Add PayloadSegmentable feature (#1585)

.github/workflows/ReleaseNotes.md

@@ -1,4 +1,5 @@
 * [Core] Added net7.0 builds (#1635, thanks to @YAJeff).
+* [Core] Added support for payload segments (#1585, thanks to @xljiulang)
 * [Client] Added support for passing MQTT v5 options (User properties etc.) for disconnects.
 * [Client] An internal exception is no longer caught silently when calling _DisconnectAsync_ to indicate that the disconnect is not clean (BREAKING CHANGE).
 * [Client] MQTTv5 features are now checked and an exception is thrown if they are used when using protocol version 3.1.1 and lower. These checks can be disabled in client options. (BREAKING CHANGE!).

Source/MQTTnet.AspNetCore.Tests/MqttConnectionContextTest.cs

@@ -103,7 +103,7 @@ namespace MQTTnet.AspNetCore.Tests
             connection.Transport = pipe;
             var ctx = new MqttConnectionContext(serializer, connection);
 
-            await ctx.SendPacketAsync(new MqttPublishPacket { Payload = new byte[20_000] }, CancellationToken.None).ConfigureAwait(false);
+            await ctx.SendPacketAsync(new MqttPublishPacket { PayloadSegment = new ArraySegment<byte>(new byte[20_000]) }, CancellationToken.None).ConfigureAwait(false);
 
             var readResult = await pipe.Send.Reader.ReadAsync();
             Assert.IsTrue(readResult.Buffer.Length > 20000);

Source/MQTTnet.AspNetCore.Tests/ReaderExtensionsTest.cs

@@ -19,7 +19,7 @@ namespace MQTTnet.AspNetCore.Tests
         {
             var serializer = new MqttPacketFormatterAdapter(MqttProtocolVersion.V311, new MqttBufferWriter(4096, 65535));
 
-            var buffer = serializer.Encode(new MqttPublishPacket {Topic = "a", Payload = new byte[5]}).Join();
+            var buffer = serializer.Encode(new MqttPublishPacket {Topic = "a", PayloadSegment = new byte[5]}).Join();
 
             var sequence = new ReadOnlySequence<byte>(buffer.Array, buffer.Offset, buffer.Count);
 

Source/MQTTnet.Extensions.Rpc/MqttRpcClient.cs

@@ -4,6 +4,7 @@
 
 using System;
 using System.Collections.Concurrent;
+using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Client;
@@ -119,7 +120,6 @@ namespace MQTTnet.Extensions.Rpc
             finally
             {
                 _waitingCalls.TryRemove(responseTopic, out _);
-
                 await _mqttClient.UnsubscribeAsync(responseTopic, CancellationToken.None).ConfigureAwait(false);
             }
         }
@@ -131,7 +131,8 @@ namespace MQTTnet.Extensions.Rpc
                 return CompletedTask.Instance;
             }
 
-            awaitable.TrySetResult(eventArgs.ApplicationMessage.Payload);
+            var payloadBuffer = eventArgs.ApplicationMessage.PayloadSegment.ToArray();
+            awaitable.TrySetResult(payloadBuffer);
 
             // Set this message to handled to that other code can avoid execution etc.
             eventArgs.IsHandled = true;

Source/MQTTnet.TestApp/ClientTest.cs

@@ -33,9 +33,18 @@ namespace MQTTnet.TestApp
 
                 client.ApplicationMessageReceivedAsync += e =>
                 {
+                    var payloadText = string.Empty;
+                    if (e.ApplicationMessage.PayloadSegment.Count > 0)
+                    {
+                        payloadText = Encoding.UTF8.GetString(
+                            e.ApplicationMessage.PayloadSegment.Array,
+                            e.ApplicationMessage.PayloadSegment.Offset,
+                            e.ApplicationMessage.PayloadSegment.Count);
+                    }
+                    
                     Console.WriteLine("### RECEIVED APPLICATION MESSAGE ###");
                     Console.WriteLine($"+ Topic = {e.ApplicationMessage.Topic}");
-                    Console.WriteLine($"+ Payload = {Encoding.UTF8.GetString(e.ApplicationMessage.Payload)}");
+                    Console.WriteLine($"+ Payload = {payloadText}");
                     Console.WriteLine($"+ QoS = {e.ApplicationMessage.QualityOfServiceLevel}");
                     Console.WriteLine($"+ Retain = {e.ApplicationMessage.Retain}");
                     Console.WriteLine();

