Fix CI again

[PR] The proj files have been updated to enable SourceLink

.github/workflows/dotnetcore.yml

@@ -1,5 +1,5 @@
 name: SharpCompress
-on: [push]
+on: [push, pull_request]
 
 jobs:
   build:
@@ -12,6 +12,13 @@ jobs:
     - uses: actions/checkout@v1
     - uses: actions/setup-dotnet@v1
       with:
-        dotnet-version: 3.1.100
-    - name: Run the Cake script
-      uses: ecampidoglio/cake-action@master
+        dotnet-version: 3.1.302
+    - run: dotnet run -p build/build.csproj
+    - uses: actions/upload-artifact@v2
+      with:
+        name: ${{ matrix.os }}-sharpcompress.nupkg
+        path: artifacts/*
+    - uses: actions/upload-artifact@v2
+      with:
+        name: ${{ matrix.os }}-sharpcompress.snupkg
+        path: artifacts/*

.gitignore

@@ -17,3 +17,4 @@ tools
 .idea/
 
 .DS_Store
+*.snupkg

README.md

@@ -1,12 +1,9 @@
 # SharpCompress
 
-SharpCompress is a compression library in pure C# for .NET Standard 1.3 and 2.0 that can unrar, un7zip, unzip, untar unbzip2 and ungzip with forward-only reading and file random access APIs. Write support for zip/tar/bzip2/gzip are implemented.
+SharpCompress is a compression library in pure C# for .NET Standard 2.0, 2.1 and NET 4.6 that can unrar, un7zip, unzip, untar unbzip2, ungzip, unlzip with forward-only reading and file random access APIs. Write support for zip/tar/bzip2/gzip/lzip are implemented.
 
 The major feature is support for non-seekable streams so large files can be processed on the fly (i.e. download stream).
 
-AppVeyor Build -
-[![Build status](https://ci.appveyor.com/api/projects/status/voxg971oemmvxh1e/branch/master?svg=true)](https://ci.appveyor.com/project/adamhathcock/sharpcompress/branch/master)
-
 GitHub Actions Build -
 [![GitHubActions](https://github.com/adamhathcock/sharpcompress/workflows/SharpCompress/badge.svg)](https://circleci.com/gh/adamhathcock/sharpcompress)
 

SharpCompress.sln

@@ -13,6 +13,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "SharpCompress", "src\SharpC
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "SharpCompress.Test", "tests\SharpCompress.Test\SharpCompress.Test.csproj", "{F2B1A1EB-0FA6-40D0-8908-E13247C7226F}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "build", "build\build.csproj", "{D4D613CB-5E94-47FB-85BE-B8423D20C545}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -27,6 +29,10 @@ Global
 		{F2B1A1EB-0FA6-40D0-8908-E13247C7226F}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{F2B1A1EB-0FA6-40D0-8908-E13247C7226F}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{F2B1A1EB-0FA6-40D0-8908-E13247C7226F}.Release|Any CPU.Build.0 = Release|Any CPU
+		{D4D613CB-5E94-47FB-85BE-B8423D20C545}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{D4D613CB-5E94-47FB-85BE-B8423D20C545}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{D4D613CB-5E94-47FB-85BE-B8423D20C545}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{D4D613CB-5E94-47FB-85BE-B8423D20C545}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

SharpCompress.sln.DotSettings

@@ -126,4 +126,7 @@
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002EAddAccessorOwnerDeclarationBracesMigration/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002ECSharpPlaceAttributeOnSameLineMigration/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002EMigrateBlankLinesAroundFieldToBlankLinesAroundProperty/@EntryIndexedValue">True</s:Boolean>
-	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002EMigrateThisQualifierSettings/@EntryIndexedValue">True</s:Boolean></wpf:ResourceDictionary>
+	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002EMigrateThisQualifierSettings/@EntryIndexedValue">True</s:Boolean>
+	<s:String x:Key="/Default/Environment/UnitTesting/UnitTestSessionStore/Sessions/=6af8f80e_002D9fdd_002D4223_002D8e02_002D473db916f9b2/@EntryIndexedValue">&lt;SessionState ContinuousTestingIsOn="False" ContinuousTestingMode="0" FrameworkVersion="{x:Null}" IsLocked="False" Name="All tests from Solution" PlatformMonoPreference="{x:Null}" PlatformType="{x:Null}" xmlns="urn:schemas-jetbrains-com:jetbrains-ut-session" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"&gt;
+  &lt;Solution /&gt;
+&lt;/SessionState&gt;</s:String></wpf:ResourceDictionary>

appveyor.yml

@@ -1,20 +0,0 @@
-version: '{build}'
-image: Visual Studio 2019
-
-pull_requests:
-  do_not_increment_build_number: true
-
-branches:
-  only:
-  - master
-
-nuget:
-  disable_publish_on_pr: true
-
-build_script:
-- ps: .\build.ps1
-
-test: off
-
-artifacts:
-- path: src\SharpCompress\bin\Release\*.nupkg

build.cake

@@ -1,89 +0,0 @@
-var target = Argument("target", "Default");
-var tag = Argument("tag", "cake");
-
-Task("Restore")
-  .Does(() =>
-{
-    DotNetCoreRestore(".");
-});
-
-Task("Build")
-  .IsDependentOn("Restore")
-  .Does(() =>
-{
-    if (IsRunningOnWindows())
-    {
-        MSBuild("./sharpcompress.sln", c => 
-        { 
-            c.SetConfiguration("Release")
-            .SetVerbosity(Verbosity.Minimal)
-            .UseToolVersion(MSBuildToolVersion.VS2019);
-        });
-    }
-    else 
-    {
-        var settings = new DotNetCoreBuildSettings
-        {
-            Framework = "netstandard1.3",
-            Configuration = "Release",
-            NoRestore = true
-        };
-
-        DotNetCoreBuild("./src/SharpCompress/SharpCompress.csproj", settings);
-
-        settings.Framework = "netstandard2.0";
-        DotNetCoreBuild("./src/SharpCompress/SharpCompress.csproj", settings);
-
-        settings.Framework = "netstandard2.1";
-        DotNetCoreBuild("./src/SharpCompress/SharpCompress.csproj", settings);
-    }
-});
-
-Task("Test")
-  .IsDependentOn("Build")
-  .Does(() =>
-{
-    var files = GetFiles("tests/**/*.csproj");
-    foreach(var file in files)
-    {
-        var settings = new DotNetCoreTestSettings
-        {
-            Configuration = "Release",
-            Framework = "netcoreapp3.1"
-        };
-        DotNetCoreTest(file.ToString(), settings);
-    }
-});
-
-Task("Pack")
-    .IsDependentOn("Build")
-    .Does(() => 
-{
-    if (IsRunningOnWindows())
-    {
-        MSBuild("src/SharpCompress/SharpCompress.csproj", c => c
-            .SetConfiguration("Release")
-            .SetVerbosity(Verbosity.Minimal)
-            .UseToolVersion(MSBuildToolVersion.VS2019)
-            .WithProperty("NoBuild", "true")
-            .WithTarget("Pack"));
-    } 
-    else 
-    {
-        Information("Skipping Pack as this is not Windows");
-    }
-});
-
-Task("Default")
-    .IsDependentOn("Restore")
-    .IsDependentOn("Build")
-    .IsDependentOn("Test")
-    .IsDependentOn("Pack");
-
- Task("RunTests")
-    .IsDependentOn("Restore")
-    .IsDependentOn("Build")
-    .IsDependentOn("Test");
-
-
-RunTarget(target);

build.ps1

@@ -1,228 +0,0 @@
-##########################################################################
-# This is the Cake bootstrapper script for PowerShell.
-# This file was downloaded from https://github.com/cake-build/resources
-# Feel free to change this file to fit your needs.
-##########################################################################
-
-<#
-
-.SYNOPSIS
-This is a Powershell script to bootstrap a Cake build.
-
-.DESCRIPTION
-This Powershell script will download NuGet if missing, restore NuGet tools (including Cake)
-and execute your Cake build script with the parameters you provide.
-
-.PARAMETER Script
-The build script to execute.
-.PARAMETER Target
-The build script target to run.
-.PARAMETER Configuration
-The build configuration to use.
-.PARAMETER Verbosity
-Specifies the amount of information to be displayed.
-.PARAMETER Experimental
-Tells Cake to use the latest Roslyn release.
-.PARAMETER WhatIf
-Performs a dry run of the build script.
-No tasks will be executed.
-.PARAMETER Mono
-Tells Cake to use the Mono scripting engine.
-.PARAMETER SkipToolPackageRestore
-Skips restoring of packages.
-.PARAMETER ScriptArgs
-Remaining arguments are added here.
-
-.LINK
-http://cakebuild.net
-
-#>
-
-[CmdletBinding()]
-Param(
-    [string]$Script = "build.cake",
-    [string]$Target = "Default",
-    [ValidateSet("Release", "Debug")]
-    [string]$Configuration = "Release",
-    [ValidateSet("Quiet", "Minimal", "Normal", "Verbose", "Diagnostic")]
-    [string]$Verbosity = "Verbose",
-    [switch]$Experimental,
-    [Alias("DryRun","Noop")]
-    [switch]$WhatIf,
-    [switch]$Mono,
-    [switch]$SkipToolPackageRestore,
-    [Parameter(Position=0,Mandatory=$false,ValueFromRemainingArguments=$true)]
-    [string[]]$ScriptArgs
-)
-
-[Reflection.Assembly]::LoadWithPartialName("System.Security") | Out-Null
-function MD5HashFile([string] $filePath)
-{
-    if ([string]::IsNullOrEmpty($filePath) -or !(Test-Path $filePath -PathType Leaf))
-    {
-        return $null
-    }
-
-    [System.IO.Stream] $file = $null;
-    [System.Security.Cryptography.MD5] $md5 = $null;
-    try
-    {
-        $md5 = [System.Security.Cryptography.MD5]::Create()
-        $file = [System.IO.File]::OpenRead($filePath)
-        return [System.BitConverter]::ToString($md5.ComputeHash($file))
-    }
-    finally
-    {
-        if ($file -ne $null)
-        {
-            $file.Dispose()
-        }
-    }
-}
-
-Write-Host "Preparing to run build script..."
-
-if(!$PSScriptRoot){
-    $PSScriptRoot = Split-Path $MyInvocation.MyCommand.Path -Parent
-}
-
-$TOOLS_DIR = Join-Path $PSScriptRoot "tools"
-$ADDINS_DIR = Join-Path $TOOLS_DIR "addins"
-$MODULES_DIR = Join-Path $TOOLS_DIR "modules"
-$NUGET_EXE = Join-Path $TOOLS_DIR "nuget.exe"
-$CAKE_EXE = Join-Path $TOOLS_DIR "Cake/Cake.exe"
-$NUGET_URL = "https://dist.nuget.org/win-x86-commandline/latest/nuget.exe"
-$PACKAGES_CONFIG = Join-Path $TOOLS_DIR "packages.config"
-$PACKAGES_CONFIG_MD5 = Join-Path $TOOLS_DIR "packages.config.md5sum"
-$ADDINS_PACKAGES_CONFIG = Join-Path $ADDINS_DIR "packages.config"
-$MODULES_PACKAGES_CONFIG = Join-Path $MODULES_DIR "packages.config"
-
-# Should we use mono?
-$UseMono = "";
-if($Mono.IsPresent) {
-    Write-Verbose -Message "Using the Mono based scripting engine."
-    $UseMono = "-mono"
-}
-
-# Should we use the new Roslyn?
-$UseExperimental = "";
-if($Experimental.IsPresent -and !($Mono.IsPresent)) {
-    Write-Verbose -Message "Using experimental version of Roslyn."
-    $UseExperimental = "-experimental"
-}
-
-# Is this a dry run?
-$UseDryRun = "";
-if($WhatIf.IsPresent) {
-    $UseDryRun = "-dryrun"
-}
-
-# Make sure tools folder exists
-if ((Test-Path $PSScriptRoot) -and !(Test-Path $TOOLS_DIR)) {
-    Write-Verbose -Message "Creating tools directory..."
-    New-Item -Path $TOOLS_DIR -Type directory | out-null
-}
-
-# Make sure that packages.config exist.
-if (!(Test-Path $PACKAGES_CONFIG)) {
-    Write-Verbose -Message "Downloading packages.config..."
-    try { (New-Object System.Net.WebClient).DownloadFile("http://cakebuild.net/download/bootstrapper/packages", $PACKAGES_CONFIG) } catch {
-        Throw "Could not download packages.config."
-    }
-}
-
-# Try find NuGet.exe in path if not exists
-if (!(Test-Path $NUGET_EXE)) {
-    Write-Verbose -Message "Trying to find nuget.exe in PATH..."
-    $existingPaths = $Env:Path -Split ';' | Where-Object { (![string]::IsNullOrEmpty($_)) -and (Test-Path $_ -PathType Container) }
-    $NUGET_EXE_IN_PATH = Get-ChildItem -Path $existingPaths -Filter "nuget.exe" | Select -First 1
-    if ($NUGET_EXE_IN_PATH -ne $null -and (Test-Path $NUGET_EXE_IN_PATH.FullName)) {
-        Write-Verbose -Message "Found in PATH at $($NUGET_EXE_IN_PATH.FullName)."
-        $NUGET_EXE = $NUGET_EXE_IN_PATH.FullName
-    }
-}
-
-# Try download NuGet.exe if not exists
-if (!(Test-Path $NUGET_EXE)) {
-    Write-Verbose -Message "Downloading NuGet.exe..."
-    try {
-        (New-Object System.Net.WebClient).DownloadFile($NUGET_URL, $NUGET_EXE)
-    } catch {
-        Throw "Could not download NuGet.exe."
-    }
-}
-
-# Save nuget.exe path to environment to be available to child processed
-$ENV:NUGET_EXE = $NUGET_EXE
-
-# Restore tools from NuGet?
-if(-Not $SkipToolPackageRestore.IsPresent) {
-    Push-Location
-    Set-Location $TOOLS_DIR
-
-    # Check for changes in packages.config and remove installed tools if true.
-    [string] $md5Hash = MD5HashFile($PACKAGES_CONFIG)
-    if((!(Test-Path $PACKAGES_CONFIG_MD5)) -Or
-      ($md5Hash -ne (Get-Content $PACKAGES_CONFIG_MD5 ))) {
-        Write-Verbose -Message "Missing or changed package.config hash..."
-        Remove-Item * -Recurse -Exclude packages.config,nuget.exe
-    }
-
-    Write-Verbose -Message "Restoring tools from NuGet..."
-    $NuGetOutput = Invoke-Expression "&`"$NUGET_EXE`" install -ExcludeVersion -OutputDirectory `"$TOOLS_DIR`""
-
-    if ($LASTEXITCODE -ne 0) {
-        Throw "An error occured while restoring NuGet tools."
-    }
-    else
-    {
-        $md5Hash | Out-File $PACKAGES_CONFIG_MD5 -Encoding "ASCII"
-    }
-    Write-Verbose -Message ($NuGetOutput | out-string)
-    
-    Pop-Location
-}
-
-# Restore addins from NuGet
-if (Test-Path $ADDINS_PACKAGES_CONFIG) {
-    Push-Location
-    Set-Location $ADDINS_DIR
-
-    Write-Verbose -Message "Restoring addins from NuGet..."
-    $NuGetOutput = Invoke-Expression "&`"$NUGET_EXE`" install -ExcludeVersion -OutputDirectory `"$ADDINS_DIR`""
-
-    if ($LASTEXITCODE -ne 0) {
-        Throw "An error occured while restoring NuGet addins."
-    }
-
-    Write-Verbose -Message ($NuGetOutput | out-string)
-
-    Pop-Location
-}
-
-# Restore modules from NuGet
-if (Test-Path $MODULES_PACKAGES_CONFIG) {
-    Push-Location
-    Set-Location $MODULES_DIR
-
-    Write-Verbose -Message "Restoring modules from NuGet..."
-    $NuGetOutput = Invoke-Expression "&`"$NUGET_EXE`" install -ExcludeVersion -OutputDirectory `"$MODULES_DIR`""
-
-    if ($LASTEXITCODE -ne 0) {
-        Throw "An error occured while restoring NuGet modules."
-    }
-
-    Write-Verbose -Message ($NuGetOutput | out-string)
-
-    Pop-Location
-}
-
-# Make sure that Cake has been installed.
-if (!(Test-Path $CAKE_EXE)) {
-    Throw "Could not find Cake.exe at $CAKE_EXE"
-}
-
-# Start Cake
-Write-Host "Running build script..."
-Invoke-Expression "& `"$CAKE_EXE`" `"$Script`" -target=`"$Target`" -configuration=`"$Configuration`" -verbosity=`"$Verbosity`" $UseMono $UseDryRun $UseExperimental $ScriptArgs"
-exit $LASTEXITCODE

