Merge branch 'develop'

Build/MQTTnet.nuspec

@@ -2,7 +2,7 @@
 <package >
   <metadata>
     <id>MQTTnet</id>
-    <version>2.7.1</version>
+    <version>2.7.2</version>
     <authors>Christian Kratky</authors>
     <owners>Christian Kratky</owners>
     <licenseUrl>https://github.com/chkr1011/MQTTnet/blob/master/LICENSE</licenseUrl>
@@ -10,15 +10,11 @@
     <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
     <description>MQTTnet is a high performance .NET library for MQTT based communication. It provides a MQTT client and a MQTT server (broker).</description>
-    <releaseNotes>* [Core] Fixed wrong parsing of ConnAck packet for protocol version 3.1.0.
-* [Core] Log messages are now overriding ToString() and providing a ready to use text representation.
-* [Client] Optimized package dispatcher and added several new exceptions.
-* [Client] The _ManagedClient_ now has an event which is fired after a queued application message was processed (including exception).
-* [Client] The _ManagedClient_ now supports unsubscribing (thanks to @lerppana)
-* [Server] Fixed some minor async issues.
-* [Server] Fixed wrong comparison of the topic and QoS for retained messages.
-* [Server] Added a property which provides access to the used options (read only).
-* [Server] Fixed a null ref expection when using an interceptor and publishing via the server directly.
+    <releaseNotes>* [Client] Added the subprotocol "mqtt" as default for web socket based connections.
+* [Client] Added a new client setting called "KeepAliveSendInterval". It allows configuring the effective interval for sending ping requests.
+* [Client] The client will no longer send ping requests if other packets are sent within the configured interval.
+* [Server] The server now generates a valid packet identifier when disaptching publish packets to clients.
+* [Core] Add several new extension methods.
     </releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2018</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin</tags> 

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/ApplicationMessagePublisherExtensions.cs

@@ -1,16 +1,41 @@
 using System;
 using System.Threading.Tasks;
+using MQTTnet.Protocol;
 
 namespace MQTTnet
 {
     public static class ApplicationMessagePublisherExtensions
     {
-        public static Task PublishAsync(this IApplicationMessagePublisher client, params MqttApplicationMessage[] applicationMessages)
+        public static Task PublishAsync(this IApplicationMessagePublisher publisher, params MqttApplicationMessage[] applicationMessages)
         {
-            if (client == null) throw new ArgumentNullException(nameof(client));
+            if (publisher == null) throw new ArgumentNullException(nameof(publisher));
             if (applicationMessages == null) throw new ArgumentNullException(nameof(applicationMessages));
 
-            return client.PublishAsync(applicationMessages);
+            return publisher.PublishAsync(applicationMessages);
+        }
+
+        public static Task PublishAsync(this IApplicationMessagePublisher publisher, string topic)
+        {
+            if (publisher == null) throw new ArgumentNullException(nameof(publisher));
+            if (topic == null) throw new ArgumentNullException(nameof(topic));
+            
+            return publisher.PublishAsync(new MqttApplicationMessageBuilder().WithTopic(topic).Build());
+        }
+
+        public static Task PublishAsync(this IApplicationMessagePublisher publisher, string topic, string payload)
+        {
+            if (publisher == null) throw new ArgumentNullException(nameof(publisher));
+            if (topic == null) throw new ArgumentNullException(nameof(topic));
+
+            return publisher.PublishAsync(new MqttApplicationMessageBuilder().WithTopic(topic).WithPayload(payload).Build());
+        }
+
+        public static Task PublishAsync(this IApplicationMessagePublisher publisher, string topic, string payload, MqttQualityOfServiceLevel qualityOfServiceLevel)
+        {
+            if (publisher == null) throw new ArgumentNullException(nameof(publisher));
+            if (topic == null) throw new ArgumentNullException(nameof(topic));
+
+            return publisher.PublishAsync(new MqttApplicationMessageBuilder().WithTopic(topic).WithPayload(payload).WithQualityOfServiceLevel(qualityOfServiceLevel).Build());
         }
     }
 }

