[iOS] MobileSafari crashes at WebCore: WebCore::VideoFullscreenInterf…

…aceAVKit::doEnterFullscreen

https://bugs.webkit.org/show_bug.cgi?id=221863
<rdar://73861140>

Patch by Jean-Yves Avenard <jya@apple.com> on 2021-02-14
Reviewed by Darin Adler.

On iPad, it's possible for AVKit to fail due to racing requests to exit full screen and enter full screen. The enterFullscreenHandler would attempt to immediately re-enter full screen.
For now we bail-out early to avoid the crash. In a follow-up patch we will ensure that the condition to enter fullscreen while there's a pending operation to exit fullscreen can't occur.
No new tests, can't reproduce. Analysis has been entirely theoretical.

* platform/ios/VideoFullscreenInterfaceAVKit.mm:
(VideoFullscreenInterfaceAVKit::enterFullscreenHandler):
Exit early if error returned.

Canonical link: https://commits.webkit.org/234077@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@272841 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Source/WebCore/ChangeLog

@@ -1,3 +1,19 @@
+2021-02-14  Jean-Yves Avenard  <jya@apple.com>
+
+        [iOS] MobileSafari crashes at WebCore: WebCore::VideoFullscreenInterfaceAVKit::doEnterFullscreen
+        https://bugs.webkit.org/show_bug.cgi?id=221863
+        <rdar://73861140>
+
+        Reviewed by Darin Adler.
+
+        On iPad, it's possible for AVKit to fail due to racing requests to exit full screen and enter full screen. The enterFullscreenHandler would attempt to immediately re-enter full screen.
+        For now we bail-out early to avoid the crash. In a follow-up patch we will ensure that the condition to enter fullscreen while there's a pending operation to exit fullscreen can't occur.
+        No new tests, can't reproduce. Analysis has been entirely theoretical.
+
+        * platform/ios/VideoFullscreenInterfaceAVKit.mm:
+        (VideoFullscreenInterfaceAVKit::enterFullscreenHandler):
+        Exit early if error returned.
+
 2021-02-13  Darin Adler  <darin@apple.com>
 
         Crash calling replaceTrack on a sender that outlives its RTCPeerConnection

Source/WebCore/platform/ios/VideoFullscreenInterfaceAVKit.mm

@@ -1576,8 +1576,11 @@ - (void)removeFromParentViewController
 
 void VideoFullscreenInterfaceAVKit::enterFullscreenHandler(BOOL success, NSError* error)
 {
-    if (!success)
+    if (!success) {
         WTFLogAlways("-[AVPlayerViewController enterFullScreenAnimated:completionHandler:] failed with error %s", [[error localizedDescription] UTF8String]);
+        ASSERT_NOT_REACHED();
+        return;
+    }
 
     LOG(Fullscreen, "VideoFullscreenInterfaceAVKit::enterFullscreenStandard - lambda(%p)", this);
     if (!m_standby) {