Refactor code.

Introduce asynchronous message processing

Build/MQTTnet.AspNetCore.nuspec

@@ -8,18 +8,19 @@
     <license type="file">LICENSE</license>
     <projectUrl>https://github.com/chkr1011/MQTTnet</projectUrl>
     <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
+    <icon>images\Logo_128x128.png</icon>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
     <description>This is a support library to integrate MQTTnet into AspNetCore.</description>
     <releaseNotes>For release notes please go to MQTTnet release notes (https://www.nuget.org/packages/MQTTnet/).</releaseNotes>
-    <copyright>Copyright Christian Kratky 2016-2019</copyright>
+    <copyright>Copyright Christian Kratky 2016-2020</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>
     <dependencies>
       <dependency id="MQTTnet" version="$nugetVersion" />
 
-      <dependency id="Microsoft.AspNetCore.Connections.Abstractions" version="2.1.3" />
-      <dependency id="Microsoft.AspNetCore.Http.Connections" version="1.0.3"  />
-      <dependency id="Microsoft.AspNetCore.WebSockets" version="2.1.1" />
-      <dependency id="Microsoft.Extensions.Hosting.Abstractions" version="2.1.1" />
+      <dependency id="Microsoft.AspNetCore.Connections.Abstractions" version="3.1.3" />
+      <dependency id="Microsoft.AspNetCore.Http.Connections" version="1.1.0"  />
+      <dependency id="Microsoft.AspNetCore.WebSockets" version="2.2.1" />
+      <dependency id="Microsoft.Extensions.Hosting.Abstractions" version="3.1.3" />
     </dependencies>
   </metadata>
 
@@ -27,6 +28,9 @@
     <!-- License -->
     <file src="..\LICENSE" />
 
+    <!-- Images -->
+    <file src="..\Images\Logo_128x128.png" target="images\" />
+
     <!-- .NET Standard 2.0 -->
     <file src="..\Source\MQTTnet.AspNetCore\bin\Release\netstandard2.0\MQTTnet.AspNetCore.*" target="lib\netstandard2.0\"/>
   </files>

Build/MQTTnet.Extensions.ManagedClient.nuspec

@@ -8,10 +8,11 @@
     <license type="file">LICENSE</license>
     <projectUrl>https://github.com/chkr1011/MQTTnet</projectUrl>
     <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
+    <icon>images\Logo_128x128.png</icon>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
     <description>This is an extension library which provides a managed MQTT client with additional features using MQTTnet.</description>
     <releaseNotes>For release notes please go to MQTTnet release notes (https://www.nuget.org/packages/MQTTnet/).</releaseNotes>
-    <copyright>Copyright Christian Kratky 2016-2019</copyright>
+    <copyright>Copyright Christian Kratky 2016-2020</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> 
     <dependencies>
       <dependency id="MQTTnet" version="$nugetVersion" />
@@ -22,6 +23,9 @@
     <!-- License -->
     <file src="..\LICENSE" />
 
+    <!-- Images -->
+    <file src="..\Images\Logo_128x128.png" target="images\" />
+
     <!-- .NET Standard 1.3 -->
     <file src="..\Source\MQTTnet.Extensions.ManagedClient\bin\Release\netstandard1.3\MQTTnet.Extensions.ManagedClient.*" target="lib\netstandard1.3\"/>
 

Build/MQTTnet.Extensions.Rpc.nuspec

@@ -8,10 +8,11 @@
     <license type="file">LICENSE</license>
     <projectUrl>https://github.com/chkr1011/MQTTnet</projectUrl>
     <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
+    <icon>images\Logo_128x128.png</icon>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
     <description>This is an extension library which allows executing synchronous device calls including a response using MQTTnet.</description>
     <releaseNotes>For release notes please go to MQTTnet release notes (https://www.nuget.org/packages/MQTTnet/).</releaseNotes>
-    <copyright>Copyright Christian Kratky 2016-2019</copyright>
+    <copyright>Copyright Christian Kratky 2016-2020</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> 
     <dependencies>
       <dependency id="MQTTnet" version="$nugetVersion" />
@@ -22,6 +23,9 @@
     <!-- License -->
     <file src="..\LICENSE" />
 
+    <!-- Images -->
+    <file src="..\Images\Logo_128x128.png" target="images\" />
+
     <!-- .NET Standard 1.3 -->
     <file src="..\Source\MQTTnet.Extensions.Rpc\bin\Release\netstandard1.3\MQTTnet.Extensions.Rpc.*" target="lib\netstandard1.3\"/>
 

Build/MQTTnet.Extensions.WebSocket4Net.nuspec

@@ -8,10 +8,11 @@
     <license type="file">LICENSE</license>
     <projectUrl>https://github.com/chkr1011/MQTTnet</projectUrl>
     <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
+    <icon>images\Logo_128x128.png</icon>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
     <description>This is an extension library which allows using _WebSocket4Net_ as transport for MQTTnet clients.</description>
     <releaseNotes>For release notes please go to MQTTnet release notes (https://www.nuget.org/packages/MQTTnet/).</releaseNotes>
-    <copyright>Copyright Christian Kratky 2016-2019</copyright>
+    <copyright>Copyright Christian Kratky 2016-2020</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> 
     <dependencies>
       <dependency id="MQTTnet" version="$nugetVersion" />
@@ -22,6 +23,9 @@
     <!-- License -->
     <file src="..\LICENSE" />
 
+    <!-- Images -->
+    <file src="..\Images\Logo_128x128.png" target="images\" />
+
     <!-- .NET Standard 1.3 -->
     <file src="..\Source\MQTTnet.Extensions.WebSocket4Net\bin\Release\netstandard1.3\MQTTnet.Extensions.WebSocket4Net.*" target="lib\netstandard1.3\"/>
 

Build/MQTTnet.NETStandard.nuspec

@@ -8,10 +8,11 @@
     <license type="file">LICENSE</license>
     <projectUrl>https://github.com/chkr1011/MQTTnet</projectUrl>
     <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
+    <icon>images\Logo_128x128.png</icon>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
     <description>This package contains the .NET Standard version of MQTTnet only.</description>
     <releaseNotes>For release notes please go to MQTTnet release notes (https://www.nuget.org/packages/MQTTnet/).</releaseNotes>
-    <copyright>Copyright Christian Kratky 2016-2019</copyright>
+    <copyright>Copyright Christian Kratky 2016-2020</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> 
     <dependencies>
       <group targetFramework="netstandard1.3">
@@ -33,6 +34,9 @@
     <!-- License -->
     <file src="..\LICENSE" />
 
+    <!-- Images -->
+    <file src="..\Images\Logo_128x128.png" target="images\" />
+
     <!-- .NET Standard 1.3 -->
     <file src="..\Source\MQTTnet\bin\Release\netstandard1.3\MQTTnet.*" target="lib\netstandard1.3\"/>
 

Build/MQTTnet.nuspec

@@ -8,13 +8,32 @@
     <license type="file">LICENSE</license>
     <projectUrl>https://github.com/chkr1011/MQTTnet</projectUrl>
     <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
+    <icon>images\Logo_128x128.png</icon>
     <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) and supports v3.1.0, v3.1.1 and v5.0.0 of the MQTT protocol.</description>
     <releaseNotes>
+* [All] Due to a merge issue not all changes are included in 3.0.8. All these changes are now included in this version.
+* [Core] Updated all nuget references.
+* [Core] Added MqttApplicationMessage.GetUserProperty() convenience method (thanks to @PMExtra).
+* [LowLevelMqttClient] Added low level MQTT client in order to provide more flexibility when using the MQTT protocol. This client requires detailed knowledge about the MQTT protocol.
+* [Client] Improve connection stability (thanks to @jltjohanlindqvist).
+* [Client] Support WithConnectionUri to configure client (thanks to @PMExtra).
+* [Client] Support PublishAsync with QoS 1 and QoS 2 from within an ApplicationMessageReceivedHandler (#648, #587, thanks to @PSanetra).
+* [Client] Fixed MqttCommunicationTimedOutExceptions, caused by a long running ApplicationMessageReceivedHandler, which blocked MQTT packets from being processed (#829, thanks to @PSanetra).
+* [ManagedClient] Added builder class for MqttClientUnsubscribeOptions (thanks to @dominikviererbe).
 * [ManagedClient] Added support for persisted sessions (thansk to @PMExtra).
+* [ManagedClient] Fixed a memory leak (thanks to @zawodskoj).
+* [ManagedClient] Improved internal subscription management (#569, thanks to @cstichlberger).
+* [ManagedClient] Refactored log messages (thanks to @cstichlberger).
 * [Server] Added support for assigned client IDs (MQTTv5 only) (thanks to @bcrosnier).
+* [Server] Added interceptor for unsubscriptions.
+* [Server] Removed exceptions when user properties are set with MQTT protocol version 3.1
+* [Server] Added custom session items to the client status.
+* [Server] Added option to check whether the server is already started properly or not.
+* [MQTTnet.AspNetCore] improved compatibility with AspNetCore 3.1
+* [MQTTnet.Server] Added interceptor for unsubscriptions.
     </releaseNotes>
-    <copyright>Copyright Christian Kratky 2016-2019</copyright>
+    <copyright>Copyright Christian Kratky 2016-2020</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> 
     <dependencies>
       <group targetFramework="netstandard1.3">
@@ -30,7 +49,7 @@
         <dependency id="System.Net.WebSockets.Client" version="4.3.2" />
       </group>
       <group targetFramework="uap10.0">
-        <dependency id="Microsoft.NETCore.UniversalWindowsPlatform" version="6.2.8" />
+        <dependency id="Microsoft.NETCore.UniversalWindowsPlatform" version="6.2.10" />
       </group>
     </dependencies>
   </metadata>
@@ -39,6 +58,9 @@
     <!-- License -->
     <file src="..\LICENSE" />
 
+    <!-- Images -->
+    <file src="..\Images\Logo_128x128.png" target="images\" />
+
     <!-- .NET Standard 1.3 -->
     <file src="..\Source\MQTTnet\bin\Release\netstandard1.3\MQTTnet.*" target="lib\netstandard1.3\"/>
     

Build/build.ps1

@@ -12,12 +12,16 @@ Write-Host "Nuget version    = $nugetVersion"
 Write-Host "MSBuild path     = $msbuild"
 Write-Host
 
-# Build and execute tests
-&$msbuild ..\Tests\MQTTnet.Core.Tests\MQTTnet.Tests.csproj /t:Build /p:Configuration="Release" /p:TargetFramework="netcoreapp2.1" /verbosity:m
-&$msbuild ..\Tests\MQTTnet.AspNetCore.Tests\MQTTnet.AspNetCore.Tests.csproj /t:Build /p:Configuration="Release" /p:TargetFramework="netcoreapp2.1" /verbosity:m
+Invoke-WebRequest -Uri "https://dist.nuget.org/win-x86-commandline/latest/nuget.exe" -OutFile "nuget.exe"
 
-vstest.console.exe ..\Tests\MQTTnet.Core.Tests\bin\Release\netcoreapp2.1\MQTTnet.Tests.dll
-vstest.console.exe ..\Tests\MQTTnet.AspNetCore.Tests\bin\Release\netcoreapp2.1\MQTTnet.AspNetCore.Tests.dll
+.\nuget.exe restore ..\MQTTnet.sln
+
+# Build and execute tests
+&$msbuild ..\Tests\MQTTnet.Core.Tests\MQTTnet.Tests.csproj /t:Build /p:Configuration="Release" /p:TargetFramework="netcoreapp3.1" /verbosity:m
+&$msbuild ..\Tests\MQTTnet.AspNetCore.Tests\MQTTnet.AspNetCore.Tests.csproj /t:Build /p:Configuration="Release" /p:TargetFramework="netcoreapp3.1" /verbosity:m
+
+vstest.console.exe ..\Tests\MQTTnet.Core.Tests\bin\Release\netcoreapp3.1\MQTTnet.Tests.dll
+vstest.console.exe ..\Tests\MQTTnet.AspNetCore.Tests\bin\Release\netcoreapp3.1\MQTTnet.AspNetCore.Tests.dll
 
 # Build the core library
 &$msbuild ..\Source\MQTTnet\MQTTnet.csproj /t:Build /p:Configuration="Release" /p:TargetFramework="net452" /p:FileVersion=$assemblyVersion /p:AssemblyVersion=$assemblyVersion /verbosity:m /p:SignAssembly=true /p:AssemblyOriginatorKeyFile=".\..\..\Build\codeSigningKey.pfx"
@@ -51,7 +55,6 @@ vstest.console.exe ..\Tests\MQTTnet.AspNetCore.Tests\bin\Release\netcoreapp2.1\M
 &$msbuild ..\Source\MQTTnet.Extensions.WebSocket4Net\MQTTnet.Extensions.WebSocket4Net.csproj /t:Build /p:Configuration="Release" /p:TargetFramework="uap10.0" /p:FileVersion=$assemblyVersion /p:AssemblyVersion=$assemblyVersion /verbosity:m /p:SignAssembly=true /p:AssemblyOriginatorKeyFile=".\..\..\Build\codeSigningKey.pfx"
 
 # Create NuGet packages.
-Invoke-WebRequest -Uri "https://dist.nuget.org/win-x86-commandline/latest/nuget.exe" -OutFile "nuget.exe"
 
 Remove-Item .\NuGet -Force -Recurse -ErrorAction SilentlyContinue
 
@@ -84,8 +87,8 @@ Remove-Item "nuget.exe" -Force -Recurse -ErrorAction SilentlyContinue
 # Build MQTTnet.Server Portable
 &dotnet publish ..\Source\MQTTnet.Server\MQTTnet.Server.csproj --configuration Release /p:FileVersion=$assemblyVersion /p:Version=$nugetVersion
 
-$source = "..\Source\MQTTnet.Server\bin\Release\netcoreapp2.2\publish"
-$destination = "..\Source\MQTTnet.Server\bin\MQTTnet.Server-Portable-v$nugetVersion.zip"
+$source = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\Release\netcoreapp3.1\publish"
+$destination = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\MQTTnet.Server-Portable-v$nugetVersion.zip"
 If(Test-path $destination) {Remove-item $destination}
  Add-Type -assembly "system.io.compression.filesystem"
 [io.compression.zipfile]::CreateFromDirectory($source, $destination) 
@@ -95,8 +98,8 @@ If(Test-path $destination) {Remove-item $destination}
 # Build MQTTnet.Server Linux-x64
 &dotnet publish ..\Source\MQTTnet.Server\MQTTnet.Server.csproj --configuration Release /p:FileVersion=$assemblyVersion /p:Version=$nugetVersion --self-contained --runtime linux-x64 
 
-$source = "..\Source\MQTTnet.Server\bin\Release\netcoreapp2.2\linux-x64\publish"
-$destination = "..\Source\MQTTnet.Server\bin\MQTTnet.Server-Linux-x64-v$nugetVersion.zip"
+$source = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\Release\netcoreapp3.1\linux-x64\publish"
+$destination = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\MQTTnet.Server-Linux-x64-v$nugetVersion.zip"
 If(Test-path $destination) {Remove-item $destination}
  Add-Type -assembly "system.io.compression.filesystem"
 [io.compression.zipfile]::CreateFromDirectory($source, $destination) 
@@ -106,8 +109,8 @@ If(Test-path $destination) {Remove-item $destination}
 # Build MQTTnet.Server Linux-ARM
 &dotnet publish ..\Source\MQTTnet.Server\MQTTnet.Server.csproj --configuration Release /p:FileVersion=$assemblyVersion /p:Version=$nugetVersion --self-contained --runtime linux-arm 
 
-$source = "..\Source\MQTTnet.Server\bin\Release\netcoreapp2.2\linux-ARM\publish"
-$destination = "..\Source\MQTTnet.Server\bin\MQTTnet.Server-Linux-ARM-v$nugetVersion.zip"
+$source = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\Release\netcoreapp3.1\linux-ARM\publish"
+$destination = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\MQTTnet.Server-Linux-ARM-v$nugetVersion.zip"
 If(Test-path $destination) {Remove-item $destination}
  Add-Type -assembly "system.io.compression.filesystem"
 [io.compression.zipfile]::CreateFromDirectory($source, $destination) 
@@ -117,8 +120,8 @@ If(Test-path $destination) {Remove-item $destination}
 # Build MQTTnet.Server Windows-x64
 &dotnet publish ..\Source\MQTTnet.Server\MQTTnet.Server.csproj --configuration Release /p:FileVersion=$assemblyVersion /p:Version=$nugetVersion --self-contained --runtime win-x64
 
-$source = "..\Source\MQTTnet.Server\bin\Release\netcoreapp2.2\win-x64\publish"
-$destination = "..\Source\MQTTnet.Server\bin\MQTTnet.Server-Windows-x64-v$nugetVersion.zip"
+$source = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\Release\netcoreapp3.1\win-x64\publish"
+$destination = (Convert-Path .) + "\..\Source\MQTTnet.Server\bin\MQTTnet.Server-Windows-x64-v$nugetVersion.zip"
 If(Test-path $destination) {Remove-item $destination}
  Add-Type -assembly "system.io.compression.filesystem"
 [io.compression.zipfile]::CreateFromDirectory($source, $destination) 

Documents/Import_CodeSigningKey.md

@@ -1,9 +1,9 @@
 # Import codeSigningKey.pfx
 In order to import the key for code signing on a new developer machine use the following command within the VS developer command line:
 
-> sn –i codeSigningKey.pfx VS_KEY_EFCA4C5B6DFD4B4F
+sn –i .\codeSigningKey.pfx VS_KEY_62CA73019ED23333
 
 The container name may be different.
 
 # Check if the assembly has a strong name
-> sn -vf MQTTnet.dll
+sn -vf MQTTnet.dll

MQTTnet.sln

@@ -53,6 +53,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Server", "Source\MQ
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MQTTnet.Extensions.WebSocket4Net", "Source\MQTTnet.Extensions.WebSocket4Net\MQTTnet.Extensions.WebSocket4Net.csproj", "{2BD01D53-4CA5-4142-BE8D-313876395E3E}"
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Apps", "Apps", "{A56E3128-1639-4F31-873A-325E14BB6295}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -270,7 +272,7 @@ Global
 	EndGlobalSection
 	GlobalSection(NestedProjects) = preSolution
 		{A7FF0C91-25DE-4BA6-B39E-F54E8DADF1CC} = {9248C2E1-B9D6-40BF-81EC-86004D7765B4}
-		{FF1F72D6-9524-4422-9497-3CC0002216ED} = {9248C2E1-B9D6-40BF-81EC-86004D7765B4}
+		{FF1F72D6-9524-4422-9497-3CC0002216ED} = {A56E3128-1639-4F31-873A-325E14BB6295}
 		{3587E506-55A2-4EB3-99C7-DC01E42D25D2} = {32A630A7-2598-41D7-B625-204CD906F5FB}
 		{3D283AAD-AAA8-4339-8394-52F80B6304DB} = {9248C2E1-B9D6-40BF-81EC-86004D7765B4}
 		{C6FF8AEA-0855-41EC-A1F3-AC262225BAB9} = {9248C2E1-B9D6-40BF-81EC-86004D7765B4}
@@ -279,7 +281,7 @@ Global
 		{998D04DD-7CB0-45F5-A393-E2495C16399E} = {9248C2E1-B9D6-40BF-81EC-86004D7765B4}
 		{C400533A-8EBA-4F0B-BF4D-295C3708604B} = {12816BCC-AF9E-44A9-9AE5-C246AF2A0587}
 		{61B62223-F5D0-48E4-BBD6-2CBA9353CB5E} = {9248C2E1-B9D6-40BF-81EC-86004D7765B4}
-		{5699FB8C-838C-4AB0-80A5-9CA809F9B65B} = {32A630A7-2598-41D7-B625-204CD906F5FB}
+		{5699FB8C-838C-4AB0-80A5-9CA809F9B65B} = {A56E3128-1639-4F31-873A-325E14BB6295}
 		{2BD01D53-4CA5-4142-BE8D-313876395E3E} = {12816BCC-AF9E-44A9-9AE5-C246AF2A0587}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution

README.md

@@ -7,8 +7,7 @@
 [![NuGet Badge](https://buildstats.info/nuget/MQTTnet)](https://www.nuget.org/packages/MQTTnet)
 [![Build status](https://ci.appveyor.com/api/projects/status/ycit86voxfevm2aa/branch/master?svg=true)](https://ci.appveyor.com/project/chkr1011/mqttnet)
 [![BCH compliance](https://bettercodehub.com/edge/badge/chkr1011/MQTTnet?branch=master)](https://bettercodehub.com/)
-[![OpenCollective](https://opencollective.com/mqttnet/backers/badge.svg)](https://opencollective.com/mqttnet) 
-[![OpenCollective](https://opencollective.com/mqttnet/sponsors/badge.svg)](https://opencollective.com/mqttnet) [![Join the chat at https://gitter.im/MQTTnet/community](https://badges.gitter.im/MQTTnet/community.svg)](https://gitter.im/MQTTnet/community?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+[![Join the chat at https://gitter.im/MQTTnet/community](https://badges.gitter.im/MQTTnet/community.svg)](https://gitter.im/MQTTnet/community?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://raw.githubusercontent.com/chkr1011/MQTTnet/master/LICENSE)
 
 # MQTTnet
@@ -93,8 +92,6 @@ Please find examples and the documentation at the Wiki of this repository (<http
 If you want to contribute to this project just create a pull request. But only pull requests which are matching the code style of this library will be accepted. Before creating a pull request please have a look at the library to get an overview of the required style.
 Also additions and updates in the Wiki are welcome.
 
-**This project, like all projects requires time and money.  If you feel compelled to support the development team, you can do so through Open Collective (https://opencollective.com/mqttnet)**.
-
 ## References
 
 This library is used in the following projects:

Source/MQTTnet.AspnetCore/Client/MqttClientConnectionContextFactory.cs

@@ -1,17 +1,16 @@
-using System;
-using System.Net;
-using MQTTnet.Adapter;
+using MQTTnet.Adapter;
 using MQTTnet.AspNetCore.Client.Tcp;
-using MQTTnet.Client;
 using MQTTnet.Client.Options;
 using MQTTnet.Diagnostics;
 using MQTTnet.Formatter;
+using System;
+using System.Net;
 
 namespace MQTTnet.AspNetCore.Client
 {
     public class MqttClientConnectionContextFactory : IMqttClientAdapterFactory
     {
-        public IMqttChannelAdapter CreateClientAdapter(IMqttClientOptions options, IMqttNetChildLogger logger)
+        public IMqttChannelAdapter CreateClientAdapter(IMqttClientOptions options, IMqttNetLogger logger)
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 

Source/MQTTnet.AspnetCore/Client/Tcp/TcpConnection.cs

@@ -1,13 +1,13 @@
-using System;
+using Microsoft.AspNetCore.Connections;
+using Microsoft.AspNetCore.Http.Features;
+using MQTTnet.Exceptions;
+using System;
 using System.Collections.Generic;
 using System.IO;
 using System.IO.Pipelines;
 using System.Net;
 using System.Net.Sockets;
 using System.Threading.Tasks;
-using Microsoft.AspNetCore.Connections;
-using Microsoft.AspNetCore.Http.Features;
-using MQTTnet.Exceptions;
 
 namespace MQTTnet.AspNetCore.Client.Tcp
 {
@@ -40,8 +40,11 @@ namespace MQTTnet.AspNetCore.Client.Tcp
             _sender = new SocketSender(_socket, PipeScheduler.ThreadPool);
             _receiver = new SocketReceiver(_socket, PipeScheduler.ThreadPool);
         }
-
-        public Task DisposeAsync()
+#if NETCOREAPP3_1
+        public override ValueTask DisposeAsync()
+#else
+        public new Task DisposeAsync()
+#endif
         {
             IsConnected = false;
 
@@ -50,8 +53,15 @@ namespace MQTTnet.AspNetCore.Client.Tcp
 
             _socket?.Dispose();
 
+#if NETCOREAPP3_1
+
+            return base.DisposeAsync();
+        }
+#else
+
             return Task.CompletedTask;
         }
+#endif
 
         public async Task StartAsync()
         {

Source/MQTTnet.AspnetCore/Extensions/ApplicationBuilderExtensions.cs

@@ -1,14 +1,13 @@
 using System;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.Extensions.DependencyInjection;
-using System.Linq;
 using MQTTnet.Server;
-using System.Collections.Generic;
 
 namespace MQTTnet.AspNetCore
 {
     public static class ApplicationBuilderExtensions
     {
+        [Obsolete("This class is obsolete and will be removed in a future version. The recommended alternative is to use MapMqtt inside Microsoft.AspNetCore.Builder.UseEndpoints(...).")]
         public static IApplicationBuilder UseMqttEndpoint(this IApplicationBuilder app, string path = "/mqtt")
         {
             app.UseWebSockets();
@@ -24,7 +23,7 @@ namespace MQTTnet.AspNetCore
 
                 if (context.Request.Headers.TryGetValue("Sec-WebSocket-Protocol", out var requestedSubProtocolValues))
                 {
-                    subProtocol = SelectSubProtocol(requestedSubProtocolValues);
+                    subProtocol = MqttSubProtocolSelector.SelectSubProtocol(requestedSubProtocolValues);
                 }
 
                 var adapter = app.ApplicationServices.GetRequiredService<MqttWebSocketServerAdapter>();
@@ -37,14 +36,6 @@ namespace MQTTnet.AspNetCore
             return app;
         }
 
-        public static string SelectSubProtocol(IList<string> requestedSubProtocolValues)
-        {
-            // Order the protocols to also match "mqtt", "mqttv-3.1", "mqttv-3.11" etc.
-            return requestedSubProtocolValues
-                .OrderByDescending(p => p.Length)
-                .FirstOrDefault(p => p.ToLower().StartsWith("mqtt"));
-        }
-
         public static IApplicationBuilder UseMqttServer(this IApplicationBuilder app, Action<IMqttServer> configure)
         {
             var server = app.ApplicationServices.GetRequiredService<IMqttServer>();

Source/MQTTnet.AspnetCore/Extensions/ConnectionRouteBuilderExtensions.cs

@@ -0,0 +1,20 @@
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Connections;
+using System;
+
+namespace MQTTnet.AspNetCore
+{
+    public static class ConnectionRouteBuilderExtensions
+    {
+#if NETCOREAPP3_1
+        [Obsolete("This class is obsolete and will be removed in a future version. The recommended alternative is to use MapMqtt inside Microsoft.AspNetCore.Builder.UseEndpoints(...).")]
+#endif
+        public static void MapMqtt(this ConnectionsRouteBuilder connection, PathString path)
+        {
+            connection.MapConnectionHandler<MqttConnectionHandler>(path, options =>
+            {
+                options.WebSockets.SubProtocolSelector = MqttSubProtocolSelector.SelectSubProtocol;
+            });
+        }
+    }
+}

Source/MQTTnet.AspnetCore/Extensions/EndpointRouterExtensions.cs

@@ -0,0 +1,21 @@
+
+#if NETCOREAPP3_1
+
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Routing;
+
+namespace MQTTnet.AspNetCore
+{
+    public static class EndpointRouterExtensions
+    {
+        public static void MapMqtt(this IEndpointRouteBuilder endpoints, string pattern) 
+        {
+            endpoints.MapConnectionHandler<MqttConnectionHandler>(pattern, options =>
+            {
+                options.WebSockets.SubProtocolSelector = MqttSubProtocolSelector.SelectSubProtocol;
+            });
+        }
+    }
+}
+
+#endif

Source/MQTTnet.AspnetCore/Extensions/ReaderExtensions.cs

@@ -80,7 +80,7 @@ namespace MQTTnet.AspNetCore
             headerLength = 0;
             bodyLength = 0;
             
-            var temp = input.Slice(0, Math.Min(5, input.Length)).GetMemory();
+            var temp = input.Slice(0, Math.Min(5, input.Length)).GetMemory().Span;
 
             do
             {
@@ -88,7 +88,7 @@ namespace MQTTnet.AspNetCore
                 {
                     return false;
                 }
-                encodedByte = temp.Span[index];
+                encodedByte = temp[index];
                 index++;
 
                 value += (byte)(encodedByte & 127) * multiplier;

Source/MQTTnet.AspnetCore/Extensions/ServiceCollectionExtensions.cs

@@ -1,10 +1,10 @@
-using System;
-using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 using MQTTnet.Adapter;
 using MQTTnet.Diagnostics;
-using MQTTnet.Server;
 using MQTTnet.Implementations;
+using MQTTnet.Server;
+using System;
 
 namespace MQTTnet.AspNetCore
 {
@@ -13,7 +13,7 @@ namespace MQTTnet.AspNetCore
         public static IServiceCollection AddHostedMqttServer(this IServiceCollection services, IMqttServerOptions options)
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
-            
+
             services.AddSingleton(options);
 
             services.AddHostedMqttServer();
@@ -23,7 +23,8 @@ namespace MQTTnet.AspNetCore
 
         public static IServiceCollection AddHostedMqttServer(this IServiceCollection services, Action<MqttServerOptionsBuilder> configure)
         {
-            services.AddSingleton<IMqttServerOptions>(s => {
+            services.AddSingleton<IMqttServerOptions>(s =>
+            {
                 var builder = new MqttServerOptionsBuilder();
                 configure(builder);
                 return builder.Build();
@@ -36,7 +37,8 @@ namespace MQTTnet.AspNetCore
 
         public static IServiceCollection AddHostedMqttServerWithServices(this IServiceCollection services, Action<AspNetMqttServerOptionsBuilder> configure)
         {
-            services.AddSingleton<IMqttServerOptions>(s => {
+            services.AddSingleton<IMqttServerOptions>(s =>
+            {
                 var builder = new AspNetMqttServerOptionsBuilder(s);
                 configure(builder);
                 return builder.Build();
@@ -60,14 +62,12 @@ namespace MQTTnet.AspNetCore
         private static IServiceCollection AddHostedMqttServer(this IServiceCollection services)
         {
             var logger = new MqttNetLogger();
-            var childLogger = logger.CreateChildLogger();
 
             services.AddSingleton<IMqttNetLogger>(logger);
-            services.AddSingleton(childLogger);
             services.AddSingleton<MqttHostedServer>();
             services.AddSingleton<IHostedService>(s => s.GetService<MqttHostedServer>());
             services.AddSingleton<IMqttServer>(s => s.GetService<MqttHostedServer>());
-            
+
             return services;
         }
 

