[Webkit-unassigned] [Bug 215805] New: Happens requests to the fallback image when the script detach and re-instert <source/> under <picture/> on document tree

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=215805

            Bug ID: 215805
           Summary: Happens requests to the fallback image when the script
                    detach and re-instert <source/> under <picture/> on
                    document tree
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Images
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: tetsuharu.ohzeki at gmail.com

Created attachment 407183

  --> https://bugs.webkit.org/attachment.cgi?id=407183&action=review

testcase

## Environments
* Safari 14 on Big Sur beta 5
        * Safari TP 112 on that is also reproducible.

## Step to Reproduce
1. Extract testcase.zip.
2. Run `python -m SimpleHTTPServer`
3. Open Safari and open safari’s developer tools’ network pane.
4. Open index.html via launched in _step 2_.

## Expected Result
For images, Safari requests only `example_webp.webp`.

## Actual Result
For images Safari requests both of `example_webp.webp` and `example_png.png`

Sadly, today’s website use react or other view libraries to conceal an actual DOM manipluations. Their library are sometimes used to  “hydrates” web page on static html served by a server-side, then this kind of bugs causes multiple undesired image requests accidentally.

With webbev’s hat, the combination of `<picture/>` and `<source type="image/webp"/>` are used as progressive enhancement techniques to use WebP images for supported browsers to reduce network bandwidth.   So this kind of bugs are not desired behavior.

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