Source/MQTTnet.TestApp/PerformanceTest.cs

@@ -196,7 +196,7 @@ namespace MQTTnet.TestApp
             return new MqttApplicationMessage
             {
                 Topic = "A/B/C",
-                Payload = Encoding.UTF8.GetBytes(Payload),
+                PayloadSegment = new ArraySegment<byte>(Encoding.UTF8.GetBytes(Payload)),
                 QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce
             };
         }
@@ -229,7 +229,7 @@ namespace MQTTnet.TestApp
                 var message = new MqttApplicationMessage
                 {
                     Topic = "A/B/C",
-                    Payload = Encoding.UTF8.GetBytes("Hello World"),
+                    PayloadSegment = new ArraySegment<byte>(Encoding.UTF8.GetBytes("Hello World")),
                     QualityOfServiceLevel = MqttQualityOfServiceLevel.ExactlyOnce
                 };
 
@@ -280,7 +280,7 @@ namespace MQTTnet.TestApp
                 var message = new MqttApplicationMessage
                 {
                     Topic = "A/B/C",
-                    Payload = Encoding.UTF8.GetBytes("Hello World"),
+                    PayloadSegment = new ArraySegment<byte>(Encoding.UTF8.GetBytes("Hello World")),
                     QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce
                 };
 
@@ -331,7 +331,7 @@ namespace MQTTnet.TestApp
                 var message = new MqttApplicationMessage
                 {
                     Topic = "A/B/C",
-                    Payload = Encoding.UTF8.GetBytes("Hello World"),
+                    PayloadSegment = new ArraySegment<byte>(Encoding.UTF8.GetBytes("Hello World")),
                     QualityOfServiceLevel = MqttQualityOfServiceLevel.AtMostOnce
                 };
 

Source/MQTTnet.TestApp/ServerTest.cs

@@ -5,6 +5,7 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using MQTTnet.Diagnostics;
@@ -100,7 +101,7 @@ namespace MQTTnet.TestApp
                     {
                         // Replace the payload with the timestamp. But also extending a JSON 
                         // based payload with the timestamp is a suitable use case.
-                        e.ApplicationMessage.Payload = Encoding.UTF8.GetBytes(DateTime.Now.ToString("O"));
+                        e.ApplicationMessage.PayloadSegment = new ArraySegment<byte>(Encoding.UTF8.GetBytes(DateTime.Now.ToString("O")));
                     }
 
                     if (e.ApplicationMessage.Topic == "not_allowed_topic")
@@ -143,10 +144,16 @@ namespace MQTTnet.TestApp
                 
                 mqttServer.InterceptingPublishAsync += e =>
                 {
-                    MqttNetConsoleLogger.PrintToConsole(
-                        $"'{e.ClientId}' reported '{e.ApplicationMessage.Topic}' > '{Encoding.UTF8.GetString(e.ApplicationMessage.Payload ?? new byte[0])}'",
-                        ConsoleColor.Magenta);
+                    var payloadText = string.Empty;
+                    if (e.ApplicationMessage.PayloadSegment.Count > 0)
+                    {
+                        payloadText = Encoding.UTF8.GetString(
+                            e.ApplicationMessage.PayloadSegment.Array,
+                            e.ApplicationMessage.PayloadSegment.Offset,
+                            e.ApplicationMessage.PayloadSegment.Count);
+                    }
                     
+                    MqttNetConsoleLogger.PrintToConsole($"'{e.ClientId}' reported '{e.ApplicationMessage.Topic}' > '{payloadText}'", ConsoleColor.Magenta);
                     return CompletedTask.Instance;
                 };
 

Source/MQTTnet.Tests/Clients/MqttClient/MqttClient_Connection_Tests.cs

@@ -151,6 +151,8 @@ namespace MQTTnet.Tests.Clients.MqttClient
                 // Perform a clean disconnect.
                 await client.DisconnectAsync(disconnectOptions);
 
+                await LongTestDelay();
+                
                 Assert.IsNotNull(eventArgs);
                 Assert.IsNotNull(eventArgs.UserProperties);
                 Assert.AreEqual(1, eventArgs.UserProperties.Count);

