Using WiX, Windows Services are not installed after a downgrade - windows-services

Question

While testing the downgrade functionality of one of our WiX-built MSIs, I have noticed something odd.
I have allowed downgrades in the MajorUpgrade element and I have scheduled that element to be afterInstallInitialize (but I have tried it thoroughly with afterInstallValidate and I experience the same problem; we can't have it after that action, but I thought I'd test it).
Many of the files (e.g. the DLLs in our Service's bin folder) are of a higher version, with each release; therefore, the version we are downgrading to includes files of a lower version. Yet all of those files are installed fine, during the downgrade, apart from the Service EXE files; further, the Services are also not installed in Windows.
Considering all of the above, after spending two days on this problem, and after much searching, I appear to be at a loss.
I have tried two things that seem to provide some hope:
1) I have tried setting the REINSTALLMODE property to amus. This ensures that the EXE files are installed, along with the Windows Services. But most things I read about that property warn against using it, and I even have to surpress ICE40, in order to get my package to build, when setting that property. This all concerns me, as I am not sure what negative effects could be missed, if I use this property in my MSI files.
2) When I remove the KeyPath attribute from the File elements that mark up the Service EXE files and place that attribute on the Component element instead, the Service EXE files are installed onto the system during the downgrade, but the Services are still not installed in Windows. After looking into this, it seems that the KeyPath attribute must be on the File element, if I'd like Services to be installed. So it seems to me as if this idea will not help.
Any help or advice would be very much appreciated. We really could do with providing downgrade functionality.
Thank you all for your time.

Answer 1

MSI is essentially opposed to the idea of downgrades. Once a file is on the machine, MSI tries very hard to keep the latest version of the file around as, among other reasons, downgrading the file can re-introduce a security vulnerability. I'd suggest not directly supporting downgrades; instead, you can show a message that tells the user to uninstall the higher version first.

Answer 2

My solution was to use Burn to provide the 'downgrade' functionality using a custom bootstrapper application.
The bootstrapper detects, downloads, and then installs the new version. In the case of a downgrade it performs an uninstall prior to the install. However, this requires that you execute the bootstrapper of the currently installed version to get the ability to uninstall.
You then also need to worry about any state that will be removed as a consequence of uninstalling, this needs to be preserved the same way as you would during an upgrade.

Answer 3

Using Wix, to allow downgrading and still have the Windows Service install properly on downgrade, use the following combination:
<Wix ...>
<Product ...>
<Property Id="REINSTALLMODE" Value="amus" />
<MajorUpgrade Schedule="afterInstallInitialize" AllowDowngrades="yes" />
I was also using WixSharp to generate the .wxs file and used this code to do so:
// https://learn.microsoft.com/en-us/windows/win32/msi/reinstallmode
// a = Force all files to be reinstalled, regardless of checksum or version.
// m = Rewrite all required registry entries from the Registry Table that go to the HKEY_LOCAL_MACHINE or HKEY_CLASSES_ROOT registry hive. Rewrite all information from the Class Table, Verb Table, PublishComponent Table, ProgID Table, MIME Table, Icon Table, Extension Table, and AppID Table regardless of machine or user assignment.Reinstall all qualified components.When reinstalling an application, this option runs the RegisterTypeLibraries and InstallODBC actions.
// u = Rewrite all required registry entries from the Registry Table that go to theHKEY_CURRENT_USER or HKEY_USERS registry hive.
// s = Reinstall all shortcuts and re-cache all icons overwriting any existing shortcuts and icons.
project.AddXml("Wix/Product", "<Property Id=\"REINSTALLMODE\" Value=\"amus\" />");
// Allow downgrading versions
// https://wixtoolset.org/documentation/manual/v3/xsd/wix/majorupgrade.html
project.AddXml("Wix/Product", "<MajorUpgrade Schedule=\"afterInstallInitialize\" AllowDowngrades=\"yes\" />");
See also:
https://learn.microsoft.com/en-us/windows/win32/msi/reinstallmode
https://wixtoolset.org/documentation/manual/v3/xsd/wix/msiproperty.html
https://wixtoolset.org/documentation/manual/v3/xsd/wix/majorupgrade.html