Frameworks/MQTTnet.NetStandard/Client/IMqttClientOptions.cs

@@ -13,6 +13,8 @@ namespace MQTTnet.Client
         
         TimeSpan CommunicationTimeout { get; }
         TimeSpan KeepAlivePeriod { get; }
+        TimeSpan? KeepAliveSendInterval { get; set; }
+
         MqttProtocolVersion ProtocolVersion { get; }
 
         IMqttClientChannelOptions ChannelOptions { get; }

Frameworks/MQTTnet.NetStandard/Client/MqttClient.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
@@ -15,6 +16,7 @@ namespace MQTTnet.Client
     public class MqttClient : IMqttClient
     {
         private readonly MqttPacketIdentifierProvider _packetIdentifierProvider = new MqttPacketIdentifierProvider();
+        private readonly Stopwatch _sendTracker = new Stopwatch();
         private readonly IMqttClientAdapterFactory _adapterFactory;
         private readonly MqttPacketDispatcher _packetDispatcher;
         private readonly IMqttNetLogger _logger;
@@ -59,10 +61,12 @@ namespace MQTTnet.Client
                 _logger.Trace<MqttClient>("Connection with server established.");
 
                 await StartReceivingPacketsAsync(_cancellationTokenSource.Token).ConfigureAwait(false);
-                var connectResponse = await AuthenticateAsync(options.WillMessage).ConfigureAwait(false);
 
+                var connectResponse = await AuthenticateAsync(options.WillMessage).ConfigureAwait(false);
                 _logger.Trace<MqttClient>("MQTT connection with server established.");
 
+                _sendTracker.Restart();
+
                 if (_options.KeepAlivePeriod != TimeSpan.Zero)
                 {
                     StartSendingKeepAliveMessages(_cancellationTokenSource.Token);
@@ -149,7 +153,7 @@ namespace MQTTnet.Client
                     case MqttQualityOfServiceLevel.AtMostOnce:
                         {
                             // No packet identifier is used for QoS 0 [3.3.2.2 Packet Identifier]
-                            await _adapter.SendPacketsAsync(_options.CommunicationTimeout, _cancellationTokenSource.Token, qosGroup).ConfigureAwait(false);
+                            await SendAsync(qosGroup.ToArray()).ConfigureAwait(false);
                             break;
                         }
                     case MqttQualityOfServiceLevel.AtLeastOnce:
@@ -167,8 +171,14 @@ namespace MQTTnet.Client
                             foreach (var publishPacket in qosGroup)
                             {
                                 publishPacket.PacketIdentifier = _packetIdentifierProvider.GetNewPacketIdentifier();
+
                                 var pubRecPacket = await SendAndReceiveAsync<MqttPubRecPacket>(publishPacket).ConfigureAwait(false);
-                                await SendAndReceiveAsync<MqttPubCompPacket>(pubRecPacket.CreateResponse<MqttPubRelPacket>()).ConfigureAwait(false);
+                                var pubRelPacket = new MqttPubRelPacket
+                                {
+                                    PacketIdentifier = pubRecPacket.PacketIdentifier
+                                };
+
+                                await SendAndReceiveAsync<MqttPubCompPacket>(pubRelPacket).ConfigureAwait(false);
                             }
 
                             break;
@@ -325,24 +335,31 @@ namespace MQTTnet.Client
 
         private Task ProcessReceivedPubRelPacket(MqttPubRelPacket pubRelPacket)
         {
-            return SendAsync(pubRelPacket.CreateResponse<MqttPubCompPacket>());
+            var response = new MqttPubCompPacket
+            {
+                PacketIdentifier = pubRelPacket.PacketIdentifier
+            };
+
+            return SendAsync(response);
         }
 