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V3_Binary_Tests.cs

@@ -111,7 +111,7 @@ namespace MQTTnet.Tests.Formatter
                 PacketIdentifier = 123,
                 Dup = true,
                 Retain = true,
-                Payload = Encoding.ASCII.GetBytes("HELLO"),
+                PayloadSegment = new ArraySegment<byte>(Encoding.ASCII.GetBytes("HELLO")),
                 QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce,
                 Topic = "A/B/C"
             };
@@ -318,10 +318,9 @@ namespace MQTTnet.Tests.Formatter
             var publishPacket = new MqttPublishPacket
             {
                 Topic = "abcdefghijklmnopqrstuvwxyz0123456789",
-                Payload = payload
+                PayloadSegment = new ArraySegment<byte>(payload)
             };
 
-
             var serializationHelper = new MqttPacketSerializationHelper();
 
             var buffer = serializationHelper.Encode(publishPacket);
@@ -329,17 +328,17 @@ namespace MQTTnet.Tests.Formatter
 
             Assert.IsNotNull(publishPacketCopy);
             Assert.AreEqual(publishPacket.Topic, publishPacketCopy.Topic);
-            CollectionAssert.AreEqual(publishPacket.Payload, publishPacketCopy.Payload);
+            CollectionAssert.AreEqual(publishPacket.PayloadSegment.ToArray(), publishPacketCopy.PayloadSegment.ToArray());
 
             // Now modify the payload and test again.
-            publishPacket.Payload = Encoding.UTF8.GetBytes("MQTT");
+            publishPacket.PayloadSegment = new ArraySegment<byte>(Encoding.UTF8.GetBytes("MQTT"));
 
             buffer = serializationHelper.Encode(publishPacket);
             var publishPacketCopy2 = serializationHelper.Decode(buffer) as MqttPublishPacket;
 
             Assert.IsNotNull(publishPacketCopy2);
             Assert.AreEqual(publishPacket.Topic, publishPacketCopy2.Topic);
-            CollectionAssert.AreEqual(publishPacket.Payload, publishPacketCopy2.Payload);
+            CollectionAssert.AreEqual(publishPacket.PayloadSegment.ToArray(), publishPacketCopy2.PayloadSegment.ToArray());
         }
 
         [TestMethod]
@@ -463,7 +462,7 @@ namespace MQTTnet.Tests.Formatter
                 PacketIdentifier = 123,
                 Dup = true,
                 Retain = true,
-                Payload = Encoding.ASCII.GetBytes("HELLO"),
+                PayloadSegment = new ArraySegment<byte>(Encoding.ASCII.GetBytes("HELLO")),
                 QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce,
                 Topic = "A/B/C"
             };

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V3_Tests.cs

@@ -2,7 +2,9 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Text;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Exceptions;
@@ -296,7 +298,7 @@ namespace MQTTnet.Tests.Formatter
                 PacketIdentifier = 123,
                 Dup = true,
                 Retain = true,
-                Payload = Encoding.ASCII.GetBytes("Payload"),
+                PayloadSegment = new ArraySegment<byte>(Encoding.ASCII.GetBytes("Payload")),
                 QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce,
                 Topic = "Topic",
                 ResponseTopic = "/Response",
@@ -320,7 +322,7 @@ namespace MQTTnet.Tests.Formatter
             Assert.AreEqual(publishPacket.PacketIdentifier, deserialized.PacketIdentifier);
             Assert.AreEqual(publishPacket.Dup, deserialized.Dup);
             Assert.AreEqual(publishPacket.Retain, deserialized.Retain);
-            CollectionAssert.AreEqual(publishPacket.Payload, deserialized.Payload);
+            CollectionAssert.AreEqual(publishPacket.PayloadSegment.ToArray(), deserialized.PayloadSegment.ToArray());
             Assert.AreEqual(publishPacket.QualityOfServiceLevel, deserialized.QualityOfServiceLevel);
             Assert.AreEqual(publishPacket.Topic, deserialized.Topic);
             Assert.AreEqual(null, deserialized.ResponseTopic); // Not supported in v3.1.1.

