.idea/.idea.TweetDuck/.idea/runConfigurations/TweetDuck.xml

@@ -11,8 +11,8 @@
     <option name="PROJECT_EXE_PATH_TRACKING" value="1" />
     <option name="PROJECT_ARGUMENTS_TRACKING" value="1" />
     <option name="PROJECT_WORKING_DIRECTORY_TRACKING" value="1" />
-    <option name="PROJECT_KIND" value="DotNetCore" />
-    <option name="PROJECT_TFM" value="net6.0-windows7.0" />
+    <option name="PROJECT_KIND" value="Console" />
+    <option name="PROJECT_TFM" value=".NETFramework,Version=v4.7.2" />
     <method v="2">
       <option name="Build" />
     </method>

README.md

@@ -43,14 +43,14 @@ Download links and system requirements are on the [official website](https://twe
 
 Building TweetDuck for Windows requires at minimum [Visual Studio 2019](https://visualstudio.microsoft.com/downloads) and Windows 7. Before opening the solution, open Visual Studio Installer and make sure you have the following Visual Studio workloads and components installed:
 * **.NET desktop development**
-  * .NET SDK
+  * .NET Framework 4.7.2 targeting pack
   * F# desktop language support
 * **Desktop development with C++**
   * MSVC v142 - VS 2019 C++ x64/x86 build tools (v14.20 / Latest)
 
-In the **Installation details** panel, you can expand the workloads you selected, and uncheck any components that are not listed above to save space. You may uncheck the .NET SDK component if you installed the [.NET 6 SDK](https://dotnet.microsoft.com/en-us/download/dotnet/6.0) directly.
+In the **Installation details** panel, you can expand the workloads you selected, and uncheck any components that are not listed above to save space.
 
-Building TweetDuck for Linux requires [.NET 6 SDK](https://docs.microsoft.com/en-us/dotnet/core/install/linux). The Linux project has its own solution file in the `linux/` folder.
+Building TweetDuck for Linux requires [.NET 5](https://docs.microsoft.com/en-us/dotnet/core/install/linux). The Linux project has its own solution file in the `linux/` folder.
 
 ### Editors
 
@@ -66,15 +66,15 @@ Icons and logos were designed in [Affinity Designer](https://affinity.serif.com/
 > If you don't want to build installers using the existing foundations, you can skip this section.
 
 Official Windows installers are built using [InnoSetup](https://jrsoftware.org/isinfo.php) and [Inno Download Plugin](https://mitrichsoftware.wordpress.com/inno-setup-tools/inno-download-plugin/), specifically:
-* [InnoSetup 6.2.1](https://files.jrsoftware.org/is/6/innosetup-6.2.1.exe)
-* [Inno Download Plugin 1.5.1](https://drive.google.com/folderview?id=0Bzw1xBVt0mokSXZrUEFIanV4azA&usp=sharing#list)
+* [InnoSetup 5.6.1](https://files.jrsoftware.org/is/5/innosetup-5.6.1.exe) with Preprocessor support
+* [Inno Download Plugin 1.5.0](https://drive.google.com/folderview?id=0Bzw1xBVt0mokSXZrUEFIanV4azA&usp=sharing#list)
 
-During installation, the download plugin will ask whether to add its include path to `ISPPBuiltins.iss`. Note that this option does not work with InnoSetup 6, so TweetDuck installers don't need it.
+When installing InnoSetup, you can choose to include Inno Script Studio which I recommend for editing and testing installer configuration files in the `bld` folder (`.iss` extension).
 
 Scripts for building installers require the `PATH` environment variable to include the InnoSetup installation folder. You can either edit `PATH` manually, or use a program like [Rapid Environment Editor](https://www.rapidee.com/en/about) to simplify the process. For example, this is the installation folder I added to `PATH` under **User variables**:
-* `C:\Program Files (x86)\Inno Setup 6`
+* `C:\Program Files (x86)\Inno Setup 5`
 
-You may need to restart Visual Studio or Rider after changing `PATH` for the change to take place.
+You may need to restart Visual Studio after changing `PATH` for the change to take place.
 
 ## Solution Overview
 
@@ -84,13 +84,13 @@ On Windows, TweetDuck uses the [CefSharp](https://github.com/cefsharp/CefSharp/)
 
 On Linux, TweetDuck uses the [ChromiumGtk](https://github.com/lunixo/ChromiumGtk) library, which combines [CefGlue](https://gitlab.com/xiliumhq/chromiumembedded/cefglue) for the browser component and [GtkSharp](https://github.com/GtkSharp/GtkSharp) for the GUI.
 
-The solution contains several C# projects for executables and libraries, and F# projects for automated tests. All projects target `.NET 6` and either `C# 10` or `F#`.
+The solution contains several C# projects for executables and libraries, and F# projects for automated tests.
 
 Projects are organized into folders:
-* Windows projects are in the `windows/` folder
-* Linux projects are in the `linux/` folder
-* Libraries (`TweetLib.*`) are in the `lib/` folder
-* Tests (`TweetTest.*`) are also in the `lib/` folder
+* Windows projects are in the `windows/` folder, and target `.NET Framework 4.7.2` + `C# 8.0`
+* Linux projects are in the `linux/` folder, and target `.NET 5` + `C#`
+* Libraries (`TweetLib.*`) are in the `lib/` folder, and target `.NET Standard 2.0` + `C# 9.0`
+* Tests (`TweetTest.*`) are also in the `lib/` folder, and target `.NET Framework 4.7.2` + `F#`
 
 Here are a few things to keep in mind:
 * Executable projects have their entry points in `Program.cs`
@@ -130,7 +130,7 @@ Main Windows executable. It has a dependency on [CefSharp](https://github.com/ce
 
 #### TweetDuck.Browser
 
-Windows executable that hosts various Chromium processes. It has a dependency on [CefSharp](https://github.com/cefsharp/CefSharp/).
+Windows executable that hosts various Chromium processes. It depends on two specific DLLs from the [CefSharp](https://github.com/cefsharp/CefSharp/) package. After updating [CefSharp](https://github.com/cefsharp/CefSharp/), run the `windows/TweetDuck/Resources/PostCefUpdate.ps1` PowerShell script to update these dependencies to the new version.
 
 #### TweetDuck.Video
 
@@ -142,10 +142,6 @@ By default, [CefSharp](https://github.com/cefsharp/CefSharp/) is not built with
 
 Windows library that implements `TweetLib.Browser.CEF` using the [CefSharp](https://github.com/cefsharp/CefSharp/) library and Windows Forms.
 
