Bootstrapping The .NET Framework Without An MSI Installer

I recently needed to test the idea of whether or not I could bootstrap .NET v4.0 onto a WinXP machine, from a USB thumb drive, without an application installer for the target app. The goal was to insert a thumb drive, run the app directly from the root of the thumb drive and have .NET 4 installed onto the system if it wasn't already there, prior to the application starting up.

The High Level Process

At a very high level, this is fairly simple:

• Check for .NET 4
• If not found, install
• If found, or after install, launch the real app

When I got down into the weeds of doing this, I found a few very helpful items on the interwebs. To check for a specific version of .NET, I found this StackOverflow question, which has an answer that outlines the various registry entries you can look for.

Framework Version  Registry Key
------------------------------------------------------------------------------------------
1.0                HKLM\Software\Microsoft\.NETFramework\Policy\v1.0\3705
1.1                HKLM\Software\Microsoft\NET Framework Setup\NDP\v1.1.4322\Install
2.0                HKLM\Software\Microsoft\NET Framework Setup\NDP\v2.0.50727\Install
3.0                HKLM\Software\Microsoft\NET Framework Setup\NDP\v3.0\Setup\InstallSuccess
3.5                HKLM\Software\Microsoft\NET Framework Setup\NDP\v3.5\Install
4.0 Client Profile HKLM\Software\Microsoft\NET Framework Setup\NDP\v4\Client\Install
4.0 Full Profile   HKLM\Software\Microsoft\NET Framework Setup\NDP\v4\Full\Install

The answer goes on to detail other aspects, such as service packs, but this information was sufficient for my needs.

I also grabbed a copy of the stand-alone .NET 4 Redistributable package. To be honest, the less-than 50 meg package size is rather surprising - especially when you see the greater-than 230 meg package size for .NET 3.5!

One other requirement was to prevent the user from having to click a bunch of "Next" and "License Agreement" buttons during the .NET 4 installation. I had a hard time finding documentation for the command line options online, but running the /? option against the redistributable gave me the information I needed. I ended up using "/passive /showfinalerror /promptrestart" as the options. This puts the installer into passive mode, which still displays progress but skips all the user interaction, will display an error message window if any problems occur, and will prompt the user to restart if a restart is required.

Implementing The Bootstrapper

Remember that this is a proof of concept, only, at this point. Given that and my general lack of C++ or Delphi skills (though I was a Pascal programmer back in high school, 15 years ago), I wanted to skip past the hard part of putting together a real bootstrapper executable. So... I chose to go with Windows Script Host and VBScript.

Fortunately, the WSH / VBScript documentation on MSDN is good enough to get me rolling - I haven't done VBScript since the classic ASP days, and haven't done VB in any form since 2005! But it all came back to me and with the help of the docs, I was able to produce this script:

Dim WshShell, value
Set WshShell = WScript.CreateObject("WScript.Shell")

ON ERROR RESUME NEXT

Sub Run(ByVal sFile)  
 Dim shell  
 Set shell = CreateObject("WScript.Shell")
 shell.Run sFile, 1, true
 Set shell = Nothing
End Sub

value = wshShell.RegRead("HKLM\Software\Microsoft\NET Framework Setup\NDP\v4\Install")
if (Err.Number <> 0) Or (value is nothing) then
 Run("dotnet\dotNetFx40_Full_x86_x64.exe /passive /showfinalerror /promptrestart")
end if

run("My.Actual.App.exe")
Yes, that's an "ON ERROR RESUME NEXT" in the 2nd line! ACK! I know... but we're limited in VBScript / WSH. The reason this is needed, is the RegRead call. If the key does not exist (and it won't, on a machine that doesn't have .NET 4 installed), an exception is thrown. We have to prevent the exception from failing the script and this is the only way I know of to do that. We then check for the presence of an error and run the .net installer if one was encountered.

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