Source/MQTTnet.Tests/Formatter/MqttPacketSerialization_V5_Tests.cs

@@ -2,7 +2,9 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Text;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using MQTTnet.Formatter;
@@ -257,7 +259,7 @@ namespace MQTTnet.Tests.Formatter
                 PacketIdentifier = 123,
                 Dup = true,
                 Retain = true,
-                Payload = Encoding.ASCII.GetBytes("Payload"),
+                PayloadSegment = new ArraySegment<byte>(Encoding.ASCII.GetBytes("Payload")),
                 QualityOfServiceLevel = MqttQualityOfServiceLevel.AtLeastOnce,
                 Topic = "Topic",
                 ResponseTopic = "/Response",
@@ -281,7 +283,7 @@ namespace MQTTnet.Tests.Formatter
             Assert.AreEqual(publishPacket.PacketIdentifier, deserialized.PacketIdentifier);
             Assert.AreEqual(publishPacket.Dup, deserialized.Dup);
             Assert.AreEqual(publishPacket.Retain, deserialized.Retain);
-            CollectionAssert.AreEqual(publishPacket.Payload, deserialized.Payload);
+            CollectionAssert.AreEqual(publishPacket.PayloadSegment.ToArray(), deserialized.PayloadSegment.ToArray());
             Assert.AreEqual(publishPacket.QualityOfServiceLevel, deserialized.QualityOfServiceLevel);
             Assert.AreEqual(publishPacket.Topic, deserialized.Topic);
             Assert.AreEqual(publishPacket.ResponseTopic, deserialized.ResponseTopic);

Source/MQTTnet.Tests/MqttApplicationMessageTest.cs

@@ -0,0 +1,48 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace MQTTnet.Tests
+{
+    [TestClass]
+    public class MqttApplicationMessageTest
+    {
+        [TestMethod]
+        public void PayloadSegment()
+        {
+            var message = new MqttApplicationMessage();
+            Assert.AreEqual(0, message.Payload.Length);
+            Assert.AreEqual(0, message.PayloadSegment.Count);
+
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.Payload));
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.PayloadSegment.Array));
+
+            message.Payload = new byte[] { 1, 2 };
+            Assert.AreEqual(2, message.Payload.Length);
+            Assert.AreEqual(2, message.PayloadSegment.Count);
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.Payload));
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.PayloadSegment.Array));
+
+            message.Payload = new byte[] { 1, 2, 3 };
+            Assert.AreEqual(3, message.Payload.Length);
+            Assert.AreEqual(3, message.PayloadSegment.Count);
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.Payload));
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.PayloadSegment.Array));
+
+            message.PayloadSegment = new ArraySegment<byte>(new byte[] { 1, 2, 3 });
+            Assert.AreEqual(3, message.Payload.Length);
+            Assert.AreEqual(3, message.PayloadSegment.Count);
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.Payload));
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.PayloadSegment.Array));
+
+            message.PayloadSegment = new ArraySegment<byte>(new byte[] { 1, 2, 3 }, 1, 1);
+            Assert.AreEqual(1, message.Payload.Length);
+            Assert.AreEqual(1, message.PayloadSegment.Count);
+            Assert.IsTrue(object.ReferenceEquals(message.Payload, message.Payload));
+            Assert.IsFalse(object.ReferenceEquals(message.Payload, message.PayloadSegment.Array));
+        }
+    }
+}

Source/MQTTnet.Tests/Server/Security_Tests.cs

@@ -164,7 +164,7 @@ namespace MQTTnet.Tests.Server
 
                 var clientOptions = new MqttClientOptionsBuilder().WithTcpServer("127.0.0.1", testEnvironment.ServerPort).WithCredentials(userName, password).Build();
 
-                var ex = await Assert.ThrowsExceptionAsync<MqttConnectingFailedException>(async () => await client.ConnectAsync(clientOptions));
+                var ex = await Assert.ThrowsExceptionAsync<MqttConnectingFailedException>(() => client.ConnectAsync(clientOptions));
                 Assert.AreEqual(MqttClientConnectResultCode.BadUserNameOrPassword, ex.Result.ResultCode);
             }
         }

Source/MQTTnet/Formatter/MqttApplicationMessageFactory.cs

@@ -19,7 +19,7 @@ namespace MQTTnet.Formatter
             return new MqttApplicationMessage
             {
                 Topic = publishPacket.Topic,
-                Payload = publishPacket.Payload,
+                PayloadSegment = publishPacket.PayloadSegment,
                 QualityOfServiceLevel = publishPacket.QualityOfServiceLevel,
                 Retain = publishPacket.Retain,
                 Dup = publishPacket.Dup,