-#### TweetLib.WinForms.Legacy
-
-Windows library that re-adds some legacy Windows Forms components that were removed in .NET Core 3.1. The sources were taken from the [.NET Core 3.0 sources of Windows Forms](https://github.com/dotnet/winforms/tree/v3.0.2), and edited to remove unnecessary features.
-
 ### Linux Projects
 
 #### TweetDuck

TweetDuck.sln

@@ -10,8 +10,6 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TweetDuck.Video", "windows\
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TweetImpl.CefSharp", "windows\TweetImpl.CefSharp\TweetImpl.CefSharp.csproj", "{44DF3E2E-F465-4A31-8B43-F40FFFB018BA}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TweetLib.WinForms.Legacy", "windows\TweetLib.WinForms.Legacy\TweetLib.WinForms.Legacy.csproj", "{B54E732A-4090-4DAA-9ABD-311368C17B68}"
-EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TweetLib.Communication", "lib\TweetLib.Communication\TweetLib.Communication.csproj", "{72473763-4B9D-4FB6-A923-9364B2680F06}"
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TweetLib.Core", "lib\TweetLib.Core\TweetLib.Core.csproj", "{93BA3CB4-A812-4949-B07D-8D393FB38937}"
@@ -50,10 +48,6 @@ Global
 		{44DF3E2E-F465-4A31-8B43-F40FFFB018BA}.Debug|x86.Build.0 = Debug|x86
 		{44DF3E2E-F465-4A31-8B43-F40FFFB018BA}.Release|x86.ActiveCfg = Release|x86
 		{44DF3E2E-F465-4A31-8B43-F40FFFB018BA}.Release|x86.Build.0 = Release|x86
-		{B54E732A-4090-4DAA-9ABD-311368C17B68}.Debug|x86.ActiveCfg = Debug|x86
-		{B54E732A-4090-4DAA-9ABD-311368C17B68}.Debug|x86.Build.0 = Debug|x86
-		{B54E732A-4090-4DAA-9ABD-311368C17B68}.Release|x86.ActiveCfg = Release|x86
-		{B54E732A-4090-4DAA-9ABD-311368C17B68}.Release|x86.Build.0 = Release|x86
 		{72473763-4B9D-4FB6-A923-9364B2680F06}.Debug|x86.ActiveCfg = Debug|x86
 		{72473763-4B9D-4FB6-A923-9364B2680F06}.Debug|x86.Build.0 = Debug|x86
 		{72473763-4B9D-4FB6-A923-9364B2680F06}.Release|x86.ActiveCfg = Release|x86

Version.cs

@@ -6,6 +6,6 @@
 
 namespace TweetDuck {
 	internal static class Version {
-		public const string Tag = "1.23";
+		public const string Tag = "1.22.1";
 	}
 }

bld/gen_full.iss

@@ -9,8 +9,6 @@
 
 #define MyAppVersion GetFileVersion("..\windows\TweetDuck\bin\x86\Release\TweetDuck.exe")
 
-#include ReadReg(HKLM, "Software\Mitrich Software\Inno Download Plugin", "InstallDir") + "\idp.iss"
-
 [Setup]
 AppId={{8C25A716-7E11-4AAD-9992-8B5D0C78AE06}
 AppName={#MyAppName}
@@ -31,11 +29,13 @@ Uninstallable=TDIsUninstallable
 UninstallDisplayName={#MyAppName}
 UninstallDisplayIcon={app}\{#MyAppExeName}
 Compression=lzma2/ultra
-LZMADictionarySize=32768
+LZMADictionarySize=15360
 SolidCompression=yes
 InternalCompressLevel=normal
 MinVersion=0,6.1
 
+#include <idp.iss>
+
 [Languages]
 Name: "english"; MessagesFile: "compiler:Default.isl"
 
@@ -68,11 +68,20 @@ AdditionalTasks=Additional shortcuts and components:
 var UpdatePath: String;
 var VisitedTasksPage: Boolean;
 
-{ Prepare installation variables. }
+function TDGetNetFrameworkVersion: Cardinal; forward;
+
+{ Check .NET Framework version on startup, ask user if they want to proceed if older than 4.7.2. }
 function InitializeSetup: Boolean;
 begin
   UpdatePath := ExpandConstant('{param:UPDATEPATH}')
   VisitedTasksPage := False
+  
+  if (TDGetNetFrameworkVersion() < 461808) and (MsgBox('{#MyAppName} requires .NET Framework 4.7.2 or newer,'+#13+#10+'please visit {#MyAppShortURL} for a download link.'+#13+#10+#13+#10'Do you want to proceed with the setup anyway?', mbCriticalError, MB_YESNO or MB_DEFBUTTON2) = IDNO) then
+  begin
+    Result := False
+    Exit
+  end;
+  
   Result := True
 end;
 
@@ -131,3 +140,17 @@ function TDIsUninstallable: Boolean;
 begin
   Result := (UpdatePath = '')
 end;
+
+{ Return DWORD value containing the build version of .NET Framework. }
+function TDGetNetFrameworkVersion: Cardinal;
+var FrameworkVersion: Cardinal;
+
+begin
+  if RegQueryDWordValue(HKEY_LOCAL_MACHINE, 'Software\Microsoft\NET Framework Setup\NDP\v4\Full', 'Release', FrameworkVersion) then
+  begin
+    Result := FrameworkVersion
+    Exit
+  end;
+  
+  Result := 0
+end;

bld/gen_port.iss

@@ -9,8 +9,6 @@
 
 #define MyAppVersion GetFileVersion("..\windows\TweetDuck\bin\x86\Release\TweetDuck.exe")
 
-#include ReadReg(HKLM, "Software\Mitrich Software\Inno Download Plugin", "InstallDir") + "\idp.iss"
-
 [Setup]
 AppId={{8C25A716-7E11-4AAD-9992-8B5D0C78AE06}
 AppName={#MyAppName} Portable
@@ -31,11 +29,13 @@ Uninstallable=no
 UsePreviousAppDir=no
 PrivilegesRequired=lowest
 Compression=lzma2/ultra
-LZMADictionarySize=32768
+LZMADictionarySize=15360
 SolidCompression=yes
 InternalCompressLevel=normal
 MinVersion=0,6.1
 
+#include <idp.iss>
+
 [Languages]
 Name: "english"; MessagesFile: "compiler:Default.isl"
 
@@ -52,10 +52,19 @@ AdditionalTasks=Additional components:
 [Code]
 var UpdatePath: String;
 
-{ Prepare installation variables. }
+function TDGetNetFrameworkVersion: Cardinal; forward;
+
+{ Check .NET Framework version on startup, ask user if they want to proceed if older than 4.7.2. }
 function InitializeSetup: Boolean;
 begin
   UpdatePath := ExpandConstant('{param:UPDATEPATH}')
+  
+  if (TDGetNetFrameworkVersion() < 461808) and (MsgBox('{#MyAppName} requires .NET Framework 4.7.2 or newer,'+#13+#10+'please visit {#MyAppShortURL} for a download link.'+#13+#10+#13+#10'Do you want to proceed with the setup anyway?', mbCriticalError, MB_YESNO or MB_DEFBUTTON2) = IDNO) then
+  begin
+    Result := False
+    Exit
+  end;
+  
   Result := True
 end;
 
@@ -93,3 +102,17 @@ begin
     end;
   end;
 end;
+
+{ Return DWORD value containing the build version of .NET Framework. }
+function TDGetNetFrameworkVersion: Cardinal;
+var FrameworkVersion: Cardinal;
+
+begin
+  if RegQueryDWordValue(HKEY_LOCAL_MACHINE, 'Software\Microsoft\NET Framework Setup\NDP\v4\Full', 'Release', FrameworkVersion) then
+  begin
+    Result := FrameworkVersion
+    Exit
+  end;
+  
+  Result := 0
+end;

bld/gen_upd.iss

@@ -11,8 +11,6 @@
 #define MyAppVersion GetFileVersion("..\windows\TweetDuck\bin\x86\Release\TweetDuck.exe")
 #define CefVersion GetFileVersion("..\windows\TweetDuck\bin\x86\Release\libcef.dll")
 