build.sh

@@ -1,42 +0,0 @@
-#!/usr/bin/env bash
-##########################################################################
-# This is the Cake bootstrapper script for Linux and OS X.
-# This file was downloaded from https://github.com/cake-build/resources
-# Feel free to change this file to fit your needs.
-##########################################################################
-
-# Define directories.
-SCRIPT_DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
-TOOLS_DIR=$SCRIPT_DIR/tools
-CAKE_VERSION=0.27.1
-CAKE_DLL=$TOOLS_DIR/Cake.CoreCLR.$CAKE_VERSION/Cake.dll
-
-# Make sure the tools folder exist.
-if [ ! -d "$TOOLS_DIR" ]; then
-  mkdir "$TOOLS_DIR"
-fi
-
-###########################################################################
-# INSTALL CAKE
-###########################################################################
-
-if [ ! -f "$CAKE_DLL" ]; then
-    curl -Lsfo Cake.CoreCLR.zip "https://www.nuget.org/api/v2/package/Cake.CoreCLR/$CAKE_VERSION" && unzip -q Cake.CoreCLR.zip -d "$TOOLS_DIR/Cake.CoreCLR.$CAKE_VERSION" && rm -f Cake.CoreCLR.zip
-    if [ $? -ne 0 ]; then
-        echo "An error occured while installing Cake."
-        exit 1
-    fi
-fi
-
-# Make sure that Cake has been installed.
-if [ ! -f "$CAKE_DLL" ]; then
-    echo "Could not find Cake.exe at '$CAKE_DLL'."
-    exit 1
-fi
-
-###########################################################################
-# RUN BUILD SCRIPT
-###########################################################################
-
-# Start Cake
-exec dotnet "$CAKE_DLL" "$@"

build/Program.cs

@@ -0,0 +1,76 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Runtime.InteropServices;
+using GlobExpressions;
+using static Bullseye.Targets;
+using static SimpleExec.Command;
+
+class Program
+{
+    private const string Clean = "clean";
+    private const string Build = "build";
+    private const string Test = "test";
+    private const string Publish = "publish";
+    
+    static void Main(string[] args)
+    {
+        Target(Clean,
+            ForEach("**/bin", "**/obj"),
+            dir =>
+            {
+                IEnumerable<string> GetDirectories(string d)
+                {
+                    return Glob.Directories(".", d);
+                }
+
+                void RemoveDirectory(string d)
+                {
+                    if (Directory.Exists(d))
+                    {
+                        Console.WriteLine(d);
+                        Directory.Delete(d, true);
+                    }
+                }
+
+                foreach (var d in GetDirectories(dir))
+                {
+                    RemoveDirectory(d);
+                }
+            });
+
+        Target(Build, ForEach("net46", "netstandard2.0", "netstandard2.1"), 
+               framework =>
+               {
+                    if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows) && framework == "net46")
+                    {
+                        return;
+                    }
+                    Run("dotnet", "build src/SharpCompress/SharpCompress.csproj -c Release");
+                });
+
+        Target(Test, DependsOn(Build), ForEach("netcoreapp3.1"), 
+            framework =>
+            {
+                IEnumerable<string> GetFiles(string d)
+                {
+                    return Glob.Files(".", d);
+                }
+
+                foreach (var file in GetFiles("**/*.Test.csproj"))
+                {
+                    Run("dotnet", $"test {file} -c Release -f {framework}");
+                }
+            });
+        
+        Target(Publish, DependsOn(Test),
+               () =>
+               {
+                   Run("dotnet", "pack src/SharpCompress/SharpCompress.csproj -c Release -o artifacts/");
+               });
+
+        Target("default", DependsOn(Publish), () => Console.WriteLine("Done!"));
+        
+        RunTargetsAndExit(args);
+    }
+}

build/build.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Bullseye" Version="3.3.0" />
+    <PackageReference Include="Glob" Version="1.1.7" />
+    <PackageReference Include="SimpleExec" Version="6.2.0" />
+  </ItemGroup>
+
+</Project>

global.json

@@ -0,0 +1,5 @@
+{
+  "sdk": {
+    "version": "3.1.302"
+  }
+}

src/SharpCompress/Archives/AbstractArchive.cs

@@ -14,11 +14,11 @@ namespace SharpCompress.Archives
         private readonly LazyReadOnlyCollection<TVolume> lazyVolumes;
         private readonly LazyReadOnlyCollection<TEntry> lazyEntries;
 
-        public event EventHandler<ArchiveExtractionEventArgs<IArchiveEntry>> EntryExtractionBegin;
-        public event EventHandler<ArchiveExtractionEventArgs<IArchiveEntry>> EntryExtractionEnd;
+        public event EventHandler<ArchiveExtractionEventArgs<IArchiveEntry>>? EntryExtractionBegin;
+        public event EventHandler<ArchiveExtractionEventArgs<IArchiveEntry>>? EntryExtractionEnd;
 
-        public event EventHandler<CompressedBytesReadEventArgs> CompressedBytesRead;
-        public event EventHandler<FilePartExtractionBeginEventArgs> FilePartExtractionBegin;
+        public event EventHandler<CompressedBytesReadEventArgs>? CompressedBytesRead;
+        public event EventHandler<FilePartExtractionBeginEventArgs>? FilePartExtractionBegin;
 
         protected ReaderOptions ReaderOptions { get; }
 
@@ -48,12 +48,14 @@ namespace SharpCompress.Archives
             lazyEntries = new LazyReadOnlyCollection<TEntry>(LoadEntries(Volumes));
         }
 
+#nullable disable
         internal AbstractArchive(ArchiveType type)
         {
             Type = type;
             lazyVolumes = new LazyReadOnlyCollection<TVolume>(Enumerable.Empty<TVolume>());
             lazyEntries = new LazyReadOnlyCollection<TEntry>(Enumerable.Empty<TEntry>());
         }
+#nullable enable
 
         public ArchiveType Type { get; }
 
@@ -121,21 +123,19 @@ namespace SharpCompress.Archives
 
         void IExtractionListener.FireCompressedBytesRead(long currentPartCompressedBytes, long compressedReadBytes)
         {
-            CompressedBytesRead?.Invoke(this, new CompressedBytesReadEventArgs
-            {
-                CurrentFilePartCompressedBytesRead = currentPartCompressedBytes,
-                CompressedBytesRead = compressedReadBytes
-            });
+            CompressedBytesRead?.Invoke(this, new CompressedBytesReadEventArgs(
+                currentFilePartCompressedBytesRead: currentPartCompressedBytes,
+                compressedBytesRead: compressedReadBytes
+            ));
         }
 
         void IExtractionListener.FireFilePartExtractionBegin(string name, long size, long compressedSize)
         {
-            FilePartExtractionBegin?.Invoke(this, new FilePartExtractionBeginEventArgs
-            {
-                CompressedSize = compressedSize,
-                Size = size,
-                Name = name
-            });
+            FilePartExtractionBegin?.Invoke(this, new FilePartExtractionBeginEventArgs(
+                compressedSize : compressedSize,
+                size           : size,
+                name           : name
+            ));
         }
 
         /// <summary>

src/SharpCompress/Archives/ArchiveFactory.cs

@@ -18,7 +18,7 @@ namespace SharpCompress.Archives
         /// <param name="stream"></param>
         /// <param name="readerOptions"></param>
         /// <returns></returns>
-        public static IArchive Open(Stream stream, ReaderOptions readerOptions = null)
+        public static IArchive Open(Stream stream, ReaderOptions? readerOptions = null)
         {
             stream.CheckNotNull(nameof(stream));
             if (!stream.CanRead || !stream.CanSeek)
@@ -86,7 +86,7 @@ namespace SharpCompress.Archives
         /// </summary>
         /// <param name="filePath"></param>
         /// <param name="options"></param>
-        public static IArchive Open(string filePath, ReaderOptions options = null)
+        public static IArchive Open(string filePath, ReaderOptions? options = null)
         {
             filePath.CheckNotNullOrEmpty(nameof(filePath));
             return Open(new FileInfo(filePath), options);
@@ -97,7 +97,7 @@ namespace SharpCompress.Archives
         /// </summary>
         /// <param name="fileInfo"></param>
         /// <param name="options"></param>
-        public static IArchive Open(FileInfo fileInfo, ReaderOptions options = null)
+        public static IArchive Open(FileInfo fileInfo, ReaderOptions? options = null)
         {
             fileInfo.CheckNotNull(nameof(fileInfo));
             options = options ?? new ReaderOptions { LeaveStreamOpen = false };
@@ -135,7 +135,7 @@ namespace SharpCompress.Archives
         /// Extract to specific directory, retaining filename
         /// </summary>
         public static void WriteToDirectory(string sourceArchive, string destinationDirectory,
-                                            ExtractionOptions options = null)
+                                            ExtractionOptions? options = null)
         {
             using (IArchive archive = Open(sourceArchive))
             {

src/SharpCompress/Archives/GZip/GZipArchive.cs

@@ -18,7 +18,7 @@ namespace SharpCompress.Archives.GZip
         /// </summary>
         /// <param name="filePath"></param>
         /// <param name="readerOptions"></param>
-        public static GZipArchive Open(string filePath, ReaderOptions readerOptions = null)
+        public static GZipArchive Open(string filePath, ReaderOptions? readerOptions = null)
         {
             filePath.CheckNotNullOrEmpty(nameof(filePath));
             return Open(new FileInfo(filePath), readerOptions ?? new ReaderOptions());
@@ -29,7 +29,7 @@ namespace SharpCompress.Archives.GZip
         /// </summary>
         /// <param name="fileInfo"></param>
         /// <param name="readerOptions"></param>
-        public static GZipArchive Open(FileInfo fileInfo, ReaderOptions readerOptions = null)
+        public static GZipArchive Open(FileInfo fileInfo, ReaderOptions? readerOptions = null)
         {
             fileInfo.CheckNotNull(nameof(fileInfo));
             return new GZipArchive(fileInfo, readerOptions ?? new ReaderOptions());
@@ -40,7 +40,7 @@ namespace SharpCompress.Archives.GZip
         /// </summary>
         /// <param name="stream"></param>
         /// <param name="readerOptions"></param>
-        public static GZipArchive Open(Stream stream, ReaderOptions readerOptions = null)
+        public static GZipArchive Open(Stream stream, ReaderOptions? readerOptions = null)
         {
             stream.CheckNotNull(nameof(stream));
             return new GZipArchive(stream, readerOptions ?? new ReaderOptions());

src/SharpCompress/Archives/GZip/GZipArchiveEntry.cs

@@ -15,7 +15,7 @@ namespace SharpCompress.Archives.GZip
         public virtual Stream OpenEntryStream()
         {
             //this is to reset the stream to be read multiple times
-            var part = Parts.Single() as GZipFilePart;
+            var part = (GZipFilePart)Parts.Single();
             if (part.GetRawStream().Position != part.EntryStartPosition)
             {
                 part.GetRawStream().Position = part.EntryStartPosition;

src/SharpCompress/Archives/GZip/GZipWritableArchiveEntry.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.IO;
 using SharpCompress.Common;
@@ -6,7 +8,7 @@ using SharpCompress.IO;
 
 namespace SharpCompress.Archives.GZip
 {
-    internal class GZipWritableArchiveEntry : GZipArchiveEntry, IWritableArchiveEntry
+    internal sealed class GZipWritableArchiveEntry : GZipArchiveEntry, IWritableArchiveEntry
     {
         private readonly bool closeStream;
         private readonly Stream stream;

src/SharpCompress/Archives/IArchiveEntryExtensions.cs

@@ -8,22 +8,17 @@ namespace SharpCompress.Archives
     {
         public static void WriteTo(this IArchiveEntry archiveEntry, Stream streamToWriteTo)
         {
-            if (archiveEntry.Archive.Type == ArchiveType.Rar && archiveEntry.Archive.IsSolid)
-            {
-                throw new InvalidFormatException("Cannot use Archive random access on SOLID Rar files.");
-            }
-
             if (archiveEntry.IsDirectory)
             {
                 throw new ExtractionException("Entry is a file directory and cannot be extracted.");
             }
 
