[Webkit-unassigned] [Bug 237317] New: PerformanceNavigationTiming Response Start unavailable when using Service Worker Cache

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=237317

            Bug ID: 237317
           Summary: PerformanceNavigationTiming Response Start unavailable
                    when using Service Worker Cache
           Product: WebKit
           Version: Safari 15
          Hardware: Mac (Apple Silicon)
                OS: macOS 12
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Service Workers
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: daniel.schulz at baqend.com

Created attachment 453487

  --> https://bugs.webkit.org/attachment.cgi?id=453487&action=review

A Document, Script and Service Worker that exhibit the described bug

When The document is being served from a Service Worker Cache, the PerofrmanceNavigationTiming API returns always 0 for its responseStart value.
When the document comes from the Network instead of the Service Worker Cache, it responds the correct value.

I expect the responseStart value to always be reported correctly, even if it's being served from Cache.

Tested in Safari 15.2 and 15.4TP on MacOS 12.1 on a MacBook Pro M1 2020.

Steps to reproduce:
- Serve the files from the attached zip
- Open the index.html in Safari
- Reload the page

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