-#include ReadReg(HKLM, "Software\Mitrich Software\Inno Download Plugin", "InstallDir") + "\idp.iss"
-
 [Setup]
 AppId={{{#MyAppID}}
 AppName={#MyAppName}
@@ -39,6 +37,8 @@ SolidCompression=True
 InternalCompressLevel=normal
 MinVersion=0,6.1
 
+#include <idp.iss>
+
 [Languages]
 Name: "english"; MessagesFile: "compiler:Default.isl"
 
@@ -84,6 +84,7 @@ Type: filesandordirs; Name: "{app}\scripts"
 function TDIsUninstallable: Boolean; forward;
 function TDGetRunArgs(Param: String): String; forward;
 function TDFindUpdatePath: String; forward;
+function TDGetNetFrameworkVersion: Cardinal; forward;
 function TDGetAppVersionClean: String; forward;
 function TDGetFullDownloadFileName: String; forward;
 function TDIsMatchingCEFVersion: Boolean; forward;
@@ -92,7 +93,7 @@ procedure TDExecuteFullDownload; forward;
 var IsPortable: Boolean;
 var UpdatePath: String;
 
-{ Prepare update installation, and the full download package if required. }
+{ Check .NET Framework version on startup, ask user if they want to proceed if older than 4.7.2. Prepare full download package if required. }
 function InitializeSetup: Boolean;
 begin
   IsPortable := ExpandConstant('{param:PORTABLE}') = '1'
@@ -110,6 +111,12 @@ begin
     idpAddFile('https://github.com/{#MyAppPublisher}/{#MyAppName}/releases/download/'+TDGetAppVersionClean()+'/'+TDGetFullDownloadFileName(), ExpandConstant('{tmp}\{#MyAppName}.Full.exe'))
   end;
   
+  if (TDGetNetFrameworkVersion() < 461808) and (MsgBox('{#MyAppName} requires .NET Framework 4.7.2 or newer,'+#13+#10+'please visit {#MyAppShortURL} for a download link.'+#13+#10+#13+#10'Do you want to proceed with the setup anyway?', mbCriticalError, MB_YESNO or MB_DEFBUTTON2) = IDNO) then
+  begin
+    Result := False
+    Exit
+  end;
+  
   Result := True
 end;
 
@@ -204,6 +211,20 @@ begin
   Result := Path
 end;
 
+{ Return DWORD value containing the build version of .NET Framework. }
+function TDGetNetFrameworkVersion: Cardinal;
+var FrameworkVersion: Cardinal;
+
+begin
+  if RegQueryDWordValue(HKEY_LOCAL_MACHINE, 'Software\Microsoft\NET Framework Setup\NDP\v4\Full', 'Release', FrameworkVersion) then
+  begin
+    Result := FrameworkVersion
+    Exit
+  end;
+  
+  Result := 0
+end;
+
 { Return the name of the full installer file to download from GitHub. }
 function TDGetFullDownloadFileName: String;
 begin

global.json

@@ -1,7 +0,0 @@
-{
-  "sdk": {
-    "version": "6.0.0",
-    "rollForward": "latestMinor",
-    "allowPrerelease": false
-  }
-}

lib/TweetLib.Browser.CEF/Data/ContextMenuActionRegistry.cs

@@ -2,7 +2,7 @@
 using System.Collections.Generic;
 
 namespace TweetLib.Browser.CEF.Data {
-	abstract class ContextMenuActionRegistry<T> where T : notnull {
+	abstract class ContextMenuActionRegistry<T> {
 		private readonly Dictionary<T, Action> actions = new ();
 
 		protected abstract T NextId(int n);

lib/TweetLib.Browser.CEF/Data/ResourceHandlerRegistry.cs

@@ -21,7 +21,7 @@ internal bool HasHandler(string url) {
 		}
 
 		private void Register(string url, Func<TResourceHandler> factory) {
-			if (!Uri.TryCreate(url, UriKind.Absolute, out var uri)) {
+			if (!Uri.TryCreate(url, UriKind.Absolute, out Uri uri)) {
 				throw new ArgumentException("Resource handler URL must be absolute!");
 			}
 

lib/TweetLib.Browser.CEF/Logic/DialogHandlerLogic.cs

@@ -29,7 +29,7 @@ public bool OnFileDialog(FileDialogType type, IEnumerable<string> acceptFilters,
 				};
 
 				fileDialogOpener.OpenFile("Open Files", multiple, filters, files => {
-					string ext = Path.GetExtension(files[0]).ToLower();
+					string ext = Path.GetExtension(files[0])!.ToLower();
 					callbackAdapter.Continue(callback, Array.FindIndex(supportedExtensions, filter => ParseFileType(filter).Contains(ext)), files);
 					callbackAdapter.Dispose(callback);
 				}, () => {

lib/TweetLib.Browser.CEF/Logic/JsDialogHandlerLogic.cs

@@ -9,7 +9,7 @@ private static (MessageDialogType, string) GetMessageDialogProperties(string tex
 			
 			int pipe = text.IndexOf('|');
 			if (pipe != -1) {
-				type = text[..pipe] switch {
+				type = text.Substring(0, pipe) switch {
 					"error"    => MessageDialogType.Error,
 					"warning"  => MessageDialogType.Warning,
 					"info"     => MessageDialogType.Information,
@@ -18,7 +18,7 @@ private static (MessageDialogType, string) GetMessageDialogProperties(string tex
 				};
 
 				if (type != MessageDialogType.None) {
-					text = text[(pipe + 1)..];
+					text = text.Substring(pipe + 1);
 				}
 			}
 

lib/TweetLib.Browser.CEF/TweetLib.Browser.CEF.csproj

@@ -1,10 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   
   <PropertyGroup>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>netstandard2.0</TargetFramework>
     <Configurations>Debug;Release</Configurations>
     <Platforms>x86;x64</Platforms>
-    <LangVersion>10</LangVersion>
+    <LangVersion>9</LangVersion>
     <Nullable>enable</Nullable>
     <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
   </PropertyGroup>

lib/TweetLib.Browser.CEF/Utils/CefUtils.cs

@@ -8,7 +8,7 @@ public static string GetCacheFolder(string storagePath) {
 			return Path.Combine(storagePath, "Cache");
 		}
 
