[webkit-dev] Runtime setting for incomplete features

Drew Wilson atwilson at google.com
Mon Oct 5 17:54:05 PDT 2009

BTW, I modeled my SharedWorker disabling after the code in
JSDOMWindowCustom::audio() that disables the audio constructor on platforms
that don't have MediaPlayer support.
I think the runtime behavior of window.audio and window.SharedWorker should
be identical in practice. Sam, it looks like you wrote
JSDOMWindowCustom::audio() - do you see its behavior as unacceptable as
well, or do you have some other code to prevent enumeration of window.audio
that I can generalize for use for SharedWorkers too?

On Mon, Oct 5, 2009 at 5:46 PM, Drew Wilson <atwilson at google.com> wrote:

> So, two weeks ago I sent an email on this thread stating exactly what I was
> planning to do, To whit:
> >>>
> I do think that we ought to be returning undefined instead of null in those
> cases, though, just to catch people who are accidentally using isUndefined()
> utility functions from common libraries. It would not be hard to define some
> kind of [mapNullToUndefined] custom attribute for the code generator.
> <<<
> Maciej and AP both chimed in saying that disabling enumeration (i.e.
> "SharedWorker in window") would be prohibitively hard, and giving a tacit OK
> to my approach (my emphasis below):
> >>>
> It would be pretty complicated to do that [disabling [LocalStorage in
> window"] based on a runtime setting. You would need a custom getter for any
> object that has properties which may appear or disappear based on settings.
> This is *probably too complicated to be worth it*. Or at least, if we
> added that level of code complexity I would begin to doubt the merits of
> supporting runtime enabling of Web platform features.
> <<<
> I'm surprised to see these objections coming up now, weeks after the
> original discussion, and only after my patch has landed in the tree. That
> said, I agree that in an ideal world, we'd hide window.audio, shared
> workers, notifications, local storage, databases, session storage and any
> other runtime/platform-disabled API from enumerations - I just agree with
> Maciej that this isn't a hugely important issue, since these features are
> only runtime-disabled while under development and so not widely available
> anyway.
> Regardless, I don't think we should rush out to roll all of those features
> out of the tree, and I certainly don't think we should be singling out
> SharedWorkers or WebSockets - if we feel strongly that this needs to be
> addressed, we can update all of those features accordingly. If people with
> knowledge of the internals of V8 and JSC can chime in, we can discuss how
> best to approach this.
> -atw
> On Mon, Oct 5, 2009 at 5:04 PM, Sam Weinig <sam.weinig at gmail.com> wrote:
>> Hi Folks,
>> I am not happy with the way these runtime settings have been implemented
>> so far as they break runtime detection using the technique we evangelize to
>> developers, specifically, using the ("property" in window) method.  A
>> feature that is turned off at runtime should not be detectable at all, using
>> any method (including Object.keys(), object.hasOwnProperty(),
>> object.propertyIsEnumerable(), for-in enumeration, etc).  I filed
>> https://bugs.webkit.org/show_bug.cgi?id=29896 when the WebSocket runtime
>> switching code went in and was disappointed to see similarly buggy code go
>> in for SharedWorkers with out this being fixed.
>> Leaving this in the tree is likely to introduce compatibility issues so I
>> would recommend that we roll out these changes if they cannot be fixed in a
>> timely manner.
>> -Sam
>> On Tue, Sep 8, 2009 at 11:47 PM, Darin Fisher <darin at chromium.org> wrote:
>>> As is described in https://bugs.webkit.org/show_bug.cgi?id=28941, for
>>> the Chromium project, we like to make incomplete features available
>>> behind a command line flag to help facilitate testing.  I understand
>>> that the norm for WebKit is to only have compile time options for new
>>> / incomplete features.  In some cases, runtime settings are defined,
>>> but these generally correspond to end user preferences or the needs of
>>> specific embedders.
>>> At any rate, I just wanted to make sure that folks were aware that
>>> some settings may only exist to help facilitate Chromium's goal of
>>> shipping incomplete features, disabled by default.
>>> Alexey asked if there are any guidelines for when these settings may
>>> be removed.  I think the main thing is that the feature has to be
>>> reasonably complete and enabled by default by embedders (e.g.,
>>> Chromium) that are compiling the feature.
>>> Regards,
>>> -Darin
>>> _______________________________________________
>>> webkit-dev mailing list
>>> webkit-dev at lists.webkit.org
>>> http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
>> _______________________________________________
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