-            var streamListener = archiveEntry.Archive as IArchiveExtractionListener;
+            var streamListener = (IArchiveExtractionListener)archiveEntry.Archive;
             streamListener.EnsureEntriesLoaded();
             streamListener.FireEntryExtractionBegin(archiveEntry);
             streamListener.FireFilePartExtractionBegin(archiveEntry.Key, archiveEntry.Size, archiveEntry.CompressedSize);
             var entryStream = archiveEntry.OpenEntryStream();
-            if (entryStream == null)
+            if (entryStream is null)
             {
                 return;
             }
@@ -41,7 +36,7 @@ namespace SharpCompress.Archives
         /// Extract to specific directory, retaining filename
         /// </summary>
         public static void WriteToDirectory(this IArchiveEntry entry, string destinationDirectory,
-                                            ExtractionOptions options = null)
+                                            ExtractionOptions? options = null)
         {
             ExtractionMethods.WriteEntryToDirectory(entry, destinationDirectory, options,
                                               entry.WriteToFile);
@@ -50,8 +45,9 @@ namespace SharpCompress.Archives
         /// <summary>
         /// Extract to specific file
         /// </summary>
-        public static void WriteToFile(this IArchiveEntry entry, string destinationFileName,
-                                       ExtractionOptions options = null)
+        public static void WriteToFile(this IArchiveEntry entry, 
+                                       string destinationFileName,
+                                       ExtractionOptions? options = null)
         {
             
             ExtractionMethods.WriteEntryToFile(entry, destinationFileName, options,

src/SharpCompress/Archives/IArchiveExtensions.cs

@@ -9,7 +9,7 @@ namespace SharpCompress.Archives
         /// Extract to specific directory, retaining filename
         /// </summary>
         public static void WriteToDirectory(this IArchive archive, string destinationDirectory,
-                                            ExtractionOptions options = null)
+                                            ExtractionOptions? options = null)
         {
             foreach (IArchiveEntry entry in archive.Entries.Where(x => !x.IsDirectory))
             {

src/SharpCompress/Archives/Rar/FileInfoRarFilePart.cs

@@ -3,9 +3,9 @@ using SharpCompress.Common.Rar.Headers;
 
 namespace SharpCompress.Archives.Rar
 {
-    internal class FileInfoRarFilePart : SeekableFilePart
+    internal sealed class FileInfoRarFilePart : SeekableFilePart
     {
-        internal FileInfoRarFilePart(FileInfoRarArchiveVolume volume, string password, MarkHeader mh, FileHeader fh, FileInfo fi)
+        internal FileInfoRarFilePart(FileInfoRarArchiveVolume volume, string? password, MarkHeader mh, FileHeader fh, FileInfo fi)
             : base(mh, fh, volume.Stream, password)
         {
             FileInfo = fi;

src/SharpCompress/Archives/Rar/RarArchive.cs

@@ -65,7 +65,7 @@ namespace SharpCompress.Archives.Rar
         /// </summary>
         /// <param name="filePath"></param>
         /// <param name="options"></param>
-        public static RarArchive Open(string filePath, ReaderOptions options = null)
+        public static RarArchive Open(string filePath, ReaderOptions? options = null)
         {
             filePath.CheckNotNullOrEmpty(nameof(filePath));
             return new RarArchive(new FileInfo(filePath), options ?? new ReaderOptions());
@@ -76,7 +76,7 @@ namespace SharpCompress.Archives.Rar
         /// </summary>
         /// <param name="fileInfo"></param>
         /// <param name="options"></param>
-        public static RarArchive Open(FileInfo fileInfo, ReaderOptions options = null)
+        public static RarArchive Open(FileInfo fileInfo, ReaderOptions? options = null)
         {
             fileInfo.CheckNotNull(nameof(fileInfo));
             return new RarArchive(fileInfo, options ?? new ReaderOptions());
@@ -87,7 +87,7 @@ namespace SharpCompress.Archives.Rar
         /// </summary>
         /// <param name="stream"></param>
         /// <param name="options"></param>
-        public static RarArchive Open(Stream stream, ReaderOptions options = null)
+        public static RarArchive Open(Stream stream, ReaderOptions? options = null)
         {
             stream.CheckNotNull(nameof(stream));
             return Open(stream.AsEnumerable(), options ?? new ReaderOptions());
@@ -98,7 +98,7 @@ namespace SharpCompress.Archives.Rar
         /// </summary>
         /// <param name="streams"></param>
         /// <param name="options"></param>
-        public static RarArchive Open(IEnumerable<Stream> streams, ReaderOptions options = null)
+        public static RarArchive Open(IEnumerable<Stream> streams, ReaderOptions? options = null)
         {
             streams.CheckNotNull(nameof(streams));
             return new RarArchive(streams, options ?? new ReaderOptions());
@@ -121,7 +121,7 @@ namespace SharpCompress.Archives.Rar
             }
         }
         
-        public static bool IsRarFile(Stream stream, ReaderOptions options = null)
+        public static bool IsRarFile(Stream stream, ReaderOptions? options = null)
         {
             try
             {

src/SharpCompress/Archives/Rar/RarArchiveEntry.cs

@@ -57,11 +57,6 @@ namespace SharpCompress.Archives.Rar
 
         public Stream OpenEntryStream()
         {
-            if (archive.IsSolid)
-            {
-                throw new InvalidOperationException("Use ExtractAllEntries to extract SOLID archives.");
-            }
-
             if (IsRarV3)
             {
                 return new RarStream(archive.UnpackV1.Value, FileHeader, new MultiVolumeReadOnlyStream(Parts.Cast<RarFilePart>(), archive));

src/SharpCompress/Archives/Rar/RarArchiveVolumeFactory.cs

@@ -34,20 +34,20 @@ namespace SharpCompress.Archives.Rar
             {
                 yield break; //if file isn't volume then there is no reason to look
             }
-            fileInfo = GetNextFileInfo(ah, part.FileParts.FirstOrDefault() as FileInfoRarFilePart);
+            fileInfo = GetNextFileInfo(ah, part.FileParts.FirstOrDefault() as FileInfoRarFilePart)!;
             //we use fileinfo because rar is dumb and looks at file names rather than archive info for another volume
             while (fileInfo != null && fileInfo.Exists)
             {
                 part = new FileInfoRarArchiveVolume(fileInfo, options);
 
-                fileInfo = GetNextFileInfo(ah, part.FileParts.FirstOrDefault() as FileInfoRarFilePart);
+                fileInfo = GetNextFileInfo(ah, part.FileParts.FirstOrDefault() as FileInfoRarFilePart)!;
                 yield return part;
             }
         }
 
-        private static FileInfo GetNextFileInfo(ArchiveHeader ah, FileInfoRarFilePart currentFilePart)
+        private static FileInfo? GetNextFileInfo(ArchiveHeader ah, FileInfoRarFilePart? currentFilePart)
         {
-            if (currentFilePart == null)
+            if (currentFilePart is null)
             {
                 return null;
             }

src/SharpCompress/Archives/Rar/SeekableFilePart.cs

@@ -7,9 +7,9 @@ namespace SharpCompress.Archives.Rar
     internal class SeekableFilePart : RarFilePart
     {
         private readonly Stream stream;
-        private readonly string password;
+        private readonly string? password;
 
-        internal SeekableFilePart(MarkHeader mh, FileHeader fh, Stream stream, string password)
+        internal SeekableFilePart(MarkHeader mh, FileHeader fh, Stream stream, string? password)
             : base(mh, fh)
         {
             this.stream = stream;
@@ -21,7 +21,7 @@ namespace SharpCompress.Archives.Rar
             stream.Position = FileHeader.DataStartPosition;
             if (FileHeader.R4Salt != null)
             {
-                return new RarCryptoWrapper(stream, password, FileHeader.R4Salt);
+                return new RarCryptoWrapper(stream, password!, FileHeader.R4Salt);
             }
             return stream;
         }

src/SharpCompress/Archives/SevenZip/SevenZipArchive.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
@@ -108,7 +110,7 @@ namespace SharpCompress.Archives.SevenZip
 
         private void LoadFactory(Stream stream)
         {
-            if (database == null)
+            if (database is null)
             {
                 stream.Position = 0;
                 var reader = new ArchiveReader();
@@ -129,12 +131,12 @@ namespace SharpCompress.Archives.SevenZip
             }
         }
 
-        private static readonly byte[] SIGNATURE = {(byte)'7', (byte)'z', 0xBC, 0xAF, 0x27, 0x1C};
+        private static ReadOnlySpan<byte> SIGNATURE => new byte[] {(byte)'7', (byte)'z', 0xBC, 0xAF, 0x27, 0x1C};
 
         private static bool SignatureMatch(Stream stream)
         {
             BinaryReader reader = new BinaryReader(stream);
-            byte[] signatureBytes = reader.ReadBytes(6);
+            ReadOnlySpan<byte> signatureBytes = reader.ReadBytes(6);
             return signatureBytes.SequenceEqual(SIGNATURE);
         }
 
@@ -154,7 +156,7 @@ namespace SharpCompress.Archives.SevenZip
             }
         }
 
-        private class SevenZipReader : AbstractReader<SevenZipEntry, SevenZipVolume>
+        private sealed class SevenZipReader : AbstractReader<SevenZipEntry, SevenZipVolume>
         {
             private readonly SevenZipArchive archive;
             private CFolder currentFolder;
@@ -180,7 +182,7 @@ namespace SharpCompress.Archives.SevenZip
                 foreach (var group in entries.Where(x => !x.IsDirectory).GroupBy(x => x.FilePart.Folder))
                 {
                     currentFolder = group.Key;
-                    if (group.Key == null)
+                    if (group.Key is null)
                     {
                         currentStream = Stream.Null;
                     }

src/SharpCompress/Archives/Tar/TarArchive.cs

@@ -20,7 +20,7 @@ namespace SharpCompress.Archives.Tar
         /// </summary>
         /// <param name="filePath"></param>
         /// <param name="readerOptions"></param>
-        public static TarArchive Open(string filePath, ReaderOptions readerOptions = null)
+        public static TarArchive Open(string filePath, ReaderOptions? readerOptions = null)
         {
             filePath.CheckNotNullOrEmpty(nameof(filePath));
             return Open(new FileInfo(filePath), readerOptions ?? new ReaderOptions());
@@ -31,7 +31,7 @@ namespace SharpCompress.Archives.Tar
         /// </summary>
         /// <param name="fileInfo"></param>
         /// <param name="readerOptions"></param>
-        public static TarArchive Open(FileInfo fileInfo, ReaderOptions readerOptions = null)
+        public static TarArchive Open(FileInfo fileInfo, ReaderOptions? readerOptions = null)
         {
             fileInfo.CheckNotNull(nameof(fileInfo));
             return new TarArchive(fileInfo, readerOptions ?? new ReaderOptions());
@@ -42,7 +42,7 @@ namespace SharpCompress.Archives.Tar
         /// </summary>
         /// <param name="stream"></param>
         /// <param name="readerOptions"></param>
-        public static TarArchive Open(Stream stream, ReaderOptions readerOptions = null)
+        public static TarArchive Open(Stream stream, ReaderOptions? readerOptions = null)
         {
             stream.CheckNotNull(nameof(stream));
             return new TarArchive(stream, readerOptions ?? new ReaderOptions());
@@ -118,8 +118,8 @@ namespace SharpCompress.Archives.Tar
         protected override IEnumerable<TarArchiveEntry> LoadEntries(IEnumerable<TarVolume> volumes)
         {
             Stream stream = volumes.Single().Stream;
-            TarHeader previousHeader = null;
-            foreach (TarHeader header in TarHeaderFactory.ReadHeader(StreamingMode.Seekable, stream, ReaderOptions.ArchiveEncoding))
+            TarHeader? previousHeader = null;
+            foreach (TarHeader? header in TarHeaderFactory.ReadHeader(StreamingMode.Seekable, stream, ReaderOptions.ArchiveEncoding))
             {
                 if (header != null)
                 {

src/SharpCompress/Archives/Tar/TarWritableArchiveEntry.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.IO;
 using SharpCompress.Common;
@@ -6,7 +8,7 @@ using SharpCompress.IO;
 
 namespace SharpCompress.Archives.Tar
 {
-    internal class TarWritableArchiveEntry : TarArchiveEntry, IWritableArchiveEntry
+    internal sealed class TarWritableArchiveEntry : TarArchiveEntry, IWritableArchiveEntry
     {
         private readonly bool closeStream;
         private readonly Stream stream;

src/SharpCompress/Archives/Zip/ZipArchive.cs

@@ -15,7 +15,9 @@ namespace SharpCompress.Archives.Zip
 {
     public class ZipArchive : AbstractWritableArchive<ZipArchiveEntry, ZipVolume>
     {
+#nullable disable
         private readonly SeekableZipHeaderFactory headerFactory;
+#nullable enable
 