Source/MQTTnet.AspnetCore/MQTTnet.AspNetCore.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netcoreapp2.1</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netcoreapp2.1;netcoreapp3.1</TargetFrameworks>
     <Product />
     <Company />
     <Authors />
@@ -14,11 +14,17 @@
     <DefineConstants>RELEASE;NETSTANDARD2_0</DefineConstants>
   </PropertyGroup>
 
-  <ItemGroup>
-    <PackageReference Include="Microsoft.AspNetCore.Connections.Abstractions" Version="2.1.3" />
-    <PackageReference Include="Microsoft.AspNetCore.Http.Connections" Version="1.0.3" />
-    <PackageReference Include="Microsoft.AspNetCore.WebSockets" Version="2.1.1" />
-    <PackageReference Include="Microsoft.Extensions.Hosting.Abstractions" Version="2.1.1" />
+  <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp3.1'">
+    <FrameworkReference Include="Microsoft.AspNetCore.App" />
+
+    <PackageReference Include="System.IO.Pipelines" Version="4.7.1" />
+  </ItemGroup>
+    
+  <ItemGroup Condition="'$(TargetFramework)' != 'netcoreapp3.1'">
+    <PackageReference Include="Microsoft.AspNetCore.Connections.Abstractions" Version="3.1.3" />
+    <PackageReference Include="Microsoft.AspNetCore.Http.Connections" Version="1.1.0" />
+    <PackageReference Include="Microsoft.AspNetCore.WebSockets" Version="2.2.1" />
+    <PackageReference Include="Microsoft.Extensions.Hosting.Abstractions" Version="3.1.3" />
   </ItemGroup>
 
   <ItemGroup>

Source/MQTTnet.AspnetCore/MqttHostedServer.cs

@@ -21,7 +21,8 @@ namespace MQTTnet.AspNetCore
 
         public Task StartAsync(CancellationToken cancellationToken)
         {
-            return StartAsync(_options);
+            _ = StartAsync(_options);
+            return Task.CompletedTask;
         }
 
         public Task StopAsync(CancellationToken cancellationToken)

Source/MQTTnet.AspnetCore/MqttSubProtocolSelector.cs

@@ -0,0 +1,16 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace MQTTnet.AspNetCore
+{
+    public static class MqttSubProtocolSelector
+    {
+        public static string SelectSubProtocol(IList<string> requestedSubProtocolValues)
+        {
+            // Order the protocols to also match "mqtt", "mqttv-3.1", "mqttv-3.11" etc.
+            return requestedSubProtocolValues
+                .OrderByDescending(p => p.Length)
+                .FirstOrDefault(p => p.ToLower().StartsWith("mqtt"));
+        }
+    }
+}

Source/MQTTnet.AspnetCore/MqttWebSocketServerAdapter.cs

@@ -1,20 +1,20 @@
-using System;
-using System.Net.WebSockets;
-using System.Threading.Tasks;
-using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http;
 using MQTTnet.Adapter;
 using MQTTnet.Diagnostics;
 using MQTTnet.Formatter;
 using MQTTnet.Implementations;
 using MQTTnet.Server;
+using System;
+using System.Net.WebSockets;
+using System.Threading.Tasks;
 
 namespace MQTTnet.AspNetCore
 {
     public class MqttWebSocketServerAdapter : IMqttServerAdapter
     {
-        private readonly IMqttNetChildLogger _logger;
+        private readonly IMqttNetLogger _logger;
 
-        public MqttWebSocketServerAdapter(IMqttNetChildLogger logger)
+        public MqttWebSocketServerAdapter(IMqttNetLogger logger)
         {
             if (logger == null) throw new ArgumentNullException(nameof(logger));
 
@@ -38,7 +38,7 @@ namespace MQTTnet.AspNetCore
             if (webSocket == null) throw new ArgumentNullException(nameof(webSocket));
 
             var endpoint = $"{httpContext.Connection.RemoteIpAddress}:{httpContext.Connection.RemotePort}";
-            
+
             var clientCertificate = await httpContext.Connection.GetClientCertificateAsync().ConfigureAwait(false);
             try
             {

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClient.cs

@@ -1,9 +1,4 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Threading;
-using System.Threading.Tasks;
-using MQTTnet.Client;
+using MQTTnet.Client;
 using MQTTnet.Client.Connecting;
 using MQTTnet.Client.Disconnecting;
 using MQTTnet.Client.Publishing;
@@ -13,18 +8,33 @@ using MQTTnet.Exceptions;
 using MQTTnet.Internal;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace MQTTnet.Extensions.ManagedClient
 {
-    public class ManagedMqttClient : IManagedMqttClient
+    public class ManagedMqttClient : Disposable, IManagedMqttClient
     {
         private readonly BlockingQueue<ManagedMqttApplicationMessage> _messageQueue = new BlockingQueue<ManagedMqttApplicationMessage>();
+
+        /// <summary>
+        /// The subscriptions are managed in 2 separate buckets:
+        /// <see cref="_subscriptions"/> and <see cref="_unsubscriptions"/> are processed during normal operation
+        /// and are moved to the <see cref="_reconnectSubscriptions"/> when they get processed. They can be accessed by
+        /// any thread and are therefore mutex'ed. <see cref="_reconnectSubscriptions"/> get sent to the broker
+        ///  at reconnect and are solely owned by <see cref="MaintainConnectionAsync"/>.
+        /// </summary>
+        private readonly Dictionary<string, MqttQualityOfServiceLevel> _reconnectSubscriptions = new Dictionary<string, MqttQualityOfServiceLevel>();
         private readonly Dictionary<string, MqttQualityOfServiceLevel> _subscriptions = new Dictionary<string, MqttQualityOfServiceLevel>();
         private readonly HashSet<string> _unsubscriptions = new HashSet<string>();
+        private readonly SemaphoreSlim _subscriptionsQueuedSignal = new SemaphoreSlim(0);
 
         private readonly IMqttClient _mqttClient;
-        private readonly IMqttNetChildLogger _logger;
-        
+        private readonly IMqttNetLogger _logger;
+
         private readonly AsyncLock _messageQueueLock = new AsyncLock();
 
         private CancellationTokenSource _connectionCancellationToken;
@@ -33,10 +43,7 @@ namespace MQTTnet.Extensions.ManagedClient
 
         private ManagedMqttClientStorageManager _storageManager;
 
-        private bool _disposed;
-        private bool _subscriptionsNotPushed;
-
-        public ManagedMqttClient(IMqttClient mqttClient, IMqttNetChildLogger logger)
+        public ManagedMqttClient(IMqttClient mqttClient, IMqttNetLogger logger)
         {
             _mqttClient = mqttClient ?? throw new ArgumentNullException(nameof(mqttClient));
 
@@ -82,10 +89,6 @@ namespace MQTTnet.Extensions.ManagedClient
             if (options == null) throw new ArgumentNullException(nameof(options));
             if (options.ClientOptions == null) throw new ArgumentException("The client options are not set.", nameof(options));
 
-            if (!options.ClientOptions.CleanSession)
-            {
-                throw new NotSupportedException("The managed client does not support existing sessions.");
-            }
 
             if (!_maintainConnectionTask?.IsCompleted ?? false) throw new InvalidOperationException("The managed client is already started.");
 
@@ -141,6 +144,7 @@ namespace MQTTnet.Extensions.ManagedClient
             ThrowIfDisposed();
 
             if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
+            if (Options == null) throw new InvalidOperationException("call StartAsync before publishing messages");
 
             MqttTopicValidator.ThrowIfInvalid(applicationMessage.ApplicationMessage.Topic);
 
@@ -169,7 +173,7 @@ namespace MQTTnet.Extensions.ManagedClient
                     }
 
                     _messageQueue.Enqueue(applicationMessage);
-                    
+
                     if (_storageManager != null)
                     {
                         if (removedMessage != null)
@@ -206,9 +210,10 @@ namespace MQTTnet.Extensions.ManagedClient
                 foreach (var topicFilter in topicFilters)
                 {
                     _subscriptions[topicFilter.Topic] = topicFilter.QualityOfServiceLevel;
-                    _subscriptionsNotPushed = true;
+                    _unsubscriptions.Remove(topicFilter.Topic);
                 }
             }
+            _subscriptionsQueuedSignal.Release();
 
             return Task.FromResult(0);
         }
@@ -223,45 +228,34 @@ namespace MQTTnet.Extensions.ManagedClient
             {
                 foreach (var topic in topics)
                 {
-                    if (_subscriptions.Remove(topic))
-                    {
-                        _unsubscriptions.Add(topic);
-                        _subscriptionsNotPushed = true;
-                    }
+                    _subscriptions.Remove(topic);
+                    _unsubscriptions.Add(topic);
                 }
             }
+            _subscriptionsQueuedSignal.Release();
 
             return Task.FromResult(0);
         }
 
-        public void Dispose()
+        protected override void Dispose(bool disposing)
         {
-            if (_disposed)
+            if (disposing)
             {
-                return;
-            }
-
-            _disposed = true;
-
-            StopPublishing();
-            StopMaintainingConnection();
-
-            if (_maintainConnectionTask != null)
-            {
-                Task.WaitAny(_maintainConnectionTask);
-                _maintainConnectionTask = null;
-            }
-
-            _messageQueueLock.Dispose();
-            _mqttClient.Dispose();
-        }
-
-        private void ThrowIfDisposed()
-        {
-            if (_disposed)
-            {
-                throw new ObjectDisposedException(nameof(ManagedMqttClient));
+                StopPublishing();
+                StopMaintainingConnection();
+
+                if (_maintainConnectionTask != null)
+                {
+                    _maintainConnectionTask.GetAwaiter().GetResult();
+                    _maintainConnectionTask = null;
+                }
+
+                _messageQueue.Dispose();
+                _messageQueueLock.Dispose();
+                _mqttClient.Dispose();
+                _subscriptionsQueuedSignal.Dispose();
             }
+            base.Dispose(disposing);
         }
 
         private async Task MaintainConnectionAsync(CancellationToken cancellationToken)
@@ -278,11 +272,11 @@ namespace MQTTnet.Extensions.ManagedClient
             }
             catch (Exception exception)
             {
-                _logger.Error(exception, "Unhandled exception while maintaining connection.");
+                _logger.Error(exception, "Error exception while maintaining connection.");
             }
             finally
             {
-                if (!_disposed)
+                if (!IsDisposed)
                 {
                     try
                     {
@@ -295,6 +289,12 @@ namespace MQTTnet.Extensions.ManagedClient
 
                     _logger.Info("Stopped");
                 }
+                _reconnectSubscriptions.Clear();
+                lock (_subscriptions)
+                {
+                    _subscriptions.Clear();
+                    _unsubscriptions.Clear();
+                }
             }
         }
 
@@ -310,16 +310,22 @@ namespace MQTTnet.Extensions.ManagedClient
                     return;
                 }
 
-                if (connectionState == ReconnectionResult.Reconnected || _subscriptionsNotPushed)
+                if (connectionState == ReconnectionResult.Reconnected)
+                {
+                    await PublishReconnectSubscriptionsAsync().ConfigureAwait(false);
+                    StartPublishing();
+                    return;
+                }
+
+                if (connectionState == ReconnectionResult.Recovered)
                 {
-                    await SynchronizeSubscriptionsAsync().ConfigureAwait(false);
                     StartPublishing();
                     return;
                 }
 
                 if (connectionState == ReconnectionResult.StillConnected)
                 {
-                    await Task.Delay(Options.ConnectionCheckInterval, cancellationToken).ConfigureAwait(false);
+                    await PublishSubscriptionsAsync(Options.ConnectionCheckInterval, cancellationToken).ConfigureAwait(false);
                 }
             }
             catch (OperationCanceledException)
@@ -327,11 +333,11 @@ namespace MQTTnet.Extensions.ManagedClient
             }
             catch (MqttCommunicationException exception)
             {
-                _logger.Warning(exception, "Communication exception while maintaining connection.");
+                _logger.Warning(exception, "Communication error while maintaining connection.");
             }
             catch (Exception exception)
             {
-                _logger.Error(exception, "Unhandled exception while maintaining connection.");
+                _logger.Error(exception, "Error exception while maintaining connection.");
             }
         }
 
@@ -349,7 +355,7 @@ namespace MQTTnet.Extensions.ManagedClient
                     // of the messages, the DropOldestQueuedMessage strategy would
                     // be unable to know which message is actually the oldest and would
                     // instead drop the first item in the queue.
-                    var message = _messageQueue.PeekAndWait();
+                    var message = _messageQueue.PeekAndWait(cancellationToken);
                     if (message == null)
                     {
                         continue;
@@ -389,7 +395,7 @@ namespace MQTTnet.Extensions.ManagedClient
                     // it from the queue.  If not, that means this.PublishAsync has already
                     // removed it, in which case we don't want to do anything.
                     _messageQueue.RemoveFirst(i => i.Id.Equals(message.Id));
-                    
+
                     if (_storageManager != null)
                     {
                         await _storageManager.RemoveAsync(message).ConfigureAwait(false);
@@ -414,7 +420,7 @@ namespace MQTTnet.Extensions.ManagedClient
                     using (await _messageQueueLock.WaitAsync(CancellationToken.None).ConfigureAwait(false)) //lock to avoid conflict with this.PublishAsync
                     {
                         _messageQueue.RemoveFirst(i => i.Id.Equals(message.Id));
-                        
+
                         if (_storageManager != null)
                         {
                             await _storageManager.RemoveAsync(message).ConfigureAwait(false);
@@ -438,50 +444,84 @@ namespace MQTTnet.Extensions.ManagedClient
             }
         }
 
-        private async Task SynchronizeSubscriptionsAsync()
+        private async Task PublishSubscriptionsAsync(TimeSpan timeout, CancellationToken cancellationToken)
         {
-            _logger.Info("Synchronizing subscriptions");
-
-            List<TopicFilter> subscriptions;
-            HashSet<string> unsubscriptions;
-
-            lock (_subscriptions)
+            var endTime = DateTime.UtcNow + timeout;
+            while (await _subscriptionsQueuedSignal.WaitAsync(GetRemainingTime(endTime), cancellationToken).ConfigureAwait(false))
             {
-                subscriptions = _subscriptions.Select(i => new TopicFilter { Topic = i.Key, QualityOfServiceLevel = i.Value }).ToList();
+                List<TopicFilter> subscriptions;
+                HashSet<string> unsubscriptions;
 
-                unsubscriptions = new HashSet<string>(_unsubscriptions);
-                _unsubscriptions.Clear();
+                lock (_subscriptions)
+                {
+                    subscriptions = _subscriptions.Select(i => new TopicFilter { Topic = i.Key, QualityOfServiceLevel = i.Value }).ToList();
+                    _subscriptions.Clear();
+                    unsubscriptions = new HashSet<string>(_unsubscriptions);
+                    _unsubscriptions.Clear();
+                }
 
-                _subscriptionsNotPushed = false;
+                if (!subscriptions.Any() && !unsubscriptions.Any())
+                {
+                    continue;
+                }
+
+                _logger.Verbose($"Publishing subscriptions ({subscriptions.Count} subscriptions and {unsubscriptions.Count} unsubscriptions)");
+
+                foreach (var unsubscription in unsubscriptions)
+                {
+                    _reconnectSubscriptions.Remove(unsubscription);
+                }
+
+                foreach (var subscription in subscriptions)
+                {
+                    _reconnectSubscriptions[subscription.Topic] = subscription.QualityOfServiceLevel;
+                }
+
+                try
+                {
+                    if (unsubscriptions.Any())
+                    {
+                        await _mqttClient.UnsubscribeAsync(unsubscriptions.ToArray()).ConfigureAwait(false);
+                    }
+
+                    if (subscriptions.Any())
+                    {
+                        await _mqttClient.SubscribeAsync(subscriptions.ToArray()).ConfigureAwait(false);
+                    }
+                }
+                catch (Exception exception)
+                {
+                    await HandleSubscriptionExceptionAsync(exception).ConfigureAwait(false);
+                }
             }
+        }
 
-            if (!subscriptions.Any() && !unsubscriptions.Any())
-            {
-                return;
-            }
+        private async Task PublishReconnectSubscriptionsAsync()
+        {
+            _logger.Info("Publishing subscriptions at reconnect");
 
             try
             {
-                if (unsubscriptions.Any())
-                {
-                    await _mqttClient.UnsubscribeAsync(unsubscriptions.ToArray()).ConfigureAwait(false);
-                }
-
-                if (subscriptions.Any())
+                if (_reconnectSubscriptions.Any())
                 {
+                    var subscriptions = _reconnectSubscriptions.Select(i => new TopicFilter { Topic = i.Key, QualityOfServiceLevel = i.Value });
                     await _mqttClient.SubscribeAsync(subscriptions.ToArray()).ConfigureAwait(false);
                 }
             }
             catch (Exception exception)
             {
-                _logger.Warning(exception, "Synchronizing subscriptions failed.");
-                _subscriptionsNotPushed = true;
+                await HandleSubscriptionExceptionAsync(exception).ConfigureAwait(false);
+            }
+        }
 
-                var synchronizingSubscriptionsFailedHandler = SynchronizingSubscriptionsFailedHandler;
-                if (SynchronizingSubscriptionsFailedHandler != null)
-                {
-                    await synchronizingSubscriptionsFailedHandler.HandleSynchronizingSubscriptionsFailedAsync(new ManagedProcessFailedEventArgs(exception)).ConfigureAwait(false);
-                }
+        private async Task HandleSubscriptionExceptionAsync(Exception exception)
+        {
+            _logger.Warning(exception, "Synchronizing subscriptions failed.");
+
+            var synchronizingSubscriptionsFailedHandler = SynchronizingSubscriptionsFailedHandler;
+            if (SynchronizingSubscriptionsFailedHandler != null)
+            {
+                await synchronizingSubscriptionsFailedHandler.HandleSynchronizingSubscriptionsFailedAsync(new ManagedProcessFailedEventArgs(exception)).ConfigureAwait(false);
             }
         }
 
@@ -494,8 +534,8 @@ namespace MQTTnet.Extensions.ManagedClient
 
             try
             {
-                await _mqttClient.ConnectAsync(Options.ClientOptions).ConfigureAwait(false);
-                return ReconnectionResult.Reconnected;
+                var result = await _mqttClient.ConnectAsync(Options.ClientOptions).ConfigureAwait(false);
+                return result.IsSessionPresent ? ReconnectionResult.Recovered : ReconnectionResult.Reconnected;
             }
             catch (Exception exception)
             {
@@ -508,7 +548,7 @@ namespace MQTTnet.Extensions.ManagedClient
                 return ReconnectionResult.NotConnected;
             }
         }
-        
+
         private void StartPublishing()
         {
             if (_publishingCancellationToken != null)
@@ -535,5 +575,11 @@ namespace MQTTnet.Extensions.ManagedClient
             _connectionCancellationToken?.Dispose();
             _connectionCancellationToken = null;
         }
+
+        private TimeSpan GetRemainingTime(DateTime endTime)
+        {
+            var remainingTime = endTime - DateTime.UtcNow;
+            return remainingTime < TimeSpan.Zero ? TimeSpan.Zero : remainingTime;
+        }
     }
 }

Source/MQTTnet.Extensions.ManagedClient/MqttFactoryExtensions.cs

@@ -1,5 +1,5 @@
-using System;
-using MQTTnet.Diagnostics;
+using MQTTnet.Diagnostics;
+using System;
 
 namespace MQTTnet.Extensions.ManagedClient
 {
@@ -9,7 +9,7 @@ namespace MQTTnet.Extensions.ManagedClient
         {
             if (factory == null) throw new ArgumentNullException(nameof(factory));
 
-            return new ManagedMqttClient(factory.CreateMqttClient(), factory.DefaultLogger.CreateChildLogger());
+            return new ManagedMqttClient(factory.CreateMqttClient(), factory.DefaultLogger);
         }
 
         public static IManagedMqttClient CreateManagedMqttClient(this IMqttFactory factory, IMqttNetLogger logger)
@@ -17,7 +17,7 @@ namespace MQTTnet.Extensions.ManagedClient
             if (factory == null) throw new ArgumentNullException(nameof(factory));
             if (logger == null) throw new ArgumentNullException(nameof(logger));
 
-            return new ManagedMqttClient(factory.CreateMqttClient(logger), logger.CreateChildLogger());
+            return new ManagedMqttClient(factory.CreateMqttClient(logger), logger);
         }
     }
 }

Source/MQTTnet.Extensions.ManagedClient/ReconnectionResult.cs

@@ -4,6 +4,7 @@
     {
         StillConnected,
         Reconnected,
+        Recovered,
         NotConnected
     }
 }

Source/MQTTnet.Extensions.Rpc/MqttRpcClient.cs

@@ -1,17 +1,17 @@
-using System;
-using System.Collections.Concurrent;
-using System.Text;
-using System.Threading;
-using System.Threading.Tasks;
-using MQTTnet.Client;
+using MQTTnet.Client;
 using MQTTnet.Exceptions;
 using MQTTnet.Extensions.Rpc.Options;
 using MQTTnet.Extensions.Rpc.Options.TopicGeneration;
 using MQTTnet.Protocol;
+using System;
+using System.Collections.Concurrent;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace MQTTnet.Extensions.Rpc
 {
-    public class MqttRpcClient : IDisposable
+    public sealed class MqttRpcClient : IDisposable
     {
         private readonly ConcurrentDictionary<string, TaskCompletionSource<byte[]>> _waitingCalls = new ConcurrentDictionary<string, TaskCompletionSource<byte[]>>();
         private readonly IMqttClient _mqttClient;
@@ -101,7 +101,7 @@ namespace MQTTnet.Extensions.Rpc
 
                 await _mqttClient.SubscribeAsync(responseTopic, qualityOfServiceLevel).ConfigureAwait(false);
                 await _mqttClient.PublishAsync(requestMessage).ConfigureAwait(false);
-                
+
                 using (var timeoutCts = new CancellationTokenSource(timeout))
                 using (var linkedCts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, timeoutCts.Token))
                 {

Source/MQTTnet.Extensions.WebSocket4Net/WebSocket4NetMqttChannel.cs

@@ -85,7 +85,12 @@ namespace MQTTnet.Extensions.WebSocket4Net
             {
                 foreach (var certificate in _webSocketOptions.TlsOptions.Certificates)
                 {
+#if WINDOWS_UWP
                     certificates.Add(new X509Certificate(certificate));
+#else
+                    certificates.Add(certificate);
+#endif
+                    
                 }
             }
 

Source/MQTTnet.Extensions.WebSocket4Net/WebSocket4NetMqttClientAdapterFactory.cs

@@ -1,15 +1,15 @@
-using System;
-using MQTTnet.Adapter;
+using MQTTnet.Adapter;
 using MQTTnet.Client.Options;
 using MQTTnet.Diagnostics;
 using MQTTnet.Formatter;
 using MQTTnet.Implementations;
+using System;
 
 namespace MQTTnet.Extensions.WebSocket4Net
 {
     public class WebSocket4NetMqttClientAdapterFactory : IMqttClientAdapterFactory
     {
-        public IMqttChannelAdapter CreateClientAdapter(IMqttClientOptions options, IMqttNetChildLogger logger)
+        public IMqttChannelAdapter CreateClientAdapter(IMqttClientOptions options, IMqttNetLogger logger)
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
             if (logger == null) throw new ArgumentNullException(nameof(logger));
@@ -17,19 +17,19 @@ namespace MQTTnet.Extensions.WebSocket4Net
             switch (options.ChannelOptions)
             {
                 case MqttClientTcpOptions _:
-                {
-                    return new MqttChannelAdapter(new MqttTcpChannel(options), new MqttPacketFormatterAdapter(options.ProtocolVersion), logger);
-                }
+                    {
+                        return new MqttChannelAdapter(new MqttTcpChannel(options), new MqttPacketFormatterAdapter(options.ProtocolVersion), logger);
+                    }
 
                 case MqttClientWebSocketOptions webSocketOptions:
-                {
-                    return new MqttChannelAdapter(new WebSocket4NetMqttChannel(options, webSocketOptions), new MqttPacketFormatterAdapter(options.ProtocolVersion), logger);
-                }
+                    {
+                        return new MqttChannelAdapter(new WebSocket4NetMqttChannel(options, webSocketOptions), new MqttPacketFormatterAdapter(options.ProtocolVersion), logger);
+                    }
 
                 default:
-                {
-                    throw new NotSupportedException();
-                }
+                    {
+                        throw new NotSupportedException();
+                    }
             }
         }
     }

Source/MQTTnet.Server/Logging/MqttNetChildLoggerWrapper.cs

@@ -1,43 +1,43 @@
-using System;
-using MQTTnet.Diagnostics;
+//using MQTTnet.Diagnostics;
+//using System;
 
-namespace MQTTnet.Server.Logging
-{
-    public class MqttNetChildLoggerWrapper : IMqttNetChildLogger
-    {
-        private readonly MqttNetLoggerWrapper _logger;
-        private readonly string _source;
+//namespace MQTTnet.Server.Logging
+//{
+//    public class MqttNetChildLoggerWrapper : IMqttNetChildLogger
+//    {
+//        private readonly MqttNetLoggerWrapper _logger;
+//        private readonly string _source;
 
-        public MqttNetChildLoggerWrapper(string source, MqttNetLoggerWrapper logger)
-        {
-            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+//        public MqttNetChildLoggerWrapper(string source, MqttNetLoggerWrapper logger)
+//        {
+//            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
 
-            _source = source;
-        }
+//            _source = source;
+//        }
 
-        public IMqttNetChildLogger CreateChildLogger(string source = null)
-        {
-            return _logger.CreateChildLogger(source);
-        }
+//        public IMqttNetLogger CreateChildLogger(string source = null)
+//        {
+//            return _logger.CreateChildLogger(source);
+//        }
 
-        public void Verbose(string message, params object[] parameters)
-        {
-            _logger.Publish(MqttNetLogLevel.Verbose, _source, message, parameters, null);
-        }
+//        public void Verbose(string message, params object[] parameters)
+//        {
+//            _logger.Publish(MqttNetLogLevel.Verbose, _source, message, parameters, null);
+//        }
 
-        public void Info(string message, params object[] parameters)
-        {
-            _logger.Publish(MqttNetLogLevel.Info, _source, message, parameters, null);
-        }
+//        public void Info(string message, params object[] parameters)
+//        {
+//            _logger.Publish(MqttNetLogLevel.Info, _source, message, parameters, null);
+//        }
 
-        public void Warning(Exception exception, string message, params object[] parameters)
-        {
-            _logger.Publish(MqttNetLogLevel.Warning, _source, message, parameters, exception);
-        }
+//        public void Warning(Exception exception, string message, params object[] parameters)
+//        {
+//            _logger.Publish(MqttNetLogLevel.Warning, _source, message, parameters, exception);
+//        }
 
-        public void Error(Exception exception, string message, params object[] parameters)
-        {
-            _logger.Publish(MqttNetLogLevel.Error, _source, message, parameters, exception);
-        }
-    }
-}
+//        public void Error(Exception exception, string message, params object[] parameters)
+//        {
+//            _logger.Publish(MqttNetLogLevel.Error, _source, message, parameters, exception);
+//        }
+//    }
+//}

Source/MQTTnet.Server/Logging/MqttNetLoggerWrapper.cs

@@ -1,13 +1,13 @@
-using System;
-using System.Threading;
-using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging;
 using MQTTnet.Diagnostics;
+using System;
+using System.Threading;
 
 namespace MQTTnet.Server.Logging
 {
     public class MqttNetLoggerWrapper : IMqttNetLogger
     {
-        private readonly ILogger<MqttServer> _logger;
+        readonly ILogger<MqttServer> _logger;
 
         public MqttNetLoggerWrapper(ILogger<MqttServer> logger)
         {
@@ -16,25 +16,39 @@ namespace MQTTnet.Server.Logging
 
         public event EventHandler<MqttNetLogMessagePublishedEventArgs> LogMessagePublished;
 
-        public IMqttNetChildLogger CreateChildLogger(string source = null)
+        public IMqttNetLogger CreateChildLogger(string source)
         {
-            return new MqttNetChildLoggerWrapper(source, this);
+            return new MqttNetLogger(source);
         }
 
-        public void Publish(MqttNetLogLevel logLevel, string source, string message, object[] parameters, Exception exception)
+        public void Publish(MqttNetLogLevel level, string source, string message, object[] parameters, Exception exception)
         {
-            var convertedLogLevel = ConvertLogLevel(logLevel);
+            var convertedLogLevel = ConvertLogLevel(level);
             _logger.Log(convertedLogLevel, exception, message, parameters);
 
             var logMessagePublishedEvent = LogMessagePublished;
             if (logMessagePublishedEvent != null)
             {
-                var logMessage = new MqttNetLogMessage(null, DateTime.UtcNow, Thread.CurrentThread.ManagedThreadId, source, logLevel, message, exception);
+                var logMessage = new MqttNetLogMessage
+                {
+                    Timestamp = DateTime.UtcNow,
+                    ThreadId = Thread.CurrentThread.ManagedThreadId,
+                    Source = source,
+                    Level = level,
+                    Message = message,
+                    Exception = exception
+                };
+
                 logMessagePublishedEvent.Invoke(this, new MqttNetLogMessagePublishedEventArgs(logMessage));
             }
         }
-        
-        private static LogLevel ConvertLogLevel(MqttNetLogLevel logLevel)
+
+        public void Publish(MqttNetLogLevel logLevel, string message, object[] parameters, Exception exception)
+        {
+            Publish(logLevel, null, message, parameters, exception);
+        }
+
+        static LogLevel ConvertLogLevel(MqttNetLogLevel logLevel)
         {
             switch (logLevel)
             {

