Refactor package object model.

Source/MQTTnet/Formatter/IMqttDataConverter.cs

@@ -1,10 +1,12 @@
-using MQTTnet.Client.Connecting;
+using System.Collections.Generic;
+using MQTTnet.Client.Connecting;
 using MQTTnet.Client.Disconnecting;
 using MQTTnet.Client.Options;
 using MQTTnet.Client.Publishing;
 using MQTTnet.Client.Subscribing;
 using MQTTnet.Client.Unsubscribing;
 using MQTTnet.Packets;
+using MQTTnet.Protocol;
 using MQTTnet.Server;
 using MqttClientSubscribeResult = MQTTnet.Client.Subscribing.MqttClientSubscribeResult;
 
@@ -30,8 +32,12 @@ namespace MQTTnet.Formatter
 
         MqttSubscribePacket CreateSubscribePacket(MqttClientSubscribeOptions options);
 
+        MqttSubAckPacket CreateSubAckPacket(MqttSubscribePacket subscribePacket, Server.MqttClientSubscribeResult subscribeResult);
+
         MqttUnsubscribePacket CreateUnsubscribePacket(MqttClientUnsubscribeOptions options);
 
+        MqttUnsubAckPacket CreateUnsubAckPacket(MqttUnsubscribePacket unsubscribePacket, List<MqttUnsubscribeReasonCode> reasonCodes);
+
         MqttDisconnectPacket CreateDisconnectPacket(MqttClientDisconnectOptions options);
 
         MqttClientPublishResult CreatePublishResult(MqttPubAckPacket pubAckPacket);

Source/MQTTnet/Formatter/MqttPacketFormatterAdapter.cs

@@ -8,7 +8,7 @@ using MQTTnet.Packets;
 
 namespace MQTTnet.Formatter
 {
-    public class MqttPacketFormatterAdapter
+    public sealed class MqttPacketFormatterAdapter
     {
         IMqttPacketFormatter _formatter;
                
@@ -77,17 +77,6 @@ namespace MQTTnet.Formatter
             UseProtocolVersion(protocolVersion);
         }
 
-        private void UseProtocolVersion(MqttProtocolVersion protocolVersion)
-        {
-            if (protocolVersion == MqttProtocolVersion.Unknown)
-            {
-                throw new InvalidOperationException("MQTT protocol version is invalid.");
-            }
-
-            ProtocolVersion = protocolVersion;
-            _formatter = GetMqttPacketFormatter(protocolVersion, Writer);
-        }
-
         public static IMqttPacketFormatter GetMqttPacketFormatter(MqttProtocolVersion protocolVersion, IMqttPacketWriter writer)
         {
             if (protocolVersion == MqttProtocolVersion.Unknown)
@@ -116,7 +105,18 @@ namespace MQTTnet.Formatter
             }
         }
 
-        MqttProtocolVersion ParseProtocolVersion(ReceivedMqttPacket receivedMqttPacket)
+        void UseProtocolVersion(MqttProtocolVersion protocolVersion)
+        {
+            if (protocolVersion == MqttProtocolVersion.Unknown)
+            {
+                throw new InvalidOperationException("MQTT protocol version is invalid.");
+            }
+
+            ProtocolVersion = protocolVersion;
+            _formatter = GetMqttPacketFormatter(protocolVersion, Writer);
+        }
+
+        static MqttProtocolVersion ParseProtocolVersion(ReceivedMqttPacket receivedMqttPacket)
         {
             if (receivedMqttPacket == null) throw new ArgumentNullException(nameof(receivedMqttPacket));
 

Source/MQTTnet/Formatter/V3/MqttV310DataConverter.cs

@@ -9,6 +9,7 @@ using MQTTnet.Packets;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using MqttClientSubscribeResult = MQTTnet.Client.Subscribing.MqttClientSubscribeResult;
 
@@ -172,6 +173,18 @@ namespace MQTTnet.Formatter.V3
             return subscribePacket;
         }
 