Source/MQTTnet/Formatter/MqttPublishPacketFactory.cs

@@ -16,7 +16,7 @@ namespace MQTTnet.Formatter
             return new MqttPublishPacket
             {
                 Topic = publishPacket.Topic,
-                Payload = publishPacket.Payload,
+                PayloadSegment = publishPacket.PayloadSegment, 
                 Retain = publishPacket.Retain,
                 QualityOfServiceLevel = publishPacket.QualityOfServiceLevel,
                 Dup = publishPacket.Dup,
@@ -36,7 +36,7 @@ namespace MQTTnet.Formatter
             var packet = new MqttPublishPacket
             {
                 Topic = applicationMessage.Topic,
-                Payload = applicationMessage.Payload,
+                PayloadSegment = applicationMessage.PayloadSegment, 
                 QualityOfServiceLevel = applicationMessage.QualityOfServiceLevel,
                 Retain = applicationMessage.Retain,
                 Dup = applicationMessage.Dup,
@@ -65,10 +65,16 @@ namespace MQTTnet.Formatter
                 throw new MqttProtocolViolationException("The CONNECT packet contains no will message (WillFlag).");
             }
 
+            ArraySegment<byte> willMessageBuffer = default;
+            if (connectPacket.WillMessage?.Length > 0)
+            {
+                willMessageBuffer = new ArraySegment<byte>(connectPacket.WillMessage);
+            }
+
             var packet = new MqttPublishPacket
             {
                 Topic = connectPacket.WillTopic,
-                Payload = connectPacket.WillMessage,
+                PayloadSegment = willMessageBuffer,
                 QualityOfServiceLevel = connectPacket.WillQoS,
                 Retain = connectPacket.WillRetain,
                 ContentType = connectPacket.WillContentType,

Source/MQTTnet/Formatter/V3/MqttV3PacketFormatter.cs

@@ -103,9 +103,10 @@ namespace MQTTnet.Formatter.V3
             var remainingLength = (uint)(_bufferWriter.Length - 5);
 
             var publishPacket = packet as MqttPublishPacket;
-            if (publishPacket?.Payload != null)
+            var payloadSegment = publishPacket?.PayloadSegment;
+            if (payloadSegment != null)
             {
-                remainingLength += (uint)publishPacket.Payload.Length;
+                remainingLength += (uint)payloadSegment.Value.Count;
             }
 
             var remainingLengthSize = MqttBufferWriter.GetVariableByteIntegerSize(remainingLength);
@@ -119,16 +120,11 @@ namespace MQTTnet.Formatter.V3
             _bufferWriter.WriteVariableByteInteger(remainingLength);
 
             var buffer = _bufferWriter.GetBuffer();
-
             var firstSegment = new ArraySegment<byte>(buffer, headerOffset, _bufferWriter.Length - headerOffset);
 
-            if (publishPacket?.Payload != null)
-            {
-                var payloadSegment = new ArraySegment<byte>(publishPacket.Payload, 0, publishPacket.Payload.Length);
-                return new MqttPacketBuffer(firstSegment, payloadSegment);
-            }
-
-            return new MqttPacketBuffer(firstSegment);
+            return payloadSegment == null
+                ? new MqttPacketBuffer(firstSegment)
+                : new MqttPacketBuffer(firstSegment, payloadSegment.Value);
         }
 
         MqttPacket DecodeConnAckPacket(ArraySegment<byte> body)
@@ -282,7 +278,7 @@ namespace MQTTnet.Formatter.V3
 
             if (!_bufferReader.EndOfStream)
             {
-                packet.Payload = _bufferReader.ReadRemainingData();
+                packet.PayloadSegment = new ArraySegment<byte>(_bufferReader.ReadRemainingData());
             }
 
             return packet;

Source/MQTTnet/Formatter/V5/MqttV5PacketDecoder.cs

@@ -528,7 +528,7 @@ namespace MQTTnet.Formatter.V5
 
             if (!_bufferReader.EndOfStream)
             {
-                packet.Payload = _bufferReader.ReadRemainingData();
+                packet.PayloadSegment = new ArraySegment<byte>(_bufferReader.ReadRemainingData());
             }
 
             return packet;