Source/MQTTnet.Server/MQTTnet.Server.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk.Web">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.2</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
     <AspNetCoreHostingModel>InProcess</AspNetCoreHostingModel>
     <AssemblyName>MQTTnet.Server</AssemblyName>
     <RootNamespace>MQTTnet.Server</RootNamespace>
@@ -43,14 +43,12 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="IronPython" Version="2.7.9" />
-    <PackageReference Include="IronPython.StdLib" Version="2.7.9" />
-    <PackageReference Include="Microsoft.AspNetCore.App" />
-    <PackageReference Include="Microsoft.AspNetCore.Razor.Design" Version="2.2.0" PrivateAssets="All" />
-    <PackageReference Include="Microsoft.AspNetCore.StaticFiles" Version="2.2.0" />
-    <PackageReference Include="Microsoft.AspNetCore.WebSockets" Version="2.2.1" />
-    <PackageReference Include="Swashbuckle.AspNetCore.SwaggerGen" Version="5.0.0-rc2" />
-    <PackageReference Include="Swashbuckle.AspNetCore.SwaggerUI" Version="5.0.0-rc2" />
+    <PackageReference Include="IronPython" Version="2.7.10-candidate1" />
+    <PackageReference Include="IronPython.StdLib" Version="2.7.10-candidate1" />
+    <PackageReference Include="Microsoft.AspNetCore.Mvc.NewtonsoftJson" Version="3.1.3" />
+    <PackageReference Include="MSTest.TestAdapter" Version="2.1.1" />
+    <PackageReference Include="Swashbuckle.AspNetCore.SwaggerGen" Version="5.3.1" />
+    <PackageReference Include="Swashbuckle.AspNetCore.SwaggerUI" Version="5.3.1" />
   </ItemGroup>
 
   <ItemGroup>

Source/MQTTnet.Server/Mqtt/MqttServerService.cs

@@ -1,11 +1,4 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Net.WebSockets;
-using System.Security.Authentication;
-using System.Text;
-using System.Threading.Tasks;
-using IronPython.Runtime;
+using IronPython.Runtime;
 using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.Logging;
 using MQTTnet.Adapter;
@@ -16,25 +9,33 @@ using MQTTnet.Protocol;
 using MQTTnet.Server.Configuration;
 using MQTTnet.Server.Scripting;
 using MQTTnet.Server.Status;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net.WebSockets;
+using System.Security.Authentication;
+using System.Text;
+using System.Threading.Tasks;
 
 namespace MQTTnet.Server.Mqtt
 {
     public class MqttServerService
     {
-        private readonly ILogger<MqttServerService> _logger;
+        readonly ILogger<MqttServerService> _logger;
 
-        private readonly MqttSettingsModel _settings;
-        private readonly MqttApplicationMessageInterceptor _mqttApplicationMessageInterceptor;
-        private readonly MqttServerStorage _mqttServerStorage;
-        private readonly MqttClientConnectedHandler _mqttClientConnectedHandler;
-        private readonly MqttClientDisconnectedHandler _mqttClientDisconnectedHandler;
-        private readonly MqttClientSubscribedTopicHandler _mqttClientSubscribedTopicHandler;
-        private readonly MqttClientUnsubscribedTopicHandler _mqttClientUnsubscribedTopicHandler;
-        private readonly MqttServerConnectionValidator _mqttConnectionValidator;
-        private readonly IMqttServer _mqttServer;
-        private readonly MqttSubscriptionInterceptor _mqttSubscriptionInterceptor;
-        private readonly PythonScriptHostService _pythonScriptHostService;
-        private readonly MqttWebSocketServerAdapter _webSocketServerAdapter;
+        readonly MqttSettingsModel _settings;
+        readonly MqttApplicationMessageInterceptor _mqttApplicationMessageInterceptor;
+        readonly MqttServerStorage _mqttServerStorage;
+        readonly MqttClientConnectedHandler _mqttClientConnectedHandler;
+        readonly MqttClientDisconnectedHandler _mqttClientDisconnectedHandler;
+        readonly MqttClientSubscribedTopicHandler _mqttClientSubscribedTopicHandler;
+        readonly MqttClientUnsubscribedTopicHandler _mqttClientUnsubscribedTopicHandler;
+        readonly MqttServerConnectionValidator _mqttConnectionValidator;
+        readonly IMqttServer _mqttServer;
+        readonly MqttSubscriptionInterceptor _mqttSubscriptionInterceptor;
+        readonly MqttUnsubscriptionInterceptor _mqttUnsubscriptionInterceptor;
+        readonly PythonScriptHostService _pythonScriptHostService;
+        readonly MqttWebSocketServerAdapter _webSocketServerAdapter;
 
         public MqttServerService(
             MqttSettingsModel mqttSettings,
@@ -45,6 +46,7 @@ namespace MQTTnet.Server.Mqtt
             MqttClientUnsubscribedTopicHandler mqttClientUnsubscribedTopicHandler,
             MqttServerConnectionValidator mqttConnectionValidator,
             MqttSubscriptionInterceptor mqttSubscriptionInterceptor,
+            MqttUnsubscriptionInterceptor mqttUnsubscriptionInterceptor,
             MqttApplicationMessageInterceptor mqttApplicationMessageInterceptor,
             MqttServerStorage mqttServerStorage,
             PythonScriptHostService pythonScriptHostService,
@@ -57,16 +59,17 @@ namespace MQTTnet.Server.Mqtt
             _mqttClientUnsubscribedTopicHandler = mqttClientUnsubscribedTopicHandler ?? throw new ArgumentNullException(nameof(mqttClientUnsubscribedTopicHandler));
             _mqttConnectionValidator = mqttConnectionValidator ?? throw new ArgumentNullException(nameof(mqttConnectionValidator));
             _mqttSubscriptionInterceptor = mqttSubscriptionInterceptor ?? throw new ArgumentNullException(nameof(mqttSubscriptionInterceptor));
+            _mqttUnsubscriptionInterceptor = mqttUnsubscriptionInterceptor ?? throw new ArgumentNullException(nameof(mqttUnsubscriptionInterceptor));
             _mqttApplicationMessageInterceptor = mqttApplicationMessageInterceptor ?? throw new ArgumentNullException(nameof(mqttApplicationMessageInterceptor));
             _mqttServerStorage = mqttServerStorage ?? throw new ArgumentNullException(nameof(mqttServerStorage));
             _pythonScriptHostService = pythonScriptHostService ?? throw new ArgumentNullException(nameof(pythonScriptHostService));
             _logger = logger ?? throw new ArgumentNullException(nameof(logger));
 
-            _webSocketServerAdapter = new MqttWebSocketServerAdapter(mqttFactory.Logger.CreateChildLogger());
+            _webSocketServerAdapter = new MqttWebSocketServerAdapter(mqttFactory.Logger);
 
             var adapters = new List<IMqttServerAdapter>
             {
-                new MqttTcpServerAdapter(mqttFactory.Logger.CreateChildLogger())
+                new MqttTcpServerAdapter(mqttFactory.Logger)
                 {
                     TreatSocketOpeningErrorAsWarning = true // Opening other ports than for HTTP is not allows in Azure App Services.
                 },
@@ -124,7 +127,7 @@ namespace MQTTnet.Server.Mqtt
             return _mqttServer.PublishAsync(applicationMessage);
         }
 
-        private void Publish(PythonDictionary parameters)
+        void Publish(PythonDictionary parameters)
         {
             try
             {
@@ -170,7 +173,7 @@ namespace MQTTnet.Server.Mqtt
             }
         }
 
-        private IMqttServerOptions CreateMqttServerOptions()
+        IMqttServerOptions CreateMqttServerOptions()
         {
             var options = new MqttServerOptionsBuilder()
                 .WithMaxPendingMessagesPerClient(_settings.MaxPendingMessagesPerClient)
@@ -178,6 +181,7 @@ namespace MQTTnet.Server.Mqtt
                 .WithConnectionValidator(_mqttConnectionValidator)
                 .WithApplicationMessageInterceptor(_mqttApplicationMessageInterceptor)
                 .WithSubscriptionInterceptor(_mqttSubscriptionInterceptor)
+                .WithUnsubscriptionInterceptor(_mqttUnsubscriptionInterceptor)
                 .WithStorage(_mqttServerStorage);
 
             // Configure unencrypted connections
@@ -211,7 +215,7 @@ namespace MQTTnet.Server.Mqtt
                 options
                     .WithEncryptedEndpoint()
                     .WithEncryptionSslProtocol(SslProtocols.Tls12);
-                
+
                 if (!string.IsNullOrEmpty(_settings.EncryptedTcpEndPoint?.Certificate?.Path))
                 {
                     IMqttServerCertificateCredentials certificateCredentials = null;
@@ -226,7 +230,7 @@ namespace MQTTnet.Server.Mqtt
 
                     options.WithEncryptionCertificate(_settings.EncryptedTcpEndPoint.Certificate.ReadCertificate(), certificateCredentials);
                 }
-                
+
                 if (_settings.EncryptedTcpEndPoint.TryReadIPv4(out var address4))
                 {
                     options.WithEncryptedEndpointBoundIPAddress(address4);

Source/MQTTnet.Server/Mqtt/MqttUnsubscriptionInterceptor.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Threading.Tasks;
+using IronPython.Runtime;
+using Microsoft.Extensions.Logging;
+using MQTTnet.Server.Scripting;
+
+namespace MQTTnet.Server.Mqtt
+{
+    public class MqttUnsubscriptionInterceptor : IMqttServerUnsubscriptionInterceptor
+    {
+        private readonly PythonScriptHostService _pythonScriptHostService;
+        private readonly ILogger _logger;
+
+        public MqttUnsubscriptionInterceptor(PythonScriptHostService pythonScriptHostService, ILogger<MqttUnsubscriptionInterceptor> logger)
+        {
+            _pythonScriptHostService = pythonScriptHostService ?? throw new ArgumentNullException(nameof(pythonScriptHostService));
+            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+        }
+
+        public Task InterceptUnsubscriptionAsync(MqttUnsubscriptionInterceptorContext context)
+        {
+            try
+            {
+                var sessionItems = (PythonDictionary)context.SessionItems[MqttServerConnectionValidator.WrappedSessionItemsKey];
+
+                var pythonContext = new PythonDictionary
+                {
+                    { "client_id", context.ClientId },
+                    { "session_items", sessionItems },
+                    { "topic", context.Topic },
+                    { "accept_unsubscription", context.AcceptUnsubscription },
+                    { "close_connection", context.CloseConnection }
+                };
+
+                _pythonScriptHostService.InvokeOptionalFunction("on_intercept_unsubscription", pythonContext);
+
+                context.AcceptUnsubscription = (bool)pythonContext["accept_unsubscription"];
+                context.CloseConnection = (bool)pythonContext["close_connection"];
+            }
+            catch (Exception exception)
+            {
+                _logger.LogError(exception, "Error while intercepting unsubscription.");
+            }
+
+            return Task.CompletedTask;
+        }
+    }
+}

Source/MQTTnet.Server/Program.cs

@@ -1,8 +1,8 @@
-using System;
-using System.Reflection;
-using Microsoft.AspNetCore;
-using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.Extensions.Hosting;
 using MQTTnet.Server.Web;
+using System;
+using System.Reflection;
 
 namespace MQTTnet.Server
 {
@@ -14,7 +14,15 @@ namespace MQTTnet.Server
             {
                 PrintLogo();
 
-                WebHost.CreateDefaultBuilder(args).UseStartup<Startup>().Build().Run();
+                Host.CreateDefaultBuilder(args)
+                    .ConfigureWebHostDefaults(webBuilder =>
+                    {
+                        webBuilder.ConfigureKestrel(serverOptions =>
+                        {
+                        })
+                        .UseStartup<Startup>();
+
+                    }).Build().Run();
 
                 return 0;
             }
@@ -25,7 +33,7 @@ namespace MQTTnet.Server
             }
         }
 
-        private static void PrintLogo()
+        static void PrintLogo()
         {
             Console.ResetColor();
             Console.ForegroundColor = ConsoleColor.Red;
@@ -46,7 +54,7 @@ namespace MQTTnet.Server
             Console.WriteLine();
             Console.ForegroundColor = ConsoleColor.White;
             Console.WriteLine("The official MQTT server implementation of MQTTnet");
-            Console.WriteLine("Copyright (c) 2017-2019 The MQTTnet Team");
+            Console.WriteLine("Copyright (c) 2017-2020 The MQTTnet Team");
             Console.WriteLine(@"https://github.com/chkr1011/MQTTnet");
 
             Console.ForegroundColor = ConsoleColor.White;

Source/MQTTnet.Server/Scripting/DataSharing/DataSharingService.cs

@@ -1,14 +1,14 @@
-using System;
+using Microsoft.Extensions.Logging;
+using System;
 using System.Collections.Generic;
-using Microsoft.Extensions.Logging;
 
 namespace MQTTnet.Server.Scripting.DataSharing
 {
     public class DataSharingService
     {
-        private readonly Dictionary<string, object> _storage = new Dictionary<string, object>();
-        private readonly PythonScriptHostService _pythonScriptHostService;
-        private readonly ILogger<DataSharingService> _logger;
+        readonly Dictionary<string, object> _storage = new Dictionary<string, object>();
+        readonly PythonScriptHostService _pythonScriptHostService;
+        readonly ILogger<DataSharingService> _logger;
 
         public DataSharingService(PythonScriptHostService pythonScriptHostService, ILogger<DataSharingService> logger)
         {

Source/MQTTnet.Server/Scripting/PythonIOStream.cs

@@ -1,14 +1,14 @@
-using System;
+using Microsoft.Extensions.Logging;
+using System;
 using System.IO;
 using System.Text;
-using Microsoft.Extensions.Logging;
 
 namespace MQTTnet.Server.Scripting
 {
     public class PythonIOStream : Stream
     {
-        private readonly ILogger _logger;
-        private readonly Encoding _encoder = Encoding.UTF8;
+        readonly ILogger _logger;
+        readonly Encoding _encoder = Encoding.UTF8;
 
         public PythonIOStream(ILogger<PythonIOStream> logger)
         {

Source/MQTTnet.Server/Scripting/PythonScriptHostService.cs

@@ -1,4 +1,8 @@
-using System;
+using Microsoft.Extensions.Logging;
+using Microsoft.Scripting;
+using Microsoft.Scripting.Hosting;
+using MQTTnet.Server.Configuration;
+using System;
 using System.Collections.Generic;
 using System.Dynamic;
 using System.IO;
@@ -6,22 +10,18 @@ using System.Linq;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
-using Microsoft.Extensions.Logging;
-using Microsoft.Scripting;
-using Microsoft.Scripting.Hosting;
-using MQTTnet.Server.Configuration;
 
 namespace MQTTnet.Server.Scripting
 {
     public class PythonScriptHostService
     {
-        private readonly IDictionary<string, object> _proxyObjects = new ExpandoObject();
-        private readonly List<PythonScriptInstance> _scriptInstances = new List<PythonScriptInstance>();
-        private readonly string _scriptsPath;
-        private readonly ScriptingSettingsModel _scriptingSettings;
-        private readonly ILogger<PythonScriptHostService> _logger;
-        private readonly ScriptEngine _scriptEngine;
-        
+        readonly IDictionary<string, object> _proxyObjects = new ExpandoObject();
+        readonly List<PythonScriptInstance> _scriptInstances = new List<PythonScriptInstance>();
+        readonly string _scriptsPath;
+        readonly ScriptingSettingsModel _scriptingSettings;
+        readonly ILogger<PythonScriptHostService> _logger;
+        readonly ScriptEngine _scriptEngine;
+
         public PythonScriptHostService(ScriptingSettingsModel scriptingSettings, PythonIOStream pythonIOStream, ILogger<PythonScriptHostService> logger)
         {
             _scriptingSettings = scriptingSettings ?? throw new ArgumentNullException(nameof(scriptingSettings));
@@ -139,7 +139,7 @@ namespace MQTTnet.Server.Scripting
             }
         }
 
-        private async Task TryInitializeScriptAsync(string path)
+        async Task TryInitializeScriptAsync(string path)
         {
             var uid = new FileInfo(path).Name.Replace(".py", string.Empty, StringComparison.OrdinalIgnoreCase);
 
@@ -155,7 +155,7 @@ namespace MQTTnet.Server.Scripting
                 {
                     _scriptInstances.Add(scriptInstance);
                 }
-                
+
                 _logger.LogInformation($"Initialized script '{uid}'.");
             }
             catch (Exception exception)
@@ -164,7 +164,7 @@ namespace MQTTnet.Server.Scripting
             }
         }
 
-        private PythonScriptInstance CreateScriptInstance(string uid, string path, string code)
+        PythonScriptInstance CreateScriptInstance(string uid, string path, string code)
         {
             var scriptScope = _scriptEngine.CreateScope();
 
@@ -173,11 +173,11 @@ namespace MQTTnet.Server.Scripting
 
             scriptScope.SetVariable("mqtt_net_server", _proxyObjects);
             compiledCode.Execute(scriptScope);
-            
+
             return new PythonScriptInstance(uid, path, scriptScope);
         }
 
-        private void AddSearchPaths(ScriptEngine scriptEngine)
+        void AddSearchPaths(ScriptEngine scriptEngine)
         {
             if (_scriptingSettings.IncludePaths?.Any() != true)
             {

Source/MQTTnet.Server/Scripting/PythonScriptInstance.cs

@@ -1,12 +1,12 @@
-using System;
-using IronPython.Runtime;
+using IronPython.Runtime;
 using Microsoft.Scripting.Hosting;
+using System;
 
 namespace MQTTnet.Server.Scripting
 {
     public class PythonScriptInstance
     {
-        private readonly ScriptScope _scriptScope;
+        readonly ScriptScope _scriptScope;
 
         public PythonScriptInstance(string uid, string path, ScriptScope scriptScope)
         {

Source/MQTTnet.Server/Web/Startup.cs

@@ -1,10 +1,5 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Net;
-using Microsoft.AspNetCore.Authentication;
+using Microsoft.AspNetCore.Authentication;
 using Microsoft.AspNetCore.Builder;
-using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
@@ -16,7 +11,12 @@ using MQTTnet.Server.Logging;
 using MQTTnet.Server.Mqtt;
 using MQTTnet.Server.Scripting;
 using MQTTnet.Server.Scripting.DataSharing;
+using Newtonsoft.Json.Converters;
 using Swashbuckle.AspNetCore.SwaggerUI;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net;
 
 namespace MQTTnet.Server.Web
 {
@@ -35,33 +35,27 @@ namespace MQTTnet.Server.Web
 
         public void Configure(
             IApplicationBuilder application,
-            IHostingEnvironment environment,
             MqttServerService mqttServerService,
             PythonScriptHostService pythonScriptHostService,
             DataSharingService dataSharingService,
             MqttSettingsModel mqttSettings)
         {
-            if (environment.IsDevelopment())
-            {
-                application.UseDeveloperExceptionPage();
-            }
-            else
-            {
-                application.UseHsts();
-            }
-
+            application.UseHsts();
+            application.UseRouting();
             application.UseCors(x => x
                 .AllowAnyOrigin()
                 .AllowAnyMethod()
-                .AllowAnyHeader()
-                .AllowCredentials());
+                .AllowAnyHeader());
 
             application.UseAuthentication();
+            application.UseAuthorization();
 
             application.UseStaticFiles();
 
-            application.UseHttpsRedirection();
-            application.UseMvc();
+            application.UseEndpoints(endpoints =>
+            {
+                endpoints.MapControllers();
+            });
 
             ConfigureWebSocketEndpoint(application, mqttServerService, mqttSettings);
 
@@ -87,11 +81,14 @@ namespace MQTTnet.Server.Web
         {
             services.AddCors();
 
+
+            services.AddControllers();
+
             services.AddMvc()
-                .SetCompatibilityVersion(CompatibilityVersion.Version_2_2)
-                .AddJsonOptions(options =>
+                .SetCompatibilityVersion(CompatibilityVersion.Version_3_0)
+                .AddNewtonsoftJson(o =>
                 {
-                    options.SerializerSettings.Converters.Add(new Newtonsoft.Json.Converters.StringEnumConverter());
+                    o.SerializerSettings.Converters.Add(new StringEnumConverter());
                 });
 
             ReadMqttSettings(services);
@@ -111,12 +108,11 @@ namespace MQTTnet.Server.Web
             services.AddSingleton<MqttClientUnsubscribedTopicHandler>();
             services.AddSingleton<MqttServerConnectionValidator>();
             services.AddSingleton<MqttSubscriptionInterceptor>();
+            services.AddSingleton<MqttUnsubscriptionInterceptor>();
             services.AddSingleton<MqttApplicationMessageInterceptor>();
 
             services.AddSwaggerGen(c =>
             {
-                c.DescribeAllEnumsAsStrings();
-                
                 var securityScheme = new OpenApiSecurityScheme
                 {
                     Scheme = "Basic",
@@ -156,7 +152,7 @@ namespace MQTTnet.Server.Web
                 .AddCookie();
         }
 
-        private void ReadMqttSettings(IServiceCollection services)
+        void ReadMqttSettings(IServiceCollection services)
         {
             var mqttSettings = new MqttSettingsModel();
             Configuration.Bind("MQTT", mqttSettings);
@@ -167,7 +163,7 @@ namespace MQTTnet.Server.Web
             services.AddSingleton(scriptingSettings);
         }
 
-        private static void ConfigureWebSocketEndpoint(
+        static void ConfigureWebSocketEndpoint(
             IApplicationBuilder application,
             MqttServerService mqttServerService,
             MqttSettingsModel mqttSettings)

Source/MQTTnet.Server/appsettings.json

@@ -52,11 +52,7 @@
     },
     "Scripting": {
         "ScriptsPath": "Scripts",
-        "IncludePaths": [
-            "Lib",
-            "/usr/lib/python2.7",
-            "C:\\Python27\\Lib"
-        ]
+        "IncludePaths": []
     },
     "Logging": {
         "LogLevel": {

Source/MQTTnet.Server/package.json

@@ -1,12 +0,0 @@
-{
-  "version": "1.0.0",
-  "name": "mqtt.test",
-  "private": true,
-  "devDependencies": {},
-  "dependencies": {
-    "@types/node": "^8.0.46",
-    "mqtt": "^2.15.1",
-    "systemjs": "^0.20.19",
-    "typescript": "^2.3.4"
-  }
-}

Source/MQTTnet/Adapter/IMqttClientAdapterFactory.cs

@@ -5,6 +5,6 @@ namespace MQTTnet.Adapter
 {
     public interface IMqttClientAdapterFactory
     {
-        IMqttChannelAdapter CreateClientAdapter(IMqttClientOptions options, IMqttNetChildLogger logger);
+        IMqttChannelAdapter CreateClientAdapter(IMqttClientOptions options, IMqttNetLogger logger);
     }
 }

Source/MQTTnet/Adapter/MqttChannelAdapter.cs

@@ -1,3 +1,9 @@
+using MQTTnet.Channel;
+using MQTTnet.Diagnostics;
+using MQTTnet.Exceptions;
+using MQTTnet.Formatter;
+using MQTTnet.Internal;
+using MQTTnet.Packets;
 using System;
 using System.IO;
 using System.Net.Sockets;
@@ -5,34 +11,26 @@ using System.Runtime.InteropServices;
 using System.Security.Cryptography.X509Certificates;
 using System.Threading;
 using System.Threading.Tasks;
-using MQTTnet.Channel;
-using MQTTnet.Diagnostics;
-using MQTTnet.Exceptions;
-using MQTTnet.Formatter;
-using MQTTnet.Internal;
-using MQTTnet.Packets;
 
 namespace MQTTnet.Adapter
 {
-    public class MqttChannelAdapter : IMqttChannelAdapter
+    public sealed class MqttChannelAdapter : Disposable, IMqttChannelAdapter
     {
-        private const uint ErrorOperationAborted = 0x800703E3;
-        private const int ReadBufferSize = 4096;  // TODO: Move buffer size to config
+        const uint ErrorOperationAborted = 0x800703E3;
+        const int ReadBufferSize = 4096;  // TODO: Move buffer size to config
 
-        private readonly SemaphoreSlim _writerSemaphore = new SemaphoreSlim(1, 1);
+        readonly IMqttNetLogger _logger;
+        readonly IMqttChannel _channel;
+        readonly MqttPacketReader _packetReader;
 
-        private readonly IMqttNetChildLogger _logger;
-        private readonly IMqttChannel _channel;
-        private readonly MqttPacketReader _packetReader;
+        readonly byte[] _fixedHeaderBuffer = new byte[2];
 
-        private readonly byte[] _fixedHeaderBuffer = new byte[2];
+        SemaphoreSlim _writerSemaphore = new SemaphoreSlim(1, 1);
 
-        private bool _isDisposed;
+        long _bytesReceived;
+        long _bytesSent;
 
-        private long _bytesReceived;
-        private long _bytesSent;
-
-        public MqttChannelAdapter(IMqttChannel channel, MqttPacketFormatterAdapter packetFormatterAdapter, IMqttNetChildLogger logger)
+        public MqttChannelAdapter(IMqttChannel channel, MqttPacketFormatterAdapter packetFormatterAdapter, IMqttNetLogger logger)
         {
             if (logger == null) throw new ArgumentNullException(nameof(logger));
 
@@ -57,7 +55,7 @@ namespace MQTTnet.Adapter
 
         public Action ReadingPacketStartedCallback { get; set; }
         public Action ReadingPacketCompletedCallback { get; set; }
-            
+
         public async Task ConnectAsync(TimeSpan timeout, CancellationToken cancellationToken)
         {
             ThrowIfDisposed();
@@ -145,7 +143,7 @@ namespace MQTTnet.Adapter
             }
             finally
             {
-                _writerSemaphore.Release();
+                _writerSemaphore?.Release();
             }
         }
 
@@ -209,7 +207,20 @@ namespace MQTTnet.Adapter
             Interlocked.Exchange(ref _bytesSent, 0L);
         }
 
-        private async Task<ReceivedMqttPacket> ReceiveAsync(CancellationToken cancellationToken)
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                _channel?.Dispose();
+
+                _writerSemaphore?.Dispose();
+                _writerSemaphore = null;
+            }
+
+            base.Dispose(disposing);
+        }
+
+        async Task<ReceivedMqttPacket> ReceiveAsync(CancellationToken cancellationToken)
         {
             var readFixedHeaderResult = await _packetReader.ReadFixedHeaderAsync(_fixedHeaderBuffer, cancellationToken).ConfigureAwait(false);
 
@@ -269,29 +280,14 @@ namespace MQTTnet.Adapter
             }
         }
 
-        public void Dispose()
-        {
-            _isDisposed = true;
-
-            _channel?.Dispose();
-        }
-
-        private void ThrowIfDisposed()
-        {
-            if (_isDisposed)
-            {
-                throw new ObjectDisposedException(nameof(MqttChannelAdapter));
-            }
-        }
-
-        private static bool IsWrappedException(Exception exception)
+        static bool IsWrappedException(Exception exception)
         {
             return exception is OperationCanceledException ||
                    exception is MqttCommunicationTimedOutException ||
                    exception is MqttCommunicationException;
         }
 
-        private static void WrapException(Exception exception)
+        static void WrapException(Exception exception)
         {
             if (exception is IOException && exception.InnerException is SocketException innerException)
             {

Source/MQTTnet/Adapter/MqttConnectingFailedException.cs

@@ -5,12 +5,13 @@ namespace MQTTnet.Adapter
 {
     public class MqttConnectingFailedException : MqttCommunicationException
     {
-        public MqttConnectingFailedException(MqttClientConnectResultCode resultCode)
-            : base($"Connecting with MQTT server failed ({resultCode.ToString()}).")
+        public MqttConnectingFailedException(MqttClientAuthenticateResult result)
+            : base($"Connecting with MQTT server failed ({result.ResultCode.ToString()}).")
         {
-            ResultCode = resultCode;
+            Result = result;
         }
 
-        public MqttClientConnectResultCode ResultCode { get; }
+        public MqttClientAuthenticateResult Result { get; }
+        public MqttClientConnectResultCode ResultCode => Result.ResultCode;
     }
 }

Source/MQTTnet/Client/MqttClient.cs

@@ -1,7 +1,3 @@
-using System;
-using System.Diagnostics;
-using System.Threading;
-using System.Threading.Tasks;
 using MQTTnet.Adapter;
 using MQTTnet.Client.Connecting;
 using MQTTnet.Client.Disconnecting;
@@ -17,26 +13,34 @@ using MQTTnet.Internal;
 using MQTTnet.PacketDispatcher;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
+using System;
+using System.Diagnostics;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace MQTTnet.Client
 {
-    public class MqttClient : IMqttClient
+    public class MqttClient : Disposable, IMqttClient
     {
-        private readonly MqttPacketIdentifierProvider _packetIdentifierProvider = new MqttPacketIdentifierProvider();
-        private readonly MqttPacketDispatcher _packetDispatcher = new MqttPacketDispatcher();
-        private readonly Stopwatch _sendTracker = new Stopwatch();
-        private readonly object _disconnectLock = new object();
+        readonly MqttPacketIdentifierProvider _packetIdentifierProvider = new MqttPacketIdentifierProvider();
+        readonly MqttPacketDispatcher _packetDispatcher = new MqttPacketDispatcher();
+        readonly Stopwatch _sendTracker = new Stopwatch();
+        readonly Stopwatch _receiveTracker = new Stopwatch();
+        readonly object _disconnectLock = new object();
 