+        public MqttSubAckPacket CreateSubAckPacket(MqttSubscribePacket subscribePacket, Server.MqttClientSubscribeResult subscribeResult)
+        {
+            var subackPacket = new MqttSubAckPacket
+            {
+                PacketIdentifier = subscribePacket.PacketIdentifier
+            };
+
+            subackPacket.ReturnCodes.AddRange(subscribeResult.ReturnCodes);
+
+            return subackPacket;
+        }
+
         public MqttUnsubscribePacket CreateUnsubscribePacket(MqttClientUnsubscribeOptions options)
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
@@ -182,6 +195,15 @@ namespace MQTTnet.Formatter.V3
             return unsubscribePacket;
         }
 
+        public MqttUnsubAckPacket CreateUnsubAckPacket(MqttUnsubscribePacket unsubscribePacket, List<MqttUnsubscribeReasonCode> reasonCodes)
+        {
+            return new MqttUnsubAckPacket
+            {
+                PacketIdentifier = unsubscribePacket.PacketIdentifier,
+                ReasonCodes = reasonCodes
+            };
+        }
+
         public MqttDisconnectPacket CreateDisconnectPacket(MqttClientDisconnectOptions options)
         {
             if (options.ReasonCode != MqttClientDisconnectReason.NormalDisconnection || options.ReasonString != null)

Source/MQTTnet/Formatter/V3/MqttV310PacketFormatter.cs

@@ -210,7 +210,7 @@ namespace MQTTnet.Formatter.V3
 
             var topic = receivedMqttPacket.Body.ReadStringWithLengthPrefix();
 
-            ushort? packetIdentifier = null;
+            ushort packetIdentifier = 0;
             if (qualityOfServiceLevel > MqttQualityOfServiceLevel.AtMostOnce)
             {
                 packetIdentifier = receivedMqttPacket.Body.ReadTwoByteInteger();
@@ -414,12 +414,12 @@ namespace MQTTnet.Formatter.V3
 
         static byte EncodePubRelPacket(MqttPubRelPacket packet, IMqttPacketWriter packetWriter)
         {
-            if (!packet.PacketIdentifier.HasValue)
+            if (packet.PacketIdentifier == 0)
             {
                 throw new MqttProtocolViolationException("PubRel packet has no packet identifier.");
             }
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
 
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.PubRel, 0x02);
         }
@@ -432,12 +432,12 @@ namespace MQTTnet.Formatter.V3
 
             if (packet.QualityOfServiceLevel > MqttQualityOfServiceLevel.AtMostOnce)
             {
-                if (!packet.PacketIdentifier.HasValue)
+                if (packet.PacketIdentifier == 0)
                 {
                     throw new MqttProtocolViolationException("Publish packet has no packet identifier.");
                 }
 
-                packetWriter.Write(packet.PacketIdentifier.Value);
+                packetWriter.Write(packet.PacketIdentifier);
             }
             else
             {
@@ -471,36 +471,36 @@ namespace MQTTnet.Formatter.V3
 
         static byte EncodePubAckPacket(MqttPubAckPacket packet, IMqttPacketWriter packetWriter)
         {
-            if (!packet.PacketIdentifier.HasValue)
+            if (packet.PacketIdentifier == 0)
             {
                 throw new MqttProtocolViolationException("PubAck packet has no packet identifier.");
             }
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
 
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.PubAck);
         }
 
         static byte EncodePubRecPacket(MqttPubRecPacket packet, IMqttPacketWriter packetWriter)
         {
-            if (!packet.PacketIdentifier.HasValue)
+            if (packet.PacketIdentifier == 0)
             {
                 throw new MqttProtocolViolationException("PubRec packet has no packet identifier.");
             }
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
 
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.PubRec);
         }
 
         static byte EncodePubCompPacket(MqttPubCompPacket packet, IMqttPacketWriter packetWriter)
         {
-            if (!packet.PacketIdentifier.HasValue)
+            if (packet.PacketIdentifier == 0)
             {
                 throw new MqttProtocolViolationException("PubComp packet has no packet identifier.");
             }
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
 
