Add WebView on iOS support with a note specifying the limitations

[Bashamega]

Summary

This PR adds webview on iOS support with a not specifying the limitations

Test results and supporting details

stackoverflow.com/a/64155509/3255152

webkit.org/blog/10882/app-bound-domains

Related issues

fixes #27470

[github-actions]

Tip: Review these changes grouped by change (recommended for most PRs), or grouped by feature (for large PRs).

[ddbeck]

This note needs to explain what "works" means. I'd expect to see something like…

The ServiceWorker API is not exposed unless the webview is configured for app bound domains…

Or depending on the particulars, this data might somewhere else, e.g.,:

The navigator.serviceWorker.register() method throws unless the webview is configured for app bound domains…

[Bashamega]

Unfortunately, I don't know the particulars for it.

[Elchi3]

@NiklasMerz Do you know anything about this? Something worth recording in BCD?

If not, we'll close this PR.

[NiklasMerz]

I haven't used ServiceWorkers in WKWebView myself but this limitation seems to be correct. I found multiple sources and this WebKit bug: https://bugs.webkit.org/show_bug.cgi?id=206741. That also states it's supported only for HTTP and HTTPs whereas some WebView developers (including Cordova, Capacitor) use custom schemes.

Supporting ServiceWorker only with AppBound domains and HTTP(S) is a serious limitation worth recording in BCD I think.

[ddbeck]

Thank you, @NiklasMerz! One follow up: do you have any idea how the limitation manifests? The linked bug doesn't explain what lack of support means exactly (e.g., does "serviceWorker" in navigator return false? Is ServiceWorker exposed regardless? Or is there some kind of exception on registration?).

[Elchi3]

It seems it is not exposed by default. However, I seem to have been testing in WKWebView 18.7. I filed WebView-CG/CanIWKWebView#7 on your repo.

[NiklasMerz]

I'm pretty sure that's just some user agent lying from WebKit. If your iOS is up-to-date you are using the most recent version of WKWebView.

[Elchi3]

OK, thank you! I enabled "Limit to App-Bound Domains" in your app's config but still no luck seeing ServiceWorker exposed. Do I also need "Web Browser entitlement"? How is that possible?

[Elchi3]

Also, where do I set the domains for "App-Bound Domains"?

[NiklasMerz]

You need to set the domains in Info.plist (there is an UI for that not sure what it's called from memory) and then webViewConfiguration.limitsNavigationsToAppBoundDomains = YES;

https://webkit.org/blog/10882/app-bound-domains/

(I tried AppBoundDomains many years ago but it didn't work for my use case so I'm not sure how it works today).