         /// <summary>
         /// Gets or sets the compression level applied to files added to the archive,
@@ -28,7 +30,7 @@ namespace SharpCompress.Archives.Zip
         /// </summary>
         /// <param name="filePath"></param>
         /// <param name="readerOptions"></param>
-        public static ZipArchive Open(string filePath, ReaderOptions readerOptions = null)
+        public static ZipArchive Open(string filePath, ReaderOptions? readerOptions = null)
         {
             filePath.CheckNotNullOrEmpty(nameof(filePath));
             return Open(new FileInfo(filePath), readerOptions ?? new ReaderOptions());
@@ -39,7 +41,7 @@ namespace SharpCompress.Archives.Zip
         /// </summary>
         /// <param name="fileInfo"></param>
         /// <param name="readerOptions"></param>
-        public static ZipArchive Open(FileInfo fileInfo, ReaderOptions readerOptions = null)
+        public static ZipArchive Open(FileInfo fileInfo, ReaderOptions? readerOptions = null)
         {
             fileInfo.CheckNotNull(nameof(fileInfo));
             return new ZipArchive(fileInfo, readerOptions ?? new ReaderOptions());
@@ -50,18 +52,18 @@ namespace SharpCompress.Archives.Zip
         /// </summary>
         /// <param name="stream"></param>
         /// <param name="readerOptions"></param>
-        public static ZipArchive Open(Stream stream, ReaderOptions readerOptions = null)
+        public static ZipArchive Open(Stream stream, ReaderOptions? readerOptions = null)
         {
             stream.CheckNotNull(nameof(stream));
             return new ZipArchive(stream, readerOptions ?? new ReaderOptions());
         }
         
-        public static bool IsZipFile(string filePath, string password = null)
+        public static bool IsZipFile(string filePath, string? password = null)
         {
             return IsZipFile(new FileInfo(filePath), password);
         }
 
-        public static bool IsZipFile(FileInfo fileInfo, string password = null)
+        public static bool IsZipFile(FileInfo fileInfo, string? password = null)
         {
             if (!fileInfo.Exists)
             {
@@ -73,14 +75,14 @@ namespace SharpCompress.Archives.Zip
             }
         }
 
-        public static bool IsZipFile(Stream stream, string password = null)
+        public static bool IsZipFile(Stream stream, string? password = null)
         {
             StreamingZipHeaderFactory headerFactory = new StreamingZipHeaderFactory(password, new ArchiveEncoding());
             try
             {
                 ZipHeader header =
                     headerFactory.ReadStreamHeader(stream).FirstOrDefault(x => x.ZipHeaderType != ZipHeaderType.Split);
-                if (header == null)
+                if (header is null)
                 {
                     return false;
                 }
@@ -147,13 +149,13 @@ namespace SharpCompress.Archives.Zip
                             {
                                 yield return new ZipArchiveEntry(this,
                                                                  new SeekableZipFilePart(headerFactory,
-                                                                                         h as DirectoryEntryHeader,
+                                                                                         (DirectoryEntryHeader)h,
                                                                                          stream));
                             }
                             break;
                         case ZipHeaderType.DirectoryEnd:
                             {
-                                byte[] bytes = (h as DirectoryEndHeader).Comment;
+                                byte[] bytes = ((DirectoryEndHeader)h).Comment ?? Array.Empty<byte>();
                                 volume.Comment = ReaderOptions.ArchiveEncoding.Decode(bytes);
                                 yield break;
                             }

src/SharpCompress/Archives/Zip/ZipArchiveEntry.cs

@@ -6,7 +6,7 @@ namespace SharpCompress.Archives.Zip
 {
     public class ZipArchiveEntry : ZipEntry, IArchiveEntry
     {
-        internal ZipArchiveEntry(ZipArchive archive, SeekableZipFilePart part)
+        internal ZipArchiveEntry(ZipArchive archive, SeekableZipFilePart? part)
             : base(part)
         {
             Archive = archive;
@@ -25,6 +25,6 @@ namespace SharpCompress.Archives.Zip
 
         #endregion
 
-        public string Comment => (Parts.Single() as SeekableZipFilePart).Comment;
+        public string? Comment => ((SeekableZipFilePart)Parts.Single()).Comment;
     }
 }

src/SharpCompress/Common/ArchiveEncoding.cs

@@ -18,24 +18,30 @@ namespace SharpCompress.Common
         /// <summary>
         /// Set this encoding when you want to force it for all encoding operations.
         /// </summary>
-        public Encoding Forced { get; set; }
+        public Encoding? Forced { get; set; }
 
         /// <summary>
         /// Set this when you want to use a custom method for all decoding operations.
         /// </summary>
         /// <returns>string Func(bytes, index, length)</returns>
-        public Func<byte[], int, int, string> CustomDecoder { get; set; }
+        public Func<byte[], int, int, string>? CustomDecoder { get; set; }
 
         public ArchiveEncoding()
+        : this(Encoding.Default, Encoding.Default)
         {
-            Default = Encoding.GetEncoding(437);
-            Password = Encoding.GetEncoding(437);
+        }
+        public ArchiveEncoding(Encoding def, Encoding password)
+        {
+            Default = def;
+            Password = password;
         }
 
+#if NETSTANDARD1_3 || NETSTANDARD2_0 || NETSTANDARD2_1
         static ArchiveEncoding()
         {
             Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
         }
+#endif
 
         public string Decode(byte[] bytes)
         {

src/SharpCompress/Common/CompressedBytesReadEventArgs.cs

@@ -2,16 +2,22 @@
 
 namespace SharpCompress.Common
 {
-    public class CompressedBytesReadEventArgs : EventArgs
+    public sealed class CompressedBytesReadEventArgs : EventArgs
     {
+        public CompressedBytesReadEventArgs(long compressedBytesRead, long currentFilePartCompressedBytesRead)
+        {
+            CompressedBytesRead = compressedBytesRead;
+            CurrentFilePartCompressedBytesRead = currentFilePartCompressedBytesRead;
+        }
+
         /// <summary>
         /// Compressed bytes read for the current entry
         /// </summary>
-        public long CompressedBytesRead { get; internal set; }
+        public long CompressedBytesRead { get; }
 
         /// <summary>
         /// Current file part read for Multipart files (e.g. Rar)
         /// </summary>
-        public long CurrentFilePartCompressedBytesRead { get; internal set; }
+        public long CurrentFilePartCompressedBytesRead { get; }
     }
 }

src/SharpCompress/Common/Entry.cs

@@ -18,7 +18,7 @@ namespace SharpCompress.Common
         /// <summary>
         /// The target of a symlink entry internal to the Archive. Will be null if not a symlink.
         /// </summary>
-        public abstract string LinkTarget { get; }
+        public abstract string? LinkTarget { get; }
 
         /// <summary>
         /// The compressed file size
@@ -71,12 +71,10 @@ namespace SharpCompress.Common
         public abstract bool IsSplitAfter { get; }
 
         /// <inheritdoc/>
-        public override string ToString()
-        {
-            return Key;
-        }
+        public override string ToString() => Key;
 
         internal abstract IEnumerable<FilePart> Parts { get; }
+
         internal bool IsSolid { get; set; }
 
         internal virtual void Close()

src/SharpCompress/Common/ExtractionMethods.cs

@@ -8,17 +8,19 @@ namespace SharpCompress.Common
         /// <summary>
         /// Extract to specific directory, retaining filename
         /// </summary>
-        public static void WriteEntryToDirectory(IEntry entry, string destinationDirectory,
-                                                 ExtractionOptions options, Action<string, ExtractionOptions> write)
+        public static void WriteEntryToDirectory(IEntry entry, 
+                                                 string destinationDirectory,
+                                                 ExtractionOptions? options, 
+                                                 Action<string, ExtractionOptions?> write)
         {
             string destinationFileName;
             string file = Path.GetFileName(entry.Key);
             string fullDestinationDirectoryPath = Path.GetFullPath(destinationDirectory);
 
-            options = options ?? new ExtractionOptions()
-                                 {
-                                     Overwrite = true
-                                 };
+            options ??= new ExtractionOptions()
+                        {
+                            Overwrite = true
+                        };
 
             if (options.ExtractFullPath)
             {
@@ -61,12 +63,12 @@ namespace SharpCompress.Common
         }
         
         public static void WriteEntryToFile(IEntry entry, string destinationFileName,
-                                            ExtractionOptions options,
+                                            ExtractionOptions? options,
                                             Action<string, FileMode> openAndWrite)
         {
             if (entry.LinkTarget != null)
             {
-                if (null == options.WriteSymbolicLink)
+                if (options?.WriteSymbolicLink is null)
                 {
                     throw new ExtractionException("Entry is a symbolic link but ExtractionOptions.WriteSymbolicLink delegate is null");
                 }
@@ -75,10 +77,10 @@ namespace SharpCompress.Common
             else
             {
                 FileMode fm = FileMode.Create;
-                options = options ?? new ExtractionOptions()
-                                     {
-                                         Overwrite = true
-                                     };
+                options ??= new ExtractionOptions()
+                                {
+                                    Overwrite = true
+                                };
 
                 if (!options.Overwrite)
                 {

src/SharpCompress/Common/ExtractionOptions.cs

@@ -1,4 +1,6 @@
-namespace SharpCompress.Common
+using System;
+
+namespace SharpCompress.Common
 {
     public class ExtractionOptions
     {
@@ -29,6 +31,10 @@
         /// </summary>
         public delegate void SymbolicLinkWriterDelegate(string sourcePath, string targetPath);
 
-        public SymbolicLinkWriterDelegate WriteSymbolicLink;
+        public SymbolicLinkWriterDelegate WriteSymbolicLink =
+            (sourcePath, targetPath) =>
+            {
+                Console.WriteLine($"Could not write symlink {sourcePath} -> {targetPath}, for more information please see https://github.com/dotnet/runtime/issues/24271");
+            };
     }
 }

src/SharpCompress/Common/FilePart.cs

@@ -14,7 +14,7 @@ namespace SharpCompress.Common
         internal abstract string FilePartName { get; }
 
         internal abstract Stream GetCompressedStream();
-        internal abstract Stream GetRawStream();
+        internal abstract Stream? GetRawStream();
         internal bool Skipped { get; set; }
     }
 }

src/SharpCompress/Common/FilePartExtractionBeginEventArgs.cs

@@ -2,21 +2,28 @@
 
 namespace SharpCompress.Common
 {
-    public class FilePartExtractionBeginEventArgs : EventArgs
+    public sealed class FilePartExtractionBeginEventArgs : EventArgs
     {
+        public FilePartExtractionBeginEventArgs(string name, long size, long compressedSize)
+        {
+            Name = name;
+            Size = size;
+            CompressedSize = compressedSize;
+        }
+
         /// <summary>
         /// File name for the part for the current entry
         /// </summary>
-        public string Name { get; internal set; }
+        public string Name { get; }
 
         /// <summary>
         /// Uncompressed size of the current entry in the part
         /// </summary>
-        public long Size { get; internal set; }
+        public long Size { get; }
 
         /// <summary>
         /// Compressed size of the current entry in the part
         /// </summary>
-        public long CompressedSize { get; internal set; }
+        public long CompressedSize { get; }
     }
 }

src/SharpCompress/Common/GZip/GZipEntry.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
-using System.Text;
 
 namespace SharpCompress.Common.GZip
 {
@@ -20,7 +19,7 @@ namespace SharpCompress.Common.GZip
 
         public override string Key => _filePart.FilePartName;
 
-        public override string LinkTarget => null;
+        public override string? LinkTarget => null;
 
         public override long CompressedSize => 0;
 

src/SharpCompress/Common/GZip/GZipFilePart.cs

@@ -10,11 +10,11 @@ namespace SharpCompress.Common.GZip
 {
     internal class GZipFilePart : FilePart
     {
-        private string _name;
+        private string? _name;
         private readonly Stream _stream;
 
         internal GZipFilePart(Stream stream, ArchiveEncoding archiveEncoding)
-        : base(archiveEncoding)
+            : base(archiveEncoding)
         {
             ReadAndValidateGzipHeader(stream);
             EntryStartPosition = stream.Position;
@@ -25,7 +25,7 @@ namespace SharpCompress.Common.GZip
 
         internal DateTime? DateModified { get; private set; }
 
-        internal override string FilePartName => _name;
+        internal override string FilePartName => _name!;
 
         internal override Stream GetCompressedStream()
         {

src/SharpCompress/Common/IEntry.Extensions.cs

@@ -1,5 +1,4 @@
 using System.IO;
-using SharpCompress.Readers;
 
 namespace SharpCompress.Common
 {

src/SharpCompress/Common/IEntry.cs

@@ -10,7 +10,7 @@ namespace SharpCompress.Common
         long Crc { get; }
         DateTime? CreatedTime { get; }
         string Key { get; }
-        string LinkTarget { get; }
+        string? LinkTarget { get; }
         bool IsDirectory { get; }
         bool IsEncrypted { get; }
         bool IsSplitAfter { get; }

src/SharpCompress/Common/Rar/Headers/AVHeader.cs

@@ -7,8 +7,10 @@ namespace SharpCompress.Common.Rar.Headers
         public AvHeader(RarHeader header, RarCrcBinaryReader reader) 
             : base(header, reader, HeaderType.Av) 
         {
-            if (IsRar5) 
+            if (IsRar5)
+            {
                 throw new InvalidFormatException("unexpected rar5 record");
+            }
         }
 
         protected override void ReadFinish(MarkingBinaryReader reader)

src/SharpCompress/Common/Rar/Headers/ArchiveCryptHeader.cs

@@ -1,4 +1,6 @@
-using SharpCompress.IO;
+#nullable disable
+
+using SharpCompress.IO;
 
 namespace SharpCompress.Common.Rar.Headers
 {

src/SharpCompress/Common/Rar/Headers/ArchiveHeader.cs

@@ -2,7 +2,7 @@ using SharpCompress.IO;
 
 namespace SharpCompress.Common.Rar.Headers
 {
-    internal class ArchiveHeader : RarHeader
+    internal sealed class ArchiveHeader : RarHeader
     {
         public ArchiveHeader(RarHeader header, RarCrcBinaryReader reader) 
             : base(header, reader, HeaderType.Archive) 
@@ -38,7 +38,11 @@ namespace SharpCompress.Common.Rar.Headers
         private void ReadLocator(MarkingBinaryReader reader) {
             var size = reader.ReadRarVIntUInt16();
             var type = reader.ReadRarVIntUInt16();
-            if (type != 1) throw new InvalidFormatException("expected locator record");
+            if (type != 1)
+            {
+                throw new InvalidFormatException("expected locator record");
+            }
+
             var flags = reader.ReadRarVIntUInt16();
             const ushort hasQuickOpenOffset = 0x01;
             const ushort hasRecoveryOffset = 0x02;
@@ -74,7 +78,7 @@ namespace SharpCompress.Common.Rar.Headers
         public bool IsVolume => HasFlag(IsRar5 ? ArchiveFlagsV5.VOLUME : ArchiveFlagsV4.VOLUME);
 