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.PubComp);
         }
@@ -509,12 +509,12 @@ namespace MQTTnet.Formatter.V3
         {
             if (!packet.TopicFilters.Any()) throw new MqttProtocolViolationException("At least one topic filter must be set [MQTT-3.8.3-3].");
 
-            if (!packet.PacketIdentifier.HasValue)
+            if (packet.PacketIdentifier == 0)
             {
                 throw new MqttProtocolViolationException("Subscribe packet has no packet identifier.");
             }
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
 
             if (packet.TopicFilters?.Count > 0)
             {
@@ -530,12 +530,12 @@ namespace MQTTnet.Formatter.V3
 
         static byte EncodeSubAckPacket(MqttSubAckPacket packet, IMqttPacketWriter packetWriter)
         {
-            if (!packet.PacketIdentifier.HasValue)
+            if (packet.PacketIdentifier == 0)
             {
                 throw new MqttProtocolViolationException("SubAck packet has no packet identifier.");
             }
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
 
             if (packet.ReturnCodes?.Any() == true)
             {
@@ -552,12 +552,12 @@ namespace MQTTnet.Formatter.V3
         {
             if (!packet.TopicFilters.Any()) throw new MqttProtocolViolationException("At least one topic filter must be set [MQTT-3.10.3-2].");
 
-            if (!packet.PacketIdentifier.HasValue)
+            if (packet.PacketIdentifier == 0)
             {
                 throw new MqttProtocolViolationException("Unsubscribe packet has no packet identifier.");
             }
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
 
             if (packet.TopicFilters?.Any() == true)
             {
@@ -572,12 +572,12 @@ namespace MQTTnet.Formatter.V3
 
         static byte EncodeUnsubAckPacket(MqttUnsubAckPacket packet, IMqttPacketWriter packetWriter)
         {
-            if (!packet.PacketIdentifier.HasValue)
+            if (packet.PacketIdentifier == 0)
             {
                 throw new MqttProtocolViolationException("UnsubAck packet has no packet identifier.");
             }
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.UnsubAck);
         }
 

Source/MQTTnet/Formatter/V3/MqttV311PacketFormatter.cs

@@ -4,7 +4,7 @@ using MQTTnet.Protocol;
 
 namespace MQTTnet.Formatter.V3
 {
-    public class MqttV311PacketFormatter : MqttV310PacketFormatter
+    public sealed class MqttV311PacketFormatter : MqttV310PacketFormatter
     {
         public MqttV311PacketFormatter(IMqttPacketWriter packetWriter)
             : base(packetWriter)

Source/MQTTnet/Formatter/V5/MqttV500DataConverter.cs

@@ -200,6 +200,18 @@ namespace MQTTnet.Formatter.V5
             return packet;
         }
 
+        public MqttSubAckPacket CreateSubAckPacket(MqttSubscribePacket subscribePacket, Server.MqttClientSubscribeResult subscribeResult)
+        {
+            var subackPacket = new MqttSubAckPacket
+            {
+                PacketIdentifier = subscribePacket.PacketIdentifier
+            };
+
+            subackPacket.ReasonCodes.AddRange(subscribeResult.ReasonCodes);
+
+            return subackPacket;
+        }
+
         public MqttUnsubscribePacket CreateUnsubscribePacket(MqttClientUnsubscribeOptions options)
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
@@ -215,6 +227,15 @@ namespace MQTTnet.Formatter.V5
             return packet;
         }
 
+        public MqttUnsubAckPacket CreateUnsubAckPacket(MqttUnsubscribePacket unsubscribePacket, List<MqttUnsubscribeReasonCode> reasonCodes)
+        {
+            return new MqttUnsubAckPacket
+            {
+                PacketIdentifier = unsubscribePacket.PacketIdentifier,
+                ReasonCodes = reasonCodes
+            };
+        }
+
         public MqttDisconnectPacket CreateDisconnectPacket(MqttClientDisconnectOptions options)
         {
             var packet = new MqttDisconnectPacket();