-        private readonly IMqttClientAdapterFactory _adapterFactory;
-        private readonly IMqttNetChildLogger _logger;
+        readonly IMqttClientAdapterFactory _adapterFactory;
+        readonly IMqttNetLogger _logger;
 
-        private CancellationTokenSource _backgroundCancellationTokenSource;
-        private Task _packetReceiverTask;
-        private Task _keepAlivePacketsSenderTask;
+        CancellationTokenSource _backgroundCancellationTokenSource;
+        Task _packetReceiverTask;
+        Task _keepAlivePacketsSenderTask;
+        Task _publishPacketReceiverTask;
 
-        private IMqttChannelAdapter _adapter;
-        private bool _cleanDisconnectInitiated;
-        private long _disconnectGate;
+        AsyncQueue<MqttPublishPacket> _publishPacketReceiverQueue;
+
+        IMqttChannelAdapter _adapter;
+        bool _cleanDisconnectInitiated;
+        long _disconnectGate;
 
         public MqttClient(IMqttClientAdapterFactory channelFactory, IMqttNetLogger logger)
         {
@@ -63,6 +67,8 @@ namespace MQTTnet.Client
 
             ThrowIfConnected("It is not allowed to connect with a server after the connection is established.");
 
+            ThrowIfDisposed();
+
             MqttClientAuthenticateResult authenticateResult = null;
 
             try
@@ -79,15 +85,22 @@ namespace MQTTnet.Client
                 var adapter = _adapterFactory.CreateClientAdapter(options, _logger);
                 _adapter = adapter;
 
-                _logger.Verbose($"Trying to connect with server '{options.ChannelOptions}' (Timeout={options.CommunicationTimeout}).");
-                await _adapter.ConnectAsync(options.CommunicationTimeout, cancellationToken).ConfigureAwait(false);
-                _logger.Verbose("Connection with server established.");
+                using (var combined = CancellationTokenSource.CreateLinkedTokenSource(backgroundCancellationToken, cancellationToken))
+                {
+                    _logger.Verbose($"Trying to connect with server '{options.ChannelOptions}' (Timeout={options.CommunicationTimeout}).");
+                    await _adapter.ConnectAsync(options.CommunicationTimeout, combined.Token).ConfigureAwait(false);
+                    _logger.Verbose("Connection with server established.");
 
-                _packetReceiverTask = Task.Run(() => TryReceivePacketsAsync(backgroundCancellationToken), backgroundCancellationToken);
+                    _publishPacketReceiverQueue = new AsyncQueue<MqttPublishPacket>();
+                    _publishPacketReceiverTask = Task.Run(() => ProcessReceivedPublishPackets(backgroundCancellationToken), backgroundCancellationToken);
 
-                authenticateResult = await AuthenticateAsync(adapter, options.WillMessage, cancellationToken).ConfigureAwait(false);
+                    _packetReceiverTask = Task.Run(() => TryReceivePacketsAsync(backgroundCancellationToken), backgroundCancellationToken);
+
+                    authenticateResult = await AuthenticateAsync(adapter, options.WillMessage, combined.Token).ConfigureAwait(false);
+                }
 
                 _sendTracker.Restart();
+                _receiveTracker.Restart();
 
                 if (Options.KeepAlivePeriod != TimeSpan.Zero)
                 {
@@ -121,6 +134,10 @@ namespace MQTTnet.Client
 
         public async Task DisconnectAsync(MqttClientDisconnectOptions options, CancellationToken cancellationToken)
         {
+            if (options is null) throw new ArgumentNullException(nameof(options));
+
+            ThrowIfDisposed();
+
             try
             {
                 _cleanDisconnectInitiated = true;
@@ -144,12 +161,15 @@ namespace MQTTnet.Client
         {
             if (data == null) throw new ArgumentNullException(nameof(data));
 
+            ThrowIfDisposed();
+            ThrowIfNotConnected();
+
             return SendAsync(new MqttAuthPacket
             {
                 Properties = new MqttAuthPacketProperties
                 {
                     // This must always be equal to the value from the CONNECT packet. So we use it here to ensure that.
-                    AuthenticationMethod = Options.AuthenticationMethod, 
+                    AuthenticationMethod = Options.AuthenticationMethod,
                     AuthenticationData = data.AuthenticationData,
                     ReasonString = data.ReasonString,
                     UserProperties = data.UserProperties
@@ -161,6 +181,7 @@ namespace MQTTnet.Client
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
+            ThrowIfDisposed();
             ThrowIfNotConnected();
 
             var subscribePacket = _adapter.PacketFormatterAdapter.DataConverter.CreateSubscribePacket(options);
@@ -174,6 +195,7 @@ namespace MQTTnet.Client
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
+            ThrowIfDisposed();
             ThrowIfNotConnected();
 
             var unsubscribePacket = _adapter.PacketFormatterAdapter.DataConverter.CreateUnsubscribePacket(options);
@@ -189,6 +211,7 @@ namespace MQTTnet.Client
 
             MqttTopicValidator.ThrowIfInvalid(applicationMessage.Topic);
 
+            ThrowIfDisposed();
             ThrowIfNotConnected();
 
             var publishPacket = _adapter.PacketFormatterAdapter.DataConverter.CreatePublishPacket(applicationMessage);
@@ -214,17 +237,32 @@ namespace MQTTnet.Client
             }
         }
 
-        public void Dispose()
+        void Cleanup()
         {
             _backgroundCancellationTokenSource?.Cancel(false);
             _backgroundCancellationTokenSource?.Dispose();
             _backgroundCancellationTokenSource = null;
 
+            _publishPacketReceiverQueue?.Dispose();
+            _publishPacketReceiverQueue = null;
+
             _adapter?.Dispose();
-            _adapter = null;
         }
 
-        private async Task<MqttClientAuthenticateResult> AuthenticateAsync(IMqttChannelAdapter channelAdapter, MqttApplicationMessage willApplicationMessage, CancellationToken cancellationToken)
+
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                Cleanup();
+
+                DisconnectedHandler = null;
+            }
+
+            base.Dispose(disposing);
+        }
+
+        async Task<MqttClientAuthenticateResult> AuthenticateAsync(IMqttChannelAdapter channelAdapter, MqttApplicationMessage willApplicationMessage, CancellationToken cancellationToken)
         {
             var connectPacket = channelAdapter.PacketFormatterAdapter.DataConverter.CreateConnectPacket(
                 willApplicationMessage,
@@ -235,7 +273,7 @@ namespace MQTTnet.Client
 
             if (result.ResultCode != MqttClientConnectResultCode.Success)
             {
-                throw new MqttConnectingFailedException(result.ResultCode);
+                throw new MqttConnectingFailedException(result);
             }
 
             _logger.Verbose("Authenticated MQTT connection with server established.");
@@ -243,44 +281,55 @@ namespace MQTTnet.Client
             return result;
         }
 
-        private void ThrowIfNotConnected()
+        void ThrowIfNotConnected()
         {
             if (!IsConnected || Interlocked.Read(ref _disconnectGate) == 1) throw new MqttCommunicationException("The client is not connected.");
         }
 
-        private void ThrowIfConnected(string message)
+        void ThrowIfConnected(string message)
         {
             if (IsConnected) throw new MqttProtocolViolationException(message);
         }
 
-        private async Task DisconnectInternalAsync(Task sender, Exception exception, MqttClientAuthenticateResult authenticateResult)
+        async Task DisconnectInternalAsync(Task sender, Exception exception, MqttClientAuthenticateResult authenticateResult)
         {
             var clientWasConnected = IsConnected;
 
             TryInitiateDisconnect();
+            IsConnected = false;
 
             try
             {
-                IsConnected = false;
-
                 if (_adapter != null)
                 {
                     _logger.Verbose("Disconnecting [Timeout={0}]", Options.CommunicationTimeout);
                     await _adapter.DisconnectAsync(Options.CommunicationTimeout, CancellationToken.None).ConfigureAwait(false);
                 }
 
-                await WaitForTaskAsync(_packetReceiverTask, sender).ConfigureAwait(false);
-                await WaitForTaskAsync(_keepAlivePacketsSenderTask, sender).ConfigureAwait(false);
-
                 _logger.Verbose("Disconnected from adapter.");
             }
             catch (Exception adapterException)
             {
                 _logger.Warning(adapterException, "Error while disconnecting from adapter.");
             }
+
+            try
+            {
+                var receiverTask = WaitForTaskAsync(_packetReceiverTask, sender);
+                var publishPacketReceiverTask = WaitForTaskAsync(_publishPacketReceiverTask, sender);
+                var keepAliveTask = WaitForTaskAsync(_keepAlivePacketsSenderTask, sender);
+
+                await Task.WhenAll(receiverTask, publishPacketReceiverTask, keepAliveTask).ConfigureAwait(false);
+
+                _publishPacketReceiverQueue.Dispose();
+            }
+            catch (Exception e)
+            {
+                _logger.Warning(e, "Error while waiting for internal tasks.");
+            }
             finally
             {
-                Dispose();
+                Cleanup();
                 _cleanDisconnectInitiated = false;
 
                 _logger.Info("Disconnected.");
@@ -295,7 +344,7 @@ namespace MQTTnet.Client
             }
         }
 
-        private void TryInitiateDisconnect()
+        void TryInitiateDisconnect()
         {
             lock (_disconnectLock)
             {
@@ -327,7 +376,7 @@ namespace MQTTnet.Client
             return _adapter.SendPacketAsync(packet, Options.CommunicationTimeout, cancellationToken);
         }
 
-        private async Task<TResponsePacket> SendAndReceiveAsync<TResponsePacket>(MqttBasePacket requestPacket, CancellationToken cancellationToken) where TResponsePacket : MqttBasePacket
+        async Task<TResponsePacket> SendAndReceiveAsync<TResponsePacket>(MqttBasePacket requestPacket, CancellationToken cancellationToken) where TResponsePacket : MqttBasePacket
         {
             cancellationToken.ThrowIfCancellationRequested();
 
@@ -344,17 +393,32 @@ namespace MQTTnet.Client
                 try
                 {
                     await _adapter.SendPacketAsync(requestPacket, Options.CommunicationTimeout, cancellationToken).ConfigureAwait(false);
-                    return await packetAwaiter.WaitOneAsync(Options.CommunicationTimeout).ConfigureAwait(false);
                 }
-                catch (MqttCommunicationTimedOutException)
+                catch (Exception e)
                 {
-                    _logger.Warning(null, "Timeout while waiting for packet of type '{0}'.", typeof(TResponsePacket).Name);
+                    _logger.Warning(e, "Error when sending packet of type '{0}'.", typeof(TResponsePacket).Name);
+                    packetAwaiter.Cancel();
+                }
+
+                try
+                {
+                    var response = await packetAwaiter.WaitOneAsync(Options.CommunicationTimeout).ConfigureAwait(false);
+                    _receiveTracker.Restart();
+                    return response;
+                }
+                catch (Exception exception)
+                {
+                    if (exception is MqttCommunicationTimedOutException)
+                    {
+                        _logger.Warning(null, "Timeout while waiting for packet of type '{0}'.", typeof(TResponsePacket).Name);
+                    }
+
                     throw;
                 }
             }
         }
 
-        private async Task TrySendKeepAliveMessagesAsync(CancellationToken cancellationToken)
+        async Task TrySendKeepAliveMessagesAsync(CancellationToken cancellationToken)
         {
             try
             {
@@ -369,14 +433,14 @@ namespace MQTTnet.Client
                         keepAliveSendInterval = Options.KeepAliveSendInterval.Value;
                     }
 
-                    var waitTime = keepAliveSendInterval - _sendTracker.Elapsed;
-                    if (waitTime <= TimeSpan.Zero)
+                    var waitTimeSend = keepAliveSendInterval - _sendTracker.Elapsed;
+                    var waitTimeReceive = keepAliveSendInterval - _receiveTracker.Elapsed;
+                    if (waitTimeSend <= TimeSpan.Zero || waitTimeReceive <= TimeSpan.Zero)
                     {
                         await SendAndReceiveAsync<MqttPingRespPacket>(new MqttPingReqPacket(), cancellationToken).ConfigureAwait(false);
-                        waitTime = keepAliveSendInterval;
                     }
 
-                    await Task.Delay(waitTime, cancellationToken).ConfigureAwait(false);
+                    await Task.Delay(keepAliveSendInterval, cancellationToken).ConfigureAwait(false);
                 }
             }
             catch (Exception exception)
@@ -391,11 +455,11 @@ namespace MQTTnet.Client
                 }
                 else if (exception is MqttCommunicationException)
                 {
-                    _logger.Warning(exception, "MQTT communication exception while sending/receiving keep alive packets.");
+                    _logger.Warning(exception, "Communication error while sending/receiving keep alive packets.");
                 }
                 else
                 {
-                    _logger.Error(exception, "Unhandled exception while sending/receiving keep alive packets.");
+                    _logger.Error(exception, "Error exception while sending/receiving keep alive packets.");
                 }
 
                 if (!DisconnectIsPending())
@@ -409,7 +473,7 @@ namespace MQTTnet.Client
             }
         }
 
-        private async Task TryReceivePacketsAsync(CancellationToken cancellationToken)
+        async Task TryReceivePacketsAsync(CancellationToken cancellationToken)
         {
             try
             {
@@ -449,11 +513,11 @@ namespace MQTTnet.Client
                 }
                 else if (exception is MqttCommunicationException)
                 {
-                    _logger.Warning(exception, "MQTT communication exception while receiving packets.");
+                    _logger.Warning(exception, "Communication error while receiving packets.");
                 }
                 else
                 {
-                    _logger.Error(exception, "Unhandled exception while receiving packets.");
+                    _logger.Error(exception, "Error while receiving packets.");
                 }
 
                 _packetDispatcher.Dispatch(exception);
@@ -469,13 +533,15 @@ namespace MQTTnet.Client
             }
         }
 
-        private async Task TryProcessReceivedPacketAsync(MqttBasePacket packet, CancellationToken cancellationToken)
+        async Task TryProcessReceivedPacketAsync(MqttBasePacket packet, CancellationToken cancellationToken)
         {
             try
             {
+                _receiveTracker.Restart();
+
                 if (packet is MqttPublishPacket publishPacket)
                 {
-                    await TryProcessReceivedPublishPacketAsync(publishPacket, cancellationToken).ConfigureAwait(false);
+                    EnqueueReceivedPublishPacket(publishPacket);
                 }
                 else if (packet is MqttPubRelPacket pubRelPacket)
                 {
@@ -521,11 +587,11 @@ namespace MQTTnet.Client
                 }
                 else if (exception is MqttCommunicationException)
                 {
-                    _logger.Warning(exception, "MQTT communication exception while receiving packets.");
+                    _logger.Warning(exception, "Communication error while receiving packets.");
                 }
                 else
                 {
-                    _logger.Error(exception, "Unhandled exception while receiving packets.");
+                    _logger.Error(exception, "Error while receiving packets.");
                 }
 
                 _packetDispatcher.Dispatch(exception);
@@ -537,64 +603,88 @@ namespace MQTTnet.Client
             }
         }
 
-        private async Task TryProcessReceivedPublishPacketAsync(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
+        void EnqueueReceivedPublishPacket(MqttPublishPacket publishPacket)
         {
             try
             {
-                if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtMostOnce)
-                {
-                    await HandleReceivedApplicationMessageAsync(publishPacket).ConfigureAwait(false);
-                }
-                else if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtLeastOnce)
-                {
-                    if (await HandleReceivedApplicationMessageAsync(publishPacket).ConfigureAwait(false))
-                    {
-                        await SendAsync(new MqttPubAckPacket
-                        {
-                            PacketIdentifier = publishPacket.PacketIdentifier,
-                            ReasonCode = MqttPubAckReasonCode.Success
-                        }, cancellationToken).ConfigureAwait(false);
-                    }
-                }
-                else if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.ExactlyOnce)
-                {
-                    if (await HandleReceivedApplicationMessageAsync(publishPacket).ConfigureAwait(false))
-                    {
-                        var pubRecPacket = new MqttPubRecPacket
-                        {
-                            PacketIdentifier = publishPacket.PacketIdentifier,
-                            ReasonCode = MqttPubRecReasonCode.Success
-                        };
-
-                        await SendAsync(pubRecPacket, cancellationToken).ConfigureAwait(false);
-                    }                    
-                }
-                else
-                {
-                    throw new MqttProtocolViolationException("Received a not supported QoS level.");
-                }
+                _publishPacketReceiverQueue.Enqueue(publishPacket);
             }
             catch (Exception exception)
             {
-                _logger.Error(exception, "Unhandled exception while handling application message.");
+                _logger.Error(exception, "Error while enqueueing application message.");
             }
         }
 
-        private async Task<MqttClientPublishResult> PublishAtMostOnce(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
+        async Task ProcessReceivedPublishPackets(CancellationToken cancellationToken)
+        {
+            while (!cancellationToken.IsCancellationRequested)
+            {
+                try
+                {
+                    var publishPacketDequeueResult = await _publishPacketReceiverQueue.TryDequeueAsync(cancellationToken);
+
+                    if (!publishPacketDequeueResult.IsSuccess)
+                    {
+                        return;
+                    }
+
+                    var publishPacket = publishPacketDequeueResult.Item;
+
+                    if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtMostOnce)
+                    {
+                        await HandleReceivedApplicationMessageAsync(publishPacket).ConfigureAwait(false);
+                    }
+                    else if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtLeastOnce)
+                    {
+                        if (await HandleReceivedApplicationMessageAsync(publishPacket).ConfigureAwait(false))
+                        {
+                            await SendAsync(new MqttPubAckPacket
+                            {
+                                PacketIdentifier = publishPacket.PacketIdentifier,
+                                ReasonCode = MqttPubAckReasonCode.Success
+                            }, cancellationToken).ConfigureAwait(false);
+                        }
+                    }
+                    else if (publishPacket.QualityOfServiceLevel == MqttQualityOfServiceLevel.ExactlyOnce)
+                    {
+                        if (await HandleReceivedApplicationMessageAsync(publishPacket).ConfigureAwait(false))
+                        {
+                            var pubRecPacket = new MqttPubRecPacket
+                            {
+                                PacketIdentifier = publishPacket.PacketIdentifier,
+                                ReasonCode = MqttPubRecReasonCode.Success
+                            };
+
+                            await SendAsync(pubRecPacket, cancellationToken).ConfigureAwait(false);
+                        }
+                    }
+                    else
+                    {
+                        throw new MqttProtocolViolationException("Received a not supported QoS level.");
+                    }
+                }
+                catch (Exception exception)
+                {
+                    _logger.Error(exception, "Error while handling application message.");
+                }
+            }
+        }
+
+        async Task<MqttClientPublishResult> PublishAtMostOnce(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
         {
             // No packet identifier is used for QoS 0 [3.3.2.2 Packet Identifier]
             await SendAsync(publishPacket, cancellationToken).ConfigureAwait(false);
             return _adapter.PacketFormatterAdapter.DataConverter.CreatePublishResult(null);
         }
 
-        private async Task<MqttClientPublishResult> PublishAtLeastOnceAsync(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
+        async Task<MqttClientPublishResult> PublishAtLeastOnceAsync(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
         {
             publishPacket.PacketIdentifier = _packetIdentifierProvider.GetNextPacketIdentifier();
             var response = await SendAndReceiveAsync<MqttPubAckPacket>(publishPacket, cancellationToken).ConfigureAwait(false);
             return _adapter.PacketFormatterAdapter.DataConverter.CreatePublishResult(response);
         }
 
-        private async Task<MqttClientPublishResult> PublishExactlyOnceAsync(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
+        async Task<MqttClientPublishResult> PublishExactlyOnceAsync(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
         {
             publishPacket.PacketIdentifier = _packetIdentifierProvider.GetNextPacketIdentifier();
 
@@ -611,7 +701,7 @@ namespace MQTTnet.Client
             return _adapter.PacketFormatterAdapter.DataConverter.CreatePublishResult(pubRecPacket, pubCompPacket);
         }
 
-        private async Task<bool> HandleReceivedApplicationMessageAsync(MqttPublishPacket publishPacket)
+        async Task<bool> HandleReceivedApplicationMessageAsync(MqttPublishPacket publishPacket)
         {
             var applicationMessage = _adapter.PacketFormatterAdapter.DataConverter.CreateApplicationMessage(publishPacket);
 
@@ -626,15 +716,25 @@ namespace MQTTnet.Client
             return true;
         }
 
-        private static async Task WaitForTaskAsync(Task task, Task sender)
+        async Task WaitForTaskAsync(Task task, Task sender)
         {
-            if (task == sender || task == null)
+            if (task == null)
             {
                 return;
             }
 
-            if (task.IsCanceled || task.IsCompleted || task.IsFaulted)
+            if (task == sender)
             {
+                // Return here to avoid deadlocks, but first any eventual exception in the task
+                // must be handled to avoid not getting an unhandled task exception
+                if (!task.IsFaulted)
+                {
+                    return;
+                }
+
+                // By accessing the Exception property the exception is considered handled and will
+                // not result in an unhandled task exception later by the finalizer
+                _logger.Warning(task.Exception, "Error while waiting for background task.");
                 return;
             }
 
@@ -647,9 +747,9 @@ namespace MQTTnet.Client
             }
         }
 
-        private bool DisconnectIsPending()
+        bool DisconnectIsPending()
         {
             return Interlocked.CompareExchange(ref _disconnectGate, 1, 0) != 0;
         }
     }
-}
+}

Source/MQTTnet/Client/MqttClientExtensions.cs

@@ -1,8 +1,4 @@
-using System;
-using System.Collections.Generic;
-using System.Threading;
-using System.Threading.Tasks;
-using MQTTnet.Client.Connecting;
+using MQTTnet.Client.Connecting;
 using MQTTnet.Client.Disconnecting;
 using MQTTnet.Client.ExtendedAuthenticationExchange;
 using MQTTnet.Client.Options;
@@ -11,6 +7,10 @@ using MQTTnet.Client.Receiving;
 using MQTTnet.Client.Subscribing;
 using MQTTnet.Client.Unsubscribing;
 using MQTTnet.Protocol;
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace MQTTnet.Client
 {
@@ -128,7 +128,7 @@ namespace MQTTnet.Client
         {
             if (client == null) throw new ArgumentNullException(nameof(client));
 
-            return client.DisconnectAsync(null);
+            return client.DisconnectAsync(new MqttClientDisconnectOptions());
         }
 
         public static Task<MqttClientSubscribeResult> SubscribeAsync(this IMqttClient client, params TopicFilter[] topicFilters)

Source/MQTTnet/Client/Options/MqttClientOptionsBuilder.cs

@@ -1,19 +1,19 @@
-using System;
+using MQTTnet.Client.ExtendedAuthenticationExchange;
+using MQTTnet.Formatter;
+using System;
 using System.Linq;
 using System.Text;
-using MQTTnet.Client.ExtendedAuthenticationExchange;
-using MQTTnet.Formatter;
 
 namespace MQTTnet.Client.Options
 {
     public class MqttClientOptionsBuilder
     {
-        private readonly MqttClientOptions _options = new MqttClientOptions();
+        readonly MqttClientOptions _options = new MqttClientOptions();
 
-        private MqttClientTcpOptions _tcpOptions;
-        private MqttClientWebSocketOptions _webSocketOptions;
-        private MqttClientOptionsBuilderTlsParameters _tlsParameters;
-        private MqttClientWebSocketProxyOptions _proxyOptions;
+        MqttClientTcpOptions _tcpOptions;
+        MqttClientWebSocketOptions _webSocketOptions;
+        MqttClientOptionsBuilderTlsParameters _tlsParameters;
+        MqttClientWebSocketProxyOptions _proxyOptions;
 
         public MqttClientOptionsBuilder WithProtocolVersion(MqttProtocolVersion value)
         {
@@ -256,7 +256,11 @@ namespace MQTTnet.Client.Options
                         UseTls = true,
                         SslProtocol = _tlsParameters.SslProtocol,
                         AllowUntrustedCertificates = _tlsParameters.AllowUntrustedCertificates,
+#if WINDOWS_UWP
                         Certificates = _tlsParameters.Certificates?.Select(c => c.ToArray()).ToList(),
+#else
+                        Certificates = _tlsParameters.Certificates?.ToList(),
+#endif
                         CertificateValidationCallback = _tlsParameters.CertificateValidationCallback,
                         IgnoreCertificateChainErrors = _tlsParameters.IgnoreCertificateChainErrors,
                         IgnoreCertificateRevocationErrors = _tlsParameters.IgnoreCertificateRevocationErrors

Source/MQTTnet/Client/Options/MqttClientOptionsBuilderTlsParameters.cs

@@ -18,7 +18,12 @@ namespace MQTTnet.Client.Options
 
         public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12;
 
+#if WINDOWS_UWP
         public IEnumerable<IEnumerable<byte>> Certificates { get; set; }
+#else
+        public IEnumerable<X509Certificate> Certificates { get; set; }
+#endif
+        
 
         public bool AllowUntrustedCertificates { get; set; }
 

Source/MQTTnet/Client/Options/MqttClientTlsOptions.cs

@@ -15,8 +15,11 @@ namespace MQTTnet.Client.Options
         public bool IgnoreCertificateChainErrors { get; set; }
 
         public bool AllowUntrustedCertificates { get; set; }
-
+#if WINDOWS_UWP
         public List<byte[]> Certificates { get; set; }
+#else
+        public List<X509Certificate> Certificates { get; set; }
+#endif
 
         public SslProtocols SslProtocol { get; set; } = SslProtocols.Tls12;
 

Source/MQTTnet/Client/Unsubscribing/MqttClientUnsubscribeOptionsBuilder.cs

@@ -0,0 +1,59 @@
+using MQTTnet.Packets;
+using System;
+using System.Collections.Generic;
+
+namespace MQTTnet.Client.Unsubscribing
+{
+    public class MqttClientUnsubscribeOptionsBuilder
+    {
+        private readonly MqttClientUnsubscribeOptions _unsubscribeOptions = new MqttClientUnsubscribeOptions();
+
+        public MqttClientUnsubscribeOptionsBuilder WithUserProperty(string name, string value)
+        {
+            if (name is null) throw new ArgumentNullException(nameof(name));
+            if (value is null) throw new ArgumentNullException(nameof(value));
+
+            return WithUserProperty(new MqttUserProperty(name, value));
+        }
+
+        public MqttClientUnsubscribeOptionsBuilder WithUserProperty(MqttUserProperty userProperty)
+        {
+            if (userProperty is null) throw new ArgumentNullException(nameof(userProperty));
+
+            if (_unsubscribeOptions.UserProperties is null)
+            {
+                _unsubscribeOptions.UserProperties = new List<MqttUserProperty>();
+            }
+
+            _unsubscribeOptions.UserProperties.Add(userProperty);
+
+            return this;
+        }
+
+        public MqttClientUnsubscribeOptionsBuilder WithTopicFilter(string topic)
+        {
+            if (topic is null) throw new ArgumentNullException(nameof(topic));
+
+            if (_unsubscribeOptions.TopicFilters is null)
+            {
+                _unsubscribeOptions.TopicFilters = new List<string>();
+            }
+
+            _unsubscribeOptions.TopicFilters.Add(topic);
+
+            return this;
+        }
+
+        public MqttClientUnsubscribeOptionsBuilder WithTopicFilter(TopicFilter topicFilter)
+        {
+            if (topicFilter is null) throw new ArgumentNullException(nameof(topicFilter));
+
+            return WithTopicFilter(topicFilter.Topic);
+        }
+
+        public MqttClientUnsubscribeOptions Build()
+        {
+            return _unsubscribeOptions;
+        }
+    }
+}

Source/MQTTnet/Diagnostics/IMqttNetChildLogger.cs

@@ -1,17 +0,0 @@
-using System;
-
-namespace MQTTnet.Diagnostics
-{
-    public interface IMqttNetChildLogger
-    {
-        IMqttNetChildLogger CreateChildLogger(string source = null);
-
-        void Verbose(string message, params object[] parameters);
-
-        void Info(string message, params object[] parameters);
-
-        void Warning(Exception exception, string message, params object[] parameters);
-
-        void Error(Exception exception, string message, params object[] parameters);
-    }
-}

Source/MQTTnet/Diagnostics/IMqttNetLogger.cs

@@ -6,8 +6,8 @@ namespace MQTTnet.Diagnostics
     {
         event EventHandler<MqttNetLogMessagePublishedEventArgs> LogMessagePublished;
 
-        IMqttNetChildLogger CreateChildLogger(string source = null);
+        IMqttNetLogger CreateChildLogger(string source);
 
-        void Publish(MqttNetLogLevel logLevel, string source, string message, object[] parameters, Exception exception);
+        void Publish(MqttNetLogLevel logLevel, string message, object[] parameters, Exception exception);
     }
 }

Source/MQTTnet/Diagnostics/MqttNetChildLogger.cs

@@ -1,51 +0,0 @@
-using System;
-
-namespace MQTTnet.Diagnostics
-{
-    public class MqttNetChildLogger : IMqttNetChildLogger
-    {
-        private readonly IMqttNetLogger _logger;
-        private readonly string _source;
-
-        public MqttNetChildLogger(IMqttNetLogger logger, string source)
-        {
-            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
-            _source = source;
-        }
-
-        public IMqttNetChildLogger CreateChildLogger(string source)
-        {
-            string childSource;
-            if (!string.IsNullOrEmpty(_source))
-            {
-                childSource = _source + "." + source;
-            }
-            else
-            {
-                childSource = source;
-            }
-
-            return new MqttNetChildLogger(_logger, childSource);
-        }
-
-        public void Verbose(string message, params object[] parameters)
-        {
-            _logger.Publish(MqttNetLogLevel.Verbose, _source, message, parameters, null);
-        }
-
-        public void Info(string message, params object[] parameters)
-        {
-            _logger.Publish(MqttNetLogLevel.Info, _source, message, parameters, null);
-        }
-
-        public void Warning(Exception exception, string message, params object[] parameters)
-        {
-            _logger.Publish(MqttNetLogLevel.Warning, _source, message, parameters, exception);
-        }
-
-        public void Error(Exception exception, string message, params object[] parameters)
-        {
-            _logger.Publish(MqttNetLogLevel.Error, _source, message, parameters, exception);
-        }
-    }
-}