-        private Task SendAsync(MqttBasePacket packet)
+        private Task SendAsync(params MqttBasePacket[] packets)
         {
-            return _adapter.SendPacketsAsync(_options.CommunicationTimeout, _cancellationTokenSource.Token, packet);
+            _sendTracker.Restart();
+            return _adapter.SendPacketsAsync(_options.CommunicationTimeout, _cancellationTokenSource.Token, packets);
         }
 
         private async Task<TResponsePacket> SendAndReceiveAsync<TResponsePacket>(MqttBasePacket requestPacket) where TResponsePacket : MqttBasePacket
         {
-            ushort identifier = 0;
+            ushort? identifier = null;
             if (requestPacket is IMqttPacketWithIdentifier requestPacketWithIdentifier)
             {
                 identifier = requestPacketWithIdentifier.PacketIdentifier;
             }
 
             var packetAwaiter = _packetDispatcher.WaitForPacketAsync(typeof(TResponsePacket), identifier, _options.CommunicationTimeout);
-            await _adapter.SendPacketsAsync(_options.CommunicationTimeout, _cancellationTokenSource.Token, requestPacket).ConfigureAwait(false);
+            await SendAsync(requestPacket).ConfigureAwait(false);
+
             return (TResponsePacket)await packetAwaiter.ConfigureAwait(false);
         }
 
@@ -354,8 +371,22 @@ namespace MQTTnet.Client
             {
                 while (!cancellationToken.IsCancellationRequested)
                 {
-                    await SendAndReceiveAsync<MqttPingRespPacket>(new MqttPingReqPacket()).ConfigureAwait(false);
-                    await Task.Delay(_options.KeepAlivePeriod, cancellationToken).ConfigureAwait(false);
+                    TimeSpan keepAliveSendInterval;
+                    if (_options.KeepAliveSendInterval.HasValue)
+                    {
+                        keepAliveSendInterval = _options.KeepAliveSendInterval.Value;
+                    }
+                    else
+                    {
+                        keepAliveSendInterval = TimeSpan.FromSeconds(_options.KeepAlivePeriod.TotalSeconds * 0.75);
+                    }
+
+                    if (_sendTracker.Elapsed > keepAliveSendInterval)
+                    {
+                        await SendAndReceiveAsync<MqttPingRespPacket>(new MqttPingReqPacket()).ConfigureAwait(false);
+                    }
+                    
+                    await Task.Delay(keepAliveSendInterval, cancellationToken).ConfigureAwait(false);
                 }
             }
             catch (OperationCanceledException)

Frameworks/MQTTnet.NetStandard/Client/MqttClientExtensions.cs

@@ -24,6 +24,14 @@ namespace MQTTnet.Client
             return client.SubscribeAsync(new TopicFilterBuilder().WithTopic(topic).WithQualityOfServiceLevel(qualityOfServiceLevel).Build());
         }
 
+        public static Task<IList<MqttSubscribeResult>> SubscribeAsync(this IMqttClient client, string topic)
+        {
+            if (client == null) throw new ArgumentNullException(nameof(client));
+            if (topic == null) throw new ArgumentNullException(nameof(topic));
+
+            return client.SubscribeAsync(new TopicFilterBuilder().WithTopic(topic).Build());
+        }
+
         public static Task UnsubscribeAsync(this IMqttClient client, params string[] topicFilters)
         {
             if (client == null) throw new ArgumentNullException(nameof(client));

Frameworks/MQTTnet.NetStandard/Client/MqttClientOptions.cs

@@ -13,7 +13,9 @@ namespace MQTTnet.Client
 
         public IMqttClientCredentials Credentials { get; set; } = new MqttClientCredentials();
 
-        public TimeSpan KeepAlivePeriod { get; set; } = TimeSpan.FromSeconds(5);
+        public TimeSpan KeepAlivePeriod { get; set; } = TimeSpan.FromSeconds(15);
+
+        public TimeSpan? KeepAliveSendInterval { get; set; }
 
         public TimeSpan CommunicationTimeout { get; set; } = TimeSpan.FromSeconds(10);
 

