[Webkit-unassigned] [Bug 236483] New: In standalone mode (PWA), page won't load when navigation preload is enabled

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=236483

            Bug ID: 236483
           Summary: In standalone mode (PWA), page won't load when
                    navigation preload is enabled
           Product: WebKit
           Version: Safari 15
          Hardware: iPhone / iPad
                OS: iOS 15
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Service Workers
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: howu at nvidia.com

Created attachment 451639

  --> https://bugs.webkit.org/attachment.cgi?id=451639&action=review

Minimal test page

On iOS 15.4 (beta), when a page runs in standalone mode with navigation preload enabled, the `preloadResponse` of the navigation request to `start_url` is a 200 with an empty response body.
If the service worker responds to the navigation request with this empty `preloadResponse`, the site cannot be loaded and the app results in a blank white screen.
This issue is not observed in non-standalone mode, nor in OS versions lower than 15.4.

Attached is a minimal test page that exhibits the issue.
Repro steps:
  1. Create a standalone homescreen icon to the attached site (on devices/simulators running iOS 15.4)
  2. Open the homescreen icon and observe that the page is loaded
  3. Swipe out the page and open it again (this time service worker is activated)
  4. Observe that the page is not loaded

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