Source/MQTTnet/Formatter/V5/MqttV5PacketEncoder.cs

@@ -37,9 +37,11 @@ namespace MQTTnet.Formatter.V5
             var remainingLength = (uint)_bufferWriter.Length - 5;
 
             var publishPacket = packet as MqttPublishPacket;
-            if (publishPacket?.Payload != null)
+            var payloadSegment = publishPacket?.PayloadSegment;
+
+            if (payloadSegment != null)
             {
-                remainingLength += (uint)publishPacket.Payload.Length;
+                remainingLength += (uint)payloadSegment.Value.Count;
             }
 
             var remainingLengthSize = MqttBufferWriter.GetVariableByteIntegerSize(remainingLength);
@@ -53,16 +55,11 @@ namespace MQTTnet.Formatter.V5
             _bufferWriter.WriteVariableByteInteger(remainingLength);
 
             var buffer = _bufferWriter.GetBuffer();
-
             var firstSegment = new ArraySegment<byte>(buffer, headerOffset, _bufferWriter.Length - headerOffset);
 
-            if (publishPacket?.Payload != null)
-            {
-                var payloadSegment = new ArraySegment<byte>(publishPacket.Payload, 0, publishPacket.Payload.Length);
-                return new MqttPacketBuffer(firstSegment, payloadSegment);
-            }
-
-            return new MqttPacketBuffer(firstSegment);
+            return payloadSegment == null
+               ? new MqttPacketBuffer(firstSegment)
+               : new MqttPacketBuffer(firstSegment, payloadSegment.Value);
         }
 
         byte EncodeAuthPacket(MqttAuthPacket packet)

Source/MQTTnet/MqttApplicationMessage.cs

@@ -2,14 +2,19 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using System.Collections.Generic;
+using MQTTnet.Internal;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
+using System;
+using System.Collections.Generic;
 
 namespace MQTTnet
 {
     public sealed class MqttApplicationMessage
     {
+        byte[] _payloadCache;
+        ArraySegment<byte> _payloadSegment = EmptyBuffer.ArraySegment;
+
         /// <summary>
         ///     Gets or sets the content type.
         ///     The content type must be a UTF-8 encoded string. The content type value identifies the kind of UTF-8 encoded
@@ -51,7 +56,50 @@ namespace MQTTnet
         /// Gets or sets the payload.
         /// The payload is the data bytes sent via the MQTT protocol.
         /// </summary>
-        public byte[] Payload { get; set; }
+        [Obsolete("Use PayloadSegment instead. This property will be removed in a future release.")]
+        public byte[] Payload
+        {
+            get
+            {
+                if (_payloadSegment.Array == null)
+                {
+                    return null;
+                }
+                
+                // just reference from _payloadSegment.Array
+                if (_payloadSegment.Count == _payloadSegment.Array.Length)
+                {
+                    return _payloadSegment.Array;
+                }
+
+                // copy from _payloadSegment
+                if (_payloadCache == null)
+                {
+                    _payloadCache = new byte[_payloadSegment.Count];
+                    MqttMemoryHelper.Copy(_payloadSegment.Array, _payloadSegment.Offset, _payloadCache, 0, _payloadCache.Length);
+                }
+
+                return _payloadCache;
+            }
+            set
+            {
+                _payloadCache = null;
+                _payloadSegment = value == null || value.Length == 0 ? EmptyBuffer.ArraySegment : new ArraySegment<byte>(value);
+            }
+        }
+
+        /// <summary>
+        /// Get or set ArraySegment style of Payload.
+        /// </summary>
+        public ArraySegment<byte> PayloadSegment
+        {
+            get => _payloadSegment;
+            set
+            {
+                _payloadCache = null;
+                _payloadSegment = value;
+            }
+        }
 
         /// <summary>
         ///     Gets or sets the payload format indicator.

Source/MQTTnet/MqttApplicationMessageBuilder.cs

@@ -2,13 +2,16 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using MQTTnet.Exceptions;
+using MQTTnet.Internal;
+using MQTTnet.Packets;
+using MQTTnet.Protocol;
+using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Runtime.InteropServices;
 using System.Text;
-using MQTTnet.Exceptions;
-using MQTTnet.Packets;
-using MQTTnet.Protocol;
 
