Appcast parser rewritten to Swift

[jozefizso]

Hi,
we are using Sparkle to update our application which integrated into Microsoft PowerPoint. Our standalone application can update using the Sparkle.framework but we need also update notifications inside PowerPoint.

As our library must be a .dylib to run inside PowerPoint, we cannot reference the full Sparkle.framework in our dynamic library target.

As we need to parse the appcast.xml file and get information if a new update is available, we need the Appcast Support part of the Sparkl project.

Would you be willing to accept PR which rewrites Appcast code to Swift?

Here is a sample code: https://github.com/slidoapp/Sparkle/tree/dev/appcast_swift_versions
And with new unit tests: https://github.com/slidoapp/Sparkle/tree/dev/appcast_swift_versions_tests

[zorgiepoo]

we are using Sparkle to update our application which integrated into Microsoft PowerPoint. Our standalone application can update using the Sparkle.framework but we need also update notifications inside PowerPoint.

As our library must be a .dylib to run inside PowerPoint, we cannot reference the full Sparkle.framework in our dynamic library target.

How does PowerPoint's or Office's plugin architecture work? If you can't bundle multiple resources it would then seem to not be very good. Is it already out-of-process from the main app or is it in-process? Sparkle's stance is to discourage injecting Sparkle into host applications that provide plug-in support and perhaps use an external tool process instead (like sparkle-cli) if needed. If multiple plug-ins use Sparkle (with the same class prefixes) injected in the same process, it's problematic.

Generally I don't want the Sparkle framework to use Swift (this is completely unrelated with how you're using Sparkle above) at least not until the deployment target is 10.14.6 or above (otherwise the framework will be bloated to include swift libraries). I don't think rewriting parts of Sparkle in Swift for the heck of it is a good justification for bumping the deployment target. Swift Package Manager sometimes causes issues when mixing Obj-C/Swift code so that would need to be assessed as well (we do provide a binary package though, so maybe the situation is different). I care about small code generation too so that would also need to be tested. Obj-C is also currently a more stable binary target (see Swift issues in swiftlang/swift#68163 for example where sometimes binary compatibility breaks).

[zorgiepoo]

Also you can dlopen a dynamic framework (Foo.framework/Foo) just like you can a dylib (foo.dylib) so I'm not sure it's actually true you're restricted to a vanilla dylib.

[jozefizso]

Yes, they use dlopen to load the addin extensions. The addin runs in-process. For simplicity of deployment we chose to use just a .dylib and not a framework.

We need only the update check to run in the PowerPoint, the whole update is implemented in our standalone app. As we parse the appcast.xml in side PowerPoint and determine there is a new version, we will call our app from command line to do the update.

[zorgiepoo]

I see. If you can call out to your app anyway, another approach is adding a CLI mode to your app that uses Sparkle to check and return if a new update is available (with checkForUpdateInformation) similar to sparkle-cli --probe

Taking parts of the appcast/downloader code for your other process is not recommended or officially supported from Sparkle's point of view.

[jozefizso]

I am exploring the use of sparkle-cli but it is not available when we reference Sparkle using Swift PM. It is not included in Sparkle-for-Swift-Package-Manager.zip neither.

[zorgiepoo]

I would just create a CLI mode in your app. It needs to create an updater (you could use SPUStandardUpdaterController still), call checkForUpdateInformation immediately after starting the updater, exit by the time -updater:didFinishUpdateCycleForUpdateCheck:error: is called, and set up a runloop. The user driver used won't matter if you exit() by then and do the update check immediately after starting the updater.

Refer to sparkle-cli code as an example of this. sparkle-cli itself is a very light wrapper around using Sparkle's framework.