Re: Preloading using JS instead of a tag

If we want WebBundles to fit into today's pages (which e.g. include
`<script src>` tags), we need an imperative mechanism to load them and tell
the browser about the resources they contain.
An imperative mechanism to load them would only be effective for
dynamically loaded resources, which are inherently slower to discover. It
would be a shame if we ended up encouraging that pattern.

Would moving away from `<link>` to e.g. `<base>` (as Mike suggested) or
`<script type=bundle>` address your concerns?

On Fri, Aug 28, 2020 at 11:33 AM Krzysztof Kotowicz <koto@google.com> wrote:

> The DOM tree can also change dynamically. If the element that controls the
> bundle loading is inserted via JS, would that also affect raciness? If so,
> there's little way around it, short of ignoring the behavior when added
> dynamically (which might be surprising for authors).
>
> On Fri, Aug 28, 2020 at 10:58 AM Yoav Weiss <yoavweiss@google.com> wrote:
>
>> An imperative mechanism to load bundles would be inherently racy - the
>> preloadScanner would not be aware of it, and can kick off script requests
>> before their bundles are discovered.
>>
>> If `<link>` is a risky choice here, I'm fine with a different tag to do
>> the same. I have no strong opinion regarding what would be a good
>> alternative.
>>
>> On Fri, Aug 28, 2020 at 10:44 AM Mike West <mkwst@google.com> wrote:
>>
>>> I don't have a strong opinion about the mechanism, but I do think the
>>> risk ascribed to the `<link>` approach is real.
>>>
>>> If declarative mechanisms are preferred, I wonder if an extension to
>>> `<base>` would be more appropriate here than an extension to `<link>`.
>>> `<base>` already affects resource loading across the page (in kinda
>>> terrible ways, but still!), and so already needs to be addressed by folks
>>> who aim to sanitize user input.
>>>
>>> It also is suggested to be invalid outside of `<head>`, which would be
>>> similarly helpful if browsers implemented that as a requirement; there
>>> doesn't seem to be a WPT for it, and Chromium at least would fail.
>>>
>>> -mike
>>>
>>>
>>> On Fri, Aug 28, 2020 at 9:18 AM Hayato Ito <hayato@google.com> wrote:
>>>
>>>> Hi Ryosuke. Thanks for sharing concerns.
>>>>
>>>> I'm wondering if we have imperative JS APIs which are *equivalent* to
>>>> declarative one, some of the security concerns will be addressed?
>>>>
>>>> Imperative JS APIs can be something like:
>>>>
>>>> <script>
>>>> // Tentative ideas. API surfaces do not matter for now.
>>>> document.webbundles.add({
>>>>   href: 'https://www.exmaple.com/foo.wbn',
>>>>   resources: ['https://www.exmaple.com/a.png', '
>>>> https://www.exmaple.com/b.css', ...]
>>>> });
>>>> </script>
>>>>
>>>> # Then, UA will try to load 'https://www.exmaple.com/a.png' (the same
>>>> origin resource of the bundle) from the specified bundle, instead of the
>>>> network.
>>>> <img src='https://www.exmaple.com/a.png'>
>>>>
>>>> Is my understanding correct?
>>>>
>>>> On Fri, Aug 28, 2020 at 2:30 PM Ryosuke Niwa <rniwa@apple.com> wrote:
>>>>
>>>>>
>>>>> On Aug 27, 2020, at 1:05 PM, Jeffrey Yasskin <jyasskin@google.com>
>>>>> wrote:
>>>>>
>>>>> Hi Web Perf experts,
>>>>>
>>>>> We're working <https://www.chromestatus.com/feature/5710618575241216>
>>>>> on using (unsigned) web bundles to help with preloading subresources. The
>>>>> current design is at
>>>>> https://github.com/WICG/webpackage/blob/master/explainers/subresource-loading.md,
>>>>> but roughly the idea is that a page would build a bundle of the
>>>>> subresources it intends to use and put a
>>>>>
>>>>> <link rel="webbundle" href="/the_bundle.wbn" scope="/resources">
>>>>>
>>>>> with their other preloads (or one of several variations). After that,
>>>>>
>>>>> <script src="/resources/foo.js">
>>>>>
>>>>> would find the version in the bundle instead of having to fetch it
>>>>> independently.
>>>>>
>>>>>
>>>>> This isn’t about preloading is it? This will actually affect the
>>>>> resource being used by that script element. preload doesn’t do that so this
>>>>> is a pretty different feature.
>>>>>
>>>>> In https://github.com/WICG/webpackage/issues/580, Krzysztof worries
>>>>> that adding any new way for a <link> tag to affect script loading is a
>>>>> security risk, because pages may not be as careful about preventing users
>>>>> from injecting <link> tags as they are about <script> tags. Instead, he
>>>>> suggests using a Javascript API to tell the browser to preload subresources
>>>>> using a bundle.
>>>>>
>>>>>
>>>>> That would be a pretty serious security risk. Putting all other
>>>>> objections against web packaging / web bundles aside, this will be a pretty
>>>>> big show stopper.
>>>>>
>>>>> - R. Niwa
>>>>>
>>>>>
>>>>
>>>> --
>>>> Hayato
>>>>
>>>
>
> --
> koto@ / Krzysztof Kotowicz / Google
>

Received on Friday, 28 August 2020 09:49:15 UTC