 namespace MQTTnet
 {
@@ -17,7 +20,8 @@ namespace MQTTnet
         string _contentType;
         byte[] _correlationData;
         uint _messageExpiryInterval;
-        byte[] _payload;
+        ArraySegment<byte> _payloadSegment;
+
         MqttPayloadFormatIndicator _payloadFormatIndicator;
         MqttQualityOfServiceLevel _qualityOfServiceLevel = MqttQualityOfServiceLevel.AtMostOnce;
         string _responseTopic;
@@ -37,7 +41,7 @@ namespace MQTTnet
             var applicationMessage = new MqttApplicationMessage
             {
                 Topic = _topic,
-                Payload = _payload,
+                PayloadSegment = _payloadSegment,
                 QualityOfServiceLevel = _qualityOfServiceLevel,
                 Retain = _retain,
                 ContentType = _contentType,
@@ -85,7 +89,15 @@ namespace MQTTnet
 
         public MqttApplicationMessageBuilder WithPayload(byte[] payload)
         {
-            _payload = payload;
+            _payloadSegment = payload == null || payload.Length == 0
+                ? EmptyBuffer.ArraySegment
+                : new ArraySegment<byte>(payload);
+            return this;
+        }
+
+        public MqttApplicationMessageBuilder WithPayloadSegment(ArraySegment<byte> payloadSegment)
+        {
+            _payloadSegment = payloadSegment;
             return this;
         }
 
@@ -93,46 +105,41 @@ namespace MQTTnet
         {
             if (payload == null)
             {
-                _payload = null;
-                return this;
+                return WithPayload(default(byte[]));
             }
 
-            _payload = payload as byte[] ?? payload.ToArray();
+            if (payload is byte[] byteArray)
+            {
+                return WithPayload(byteArray);
+            }
 
-            return this;
+            if (payload is ArraySegment<byte> arraySegment)
+            {
+                return WithPayloadSegment(arraySegment);
+            }
+
+            return WithPayload(payload.ToArray());
         }
 
         public MqttApplicationMessageBuilder WithPayload(Stream payload)
         {
-            if (payload == null)
-            {
-                _payload = null;
-                return this;
-            }
-
-            return WithPayload(payload, payload.Length - payload.Position);
+            return payload == null
+                ? WithPayload(default(byte[]))
+                : WithPayload(payload, payload.Length - payload.Position);
         }
 
         public MqttApplicationMessageBuilder WithPayload(Stream payload, long length)
         {
-            if (payload == null)
+            if (payload == null || length == 0)
             {
-                _payload = null;
-                return this;
+                return WithPayload(default(byte[]));
             }
 
-            if (payload.Length == 0)
-            {
-                _payload = null;
-            }
-            else
-            {
-                _payload = new byte[length];
-
+            var payloadBuffer = new byte[length];
             var totalRead = 0;
             do
             {
-                    var bytesRead = payload.Read(_payload, totalRead, _payload.Length - totalRead);
+                var bytesRead = payload.Read(payloadBuffer, totalRead, payloadBuffer.Length - totalRead);
                 if (bytesRead == 0)
                 {
                     break;
@@ -140,23 +147,31 @@ namespace MQTTnet
 
                 totalRead += bytesRead;
             } while (totalRead < length);
-            }
 
-            return this;
+            return WithPayload(payloadBuffer);
         }
 
         public MqttApplicationMessageBuilder WithPayload(string payload)
         {
-            if (payload == null)
+            if (string.IsNullOrEmpty(payload))
             {
-                _payload = null;
-                return this;
+                return WithPayload(default(byte[]));
             }
 
-            _payload = string.IsNullOrEmpty(payload) ? null : Encoding.UTF8.GetBytes(payload);
-            return this;
+            var payloadBuffer = Encoding.UTF8.GetBytes(payload);
+            return WithPayload(payloadBuffer);
         }
 
+
+#if NETCOREAPP3_1_OR_GREATER || NETSTANDARD2_1
+        public MqttApplicationMessageBuilder WithPayloadSegment(ReadOnlyMemory<byte> payloadSegment)
+        {
+            return MemoryMarshal.TryGetArray(payloadSegment, out var segment)
+                ? WithPayloadSegment(segment)
+                : WithPayload(payloadSegment.ToArray());
+        }
+#endif
+
         /// <summary>
         ///     Adds the payload format indicator to the message.
         ///     <remarks>MQTT 5.0.0+ feature.</remarks>

Source/MQTTnet/MqttApplicationMessageExtensions.cs

@@ -11,19 +11,13 @@ namespace MQTTnet
     {
         public static string ConvertPayloadToString(this MqttApplicationMessage applicationMessage)
         {
-            if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
-
-            if (applicationMessage.Payload == null)
+            if (applicationMessage == null)
             {
-                return null;
+                throw new ArgumentNullException(nameof(applicationMessage));
             }
 
