[webkit-dev] Blob scheme implementation

[Darin Fisher]

On Wed, Sep 15, 2010 at 1:06 PM, Darin Fisher <darin at chromium.org> wrote:

> On Wed, Sep 15, 2010 at 12:56 PM, Maciej Stachowiak <mjs at apple.com> wrote:
>
>>
>> On Sep 15, 2010, at 9:15 AM, Darin Fisher wrote:
>>
>> On Wed, Sep 15, 2010 at 8:58 AM, Alexey Proskuryakov <ap at webkit.org>wrote:
>>
>>>
>>> 14.09.2010, в 22:15, Darin Fisher написал(а):
>>>
>>> > I think it makes sense to extend ResourceHandle.cpp to access the
>>> BlobRegistry singleton in order to support blob URLs.
>>>
>>>
>>> The problem I see with adding blob support to ResourceHandle is that it
>>> makes it too difficult to maintain. It used to be a platform abstraction,
>>> and it was hard enough to make sure it worked well across platforms. Adding
>>> a significant amount of cross-platform logic on top of that isn't going to
>>> make it easier - especially when it's done via subclassing.
>>>
>>
>> I don't understand why this seems so complicated.  ResourceHandle.cpp
>> contains some code that is shared by all WebKit ports that can access their
>> network stack directly from the WebKit main thread.  It already has some
>> common code for handling certain error cases (invalid URL, bad port).  This
>> is the best point in the code to integrate blob URL support.
>>
>> Maybe subclassing ResourceHandle is not the best way to go about this.  It
>> seems fairly clean to me, but then, I'm not sure what the alternative
>> proposals look like.
>>
>>
>> I posted a proposal yesterday (do it at the ResourceLoader layer, since
>> that's how the app cache hooks in).
>>
>
> That means that app cache doesn't work for HTML5 media in !Chromium.  It
> also means that blob URLs won't work for HTML5 media in !Chromium.
>
>
>>
>>
>>
>>
>>>
>>> An example that prompted me to look into this was <
>>> http://trac.webkit.org/changeset/67503>. Here, a static function that
>>> reported platform capabilities had to become virtual, so that it could take
>>> blob loading logic into account. There is nothing in common between "are we
>>> running on a version of Mac OS X that supports this" and "are we loading a
>>> blob", and remembering this twist won't be easy.
>>>
>>
>> Perhaps the static function should remain but be renamed?  That way it can
>> remain the function that reports platform capabilities.  However, as this
>> patch demonstrates, from WebCore's point of view, this needs to be a
>> property of ResourceHandle.
>>
>> Maybe it would help if we better formalized the abstraction to the network
>> stack and let ResourceHandle grow to be a smart (contains cross-platform
>> helper code) front-end to that.
>>
>>
>> I think that's not the right design. ResourceHandle is supposed to be a
>> thin abstraction on top of the network library. ResourceLoader is supposed
>> to be the "smart" layer.
>>
>>
> I don't see any other examples of URL schemes being handled at the
> ResourceLoader level.
>

I'm ignoring javascript: URLs because they are super weird... evaluation
happens synchronously and can have side effects such as causing other
navigations.  It does not fit the normal mold of URL loading.  Mozilla tries
to express javascript: URLs as a protocol handler, and it only adds
complexity.  The WebKit approach of implementing javascript: URLs as special
cases in FrameLoader is superior because it makes the code easier to
understand.

-Darin


>
> I'm not thrilled to introduce more ways in which Chromium and !Chromium
> differ, but integrating blob URLs at the ResourceLoader is not an option for
> Chromium.
>
> -Darin
>
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