Source/MQTTnet/Formatter/V5/MqttV500PacketEncoder.cs

@@ -6,14 +6,13 @@ using MQTTnet.Protocol;
 
 namespace MQTTnet.Formatter.V5
 {
-    public class MqttV500PacketEncoder
+    public sealed class MqttV500PacketEncoder
     {
-        private readonly IMqttPacketWriter _packetWriter;
+        readonly IMqttPacketWriter _packetWriter;
 
         public MqttV500PacketEncoder()
             : this(new MqttPacketWriter())
         {
-
         }
 
         public MqttV500PacketEncoder(IMqttPacketWriter packetWriter)
@@ -21,7 +20,6 @@ namespace MQTTnet.Formatter.V5
             _packetWriter = packetWriter;
         }
 
-
         public ArraySegment<byte> Encode(MqttBasePacket packet)
         {
             if (packet == null) throw new ArgumentNullException(nameof(packet));
@@ -52,7 +50,7 @@ namespace MQTTnet.Formatter.V5
             _packetWriter.FreeBuffer();
         }
 
-        private static byte EncodePacket(MqttBasePacket packet, IMqttPacketWriter packetWriter)
+        static byte EncodePacket(MqttBasePacket packet, IMqttPacketWriter packetWriter)
         {
             switch (packet)
             {
@@ -76,7 +74,7 @@ namespace MQTTnet.Formatter.V5
             }
         }
 
-        private static byte EncodeConnectPacket(MqttConnectPacket packet, IMqttPacketWriter packetWriter)
+        static byte EncodeConnectPacket(MqttConnectPacket packet, IMqttPacketWriter packetWriter)
         {
             if (packet == null) throw new ArgumentNullException(nameof(packet));
             if (packetWriter == null) throw new ArgumentNullException(nameof(packetWriter));
@@ -176,7 +174,7 @@ namespace MQTTnet.Formatter.V5
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.Connect);
         }
 
-        private static byte EncodeConnAckPacket(MqttConnAckPacket packet, IMqttPacketWriter packetWriter)
+        static byte EncodeConnAckPacket(MqttConnAckPacket packet, IMqttPacketWriter packetWriter)
         {
             if (packet == null) throw new ArgumentNullException(nameof(packet));
             if (packetWriter == null) throw new ArgumentNullException(nameof(packetWriter));
@@ -221,7 +219,7 @@ namespace MQTTnet.Formatter.V5
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.ConnAck);
         }
 
-        private static byte EncodePublishPacket(MqttPublishPacket packet, IMqttPacketWriter packetWriter)
+        static byte EncodePublishPacket(MqttPublishPacket packet, IMqttPacketWriter packetWriter)
         {
             if (packet == null) throw new ArgumentNullException(nameof(packet));
             if (packetWriter == null) throw new ArgumentNullException(nameof(packetWriter));
@@ -235,12 +233,12 @@ namespace MQTTnet.Formatter.V5
 
             if (packet.QualityOfServiceLevel > MqttQualityOfServiceLevel.AtMostOnce)
             {
-                if (!packet.PacketIdentifier.HasValue)
+                if (packet.PacketIdentifier == 0)
                 {
                     throw new MqttProtocolViolationException("Publish packet has no packet identifier.");
                 }
 
-                packetWriter.Write(packet.PacketIdentifier.Value);
+                packetWriter.Write(packet.PacketIdentifier);
             }
             else
             {
@@ -287,12 +285,12 @@ namespace MQTTnet.Formatter.V5
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.Publish, fixedHeader);
         }
 
-        private static byte EncodePubAckPacket(MqttPubAckPacket packet, IMqttPacketWriter packetWriter)
+        static byte EncodePubAckPacket(MqttPubAckPacket packet, IMqttPacketWriter packetWriter)
         {
             if (packet == null) throw new ArgumentNullException(nameof(packet));
             if (packetWriter == null) throw new ArgumentNullException(nameof(packetWriter));
 
