Bug 238442 – SharedArrayBuffers do not get cloned on some messaging APIs

• Status: NEW
• Component: JavaScriptCore

Created attachment 455893 [details]
reproduction with visible console and Safari version

Example repro: https://github.com/jrvidal/message-port-repro/tree/master/clone
Working deployment: https://sab-clone.herokuapp.com/

When sending a message containing a `SharedArrayBuffer`, the receiving end sometimes receives a regular, deep copied `ArrayBuffer` instead of a proper clone pointing to the same bytes.

In the example provided, it can be consistently reproduced when posting a message through a `MessagePort` or a `BroadcastChannel`.

[Radar WebKit Bug Importer]

<rdar://problem/90919367>

[Ahmad Saleem]

All browsers result:

*** Safari 16 on macOS 12.6 ***

from worker - SharedArrayBuffer (length 10)
from broadcast - ArrayBuffer (length 10)
from port - ArrayBuffer (length 10)

*** Safari Technology Preview 153 ***

from worker - SharedArrayBuffer (length 10)
from broadcast - ArrayBuffer (length 10)
from port - ArrayBuffer (length 10)

*** Chrome Canary 107 ***

from worker - SharedArrayBuffer (length 10)
from broadcast - null
from port - SharedArrayBuffer (length 10)

*** Firefox Nightly 106 ***

Did not get anything in Console

_______

Just wanted to share updated status. Thanks!

[Sam Verschueren]

I've just tested this again in Safari Technology Preview and this seems to be fixed.

from worker - SharedArrayBuffer (length 10)
from broadcast - SharedArrayBuffer (length 10)
from port - SharedArrayBuffer (length 10)

However, it's weird that Safari sends the SAB over a broadcast channel while Chrome receives `null`. So maybe that's still a bug.

[Yusuke Suzuki]

(In reply to Sam Verschueren from comment #3)
> I've just tested this again in Safari Technology Preview and this seems to
> be fixed.
> 
> from worker - SharedArrayBuffer (length 10)
> from broadcast - SharedArrayBuffer (length 10)
> from port - SharedArrayBuffer (length 10)
> 
> However, it's weird that Safari sends the SAB over a broadcast channel while
> Chrome receives `null`. So maybe that's still a bug.

Isn't it a Chrome bug?
CC @Chris.

[Sam Verschueren]

Yes this might be on Chrome actually. In Firefox it’s also a SharedArrayBuffer. Not sure what the spec says about it, but my assumption is that it should be a SAB instead of null.