Frameworks/MQTTnet.NetStandard/Client/MqttClientWebSocketOptions.cs

@@ -9,7 +9,7 @@ namespace MQTTnet.Client
 
         public IDictionary<string, string> RequestHeaders { get; set; }
 
-        public ICollection<string> SubProtocols { get; set; }
+        public ICollection<string> SubProtocols { get; set; } = new List<string> { "mqtt" };
 
         public CookieContainer CookieContainer { get; set; }
 

Frameworks/MQTTnet.NetStandard/Client/MqttPacketDispatcher.cs

@@ -18,7 +18,7 @@ namespace MQTTnet.Client
             _logger = logger ?? throw new ArgumentNullException(nameof(logger));
         }
 
-        public async Task<MqttBasePacket> WaitForPacketAsync(Type responseType, ushort identifier, TimeSpan timeout)
+        public async Task<MqttBasePacket> WaitForPacketAsync(Type responseType, ushort? identifier, TimeSpan timeout)
         {
             var packetAwaiter = AddPacketAwaiter(responseType, identifier);
             try
@@ -44,13 +44,13 @@ namespace MQTTnet.Client
 
             if (_awaiters.TryGetValue(type, out var byId))
             {
-                ushort identifier = 0;
+                ushort? identifier = 0;
                 if (packet is IMqttPacketWithIdentifier packetWithIdentifier)
                 {
                     identifier = packetWithIdentifier.PacketIdentifier;
                 }
 
-                if (byId.TryRemove(identifier, out var tcs))
+                if (byId.TryRemove(identifier.Value, out var tcs))
                 {
                     tcs.TrySetResult(packet);
                     return;
@@ -65,12 +65,17 @@ namespace MQTTnet.Client
             _awaiters.Clear();
         }
 
-        private TaskCompletionSource<MqttBasePacket> AddPacketAwaiter(Type responseType, ushort identifier)
+        private TaskCompletionSource<MqttBasePacket> AddPacketAwaiter(Type responseType, ushort? identifier)
         {
             var tcs = new TaskCompletionSource<MqttBasePacket>();
 
+            if (!identifier.HasValue)
+            {
+                identifier = 0;
+            }
+
             var byId = _awaiters.GetOrAdd(responseType, key => new ConcurrentDictionary<ushort, TaskCompletionSource<MqttBasePacket>>());
-            if (!byId.TryAdd(identifier, tcs))
+            if (!byId.TryAdd(identifier.Value, tcs))
             {
                 throw new InvalidOperationException($"The packet dispatcher already has an awaiter for packet of type '{responseType}' with identifier {identifier}.");
             }
@@ -78,10 +83,15 @@ namespace MQTTnet.Client
             return tcs;
         }
 
-        private void RemovePacketAwaiter(Type responseType, ushort identifier)
+        private void RemovePacketAwaiter(Type responseType, ushort? identifier)
         {
+            if (!identifier.HasValue)
+            {
+                identifier = 0;
+            }
+
             var byId = _awaiters.GetOrAdd(responseType, key => new ConcurrentDictionary<ushort, TaskCompletionSource<MqttBasePacket>>());
-            byId.TryRemove(identifier, out var _);
+            byId.TryRemove(identifier.Value, out var _);
         }
     }
 }

Frameworks/MQTTnet.NetStandard/Implementations/MqttTcpChannel.Uwp.cs

@@ -69,12 +69,6 @@ namespace MQTTnet.Implementations
 
         public void Dispose()
         {
-            SendStream?.Dispose();
-            SendStream = null;
-
-            ReceiveStream?.Dispose();
-            ReceiveStream = null;
-
             _socket?.Dispose();
             _socket = null;
         }

