException("PubComp packet has no packet identifier.");
+            }
+
+            writer.Write(packet.PacketIdentifier.Value);
 
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.PubComp);
         }
@@ -467,7 +492,12 @@ namespace MQTTnet.Serializer
         {
             if (!packet.TopicFilters.Any()) throw new MqttProtocolViolationException("At least one topic filter must be set [MQTT-3.8.3-3].");
 
-            writer.Write(packet.PacketIdentifier);
+            if (!packet.PacketIdentifier.HasValue)
+            {
+                throw new MqttProtocolViolationException("Subscribe packet has no packet identifier.");
+            }
+
+            writer.Write(packet.PacketIdentifier.Value);
 
             if (packet.TopicFilters?.Count > 0)
             {
@@ -483,7 +513,12 @@ namespace MQTTnet.Serializer
 
         private static byte Serialize(MqttSubAckPacket packet, MqttPacketWriter writer)
         {
-            writer.Write(packet.PacketIdentifier);
+            if (!packet.PacketIdentifier.HasValue)
+            {
+                throw new MqttProtocolViolationException("SubAck packet has no packet identifier.");
+            }
+
+            writer.Write(packet.PacketIdentifier.Value);
 
             if (packet.SubscribeReturnCodes?.Any() == true)
             {
@@ -500,7 +535,12 @@ namespace MQTTnet.Serializer
         {
             if (!packet.TopicFilters.Any()) throw new MqttProtocolViolationException("At least one topic filter must be set [MQTT-3.10.3-2].");
 
-            writer.Write(packet.PacketIdentifier);
+            if (!packet.PacketIdentifier.HasValue)
+            {
+                throw new MqttProtocolViolationException("Unsubscribe packet has no packet identifier.");
+            }
+
+            writer.Write(packet.PacketIdentifier.Value);
 
             if (packet.TopicFilters?.Any() == true)
             {
@@ -513,9 +553,14 @@ namespace MQTTnet.Serializer
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.Unsubscibe, 0x02);
         }
 
-        private static byte Serialize(IMqttPacketWithIdentifier packet, BinaryWriter writer)
+        private static byte Serialize(MqttUnsubAckPacket packet, BinaryWriter writer)
         {
-            writer.Write(packet.PacketIdentifier);
+            if (!packet.PacketIdentifier.HasValue)
+            {
+                throw new MqttProtocolViolationException("UnsubAck packet has no packet identifier.");
+            }
+
+            writer.Write(packet.PacketIdentifier.Value);
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.UnsubAck);
         }
 

Frameworks/MQTTnet.NetStandard/Server/MqttClientPendingMessagesQueue.cs

@@ -78,7 +78,7 @@ namespace MQTTnet.Server
                     throw new InvalidOperationException(); // should not happen
                 }
 
-                await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, packet).ConfigureAwait(false);
+                await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new[] { packet }).ConfigureAwait(false);
 
                 _logger.Trace<MqttClientPendingMessagesQueue>("Enqueued packet sent (ClientId: {0}).", _clientSession.ClientId);
             }

Frameworks/MQTTnet.NetStandard/Server/MqttClientSession.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Adapter;
+using MQTTnet.Client;
 using MQTTnet.Diagnostics;
 using MQTTnet.Exceptions;
 using MQTTnet.Internal;
@@ -14,6 +15,7 @@ namespace MQTTnet.Server
 {
     public sealed class MqttClientSession : IDisposable
     {
+        private readonly MqttPacketIdentifierProvider _packetIdentifierProvider = new MqttPacketIdentifierProvider();
         private readonly IMqttServerOptions _options;
         private readonly IMqttNetLogger _logger;
         private readonly MqttRetainedMessagesManager _retainedMessagesManager;
@@ -129,6 +131,11 @@ namespace MQTTnet.Server
             var publishPacket = applicationMessage.ToPublishPacket();
             publishPacket.QualityOfServiceLevel = result.QualityOfServiceLevel;
 
+            if (publishPacket.QualityOfServiceLevel > 0)
+            {
+                publishPacket.PacketIdentifier = _packetIdentifierProvider.GetNewPacketIdentifier();
+            }
+
             PendingMessagesQueue.Enqueue(publishPacket);
         }
 
@@ -205,7 +212,7 @@ namespace MQTTnet.Server
 
             if (packet is MqttPingReqPacket)
             {
-                return adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new MqttPingRespPacket());
+                return adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new[] { new MqttPingRespPacket() });
             }
 
             if (packet is MqttPubRelPacket pubRelPacket)
@@ -215,7 +222,12 @@ namespace MQTTnet.Server
 
             if (packet is MqttPubRecPacket pubRecPacket)
             {
-                return adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, pubRecPacket.CreateResponse<MqttPubRelPacket>());
+                var responsePacket = new MqttPubRelPacket
+                {
+                    PacketIdentifier = pubRecPacket.PacketIdentifier
+                };
+
+                return adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new[] { responsePacket });
             }
 
             if (packet is MqttPubAckPacket || packet is MqttPubCompPacket)
@@ -246,11 +258,11 @@ namespace MQTTnet.Server
         private async Task HandleIncomingSubscribePacketAsync(IMqttChannelAdapter adapter, MqttSubscribePacket subscribePacket, CancellationToken cancellationToken)
         {
             var subscribeResult = await SubscriptionsManager.SubscribeAsync(subscribePacket).ConfigureAwait(false);
-            await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, subscribeResult.ResponsePacket).ConfigureAwait(false);
+            await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new[] { subscribeResult.ResponsePacket }).ConfigureAwait(false);
 
             if (subscribeResult.CloseConnection)
             {
-                await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new MqttDisconnectPacket()).ConfigureAwait(false);
+                await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new[] { new MqttDisconnectPacket() }).ConfigureAwait(false);
                 await StopAsync().ConfigureAwait(false);
             }
 