-		public static CommandLineArgs ParseCommandLineArguments(string? argumentString) {
+		public static CommandLineArgs ParseCommandLineArguments(string argumentString) {
 			CommandLineArgs args = new CommandLineArgs();
 
 			if (string.IsNullOrWhiteSpace(argumentString)) {
@@ -26,8 +26,8 @@ public static CommandLineArgs ParseCommandLineArguments(string? argumentString)
 					value = "1";
 				}
 				else {
-					key = matchValue[..indexEquals].TrimStart('-');
-					value = matchValue[(indexEquals + 1)..].Trim('"');
+					key = matchValue.Substring(0, indexEquals).TrimStart('-');
+					value = matchValue.Substring(indexEquals + 1).Trim('"');
 				}
 
 				if (key.Length != 0) {

lib/TweetLib.Browser/Contexts/Notification.cs

@@ -1,9 +1,9 @@
 namespace TweetLib.Browser.Contexts {
 	public struct Notification {
-		public string? TweetUrl { get; }
+		public string TweetUrl { get; }
 		public string? QuoteUrl { get; }
 
-		public Notification(string? tweetUrl, string? quoteUrl) {
+		public Notification(string tweetUrl, string? quoteUrl) {
 			TweetUrl = tweetUrl;
 			QuoteUrl = quoteUrl;
 		}

lib/TweetLib.Browser/TweetLib.Browser.csproj

@@ -1,10 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   
   <PropertyGroup>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>netstandard2.0</TargetFramework>
     <Configurations>Debug;Release</Configurations>
     <Platforms>x86;x64</Platforms>
-    <LangVersion>10</LangVersion>
+    <LangVersion>9</LangVersion>
     <Nullable>enable</Nullable>
     <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
   </PropertyGroup>

lib/TweetLib.Communication/Pipe/DuplexPipe.cs

@@ -13,11 +13,13 @@ public static Server CreateServer() {
 
 		public static Client CreateClient(string token) {
 			int space = token.IndexOf(' ');
-			return new Client(token[..space], token[(space + 1)..]);
+			return new Client(token.Substring(0, space), token.Substring(space + 1));
 		}
 
 		private readonly PipeStream pipeIn;
 		private readonly PipeStream pipeOut;
+
+		private readonly Thread readerThread;
 		private readonly StreamWriter writerStream;
 
 		public event EventHandler<PipeReadEventArgs>? DataIn;
@@ -25,21 +27,22 @@ public static Client CreateClient(string token) {
 		private DuplexPipe(PipeStream pipeIn, PipeStream pipeOut) {
 			this.pipeIn = pipeIn;
 			this.pipeOut = pipeOut;
-			this.writerStream = new StreamWriter(this.pipeOut);
 
-			new Thread(ReaderThread) { IsBackground = true }.Start();
+			this.readerThread = new Thread(ReaderThread) {
+				IsBackground = true
+			};
+
+			this.readerThread.Start();
+			this.writerStream = new StreamWriter(this.pipeOut);
 		}
 
 		private void ReaderThread() {
 			using StreamReader read = new StreamReader(pipeIn);
+			string? data;
 
-			try {
-				while (read.ReadLine() is {} data) {
+			while ((data = read.ReadLine()) != null) {
 				DataIn?.Invoke(this, new PipeReadEventArgs(data));
 			}
-			} catch (ObjectDisposedException) {
-				// expected
-			}
 		}
 
 		public void Write(string key) {
@@ -53,6 +56,12 @@ public void Write(string key, string data) {
 		}
 
 		public void Dispose() {
+			try {
+				readerThread.Abort();
+			} catch {
+				// /shrug
+			}
+
 			pipeIn.Dispose();
 			writerStream.Dispose();
 		}
@@ -89,8 +98,8 @@ internal PipeReadEventArgs(string line) {
 					Data = string.Empty;
 				}
 				else {
-					Key = line[..separatorIndex];
-					Data = line[(separatorIndex + 1)..];
+					Key = line.Substring(0, separatorIndex);
+					Data = line.Substring(separatorIndex + 1);
 				}
 			}
 		}

lib/TweetLib.Communication/TweetLib.Communication.csproj

@@ -1,9 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>netstandard2.0</TargetFramework>
     <Platforms>x86</Platforms>
-    <LangVersion>10</LangVersion>
+    <LangVersion>9</LangVersion>
     <Nullable>enable</Nullable>
     <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
   </PropertyGroup>

lib/TweetLib.Core/App.cs

@@ -110,11 +110,11 @@ private static T Validate<T>(T? obj, string name) where T : class {
 	}
 
 	public sealed class AppBuilder {
-		public IAppSetup? Setup { get; init; }
-		public IAppErrorHandler? ErrorHandler { get; init; }
-		public IAppSystemHandler? SystemHandler { get; init; }
-		public IAppMessageDialogs? MessageDialogs { get; init; }
-		public IAppFileDialogs? FileDialogs { get; init; }
+		public IAppSetup? Setup { get; set; }
+		public IAppErrorHandler? ErrorHandler { get; set; }
+		public IAppSystemHandler? SystemHandler { get; set; }
+		public IAppMessageDialogs? MessageDialogs { get; set; }
+		public IAppFileDialogs? FileDialogs { get; set; }
 
 		internal static AppBuilder? Instance { get; private set; }
 

lib/TweetLib.Core/Features/BaseResourceRequestHandler.cs

@@ -34,7 +34,7 @@ public static void LoadResourceRewriteRules(string rules) {
 			if (resourceType is ResourceType.Script or ResourceType.Stylesheet && TweetDeckHashes.Count > 0) {
 				Match match = TweetDeckResourceUrl.Match(url);
 
-				if (match.Success && TweetDeckHashes.TryGetValue($"{match.Groups[1]}.{match.Groups[3]}", out var hash)) {
+				if (match.Success && TweetDeckHashes.TryGetValue($"{match.Groups[1]}.{match.Groups[3]}", out string hash)) {
 					if (match.Groups[2].Value == hash) {
 						App.Logger.Debug("[RequestHandlerBase] Accepting " + url);
 					}

lib/TweetLib.Core/Features/FileDownloadManager.cs

@@ -84,7 +84,7 @@ public void SaveImages(string[] urls, string? author) {
 			var settings = new SaveFileDialogSettings {
 				DialogTitle = oneImage ? "Save Image" : "Save Images",
 				OverwritePrompt = oneImage,
-				FileName = qualityIndex == -1 ? filename : $"{author} {Path.ChangeExtension(filename, null)} {firstImageLink[(qualityIndex + 1)..]}".Trim() + ext,
+				FileName = qualityIndex == -1 ? filename : $"{author} {Path.ChangeExtension(filename, null)} {firstImageLink.Substring(qualityIndex + 1)}".Trim() + ext,
 				Filters = new [] { new FileDialogFilter(oneImage ? "Image" : "Images", string.IsNullOrEmpty(ext) ? Array.Empty<string>() : new [] { ext }) }
 			};
 

lib/TweetLib.Core/Features/Notifications/NotificationBrowser.Tweet.cs

@@ -56,9 +56,7 @@ public override void Show(IContextMenuBuilder menu, Context context) {
 					menu.AddSeparator();
 
 					if (context.Notification is {} notification) {
-						if (!string.IsNullOrEmpty(notification.TweetUrl)) {
 						AddCopyAction(menu, "Copy tweet address", notification.TweetUrl);
-						}
 
 						if (!string.IsNullOrEmpty(notification.QuoteUrl)) {
 							AddCopyAction(menu, "Copy quoted tweet address", notification.QuoteUrl!);
@@ -74,7 +72,7 @@ public override void Dispose() {
 				this.browserComponent.PageLoadEnd -= BrowserComponentOnPageLoadEnd;
 			}
 