Source/MQTTnet/Diagnostics/MqttNetLogMessage.cs

@@ -4,30 +4,19 @@ namespace MQTTnet.Diagnostics
 {
     public class MqttNetLogMessage
     {
-        public MqttNetLogMessage(string logId, DateTime timestamp, int threadId, string source, MqttNetLogLevel level, string message, Exception exception)
-        {
-            LogId = logId;
-            Timestamp = timestamp;
-            ThreadId = threadId;
-            Source = source;
-            Level = level;
-            Message = message;
-            Exception = exception;
-        }
+        public string LogId { get; set; }
 
-        public string LogId { get; }
+        public DateTime Timestamp { get; set; }
 
-        public DateTime Timestamp { get; }
+        public int ThreadId { get; set; }
 
-        public int ThreadId { get; }
+        public string Source { get; set; }
 
-        public string Source { get; }
+        public MqttNetLogLevel Level { get; set; }
 
-        public MqttNetLogLevel Level { get; }
+        public string Message { get; set; }
 
-        public string Message { get; }
-
-        public Exception Exception { get; }
+        public Exception Exception { get; set; }
 
         public override string ToString()
         {

Source/MQTTnet/Diagnostics/MqttNetLogMessagePublishedEventArgs.cs

@@ -6,9 +6,16 @@ namespace MQTTnet.Diagnostics
     {
         public MqttNetLogMessagePublishedEventArgs(MqttNetLogMessage logMessage)
         {
+            LogMessage = logMessage ?? throw new ArgumentNullException(nameof(logMessage));
+
+#pragma warning disable CS0618 // Type or member is obsolete
             TraceMessage = logMessage ?? throw new ArgumentNullException(nameof(logMessage));
+#pragma warning restore CS0618 // Type or member is obsolete
         }
 
+        [Obsolete("Use new proeprty LogMessage instead.")]
         public MqttNetLogMessage TraceMessage { get; }
+
+        public MqttNetLogMessage LogMessage { get; }
     }
 }

Source/MQTTnet/Diagnostics/MqttNetLogger.cs

@@ -4,26 +4,51 @@ namespace MQTTnet.Diagnostics
 {
     public class MqttNetLogger : IMqttNetLogger
     {
-        private readonly string _logId;
+        readonly string _logId;
+        readonly string _source;
 
-        public MqttNetLogger(string logId = null)
+        readonly MqttNetLogger _parentLogger;
+
+        public MqttNetLogger(string source, string logId)
         {
+            _source = source;
+            _logId = logId;
+        }
+
+        public MqttNetLogger()
+        {
+        }
+
+        public MqttNetLogger(string logId)
+        {
+            _logId = logId;
+        }
+
+        MqttNetLogger(MqttNetLogger parentLogger, string logId, string source)
+        {
+            _parentLogger = parentLogger ?? throw new ArgumentNullException(nameof(parentLogger));
+            _source = source ?? throw new ArgumentNullException(nameof(source));
+
             _logId = logId;
         }
 
         public event EventHandler<MqttNetLogMessagePublishedEventArgs> LogMessagePublished;
 
-        public IMqttNetChildLogger CreateChildLogger(string source = null)
+        // TODO: Consider creating a LoggerFactory which will allow creating loggers. The logger factory will
+        // be the only place which has the published event.
+        public IMqttNetLogger CreateChildLogger(string source)
         {
-            return new MqttNetChildLogger(this, source);
+            if (source is null) throw new ArgumentNullException(nameof(source));
+
+            return new MqttNetLogger(this, _logId, source);
         }
 
-        public void Publish(MqttNetLogLevel logLevel, string source, string message, object[] parameters, Exception exception)
+        public void Publish(MqttNetLogLevel level, string message, object[] parameters, Exception exception)
         {
             var hasLocalListeners = LogMessagePublished != null;
             var hasGlobalListeners = MqttNetGlobalLogger.HasListeners;
 
-            if (!hasLocalListeners && !hasGlobalListeners)
+            if (!hasLocalListeners && !hasGlobalListeners && _parentLogger == null)
             {
                 return;
             }
@@ -40,17 +65,35 @@ namespace MQTTnet.Diagnostics
                 }
             }
 
-            var traceMessage = new MqttNetLogMessage(_logId, DateTime.UtcNow, Environment.CurrentManagedThreadId, source, logLevel, message, exception);
+            var logMessage = new MqttNetLogMessage
+            {
+                LogId = _logId,
+                Timestamp = DateTime.UtcNow,
+                Source = _source,
+                ThreadId = Environment.CurrentManagedThreadId,
+                Level = level,
+                Message = message,
+                Exception = exception
+            };
 
             if (hasGlobalListeners)
             {
-                MqttNetGlobalLogger.Publish(traceMessage);
+                MqttNetGlobalLogger.Publish(logMessage);
             }
 
             if (hasLocalListeners)
             {
-                LogMessagePublished?.Invoke(this, new MqttNetLogMessagePublishedEventArgs(traceMessage));
+                LogMessagePublished?.Invoke(this, new MqttNetLogMessagePublishedEventArgs(logMessage));
             }
+
+            _parentLogger?.Publish(logMessage);
+        }
+
+        void Publish(MqttNetLogMessage logMessage)
+        {
+            LogMessagePublished?.Invoke(this, new MqttNetLogMessagePublishedEventArgs(logMessage));
+
+            _parentLogger?.Publish(logMessage);
         }
     }
 }

Source/MQTTnet/Diagnostics/MqttNetLoggerExtensions.cs

@@ -0,0 +1,35 @@
+using System;
+
+namespace MQTTnet.Diagnostics
+{
+    public static class MqttNetLoggerExtensions
+    {
+        public static void Verbose(this IMqttNetLogger logger, string message, params object[] parameters)
+        {
+            if (logger is null) throw new ArgumentNullException(nameof(logger));
+
+            logger.Publish(MqttNetLogLevel.Verbose, message, parameters, null);
+        }
+
+        public static void Info(this IMqttNetLogger logger, string message, params object[] parameters)
+        {
+            if (logger is null) throw new ArgumentNullException(nameof(logger));
+
+            logger.Publish(MqttNetLogLevel.Info, message, parameters, null);
+        }
+
+        public static void Warning(this IMqttNetLogger logger, Exception exception, string message, params object[] parameters)
+        {
+            if (logger is null) throw new ArgumentNullException(nameof(logger));
+
+            logger.Publish(MqttNetLogLevel.Warning, message, parameters, exception);
+        }
+
+        public static void Error(this IMqttNetLogger logger, Exception exception, string message, params object[] parameters)
+        {
+            if (logger is null) throw new ArgumentNullException(nameof(logger));
+
+            logger.Publish(MqttNetLogLevel.Error, message, parameters, exception);
+        }
+    }
+}

Source/MQTTnet/Diagnostics/TargetFrameworkProvider.cs

@@ -1,6 +1,6 @@
 namespace MQTTnet.Diagnostics
 {
-    public static class TargetFrameworkInfoProvider
+    public static class TargetFrameworkProvider
     {
         public static string TargetFramework
         {

Source/MQTTnet/Exceptions/MqttConfigurationException.cs

@@ -0,0 +1,21 @@
+using System;
+
+namespace MQTTnet.Exceptions
+{
+    public class MqttConfigurationException : Exception
+    {
+        protected MqttConfigurationException()
+        {
+        }
+
+        public MqttConfigurationException(Exception innerException)
+            : base(innerException.Message, innerException)
+        {
+        }
+
+        public MqttConfigurationException(string message)
+            : base(message)
+        {
+        }
+    }
+}

Source/MQTTnet/Extensions/MqttClientOptionsBuilderExtension.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Linq;
+using MQTTnet.Client.Options;
+
+namespace MQTTnet.Extensions
+{
+    public static class MqttClientOptionsBuilderExtension
+    {
+        public static MqttClientOptionsBuilder WithConnectionUri(this MqttClientOptionsBuilder builder, Uri uri)
+        {
+            var port = uri.IsDefaultPort ? null : (int?) uri.Port;
+            switch (uri.Scheme.ToLower())
+            {
+                case "tcp":
+                case "mqtt":
+                    builder.WithTcpServer(uri.Host, port);
+                    break;
+
+                case "mqtts":
+                    builder.WithTcpServer(uri.Host, port).WithTls();
+                    break;
+
+                case "ws":
+                case "wss":
+                    builder.WithWebSocketServer(uri.ToString());
+                    break;
+
+                default:
+                    throw new ArgumentException("Unexpected scheme in uri.");
+            }
+            
+            if (!string.IsNullOrEmpty(uri.UserInfo))
+            {
+                var userInfo = uri.UserInfo.Split(':');
+                var username = userInfo[0];
+                var password = userInfo.Length > 1 ? userInfo[1] : "";
+                builder.WithCredentials(username, password);
+            }
+
+            return builder;
+        }
+
+        public static MqttClientOptionsBuilder WithConnectionUri(this MqttClientOptionsBuilder builder, string uri)
+        {
+            return WithConnectionUri(builder, new Uri(uri, UriKind.Absolute));
+        }
+    }
+}

Source/MQTTnet/Extensions/UserPropertyExtension.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Linq;
+
+namespace MQTTnet.Extensions
+{
+    public static class UserPropertyExtension
+    {
+        public static string GetUserProperty(this MqttApplicationMessage message, string propertyName, StringComparison comparisonType = StringComparison.Ordinal)
+        {
+            if (message == null) throw new ArgumentNullException(nameof(message));
+            if (propertyName == null) throw new ArgumentNullException(nameof(propertyName));
+
+            return message.UserProperties?.SingleOrDefault(up => up.Name.Equals(propertyName, comparisonType))?.Value;
+        }
+    }
+}

Source/MQTTnet/Formatter/V3/MqttV310DataConverter.cs

@@ -1,6 +1,4 @@
-using System;
-using System.Linq;
-using MQTTnet.Client.Connecting;
+using MQTTnet.Client.Connecting;
 using MQTTnet.Client.Disconnecting;
 using MQTTnet.Client.Options;
 using MQTTnet.Client.Publishing;
@@ -10,6 +8,8 @@ using MQTTnet.Exceptions;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
+using System;
+using System.Linq;
 using MqttClientSubscribeResult = MQTTnet.Client.Subscribing.MqttClientSubscribeResult;
 
 namespace MQTTnet.Formatter.V3
@@ -20,11 +20,6 @@ namespace MQTTnet.Formatter.V3
         {
             if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
 
-            if (applicationMessage.UserProperties?.Any() == true)
-            {
-                throw new MqttProtocolViolationException("User properties are not supported in MQTT version 3.");
-            }
-
             return new MqttPublishPacket
             {
                 Topic = applicationMessage.Topic,
@@ -158,7 +153,7 @@ namespace MQTTnet.Formatter.V3
         {
             if (unsubscribePacket == null) throw new ArgumentNullException(nameof(unsubscribePacket));
             if (unsubAckPacket == null) throw new ArgumentNullException(nameof(unsubAckPacket));
-            
+
             var result = new MqttClientUnsubscribeResult();
 
             result.Items.AddRange(unsubscribePacket.TopicFilters.Select((t, i) =>
@@ -171,14 +166,9 @@ namespace MQTTnet.Formatter.V3
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
-            if (options.UserProperties?.Any() == true)
-            {
-                throw new MqttProtocolViolationException("User properties are not supported in MQTT version 3.");
-            }
-
             var subscribePacket = new MqttSubscribePacket();
             subscribePacket.TopicFilters.AddRange(options.TopicFilters);
-            
+
             return subscribePacket;
         }
 
@@ -186,11 +176,6 @@ namespace MQTTnet.Formatter.V3
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
-            if (options.UserProperties?.Any() == true)
-            {
-                throw new MqttProtocolViolationException("User properties are not supported in MQTT version 3.");
-            }
-
             var unsubscribePacket = new MqttUnsubscribePacket();
             unsubscribePacket.TopicFilters.AddRange(options.TopicFilters);
 
@@ -199,9 +184,9 @@ namespace MQTTnet.Formatter.V3
 
         public MqttDisconnectPacket CreateDisconnectPacket(MqttClientDisconnectOptions options)
         {
-            if (options != null)
+            if (options.ReasonCode != MqttClientDisconnectReason.NormalDisconnection || options.ReasonString != null)
             {
-                throw new MqttProtocolViolationException("Reason codes for disconnect are only supported for MQTTv5.");
+                throw new MqttProtocolViolationException("Reason codes and reason string for disconnect are only supported for MQTTv5.");
             }
 
             return new MqttDisconnectPacket();

Source/MQTTnet/Formatter/V5/MqttV500DataConverter.cs

@@ -139,7 +139,7 @@ namespace MQTTnet.Formatter.V5
                 ReasonCode = connectionValidatorContext.ReasonCode,
                 Properties = new MqttConnAckPacketProperties
                 {
-                    UserProperties = connectionValidatorContext.UserProperties,
+                    UserProperties = connectionValidatorContext.ResponseUserProperties,
                     AuthenticationMethod = connectionValidatorContext.AuthenticationMethod,
                     AuthenticationData = connectionValidatorContext.ResponseAuthenticationData,
                     AssignedClientIdentifier = connectionValidatorContext.AssignedClientIdentifier,

Source/MQTTnet/Implementations/CrossPlatformSocket.cs

@@ -0,0 +1,229 @@
+using System;
+using System.Net;
+using System.Net.Sockets;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace MQTTnet.Implementations
+{
+    public sealed class CrossPlatformSocket : IDisposable
+    {
+        readonly Socket _socket;
+
+        public CrossPlatformSocket(AddressFamily addressFamily)
+        {
+            _socket = new Socket(addressFamily, SocketType.Stream, ProtocolType.Tcp);
+        }
+
+        public CrossPlatformSocket()
+        {
+            // Having this contructor is important because avoiding the address family as parameter
+            // will make use of dual mode in the .net framework.
+            _socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
+        }
+
+        public CrossPlatformSocket(Socket socket)
+        {
+            _socket = socket ?? throw new ArgumentNullException(nameof(socket));
+        }
+
+        public bool NoDelay
+        {
+            get
+            {
+                return (int)_socket.GetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.NoDelay) > 0;
+            }
+
+            set
+            {
+                _socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.NoDelay, value ? 1 : 0);
+            }
+        }
+
+        public bool DualMode
+        {
+            get
+            {
+                return _socket.DualMode;
+            }
+
+            set
+            {
+                _socket.DualMode = value;
+            }
+        }
+
+        public int ReceiveBufferSize
+        {
+            get
+            {
+                return _socket.ReceiveBufferSize;
+            }
+
+            set
+            {
+                _socket.ReceiveBufferSize = value;
+            }
+        }
+
+        public int SendBufferSize
+        {
+            get
+            {
+                return _socket.SendBufferSize;
+            }
+
+            set
+            {
+                _socket.SendBufferSize = value;
+            }
+        }
+
+        public EndPoint RemoteEndPoint
+        {
+            get
+            {
+                return _socket.RemoteEndPoint;
+            }
+        }
+
+        public bool ReuseAddress
+        {
+            get
+            {
+                return (int)_socket.GetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress) != 0;
+            }
+
+            set
+            {
+                _socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, value ? 1 : 0);
+            }
+        }
+
+        public async Task<CrossPlatformSocket> AcceptAsync()
+        {
+            try
+            {
+#if NET452 || NET461
+                var clientSocket = await Task.Factory.FromAsync(_socket.BeginAccept, _socket.EndAccept, null).ConfigureAwait(false);
+                return new CrossPlatformSocket(clientSocket);
+#else
+                var clientSocket = await _socket.AcceptAsync().ConfigureAwait(false);
+                return new CrossPlatformSocket(clientSocket);
+#endif
+            }
+            catch (ObjectDisposedException)
+            {
+                // This will happen when _socket.EndAccept gets called by Task library but the socket is already disposed.
+                return null;
+            }
+        }
+
+        public void Bind(EndPoint localEndPoint)
+        {
+            if (localEndPoint is null) throw new ArgumentNullException(nameof(localEndPoint));
+
+            _socket.Bind(localEndPoint);
+        }
+
+        public void Listen(int connectionBacklog)
+        {
+            _socket.Listen(connectionBacklog);
+        }
+
+        public async Task ConnectAsync(string host, int port, CancellationToken cancellationToken)
+        {
+            if (host is null) throw new ArgumentNullException(nameof(host));
+
+            try
+            {
+                // Workaround for: workaround for https://github.com/dotnet/corefx/issues/24430
+                using (cancellationToken.Register(() => _socket.Dispose()))
+                {
+                    cancellationToken.ThrowIfCancellationRequested();
+
+#if NET452 || NET461
+                    await Task.Factory.FromAsync(_socket.BeginConnect, _socket.EndConnect, host, port, null).ConfigureAwait(false);
+#else
+                    await _socket.ConnectAsync(host, port).ConfigureAwait(false);
+#endif
+                }
+            }
+            catch (ObjectDisposedException)
+            {
+                // This will happen when _socket.EndConnect gets called by Task library but the socket is already disposed.
+            }
+        }
+
+        public async Task SendAsync(ArraySegment<byte> buffer, SocketFlags socketFlags)
+        {
+            try
+            {
+#if NET452 || NET461
+                await Task.Factory.FromAsync(SocketWrapper.BeginSend, _socket.EndSend, new SocketWrapper(_socket, buffer, socketFlags)).ConfigureAwait(false);
+#else
+                await _socket.SendAsync(buffer, socketFlags).ConfigureAwait(false);
+#endif
+            }
+            catch (ObjectDisposedException)
+            {
+                // This will happen when _socket.EndConnect gets called by Task library but the socket is already disposed.
+            }
+        }
+
+        public async Task<int> ReceiveAsync(ArraySegment<byte> buffer, SocketFlags socketFlags)
+        {
+            try
+            {
+#if NET452 || NET461
+                return await Task.Factory.FromAsync(SocketWrapper.BeginReceive, _socket.EndReceive, new SocketWrapper(_socket, buffer, socketFlags)).ConfigureAwait(false);
+#else
+                return await _socket.ReceiveAsync(buffer, socketFlags).ConfigureAwait(false);
+#endif
+            }
+            catch (ObjectDisposedException)
+            {
+                // This will happen when _socket.EndReceive gets called by Task library but the socket is already disposed.
+                return -1;
+            }
+        }
+
+        public NetworkStream GetStream()
+        {
+            return new NetworkStream(_socket, true);
+        }
+
+        public void Dispose()
+        {
+            _socket?.Dispose();
+        }
+
+#if NET452 || NET461
+        class SocketWrapper
+        {
+            readonly Socket _socket;
+            readonly ArraySegment<byte> _buffer;
+            readonly SocketFlags _socketFlags;
+
+            public SocketWrapper(Socket socket, ArraySegment<byte> buffer, SocketFlags socketFlags)
+            {
+                _socket = socket;
+                _buffer = buffer;
+                _socketFlags = socketFlags;
+            }
+
+            public static IAsyncResult BeginSend(AsyncCallback callback, object state)
+            {
+                var socketWrapper = (SocketWrapper)state;
+                return socketWrapper._socket.BeginSend(socketWrapper._buffer.Array, socketWrapper._buffer.Offset, socketWrapper._buffer.Count, socketWrapper._socketFlags, callback, state);
+            }
+
+            public static IAsyncResult BeginReceive(AsyncCallback callback, object state)
+            {
+                var socketWrapper = (SocketWrapper)state;
+                return socketWrapper._socket.BeginReceive(socketWrapper._buffer.Array, socketWrapper._buffer.Offset, socketWrapper._buffer.Count, socketWrapper._socketFlags, callback, state);
+            }
+        }
+#endif
+    }
+}

Source/MQTTnet/Implementations/MqttClientAdapterFactory.cs

@@ -1,17 +1,17 @@
-using System;
-using MQTTnet.Adapter;
+using MQTTnet.Adapter;
 using MQTTnet.Client.Options;
 using MQTTnet.Diagnostics;
 using MQTTnet.Formatter;
+using System;
 
 namespace MQTTnet.Implementations
 {
     public class MqttClientAdapterFactory : IMqttClientAdapterFactory
     {
-        public IMqttChannelAdapter CreateClientAdapter(IMqttClientOptions options, IMqttNetChildLogger logger)
+        public IMqttChannelAdapter CreateClientAdapter(IMqttClientOptions options, IMqttNetLogger logger)
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
-            
+
             switch (options.ChannelOptions)
             {
                 case MqttClientTcpOptions _:

Source/MQTTnet/Implementations/MqttTcpChannel.cs

@@ -1,24 +1,24 @@
 #if !WINDOWS_UWP
-using System;
-using System.Net.Security;
-using System.Net.Sockets;
-using System.Security.Cryptography.X509Certificates;
-using System.Threading.Tasks;
-using System.IO;
-using System.Linq;
-using System.Runtime.ExceptionServices;
-using System.Threading;
 using MQTTnet.Channel;
 using MQTTnet.Client.Options;
+using System;
+using System.IO;
+using System.Linq;
+using System.Net.Security;
+using System.Net.Sockets;
+using System.Runtime.ExceptionServices;
+using System.Security.Cryptography.X509Certificates;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace MQTTnet.Implementations
 {
-    public class MqttTcpChannel : IMqttChannel
+    public sealed class MqttTcpChannel : IDisposable, IMqttChannel
     {
-        private readonly IMqttClientOptions _clientOptions;
-        private readonly MqttClientTcpOptions _options;
+        readonly IMqttClientOptions _clientOptions;
+        readonly MqttClientTcpOptions _options;
 
-        private Stream _stream;
+        Stream _stream;
 
         public MqttTcpChannel(IMqttClientOptions clientOptions)
         {
@@ -46,15 +46,15 @@ namespace MQTTnet.Implementations
 
         public async Task ConnectAsync(CancellationToken cancellationToken)
         {
-            Socket socket;
+            CrossPlatformSocket socket;
 
             if (_options.AddressFamily == AddressFamily.Unspecified)
             {
-                socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
+                socket = new CrossPlatformSocket();
             }
             else
             {
-                socket = new Socket(_options.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
+                socket = new CrossPlatformSocket(_options.AddressFamily);
             }
 
             socket.ReceiveBufferSize = _options.BufferSize;
@@ -68,25 +68,25 @@ namespace MQTTnet.Implementations
                 // of the actual value.
                 socket.DualMode = _options.DualMode.Value;
             }
-            
-            // Workaround for: workaround for https://github.com/dotnet/corefx/issues/24430
-            using (cancellationToken.Register(() => socket.Dispose()))
-            {
-#if NET452 || NET461
-                await Task.Factory.FromAsync(socket.BeginConnect, socket.EndConnect, _options.Server, _options.GetPort(), null).ConfigureAwait(false);
-#else
-                await socket.ConnectAsync(_options.Server, _options.GetPort()).ConfigureAwait(false);
-#endif
-            }
 
-            var networkStream = new NetworkStream(socket, true);
+            await socket.ConnectAsync(_options.Server, _options.GetPort(), cancellationToken).ConfigureAwait(false);
+
+            var networkStream = socket.GetStream();
 
             if (_options.TlsOptions.UseTls)
             {
                 var sslStream = new SslStream(networkStream, false, InternalUserCertificateValidationCallback);
-                _stream = sslStream;
+                try
+                {
+                    await sslStream.AuthenticateAsClientAsync(_options.Server, LoadCertificates(), _options.TlsOptions.SslProtocol, !_options.TlsOptions.IgnoreCertificateRevocationErrors).ConfigureAwait(false);
+                }
+                catch
+                {
+                    sslStream.Dispose();
+                    throw;
+                }
 
-                await sslStream.AuthenticateAsClientAsync(_options.Server, LoadCertificates(), _options.TlsOptions.SslProtocol, !_options.TlsOptions.IgnoreCertificateRevocationErrors).ConfigureAwait(false);                
+                _stream = sslStream;
             }
             else
             {
@@ -104,19 +104,22 @@ namespace MQTTnet.Implementations
 
         public async Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {
+            if (buffer is null) throw new ArgumentNullException(nameof(buffer));
+
             try
             {
                 // Workaround for: https://github.com/dotnet/corefx/issues/24430
                 using (cancellationToken.Register(Dispose))
                 {
-                    if (cancellationToken.IsCancellationRequested)
-                    {
-                        return 0;
-                    }
+                    cancellationToken.ThrowIfCancellationRequested();
 
                     return await _stream.ReadAsync(buffer, offset, count, cancellationToken).ConfigureAwait(false);
                 }
             }
+            catch (ObjectDisposedException)
+            {
+                return -1;
+            }
             catch (IOException exception)
             {
                 if (exception.InnerException is SocketException socketException)
@@ -130,19 +133,22 @@ namespace MQTTnet.Implementations
 
         public async Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {
+            if (buffer is null) throw new ArgumentNullException(nameof(buffer));
+
             try
             {
                 // Workaround for: https://github.com/dotnet/corefx/issues/24430
                 using (cancellationToken.Register(Dispose))
                 {
-                    if (cancellationToken.IsCancellationRequested)
-                    {
-                        return;
-                    }
+                    cancellationToken.ThrowIfCancellationRequested();
 
                     await _stream.WriteAsync(buffer, offset, count, cancellationToken).ConfigureAwait(false);
                 }
             }
+            catch (ObjectDisposedException)
+            {
+                return;
+            }
             catch (IOException exception)
             {
                 if (exception.InnerException is SocketException socketException)
@@ -173,7 +179,7 @@ namespace MQTTnet.Implementations
             _stream = null;
         }
 
-        private bool InternalUserCertificateValidationCallback(object sender, X509Certificate x509Certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
+        bool InternalUserCertificateValidationCallback(object sender, X509Certificate x509Certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
         {
             if (_options.TlsOptions.CertificateValidationCallback != null)
             {
@@ -204,7 +210,7 @@ namespace MQTTnet.Implementations
             return _options.TlsOptions.AllowUntrustedCertificates;
         }
 
-        private X509CertificateCollection LoadCertificates()
+        X509CertificateCollection LoadCertificates()
         {
             var certificates = new X509CertificateCollection();
             if (_options.TlsOptions.Certificates == null)
@@ -214,7 +220,7 @@ namespace MQTTnet.Implementations
 
             foreach (var certificate in _options.TlsOptions.Certificates)
             {
-                certificates.Add(new X509Certificate2(certificate));
+                certificates.Add(certificate);
             }
 
             return certificates;

Source/MQTTnet/Implementations/MqttTcpServerAdapter.Uwp.cs

@@ -11,14 +11,14 @@ using System.Threading.Tasks;
 
 namespace MQTTnet.Implementations
 {
-    public class MqttTcpServerAdapter : IMqttServerAdapter
+    public sealed class MqttTcpServerAdapter : IMqttServerAdapter
     {
-        private readonly IMqttNetChildLogger _logger;
+        readonly IMqttNetLogger _logger;
 
-        private IMqttServerOptions _options;
-        private StreamSocketListener _listener;
+        IMqttServerOptions _options;
+        StreamSocketListener _listener;
 
-        public MqttTcpServerAdapter(IMqttNetChildLogger logger)
+        public MqttTcpServerAdapter(IMqttNetLogger logger)
         {
             if (logger == null) throw new ArgumentNullException(nameof(logger));
 
@@ -68,7 +68,7 @@ namespace MQTTnet.Implementations
             _listener = null;
         }
 
-        private async void OnConnectionReceivedAsync(StreamSocketListener sender, StreamSocketListenerConnectionReceivedEventArgs args)
+        async void OnConnectionReceivedAsync(StreamSocketListener sender, StreamSocketListenerConnectionReceivedEventArgs args)
         {
             try
             {

Source/MQTTnet/Implementations/MqttTcpServerAdapter.cs

@@ -1,4 +1,8 @@
 #if !WINDOWS_UWP
+using MQTTnet.Adapter;
+using MQTTnet.Diagnostics;
+using MQTTnet.Internal;
+using MQTTnet.Server;
 using System;
 using System.Collections.Generic;
 using System.Net;
@@ -6,20 +10,17 @@ using System.Net.Sockets;
 using System.Security.Cryptography.X509Certificates;
 using System.Threading;
 using System.Threading.Tasks;
-using MQTTnet.Adapter;
-using MQTTnet.Diagnostics;
-using MQTTnet.Server;
 
 namespace MQTTnet.Implementations
 {
-    public class MqttTcpServerAdapter : IMqttServerAdapter
+    public sealed class MqttTcpServerAdapter : Disposable, IMqttServerAdapter
     {
-        private readonly List<MqttTcpServerListener> _listeners = new List<MqttTcpServerListener>();
-        private readonly IMqttNetChildLogger _logger;
+        readonly List<MqttTcpServerListener> _listeners = new List<MqttTcpServerListener>();
+        readonly IMqttNetLogger _logger;
 
-        private CancellationTokenSource _cancellationTokenSource;
+        CancellationTokenSource _cancellationTokenSource;
 
-        public MqttTcpServerAdapter(IMqttNetChildLogger logger)
+        public MqttTcpServerAdapter(IMqttNetLogger logger)
         {
             if (logger == null) throw new ArgumentNullException(nameof(logger));
 