         // RAR5: Volume number field is present. True for all volumes except first.
-        public bool IsFirstVolume => IsRar5 ? VolumeNumber == null : HasFlag(ArchiveFlagsV4.FIRST_VOLUME);
+        public bool IsFirstVolume => IsRar5 ? VolumeNumber is null : HasFlag(ArchiveFlagsV4.FIRST_VOLUME);
 
         public bool IsSolid => HasFlag(IsRar5 ? ArchiveFlagsV5.SOLID : ArchiveFlagsV4.SOLID);
     }

src/SharpCompress/Common/Rar/Headers/CommentHeader.cs

@@ -7,7 +7,10 @@ namespace SharpCompress.Common.Rar.Headers
         protected CommentHeader(RarHeader header, RarCrcBinaryReader reader)
             : base(header, reader, HeaderType.Comment) 
         { 
-            if (IsRar5) throw new InvalidFormatException("unexpected rar5 record");
+            if (IsRar5)
+            {
+                throw new InvalidFormatException("unexpected rar5 record");
+            }
         }
 
         protected override void ReadFinish(MarkingBinaryReader reader)

src/SharpCompress/Common/Rar/Headers/FileHeader.cs

@@ -1,3 +1,5 @@
+#nullable disable
+
 #if !Rar2017_64bit
 using nint = System.Int32;
 using nuint = System.UInt32;

src/SharpCompress/Common/Rar/Headers/MarkHeader.cs

@@ -46,19 +46,38 @@ namespace SharpCompress.Common.Rar.Headers
                         if (b == 0x61) 
                         {
                             b = GetByte(stream); start++;
-                            if (b != 0x72) continue;
+                            if (b != 0x72)
+                            {
+                                continue;
+                            }
+
                             b = GetByte(stream); start++;
-                            if (b != 0x21) continue;
+                            if (b != 0x21)
+                            {
+                                continue;
+                            }
+
                             b = GetByte(stream); start++;
-                            if (b != 0x1a) continue;
+                            if (b != 0x1a)
+                            {
+                                continue;
+                            }
+
                             b = GetByte(stream); start++;
-                            if (b != 0x07) continue;
+                            if (b != 0x07)
+                            {
+                                continue;
+                            }
 
                             b = GetByte(stream); start++;
                             if (b == 1) 
                             {
                                 b = GetByte(stream); start++;
-                                if (b != 0) continue;
+                                if (b != 0)
+                                {
+                                    continue;
+                                }
+
                                 return new MarkHeader(true); // Rar5
                             } 
                             else if (b == 0) 
@@ -69,9 +88,17 @@ namespace SharpCompress.Common.Rar.Headers
                         else if (b == 0x45) 
                         {
                             b = GetByte(stream); start++;
-                            if (b != 0x7e) continue;
+                            if (b != 0x7e)
+                            {
+                                continue;
+                            }
+
                             b = GetByte(stream); start++;
-                            if (b != 0x5e) continue;
+                            if (b != 0x5e)
+                            {
+                                continue;
+                            }
+
                             throw new InvalidFormatException("Rar format version pre-4 is unsupported.");
                         } 
                     } 

src/SharpCompress/Common/Rar/Headers/ProtectHeader.cs

@@ -3,12 +3,15 @@
 namespace SharpCompress.Common.Rar.Headers
 {
     // ProtectHeader is part of the Recovery Record feature
-    internal class ProtectHeader : RarHeader
+    internal sealed class ProtectHeader : RarHeader
     {
         public ProtectHeader(RarHeader header, RarCrcBinaryReader reader) 
             : base(header, reader, HeaderType.Protect) 
         {
-            if (IsRar5) throw new InvalidFormatException("unexpected rar5 record");
+            if (IsRar5)
+            {
+                throw new InvalidFormatException("unexpected rar5 record");
+            }
         }
 
         protected override void ReadFinish(MarkingBinaryReader reader)
@@ -23,6 +26,6 @@ namespace SharpCompress.Common.Rar.Headers
         internal byte Version { get; private set; }
         internal ushort RecSectors { get; private set; }
         internal uint TotalBlocks { get; private set; }
-        internal byte[] Mark { get; private set; }
+        internal byte[]? Mark { get; private set; }
     }
 }

src/SharpCompress/Common/Rar/Headers/RarHeader.cs

@@ -11,7 +11,7 @@ namespace SharpCompress.Common.Rar.Headers
         private readonly HeaderType _headerType;
         private readonly bool _isRar5;
 
-        internal static RarHeader TryReadBase(RarCrcBinaryReader reader, bool isRar5, ArchiveEncoding archiveEncoding)
+        internal static RarHeader? TryReadBase(RarCrcBinaryReader reader, bool isRar5, ArchiveEncoding archiveEncoding)
         {
             try
             {

src/SharpCompress/Common/Rar/Headers/RarHeaderFactory.cs

@@ -1,4 +1,3 @@
-using System;
 using System.Collections.Generic;
 using System.IO;
 using SharpCompress.IO;
@@ -26,7 +25,7 @@ namespace SharpCompress.Common.Rar.Headers
             _isRar5 = markHeader.IsRar5;
             yield return markHeader;
 
-            RarHeader header;
+            RarHeader? header;
             while ((header = TryReadNextHeader(stream)) != null)
             {
                 yield return header;
@@ -39,7 +38,7 @@ namespace SharpCompress.Common.Rar.Headers
             }
         }
 
-        private RarHeader TryReadNextHeader(Stream stream)
+        private RarHeader? TryReadNextHeader(Stream stream)
         {
             RarCrcBinaryReader reader;
             if (!IsEncrypted) 
@@ -48,7 +47,7 @@ namespace SharpCompress.Common.Rar.Headers
             } 
             else 
             {
-                if (Options.Password == null)
+                if (Options.Password is null)
                 {
                     throw new CryptographicException("Encrypted Rar archive has no password specified.");
                 }
@@ -56,7 +55,7 @@ namespace SharpCompress.Common.Rar.Headers
             }
 
             var header = RarHeader.TryReadBase(reader, _isRar5, Options.ArchiveEncoding);
-            if (header == null)
+            if (header is null)
             {
                 return null;
             }
@@ -128,13 +127,13 @@ namespace SharpCompress.Common.Rar.Headers
                             case StreamingMode.Streaming:
                                 {
                                     var ms = new ReadOnlySubStream(reader.BaseStream, fh.CompressedSize);
-                                    if (fh.R4Salt == null)
+                                    if (fh.R4Salt is null)
                                     {
                                         fh.PackedStream = ms;
                                     }
                                     else
                                     {
-                                        fh.PackedStream = new RarCryptoWrapper(ms, Options.Password, fh.R4Salt);
+                                        fh.PackedStream = new RarCryptoWrapper(ms, Options.Password!, fh.R4Salt);
                                     }
                                 }
                                 break;

src/SharpCompress/Common/Rar/Headers/SignHeader.cs

@@ -7,7 +7,10 @@ namespace SharpCompress.Common.Rar.Headers
         protected SignHeader(RarHeader header, RarCrcBinaryReader reader)
             : base(header, reader, HeaderType.Sign) 
         { 
-            if (IsRar5) throw new InvalidFormatException("unexpected rar5 record");
+            if (IsRar5)
+            {
+                throw new InvalidFormatException("unexpected rar5 record");
+            }
         }
 
         protected override void ReadFinish(MarkingBinaryReader reader)

src/SharpCompress/Common/Rar/RarCryptoBinaryReader.cs

@@ -3,7 +3,7 @@ using System.IO;
 
 namespace SharpCompress.Common.Rar
 {
-    internal class RarCryptoBinaryReader : RarCrcBinaryReader
+    internal sealed class RarCryptoBinaryReader : RarCrcBinaryReader
     {
         private RarRijndael _rijndael;
         private byte[] _salt;
@@ -19,7 +19,9 @@ namespace SharpCompress.Common.Rar
             // coderb: not sure why this was being done at this logical point
             //SkipQueue();
             byte[] salt = ReadBytes(8);
-            InitializeAes(salt);
+
+            _salt = salt;
+            _rijndael = RarRijndael.InitializeFrom(_password, salt);
         }
 
         // track read count ourselves rather than using the underlying stream since we buffer
@@ -39,12 +41,6 @@ namespace SharpCompress.Common.Rar
 
         private bool UseEncryption => _salt != null;
 
-        internal void InitializeAes(byte[] salt)
-        {
-            _salt = salt;
-            _rijndael = RarRijndael.InitializeFrom(_password, salt);
-        }
-
         public override byte ReadByte()
         {
             if (UseEncryption)
@@ -81,7 +77,9 @@ namespace SharpCompress.Common.Rar
                     byte[] cipherText = ReadBytesNoCrc(16);
                     var readBytes = _rijndael.ProcessBlock(cipherText);
                     foreach (var readByte in readBytes)
+                    {
                         _data.Enqueue(readByte);
+                    }
                 }
             }
 

src/SharpCompress/Common/Rar/RarCryptoWrapper.cs

@@ -4,7 +4,7 @@ using System.IO;
 
 namespace SharpCompress.Common.Rar
 {
-    internal class RarCryptoWrapper : Stream
+    internal sealed class RarCryptoWrapper : Stream
     {
         private readonly Stream _actualStream;
         private readonly byte[] _salt;
@@ -35,7 +35,7 @@ namespace SharpCompress.Common.Rar
 
         public override int Read(byte[] buffer, int offset, int count)
         {
-            if (_salt == null)
+            if (_salt is null)
             {
                 return _actualStream.Read(buffer, offset, count);
             }
@@ -58,12 +58,15 @@ namespace SharpCompress.Common.Rar
 
                     var readBytes = _rijndael.ProcessBlock(cipherText);
                     foreach (var readByte in readBytes)
+                    {
                         _data.Enqueue(readByte);
-
+                    }
                 }
 
                 for (int i = 0; i < count; i++)
+                {
                     buffer[offset + i] = _data.Dequeue();
+                }
             }
             return count;
         }
@@ -88,7 +91,7 @@ namespace SharpCompress.Common.Rar
             if (_rijndael != null)
             {
                 _rijndael.Dispose();
-                _rijndael = null;
+                _rijndael = null!;
             }
             base.Dispose(disposing);
         }

src/SharpCompress/Common/Rar/RarEntry.cs

@@ -22,7 +22,7 @@ namespace SharpCompress.Common.Rar
         /// </summary>
         public override string Key => FileHeader.FileName;
 
-        public override string LinkTarget => null;
+        public override string? LinkTarget => null;
 
         /// <summary>
         /// The entry last modified time in the archive, if recorded

src/SharpCompress/Common/Rar/RarFilePart.cs

@@ -19,7 +19,7 @@ namespace SharpCompress.Common.Rar
 
         internal FileHeader FileHeader { get; }
 
-        internal override Stream GetRawStream()
+        internal override Stream? GetRawStream()
         {
             return null;
         }

src/SharpCompress/Common/Rar/RarRijndael.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Security.Cryptography;
 using System.Text;
 using SharpCompress.Crypto;

src/SharpCompress/Common/Rar/RarVolume.cs

@@ -21,7 +21,9 @@ namespace SharpCompress.Common.Rar
             _headerFactory = new RarHeaderFactory(mode, options);
         }
 
+#nullable disable
         internal ArchiveHeader ArchiveHeader { get; private set; }
+#nullable enable
 
         internal StreamingMode Mode => _headerFactory.StreamingMode;
 
@@ -31,25 +33,25 @@ namespace SharpCompress.Common.Rar
 
         internal IEnumerable<RarFilePart> GetVolumeFileParts()
         {
-            MarkHeader lastMarkHeader = null;
+            MarkHeader? lastMarkHeader = null;
             foreach (var header in _headerFactory.ReadHeaders(Stream))
             {
                 switch (header.HeaderType)
                 {
                     case HeaderType.Mark:
                     {
-                        lastMarkHeader = header as MarkHeader;
+                        lastMarkHeader = (MarkHeader)header;
                     }
                         break;
                     case HeaderType.Archive:
                     {
-                        ArchiveHeader = header as ArchiveHeader;
+                        ArchiveHeader = (ArchiveHeader)header;
                     }
                         break;
                     case HeaderType.File:
                     {
-                        var fh = header as FileHeader;
-                        yield return CreateFilePart(lastMarkHeader, fh);
+                        var fh = (FileHeader)header;
+                        yield return CreateFilePart(lastMarkHeader!, fh);
                     }
                         break;
                 }
@@ -58,7 +60,7 @@ namespace SharpCompress.Common.Rar
 
         private void EnsureArchiveHeaderLoaded()
         {
-            if (ArchiveHeader == null)
+            if (ArchiveHeader is null)
             {
                 if (Mode == StreamingMode.Streaming)
                 {

src/SharpCompress/Common/ReaderExtractionEventArgs.cs

@@ -3,15 +3,16 @@ using SharpCompress.Readers;
 
 namespace SharpCompress.Common
 {
-    public class ReaderExtractionEventArgs<T> : EventArgs
+    public sealed class ReaderExtractionEventArgs<T> : EventArgs
     {
-        internal ReaderExtractionEventArgs(T entry, ReaderProgress readerProgress = null)
+        internal ReaderExtractionEventArgs(T entry, ReaderProgress? readerProgress = null)
         {
             Item = entry;
             ReaderProgress = readerProgress;
         }
 
         public T Item { get; }
-        public ReaderProgress ReaderProgress { get; }
+
+        public ReaderProgress? ReaderProgress { get; }
     }
 }

src/SharpCompress/Common/SevenZip/ArchiveDatabase.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.IO;
 using SharpCompress.Compressors.LZMA;
@@ -35,7 +37,7 @@ namespace SharpCompress.Common.SevenZip
             _packSizes.Clear();
             _packCrCs.Clear();
             _folders.Clear();
-            _numUnpackStreamsVector = null;
+            _numUnpackStreamsVector = null!;
             _files.Clear();
 