-            if (applicationMessage.Payload.Length == 0)
-            {
-                return string.Empty;
-            }
-
-            return Encoding.UTF8.GetString(applicationMessage.Payload, 0, applicationMessage.Payload.Length);
+            var payloadSegment = applicationMessage.PayloadSegment;
+            return Encoding.UTF8.GetString(payloadSegment.Array, payloadSegment.Offset, payloadSegment.Count);
         }
     }
 }

Source/MQTTnet/Packets/MqttPublishPacket.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Generic;
 using MQTTnet.Protocol;
 
@@ -17,10 +18,10 @@ namespace MQTTnet.Packets
 
         public uint MessageExpiryInterval { get; set; }
 
-        public byte[] Payload { get; set; }
-
         public MqttPayloadFormatIndicator PayloadFormatIndicator { get; set; } = MqttPayloadFormatIndicator.Unspecified;
 
+        public ArraySegment<byte> PayloadSegment { get; set; }
+
         public MqttQualityOfServiceLevel QualityOfServiceLevel { get; set; } = MqttQualityOfServiceLevel.AtMostOnce;
 
         public string ResponseTopic { get; set; }
@@ -38,7 +39,7 @@ namespace MQTTnet.Packets
         public override string ToString()
         {
             return
-                $"Publish: [Topic={Topic}] [Payload.Length={Payload?.Length}] [QoSLevel={QualityOfServiceLevel}] [Dup={Dup}] [Retain={Retain}] [PacketIdentifier={PacketIdentifier}]";
+                $"Publish: [Topic={Topic}] [PayloadLength={PayloadSegment.Count}] [QoSLevel={QualityOfServiceLevel}] [Dup={Dup}] [Retain={Retain}] [PacketIdentifier={PacketIdentifier}]";
         }
     }
 }

Source/MQTTnet/Server/Internal/MqttRetainedMessagesManager.cs

@@ -25,6 +25,7 @@ namespace MQTTnet.Server
 
             if (logger == null)
                 throw new ArgumentNullException(nameof(logger));
+
             _logger = logger.WithSource(nameof(MqttRetainedMessagesManager));
         }
 
@@ -68,7 +69,8 @@ namespace MQTTnet.Server
 
                 lock (_messages)
                 {
-                    var hasPayload = applicationMessage.Payload != null && applicationMessage.Payload.Length > 0;
+                    var payloadSegment = applicationMessage.PayloadSegment;
+                    var hasPayload = payloadSegment.Count > 0;
 
                     if (!hasPayload)
                     {
@@ -84,8 +86,7 @@ namespace MQTTnet.Server
                         }
                         else
                         {
-                            if (existingMessage.QualityOfServiceLevel != applicationMessage.QualityOfServiceLevel ||
-                                !existingMessage.Payload.SequenceEqual(applicationMessage.Payload ?? EmptyBuffer.Array))
+                            if (existingMessage.QualityOfServiceLevel != applicationMessage.QualityOfServiceLevel || !SequenceEqual(existingMessage.PayloadSegment, payloadSegment))
                             {
                                 _messages[applicationMessage.Topic] = applicationMessage;
                                 saveIsRequired = true;
@@ -150,5 +151,14 @@ namespace MQTTnet.Server
                 await _eventContainer.RetainedMessagesClearedEvent.InvokeAsync(EventArgs.Empty).ConfigureAwait(false);
             }
         }
+
+        private static bool SequenceEqual(ArraySegment<byte> source, ArraySegment<byte> target)
+        {
+#if NETCOREAPP3_1_OR_GREATER || NETSTANDARD2_1
+            return source.AsSpan().SequenceEqual(target);
+#else
+            return source.Count == target.Count && Enumerable.SequenceEqual(source, target);
+#endif
+        }
     }
 }

Source/MQTTnet/Server/MqttServerExtensions.cs

@@ -41,7 +41,7 @@ namespace MQTTnet.Server
                     new MqttApplicationMessage
                     {
                         Topic = topic,
-                        Payload = payloadBuffer,
+                        PayloadSegment = new ArraySegment<byte>(payloadBuffer),
                         QualityOfServiceLevel = qualityOfServiceLevel,
                         Retain = retain
                     }));