Bug 188329 – navigator.sendBeacon does not work in pagehide callbacks

• Status: RESOLVED
• Resolution: FIXED
• Component: WebCore Misc.

[Philip Walton]

Initial support for navigator.sendBeacon was added here: https://bugs.webkit.org/show_bug.cgi?id=175007,
but if you try to invoke navigator.sendBeacon() in a pagehide event listener, it fails and you get a warning in the console:

> Beacon API cannot load ... due to access control checks

Note that this is the same error you'd get if you tried to do a fetch() or xhr in a pagehide event listener, so I suspect the same rules are being enforced. However, beacons should not be subject to the same restrictions since they're designed to not block or require waiting for a response. (Note, this is also true of any fetch() with the keepalive flag set to true and should be considered when webkit implements keepalive: https://bugs.webkit.org/show_bug.cgi?id=168865).

All other browsers that support the Beacon API or fetch keepalive allow these requests to be sent in the pagehide event listener.

[Chris Dumez]

Likely caused:
    // Prevent new loads if we are in the PageCache or being added to the PageCache.
    // We query the top document because new frames may be created in pagehide event handlers
    // and their pageCacheState will not reflect the fact that they are about to enter page
    // cache.
    if (auto* topDocument = frame.mainFrame().document()) {
        if (topDocument->pageCacheState() != Document::NotInPageCache) {
            RELEASE_LOG_IF_ALLOWED("load: Already in page cache or being added to it (frame = %p)", &frame);
            failBeforeStarting();
            return;
        }
    }

in CachedResource::load(CachedResourceLoader&).

Seems like a bad bug indeed.

[Chris Dumez]

Created attachment 346740 [details]
Patch

[WebKit Commit Bot]

Comment on attachment 346740 [details]
Patch

Clearing flags on attachment: 346740

Committed r234684: <https://trac.webkit.org/changeset/234684>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.

[Radar WebKit Bug Importer]

<rdar://problem/43030256>

[Martin Kuba]

I am still seeing this in Safari 12.  Has this patch been included in Safari 12?

[Chris Dumez]

(In reply to martin from comment #6)
> I am still seeing this in Safari 12.  Has this patch been included in Safari
> 12?

No, the change missed the cut-off date for iOS 12. It will be fixed in a later release but cannot comment on when.

[Ryosuke Niwa]

You can try out Safari Technology Preview, which has this fix: https://developer.apple.com/safari/technology-preview/

[Chris Dumez]

This fix shipped in iOS 12.2 and macOS 10.14.4.

This was supposed to have been fixed with iOS 12.2, but I'm still experiencing this issue on an iPad (5th generation) with iPadOS 14.0.1. I now updated it to 14.2, but the issue persists.

Here's a very simple test file that should create an empty file with the current timestamp via PHP if the beacon is sent:

<?php
if (isset($_GET['beacon'])) {
    file_put_contents(microtime(true), '');
    exit;
}
?>
<script>
document.addEventListener('visibilitychange', function() {
    console.log(navigator.sendBeacon(window.location.href + '?beacon=1', new ArrayBuffer([])));
});
document.addEventListener('pagehide', function() {
    console.log(navigator.sendBeacon(window.location.href + '?beacon=1', new ArrayBuffer([])));
});
</script>
<a href="../">Link</a>
?>

It works when switching to another tab and back, but not when following a link or closing the tab.

[Ryosuke Niwa]

(In reply to connum+webkitbugzilla from comment #10)
> This was supposed to have been fixed with iOS 12.2, but I'm still
> experiencing this issue on an iPad (5th generation) with iPadOS 14.0.1. I
> now updated it to 14.2, but the issue persists.
> 
> Here's a very simple test file that should create an empty file with the
> current timestamp via PHP if the beacon is sent:
> 
> <?php
> if (isset($_GET['beacon'])) {
>     file_put_contents(microtime(true), '');
>     exit;
> }
> ?>
> <script>
> document.addEventListener('visibilitychange', function() {
>     console.log(navigator.sendBeacon(window.location.href + '?beacon=1', new
> ArrayBuffer([])));
> });
> document.addEventListener('pagehide', function() {
>     console.log(navigator.sendBeacon(window.location.href + '?beacon=1', new
> ArrayBuffer([])));
> });
> </script>
> <a href="../">Link</a>
> ?>
> 
> It works when switching to another tab and back, but not when following a
> link or closing the tab.

I think Chris recently fixed a bug that iOS WebKit didn't fire visibilitychange or pagehide event when we navigated to a new page or closed the tab.

[Chris Dumez]

(In reply to Ryosuke Niwa from comment #11)
> (In reply to connum+webkitbugzilla from comment #10)
> > This was supposed to have been fixed with iOS 12.2, but I'm still
> > experiencing this issue on an iPad (5th generation) with iPadOS 14.0.1. I
> > now updated it to 14.2, but the issue persists.
> > 
> > Here's a very simple test file that should create an empty file with the
> > current timestamp via PHP if the beacon is sent:
> > 
> > <?php
> > if (isset($_GET['beacon'])) {
> >     file_put_contents(microtime(true), '');
> >     exit;
> > }
> > ?>
> > <script>
> > document.addEventListener('visibilitychange', function() {
> >     console.log(navigator.sendBeacon(window.location.href + '?beacon=1', new
> > ArrayBuffer([])));
> > });
> > document.addEventListener('pagehide', function() {
> >     console.log(navigator.sendBeacon(window.location.href + '?beacon=1', new
> > ArrayBuffer([])));
> > });
> > </script>
> > <a href="../">Link</a>
> > ?>
> > 
> > It works when switching to another tab and back, but not when following a
> > link or closing the tab.
> 
> I think Chris recently fixed a bug that iOS WebKit didn't fire
> visibilitychange or pagehide event when we navigated to a new page or closed
> the tab.

pagehide should reliably fire when navigating away. It was "visibilitychange not firing on navigating away" that I fixed recently.

[Daniel Dickison]

FWIW, I'm also seeing sendBeacon fail to send when triggered from a pagehide event listener on iOS 14. I don't see the error message quoted in the original bug report:

> Beacon API cannot load ... due to access control checks

In fact, I don't see anything in the console when navigating away from a page with Preserve Log enabled. I'm only deducing that pagehide is firing by experimenting with https://event-logger.glitch.me

This is with iOS 14.2.1 on an iPhone 12 mini.

Should this be filed as a new bug?

[Daniel Dickison]

I apologize, my last comment is inaccurate. I was mislead by the fact the console.log during some page navigation pagehide events don't appear even with Preserve Log enabled, but the beacon requests do go out.

tl;dr: It's working for me on iOS 14.2.1.

(In reply to Daniel Dickison from comment #13)
> FWIW, I'm also seeing sendBeacon fail to send when triggered from a pagehide
> event listener on iOS 14. I don't see the error message quoted in the
> original bug report:
> 
> > Beacon API cannot load ... due to access control checks
> 
> In fact, I don't see anything in the console when navigating away from a
> page with Preserve Log enabled. I'm only deducing that pagehide is firing by
> experimenting with https://event-logger.glitch.me
> 
> This is with iOS 14.2.1 on an iPhone 12 mini.
> 
> Should this be filed as a new bug?