@@ -58,7 +59,7 @@ namespace MQTTnet.Implementations
                 {
                     tlsCertificate = new X509Certificate2(options.TlsEndpointOptions.Certificate, options.TlsEndpointOptions.CertificateCredentials.Password);
                 }
-                
+
                 if (!tlsCertificate.HasPrivateKey)
                 {
                     throw new InvalidOperationException("The certificate for TLS encryption must contain the private key.");
@@ -72,11 +73,21 @@ namespace MQTTnet.Implementations
 
         public Task StopAsync()
         {
-            Dispose();
+            Cleanup();
             return Task.FromResult(0);
         }
 
-        public void Dispose()
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                Cleanup();
+            }
+
+            base.Dispose(disposing);
+        }
+
+        void Cleanup()
         {
             _cancellationTokenSource?.Cancel(false);
             _cancellationTokenSource?.Dispose();
@@ -90,7 +101,7 @@ namespace MQTTnet.Implementations
             _listeners.Clear();
         }
 
-        private void RegisterListeners(MqttServerTcpEndpointBaseOptions options, X509Certificate2 tlsCertificate, CancellationToken cancellationToken)
+        void RegisterListeners(MqttServerTcpEndpointBaseOptions options, X509Certificate2 tlsCertificate, CancellationToken cancellationToken)
         {
             if (!options.BoundInterNetworkAddress.Equals(IPAddress.None))
             {

Source/MQTTnet/Implementations/MqttTcpServerListener.cs

@@ -1,4 +1,9 @@
 #if !WINDOWS_UWP
+using MQTTnet.Adapter;
+using MQTTnet.Diagnostics;
+using MQTTnet.Formatter;
+using MQTTnet.Internal;
+using MQTTnet.Server;
 using System;
 using System.IO;
 using System.Net;
@@ -7,30 +12,25 @@ using System.Net.Sockets;
 using System.Security.Cryptography.X509Certificates;
 using System.Threading;
 using System.Threading.Tasks;
-using MQTTnet.Adapter;
-using MQTTnet.Diagnostics;
-using MQTTnet.Formatter;
-using MQTTnet.Internal;
-using MQTTnet.Server;
 
 namespace MQTTnet.Implementations
 {
-    public class MqttTcpServerListener : IDisposable
+    public sealed class MqttTcpServerListener : IDisposable
     {
-        private readonly IMqttNetChildLogger _logger;
-        private readonly AddressFamily _addressFamily;
-        private readonly MqttServerTcpEndpointBaseOptions _options;
-        private readonly MqttServerTlsTcpEndpointOptions _tlsOptions;
-        private readonly X509Certificate2 _tlsCertificate;
+        readonly IMqttNetLogger _logger;
+        readonly AddressFamily _addressFamily;
+        readonly MqttServerTcpEndpointBaseOptions _options;
+        readonly MqttServerTlsTcpEndpointOptions _tlsOptions;
+        readonly X509Certificate2 _tlsCertificate;
 
-        private Socket _socket;
+        private CrossPlatformSocket _socket;
         private IPEndPoint _localEndPoint;
 
         public MqttTcpServerListener(
             AddressFamily addressFamily,
             MqttServerTcpEndpointBaseOptions options,
             X509Certificate2 tlsCertificate,
-            IMqttNetChildLogger logger)
+            IMqttNetLogger logger)
         {
             _addressFamily = addressFamily;
             _options = options;
@@ -59,20 +59,20 @@ namespace MQTTnet.Implementations
 
                 _logger.Info($"Starting TCP listener for {_localEndPoint} TLS={_tlsCertificate != null}.");
 
-                _socket = new Socket(_addressFamily, SocketType.Stream, ProtocolType.Tcp);
+                _socket = new CrossPlatformSocket(_addressFamily);
 
                 // Usage of socket options is described here: https://docs.microsoft.com/en-us/dotnet/api/system.net.sockets.socket.setsocketoption?view=netcore-2.2
 
                 if (_options.ReuseAddress)
                 {
-                    _socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
+                    _socket.ReuseAddress = true;
                 }
-                
+
                 if (_options.NoDelay)
                 {
-                    _socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.NoDelay, true);
+                    _socket.NoDelay = true;
                 }
-                
+
                 _socket.Bind(_localEndPoint);
                 _socket.Listen(_options.ConnectionBacklog);
 
@@ -87,7 +87,7 @@ namespace MQTTnet.Implementations
                     throw;
                 }
 
-                _logger.Warning(exception,"Error while creating listener socket for local end point '{0}'.", _localEndPoint);
+                _logger.Warning(exception, "Error while creating listener socket for local end point '{0}'.", _localEndPoint);
                 return false;
             }
         }
@@ -101,18 +101,13 @@ namespace MQTTnet.Implementations
 #endif
         }
 
-        private async Task AcceptClientConnectionsAsync(CancellationToken cancellationToken)
+        async Task AcceptClientConnectionsAsync(CancellationToken cancellationToken)
         {
             while (!cancellationToken.IsCancellationRequested)
             {
                 try
                 {
-#if NET452 || NET461
-                    var clientSocket = await Task.Factory.FromAsync(_socket.BeginAccept, _socket.EndAccept, null).ConfigureAwait(false);
-#else
                     var clientSocket = await _socket.AcceptAsync().ConfigureAwait(false);
-#endif
-
                     if (clientSocket == null)
                     {
                         continue;
@@ -121,7 +116,7 @@ namespace MQTTnet.Implementations
                     Task.Run(() => TryHandleClientConnectionAsync(clientSocket), cancellationToken).Forget(_logger);
                 }
                 catch (OperationCanceledException)
-                {  
+                {
                 }
                 catch (Exception exception)
                 {
@@ -133,14 +128,14 @@ namespace MQTTnet.Implementations
                             continue;
                         }
                     }
-                   
+
                     _logger.Error(exception, $"Error while accepting connection at TCP listener {_localEndPoint} TLS={_tlsCertificate != null}.");
                     await Task.Delay(TimeSpan.FromSeconds(1), cancellationToken).ConfigureAwait(false);
                 }
             }
         }
 
-        private async Task TryHandleClientConnectionAsync(Socket clientSocket)
+        async Task TryHandleClientConnectionAsync(CrossPlatformSocket clientSocket)
         {
             Stream stream = null;
             string remoteEndPoint = null;
@@ -156,7 +151,7 @@ namespace MQTTnet.Implementations
 
                 clientSocket.NoDelay = _options.NoDelay;
 
-                stream = new NetworkStream(clientSocket, true);
+                stream = clientSocket.GetStream();
 
                 X509Certificate2 clientCertificate = null;
 
@@ -165,9 +160,9 @@ namespace MQTTnet.Implementations
                     var sslStream = new SslStream(stream, false, _tlsOptions.RemoteCertificateValidationCallback);
 
                     await sslStream.AuthenticateAsServerAsync(
-                        _tlsCertificate, 
-                        _tlsOptions.ClientCertificateRequired, 
-                        _tlsOptions.SslProtocol, 
+                        _tlsCertificate,
+                        _tlsOptions.ClientCertificateRequired,
+                        _tlsOptions.SslProtocol,
                         _tlsOptions.CheckCertificateRevocation).ConfigureAwait(false);
 
                     stream = sslStream;

Source/MQTTnet/Implementations/MqttWebSocketChannel.cs

@@ -6,10 +6,11 @@ using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Channel;
 using MQTTnet.Client.Options;
+using MQTTnet.Internal;
 
 namespace MQTTnet.Implementations
 {
-    public class MqttWebSocketChannel : IMqttChannel
+    public class MqttWebSocketChannel : Disposable, IMqttChannel
     {
         private readonly MqttClientWebSocketOptions _options;
 
@@ -84,7 +85,12 @@ namespace MQTTnet.Implementations
                 clientWebSocket.Options.ClientCertificates = new X509CertificateCollection();
                 foreach (var certificate in _options.TlsOptions.Certificates)
                 {
+#if WINDOWS_UWP
                     clientWebSocket.Options.ClientCertificates.Add(new X509Certificate(certificate));
+#else
+                    clientWebSocket.Options.ClientCertificates.Add(certificate);
+#endif
+                    
                 }
             }
 
@@ -106,7 +112,7 @@ namespace MQTTnet.Implementations
                 await _webSocket.CloseAsync(WebSocketCloseStatus.NormalClosure, string.Empty, cancellationToken).ConfigureAwait(false);
             }
 
-            Dispose();
+            Cleanup();
         }
 
         public async Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
@@ -136,7 +142,16 @@ namespace MQTTnet.Implementations
             }
         }
 
-        public void Dispose()
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                Cleanup();
+            }
+            base.Dispose(disposing);
+        }
+
+        private void Cleanup()
         {
             _sendLock?.Dispose();
             _sendLock = null;

Source/MQTTnet/Implementations/PlatformAbstractionLayer.cs

@@ -0,0 +1,20 @@
+using System.Threading.Tasks;
+
+namespace MQTTnet.Implementations
+{
+    public static class PlatformAbstractionLayer
+    {
+        public static Task CompletedTask
+        {
+            get
+            {
+#if NET452 
+                return Task.FromResult(0);
+#else
+                return Task.CompletedTask;
+#endif
+            }
+        }
+
+    }
+}

Source/MQTTnet/Internal/AsyncAutoResetEvent.cs

@@ -1,131 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Threading;
-using System.Threading.Tasks;
-
-namespace MQTTnet.Internal
-{
-    // Inspired from Stephen Toub (https://blogs.msdn.microsoft.com/pfxteam/2012/02/11/building-async-coordination-primitives-part-2-asyncautoresetevent/) and Chris Gillum (https://stackoverflow.com/a/43012490)
-    public class AsyncAutoResetEvent
-    {
-        private readonly LinkedList<TaskCompletionSource<bool>> _waiters = new LinkedList<TaskCompletionSource<bool>>();
-
-        private bool _isSignaled;
-
-        public AsyncAutoResetEvent()
-            : this(false)
-        {
-        }
-
-        public AsyncAutoResetEvent(bool signaled)
-        {
-            _isSignaled = signaled;
-        }
-
-        public int WaitersCount
-        {
-            get
-            {
-                lock (_waiters)
-                {
-                    return _waiters.Count;
-                }
-            }
-        }
-
-        public Task<bool> WaitOneAsync()
-        {
-            return WaitOneAsync(CancellationToken.None);
-        }
-
-        public Task<bool> WaitOneAsync(TimeSpan timeout)
-        {
-            return WaitOneAsync(timeout, CancellationToken.None);
-        }
-
-        public Task<bool> WaitOneAsync(CancellationToken cancellationToken)
-        {
-            return WaitOneAsync(Timeout.InfiniteTimeSpan, cancellationToken);
-        }
-
-        public async Task<bool> WaitOneAsync(TimeSpan timeout, CancellationToken cancellationToken)
-        {
-            cancellationToken.ThrowIfCancellationRequested();
-
-            TaskCompletionSource<bool> tcs;
-
-            lock (_waiters)
-            {
-                if (_isSignaled)
-                {
-                    _isSignaled = false;
-                    return true;
-                }
-
-                if (timeout == TimeSpan.Zero)
-                {
-                    return _isSignaled;
-                }
-
-                tcs = new TaskCompletionSource<bool>();
-                _waiters.AddLast(tcs);
-            }
-
-            Task winner;
-            if (timeout == Timeout.InfiniteTimeSpan)
-            {
-                using (cancellationToken.Register(() => { tcs.TrySetCanceled(); }))
-                {
-                    await tcs.Task.ConfigureAwait(false);
-                    winner = tcs.Task;
-                }               
-            }
-            else
-            {
-                winner = await Task.WhenAny(tcs.Task, Task.Delay(timeout, cancellationToken)).ConfigureAwait(false);
-            }
-            
-            var taskWasSignaled = winner == tcs.Task;
-            if (taskWasSignaled)
-            {
-                return true;
-            }
-
-            // We timed-out; remove our reference to the task.
-            // This is an O(n) operation since waiters is a LinkedList<T>.
-            lock (_waiters)
-            {
-                _waiters.Remove(tcs);
-
-                if (winner.Status == TaskStatus.Canceled)
-                {
-                    throw new OperationCanceledException(cancellationToken);
-                }
-
-                throw new TimeoutException();
-            }
-        }
-
-        public void Set()
-        {
-            TaskCompletionSource<bool> toRelease = null;
-
-            lock (_waiters)
-            {
-                if (_waiters.Count > 0)
-                {
-                    // Signal the first task in the waiters list.
-                    toRelease = _waiters.First.Value;
-                    _waiters.RemoveFirst();
-                }
-                else if (!_isSignaled)
-                {
-                    // No tasks are pending
-                    _isSignaled = true;
-                }
-            }
-
-            toRelease?.TrySetResult(true);
-        }
-    }
-}

Source/MQTTnet/Internal/AsyncQueue.cs

@@ -23,9 +23,15 @@ namespace MQTTnet.Internal
         {
             while (!cancellationToken.IsCancellationRequested)
             {
-                await _semaphore.WaitAsync(cancellationToken).ConfigureAwait(false);
-
-                cancellationToken.ThrowIfCancellationRequested();
+                try
+                {
+                    await _semaphore.WaitAsync(cancellationToken).ConfigureAwait(false);
+                    cancellationToken.ThrowIfCancellationRequested();
+                }
+                catch (OperationCanceledException)
+                {
+                    return new AsyncQueueDequeueResult<TItem>(false, default(TItem));
+                }
 
                 if (_queue.TryDequeue(out var item))
                 {

Source/MQTTnet/Internal/BlockingQueue.cs

@@ -4,11 +4,11 @@ using System.Threading;
 
 namespace MQTTnet.Internal
 {
-    public class BlockingQueue<TItem>
+    public class BlockingQueue<TItem> : Disposable
     {
         private readonly object _syncRoot = new object();
         private readonly LinkedList<TItem> _items = new LinkedList<TItem>();
-        private readonly ManualResetEvent _gate = new ManualResetEvent(false);
+        private readonly ManualResetEventSlim _gate = new ManualResetEventSlim(false);
 
         public int Count
         {
@@ -32,7 +32,7 @@ namespace MQTTnet.Internal
             }
         }
 
-        public TItem Dequeue()
+        public TItem Dequeue(CancellationToken cancellationToken = default(CancellationToken))
         {
             while (true)
             {
@@ -52,11 +52,11 @@ namespace MQTTnet.Internal
                     }
                 }
 
-                _gate.WaitOne();
+                _gate.Wait(cancellationToken);
             }
         }
         
-        public TItem PeekAndWait()
+        public TItem PeekAndWait(CancellationToken cancellationToken = default(CancellationToken))
         {
             while (true)
             {
@@ -73,7 +73,7 @@ namespace MQTTnet.Internal
                     }
                 }
 
-                _gate.WaitOne();
+                _gate.Wait(cancellationToken);
             }
         }
 
@@ -108,5 +108,14 @@ namespace MQTTnet.Internal
                 _items.Clear();
             }
         }
+
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                _gate.Dispose();
+            }
+            base.Dispose(disposing);
+        }
     }
 }

Source/MQTTnet/Internal/Disposable.cs

@@ -0,0 +1,44 @@
+using System;
+
+namespace MQTTnet.Internal
+{
+    public abstract class Disposable : IDisposable
+    {
+        protected bool IsDisposed { get; private set; } = false;
+
+        protected void ThrowIfDisposed()
+        {
+            if (IsDisposed)
+            {
+                throw new ObjectDisposedException(GetType().Name);
+            }
+        }
+
+        protected virtual void Dispose(bool disposing)
+        {
+        }
+
+        // TODO: override a finalizer only if Dispose(bool disposing) above has code to free unmanaged resources.
+        // ~Disposable()
+        // {
+        //   // Do not change this code. Put cleanup code in Dispose(bool disposing) above.
+        //   Dispose(false);
+        // }
+
+        // This code added to correctly implement the disposable pattern.
+        public void Dispose()
+        {
+            // Do not change this code. Put cleanup code in Dispose(bool disposing) above.
+
+            if (IsDisposed)
+            {
+                return;
+            }
+
+            IsDisposed = true;
+
+            Dispose(true);
+            GC.SuppressFinalize(this);
+        }
+    }
+}

Source/MQTTnet/Internal/TaskExtensions.cs

@@ -1,11 +1,11 @@
-using System.Threading.Tasks;
-using MQTTnet.Diagnostics;
+using MQTTnet.Diagnostics;
+using System.Threading.Tasks;
 
 namespace MQTTnet.Internal
 {
     public static class TaskExtensions
     {
-        public static void Forget(this Task task, IMqttNetChildLogger logger)
+        public static void Forget(this Task task, IMqttNetLogger logger)
         {
             task?.ContinueWith(t =>
                 {

Source/MQTTnet/LowLevelClient/ILowLevelMqttClient.cs

@@ -0,0 +1,19 @@
+using MQTTnet.Client.Options;
+using MQTTnet.Packets;
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace MQTTnet.LowLevelClient
+{
+    public interface ILowLevelMqttClient : IDisposable
+    {
+        Task ConnectAsync(IMqttClientOptions options, CancellationToken cancellationToken);
+
+        Task DisconnectAsync(CancellationToken cancellationToken);
+
+        Task SendAsync(MqttBasePacket packet, CancellationToken cancellationToken);
+
+        Task<MqttBasePacket> ReceiveAsync(CancellationToken cancellationToken);
+    }
+}

Source/MQTTnet/LowLevelClient/LowLevelMqttClient.cs

@@ -0,0 +1,128 @@
+using MQTTnet.Adapter;
+using MQTTnet.Client.Options;
+using MQTTnet.Diagnostics;
+using MQTTnet.Packets;
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace MQTTnet.LowLevelClient
+{
+    public sealed class LowLevelMqttClient : ILowLevelMqttClient
+    {
+        readonly IMqttNetLogger _logger;
+        readonly IMqttClientAdapterFactory _clientAdapterFactory;
+
+        IMqttChannelAdapter _adapter;
+        IMqttClientOptions _options;
+
+        public LowLevelMqttClient(IMqttClientAdapterFactory clientAdapterFactory, IMqttNetLogger logger)
+        {
+            if (clientAdapterFactory is null) throw new ArgumentNullException(nameof(clientAdapterFactory));
+            if (logger is null) throw new ArgumentNullException(nameof(logger));
+
+            _clientAdapterFactory = clientAdapterFactory;
+            _logger = logger.CreateChildLogger(nameof(LowLevelMqttClient));
+        }
+
+        bool IsConnected => _adapter != null;
+
+        public async Task ConnectAsync(IMqttClientOptions options, CancellationToken cancellationToken)
+        {
+            if (options is null) throw new ArgumentNullException(nameof(options));
+
+            if (_adapter != null)
+            {
+                throw new InvalidOperationException("Low level MQTT client is already connected. Disconnect first before connecting again.");
+            }
+
+            var newAdapter = _clientAdapterFactory.CreateClientAdapter(options, _logger);
+
+            try
+            {
+                _logger.Verbose($"Trying to connect with server '{options.ChannelOptions}' (Timeout={options.CommunicationTimeout}).");
+                await newAdapter.ConnectAsync(options.CommunicationTimeout, cancellationToken).ConfigureAwait(false);
+                _logger.Verbose("Connection with server established.");
+
+                _options = options;
+            }
+            catch (Exception)
+            {
+                _adapter.Dispose();
+                throw;
+            }
+
+            _adapter = newAdapter;
+        }
+
+        public async Task DisconnectAsync(CancellationToken cancellationToken)
+        {
+            if (_adapter == null)
+            {
+                return;
+            }
+
+            await SafeDisconnect(cancellationToken).ConfigureAwait(false);
+            _adapter = null;
+        }
+
+        public async Task SendAsync(MqttBasePacket packet, CancellationToken cancellationToken)
+        {
+            if (packet is null) throw new ArgumentNullException(nameof(packet));
+
+            if (_adapter == null)
+            {
+                throw new InvalidOperationException("Low level MQTT client is not connected.");
+            }
+
+            try
+            {
+                await _adapter.SendPacketAsync(packet, _options.CommunicationTimeout, cancellationToken).ConfigureAwait(false);
+            }
+            catch (Exception)
+            {
+                await SafeDisconnect(cancellationToken).ConfigureAwait(false);
+                throw;
+            }
+        }
+
+        public async Task<MqttBasePacket> ReceiveAsync(CancellationToken cancellationToken)
+        {
+            if (_adapter == null)
+            {
+                throw new InvalidOperationException("Low level MQTT client is not connected.");
+            }
+
+            try
+            {
+                return await _adapter.ReceivePacketAsync(_options.CommunicationTimeout, cancellationToken).ConfigureAwait(false);
+            }
+            catch (Exception)
+            {
+                await SafeDisconnect(cancellationToken).ConfigureAwait(false);
+                throw;
+            }
+        }
+
+        public void Dispose()
+        {
+            _adapter?.Dispose();
+        }
+
+        async Task SafeDisconnect(CancellationToken cancellationToken)
+        {
+            try
+            {
+                await _adapter.DisconnectAsync(_options.CommunicationTimeout, cancellationToken).ConfigureAwait(false);
+            }
+            catch (Exception exception)
+            {
+                _logger.Error(exception, "Error while disconnecting.");
+            }
+            finally
+            {
+                _adapter.Dispose();
+            }
+        }
+    }
+}

Source/MQTTnet/MQTTnet.csproj

@@ -62,5 +62,9 @@
 
   <ItemGroup Condition="'$(TargetFramework)'=='net461'">
   </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NETCore.UniversalWindowsPlatform" Version="6.2.10" />
+  </ItemGroup>
   
 </Project>

Source/MQTTnet/MqttFactory.cs

@@ -1,16 +1,17 @@
-using System;
-using System.Collections.Generic;
-using MQTTnet.Adapter;
+using MQTTnet.Adapter;
 using MQTTnet.Client;
 using MQTTnet.Diagnostics;
 using MQTTnet.Implementations;
+using MQTTnet.LowLevelClient;
 using MQTTnet.Server;
+using System;
+using System.Collections.Generic;
 
 namespace MQTTnet
 {
-    public class MqttFactory : IMqttFactory
+    public sealed class MqttFactory : IMqttFactory
     {
-        private IMqttClientAdapterFactory _clientAdapterFactory = new MqttClientAdapterFactory();
+        IMqttClientAdapterFactory _clientAdapterFactory = new MqttClientAdapterFactory();
 
         public MqttFactory() : this(new MqttNetLogger())
         {
@@ -29,6 +30,33 @@ namespace MQTTnet
             return this;
         }
 
+        public ILowLevelMqttClient CreateLowLevelMqttClient()
+        {
+            return CreateLowLevelMqttClient(DefaultLogger);
+        }
+
+        public ILowLevelMqttClient CreateLowLevelMqttClient(IMqttNetLogger logger)
+        {
+            if (logger == null) throw new ArgumentNullException(nameof(logger));
+
+            return new LowLevelMqttClient(_clientAdapterFactory, logger);
+        }
+
+        public ILowLevelMqttClient CreateLowLevelMqttClient(IMqttClientAdapterFactory clientAdapterFactory)
+        {
+            if (clientAdapterFactory == null) throw new ArgumentNullException(nameof(clientAdapterFactory));
+
+            return new LowLevelMqttClient(_clientAdapterFactory, DefaultLogger);
+        }
+
+        public ILowLevelMqttClient CreateLowLevelMqttClient(IMqttNetLogger logger, IMqttClientAdapterFactory clientAdapterFactoryy)
+        {
+            if (logger == null) throw new ArgumentNullException(nameof(logger));
+            if (clientAdapterFactoryy == null) throw new ArgumentNullException(nameof(clientAdapterFactoryy));
+
+            return new LowLevelMqttClient(_clientAdapterFactory, logger);
+        }
+
         public IMqttClient CreateMqttClient()
         {
             return CreateMqttClient(DefaultLogger);
@@ -65,7 +93,7 @@ namespace MQTTnet
         {
             if (logger == null) throw new ArgumentNullException(nameof(logger));
 
-            return CreateMqttServer(new List<IMqttServerAdapter> { new MqttTcpServerAdapter(logger.CreateChildLogger()) }, logger);
+            return CreateMqttServer(new List<IMqttServerAdapter> { new MqttTcpServerAdapter(logger) }, logger);
         }
 
         public IMqttServer CreateMqttServer(IEnumerable<IMqttServerAdapter> serverAdapters, IMqttNetLogger logger)
@@ -73,14 +101,14 @@ namespace MQTTnet
             if (serverAdapters == null) throw new ArgumentNullException(nameof(serverAdapters));
             if (logger == null) throw new ArgumentNullException(nameof(logger));
 
-            return new MqttServer(serverAdapters, logger.CreateChildLogger());
+            return new MqttServer(serverAdapters, logger);
         }
 
         public IMqttServer CreateMqttServer(IEnumerable<IMqttServerAdapter> serverAdapters)
         {
             if (serverAdapters == null) throw new ArgumentNullException(nameof(serverAdapters));
-            
-            return new MqttServer(serverAdapters, DefaultLogger.CreateChildLogger());
+
+            return new MqttServer(serverAdapters, DefaultLogger);
         }
     }
 }

Source/MQTTnet/PacketDispatcher/MqttPacketAwaiter.cs

@@ -1,28 +1,34 @@
-using System;
+using MQTTnet.Exceptions;
+using MQTTnet.Internal;
+using MQTTnet.Packets;
+using System;
 using System.Threading;
 using System.Threading.Tasks;
-using MQTTnet.Exceptions;
-using MQTTnet.Packets;
 
 namespace MQTTnet.PacketDispatcher
 {
-    public sealed class MqttPacketAwaiter<TPacket> : IMqttPacketAwaiter where TPacket : MqttBasePacket
+    public sealed class MqttPacketAwaiter<TPacket> : Disposable, IMqttPacketAwaiter where TPacket : MqttBasePacket
     {
-        private readonly TaskCompletionSource<MqttBasePacket> _taskCompletionSource = new TaskCompletionSource<MqttBasePacket>();
+        private readonly TaskCompletionSource<MqttBasePacket> _taskCompletionSource;
         private readonly ushort? _packetIdentifier;
         private readonly MqttPacketDispatcher _owningPacketDispatcher;
-        
+
         public MqttPacketAwaiter(ushort? packetIdentifier, MqttPacketDispatcher owningPacketDispatcher)
         {
             _packetIdentifier = packetIdentifier;
             _owningPacketDispatcher = owningPacketDispatcher ?? throw new ArgumentNullException(nameof(owningPacketDispatcher));
+#if NET452
+            _taskCompletionSource = new TaskCompletionSource<MqttBasePacket>();
+#else
+            _taskCompletionSource = new TaskCompletionSource<MqttBasePacket>(TaskCreationOptions.RunContinuationsAsynchronously);
+#endif
         }
 
         public async Task<TPacket> WaitOneAsync(TimeSpan timeout)
         {
             using (var timeoutToken = new CancellationTokenSource(timeout))
             {
-                timeoutToken.Token.Register(() => _taskCompletionSource.TrySetException(new MqttCommunicationTimedOutException()));
+                timeoutToken.Token.Register(() => Fail(new MqttCommunicationTimedOutException()));
 
                 var packet = await _taskCompletionSource.Task.ConfigureAwait(false);
                 return (TPacket)packet;
@@ -32,29 +38,57 @@ namespace MQTTnet.PacketDispatcher
         public void Complete(MqttBasePacket packet)
         {
             if (packet == null) throw new ArgumentNullException(nameof(packet));
-            
+
+
+#if NET452
             // To prevent deadlocks it is required to call the _TrySetResult_ method
             // from a new thread because the awaiting code will not(!) be executed in
             // a new thread automatically (due to await). Furthermore _this_ thread will
             // do it. But _this_ thread is also reading incoming packets -> deadlock.
+            // NET452 does not support RunContinuationsAsynchronously
             Task.Run(() => _taskCompletionSource.TrySetResult(packet));
+#else
+            _taskCompletionSource.TrySetResult(packet);
+#endif
         }
 
         public void Fail(Exception exception)
         {
             if (exception == null) throw new ArgumentNullException(nameof(exception));
-
+#if NET452
+            // To prevent deadlocks it is required to call the _TrySetResult_ method
+            // from a new thread because the awaiting code will not(!) be executed in
+            // a new thread automatically (due to await). Furthermore _this_ thread will
+            // do it. But _this_ thread is also reading incoming packets -> deadlock.
+            // NET452 does not support RunContinuationsAsynchronously
             Task.Run(() => _taskCompletionSource.TrySetException(exception));
+#else
+            _taskCompletionSource.TrySetException(exception);
+#endif
         }
 
         public void Cancel()
         {
+#if NET452
+            // To prevent deadlocks it is required to call the _TrySetResult_ method
+            // from a new thread because the awaiting code will not(!) be executed in
+            // a new thread automatically (due to await). Furthermore _this_ thread will
+            // do it. But _this_ thread is also reading incoming packets -> deadlock.
+            // NET452 does not support RunContinuationsAsynchronously
             Task.Run(() => _taskCompletionSource.TrySetCanceled());
+#else
+            _taskCompletionSource.TrySetCanceled();
+#endif
         }
 
-        public void Dispose()
+        protected override void Dispose(bool disposing)
         {
-            _owningPacketDispatcher.RemovePacketAwaiter<TPacket>(_packetIdentifier);
+            if (disposing)
+            {
+                _owningPacketDispatcher.RemovePacketAwaiter<TPacket>(_packetIdentifier);
+            }
+
+            base.Dispose(disposing);
         }
     }
 }