-			private void BrowserComponentOnPageLoadEnd(object? sender, PageLoadEventArgs e) {
+			private void BrowserComponentOnPageLoadEnd(object sender, PageLoadEventArgs e) {
 				string url = e.Url;
 
 				if (TwitterUrls.IsTweetDeck(url) && url != BlankURL) {

lib/TweetLib.Core/Features/Plugins/Plugin.cs

@@ -93,7 +93,7 @@ public override int GetHashCode() {
 			return Identifier.GetHashCode();
 		}
 
-		public override bool Equals(object? obj) {
+		public override bool Equals(object obj) {
 			return obj is Plugin plugin && plugin.Identifier.Equals(Identifier);
 		}
 

lib/TweetLib.Core/Features/Plugins/PluginBridge.cs

@@ -48,17 +48,17 @@ internal int GetTokenFromPlugin(Plugin plugin) {
 		}
 
 		internal Plugin? GetPluginFromToken(int token) {
-			return tokens.TryGetValue(token, out var plugin) ? plugin : null;
+			return tokens.TryGetValue(token, out Plugin plugin) ? plugin : null;
 		}
 
 		// Event handlers
 
-		private void manager_Reloaded(object? sender, PluginErrorEventArgs e) {
+		private void manager_Reloaded(object sender, PluginErrorEventArgs e) {
 			tokens.Clear();
 			fileCache.Clear();
 		}
 
-		private void Config_PluginChangedState(object? sender, PluginChangedStateEventArgs e) {
+		private void Config_PluginChangedState(object sender, PluginChangedStateEventArgs e) {
 			if (!e.IsEnabled) {
 				int token = GetTokenFromPlugin(e.Plugin);
 
@@ -88,7 +88,7 @@ private string GetFullPathOrThrow(int token, PluginFolder folder, string path) {
 		private string ReadFileUnsafe(int token, PluginFolder folder, string path, bool readCached) {
 			string fullPath = GetFullPathOrThrow(token, folder, path);
 
-			if (readCached && fileCache.TryGetValue(token, folder, path, out var cachedContents)) {
+			if (readCached && fileCache.TryGetValue(token, folder, path, out string cachedContents)) {
 				return cachedContents;
 			}
 
@@ -161,7 +161,7 @@ public void Clear() {
 				cache.Clear();
 			}
 
-			public bool TryGetValue(int token, PluginFolder folder, string path, [MaybeNullWhen(false)] out string contents) {
+			public bool TryGetValue(int token, PluginFolder folder, string path, out string contents) {
 				return cache.TryGetValue(token, Key(folder, path), out contents);
 			}
 

lib/TweetLib.Core/Features/Plugins/PluginLoader.cs

@@ -41,7 +41,7 @@ public static IEnumerable<Result<Plugin>> AllInFolder(string pluginFolder, strin
 		private static Plugin FromFolder(string name, string pathRoot, string pathData, PluginGroup group) {
 			Plugin.Builder builder = new Plugin.Builder(group, name, pathRoot, pathData);
 
-			foreach (var environment in Directory.EnumerateFiles(pathRoot, "*.js", SearchOption.TopDirectoryOnly).Select(Path.GetFileName).Select(EnvironmentFromFileName!)) {
+			foreach (var environment in Directory.EnumerateFiles(pathRoot, "*.js", SearchOption.TopDirectoryOnly).Select(Path.GetFileName).Select(EnvironmentFromFileName)) {
 				builder.AddEnvironment(environment);
 			}
 
@@ -55,7 +55,7 @@ private static Plugin FromFolder(string name, string pathRoot, string pathData,
 			string currentContents = string.Empty;
 
 			foreach (string line in File.ReadAllLines(metaFile, Encoding.UTF8).Concat(EndTag).Select(static line => line.TrimEnd()).Where(static line => line.Length > 0)) {
-				if (line[0] == '[' && line[^1] == ']') {
+				if (line[0] == '[' && line[line.Length - 1] == ']') {
 					if (currentTag != null) {
 						SetProperty(builder, currentTag, currentContents);
 					}
@@ -106,7 +106,7 @@ private static void SetProperty(Plugin.Builder builder, string tag, string value
 					builder.ConfigDefault = value;
 					break;
 				case "REQUIRES":
-					builder.RequiredVersion = Version.TryParse(value, out var version) ? version : throw new FormatException($"Invalid required minimum version: {value}");
+					builder.RequiredVersion = Version.TryParse(value, out Version version) ? version : throw new FormatException($"Invalid required minimum version: {value}");
 					break;
 				default:
 					throw new FormatException($"Invalid metadata tag: {tag}");

lib/TweetLib.Core/Features/Plugins/PluginManager.cs

@@ -102,7 +102,7 @@ internal void Execute(PluginEnvironment environment, IScriptExecutor executor) {
 			Executed?.Invoke(this, new PluginErrorEventArgs(errors));
 		}
 
-		private void Config_PluginChangedState(object? sender, PluginChangedStateEventArgs e) {
+		private void Config_PluginChangedState(object sender, PluginChangedStateEventArgs e) {
 			browserExecutor?.RunFunction("TDPF_setPluginState", e.Plugin, e.IsEnabled);
 		}
 

lib/TweetLib.Core/Features/TweetDeck/TweetDeckBrowser.cs

@@ -71,12 +71,12 @@ public override void Dispose() {
 			App.UserConfiguration.SoundNotificationChanged -= UserConfiguration_SoundNotificationChanged;
 		}
 
-		private void browserComponent_BrowserLoaded(object? sender, BrowserLoadedEventArgs e) {
+		private void browserComponent_BrowserLoaded(object sender, BrowserLoadedEventArgs e) {
 			e.AddDictionaryWords("tweetdeck", "TweetDeck", "tweetduck", "TweetDuck", "TD");
 			isBrowserReady = true;
 		}
 
-		private void browserComponent_PageLoadStart(object? sender, PageLoadEventArgs e) {
+		private void browserComponent_PageLoadStart(object sender, PageLoadEventArgs e) {
 			string url = e.Url;
 
 			if (TwitterUrls.IsTweetDeck(url) || (TwitterUrls.IsTwitter(url) && !TwitterUrls.IsTwitterLogin2Factor(url))) {
@@ -84,7 +84,7 @@ private void browserComponent_PageLoadStart(object? sender, PageLoadEventArgs e)
 			}
 		}
 
-		private void browserComponent_PageLoadEnd(object? sender, PageLoadEventArgs e) {
+		private void browserComponent_PageLoadEnd(object sender, PageLoadEventArgs e) {
 			string url = e.Url;
 
 			if (TwitterUrls.IsTweetDeck(url)) {
@@ -105,7 +105,7 @@ private void browserComponent_PageLoadEnd(object? sender, PageLoadEventArgs e) {
 			browserComponent.RunBootstrap("update");
 		}
 
