[webkit-dev] [Proposal] Remove support for 'multipart/x-mixed-replace' main resources

Chris Dumez cdumez at apple.com
Thu Apr 23 13:11:14 PDT 2015

> On Apr 23, 2015, at 1:07 PM, Brady Eidson <beidson at apple.com> wrote:
>> On Apr 21, 2015, at 3:39 PM, Chris Dumez <cdumez at apple.com> wrote:
>> Hi,
>> I would like to suggest we remove support for 'multipart/x-mixed-replace’ main resources while keeping support for multipart images.
>> Based on Chrome usage data, this feature is extremely rarely used by Web sites (less than 0.00001% of page loads) [1]. This feature adds complexity to the loader and is a source of (security) bugs (e.g. [2] recently), current support also seems buggy.
>> Current support in Safari / WebKit:
>> - Support is not great is WebKit. If you load a Motion JPEG main resource for example, it will keep creating a new ImageDocument and all its DOM tree for every frame (tested on Safari / Mac).
>> - It looks like support is broken on Safari on iOS (I tried a Motion JPEG main resource on iOS8, I see the first frame then a blank page that never finishes loading).
>> Other browsers:
>> - Never supported by IE (including IE11) for any resource
>> - Chrome already dropped support for this (main resources only) almost 2 years ago [3].
>> - Firefox 37 still supports this based on local testing.
>> Again, I am only proposing dropping support for main resources. For e.g., having an <IMG> element in a page whose src attribute points to a Motion JPEG would still work as intended.
> I think it’s fine to drop support for multipart main resources besides MPJEG.
> I think loading MJPEG as a main resource and having it be displayed as an ImageDocument is a valuable feature, and I object to dropping support for it. I’m not sure if that’s what you’re proposing, since it’s both a main resource and a multipart image.

Yes, my proposal would break MJPEG as main resource. MJPEG is the main user of 'multipart/x-mixed-replace’ I believe. If we do want to keep supporting it, then we should probably fix support on both Mac (keeps recreating the ImageDocument) and iOS (Only shows the first frame).

 Chris Dumez - Apple Inc. - Cupertino, CA
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