Source/MQTTnet/Server/IMqttRetainedMessagesManager.cs

@@ -0,0 +1,21 @@
+using MQTTnet.Diagnostics;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+namespace MQTTnet.Server
+{
+    public interface IMqttRetainedMessagesManager
+    {
+        Task Start(IMqttServerOptions options, IMqttNetLogger logger);
+
+        Task LoadMessagesAsync();
+
+        Task ClearMessagesAsync();
+
+        Task HandleMessageAsync(string clientId, MqttApplicationMessage applicationMessage);
+
+        Task<IList<MqttApplicationMessage>> GetMessagesAsync();
+
+        Task<IList<MqttApplicationMessage>> GetSubscribedMessagesAsync(ICollection<TopicFilter> topicFilters);
+    }
+}

Source/MQTTnet/Server/IMqttServer.cs

@@ -1,11 +1,12 @@
-using System.Collections.Generic;
+using MQTTnet.Server.Status;
+using System.Collections.Generic;
 using System.Threading.Tasks;
-using MQTTnet.Server.Status;
 
 namespace MQTTnet.Server
 {
     public interface IMqttServer : IApplicationMessageReceiver, IApplicationMessagePublisher
     {
+        bool IsStarted { get; }
         IMqttServerStartedHandler StartedHandler { get; set; }
         IMqttServerStoppedHandler StoppedHandler { get; set; }
 
@@ -13,7 +14,7 @@ namespace MQTTnet.Server
         IMqttServerClientDisconnectedHandler ClientDisconnectedHandler { get; set; }
         IMqttServerClientSubscribedTopicHandler ClientSubscribedTopicHandler { get; set; }
         IMqttServerClientUnsubscribedTopicHandler ClientUnsubscribedTopicHandler { get; set; }
-        
+
         IMqttServerOptions Options { get; }
 
         Task<IList<IMqttClientStatus>> GetClientStatusAsync();

Source/MQTTnet/Server/IMqttServerOptions.cs

@@ -15,14 +15,15 @@ namespace MQTTnet.Server
 
         IMqttServerConnectionValidator ConnectionValidator { get; }
         IMqttServerSubscriptionInterceptor SubscriptionInterceptor { get; }
+        IMqttServerUnsubscriptionInterceptor UnsubscriptionInterceptor { get; }
         IMqttServerApplicationMessageInterceptor ApplicationMessageInterceptor { get; }
         IMqttServerClientMessageQueueInterceptor ClientMessageQueueInterceptor { get; }
 
         MqttServerTcpEndpointOptions DefaultEndpointOptions { get; }
         MqttServerTlsTcpEndpointOptions TlsEndpointOptions { get; }
 
-        IMqttServerStorage Storage { get; }       
-        
+        IMqttServerStorage Storage { get; }
 
+        IMqttRetainedMessagesManager RetainedMessagesManager { get; }
     }
 }

Source/MQTTnet/Server/IMqttServerUnsubscriptionInterceptor.cs

@@ -0,0 +1,9 @@
+using System.Threading.Tasks;
+
+namespace MQTTnet.Server
+{
+    public interface IMqttServerUnsubscriptionInterceptor
+    {
+        Task InterceptUnsubscriptionAsync(MqttUnsubscriptionInterceptorContext context);
+    }
+}

Source/MQTTnet/Server/MqttClientConnection.cs

@@ -1,46 +1,51 @@
-using System;
-using System.Collections.Generic;
-using System.Threading;
-using System.Threading.Tasks;
-using MQTTnet.Adapter;
+using MQTTnet.Adapter;
 using MQTTnet.Client;
 using MQTTnet.Diagnostics;
 using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
+using MQTTnet.Implementations;
 using MQTTnet.Internal;
 using MQTTnet.PacketDispatcher;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
 using MQTTnet.Server.Status;
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace MQTTnet.Server
 {
-    public class MqttClientConnection : IDisposable
+    public sealed class MqttClientConnection : IDisposable
     {
-        private readonly MqttPacketIdentifierProvider _packetIdentifierProvider = new MqttPacketIdentifierProvider();
-        private readonly MqttPacketDispatcher _packetDispatcher = new MqttPacketDispatcher();
-        private readonly CancellationTokenSource _cancellationToken = new CancellationTokenSource();
+        readonly MqttPacketIdentifierProvider _packetIdentifierProvider = new MqttPacketIdentifierProvider();
+        readonly MqttPacketDispatcher _packetDispatcher = new MqttPacketDispatcher();
+        readonly CancellationTokenSource _cancellationToken = new CancellationTokenSource();
 
-        private readonly MqttRetainedMessagesManager _retainedMessagesManager;
-        private readonly MqttClientKeepAliveMonitor _keepAliveMonitor;
-        private readonly MqttClientSessionsManager _sessionsManager;
+        readonly IMqttRetainedMessagesManager _retainedMessagesManager;
+        readonly Func<Task> _onStart;
+        readonly Func<MqttClientDisconnectType, Task> _onStop;
+        readonly MqttClientKeepAliveMonitor _keepAliveMonitor;
+        readonly MqttClientSessionsManager _sessionsManager;
 
-        private readonly IMqttNetChildLogger _logger;
-        private readonly IMqttServerOptions _serverOptions;
+        readonly IMqttNetLogger _logger;
+        readonly IMqttServerOptions _serverOptions;
 
-        private readonly IMqttChannelAdapter _channelAdapter;
-        private readonly IMqttDataConverter _dataConverter;
-        private readonly string _endpoint;
-        private readonly DateTime _connectedTimestamp;
+        readonly IMqttChannelAdapter _channelAdapter;
+        readonly IMqttDataConverter _dataConverter;
+        readonly string _endpoint;
+        readonly DateTime _connectedTimestamp;
 
-        private Task<MqttClientDisconnectType> _packageReceiverTask;
-        private DateTime _lastPacketReceivedTimestamp;
-        private DateTime _lastNonKeepAlivePacketReceivedTimestamp;
-        
-        private long _receivedPacketsCount;
-        private long _sentPacketsCount = 1; // Start with 1 because the CONNECT packet is not counted anywhere.
-        private long _receivedApplicationMessagesCount;
-        private long _sentApplicationMessagesCount;
+        volatile Task _packageReceiverTask;
+        DateTime _lastPacketReceivedTimestamp;
+        DateTime _lastNonKeepAlivePacketReceivedTimestamp;
+
+        long _receivedPacketsCount;
+        long _sentPacketsCount = 1; // Start with 1 because the CONNECT packet is not counted anywhere.
+        long _receivedApplicationMessagesCount;
+        long _sentApplicationMessagesCount;
+
+        volatile bool _isTakeover;
 
         public MqttClientConnection(
             MqttConnectPacket connectPacket,
@@ -48,14 +53,18 @@ namespace MQTTnet.Server
             MqttClientSession session,
             IMqttServerOptions serverOptions,
             MqttClientSessionsManager sessionsManager,
-            MqttRetainedMessagesManager retainedMessagesManager,
-            IMqttNetChildLogger logger)
+            IMqttRetainedMessagesManager retainedMessagesManager,
+            Func<Task> onStart,
+            Func<MqttClientDisconnectType, Task> onStop,
+            IMqttNetLogger logger)
         {
             Session = session ?? throw new ArgumentNullException(nameof(session));
             _serverOptions = serverOptions ?? throw new ArgumentNullException(nameof(serverOptions));
             _sessionsManager = sessionsManager ?? throw new ArgumentNullException(nameof(sessionsManager));
             _retainedMessagesManager = retainedMessagesManager ?? throw new ArgumentNullException(nameof(retainedMessagesManager));
-            
+            _onStart = onStart ?? throw new ArgumentNullException(nameof(onStart));
+            _onStop = onStop ?? throw new ArgumentNullException(nameof(onStop));
+
             _channelAdapter = channelAdapter ?? throw new ArgumentNullException(nameof(channelAdapter));
             _dataConverter = _channelAdapter.PacketFormatterAdapter.DataConverter;
             _endpoint = _channelAdapter.Endpoint;
@@ -64,7 +73,7 @@ namespace MQTTnet.Server
             if (logger == null) throw new ArgumentNullException(nameof(logger));
             _logger = logger.CreateChildLogger(nameof(MqttClientConnection));
 
-            _keepAliveMonitor = new MqttClientKeepAliveMonitor(ConnectPacket.ClientId, StopAsync, _logger);
+            _keepAliveMonitor = new MqttClientKeepAliveMonitor(ConnectPacket.ClientId, () => StopAsync(), _logger);
 
             _connectedTimestamp = DateTime.UtcNow;
             _lastPacketReceivedTimestamp = _connectedTimestamp;
@@ -76,16 +85,20 @@ namespace MQTTnet.Server
         public string ClientId => ConnectPacket.ClientId;
 
         public MqttClientSession Session { get; }
-        
-        public async Task StopAsync()
+
+        public Task StopAsync(bool isTakeover = false)
         {
+            _isTakeover = isTakeover;
+            var task = _packageReceiverTask;
+
             StopInternal();
 
-            var task = _packageReceiverTask;
             if (task != null)
             {
-                await task.ConfigureAwait(false);
+                return task;
             }
+
+            return PlatformAbstractionLayer.CompletedTask;
         }
 
         public void ResetStatistics()
@@ -112,25 +125,26 @@ namespace MQTTnet.Server
             status.BytesSent = _channelAdapter.BytesSent;
             status.BytesReceived = _channelAdapter.BytesReceived;
         }
-        
+
         public void Dispose()
         {
             _cancellationToken.Dispose();
         }
 
-        public Task<MqttClientDisconnectType> RunAsync()
+        public Task RunAsync(MqttConnectionValidatorContext connectionValidatorContext)
         {
-            _packageReceiverTask = RunInternalAsync();
+            _packageReceiverTask = RunInternalAsync(connectionValidatorContext);
             return _packageReceiverTask;
         }
 
-        private async Task<MqttClientDisconnectType> RunInternalAsync()
+        async Task RunInternalAsync(MqttConnectionValidatorContext connectionValidatorContext)
         {
             var disconnectType = MqttClientDisconnectType.NotClean;
             try
             {
+                await _onStart();
                 _logger.Info("Client '{0}': Session started.", ClientId);
-                
+
                 _channelAdapter.ReadingPacketStartedCallback = OnAdapterReadingPacketStarted;
                 _channelAdapter.ReadingPacketCompletedCallback = OnAdapterReadingPacketCompleted;
 
@@ -142,12 +156,8 @@ namespace MQTTnet.Server
                 _keepAliveMonitor.Start(ConnectPacket.KeepAlivePeriod, _cancellationToken.Token);
 
                 await SendAsync(
-                    new MqttConnAckPacket
-                    {
-                        ReturnCode = MqttConnectReturnCode.ConnectionAccepted,
-                        ReasonCode = MqttConnectReasonCode.Success,
-                        IsSessionPresent = !Session.IsCleanSession
-                    }).ConfigureAwait(false);
+                    _channelAdapter.PacketFormatterAdapter.DataConverter.CreateConnAckPacket(connectionValidatorContext)
+                    ).ConfigureAwait(false);
 
                 Session.IsCleanSession = false;
 
@@ -236,6 +246,11 @@ namespace MQTTnet.Server
             }
             finally
             {
+                if (_isTakeover)
+                {
+                    disconnectType = MqttClientDisconnectType.Takeover;
+                }
+                
                 if (Session.WillMessage != null)
                 {
                     _sessionsManager.DispatchApplicationMessage(Session.WillMessage, this);
@@ -247,20 +262,27 @@ namespace MQTTnet.Server
                 _channelAdapter.ReadingPacketStartedCallback = null;
                 _channelAdapter.ReadingPacketCompletedCallback = null;
 
-                _logger.Info("Client '{0}': Session stopped.", ClientId);
-                
-                _packageReceiverTask = null;
-            }
+                _logger.Info("Client '{0}': Connection stopped.", ClientId);
 
-            return disconnectType;
+                _packageReceiverTask = null;
+
+                try
+                {
+                    await _onStop(disconnectType);
+                }
+                catch (Exception e)
+                {
+                    _logger.Error(e, "client '{0}': Error while cleaning up", ClientId);
+                }
+            }
         }
 
-        private void StopInternal()
+        void StopInternal()
         {
             _cancellationToken.Cancel(false);
         }
 
-        private async Task EnqueueSubscribedRetainedMessagesAsync(ICollection<TopicFilter> topicFilters)
+        async Task EnqueueSubscribedRetainedMessagesAsync(ICollection<TopicFilter> topicFilters)
         {
             var retainedMessages = await _retainedMessagesManager.GetSubscribedMessagesAsync(topicFilters).ConfigureAwait(false);
             foreach (var applicationMessage in retainedMessages)
@@ -269,7 +291,7 @@ namespace MQTTnet.Server
             }
         }
 
-        private async Task HandleIncomingSubscribePacketAsync(MqttSubscribePacket subscribePacket)
+        async Task HandleIncomingSubscribePacketAsync(MqttSubscribePacket subscribePacket)
         {
             // TODO: Let the channel adapter create the packet.
             var subscribeResult = await Session.SubscriptionsManager.SubscribeAsync(subscribePacket, ConnectPacket).ConfigureAwait(false);
@@ -285,14 +307,14 @@ namespace MQTTnet.Server
             await EnqueueSubscribedRetainedMessagesAsync(subscribePacket.TopicFilters).ConfigureAwait(false);
         }
 
-        private async Task HandleIncomingUnsubscribePacketAsync(MqttUnsubscribePacket unsubscribePacket)
+        async Task HandleIncomingUnsubscribePacketAsync(MqttUnsubscribePacket unsubscribePacket)
         {
             // TODO: Let the channel adapter create the packet.
             var unsubscribeResult = await Session.SubscriptionsManager.UnsubscribeAsync(unsubscribePacket).ConfigureAwait(false);
             await SendAsync(unsubscribeResult).ConfigureAwait(false);
         }
 
-        private Task HandleIncomingPublishPacketAsync(MqttPublishPacket publishPacket)
+        Task HandleIncomingPublishPacketAsync(MqttPublishPacket publishPacket)
         {
             Interlocked.Increment(ref _sentApplicationMessagesCount);
 
@@ -317,16 +339,16 @@ namespace MQTTnet.Server
             }
         }
 
-        private Task HandleIncomingPublishPacketWithQoS0Async(MqttPublishPacket publishPacket)
+        Task HandleIncomingPublishPacketWithQoS0Async(MqttPublishPacket publishPacket)
         {
             var applicationMessage = _dataConverter.CreateApplicationMessage(publishPacket);
 
             _sessionsManager.DispatchApplicationMessage(applicationMessage, this);
 
-            return Task.FromResult(0);
+            return PlatformAbstractionLayer.CompletedTask;
         }
 
-        private Task HandleIncomingPublishPacketWithQoS1Async(MqttPublishPacket publishPacket)
+        Task HandleIncomingPublishPacketWithQoS1Async(MqttPublishPacket publishPacket)
         {
             var applicationMessage = _dataConverter.CreateApplicationMessage(publishPacket);
             _sessionsManager.DispatchApplicationMessage(applicationMessage, this);
@@ -335,7 +357,7 @@ namespace MQTTnet.Server
             return SendAsync(pubAckPacket);
         }
 
-        private Task HandleIncomingPublishPacketWithQoS2Async(MqttPublishPacket publishPacket)
+        Task HandleIncomingPublishPacketWithQoS2Async(MqttPublishPacket publishPacket)
         {
             var applicationMessage = _dataConverter.CreateApplicationMessage(publishPacket);
             _sessionsManager.DispatchApplicationMessage(applicationMessage, this);
@@ -349,7 +371,7 @@ namespace MQTTnet.Server
             return SendAsync(pubRecPacket);
         }
 
-        private async Task SendPendingPacketsAsync(CancellationToken cancellationToken)
+        async Task SendPendingPacketsAsync(CancellationToken cancellationToken)
         {
             MqttQueuedApplicationMessage queuedApplicationMessage = null;
             MqttPublishPacket publishPacket = null;
@@ -426,9 +448,6 @@ namespace MQTTnet.Server
                     }
 
                     _logger.Verbose("Queued application message sent (ClientId: {0}).", ClientId);
-
-                    // TODO:
-                    //Interlocked.Increment(ref _sentPacketsCount);
                 }
             }
             catch (Exception exception)
@@ -441,9 +460,8 @@ namespace MQTTnet.Server
                 {
                     _logger.Warning(exception, "Sending publish packet failed: Communication exception (ClientId: {0}).", ClientId);
                 }
-                else if (exception is OperationCanceledException && _cancellationToken.Token.IsCancellationRequested)
+                else if (exception is OperationCanceledException)
                 {
-                    // The cancellation was triggered externally.
                 }
                 else
                 {
@@ -464,7 +482,7 @@ namespace MQTTnet.Server
             }
         }
 
-        private async Task SendAsync(MqttBasePacket packet)
+        async Task SendAsync(MqttBasePacket packet)
         {
             await _channelAdapter.SendPacketAsync(packet, _serverOptions.DefaultCommunicationTimeout, _cancellationToken.Token).ConfigureAwait(false);
 
@@ -476,12 +494,12 @@ namespace MQTTnet.Server
             }
         }
 
-        private void OnAdapterReadingPacketCompleted()
+        void OnAdapterReadingPacketCompleted()
         {
             _keepAliveMonitor?.Resume();
         }
 
-        private void OnAdapterReadingPacketStarted()
+        void OnAdapterReadingPacketStarted()
         {
             _keepAliveMonitor?.Pause();
         }

Source/MQTTnet/Server/MqttClientKeepAliveMonitor.cs

@@ -1,27 +1,27 @@
-using System;
+using MQTTnet.Diagnostics;
+using MQTTnet.Internal;
+using System;
 using System.Diagnostics;
 using System.Threading;
 using System.Threading.Tasks;
-using MQTTnet.Diagnostics;
-using MQTTnet.Internal;
 
 namespace MQTTnet.Server
 {
     public class MqttClientKeepAliveMonitor
     {
-        private readonly Stopwatch _lastPacketReceivedTracker = new Stopwatch();
+        readonly Stopwatch _lastPacketReceivedTracker = new Stopwatch();
 
-        private readonly string _clientId;
-        private readonly Func<Task> _keepAliveElapsedCallback;
-        private readonly IMqttNetChildLogger _logger;
+        readonly string _clientId;
+        readonly Func<Task> _keepAliveElapsedCallback;
+        readonly IMqttNetLogger _logger;
 
-        private bool _isPaused;
+        bool _isPaused;
 
-        public MqttClientKeepAliveMonitor(string clientId, Func<Task> keepAliveElapsedCallback, IMqttNetChildLogger logger)
+        public MqttClientKeepAliveMonitor(string clientId, Func<Task> keepAliveElapsedCallback, IMqttNetLogger logger)
         {
             _clientId = clientId ?? throw new ArgumentNullException(nameof(clientId));
             _keepAliveElapsedCallback = keepAliveElapsedCallback ?? throw new ArgumentNullException(nameof(keepAliveElapsedCallback));
-            
+
             if (logger == null) throw new ArgumentNullException(nameof(logger));
             _logger = logger.CreateChildLogger(nameof(MqttClientKeepAliveMonitor));
         }
@@ -32,7 +32,7 @@ namespace MQTTnet.Server
             {
                 return;
             }
-            
+
             Task.Run(() => RunAsync(keepAlivePeriod, cancellationToken), cancellationToken).Forget(_logger);
         }
 
@@ -51,7 +51,7 @@ namespace MQTTnet.Server
             _lastPacketReceivedTracker.Restart();
         }
 
-        private async Task RunAsync(int keepAlivePeriod, CancellationToken cancellationToken)
+        async Task RunAsync(int keepAlivePeriod, CancellationToken cancellationToken)
         {
             try
             {

Source/MQTTnet/Server/MqttClientSession.cs

@@ -1,22 +1,23 @@
-using System;
+using MQTTnet.Diagnostics;
+using MQTTnet.Server.Status;
+using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
-using MQTTnet.Diagnostics;
-using MQTTnet.Server.Status;
 
 namespace MQTTnet.Server
 {
     public class MqttClientSession
     {
-        private readonly IMqttNetChildLogger _logger;
+        readonly IMqttNetLogger _logger;
 
-        private readonly DateTime _createdTimestamp = DateTime.UtcNow;
+        readonly DateTime _createdTimestamp = DateTime.UtcNow;
+        readonly IMqttRetainedMessagesManager _retainedMessagesManager;
 
-        public MqttClientSession(string clientId, IDictionary<object, object> items, MqttServerEventDispatcher eventDispatcher, IMqttServerOptions serverOptions, IMqttNetChildLogger logger)
+        public MqttClientSession(string clientId, IDictionary<object, object> items, MqttServerEventDispatcher eventDispatcher, IMqttServerOptions serverOptions, IMqttRetainedMessagesManager retainedMessagesManager, IMqttNetLogger logger)
         {
             ClientId = clientId ?? throw new ArgumentNullException(nameof(clientId));
             Items = items ?? throw new ArgumentNullException(nameof(items));
-
+            _retainedMessagesManager = retainedMessagesManager ?? throw new ArgumentNullException(nameof(retainedMessagesManager));
             SubscriptionsManager = new MqttClientSubscriptionsManager(this, eventDispatcher, serverOptions);
             ApplicationMessagesQueue = new MqttClientSessionApplicationMessagesQueue(serverOptions);
 
@@ -52,11 +53,13 @@ namespace MQTTnet.Server
             ApplicationMessagesQueue.Enqueue(applicationMessage, senderClientId, checkSubscriptionsResult.QualityOfServiceLevel, isRetainedApplicationMessage);
         }
 
-        public async Task SubscribeAsync(ICollection<TopicFilter> topicFilters, MqttRetainedMessagesManager retainedMessagesManager)
+        public async Task SubscribeAsync(ICollection<TopicFilter> topicFilters)
         {
+            if (topicFilters is null) throw new ArgumentNullException(nameof(topicFilters));
+
             await SubscriptionsManager.SubscribeAsync(topicFilters).ConfigureAwait(false);
 
-            var matchingRetainedMessages = await retainedMessagesManager.GetSubscribedMessagesAsync(topicFilters).ConfigureAwait(false);
+            var matchingRetainedMessages = await _retainedMessagesManager.GetSubscribedMessagesAsync(topicFilters).ConfigureAwait(false);
             foreach (var matchingRetainedMessage in matchingRetainedMessages)
             {
                 EnqueueApplicationMessage(matchingRetainedMessage, null, true);
@@ -65,6 +68,8 @@ namespace MQTTnet.Server
 
         public Task UnsubscribeAsync(IEnumerable<string> topicFilters)
         {
+            if (topicFilters is null) throw new ArgumentNullException(nameof(topicFilters));
+
             return SubscriptionsManager.UnsubscribeAsync(topicFilters);
         }
 
@@ -73,6 +78,7 @@ namespace MQTTnet.Server
             status.ClientId = ClientId;
             status.CreatedTimestamp = _createdTimestamp;
             status.PendingApplicationMessagesCount = ApplicationMessagesQueue.Count;
+            status.Items = Items;
         }
     }
 }

Source/MQTTnet/Server/MqttClientSessionApplicationMessagesQueue.cs

@@ -6,7 +6,7 @@ using System.Threading.Tasks;
 
 namespace MQTTnet.Server
 {
-    public class MqttClientSessionApplicationMessagesQueue : IDisposable
+    public class MqttClientSessionApplicationMessagesQueue : Disposable
     {
         private readonly AsyncQueue<MqttQueuedApplicationMessage> _messageQueue = new AsyncQueue<MqttQueuedApplicationMessage>();
         
@@ -71,9 +71,14 @@ namespace MQTTnet.Server
             }
         }
 
-        public void Dispose()
+        protected override void Dispose(bool disposing)
         {
-            _messageQueue.Dispose();
+            if (disposing)
+            {
+                _messageQueue.Dispose();
+            }
+
+            base.Dispose(disposing);
         }
     }
 }

Source/MQTTnet/Server/MqttClientSessionsManager.cs

@@ -1,40 +1,41 @@
-using System;
-using System.Collections.Concurrent;
-using System.Collections.Generic;
-using System.Threading;
-using System.Threading.Tasks;
-using MQTTnet.Adapter;
+using MQTTnet.Adapter;
 using MQTTnet.Diagnostics;
+using MQTTnet.Exceptions;
 using MQTTnet.Formatter;
 using MQTTnet.Internal;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
 using MQTTnet.Server.Status;
+using System;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace MQTTnet.Server
 {
-    public class MqttClientSessionsManager : IDisposable
+    public class MqttClientSessionsManager : Disposable
     {
-        private readonly AsyncQueue<MqttEnqueuedApplicationMessage> _messageQueue = new AsyncQueue<MqttEnqueuedApplicationMessage>();
+        readonly AsyncQueue<MqttEnqueuedApplicationMessage> _messageQueue = new AsyncQueue<MqttEnqueuedApplicationMessage>();
 
-        private readonly SemaphoreSlim _createConnectionGate = new SemaphoreSlim(1, 1);
-        private readonly ConcurrentDictionary<string, MqttClientConnection> _connections = new ConcurrentDictionary<string, MqttClientConnection>();
-        private readonly ConcurrentDictionary<string, MqttClientSession> _sessions = new ConcurrentDictionary<string, MqttClientSession>();
-        private readonly IDictionary<object, object> _serverSessionItems = new ConcurrentDictionary<object, object>();
+        readonly AsyncLock _createConnectionGate = new AsyncLock();
+        readonly ConcurrentDictionary<string, MqttClientConnection> _connections = new ConcurrentDictionary<string, MqttClientConnection>();
+        readonly ConcurrentDictionary<string, MqttClientSession> _sessions = new ConcurrentDictionary<string, MqttClientSession>();
+        readonly IDictionary<object, object> _serverSessionItems = new ConcurrentDictionary<object, object>();
 
-        private readonly CancellationToken _cancellationToken;
-        private readonly MqttServerEventDispatcher _eventDispatcher;
+        readonly CancellationToken _cancellationToken;
+        readonly MqttServerEventDispatcher _eventDispatcher;
 
-        private readonly MqttRetainedMessagesManager _retainedMessagesManager;
-        private readonly IMqttServerOptions _options;
-        private readonly IMqttNetChildLogger _logger;
+        readonly IMqttRetainedMessagesManager _retainedMessagesManager;
+        readonly IMqttServerOptions _options;
+        readonly IMqttNetLogger _logger;
 
         public MqttClientSessionsManager(
             IMqttServerOptions options,
-            MqttRetainedMessagesManager retainedMessagesManager,
+            IMqttRetainedMessagesManager retainedMessagesManager,
             CancellationToken cancellationToken,
             MqttServerEventDispatcher eventDispatcher,
-            IMqttNetChildLogger logger)
+            IMqttNetLogger logger)
         {
             _cancellationToken = cancellationToken;
 
@@ -59,9 +60,11 @@ namespace MQTTnet.Server
             }
         }
 
-        public Task HandleClientAsync(IMqttChannelAdapter clientAdapter)
+        public Task HandleClientConnectionAsync(IMqttChannelAdapter clientAdapter)
         {
-            return HandleClientAsync(clientAdapter, _cancellationToken);
+            if (clientAdapter is null) throw new ArgumentNullException(nameof(clientAdapter));
+
+            return HandleClientConnectionAsync(clientAdapter, _cancellationToken);
         }
 
         public Task<IList<IMqttClientStatus>> GetClientStatusAsync()
@@ -72,7 +75,7 @@ namespace MQTTnet.Server
             {
                 var clientStatus = new MqttClientStatus(connection);
                 connection.FillStatus(clientStatus);
-                
+
                 var sessionStatus = new MqttSessionStatus(connection.Session, this);
                 connection.Session.FillStatus(sessionStatus);
                 clientStatus.Session = sessionStatus;
@@ -91,7 +94,7 @@ namespace MQTTnet.Server
             {
                 var sessionStatus = new MqttSessionStatus(session, this);
                 session.FillStatus(sessionStatus);
-    
+
                 result.Add(sessionStatus);
             }
 
@@ -115,7 +118,7 @@ namespace MQTTnet.Server
                 throw new InvalidOperationException($"Client session '{clientId}' is unknown.");
             }
 
-            return session.SubscribeAsync(topicFilters, _retainedMessagesManager);
+            return session.SubscribeAsync(topicFilters);
         }
 
         public Task UnsubscribeAsync(string clientId, IEnumerable<string> topicFilters)
@@ -145,12 +148,16 @@ namespace MQTTnet.Server
             _logger.Verbose("Session for client '{0}' deleted.", clientId);
         }
 
-        public void Dispose()
+        protected override void Dispose(bool disposing)
         {
-            _messageQueue?.Dispose();
+            if (disposing)
+            {
+                _messageQueue?.Dispose();
+            }
+            base.Dispose(disposing);
         }
 
-        private async Task TryProcessQueuedApplicationMessagesAsync(CancellationToken cancellationToken)
+        async Task TryProcessQueuedApplicationMessagesAsync(CancellationToken cancellationToken)
         {
             while (!cancellationToken.IsCancellationRequested)
             {
@@ -168,7 +175,7 @@ namespace MQTTnet.Server
             }
         }
 
-        private async Task TryProcessNextQueuedApplicationMessageAsync(CancellationToken cancellationToken)
+        async Task TryProcessNextQueuedApplicationMessageAsync(CancellationToken cancellationToken)
         {
             try
             {
@@ -178,6 +185,12 @@ namespace MQTTnet.Server
                 }
 
                 var dequeueResult = await _messageQueue.TryDequeueAsync(cancellationToken).ConfigureAwait(false);
+
+                if (!dequeueResult.IsSuccess)
+                {
+                    return;
+                }
+
                 var queuedApplicationMessage = dequeueResult.Item;
 
                 var sender = queuedApplicationMessage.Sender;
@@ -202,7 +215,7 @@ namespace MQTTnet.Server
                     applicationMessage = interceptorContext.ApplicationMessage;
                 }
 