             _packStreamStartPositions.Clear();
@@ -96,7 +98,7 @@ namespace SharpCompress.Common.SevenZip
 
                         _folderStartFileIndex.Add(i); // check it
 
-                        if (_numUnpackStreamsVector[folderIndex] != 0)
+                        if (_numUnpackStreamsVector![folderIndex] != 0)
                         {
                             break;
                         }
@@ -114,7 +116,7 @@ namespace SharpCompress.Common.SevenZip
 
                 indexInFolder++;
 
-                if (indexInFolder >= _numUnpackStreamsVector[folderIndex])
+                if (indexInFolder >= _numUnpackStreamsVector![folderIndex])
                 {
                     folderIndex++;
                     indexInFolder = 0;

src/SharpCompress/Common/SevenZip/ArchiveReader.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
@@ -465,7 +467,7 @@ namespace SharpCompress.Common.SevenZip
                     SkipData();
                 }
 
-                if (packCrCs == null)
+                if (packCrCs is null)
                 {
                     packCrCs = new List<uint?>(numPackStreams);
                     for (int i = 0; i < numPackStreams; i++)
@@ -611,7 +613,7 @@ namespace SharpCompress.Common.SevenZip
                     SkipData();
                 }
 
-                if (numUnpackStreamsInFolders == null)
+                if (numUnpackStreamsInFolders is null)
                 {
                     numUnpackStreamsInFolders = new List<int>(folders.Count);
                     for (int i = 0; i < folders.Count; i++)
@@ -703,7 +705,7 @@ namespace SharpCompress.Common.SevenZip
                     }
                     else if (type == BlockType.End)
                     {
-                        if (digests == null)
+                        if (digests is null)
                         {
                             digests = new List<uint?>(numDigestsTotal);
                             for (int i = 0; i < numDigestsTotal; i++)
@@ -1487,17 +1489,12 @@ namespace SharpCompress.Common.SevenZip
 
         public void Extract(ArchiveDatabase db, int[] indices)
         {
-            int numItems;
-            bool allFilesMode = (indices == null);
-            if (allFilesMode)
-            {
-                numItems = db._files.Count;
-            }
-            else
-            {
-                numItems = indices.Length;
-            }
+            bool allFilesMode = (indices is null);
 
+            int numItems = allFilesMode
+                ? db._files.Count
+                : indices.Length;
+            
             if (numItems == 0)
             {
                 return;

src/SharpCompress/Common/SevenZip/CCoderInfo.cs

@@ -1,4 +1,6 @@
-namespace SharpCompress.Common.SevenZip
+#nullable disable
+
+namespace SharpCompress.Common.SevenZip
 {
     internal class CCoderInfo
     {

src/SharpCompress/Common/SevenZip/CFileItem.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 
 namespace SharpCompress.Common.SevenZip
 {

src/SharpCompress/Common/SevenZip/SevenZipEntry.cs

@@ -18,7 +18,7 @@ namespace SharpCompress.Common.SevenZip
 
         public override string Key => FilePart.Header.Name;
 
-        public override string LinkTarget => null;
+        public override string? LinkTarget => null;
 
         public override long CompressedSize => 0;
 
@@ -38,7 +38,7 @@ namespace SharpCompress.Common.SevenZip
 
         public override bool IsSplitAfter => false;
 
-        public override int? Attrib => (int)FilePart.Header.Attrib;
+        public override int? Attrib => FilePart.Header.Attrib.HasValue ? (int?)FilePart.Header.Attrib.Value : null;
 
         internal override IEnumerable<FilePart> Parts => FilePart.AsEnumerable<FilePart>();
     }

src/SharpCompress/Common/SevenZip/SevenZipFilePart.cs

@@ -25,12 +25,12 @@ namespace SharpCompress.Common.SevenZip
         }
 
         internal CFileItem Header { get; }
-        internal CFolder Folder { get; }
+        internal CFolder? Folder { get; }
         internal int Index { get; }
 
         internal override string FilePartName => Header.Name;
 
-        internal override Stream GetRawStream()
+        internal override Stream? GetRawStream()
         {
             return null;
         }
@@ -39,11 +39,11 @@ namespace SharpCompress.Common.SevenZip
         {
             if (!Header.HasStream)
             {
-                return null;
+                return null!;
             }
-            var folderStream = _database.GetFolderStream(_stream, Folder, _database.PasswordProvider);
+            var folderStream = _database.GetFolderStream(_stream, Folder!, _database.PasswordProvider);
 
-            int firstFileIndex = _database._folderStartFileIndex[_database._folders.IndexOf(Folder)];
+            int firstFileIndex = _database._folderStartFileIndex[_database._folders.IndexOf(Folder!)];
             int skipCount = Index - firstFileIndex;
             long skipSize = 0;
             for (int i = 0; i < skipCount; i++)
@@ -61,7 +61,7 @@ namespace SharpCompress.Common.SevenZip
         {
             get
             {
-                if (_type == null)
+                if (_type is null)
                 {
                     _type = GetCompression();
                 }
@@ -82,7 +82,7 @@ namespace SharpCompress.Common.SevenZip
 
         internal CompressionType GetCompression()
         {
-            var coder = Folder._coders.First();
+            var coder = Folder!._coders.First();
             switch (coder._methodId._id)
             {                
                 case K_LZMA:

src/SharpCompress/Common/SevenZip/SevenZipVolume.cs

@@ -1,5 +1,4 @@
 using System.IO;
-using SharpCompress.Archives;
 using SharpCompress.Readers;
 
 namespace SharpCompress.Common.SevenZip

src/SharpCompress/Common/Tar/Headers/TarHeader.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Buffers.Binary;
 using System.IO;
 using System.Text;
@@ -196,7 +198,7 @@ namespace SharpCompress.Common.Tar.Headers
         {
             name.CopyTo(buffer);
             int i = Math.Min(length, name.Length);
-            buffer.Slice(i, length - i).Fill(0);
+            buffer.Slice(i, length - i).Clear();
         }
 
         private static void WriteStringBytes(string name, byte[] buffer, int offset, int length)

src/SharpCompress/Common/Tar/TarEntry.cs

@@ -1,9 +1,10 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.IO;
 using SharpCompress.Common.Tar.Headers;
 using SharpCompress.IO;
-using System.Text;
 
 namespace SharpCompress.Common.Tar
 {

src/SharpCompress/Common/Tar/TarFilePart.cs

@@ -4,7 +4,7 @@ using SharpCompress.IO;
 
 namespace SharpCompress.Common.Tar
 {
-    internal class TarFilePart : FilePart
+    internal sealed class TarFilePart : FilePart
     {
         private readonly Stream _seekableStream;
 
@@ -23,13 +23,13 @@ namespace SharpCompress.Common.Tar
         {
             if (_seekableStream != null)
             {
-                _seekableStream.Position = Header.DataStartPosition.Value;
-                return new ReadOnlySubStream(_seekableStream, Header.Size);
+                _seekableStream.Position = Header.DataStartPosition!.Value;
+                return new TarReadOnlySubStream(_seekableStream, Header.Size);
             }
             return Header.PackedStream;
         }
 
-        internal override Stream GetRawStream()
+        internal override Stream? GetRawStream()
         {
             return null;
         }

src/SharpCompress/Common/Tar/TarHeaderFactory.cs

@@ -2,17 +2,16 @@
 using System.IO;
 using SharpCompress.Common.Tar.Headers;
 using SharpCompress.IO;
-using System.Text;
 
 namespace SharpCompress.Common.Tar
 {
     internal static class TarHeaderFactory
     {
-        internal static IEnumerable<TarHeader> ReadHeader(StreamingMode mode, Stream stream, ArchiveEncoding archiveEncoding)
+        internal static IEnumerable<TarHeader?> ReadHeader(StreamingMode mode, Stream stream, ArchiveEncoding archiveEncoding)
         {
             while (true)
             {
-                TarHeader header = null;
+                TarHeader? header = null;
                 try
                 {
                     BinaryReader reader = new BinaryReader(stream);

src/SharpCompress/Common/Tar/TarReadOnlySubStream.cs

@@ -20,22 +20,24 @@ namespace SharpCompress.Common.Tar
             {
                 return;
             }
+
             _isDisposed = true;
+
             if (disposing)
             {
-                long skipBytes = _amountRead % 512;
-                if (skipBytes == 0)
+                // Ensure we read all remaining blocks for this entry.
+                Stream.Skip(BytesLeftToRead);
+                _amountRead += BytesLeftToRead;
+
+                // If the last block wasn't a full 512 bytes, skip the remaining padding bytes.
+                var bytesInLastBlock = _amountRead % 512;
+
+                if (bytesInLastBlock != 0)
                 {
-                    return;
+                    Stream.Skip(512 - bytesInLastBlock);
                 }
-                skipBytes = 512 - skipBytes;
-                if (skipBytes == 0)
-                {
-                    return;
-                }
-                var buffer = new byte[skipBytes];
-                Stream.ReadFully(buffer);
             }
+
             base.Dispose(disposing);
         }
 

src/SharpCompress/Common/Zip/Headers/DirectoryEndHeader.cs

@@ -33,7 +33,7 @@ namespace SharpCompress.Common.Zip.Headers
 
         public ushort CommentLength { get; private set; }
 
-        public byte[] Comment { get; private set; }
+        public byte[]? Comment { get; private set; }
 
         public ushort TotalNumberOfEntries { get; private set; }
 

src/SharpCompress/Common/Zip/Headers/DirectoryEntryHeader.cs

@@ -1,6 +1,5 @@
 using System.IO;
 using System.Linq;
-using System.Text;
 
 namespace SharpCompress.Common.Zip.Headers
 {
@@ -93,6 +92,6 @@ namespace SharpCompress.Common.Zip.Headers
 
         public ushort DiskNumberStart { get; set; }
 
-        public string Comment { get; private set; }
+        public string? Comment { get; private set; }
     }
 }

src/SharpCompress/Common/Zip/Headers/IgnoreHeader.cs

@@ -1,5 +1,4 @@
-using System;
-using System.IO;
+using System.IO;
 
 namespace SharpCompress.Common.Zip.Headers
 {

src/SharpCompress/Common/Zip/Headers/LocalEntryHeader.cs

@@ -1,6 +1,5 @@
 using System.IO;
 using System.Linq;
-using System.Text;
 
 namespace SharpCompress.Common.Zip.Headers
 {

src/SharpCompress/Common/Zip/Headers/LocalEntryHeaderExtraFactory.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Buffers.Binary;
 using System.Text;
 

src/SharpCompress/Common/Zip/Headers/Zip64DirectoryEndHeader.cs

@@ -1,5 +1,4 @@
-using System;
-using System.IO;
+using System.IO;
 
 namespace SharpCompress.Common.Zip.Headers
 {
@@ -44,6 +43,6 @@ namespace SharpCompress.Common.Zip.Headers
 
         public long DirectoryStartOffsetRelativeToDisk { get; private set; }
 
-        public byte[] DataSector { get; private set; }
+        public byte[]? DataSector { get; private set; }
     }
 }

src/SharpCompress/Common/Zip/Headers/ZipFileEntry.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Buffers.Binary;
 using System.Collections.Generic;
 using System.IO;
@@ -52,7 +54,7 @@ namespace SharpCompress.Common.Zip.Headers
 
         internal PkwareTraditionalEncryptionData ComposeEncryptionData(Stream archiveStream)
         {
-            if (archiveStream == null)
+            if (archiveStream is null)
             {
                 throw new ArgumentNullException(nameof(archiveStream));
             }
@@ -60,7 +62,7 @@ namespace SharpCompress.Common.Zip.Headers
             var buffer = new byte[12];
             archiveStream.ReadFully(buffer);
 
-            PkwareTraditionalEncryptionData encryptionData = PkwareTraditionalEncryptionData.ForRead(Password, this, buffer);
+            PkwareTraditionalEncryptionData encryptionData = PkwareTraditionalEncryptionData.ForRead(Password!, this, buffer);
 
             return encryptionData;
         }

src/SharpCompress/Common/Zip/PkwareTraditionalCryptoStream.cs

@@ -40,7 +40,7 @@ namespace SharpCompress.Common.Zip
                 throw new NotSupportedException("This stream does not encrypt via Read()");
             }
 
-            if (buffer == null)
+            if (buffer is null)
             {
                 throw new ArgumentNullException(nameof(buffer));
             }
@@ -64,7 +64,7 @@ namespace SharpCompress.Common.Zip
                 return;
             }
 
-            byte[] plaintext = null;
+            byte[] plaintext;
             if (offset != 0)
             {
                 plaintext = new byte[count];

src/SharpCompress/Common/Zip/PkwareTraditionalEncryptionData.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Text;
 using SharpCompress.Common.Zip.Headers;
 using SharpCompress.Compressors.Deflate;
 
@@ -65,9 +64,9 @@ namespace SharpCompress.Common.Zip
 
         public byte[] Encrypt(byte[] plainText, int length)
         {
-            if (plainText == null)
+            if (plainText is null)
             {
-                throw new ArgumentNullException("plaintext");
+                throw new ArgumentNullException(nameof(plainText));
             }
 
             if (length > plainText.Length)

src/SharpCompress/Common/Zip/SeekableZipFilePart.cs

@@ -27,25 +27,25 @@ namespace SharpCompress.Common.Zip
             return base.GetCompressedStream();
         }
 