-            if (!packet.PacketIdentifier.HasValue)
+            if (packet.PacketIdentifier == 0)
             {
                 throw new MqttProtocolViolationException("PubAck packet has no packet identifier.");
             }
@@ -302,7 +300,7 @@ namespace MQTTnet.Formatter.V5
                 throw new MqttProtocolViolationException("PubAck packet must contain a reason code.");
             }
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
             
             var propertiesWriter = new MqttV500PropertiesWriter();
             if (packet.Properties != null)
@@ -320,9 +318,9 @@ namespace MQTTnet.Formatter.V5
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.PubAck);
         }
 
-        private static byte EncodePubRecPacket(MqttPubRecPacket packet, IMqttPacketWriter packetWriter)
+        static byte EncodePubRecPacket(MqttPubRecPacket packet, IMqttPacketWriter packetWriter)
         {
-            ThrowIfPacketIdentifierIsInvalid(packet);
+            ThrowIfPacketIdentifierIsInvalid(packet.PacketIdentifier, packet);
 
             if (!packet.ReasonCode.HasValue)
             {
@@ -336,7 +334,7 @@ namespace MQTTnet.Formatter.V5
                 propertiesWriter.WriteUserProperties(packet.Properties.UserProperties);
             }
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
 
             if (packetWriter.Length > 0 || packet.ReasonCode.Value != MqttPubRecReasonCode.Success)
             {
@@ -347,9 +345,9 @@ namespace MQTTnet.Formatter.V5
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.PubRec);
         }
 
-        private static byte EncodePubRelPacket(MqttPubRelPacket packet, IMqttPacketWriter packetWriter)
+        static byte EncodePubRelPacket(MqttPubRelPacket packet, IMqttPacketWriter packetWriter)
         {
-            ThrowIfPacketIdentifierIsInvalid(packet);
+            ThrowIfPacketIdentifierIsInvalid(packet.PacketIdentifier, packet);
 
             if (!packet.ReasonCode.HasValue)
             {
@@ -363,7 +361,7 @@ namespace MQTTnet.Formatter.V5
                 propertiesWriter.WriteUserProperties(packet.Properties.UserProperties);
             }
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
             
             if (propertiesWriter.Length > 0 || packet.ReasonCode.Value != MqttPubRelReasonCode.Success)
             {
@@ -374,16 +372,16 @@ namespace MQTTnet.Formatter.V5
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.PubRel, 0x02);
         }
 
-        private static byte EncodePubCompPacket(MqttPubCompPacket packet, IMqttPacketWriter packetWriter)
+        static byte EncodePubCompPacket(MqttPubCompPacket packet, IMqttPacketWriter packetWriter)
         {
-            ThrowIfPacketIdentifierIsInvalid(packet);
+            ThrowIfPacketIdentifierIsInvalid(packet.PacketIdentifier, packet);
 
             if (!packet.ReasonCode.HasValue)
             {
                 ThrowReasonCodeNotSetException();
             }
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
             
             var propertiesWriter = new MqttV500PropertiesWriter();
             if (packet.Properties != null)
@@ -401,13 +399,13 @@ namespace MQTTnet.Formatter.V5
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.PubComp);
         }
 
-        private static byte EncodeSubscribePacket(MqttSubscribePacket packet, IMqttPacketWriter packetWriter)
+        static byte EncodeSubscribePacket(MqttSubscribePacket packet, IMqttPacketWriter packetWriter)
         {
             if (packet.TopicFilters?.Any() != true) throw new MqttProtocolViolationException("At least one topic filter must be set [MQTT-3.8.3-3].");
 