-		private void pluginManager_Reloaded(object? sender, PluginErrorEventArgs e) {
+		private void pluginManager_Reloaded(object sender, PluginErrorEventArgs e) {
 			if (e.HasErrors) {
 				App.MessageDialogs.Error("Error Loading Plugins", "The following plugins will not be available until the issues are resolved:\n\n" + string.Join("\n\n", e.Errors));
 			}
@@ -115,14 +115,14 @@ private void pluginManager_Reloaded(object? sender, PluginErrorEventArgs e) {
 			}
 		}
 
-		private void pluginManager_Executed(object? sender, PluginErrorEventArgs e) {
+		private void pluginManager_Executed(object sender, PluginErrorEventArgs e) {
 			if (e.HasErrors) {
 				App.MessageDialogs.Error("Error Executing Plugins", "Failed to execute the following plugins:\n\n" + string.Join("\n\n", e.Errors));
 			}
 		}
 
-		private void updateChecker_CheckFinished(object? sender, UpdateCheckEventArgs e) {
-			var updateChecker = (UpdateChecker) sender!;
+		private void updateChecker_CheckFinished(object sender, UpdateCheckEventArgs e) {
+			var updateChecker = (UpdateChecker) sender;
 
 			e.Result.Handle(update => {
 				string tag = update.VersionTag;
@@ -144,7 +144,7 @@ private void updateChecker_CheckFinished(object? sender, UpdateCheckEventArgs e)
 			ignoreUpdateCheckError = true;
 		}
 
-		private void UserConfiguration_GeneralEventHandler(object? sender, EventArgs e) {
+		private void UserConfiguration_GeneralEventHandler(object sender, EventArgs e) {
 			UpdatePropertyObject();
 		}
 
@@ -236,11 +236,6 @@ private sealed class ResourceRequestHandler : BaseResourceRequestHandler {
 			private const string UrlVersionCheck = "/web/dist/version.json";
 
 			public override RequestHandleResult? Handle(string url, ResourceType resourceType) {
-				var result = base.Handle(url, resourceType);
-				if (result != null) {
-					return result;
-				}
-				
 				switch (resourceType) {
 					case ResourceType.MainFrame when url.EndsWithOrdinal("://twitter.com/"):
 						return new RequestHandleResult.Redirect(TwitterUrls.TweetDeck); // redirect plain twitter.com requests, fixes bugs with login 2FA
@@ -261,7 +256,7 @@ private sealed class ResourceRequestHandler : BaseResourceRequestHandler {
 						return new RequestHandleResult.Redirect(url.Replace("include_entities=1", "include_entities=1&include_ext_has_nft_avatar=1"));
 
 					default:
-						return null;
+						return base.Handle(url, resourceType);
 				}
 			}
 		}

lib/TweetLib.Core/Features/TweetDeck/TweetDeckExtraContext.cs

@@ -24,15 +24,15 @@ public void SetLink(string type, string? url) {
 
 			switch (type) {
 				case "link":
-					Link = new Link(url, url);
+					Link = new Link(url!, url!);
 					break;
 
 				case "image":
-					Media = new Media(Type.Image, TwitterUrls.GetMediaLink(url, App.UserConfiguration.TwitterImageQuality));
+					Media = new Media(Type.Image, TwitterUrls.GetMediaLink(url!, App.UserConfiguration.TwitterImageQuality));
 					break;
 
 				case "video":
-					Media = new Media(Type.Video, url);
+					Media = new Media(Type.Video, url!);
 					break;
 			}
 		}

lib/TweetLib.Core/Features/Twitter/ImageUrl.cs

@@ -57,7 +57,7 @@ public static bool TryParse(string url, out ImageUrl obj) {
 				return false;
 			}
 
-			string originalUrl = url[..question];
+			string originalUrl = url.Substring(0, question);
 
 			obj = new ImageUrl(Path.HasExtension(originalUrl) ? originalUrl : originalUrl + imageExtension, imageQuality);
 			return true;

lib/TweetLib.Core/Features/Twitter/TwitterUrls.cs

@@ -49,11 +49,11 @@ public enum UrlType {
 		}
 
 		public static UrlType Check(string url) {
-			if (url.Contains('"')) {
+			if (url.Contains("\"")) {
 				return UrlType.Invalid;
 			}
 
-			if (Uri.TryCreate(url, UriKind.Absolute, out var uri)) {
+			if (Uri.TryCreate(url, UriKind.Absolute, out Uri uri)) {
 				string scheme = uri.Scheme;
 
 				if (scheme == Uri.UriSchemeHttps || scheme == Uri.UriSchemeHttp || scheme == Uri.UriSchemeFtp || scheme == Uri.UriSchemeMailto) {

lib/TweetLib.Core/Systems/Configuration/ConfigManager.cs

@@ -16,7 +16,7 @@ static ConfigManager() {
 			ConverterRegistry.Register(typeof(WindowState), new BasicTypeConverter<WindowState> {
 				ConvertToString = static value => $"{(value.IsMaximized ? 'M' : '_')}{value.Bounds.X} {value.Bounds.Y} {value.Bounds.Width} {value.Bounds.Height}",
 				ConvertToObject = static value => {
-					int[] elements = StringUtils.ParseInts(value[1..], ' ');
+					int[] elements = StringUtils.ParseInts(value.Substring(1), ' ');
 
 					return new WindowState {
 						Bounds = new Rectangle(elements[0], elements[1], elements[2], elements[3]),

lib/TweetLib.Core/Systems/Logging/Logger.cs

@@ -43,7 +43,7 @@ private bool Log(string level, string message) {
 				build.Append("Please, report all issues to: ").Append(Lib.IssueTrackerUrl).Append("\r\n\r\n");
 			}
 
-			build.Append('[').Append(DateTime.Now.ToString("G", Lib.Culture)).Append("] ").Append(level).Append("\r\n");
+			build.Append("[").Append(DateTime.Now.ToString("G", Lib.Culture)).Append("] ").Append(level).Append("\r\n");
 			build.Append(message).Append("\r\n\r\n");
 
 			try {

lib/TweetLib.Core/Systems/Updates/UpdateChecker.cs

@@ -37,7 +37,7 @@ public void Dispose() {
 			InteractionManager.Dispose();
 		}
 
-		private void timer_Elapsed(object? sender, ElapsedEventArgs e) {
+		private void timer_Elapsed(object sender, ElapsedEventArgs e) {
 			Check(false);
 		}
 

lib/TweetLib.Core/Systems/Updates/UpdateInteractionManager.cs

@@ -26,7 +26,7 @@ public void ClearUpdate() {
 			nextUpdate = null;
 		}
 
-		private void updates_CheckFinished(object? sender, UpdateCheckEventArgs e) {
+		private void updates_CheckFinished(object sender, UpdateCheckEventArgs e) {
 			UpdateInfo? foundUpdate = e.Result.HasValue ? e.Result.Value : null;
 
 			if (nextUpdate != null && !nextUpdate.Equals(foundUpdate)) {

lib/TweetLib.Core/TweetLib.Core.csproj

@@ -1,10 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>netstandard2.0</TargetFramework>
     <Configurations>Debug;Release</Configurations>
     <Platforms>x86;x64</Platforms>
-    <LangVersion>10</LangVersion>
+    <LangVersion>9</LangVersion>
     <Nullable>enable</Nullable>
     <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
   </PropertyGroup>