-        internal string Comment => (Header as DirectoryEntryHeader).Comment;
+        internal string? Comment => ((DirectoryEntryHeader)Header).Comment;
 
         private void LoadLocalHeader()
         {
             bool hasData = Header.HasData;
-            Header = _headerFactory.GetLocalHeader(BaseStream, Header as DirectoryEntryHeader);
+            Header = _headerFactory.GetLocalHeader(BaseStream, ((DirectoryEntryHeader)Header));
             Header.HasData = hasData;
         }
 
         protected override Stream CreateBaseStream()
         {
-            BaseStream.Position = Header.DataStartPosition.Value;
+            BaseStream.Position = Header.DataStartPosition!.Value;
 
             if ((Header.CompressedSize == 0)
                 && FlagUtility.HasFlag(Header.Flags, HeaderFlags.UsePostDataDescriptor)
                 && (_directoryEntryHeader?.HasData == true)
                 && (_directoryEntryHeader?.CompressedSize != 0))
             {
-                return new ReadOnlySubStream(BaseStream, _directoryEntryHeader.CompressedSize);
+                return new ReadOnlySubStream(BaseStream, _directoryEntryHeader!.CompressedSize);
             }
 
             return BaseStream;

src/SharpCompress/Common/Zip/SeekableZipHeaderFactory.cs

@@ -3,16 +3,15 @@ using System.Collections.Generic;
 using System.IO;
 using SharpCompress.Common.Zip.Headers;
 using SharpCompress.IO;
-using System.Text;
 
 namespace SharpCompress.Common.Zip
 {
-    internal class SeekableZipHeaderFactory : ZipHeaderFactory
+    internal sealed class SeekableZipHeaderFactory : ZipHeaderFactory
     {
         private const int MAX_ITERATIONS_FOR_DIRECTORY_HEADER = 4096;
         private bool _zip64;
 
-        internal SeekableZipHeaderFactory(string password, ArchiveEncoding archiveEncoding)
+        internal SeekableZipHeaderFactory(string? password, ArchiveEncoding archiveEncoding)
             : base(StreamingMode.Seekable, password, archiveEncoding)
         {
         }
@@ -35,7 +34,9 @@ namespace SharpCompress.Common.Zip
                 stream.Seek(zip64Locator.RelativeOffsetOfTheEndOfDirectoryRecord, SeekOrigin.Begin);
                 uint zip64Signature = reader.ReadUInt32();
                 if (zip64Signature != ZIP64_END_OF_CENTRAL_DIRECTORY)
+                {
                     throw new ArchiveException("Failed to locate the Zip64 Header");
+                }
 
                 var zip64Entry = new Zip64DirectoryEndHeader();
                 zip64Entry.Read(reader);
@@ -54,8 +55,10 @@ namespace SharpCompress.Common.Zip
                 var nextHeader = ReadHeader(signature, reader, _zip64);
                 position = stream.Position;
 
-                if (nextHeader == null)
+                if (nextHeader is null)
+                {
                     yield break;
+                }
 
                 if (nextHeader is DirectoryEntryHeader entryHeader)
                 {
@@ -99,7 +102,7 @@ namespace SharpCompress.Common.Zip
             BinaryReader reader = new BinaryReader(stream);
             uint signature = reader.ReadUInt32();
             var localEntryHeader = ReadHeader(signature, reader, _zip64) as LocalEntryHeader;
-            if (localEntryHeader == null)
+            if (localEntryHeader is null)
             {
                 throw new InvalidOperationException();
             }

src/SharpCompress/Common/Zip/StreamingZipFilePart.cs

@@ -5,9 +5,9 @@ using SharpCompress.IO;
 
 namespace SharpCompress.Common.Zip
 {
-    internal class StreamingZipFilePart : ZipFilePart
+    internal sealed class StreamingZipFilePart : ZipFilePart
     {
-        private Stream _decompressionStream;
+        private Stream? _decompressionStream;
 
         internal StreamingZipFilePart(ZipFileEntry header, Stream stream)
             : base(header, stream)
@@ -41,14 +41,11 @@ namespace SharpCompress.Common.Zip
             }
             if (Header.HasData && !Skipped)
             {
-                if (_decompressionStream == null)
-                {
-                    _decompressionStream = GetCompressedStream();
-                }
+                _decompressionStream ??= GetCompressedStream();
+                
                 _decompressionStream.Skip();
 
-                DeflateStream deflateStream = _decompressionStream as DeflateStream;
-                if (deflateStream != null)
+                if (_decompressionStream is DeflateStream deflateStream)
                 {
                     rewindableStream.Rewind(deflateStream.InputBuffer);
                 }

src/SharpCompress/Common/Zip/StreamingZipHeaderFactory.cs

@@ -2,13 +2,12 @@
 using System.IO;
 using SharpCompress.Common.Zip.Headers;
 using SharpCompress.IO;
-using System.Text;
 
 namespace SharpCompress.Common.Zip
 {
     internal class StreamingZipHeaderFactory : ZipHeaderFactory
     {
-        internal StreamingZipHeaderFactory(string password, ArchiveEncoding archiveEncoding)
+        internal StreamingZipHeaderFactory(string? password, ArchiveEncoding archiveEncoding)
             : base(StreamingMode.Streaming, password, archiveEncoding)
         {
         }
@@ -16,9 +15,10 @@ namespace SharpCompress.Common.Zip
         internal IEnumerable<ZipHeader> ReadStreamHeader(Stream stream)
         {
             RewindableStream rewindableStream;
-            if (stream is RewindableStream)
+
+            if (stream is RewindableStream rs)
             {
-                rewindableStream = stream as RewindableStream;
+                rewindableStream = rs;
             }
             else
             {
@@ -26,12 +26,12 @@ namespace SharpCompress.Common.Zip
             }
             while (true)
             {
-                ZipHeader header = null;
+                ZipHeader? header;
                 BinaryReader reader = new BinaryReader(rewindableStream);
                 if (_lastEntryHeader != null &&
                     (FlagUtility.HasFlag(_lastEntryHeader.Flags, HeaderFlags.UsePostDataDescriptor) || _lastEntryHeader.IsZip64))
                 {
-                    reader = (_lastEntryHeader.Part as StreamingZipFilePart).FixStreamedFileLocation(ref rewindableStream);
+                    reader = ((StreamingZipFilePart)_lastEntryHeader.Part).FixStreamedFileLocation(ref rewindableStream);
                     long? pos = rewindableStream.CanSeek ? (long?)rewindableStream.Position : null;
                     uint crc = reader.ReadUInt32();
                     if (crc == POST_DATA_DESCRIPTOR)
@@ -49,7 +49,7 @@ namespace SharpCompress.Common.Zip
                 _lastEntryHeader = null;
                 uint headerBytes = reader.ReadUInt32();
                 header = ReadHeader(headerBytes, reader);
-                if (header == null) { yield break; }
+                if (header is null) { yield break; }
 
                 //entry could be zero bytes so we need to know that.
                 if (header.ZipHeaderType == ZipHeaderType.LocalEntry)

src/SharpCompress/Common/Zip/WinzipAesEncryptionData.cs

@@ -1,3 +1,5 @@
+#nullable disable
+
 using System;
 using System.Buffers.Binary;
 using System.Security.Cryptography;
@@ -25,14 +27,9 @@ namespace SharpCompress.Common.Zip
             Initialize();
         }
 
-        internal byte[] IvBytes
-{
-    get; set;
-}
-        internal byte[] KeyBytes
-{
-    get; set;
-}
+        internal byte[] IvBytes { get; set; }
+
+        internal byte[] KeyBytes { get; set; }
 
         private int KeySizeInBytes
         {
@@ -42,16 +39,13 @@ namespace SharpCompress.Common.Zip
 
         internal static int KeyLengthInBytes(WinzipAesKeySize keySize)
         {
-            switch (keySize)
+            return keySize switch
             {
-                case WinzipAesKeySize.KeySize128:
-                    return 16;
-                case WinzipAesKeySize.KeySize192:
-                    return 24;
-                case WinzipAesKeySize.KeySize256:
-                    return 32;
-            }
-            throw new InvalidOperationException();
+                WinzipAesKeySize.KeySize128 => 16,
+                WinzipAesKeySize.KeySize192 => 24,
+                WinzipAesKeySize.KeySize256 => 32,
+                _ => throw new InvalidOperationException(),
+            };
         }
 
         private void Initialize()

src/SharpCompress/Common/Zip/ZipEntry.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using SharpCompress.Common.Zip.Headers;
 

src/SharpCompress/Common/Zip/ZipFilePart.cs

@@ -100,7 +100,7 @@ namespace SharpCompress.Common.Zip
                 case ZipCompressionMethod.WinzipAes:
                 {
                     ExtraData data = Header.Extra.Where(x => x.Type == ExtraDataType.WinZipAes).SingleOrDefault();
-                    if (data == null)
+                    if (data is null)
                     {
                         throw new InvalidFormatException("No Winzip AES extra data found.");
                     }

src/SharpCompress/Common/Zip/ZipHeaderFactory.cs

@@ -3,7 +3,6 @@ using System.IO;
 using System.Linq;
 using SharpCompress.Common.Zip.Headers;
 using SharpCompress.IO;
-using System.Text;
 
 namespace SharpCompress.Common.Zip
 {
@@ -19,19 +18,19 @@ namespace SharpCompress.Common.Zip
         internal const uint ZIP64_END_OF_CENTRAL_DIRECTORY = 0x06064b50;
         internal const uint ZIP64_END_OF_CENTRAL_DIRECTORY_LOCATOR = 0x07064b50;
 
-        protected LocalEntryHeader _lastEntryHeader;
-        private readonly string _password;
+        protected LocalEntryHeader? _lastEntryHeader;
+        private readonly string? _password;
         private readonly StreamingMode _mode;
         private readonly ArchiveEncoding _archiveEncoding;
 
-        protected ZipHeaderFactory(StreamingMode mode, string password, ArchiveEncoding archiveEncoding)
+        protected ZipHeaderFactory(StreamingMode mode, string? password, ArchiveEncoding archiveEncoding)
         {
             this._mode = mode;
             this._password = password;
             this._archiveEncoding = archiveEncoding;
         }
 
-        protected ZipHeader ReadHeader(uint headerBytes, BinaryReader reader, bool zip64 = false)
+        protected ZipHeader? ReadHeader(uint headerBytes, BinaryReader reader, bool zip64 = false)
         {
             switch (headerBytes)
             {
@@ -52,7 +51,7 @@ namespace SharpCompress.Common.Zip
                 }
                 case POST_DATA_DESCRIPTOR:
                     {
-                        if (FlagUtility.HasFlag(_lastEntryHeader.Flags, HeaderFlags.UsePostDataDescriptor))
+                        if (FlagUtility.HasFlag(_lastEntryHeader!.Flags, HeaderFlags.UsePostDataDescriptor))
                         {
                             _lastEntryHeader.Crc = reader.ReadUInt32();
                             _lastEntryHeader.CompressedSize = zip64 ? (long)reader.ReadUInt64() : reader.ReadUInt32();
@@ -121,7 +120,7 @@ namespace SharpCompress.Common.Zip
                     throw new NotSupportedException("SharpCompress cannot currently read non-seekable Zip Streams with encrypted data that has been written in a non-seekable manner.");
                 }
 
-                if (_password == null)
+                if (_password is null)
                 {
                     throw new CryptographicException("No password supplied for encrypted zip.");
                 }

src/SharpCompress/Common/Zip/ZipVolume.cs

@@ -10,6 +10,6 @@ namespace SharpCompress.Common.Zip
         {
         }
 
-        public string Comment { get; internal set; }
+        public string? Comment { get; internal set; }
     }
 }

src/SharpCompress/Compressors/ADC/ADCBase.cs

@@ -87,7 +87,7 @@ namespace SharpCompress.Compressors.ADC
         /// <param name="output">Buffer to hold decompressed data</param>
         /// <param name="bufferSize">Max size for decompressed data</param>
         /// <returns>How many bytes are stored on <paramref name="output"/></returns>
-        public static int Decompress(byte[] input, out byte[] output, int bufferSize = 262144)
+        public static int Decompress(byte[] input, out byte[]? output, int bufferSize = 262144)
         {
             return Decompress(new MemoryStream(input), out output, bufferSize);
         }
@@ -99,11 +99,11 @@ namespace SharpCompress.Compressors.ADC
         /// <param name="output">Buffer to hold decompressed data</param>
         /// <param name="bufferSize">Max size for decompressed data</param>
         /// <returns>How many bytes are stored on <paramref name="output"/></returns>
-        public static int Decompress(Stream input, out byte[] output, int bufferSize = 262144)
+        public static int Decompress(Stream input, out byte[]? output, int bufferSize = 262144)
         {
             output = null;
 
-            if (input == null || input.Length == 0)
+            if (input is null || input.Length == 0)
             {
                 return 0;
             }
@@ -211,7 +211,7 @@ namespace SharpCompress.Compressors.ADC
             }
 
             output = new byte[outPosition];
-            Array.Copy(buffer, 0, output, 0, outPosition);
+            Array.Copy(buffer, output, outPosition);
             return position - start;
         }
     }

src/SharpCompress/Compressors/ADC/ADCStream.cs

@@ -23,6 +23,9 @@
 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
+
+#nullable disable
+
 using System;
 using System.IO;
 
@@ -31,7 +34,7 @@ namespace SharpCompress.Compressors.ADC
     /// <summary>
     /// Provides a forward readable only stream that decompresses ADC data
     /// </summary>
-    public class ADCStream : Stream
+    public sealed class ADCStream : Stream
     {
         /// <summary>
         /// This stream holds the compressed data
@@ -103,7 +106,7 @@ namespace SharpCompress.Compressors.ADC
             {
                 return 0;
             }
-            if (buffer == null)
+            if (buffer is null)
             {
                 throw new ArgumentNullException(nameof(buffer));
             }
@@ -122,7 +125,7 @@ namespace SharpCompress.Compressors.ADC
 
             int size = -1;
 
-            if (_outBuffer == null)
+            if (_outBuffer is null)
             {
                 size = ADCBase.Decompress(_stream, out _outBuffer);
                 _outPosition = 0;
@@ -142,7 +145,7 @@ namespace SharpCompress.Compressors.ADC
                 toCopy -= piece;
                 size = ADCBase.Decompress(_stream, out _outBuffer);
                 _outPosition = 0;
-                if (size == 0 || _outBuffer == null || _outBuffer.Length == 0)
+                if (size == 0 || _outBuffer is null || _outBuffer.Length == 0)
                 {
                     return copied;
                 }

src/SharpCompress/Compressors/BZip2/CBZip2InputStream.cs

@@ -1,4 +1,6 @@
-using System.IO;
+#nullable disable
+
+using System.IO;
 
