Bug 217949

Summary:	resize event is not fired while the page is still loading
Product:	WebKit	Reporter:	Maxim Tsoy <muodov>
Component:	Layout and Rendering	Assignee:	Nobody <webkit-unassigned>
Status:	NEW ---
Severity:	Normal	CC:	ahmad.saleem792, ap, bfulgham, cdumez, dbates, muodov, rniwa, simon.fraser, smoley, thorton, webkit-bug-importer, wenson_hsieh, zalan
Priority:	P2	Keywords:	InRadar
Version:	Safari 14
Hardware:	iPhone / iPad
OS:	Unspecified
URL:	http://x.zok.pw/ios-iframe-resize/parent.html

Description Maxim Tsoy 2020-10-20 05:25:08 PDT

It seems like Safari on iOS/iPadOS does not trigger resize events until all the page resources are loaded.

Steps to reproduce:
1. Open http://x.zok.pw/ios-iframe-resize/parent.html
2. Press the "open slowchild" button
3. Observe that there is no messages about resize events inside the iframe

Expected behaviour: there should be a resize event detected at step 3.

The test page contains the second button "open child", which opens a similar frame without slow resources. In this case, `onload` event is fired before the resize, and resize event is correctly fired inside the frame.

Notes:
I could reproduce this bug only on iOS. Desktop Safari, Chrome and Firefox trigger the resize vent as expected.

According to the HTML spec (Step 4 of https://html.spec.whatwg.org/multipage/webappapis.html#update-the-rendering), user agent can decide to skip the resize steps, but in this case the viewport has actually changed. This is also detected in the test page.

Comment 1 Maxim Tsoy 2020-10-20 08:21:47 PDT

After some more testing, I could reproduce the issue even after the iframe reached the `complete` document state, so I'm not sure if it's related to the DOM ready state.
It seems to reproduce reliably on the provided test page, so hopefully it will be helpful to find the root cause.

Comment 2 Alexey Proskuryakov 2020-10-21 17:33:04 PDT

I can reproduce. The resize event also fails to trigger when rotating.

See this code in FrameView.cpp:

#if PLATFORM(IOS_FAMILY)
    // Don't send the resize event if the document is loading. Some pages automatically reload
    // when the window is resized; Safari on iOS often resizes the window while setting up its
    // viewport. This obviously can cause problems.
    if (DocumentLoader* documentLoader = frame().loader().documentLoader()) {
        if (documentLoader->isLoadingInAPISense())
            return;
    }
#endif

Comment 3 Radar WebKit Bug Importer 2020-10-22 10:29:12 PDT

<rdar://problem/70579052>

Comment 4 Simon Fraser (smfr) 2020-10-22 11:11:22 PDT

That's on old change from iOS WebKit upstreaming. Could potentially be re-visited.

Comment 5 Ahmad Saleem 2022-09-12 14:43:42 PDT

I am able to reproduce this on iOS 16 (Safari 16) as well.

>> Safari Desktop:

I'm a slow child window

Mon Sep 12 2022 22:41:23 GMT+0100 (British Summer Time) resize event fired

Broken Image icon

>> Safari iOS:

I'm a slow child window

Broken Image icon