-            ThrowIfPacketIdentifierIsInvalid(packet);
+            ThrowIfPacketIdentifierIsInvalid(packet.PacketIdentifier, packet);
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
 
             var propertiesWriter = new MqttV500PropertiesWriter();
             if (packet.Properties != null)
@@ -448,13 +446,13 @@ namespace MQTTnet.Formatter.V5
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.Subscribe, 0x02);
         }
 
-        private static byte EncodeSubAckPacket(MqttSubAckPacket packet, IMqttPacketWriter packetWriter)
+        static byte EncodeSubAckPacket(MqttSubAckPacket packet, IMqttPacketWriter packetWriter)
         {
             if (packet.ReasonCodes?.Any() != true) throw new MqttProtocolViolationException("At least one reason code must be set[MQTT - 3.8.3 - 3].");
 
-            ThrowIfPacketIdentifierIsInvalid(packet);
+            ThrowIfPacketIdentifierIsInvalid(packet.PacketIdentifier, packet);
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
 
             var propertiesWriter = new MqttV500PropertiesWriter();
             if (packet.Properties != null)
@@ -473,13 +471,13 @@ namespace MQTTnet.Formatter.V5
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.SubAck);
         }
 
-        private static byte EncodeUnsubscribePacket(MqttUnsubscribePacket packet, IMqttPacketWriter packetWriter)
+        static byte EncodeUnsubscribePacket(MqttUnsubscribePacket packet, IMqttPacketWriter packetWriter)
         {
             if (packet.TopicFilters?.Any() != true) throw new MqttProtocolViolationException("At least one topic filter must be set [MQTT-3.10.3-2].");
 
-            ThrowIfPacketIdentifierIsInvalid(packet);
+            ThrowIfPacketIdentifierIsInvalid(packet.PacketIdentifier, packet);
 
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
 
             var propertiesWriter = new MqttV500PropertiesWriter();
             if (packet.Properties != null)
@@ -497,13 +495,13 @@ namespace MQTTnet.Formatter.V5
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.Unsubscibe, 0x02);
         }
 
-        private static byte EncodeUnsubAckPacket(MqttUnsubAckPacket packet, IMqttPacketWriter packetWriter)
+        static byte EncodeUnsubAckPacket(MqttUnsubAckPacket packet, IMqttPacketWriter packetWriter)
         {
             if (packet.ReasonCodes?.Any() != true) throw new MqttProtocolViolationException("At least one reason code must be set[MQTT - 3.8.3 - 3].");
 
-            ThrowIfPacketIdentifierIsInvalid(packet);
+            ThrowIfPacketIdentifierIsInvalid(packet.PacketIdentifier, packet);
             
-            packetWriter.Write(packet.PacketIdentifier.Value);
+            packetWriter.Write(packet.PacketIdentifier);
 
             var propertiesWriter = new MqttV500PropertiesWriter();
             if (packet.Properties != null)
@@ -522,7 +520,7 @@ namespace MQTTnet.Formatter.V5
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.UnsubAck);
         }
 
-        private static byte EncodeDisconnectPacket(MqttDisconnectPacket packet, IMqttPacketWriter packetWriter)
+        static byte EncodeDisconnectPacket(MqttDisconnectPacket packet, IMqttPacketWriter packetWriter)
         {
             if (!packet.ReasonCode.HasValue)
             {
@@ -545,17 +543,17 @@ namespace MQTTnet.Formatter.V5
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.Disconnect);
         }
 
-        private static byte EncodePingReqPacket()
+        static byte EncodePingReqPacket()
         {
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.PingReq);
         }
 
-        private static byte EncodePingRespPacket()
+        static byte EncodePingRespPacket()
         {
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.PingResp);
         }
 
-        private static byte EncodeAuthPacket(MqttAuthPacket packet, IMqttPacketWriter packetWriter)
+        static byte EncodeAuthPacket(MqttAuthPacket packet, IMqttPacketWriter packetWriter)
         {
             packetWriter.Write((byte)packet.ReasonCode);
 