 /*
  * Copyright 2001,2004-2005 The Apache Software Foundation

src/SharpCompress/Compressors/BZip2/CBZip2OutputStream.cs

@@ -22,6 +22,8 @@
  * great code.
  */
 
+#nullable disable
+
 namespace SharpCompress.Compressors.BZip2
 {
     /**
@@ -35,14 +37,14 @@ namespace SharpCompress.Compressors.BZip2
       * start of the BZIP2 stream to make it compatible with other PGP programs.
       */
 
-    internal class CBZip2OutputStream : Stream
+    internal sealed class CBZip2OutputStream : Stream
     {
-        protected const int SETMASK = (1 << 21);
-        protected const int CLEARMASK = (~SETMASK);
-        protected const int GREATER_ICOST = 15;
-        protected const int LESSER_ICOST = 0;
-        protected const int SMALL_THRESH = 20;
-        protected const int DEPTH_THRESH = 10;
+        private const int SETMASK = (1 << 21);
+        private const int CLEARMASK = (~SETMASK);
+        private const int GREATER_ICOST = 15;
+        private const int LESSER_ICOST = 0;
+        private const int SMALL_THRESH = 20;
+        private const int DEPTH_THRESH = 10;
 
         /*
         If you are ever unlucky/improbable enough
@@ -52,7 +54,7 @@ namespace SharpCompress.Compressors.BZip2
         stack go above 27 elems, so the following
         limit seems very generous.
         */
-        protected const int QSORT_STACK_SIZE = 1000;
+        private const int QSORT_STACK_SIZE = 1000;
         private bool finished;
 
         private static void Panic()
@@ -76,7 +78,7 @@ namespace SharpCompress.Compressors.BZip2
             }
         }
 
-        protected static void HbMakeCodeLengths(char[] len, int[] freq,
+        private static void HbMakeCodeLengths(char[] len, int[] freq,
                                                 int alphaSize, int maxLen)
         {
             /*
@@ -1786,8 +1788,7 @@ namespace SharpCompress.Compressors.BZip2
             zptr = new int[n];
             ftab = new int[65537];
 
-            if (block == null || quadrant == null || zptr == null
-                || ftab == null)
+            if (block is null || quadrant is null || zptr is null || ftab is null)
             {
                 //int totalDraw = (n + 1 + NUM_OVERSHOOT_BYTES) + (n + NUM_OVERSHOOT_BYTES) + n + 65537;
                 //compressOutOfMemory ( totalDraw, n );

src/SharpCompress/Compressors/Deflate/CRC32.cs

@@ -111,9 +111,9 @@ namespace SharpCompress.Compressors.Deflate
         /// <param name="input">The stream over which to calculate the CRC32</param>
         /// <param name="output">The stream into which to deflate the input</param>
         /// <returns>the CRC32 calculation</returns>
-        public UInt32 GetCrc32AndCopy(Stream input, Stream output)
+        public UInt32 GetCrc32AndCopy(Stream input, Stream? output)
         {
-            if (input == null)
+            if (input is null)
             {
                 throw new ZlibException("The input stream must not be null.");
             }
@@ -159,7 +159,7 @@ namespace SharpCompress.Compressors.Deflate
             return _InternalComputeCrc32((UInt32)W, B);
         }
 
-        internal Int32 _InternalComputeCrc32(UInt32 W, byte B)
+        internal int _InternalComputeCrc32(UInt32 W, byte B)
         {
             return (Int32)(crc32Table[(W ^ B) & 0xFF] ^ (W >> 8));
         }
@@ -173,7 +173,7 @@ namespace SharpCompress.Compressors.Deflate
         /// <param name="count">how many bytes within the block to slurp</param>
         public void SlurpBlock(byte[] block, int offset, int count)
         {
-            if (block == null)
+            if (block is null)
             {
                 throw new ZlibException("The data buffer must not be null.");
             }

src/SharpCompress/Compressors/Deflate/DeflateManager.cs

@@ -1,3 +1,5 @@
+#nullable disable
+
 // Deflate.cs
 // ------------------------------------------------------------------
 //
@@ -1756,7 +1758,7 @@ namespace SharpCompress.Compressors.Deflate
             int length = dictionary.Length;
             int index = 0;
 
-            if (dictionary == null || status != INIT_STATE)
+            if (dictionary is null || status != INIT_STATE)
             {
                 throw new ZlibException("Stream error.");
             }
@@ -1796,8 +1798,8 @@ namespace SharpCompress.Compressors.Deflate
         {
             int old_flush;
 
-            if (_codec.OutputBuffer == null ||
-                (_codec.InputBuffer == null && _codec.AvailableBytesIn != 0) ||
+            if (_codec.OutputBuffer is null ||
+                (_codec.InputBuffer is null && _codec.AvailableBytesIn != 0) ||
                 (status == FINISH_STATE && flush != FlushType.Finish))
             {
                 _codec.Message = _ErrorMessage[ZlibConstants.Z_NEED_DICT - (ZlibConstants.Z_STREAM_ERROR)];

src/SharpCompress/Compressors/Deflate/DeflateStream.cs

@@ -37,7 +37,7 @@ namespace SharpCompress.Compressors.Deflate
 
         public DeflateStream(Stream stream, CompressionMode mode,
                              CompressionLevel level = CompressionLevel.Default,
-                             Encoding forceEncoding = null)
+                             Encoding? forceEncoding = null)
         {
             _baseStream = new ZlibBaseStream(stream, mode, level, ZlibStreamFlavor.DEFLATE, forceEncoding);
         }

src/SharpCompress/Compressors/Deflate/GZipStream.cs

@@ -39,8 +39,8 @@ namespace SharpCompress.Compressors.Deflate
 
         public DateTime? LastModified { get; set; }
 
-        private string _comment;
-        private string _fileName;
+        private string? _comment;
+        private string? _fileName;
 
         internal ZlibBaseStream BaseStream;
         private bool _disposed;
@@ -345,44 +345,43 @@ namespace SharpCompress.Compressors.Deflate
 
         #endregion Stream methods
 
-        public String Comment
+        public string? Comment
         {
             get => _comment;
             set
             {
                 if (_disposed)
                 {
-                    throw new ObjectDisposedException("GZipStream");
+                    throw new ObjectDisposedException(nameof(GZipStream));
                 }
                 _comment = value;
             }
         }
 
-        public string FileName
+        public string? FileName
         {
             get => _fileName;
             set
             {
                 if (_disposed)
                 {
-                    throw new ObjectDisposedException("GZipStream");
+                    throw new ObjectDisposedException(nameof(GZipStream));
                 }
                 _fileName = value;
-                if (_fileName == null)
+                if (_fileName is null)
                 {
                     return;
                 }
-                if (_fileName.IndexOf("/") != -1)
+                if (_fileName.Contains("/"))
                 {
-                    _fileName = _fileName.Replace("/", "\\");
+                    _fileName = _fileName.Replace('/', '\\');
                 }
                 if (_fileName.EndsWith("\\"))
                 {
                     throw new InvalidOperationException("Illegal filename");
                 }
 
-                var index = _fileName.IndexOf("\\");
-                if (index != -1)
+                if (_fileName.Contains("\\"))
                 {
                     // trim any leading path
                     int length = _fileName.Length;
@@ -403,13 +402,13 @@ namespace SharpCompress.Compressors.Deflate
 
         private int EmitHeader()
         {
-            byte[] commentBytes = (Comment == null) ? null
+            byte[]? commentBytes = (Comment is null) ? null
                 : _encoding.GetBytes(Comment);
-            byte[] filenameBytes = (FileName == null) ? null
+            byte[]? filenameBytes = (FileName is null) ? null
                 : _encoding.GetBytes(FileName);
 
-            int cbLength = (Comment == null) ? 0 : commentBytes.Length + 1;
-            int fnLength = (FileName == null) ? 0 : filenameBytes.Length + 1;
+            int cbLength = (commentBytes is null) ? 0 : commentBytes.Length + 1;
+            int fnLength = (filenameBytes is null) ? 0 : filenameBytes.Length + 1;
 
             int bufferLength = 10 + cbLength + fnLength;
             var header = new byte[bufferLength];
@@ -440,7 +439,7 @@ namespace SharpCompress.Compressors.Deflate
                 LastModified = DateTime.Now;
             }
             TimeSpan delta = LastModified.Value - UNIX_EPOCH;
-            var timet = (Int32)delta.TotalSeconds;
+            var timet = (int)delta.TotalSeconds;
             BinaryPrimitives.WriteInt32LittleEndian(header.AsSpan(i), timet);
             i += 4;
 

src/SharpCompress/Compressors/Deflate/InfTree.cs

@@ -59,6 +59,8 @@
 //
 // -----------------------------------------------------------------------
 
+#nullable disable
+
 using System;
 
 namespace SharpCompress.Compressors.Deflate
@@ -542,7 +544,7 @@ namespace SharpCompress.Compressors.Deflate
 
         private void initWorkArea(int vsize)
         {
-            if (hn == null)
+            if (hn is null)
             {
                 hn = new int[1];
                 v = new int[vsize];

src/SharpCompress/Compressors/Deflate/Inflate.cs

@@ -1,3 +1,5 @@
+#nullable disable
+
 // Inflate.cs
 // ------------------------------------------------------------------
 //
@@ -367,7 +369,7 @@ namespace SharpCompress.Compressors.Deflate
                             return Flush(r);
                         }
                         t = 258 + (t & 0x1f) + ((t >> 5) & 0x1f);
-                        if (blens == null || blens.Length < t)
+                        if (blens is null || blens.Length < t)
                         {
                             blens = new int[t];
                         }
@@ -1651,7 +1653,7 @@ namespace SharpCompress.Compressors.Deflate
         {
             int b;
 
-            if (_codec.InputBuffer == null)
+            if (_codec.InputBuffer is null)
             {
                 throw new ZlibException("InputBuffer is null. ");
             }

src/SharpCompress/Compressors/Deflate/Tree.cs

@@ -1,3 +1,5 @@
+#nullable disable
+
 // Tree.cs
 // ------------------------------------------------------------------
 //

src/SharpCompress/Compressors/Deflate/Zlib.cs

@@ -380,13 +380,13 @@ namespace SharpCompress.Compressors.Deflate
         internal static readonly StaticTree Distances;
         internal static readonly StaticTree BitLengths;
 
-        internal short[] treeCodes; // static tree or null
-        internal int[] extraBits; // extra bits for each code or null
+        internal short[]? treeCodes; // static tree or null
+        internal int[]? extraBits; // extra bits for each code or null
         internal int extraBase; // base index for extra_bits
         internal int elems; // max number of elements in the tree
         internal int maxLength; // max bit length for the codes
 
-        private StaticTree(short[] treeCodes, int[] extraBits, int extraBase, int elems, int maxLength)
+        private StaticTree(short[]? treeCodes, int[]? extraBits, int extraBase, int elems, int maxLength)
         {
             this.treeCodes = treeCodes;
             this.extraBits = extraBits;
@@ -423,9 +423,9 @@ namespace SharpCompress.Compressors.Deflate
         // NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1
         private static readonly int NMAX = 5552;
 
-        internal static uint Adler32(uint adler, byte[] buf, int index, int len)
+        internal static uint Adler32(uint adler, byte[]? buf, int index, int len)
         {
-            if (buf == null)
+            if (buf is null)
             {
                 return 1;
             }

src/SharpCompress/Compressors/Deflate/ZlibBaseStream.cs

@@ -1,3 +1,5 @@
+#nullable disable
+
 // ZlibBaseStream.cs
 // ------------------------------------------------------------------
 //
@@ -65,17 +67,7 @@ namespace SharpCompress.Compressors.Deflate
 
         private readonly Encoding _encoding;
 
-        internal int Crc32
-        {
-            get
-            {
-                if (crc == null)
-                {
-                    return 0;
-                }
-                return crc.Crc32Result;
-            }
-        }
+        internal int Crc32 => crc?.Crc32Result ?? 0;
 
         public ZlibBaseStream(Stream stream,
                               CompressionMode compressionMode,
@@ -106,7 +98,7 @@ namespace SharpCompress.Compressors.Deflate
         {
             get
             {
-                if (_z == null)
+                if (_z is null)
                 {
                     bool wantRfc1950Header = (_flavor == ZlibStreamFlavor.ZLIB);
                     _z = new ZlibCodec();
@@ -126,17 +118,10 @@ namespace SharpCompress.Compressors.Deflate
 
         private byte[] workingBuffer
         {
-            get
-            {
-                if (_workingBuffer == null)
-                {
-                    _workingBuffer = new byte[_bufferSize];
-                }
-                return _workingBuffer;
-            }
+            get => _workingBuffer ??= new byte[_bufferSize];
         }
 
-        public override void Write(Byte[] buffer, int offset, int count)
+        public override void Write(byte[] buffer, int offset, int count)
         {
             // workitem 7159
             // calculate the CRC on the unccompressed data  (before writing)
@@ -193,7 +178,7 @@ namespace SharpCompress.Compressors.Deflate
 
         private void finish()
         {
-            if (_z == null)
+            if (_z is null)
             {
                 return;
             }
@@ -213,7 +198,7 @@ namespace SharpCompress.Compressors.Deflate
                     if (rc != ZlibConstants.Z_STREAM_END && rc != ZlibConstants.Z_OK)
                     {
                         string verb = (_wantCompress ? "de" : "in") + "flating";
-                        if (_z.Message == null)
+                        if (_z.Message is null)
                         {
                             throw new ZlibException(String.Format("{0}: (rc = {1})", verb, rc));
                         }
@@ -323,7 +308,7 @@ namespace SharpCompress.Compressors.Deflate
 
         private void end()
         {
-            if (z == null)
+            if (z is null)
             {
                 return;
             }
@@ -348,7 +333,7 @@ namespace SharpCompress.Compressors.Deflate
             base.Dispose(disposing);
             if (disposing)
             {
-                if (_stream == null)
+                if (_stream is null)
                 {
                     return;
                 }
@@ -527,7 +512,7 @@ namespace SharpCompress.Compressors.Deflate
             {
                 return 0; // workitem 8557
             }
-            if (buffer == null)
+            if (buffer is null)
             {
                 throw new ArgumentNullException(nameof(buffer));
             }