@@ -260,7 +272,7 @@ namespace MQTTnet.Server
         private async Task HandleIncomingUnsubscribePacketAsync(IMqttChannelAdapter adapter, MqttUnsubscribePacket unsubscribePacket, CancellationToken cancellationToken)
         {
             var unsubscribeResult = await SubscriptionsManager.UnsubscribeAsync(unsubscribePacket).ConfigureAwait(false);
-            await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, unsubscribeResult);
+            await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new[] { unsubscribeResult });
         }
 
         private async Task EnqueueSubscribedRetainedMessagesAsync(ICollection<TopicFilter> topicFilters)
@@ -302,7 +314,7 @@ namespace MQTTnet.Server
             await ApplicationMessageReceivedCallback(this, applicationMessage).ConfigureAwait(false);
 
             var response = new MqttPubAckPacket { PacketIdentifier = publishPacket.PacketIdentifier };
-            await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, response).ConfigureAwait(false);
+            await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new[] { response }).ConfigureAwait(false);
         }
 
         private async Task HandleIncomingPublishPacketWithQoS2(IMqttChannelAdapter adapter, MqttApplicationMessage applicationMessage, MqttPublishPacket publishPacket, CancellationToken cancellationToken)
@@ -311,13 +323,13 @@ namespace MQTTnet.Server
             await ApplicationMessageReceivedCallback(this, applicationMessage).ConfigureAwait(false);
 
             var response = new MqttPubRecPacket { PacketIdentifier = publishPacket.PacketIdentifier };
-            await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, response).ConfigureAwait(false);
+            await adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new[] { response }).ConfigureAwait(false);
         }
 
         private Task HandleIncomingPubRelPacketAsync(IMqttChannelAdapter adapter, MqttPubRelPacket pubRelPacket, CancellationToken cancellationToken)
         {
             var response = new MqttPubCompPacket { PacketIdentifier = pubRelPacket.PacketIdentifier };
-            return adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, response);
+            return adapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new[] { response });
         }
     }
 }

Frameworks/MQTTnet.NetStandard/Server/MqttClientSessionsManager.cs

@@ -53,10 +53,10 @@ namespace MQTTnet.Server
                 var connectReturnCode = ValidateConnection(connectPacket);
                 if (connectReturnCode != MqttConnectReturnCode.ConnectionAccepted)
                 {
-                    await clientAdapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new MqttConnAckPacket
+                    await clientAdapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new[] { new MqttConnAckPacket
                     {
                         ConnectReturnCode = connectReturnCode
-                    }).ConfigureAwait(false);
+                    }}).ConfigureAwait(false);
 
                     return;
                 }
@@ -64,11 +64,11 @@ namespace MQTTnet.Server
                 var result = await GetOrCreateClientSessionAsync(connectPacket).ConfigureAwait(false);
                 clientSession = result.Session;
 
-                await clientAdapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new MqttConnAckPacket
+                await clientAdapter.SendPacketsAsync(_options.DefaultCommunicationTimeout, cancellationToken, new[] { new MqttConnAckPacket
                 {
                     ConnectReturnCode = connectReturnCode,
                     IsSessionPresent = result.IsExistingSession
-                }).ConfigureAwait(false);
+                }}).ConfigureAwait(false);
 
                 ClientConnectedCallback?.Invoke(new ConnectedMqttClient
                 {

Frameworks/MQTTnet.NetStandard/Server/MqttClientSubscriptionsManager.cs

@@ -14,7 +14,7 @@ namespace MQTTnet.Server
         private readonly Dictionary<string, MqttQualityOfServiceLevel> _subscriptions = new Dictionary<string, MqttQualityOfServiceLevel>();
         private readonly IMqttServerOptions _options;
         private readonly string _clientId;
-        
+
         public MqttClientSubscriptionsManager(IMqttServerOptions options, string clientId)
         {
             _options = options ?? throw new ArgumentNullException(nameof(options));
@@ -30,7 +30,11 @@ namespace MQTTnet.Server
 
             var result = new MqttClientSubscribeResult
             {
-                ResponsePacket = subscribePacket.CreateResponse<MqttSubAckPacket>(),
+                ResponsePacket = new MqttSubAckPacket
+                {
+                    PacketIdentifier = subscribePacket.PacketIdentifier
+                },
+
                 CloseConnection = false
             };
 
@@ -87,7 +91,10 @@ namespace MQTTnet.Server
                 _semaphore.Release();
             }
 
-            return unsubscribePacket.CreateResponse<MqttUnsubAckPacket>();
+            return new MqttUnsubAckPacket
+            {
+                PacketIdentifier = unsubscribePacket.PacketIdentifier
+            };
         }
 
         public async Task<CheckSubscriptionsResult> CheckSubscriptionsAsync(MqttApplicationMessage applicationMessage)