@@ -573,14 +571,16 @@ namespace MQTTnet.Formatter.V5
             return MqttPacketWriter.BuildFixedHeader(MqttControlPacketType.Auth);
         }
 
-        private static void ThrowReasonCodeNotSetException()
+        static void ThrowReasonCodeNotSetException()
         {
             throw new MqttProtocolViolationException("The ReasonCode must be set for MQTT version 5.");
         }
 
-        private static void ThrowIfPacketIdentifierIsInvalid(IMqttPacketWithIdentifier packet)
+        static void ThrowIfPacketIdentifierIsInvalid(ushort packetIdentifier, MqttBasePacket packet)
         {
-            if (!packet.PacketIdentifier.HasValue)
+            // SUBSCRIBE, UNSUBSCRIBE, and PUBLISH(in cases where QoS > 0) Control Packets MUST contain a non-zero 16 - bit Packet Identifier[MQTT - 2.3.1 - 1]. 
+
+            if (packetIdentifier == 0)
             {
                 throw new MqttProtocolViolationException($"Packet identifier is not set for {packet.GetType().Name}.");
             }

Source/MQTTnet/Formatter/V5/MqttV500PropertiesWriter.cs

@@ -5,10 +5,9 @@ using MQTTnet.Protocol;
 
 namespace MQTTnet.Formatter.V5
 {
-    public class MqttV500PropertiesWriter
+    public sealed class MqttV500PropertiesWriter
     {
-        // TODO: Consider lazy init on first write to avoid useless allocations.
-        private readonly MqttPacketWriter _packetWriter = new MqttPacketWriter();
+        readonly MqttPacketWriter _packetWriter = new MqttPacketWriter();
 
         public int Length => _packetWriter.Length;
 
@@ -178,7 +177,7 @@ namespace MQTTnet.Formatter.V5
             Write(MqttPropertyId.ResponseInformation, value);
         }
 
-        private void Write(MqttPropertyId id, bool? value)
+        void Write(MqttPropertyId id, bool? value)
         {
             if (!value.HasValue)
             {
@@ -189,7 +188,7 @@ namespace MQTTnet.Formatter.V5
             _packetWriter.Write(value.Value ? (byte)0x1 : (byte)0x0);
         }
 
-        private void Write(MqttPropertyId id, byte? value)
+        void Write(MqttPropertyId id, byte? value)
         {
             if (!value.HasValue)
             {
@@ -200,7 +199,7 @@ namespace MQTTnet.Formatter.V5
             _packetWriter.Write(value.Value);
         }
 
-        private void Write(MqttPropertyId id, ushort? value)
+        void Write(MqttPropertyId id, ushort? value)
         {
             if (!value.HasValue)
             {
@@ -211,7 +210,7 @@ namespace MQTTnet.Formatter.V5
             _packetWriter.Write(value.Value);
         }
 
-        private void WriteAsVariableLengthInteger(MqttPropertyId id, uint? value)
+        void WriteAsVariableLengthInteger(MqttPropertyId id, uint? value)
         {
             if (!value.HasValue)
             {
@@ -222,7 +221,7 @@ namespace MQTTnet.Formatter.V5
             _packetWriter.WriteVariableLengthInteger(value.Value);
         }
 
-        private void WriteAsFourByteInteger(MqttPropertyId id, uint? value)
+        void WriteAsFourByteInteger(MqttPropertyId id, uint? value)
         {
             if (!value.HasValue)
             {
@@ -236,7 +235,7 @@ namespace MQTTnet.Formatter.V5
             _packetWriter.Write((byte)value.Value);
         }
 
-        private void Write(MqttPropertyId id, string value)
+        void Write(MqttPropertyId id, string value)
         {
             if (value == null)
             {
@@ -247,7 +246,7 @@ namespace MQTTnet.Formatter.V5
             _packetWriter.WriteWithLengthPrefix(value);
         }
 
-        private void Write(MqttPropertyId id, byte[] value)
+        void Write(MqttPropertyId id, byte[] value)
         {
             if (value == null)
             {