Fix message encoding bugs.

Build/MQTTnet.nuspec

@@ -11,7 +11,9 @@
     <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>
-* [Server] Fixed a bug which returns wrong flag for existing sessions (thanks to @avengerstark).
+* [Core] Fixed missing properties from PUBLISH packet in _MqttApplicationMessage_ (thanks to @pcbing).
+* [Core] Fixed wrong encoding of PUBREL and PUBCOMP packets for MQTTv5 (thanks to @perphilipp).
+* [Server] Fixed a bug which returns wrong flag for existing session in CONNACK packet (thanks to @avengerstark).
 * [nuget] .NET Framework builds are now using 4.5.2 or 4.6.1 builds instead of netstandard 2.0.
     </releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2019</copyright>

Source/MQTTnet/Formatter/V5/MqttV500DataConverter.cs

@@ -63,6 +63,13 @@ namespace MQTTnet.Formatter.V5
                 Payload = publishPacket.Payload,
                 QualityOfServiceLevel = publishPacket.QualityOfServiceLevel,
                 Retain = publishPacket.Retain,
+                ResponseTopic = publishPacket.Properties?.ResponseTopic,
+                ContentType = publishPacket.Properties?.ContentType,
+                CorrelationData = publishPacket.Properties?.CorrelationData,
+                MessageExpiryInterval = publishPacket.Properties?.MessageExpiryInterval,
+                SubscriptionIdentifier = publishPacket.Properties?.SubscriptionIdentifier,
+                TopicAlias = publishPacket.Properties?.TopicAlias,
+                PayloadFormatIndicator = publishPacket.Properties?.PayloadFormatIndicator,
                 UserProperties = publishPacket.Properties?.UserProperties ?? new List<MqttUserProperty>()
             };
         }

Source/MQTTnet/Formatter/V5/MqttV500PacketEncoder.cs

@@ -343,9 +343,6 @@ namespace MQTTnet.Formatter.V5
                 ThrowReasonCodeNotSetException();
             }
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
-            packetWriter.Write((byte)packet.ReasonCode.Value);
-
             var propertiesWriter = new MqttV500PropertiesWriter();
             if (packet.Properties != null)
             {
@@ -353,7 +350,9 @@ namespace MQTTnet.Formatter.V5
                 propertiesWriter.WriteUserProperties(packet.Properties.UserProperties);
             }
 
-            if (packetWriter.Length > 0 || packet.ReasonCode.Value != MqttPubRelReasonCode.Success)
+            packetWriter.Write(packet.PacketIdentifier.Value);
+            
+            if (propertiesWriter.Length > 0 || packet.ReasonCode.Value != MqttPubRelReasonCode.Success)
             {
                 packetWriter.Write((byte)packet.ReasonCode.Value);
                 propertiesWriter.WriteToPacket(packetWriter);
@@ -372,8 +371,7 @@ namespace MQTTnet.Formatter.V5
             }
 
             packetWriter.Write(packet.PacketIdentifier.Value);
-            packetWriter.Write((byte)packet.ReasonCode.Value);
-
+            
             var propertiesWriter = new MqttV500PropertiesWriter();
             if (packet.Properties != null)
             {
@@ -381,7 +379,7 @@ namespace MQTTnet.Formatter.V5
                 propertiesWriter.WriteUserProperties(packet.Properties.UserProperties);
             }
 
-            if (packetWriter.Length > 0 || packet.ReasonCode.Value != MqttPubCompReasonCode.Success)
+            if (propertiesWriter.Length > 0 || packet.ReasonCode.Value != MqttPubCompReasonCode.Success)
             {
                 packetWriter.Write((byte)packet.ReasonCode.Value);
                 propertiesWriter.WriteToPacket(packetWriter);

Source/MQTTnet/Formatter/V5/MqttV500PropertiesWriter.cs

@@ -7,8 +7,11 @@ namespace MQTTnet.Formatter.V5
 {
     public class MqttV500PropertiesWriter
     {
+        // TODO: Consider lazy init on first write to avoid useless allocations.
         private readonly MqttPacketWriter _packetWriter = new MqttPacketWriter();
 
+        public int Length => _packetWriter.Length;
+
         public void WriteUserProperties(List<MqttUserProperty> userProperties)
         {
             if (userProperties == null || userProperties.Count == 0)