Frameworks/MQTTnet.NetStandard/Implementations/WebSocketStream.cs

@@ -11,9 +11,9 @@ namespace MQTTnet.Implementations
 {
     public class WebSocketStream : Stream
     {
-        private readonly WebSocket _webSocket;
-        private readonly byte[] _chunkBuffer = new byte[MqttWebSocketChannel.BufferSize];
+        private readonly byte[] _chunckBuffer = new byte[MqttWebSocketChannel.BufferSize];
         private readonly Queue<byte> _buffer = new Queue<byte>(MqttWebSocketChannel.BufferSize);
+        private readonly WebSocket _webSocket;
 
         public WebSocketStream(WebSocket webSocket)
         {
@@ -55,25 +55,28 @@ namespace MQTTnet.Implementations
             // Use existing date from buffer.
             while (count > 0 && _buffer.Any())
             {
-                buffer[offset++] = _buffer.Dequeue();
+                buffer[offset] = _buffer.Dequeue();
                 count--;
                 bytesRead++;
+                offset++;
             }
 
             if (count == 0)
             {
                 return bytesRead;
             }
-            
+
+            // Fetch new data if the buffer is not full.
             while (_webSocket.State == WebSocketState.Open)
             {
-                await FetchChunkAsync(cancellationToken);
+                await FetchChunkAsync(cancellationToken).ConfigureAwait(false);
 
                 while (count > 0 && _buffer.Any())
                 {
-                    buffer[offset++] = _buffer.Dequeue();
+                    buffer[offset] = _buffer.Dequeue();
                     count--;
                     bytesRead++;
+                    offset++;
                 }
 
                 if (count == 0)
@@ -111,19 +114,24 @@ namespace MQTTnet.Implementations
         }
 
         private async Task FetchChunkAsync(CancellationToken cancellationToken)
-        {
-            var response = await _webSocket.ReceiveAsync(new ArraySegment<byte>(_chunkBuffer, 0, _chunkBuffer.Length), cancellationToken).ConfigureAwait(false);
-
-            for (var i = 0; i < response.Count; i++)
-            {
-                var @byte = _chunkBuffer[i];
-                _buffer.Enqueue(@byte);
-            }
+        {   
+            var response = await _webSocket.ReceiveAsync(new ArraySegment<byte>(_chunckBuffer, 0, _chunckBuffer.Length), cancellationToken).ConfigureAwait(false);
 
             if (response.MessageType == WebSocketMessageType.Close)
             {
                 await _webSocket.CloseAsync(WebSocketCloseStatus.NormalClosure, string.Empty, cancellationToken).ConfigureAwait(false);
             }
+            else if (response.MessageType == WebSocketMessageType.Binary)
+            {
+                for (var i = 0; i < response.Count; i++)
+                {
+                    _buffer.Enqueue(_chunckBuffer[i]);
+                }
+            }
+            else if (response.MessageType == WebSocketMessageType.Text)
+            {
+                throw new MqttProtocolViolationException("WebSocket channel received TEXT message.");
+            }
         }
     }
 }

Frameworks/MQTTnet.NetStandard/ManagedClient/ManagedMqttClientOptionsBuilder.cs

@@ -6,6 +6,7 @@ namespace MQTTnet.ManagedClient
     public class ManagedMqttClientOptionsBuilder
     {
         private readonly ManagedMqttClientOptions _options = new ManagedMqttClientOptions();
+        private MqttClientOptionsBuilder _clientOptionsBuilder;
 
         public ManagedMqttClientOptionsBuilder WithAutoReconnectDelay(TimeSpan value)
         {
@@ -21,7 +22,24 @@ namespace MQTTnet.ManagedClient
 
         public ManagedMqttClientOptionsBuilder WithClientOptions(IMqttClientOptions value)
         {
+            if (_clientOptionsBuilder != null)
+            {
+                throw new InvalidOperationException("Cannot use client options builder and client options at the same time.");
+            }
+
             _options.ClientOptions = value ?? throw new ArgumentNullException(nameof(value));
+
+            return this;
+        }
+
+        public ManagedMqttClientOptionsBuilder WithClientOptions(MqttClientOptionsBuilder builder)
+        {
+            if (_options.ClientOptions != null)
+            {
+                throw new InvalidOperationException("Cannot use client options builder and client options at the same time.");
+            }
+
+            _clientOptionsBuilder = builder;
             return this;
         }
 