lib/TweetLib.Utils/Collections/CommandLineArgs.cs

@@ -57,7 +57,7 @@ public void SetValue(string key, string value) {
 		}
 
 		public string? GetValue(string key) {
-			return values.TryGetValue(key.ToLower(), out var val) ? val : null;
+			return values.TryGetValue(key.ToLower(), out string val) ? val : null;
 		}
 
 		public void RemoveValue(string key) {

lib/TweetLib.Utils/Collections/TwoKeyDictionary.cs

@@ -11,7 +11,7 @@ namespace TweetLib.Utils.Collections {
 	/// <typeparam name="V">The type of the values.</typeparam>
 	[SuppressMessage("ReSharper", "UnusedMethodReturnValue.Global")]
 	[SuppressMessage("ReSharper", "UnusedMember.Global")]
-	public sealed class TwoKeyDictionary<K1, K2, V> where K1 : notnull where K2 : notnull {
+	public sealed class TwoKeyDictionary<K1, K2, V> {
 		private readonly Dictionary<K1, Dictionary<K2, V>> dict;
 		private readonly int innerCapacity;
 
@@ -41,7 +41,7 @@ public TwoKeyDictionary(int outerCapacity, int innerCapacity) {
 			}
 
 			set {
-				if (!dict.TryGetValue(outerKey, out Dictionary<K2, V>? innerDict)) {
+				if (!dict.TryGetValue(outerKey, out Dictionary<K2, V> innerDict)) {
 					dict.Add(outerKey, innerDict = new Dictionary<K2, V>(innerCapacity));
 				}
 
@@ -67,7 +67,7 @@ public IEnumerable<V> InnerValues {
 		/// Throws if the key pair already exists.
 		/// </summary>
 		public void Add(K1 outerKey, K2 innerKey, V value) {
-			if (!dict.TryGetValue(outerKey, out Dictionary<K2, V>? innerDict)) {
+			if (!dict.TryGetValue(outerKey, out Dictionary<K2, V> innerDict)) {
 				dict.Add(outerKey, innerDict = new Dictionary<K2, V>(innerCapacity));
 			}
 
@@ -100,7 +100,7 @@ public bool Contains(K1 outerKey) {
 		/// Determines whether the dictionary contains the key pair.
 		/// </summary>
 		public bool Contains(K1 outerKey, K2 innerKey) {
-			return dict.TryGetValue(outerKey, out Dictionary<K2, V>? innerDict) && innerDict.ContainsKey(innerKey);
+			return dict.TryGetValue(outerKey, out Dictionary<K2, V> innerDict) && innerDict.ContainsKey(innerKey);
 		}
 
 		/// <summary>
@@ -122,8 +122,8 @@ public int Count(K1 outerKey) {
 		/// Gets the value associated with the key pair.
 		/// Returns true if the key pair was present.
 		/// </summary>
-		public bool TryGetValue(K1 outerKey, K2 innerKey, [MaybeNullWhen(false)] out V value) {
-			if (dict.TryGetValue(outerKey, out Dictionary<K2, V>? innerDict)) {
+		public bool TryGetValue(K1 outerKey, K2 innerKey, out V value) {
+			if (dict.TryGetValue(outerKey, out Dictionary<K2, V> innerDict)) {
 				return innerDict.TryGetValue(innerKey, out value);
 			}
 			else {
@@ -145,7 +145,7 @@ public bool Remove(K1 outerKey) {
 		/// Returns true if the key pair was present.
 		/// </summary>
 		public bool Remove(K1 outerKey, K2 innerKey) {
-			if (dict.TryGetValue(outerKey, out Dictionary<K2, V>? innerDict) && innerDict.Remove(innerKey)) {
+			if (dict.TryGetValue(outerKey, out Dictionary<K2, V> innerDict) && innerDict.Remove(innerKey)) {
 				if (innerDict.Count == 0) {
 					dict.Remove(outerKey);
 				}

lib/TweetLib.Utils/Dialogs/SaveFileDialogSettings.cs

@@ -2,9 +2,9 @@
 
 namespace TweetLib.Utils.Dialogs {
 	public sealed class SaveFileDialogSettings {
-		public string DialogTitle { get; init; } = "Save File";
-		public bool OverwritePrompt { get; init; } = true;
-		public string? FileName { get; init; }
-		public IReadOnlyList<FileDialogFilter>? Filters { get; init; }
+		public string DialogTitle { get; set; } = "Save File";
+		public bool OverwritePrompt { get; set; } = true;
+		public string? FileName { get; set; }
+		public IReadOnlyList<FileDialogFilter>? Filters { get; set; }
 	}
 }

lib/TweetLib.Utils/Globalization/Language.cs

@@ -21,7 +21,7 @@ public Language(string code, string? alt = null) {
 			}
 		}
 
-		public override bool Equals(object? obj) {
+		public override bool Equals(object obj) {
 			return obj is Language other && Code.Equals(other.Code, StringComparison.OrdinalIgnoreCase);
 		}
 
@@ -38,8 +38,8 @@ public override string ToString() {
 			return cultureInfo.DisplayName == cultureInfo.NativeName ? capitalizedName : $"{capitalizedName}, {cultureInfo.DisplayName}";
 		}
 
-		public int CompareTo(Language? other) {
-			return string.Compare(Name, other?.Name, false, CultureInfo.InvariantCulture);
+		public int CompareTo(Language other) {
+			return string.Compare(Name, other.Name, false, CultureInfo.InvariantCulture);
 		}
 	}
 }

lib/TweetLib.Utils/IO/CombinedFileStream.cs

@@ -134,7 +134,7 @@ public sealed class Entry {
 			public string[] KeyValue {
 				get {
 					int index = Identifier.IndexOf(KeySeparator);
-					return index == -1 ? StringUtils.EmptyArray : Identifier[(index + 1)..].Split(KeySeparator);
+					return index == -1 ? StringUtils.EmptyArray : Identifier.Substring(index + 1).Split(KeySeparator);
 				}
 			}
 

lib/TweetLib.Utils/Serialization/Converters/BasicTypeConverter.cs

@@ -2,12 +2,12 @@
 
 namespace TweetLib.Utils.Serialization.Converters {
 	public sealed class BasicTypeConverter<T> : ITypeConverter {
-		public Func<T, string>? ConvertToString { get; init; }
-		public Func<string, T>? ConvertToObject { get; init; }
+		public Func<T, string>? ConvertToString { get; set; }
+		public Func<string, T>? ConvertToObject { get; set; }
 