-                await _eventDispatcher.HandleApplicationMessageReceivedAsync(sender?.ClientId, applicationMessage).ConfigureAwait(false);
+                await _eventDispatcher.SafeNotifyApplicationMessageReceivedAsync(sender?.ClientId, applicationMessage).ConfigureAwait(false);
 
                 if (applicationMessage.Retain)
                 {
@@ -226,22 +239,29 @@ namespace MQTTnet.Server
             }
         }
 
-        private async Task HandleClientAsync(IMqttChannelAdapter channelAdapter, CancellationToken cancellationToken)
+        async Task HandleClientConnectionAsync(IMqttChannelAdapter channelAdapter, CancellationToken cancellationToken)
         {
-            var disconnectType = MqttClientDisconnectType.NotClean;
             string clientId = null;
 
+            MqttConnectPacket connectPacket;
             try
             {
-                var firstPacket = await channelAdapter.ReceivePacketAsync(_options.DefaultCommunicationTimeout, cancellationToken).ConfigureAwait(false);
-                if (!(firstPacket is MqttConnectPacket connectPacket))
+                try
                 {
-                    _logger.Warning(null, "The first packet from client '{0}' was no 'CONNECT' packet [MQTT-3.1.0-1].", channelAdapter.Endpoint);
+                    var firstPacket = await channelAdapter.ReceivePacketAsync(_options.DefaultCommunicationTimeout, cancellationToken).ConfigureAwait(false);
+                    connectPacket = firstPacket as MqttConnectPacket;
+                    if (connectPacket == null)
+                    {
+                        _logger.Warning(null, "The first packet from client '{0}' was no 'CONNECT' packet [MQTT-3.1.0-1].", channelAdapter.Endpoint);
+                        return;
+                    }
+                }
+                catch (MqttCommunicationTimedOutException)
+                {
+                    _logger.Warning(null, "Client '{0}' connected but did not sent a CONNECT packet.", channelAdapter.Endpoint);
                     return;
                 }
 
-                clientId = connectPacket.ClientId;
-
                 var connectionValidatorContext = await ValidateConnectionAsync(connectPacket, channelAdapter).ConfigureAwait(false);
 
                 if (connectionValidatorContext.ReasonCode != MqttConnectReasonCode.Success)
@@ -254,11 +274,17 @@ namespace MQTTnet.Server
                     return;
                 }
 
-                var connection = await CreateConnectionAsync(connectPacket, connectionValidatorContext, channelAdapter).ConfigureAwait(false);
+                clientId = connectPacket.ClientId;
 
-                await _eventDispatcher.HandleClientConnectedAsync(clientId).ConfigureAwait(false);
-                
-                disconnectType = await connection.RunAsync().ConfigureAwait(false);
+                var connection = await CreateClientConnectionAsync(
+                    connectPacket,
+                    connectionValidatorContext,
+                    channelAdapter,
+                    async () => await _eventDispatcher.SafeNotifyClientConnectedAsync(clientId).ConfigureAwait(false),
+                    async disconnectType => await CleanUpClient(clientId, channelAdapter, disconnectType)
+                ).ConfigureAwait(false);
+
+                await connection.RunAsync(connectionValidatorContext).ConfigureAwait(false);
             }
             catch (OperationCanceledException)
             {
@@ -267,28 +293,29 @@ namespace MQTTnet.Server
             {
                 _logger.Error(exception, exception.Message);
             }
-            finally
+        }
+
+        private async Task CleanUpClient(string clientId, IMqttChannelAdapter channelAdapter, MqttClientDisconnectType disconnectType)
+        {
+            if (clientId != null)
             {
-                if (clientId != null)
+                _connections.TryRemove(clientId, out _);
+
+                if (!_options.EnablePersistentSessions)
                 {
-                    _connections.TryRemove(clientId, out _);
-
-                    if (!_options.EnablePersistentSessions)
-                    {
-                        await DeleteSessionAsync(clientId).ConfigureAwait(false);
-                    }
+                    await DeleteSessionAsync(clientId).ConfigureAwait(false);
                 }
+            }
 
-                await TryCleanupChannelAsync(channelAdapter).ConfigureAwait(false);
+            await SafeCleanupChannelAsync(channelAdapter).ConfigureAwait(false);
 
-                if (clientId != null)
-                {
-                    await _eventDispatcher.TryHandleClientDisconnectedAsync(clientId, disconnectType).ConfigureAwait(false);
-                }
+            if (clientId != null)
+            {
+                await _eventDispatcher.SafeNotifyClientDisconnectedAsync(clientId, disconnectType).ConfigureAwait(false);
             }
         }
 
-        private async Task<MqttConnectionValidatorContext> ValidateConnectionAsync(MqttConnectPacket connectPacket, IMqttChannelAdapter channelAdapter)
+        async Task<MqttConnectionValidatorContext> ValidateConnectionAsync(MqttConnectPacket connectPacket, IMqttChannelAdapter channelAdapter)
         {
             var context = new MqttConnectionValidatorContext(connectPacket, channelAdapter, new ConcurrentDictionary<object, object>());
 
@@ -316,25 +343,24 @@ namespace MQTTnet.Server
             return context;
         }
 
-        private async Task<MqttClientConnection> CreateConnectionAsync(MqttConnectPacket connectPacket, MqttConnectionValidatorContext connectionValidatorContext, IMqttChannelAdapter channelAdapter)
+        async Task<MqttClientConnection> CreateClientConnectionAsync(MqttConnectPacket connectPacket, MqttConnectionValidatorContext connectionValidatorContext, IMqttChannelAdapter channelAdapter, Func<Task> onStart, Func<MqttClientDisconnectType, Task> onStop)
         {
-            await _createConnectionGate.WaitAsync(_cancellationToken).ConfigureAwait(false);
-            try
+            using (await _createConnectionGate.WaitAsync(_cancellationToken).ConfigureAwait(false))
             {
                 var isSessionPresent = _sessions.TryGetValue(connectPacket.ClientId, out var session);
 
                 var isConnectionPresent = _connections.TryGetValue(connectPacket.ClientId, out var existingConnection);
                 if (isConnectionPresent)
                 {
-                    await existingConnection.StopAsync().ConfigureAwait(false);
+                    await existingConnection.StopAsync(true).ConfigureAwait(false);
                 }
-                
+
                 if (isSessionPresent)
                 {
                     if (connectPacket.CleanSession)
                     {
                         session = null;
-                        
+
                         _logger.Verbose("Deleting existing session of client '{0}'.", connectPacket.ClientId);
                     }
                     else
@@ -345,24 +371,20 @@ namespace MQTTnet.Server
 
                 if (session == null)
                 {
-                    session = new MqttClientSession(connectPacket.ClientId, connectionValidatorContext.SessionItems, _eventDispatcher, _options, _logger);
+                    session = new MqttClientSession(connectPacket.ClientId, connectionValidatorContext.SessionItems, _eventDispatcher, _options, _retainedMessagesManager, _logger);
                     _logger.Verbose("Created a new session for client '{0}'.", connectPacket.ClientId);
                 }
 
-                var connection = new MqttClientConnection(connectPacket, channelAdapter, session, _options, this, _retainedMessagesManager, _logger);
+                var connection = new MqttClientConnection(connectPacket, channelAdapter, session, _options, this, _retainedMessagesManager, onStart, onStop, _logger);
 
                 _connections[connection.ClientId] = connection;
                 _sessions[session.ClientId] = session;
 
                 return connection;
             }
-            finally
-            {
-                _createConnectionGate.Release();
-            }
         }
 
-        private async Task<MqttApplicationMessageInterceptorContext> InterceptApplicationMessageAsync(MqttClientConnection senderConnection, MqttApplicationMessage applicationMessage)
+        async Task<MqttApplicationMessageInterceptorContext> InterceptApplicationMessageAsync(MqttClientConnection senderConnection, MqttApplicationMessage applicationMessage)
         {
             var interceptor = _options.ApplicationMessageInterceptor;
             if (interceptor == null)
@@ -390,7 +412,7 @@ namespace MQTTnet.Server
             return interceptorContext;
         }
 
-        private async Task TryCleanupChannelAsync(IMqttChannelAdapter channelAdapter)
+        async Task SafeCleanupChannelAsync(IMqttChannelAdapter channelAdapter)
         {
             try
             {

Source/MQTTnet/Server/MqttClientSubscriptionsManager.cs

@@ -1,9 +1,9 @@
-using System;
+using MQTTnet.Packets;
+using MQTTnet.Protocol;
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
-using MQTTnet.Packets;
-using MQTTnet.Protocol;
 
 namespace MQTTnet.Server
 {
@@ -67,7 +67,7 @@ namespace MQTTnet.Server
                         _subscriptions[finalTopicFilter.Topic] = finalTopicFilter;
                     }
 
-                    await _eventDispatcher.HandleClientSubscribedTopicAsync(_clientSession.ClientId, finalTopicFilter).ConfigureAwait(false);
+                    await _eventDispatcher.SafeNotifyClientSubscribedTopicAsync(_clientSession.ClientId, finalTopicFilter).ConfigureAwait(false);
                 }
             }
 
@@ -83,7 +83,7 @@ namespace MQTTnet.Server
                 var interceptorContext = await InterceptSubscribeAsync(topicFilter).ConfigureAwait(false);
                 if (!interceptorContext.AcceptSubscription)
                 {
-                   continue;
+                    continue;
                 }
 
                 if (interceptorContext.AcceptSubscription)
@@ -93,7 +93,7 @@ namespace MQTTnet.Server
                         _subscriptions[topicFilter.Topic] = topicFilter;
                     }
 
-                    await _eventDispatcher.HandleClientSubscribedTopicAsync(_clientSession.ClientId, topicFilter).ConfigureAwait(false);
+                    await _eventDispatcher.SafeNotifyClientSubscribedTopicAsync(_clientSession.ClientId, topicFilter).ConfigureAwait(false);
                 }
             }
         }
@@ -107,9 +107,16 @@ namespace MQTTnet.Server
                 PacketIdentifier = unsubscribePacket.PacketIdentifier
             };
 
-            lock (_subscriptions)
+            foreach (var topicFilter in unsubscribePacket.TopicFilters)
             {
-                foreach (var topicFilter in unsubscribePacket.TopicFilters)
+                var interceptorContext = await InterceptUnsubscribeAsync(topicFilter).ConfigureAwait(false);
+                if (!interceptorContext.AcceptUnsubscription)
+                {
+                    unsubAckPacket.ReasonCodes.Add(MqttUnsubscribeReasonCode.ImplementationSpecificError);
+                    continue;
+                }
+
+                lock (_subscriptions)
                 {
                     if (_subscriptions.Remove(topicFilter))
                     {
@@ -124,25 +131,29 @@ namespace MQTTnet.Server
 
             foreach (var topicFilter in unsubscribePacket.TopicFilters)
             {
-                await _eventDispatcher.HandleClientUnsubscribedTopicAsync(_clientSession.ClientId, topicFilter).ConfigureAwait(false);
+                await _eventDispatcher.SafeNotifyClientUnsubscribedTopicAsync(_clientSession.ClientId, topicFilter).ConfigureAwait(false);
             }
-            
+
             return unsubAckPacket;
         }
 
-        public Task UnsubscribeAsync(IEnumerable<string> topicFilters)
+        public async Task UnsubscribeAsync(IEnumerable<string> topicFilters)
         {
             if (topicFilters == null) throw new ArgumentNullException(nameof(topicFilters));
 
-            lock (_subscriptions)
+            foreach (var topicFilter in topicFilters)
             {
-                foreach (var topicFilter in topicFilters)
+                var interceptorContext = await InterceptUnsubscribeAsync(topicFilter).ConfigureAwait(false);
+                if (!interceptorContext.AcceptUnsubscription)
+                {
+                    continue;
+                }
+
+                lock (_subscriptions)
                 {
                     _subscriptions.Remove(topicFilter);
                 }
             }
-
-            return Task.FromResult(0);
         }
 
         public CheckSubscriptionsResult CheckSubscriptions(string topic, MqttQualityOfServiceLevel qosLevel)
@@ -206,6 +217,17 @@ namespace MQTTnet.Server
             return context;
         }
 
+        private async Task<MqttUnsubscriptionInterceptorContext> InterceptUnsubscribeAsync(string topicFilter)
+        {
+            var context = new MqttUnsubscriptionInterceptorContext(_clientSession.ClientId, topicFilter, _clientSession.Items);
+            if (_serverOptions.UnsubscriptionInterceptor != null)
+            {
+                await _serverOptions.UnsubscriptionInterceptor.InterceptUnsubscriptionAsync(context).ConfigureAwait(false);
+            }
+
+            return context;
+        }
+
         private static CheckSubscriptionsResult CreateSubscriptionResult(MqttQualityOfServiceLevel qosLevel, HashSet<MqttQualityOfServiceLevel> subscribedQoSLevels)
         {
             MqttQualityOfServiceLevel effectiveQoS;

Source/MQTTnet/Server/MqttRetainedMessagesManager.cs

@@ -1,26 +1,28 @@
-using System;
+using MQTTnet.Diagnostics;
+using MQTTnet.Implementations;
+using MQTTnet.Internal;
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
-using MQTTnet.Diagnostics;
-using MQTTnet.Internal;
 
 namespace MQTTnet.Server
 {
-    public class MqttRetainedMessagesManager
+    public class MqttRetainedMessagesManager : IMqttRetainedMessagesManager
     {
         private readonly byte[] _emptyArray = new byte[0];
         private readonly AsyncLock _messagesLock = new AsyncLock();
         private readonly Dictionary<string, MqttApplicationMessage> _messages = new Dictionary<string, MqttApplicationMessage>();
 
-        private readonly IMqttNetChildLogger _logger;
-        private readonly IMqttServerOptions _options;
+        private IMqttNetLogger _logger;
+        private IMqttServerOptions _options;
 
-        public MqttRetainedMessagesManager(IMqttServerOptions options, IMqttNetChildLogger logger)
+        public Task Start(IMqttServerOptions options, IMqttNetLogger logger)
         {
             if (logger == null) throw new ArgumentNullException(nameof(logger));
             _logger = logger.CreateChildLogger(nameof(MqttRetainedMessagesManager));
             _options = options ?? throw new ArgumentNullException(nameof(options));
+            return PlatformAbstractionLayer.CompletedTask;
         }
 
         public async Task LoadMessagesAsync()
@@ -103,7 +105,7 @@ namespace MQTTnet.Server
             }
         }
 
-        public async Task<List<MqttApplicationMessage>> GetSubscribedMessagesAsync(ICollection<TopicFilter> topicFilters)
+        public async Task<IList<MqttApplicationMessage>> GetSubscribedMessagesAsync(ICollection<TopicFilter> topicFilters)
         {
             if (topicFilters == null) throw new ArgumentNullException(nameof(topicFilters));
 
@@ -128,7 +130,7 @@ namespace MQTTnet.Server
                     break;
                 }
             }
-            
+
             return matchingRetainedMessages;
         }
 

Source/MQTTnet/Server/MqttServer.cs

@@ -1,28 +1,29 @@
-using System;
+using MQTTnet.Adapter;
+using MQTTnet.Client.Publishing;
+using MQTTnet.Client.Receiving;
+using MQTTnet.Diagnostics;
+using MQTTnet.Exceptions;
+using MQTTnet.Protocol;
+using MQTTnet.Server.Status;
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
-using MQTTnet.Adapter;
-using MQTTnet.Client.Publishing;
-using MQTTnet.Client.Receiving;
-using MQTTnet.Diagnostics;
-using MQTTnet.Protocol;
-using MQTTnet.Server.Status;
 
 namespace MQTTnet.Server
 {
     public class MqttServer : IMqttServer
     {
-        private readonly MqttServerEventDispatcher _eventDispatcher;
-        private readonly ICollection<IMqttServerAdapter> _adapters;
-        private readonly IMqttNetChildLogger _logger;
+        readonly MqttServerEventDispatcher _eventDispatcher;
+        readonly ICollection<IMqttServerAdapter> _adapters;
+        readonly IMqttNetLogger _logger;
 
-        private MqttClientSessionsManager _clientSessionsManager;
-        private MqttRetainedMessagesManager _retainedMessagesManager;
-        private CancellationTokenSource _cancellationTokenSource;
+        MqttClientSessionsManager _clientSessionsManager;
+        IMqttRetainedMessagesManager _retainedMessagesManager;
+        CancellationTokenSource _cancellationTokenSource;
 
-        public MqttServer(IEnumerable<IMqttServerAdapter> adapters, IMqttNetChildLogger logger)
+        public MqttServer(IEnumerable<IMqttServerAdapter> adapters, IMqttNetLogger logger)
         {
             if (adapters == null) throw new ArgumentNullException(nameof(adapters));
             _adapters = adapters.ToList();
@@ -33,6 +34,8 @@ namespace MQTTnet.Server
             _eventDispatcher = new MqttServerEventDispatcher(logger.CreateChildLogger(nameof(MqttServerEventDispatcher)));
         }
 
+        public bool IsStarted => _cancellationTokenSource != null;
+
         public IMqttServerStartedHandler StartedHandler { get; set; }
 
         public IMqttServerStoppedHandler StoppedHandler { get; set; }
@@ -48,7 +51,7 @@ namespace MQTTnet.Server
             get => _eventDispatcher.ClientDisconnectedHandler;
             set => _eventDispatcher.ClientDisconnectedHandler = value;
         }
-        
+
         public IMqttServerClientSubscribedTopicHandler ClientSubscribedTopicHandler
         {
             get => _eventDispatcher.ClientSubscribedTopicHandler;
@@ -60,7 +63,7 @@ namespace MQTTnet.Server
             get => _eventDispatcher.ClientUnsubscribedTopicHandler;
             set => _eventDispatcher.ClientUnsubscribedTopicHandler = value;
         }
-        
+
         public IMqttApplicationMessageReceivedHandler ApplicationMessageReceivedHandler
         {
             get => _eventDispatcher.ApplicationMessageReceivedHandler;
@@ -117,11 +120,14 @@ namespace MQTTnet.Server
         {
             Options = options ?? throw new ArgumentNullException(nameof(options));
 
+            if (Options.RetainedMessagesManager == null) throw new MqttConfigurationException("options.RetainedMessagesManager should not be null.");
+
             if (_cancellationTokenSource != null) throw new InvalidOperationException("The server is already started.");
 
             _cancellationTokenSource = new CancellationTokenSource();
 
-            _retainedMessagesManager = new MqttRetainedMessagesManager(Options, _logger);
+            _retainedMessagesManager = Options.RetainedMessagesManager;
+            await _retainedMessagesManager.Start(Options, _logger);
             await _retainedMessagesManager.LoadMessagesAsync().ConfigureAwait(false);
 
             _clientSessionsManager = new MqttClientSessionsManager(Options, _retainedMessagesManager, _cancellationTokenSource.Token, _eventDispatcher, _logger);
@@ -150,9 +156,9 @@ namespace MQTTnet.Server
                 {
                     return;
                 }
-                
+
                 await _clientSessionsManager.StopAsync().ConfigureAwait(false);
-                
+
                 _cancellationTokenSource.Cancel(false);
 
                 foreach (var adapter in _adapters)
@@ -186,9 +192,9 @@ namespace MQTTnet.Server
             return _retainedMessagesManager?.ClearMessagesAsync();
         }
 
-        private Task OnHandleClient(IMqttChannelAdapter channelAdapter)
+        Task OnHandleClient(IMqttChannelAdapter channelAdapter)
         {
-            return _clientSessionsManager.HandleClientAsync(channelAdapter);
+            return _clientSessionsManager.HandleClientConnectionAsync(channelAdapter);
         }
     }
 }

Source/MQTTnet/Server/MqttServerEventDispatcher.cs

@@ -1,15 +1,15 @@
-using System;
-using System.Threading.Tasks;
-using MQTTnet.Client.Receiving;
+using MQTTnet.Client.Receiving;
 using MQTTnet.Diagnostics;
+using System;
+using System.Threading.Tasks;
 
 namespace MQTTnet.Server
 {
     public class MqttServerEventDispatcher
     {
-        private readonly IMqttNetChildLogger _logger;
+        readonly IMqttNetLogger _logger;
 
-        public MqttServerEventDispatcher(IMqttNetChildLogger logger)
+        public MqttServerEventDispatcher(IMqttNetLogger logger)
         {
             _logger = logger ?? throw new ArgumentNullException(nameof(logger));
         }
@@ -24,18 +24,25 @@ namespace MQTTnet.Server
 
         public IMqttApplicationMessageReceivedHandler ApplicationMessageReceivedHandler { get; set; }
 
-        public Task HandleClientConnectedAsync(string clientId)
+        public async Task SafeNotifyClientConnectedAsync(string clientId)
         {
-            var handler = ClientConnectedHandler;
-            if (handler == null)
+            try
             {
-                return Task.FromResult(0);
-            }
+                var handler = ClientConnectedHandler;
+                if (handler == null)
+                {
+                    return;
+                }
 
-            return handler.HandleClientConnectedAsync(new MqttServerClientConnectedEventArgs(clientId));
+                await handler.HandleClientConnectedAsync(new MqttServerClientConnectedEventArgs(clientId)).ConfigureAwait(false);
+            }
+            catch (Exception exception)
+            {
+                _logger.Error(exception, "Error while handling custom 'ClientConnected' event.");
+            }
         }
 
-        public async Task TryHandleClientDisconnectedAsync(string clientId, MqttClientDisconnectType disconnectType)
+        public async Task SafeNotifyClientDisconnectedAsync(string clientId, MqttClientDisconnectType disconnectType)
         {
             try
             {
@@ -49,41 +56,62 @@ namespace MQTTnet.Server
             }
             catch (Exception exception)
             {
-                _logger.Error(exception, "Error while handling 'ClientDisconnected' event.");
+                _logger.Error(exception, "Error while handling custom 'ClientDisconnected' event.");
             }
         }
 
-        public Task HandleClientSubscribedTopicAsync(string clientId, TopicFilter topicFilter)
+        public async Task SafeNotifyClientSubscribedTopicAsync(string clientId, TopicFilter topicFilter)
         {
-            var handler = ClientSubscribedTopicHandler;
-            if (handler == null)
+            try
             {
-                return Task.FromResult(0);
-            }
+                var handler = ClientSubscribedTopicHandler;
+                if (handler == null)
+                {
+                    return;
+                }
 
-            return handler.HandleClientSubscribedTopicAsync(new MqttServerClientSubscribedTopicEventArgs(clientId, topicFilter));
+                await handler.HandleClientSubscribedTopicAsync(new MqttServerClientSubscribedTopicEventArgs(clientId, topicFilter)).ConfigureAwait(false);
+            }
+            catch (Exception exception)
+            {
+                _logger.Error(exception, "Error while handling custom 'ClientSubscribedTopic' event.");
+            }
         }
 
-        public Task HandleClientUnsubscribedTopicAsync(string clientId, string topicFilter)
+        public async Task SafeNotifyClientUnsubscribedTopicAsync(string clientId, string topicFilter)
         {
-            var handler = ClientUnsubscribedTopicHandler;
-            if (handler == null)
+            try
             {
-                return Task.FromResult(0);
-            }
+                var handler = ClientUnsubscribedTopicHandler;
+                if (handler == null)
+                {
+                    return;
+                }
 
-            return handler.HandleClientUnsubscribedTopicAsync(new MqttServerClientUnsubscribedTopicEventArgs(clientId, topicFilter));
+                await handler.HandleClientUnsubscribedTopicAsync(new MqttServerClientUnsubscribedTopicEventArgs(clientId, topicFilter)).ConfigureAwait(false);
+            }
+            catch (Exception exception)
+            {
+                _logger.Error(exception, "Error while handling custom 'ClientUnsubscribedTopic' event.");
+            }
         }
 
-        public Task HandleApplicationMessageReceivedAsync(string senderClientId, MqttApplicationMessage applicationMessage)
+        public async Task SafeNotifyApplicationMessageReceivedAsync(string senderClientId, MqttApplicationMessage applicationMessage)
         {
-            var handler = ApplicationMessageReceivedHandler;
-            if (handler == null)
+            try
             {
-                return Task.FromResult(0);
-            }
+                var handler = ApplicationMessageReceivedHandler;
+                if (handler == null)
+                {
+                    return;
+                }
 
-            return handler.HandleApplicationMessageReceivedAsync(new MqttApplicationMessageReceivedEventArgs(senderClientId, applicationMessage));
+                await handler.HandleApplicationMessageReceivedAsync(new MqttApplicationMessageReceivedEventArgs(senderClientId, applicationMessage)).ConfigureAwait(false); ;
+            }
+            catch (Exception exception)
+            {
+                _logger.Error(exception, "Error while handling custom 'ApplicationMessageReceived' event.");
+            }
         }
     }
 }

Source/MQTTnet/Server/MqttServerOptions.cs

@@ -21,11 +21,15 @@ namespace MQTTnet.Server
         public IMqttServerConnectionValidator ConnectionValidator { get; set; }
 
         public IMqttServerApplicationMessageInterceptor ApplicationMessageInterceptor { get; set; }
-        
+
         public IMqttServerClientMessageQueueInterceptor ClientMessageQueueInterceptor { get; set; }
 
         public IMqttServerSubscriptionInterceptor SubscriptionInterceptor { get; set; }
 
+        public IMqttServerUnsubscriptionInterceptor UnsubscriptionInterceptor { get; set; }
+
         public IMqttServerStorage Storage { get; set; }
+
+        public IMqttRetainedMessagesManager RetainedMessagesManager { get; set; } = new MqttRetainedMessagesManager();
     }
 }

Source/MQTTnet/Server/MqttServerOptionsBuilder.cs

@@ -57,7 +57,7 @@ namespace MQTTnet.Server
             _options.DefaultEndpointOptions.IsEnabled = false;
             return this;
         }
-        
+
         public MqttServerOptionsBuilder WithEncryptedEndpoint()
         {
             _options.TlsEndpointOptions.IsEnabled = true;
@@ -118,13 +118,19 @@ namespace MQTTnet.Server
             return this;
         }
 #endif
-        
+
         public MqttServerOptionsBuilder WithStorage(IMqttServerStorage value)
         {
             _options.Storage = value;
             return this;
         }
 
+        public MqttServerOptionsBuilder WithRetainedMessagesManager(IMqttRetainedMessagesManager value)
+        {
+            _options.RetainedMessagesManager = value;
+            return this;
+        }
+
         public MqttServerOptionsBuilder WithConnectionValidator(IMqttServerConnectionValidator value)
         {
             _options.ConnectionValidator = value;
@@ -155,6 +161,12 @@ namespace MQTTnet.Server
             return this;
         }
 
+        public MqttServerOptionsBuilder WithUnsubscriptionInterceptor(IMqttServerUnsubscriptionInterceptor value)
+        {
+            _options.UnsubscriptionInterceptor = value;
+            return this;
+        }
+
         public MqttServerOptionsBuilder WithSubscriptionInterceptor(Action<MqttSubscriptionInterceptorContext> value)
         {
             _options.SubscriptionInterceptor = new MqttServerSubscriptionInterceptorDelegate(value);

Source/MQTTnet/Server/MqttUnsubscriptionInterceptorContext.cs

@@ -0,0 +1,27 @@
+using System.Collections.Generic;
+
+namespace MQTTnet.Server
+{
+    public class MqttUnsubscriptionInterceptorContext
+    {
+        public MqttUnsubscriptionInterceptorContext(string clientId, string topic, IDictionary<object, object> sessionItems)
+        {
+            ClientId = clientId;
+            Topic = topic;
+            SessionItems = sessionItems;
+        }
+
+        public string ClientId { get; }
+
+        public string Topic { get; set; }
+
+        /// <summary>
+        /// Gets or sets a key/value collection that can be used to share data within the scope of this session.
+        /// </summary>
+        public IDictionary<object, object> SessionItems { get; }
+
+        public bool AcceptUnsubscription { get; set; } = true;
+
+        public bool CloseConnection { get; set; }
+    }
+}

Source/MQTTnet/Server/Status/IMqttClientStatus.cs

@@ -1,6 +1,6 @@
-using System;
+using MQTTnet.Formatter;
+using System;
 using System.Threading.Tasks;
-using MQTTnet.Formatter;
 
 namespace MQTTnet.Server.Status
 {
@@ -9,7 +9,7 @@ namespace MQTTnet.Server.Status
         string ClientId { get; }
 
         string Endpoint { get; }
-        
+
         MqttProtocolVersion ProtocolVersion { get; }
 
         DateTime LastPacketReceivedTimestamp { get; }
@@ -29,7 +29,7 @@ namespace MQTTnet.Server.Status
         long BytesSent { get; }
 
         long BytesReceived { get; }
-        
+
         Task DisconnectAsync();
 
         void ResetStatistics();

Source/MQTTnet/Server/Status/IMqttSessionStatus.cs

@@ -1,12 +1,15 @@
-using System.Threading.Tasks;
+using System.Collections.Generic;
+using System.Threading.Tasks;
 
 namespace MQTTnet.Server.Status
 {
     public interface IMqttSessionStatus
     {
-        string ClientId { get; set; }
+        string ClientId { get; }
 
-        long PendingApplicationMessagesCount { get; set; }
+        long PendingApplicationMessagesCount { get; }
+
+        IDictionary<object, object> Items { get; }
 
         Task ClearPendingApplicationMessagesAsync();
 

Source/MQTTnet/Server/Status/MqttClientStatus.cs

@@ -1,16 +1,16 @@
-using System;
+using MQTTnet.Formatter;
+using System;
 using System.Threading.Tasks;
-using MQTTnet.Formatter;
 
 namespace MQTTnet.Server.Status
 {
     public class MqttClientStatus : IMqttClientStatus
     {
-        private readonly MqttClientConnection _connection;
+        readonly MqttClientConnection _connection;
 
         public MqttClientStatus(MqttClientConnection connection)
         {
-            _connection = connection;
+            _connection = connection ?? throw new ArgumentNullException(nameof(connection));
         }
 
         public string ClientId { get; set; }