@@ -29,15 +47,22 @@ namespace MQTTnet.ManagedClient
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
-            var builder = new MqttClientOptionsBuilder();
-            options(builder);
-            _options.ClientOptions = builder.Build();
+            if (_clientOptionsBuilder != null)
+            {
+                _clientOptionsBuilder = new MqttClientOptionsBuilder();
+            }
 
+            options(_clientOptionsBuilder);
             return this;
         }
 
         public ManagedMqttClientOptions Build()
         {
+            if (_clientOptionsBuilder != null)
+            {
+                _options.ClientOptions = _clientOptionsBuilder.Build();
+            }
+
             if (_options.ClientOptions == null)
             {
                 throw new InvalidOperationException("The ClientOptions cannot be null.");

Frameworks/MQTTnet.NetStandard/MqttApplicationMessageExtensions.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Text;
+
+namespace MQTTnet
+{
+    public static class MqttApplicationMessageExtensions
+    {
+        public static string ConvertPayloadToString(this MqttApplicationMessage applicationMessage)
+        {
+            if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
+
+            if (applicationMessage.Payload == null)
+            {
+                return null;
+            }
+
+            if (applicationMessage.Payload.Length == 0)
+            {
+                return string.Empty;
+            }
+
+            return Encoding.UTF8.GetString(applicationMessage.Payload, 0, applicationMessage.Payload.Length);
+        }
+    }
+}

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)

Tests/MQTTnet.TestApp.UniversalWindows/MQTTnet.TestApp.UniversalWindows.csproj

@@ -12,7 +12,7 @@
     <DefaultLanguage>en-US</DefaultLanguage>
     <TargetPlatformIdentifier>UAP</TargetPlatformIdentifier>
     <TargetPlatformVersion Condition=" '$(TargetPlatformVersion)' == '' ">10.0.16299.0</TargetPlatformVersion>
-    <TargetPlatformMinVersion>10.0.15063.0</TargetPlatformMinVersion>
+    <TargetPlatformMinVersion>10.0.16299.0</TargetPlatformMinVersion>
     <MinimumVisualStudioVersion>14</MinimumVisualStudioVersion>
     <FileAlignment>512</FileAlignment>
     <ProjectTypeGuids>{A5A43C5B-DE2A-4C0C-9213-0A381AF9435A};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>

Tests/MQTTnet.TestApp.UniversalWindows/MainPage.xaml

@@ -148,7 +148,7 @@
             </PivotItem>
             <PivotItem Header="Log">
                 <StackPanel Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
-                    <Button Click="Clear" Width="120">Clear</Button>
+                    <Button Click="ClearLog" Width="120">Clear</Button>
                 </StackPanel>
             </PivotItem>
         </Pivot>

Tests/MQTTnet.TestApp.UniversalWindows/MainPage.xaml.cs

@@ -42,7 +42,8 @@ namespace MQTTnet.TestApp.UniversalWindows
             foreach (var traceMessage in _traceMessages)
             {
                 logText.AppendFormat(
-                    "[{0:yyyy-MM-dd HH:mm:ss.fff}] [{1}] [{2}] [{3}] [{4}]{5}", traceMessage.Timestamp,
+                    "[{0:yyyy-MM-dd HH:mm:ss.fff}] [{1}] [{2}] [{3}] [{4}]{5}",
+                    traceMessage.Timestamp,
                     traceMessage.Level,
                     traceMessage.Source,
                     traceMessage.ThreadId,
@@ -197,8 +198,13 @@ namespace MQTTnet.TestApp.UniversalWindows
             }
         }
 
-        private void Clear(object sender, RoutedEventArgs e)
+        private void ClearLog(object sender, RoutedEventArgs e)
         {
+            while (_traceMessages.Count > 0)
+            {
+                _traceMessages.TryDequeue(out _);
+            }
+
             Trace.Text = string.Empty;
         }