-		bool ITypeConverter.TryWriteType(Type type, object? value, out string? converted) {
+		bool ITypeConverter.TryWriteType(Type type, object value, out string? converted) {
 			try {
-				converted = ConvertToString!((T) value!);
+				converted = ConvertToString!((T) value);
 				return true;
 			} catch {
 				converted = null;

lib/TweetLib.Utils/Serialization/Converters/ClrTypeConverter.cs

@@ -6,17 +6,18 @@ sealed class ClrTypeConverter : ITypeConverter {
 
 		private ClrTypeConverter() {}
 
-		bool ITypeConverter.TryWriteType(Type type, object? value, out string? converted) {
+		bool ITypeConverter.TryWriteType(Type type, object value, out string? converted) {
 			switch (Type.GetTypeCode(type)) {
 				case TypeCode.Boolean:
-					converted = value!.ToString();
+					converted = value.ToString();
 					return true;
 
 				case TypeCode.Int32:
-					converted = ((int) value!).ToString(); // cast required for enums
+					converted = ((int) value).ToString(); // cast required for enums
 					return true;
 
 				case TypeCode.String:
+					// ReSharper disable once ConstantConditionalAccessQualifier
 					converted = value?.ToString();
 					return true;
 

lib/TweetLib.Utils/Serialization/ITypeConverter.cs

@@ -2,7 +2,7 @@
 
 namespace TweetLib.Utils.Serialization {
 	public interface ITypeConverter {
-		bool TryWriteType(Type type, object? value, out string? converted);
+		bool TryWriteType(Type type, object value, out string? converted);
 		bool TryReadType(Type type, string value, out object? converted);
 	}
 }

lib/TweetLib.Utils/Serialization/SimpleObjectSerializer.cs

@@ -28,7 +28,7 @@ private static string UnescapeStream(StreamReader reader) {
 					break;
 				}
 				else {
-					build.Append(data[index..nextIndex]);
+					build.Append(data.Substring(index, nextIndex - index));
 
 					char next = data[nextIndex + 1];
 
@@ -47,7 +47,7 @@ private static string UnescapeStream(StreamReader reader) {
 				}
 			}
 
-			return build.Append(data[index..]).ToString();
+			return build.Append(data.Substring(index)).ToString();
 		}
 
 		private readonly TypeConverterRegistry converterRegistry;
@@ -114,7 +114,7 @@ public void Read(string file, T obj) {
 				int nextPos = contents.IndexOf(NewLineReal, currentPos);
 
 				if (nextPos == -1) {
-					line = contents[currentPos..];
+					line = contents.Substring(currentPos);
 					currentPos = -1;
 
 					if (string.IsNullOrEmpty(line)) {
@@ -133,10 +133,10 @@ public void Read(string file, T obj) {
 					continue;
 				}
 
-				string property = line[..space];
-				string value = UnescapeLine(line[(space + 1)..]);
+				string property = line.Substring(0, space);
+				string value = UnescapeLine(line.Substring(space + 1));
 
-				if (props.TryGetValue(property, out var info)) {
+				if (props.TryGetValue(property, out PropertyInfo info)) {
 					var type = info.PropertyType;
 					var converter = converterRegistry.TryGet(type) ?? ClrTypeConverter.Instance;
 

lib/TweetLib.Utils/Startup/LockFile.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Threading;
 using TweetLib.Utils.Static;
@@ -90,6 +91,7 @@ public UnlockResult Unlock() {
 			return UnlockResult.Success;
 		}
 
+		[SuppressMessage("ReSharper", "PossibleNullReferenceException")]
 		private LockResult DetermineLockingProcessOrFail(Exception originalException) {
 			try {
 				int pid;
@@ -108,7 +110,7 @@ private LockResult DetermineLockingProcessOrFail(Exception originalException) {
 					var foundProcess = Process.GetProcessById(pid);
 					using var currentProcess = Process.GetCurrentProcess();
 
-					if (currentProcess.MainModule!.FileVersionInfo.InternalName == foundProcess.MainModule!.FileVersionInfo.InternalName) {
+					if (currentProcess.MainModule.FileVersionInfo.InternalName == foundProcess.MainModule.FileVersionInfo.InternalName) {
 						return new LockResult.HasProcess(foundProcess);
 					}
 					else {

lib/TweetLib.Utils/Static/StringUtils.cs

@@ -40,7 +40,7 @@ public static (string before, string after)? SplitInTwo(string str, char search,
 				return null;
 			}
 
-			return (str[..index], str[(index + 1)..]);
+			return (str.Substring(0, index), str.Substring(index + 1));
 		}
 
 		/// <summary>
@@ -49,7 +49,7 @@ public static (string before, string after)? SplitInTwo(string str, char search,
 		/// </summary>
 		public static string ExtractBefore(string str, char search, int startIndex = 0) {
 			int index = str.IndexOf(search, startIndex);
-			return index == -1 ? str : str[..index];
+			return index == -1 ? str : str.Substring(0, index);
 		}
 
 		/// <summary>

lib/TweetLib.Utils/Static/WebUtils.cs

@@ -10,12 +10,10 @@ public static class WebUtils {
 		private static bool hasMicrosoftBeenBroughtTo2008Yet;
 		private static bool hasSystemProxyBeenEnabled;
 
-		private static void EnsureModernTLS() {
+		private static void EnsureTLS12() {
 			if (!hasMicrosoftBeenBroughtTo2008Yet) {
-				#pragma warning disable CS0618
-				ServicePointManager.SecurityProtocol |= SecurityProtocolType.Tls12 | SecurityProtocolType.Tls13;
+				ServicePointManager.SecurityProtocol |= SecurityProtocolType.Tls12;
 				ServicePointManager.SecurityProtocol &= ~(SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11);
-				#pragma warning restore CS0618
 				hasMicrosoftBeenBroughtTo2008Yet = true;
 			}
 		}
@@ -30,7 +28,7 @@ public static void EnableSystemProxy() {
 		}
 
 		public static WebClient NewClient(string? userAgent = null) {
-			EnsureModernTLS();
+			EnsureTLS12();
 
 			WebClient client = new WebClient();
 

lib/TweetLib.Utils/TweetLib.Utils.csproj

@@ -1,10 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   
   <PropertyGroup>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>netstandard2.0</TargetFramework>
     <Configurations>Debug;Release</Configurations>
     <Platforms>x86;x64</Platforms>
-    <LangVersion>10</LangVersion>
+    <LangVersion>9</LangVersion>
     <Nullable>enable</Nullable>
     <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
   </PropertyGroup>

lib/TweetTest.Browser.CEF/TweetTest.Browser.CEF.fsproj

@@ -1,9 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   
   <PropertyGroup>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net472</TargetFramework>
     <Platforms>x86</Platforms>
-    <RuntimeIdentifiers>win7-x86;linux-x64</RuntimeIdentifiers>
   </PropertyGroup>
   
   <ItemGroup>

lib/TweetTest.Core/Features/Twitter/TestTwitterUrls.fs

@@ -47,7 +47,7 @@ module RegexAccount =
             Assert.True(isMatch("https://twitter.com/" + name))
 
     module Match =
-        let extract str = TwitterUrls.RegexAccount.Match(str).Groups[1].Value
+        let extract str = TwitterUrls.RegexAccount.Match(str).Groups.[1].Value
 
         [<Fact>]
         let ``extracts account name from simple URL`` () =

lib/TweetTest.Core/TweetTest.Core.fsproj

@@ -1,9 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   
   <PropertyGroup>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net472</TargetFramework>
     <Platforms>x86</Platforms>
-    <RuntimeIdentifiers>win7-x86;linux-x64</RuntimeIdentifiers>
   </PropertyGroup>
   
   <ItemGroup>