[webkit-dev] AppCache functionality provided by the embedder of webkit

Michael Nordman michaeln at google.com
Tue Apr 7 12:23:44 PDT 2009

On Tue, Apr 7, 2009 at 11:27 AM, Maciej Stachowiak <mjs at apple.com> wrote:

> On Apr 7, 2009, at 10:52 AM, Michael Nordman wrote:
>  I'm working on the app cache for Chrome. We've decided to hoist most the
>> functionality provided by the app cache into Chrome's main browser process,
>> so we won't be using most of the implementation provided by WebKit. I'd like
>> to work through what changes to make within WebKit/WebCore to allow an
>> embedder pull that off. Any suggestions would be much appreciated.
> One downside of this approach is that, if the application cache ever needs
> to change, it may be necessary to make changes to two separate
> implementations hosted in different repositories. In addition,
> quality-of-implementation improvements to one version won't benefit the
> other.

Please see my response to Darin earlier. There may be an opportunity to
replace WebKit's impl of this feature with one that has more manageable
dependencies. Perhaps chrome's implementation could be the basis for that
replacement which could then be used within webkiit proper and within
chrome's browser process.

A first step along this path could be enabling somebody to wire in a
different implementation that is lagging the current incarnation found in
webkit at the moment and not ready for the prime time just yet.

Some additional info about Chrome's as yet non-existent impl. It needs to be
fairly independent of the core chrome codebase in order for it to be
testable in our current testing infrastructure for the layout tests. This is
a design constraint which will keep me honest regarding dependencies.

> It's been a recurring theme for the Chrome team to request hooks to bypass
> WebKit functionality and replace it with Chrome-specific code that lives
> outside the WebKit tree. So far this has been mostly for code developed when
> Chrome was originally a secret project. While we felt it was best to
> grandfather in the existing carve-outs, in general I believe this is not the
> best way to move the WebKit project forward. I would not like to see this
> pattern replicated for newly developed functionality.

WebKit could grow a stronger sense of frontend vs backend that don't share
an address space for features that require touching browser wide state. The
current model for webkit doesn't lend itself well for that. We struggle with
that a fair amount.

> Regards,
> Maciej
>> In the code base right now, a single compilation flag enables or disables
>> everything to do with app cache in WebKit, ENABLE(OFFLINE_APPLICATION). This
>> turns on/off the scriptable interface bits as well as the backend
>> implementation within webcore. I think I'd like a way to reuse the
>> scriptable interface related bits provided by webkit, but to slide a chrome
>> specific implementation under that interface. One thought was to separate
>> this single flag into two flags, one for the scriptable interface bits and
>> the other for the back end implementation.
>> - surfaces the window.applicationCache property
>> - pulls in the DOMApplicationCache.idl file
>> - enables event targeting stuff for DOMApplicationCache
>> - perhaps defines an abstract interface that a c++ class backing
>> DOMApplicationCache scriptable API must implement
>> also enabled
>> - turns on the rest of the stuff in webkit for app cache, including a
>> concrete implementation of that abstract interface mentioned above.
>> Does something along these lines make sense, or perhaps there is another
>> way to approach this?
>> Thnx
>> Michael
>> _______________________________________________
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>> webkit-dev at lists.webkit.org
>> http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
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