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Re: UserAgent-specific files in Web Platform Tests

From: Mike Pennisi <mike@bocoup.com>
Date: Mon, 3 Apr 2017 10:42:51 -0400
To: Philip Jägenstedt <foolip@chromium.org>, Vincent Scheib <scheib@chromium.org>, Reilly Grant <reillyg@chromium.org>
Cc: Matt Giuca <mgiuca@chromium.org>, Giovanni Ortuño <ortuno@chromium.org>, public-test-infra@w3.org, Jeffrey Yasskin <jyasskin@chromium.org>
Message-ID: <76ce23a8-cfb2-e05f-d302-9c8bf0a8c865@bocoup.com>
I'm wondering about extending WebDriver for testing internals. By using its
built-in "Protocol Extensions" mechanism [1], each specification could 
its own definition of the API it required.

This was discussed at the "Web Platform Test Integration Convergence" 
in January. The minutes from that meeting [2] suggest some additional
considerations that I may not fully appreciate:

 > Security limitation: webdriver cannot do more things than the user can.
 > Principle is that a compromised browser shouldn't have any additional
 > ability.

It's not clear why this is taken as a principle, especially in light of the
discussion here (i.e. a JavaScript API that can do more things than the user

 > WebDriver would commit us to not using sync testing

I believe this is related to the fact that WebDriver is an HTTP-based 
so if tests were written from with the browser, they would need to be built
from asynchronous Fetch requests. I'm not sure if this is a problem, though.
Tests could be expressed with out-of-process scripts where synchronous HTTP
communication is possible. Even within the browser, support for async 
is improving rapidly [3], and this greatly reduces the cognitive overhead
usually associated with asynchronous programming in the browser.

In my mind, one of the major considerations here is security. The behaviors
we're trying to automate are taken for granted by end users. If this
functionality were mistakenly enabled on the web at large, the "User agent"
trust model would break down. It seems critical that these testing 
are only enabled in the most specific circumstances, and that they are
otherwise isolated from the web platform at large.

My concern is that if we design this functionality *too* organically, our
solution will be optimized for developer ergonomics and architectural
simplicity, and that this will be more susceptible to security 

I've read some limited criticism about the scalability of a WebDriver-backed
solution for platform testing [4], but the traits that increase overhead 
an efficiency standpoint (e.g. "a lot of communication across difference
processes") are the same traits that would discourage accidental deployment.

I'm also interested in consolidating efforts more generally; WebDriver 
is just
entering the CR phase, but it is a well-established project that was created
to address many of the needs we're discussing here. When I consider the use
cases for WebDriver and the use cases for the kind of JavaScript testing API
that's being discussed here, I see a lot of overlap. I may be missing a
distinction, though. Are their differences in the use cases? Or would a pure
JavaScript testing API make WebDriver obsolete?

This is a really important issue, so kudos to the Bluetooth team (and 
else involved) for starting the discussion early!

[1] W3C WebDriver working draft, "Protocol Extensions"
[2] "Web Platform Test Integration Convergence"
[3] caniuse.com, "Async Functions"
[4] "Input Automation in WPT Repo"

On 03/29/2017 11:08 AM, Philip Jägenstedt wrote:
> We need to figure this out for lots of specs now, and I think the 
> approach taken makes a lot of sense: specs simply define the APIs that 
> are needed to test them, it's not somebody else's problem.
> However, I would like to go a bit further and treat this more like we 
> treat any bit of API that tests define. Tests should simply assume 
> that the APIs exist, and otherwise fail. Having stubs of the APIs 
> could make test failures more explicit, but it seems like we could do 
> without them. It could be something like:
> async_test(t => {
> navigator.bluetooth.test.setLEAvailability(false);
>   // and so on
> });
> If lots of tests need the same setup, one can of course put that in a 
> shared bluetooth.js that fails more gracefully than the above one-liner.
> In order to actually make the test APIs available Chromium might need 
> to do some things in its testharnessreport.js, or perhaps provide a 
> command-line flag if we can figure out how to make it work for vanilla 
> Chrome builds. In any case, web-platform-tests would just assume their 
> presence.
> Would that work?
> Since we're trying to come up with a solution that can be copy-pasted 
> into other areas, there is the question of a namespace. One approach 
> is to just say that all specs are free to put their testing APIs 
> wherever they like. To be specified using Web IDL, if not implemented 
> that way, it might end up requiring a [Testing] extended attribute so 
> that it's clear what things are for testing only.
> Another approach which I've argued for is to have a testing namespace, 
> and that all specs would put their testing stuff in a "partial 
> namespace testing", leaving us with a single object to expose or not 
> expose.
> At this point, I'm inclined to say we should /not/ enforce a testing 
> namespace, and just see what people end up doing organically. As long 
> as the APIs are only used in web-platform-tests, making changes to 
> harmonize after the fact will be possible, if so desired.
> Feedback from non-Chromium folks much appreciated :)
> On Thu, Mar 16, 2017 at 5:26 AM Vincent Scheib <scheib@chromium.org 
> <mailto:scheib@chromium.org>> wrote:
>     +1
>     stubs sounds good, and if possible the stubs would throw an assert
>     pointing to instructions regarding how the platform-fakes files
>     are intended to be replaced with implementations.
>     On Wed, Mar 15, 2017 at 11:42 AM, Reilly Grant
>     <reillyg@chromium.org <mailto:reillyg@chromium.org>> wrote:
>         I would like to try formally specifying this for WebUSB as well.
>         On Thu, Mar 9, 2017 at 8:05 PM Matt Giuca <mgiuca@chromium.org
>         <mailto:mgiuca@chromium.org>> wrote:
>             I love this approach! Thanks for sharing and the write-up,
>             Gio.
>             > On the main repo that file would be empty but on the Chromium repo that file
>             would have the necessary code to fake devices in Chromium.
>             s/empty/stubs?
>             I would definitely be up for converting my navigator.share
>             <https://cs.chromium.org/chromium/src/third_party/WebKit/LayoutTests/webshare/share-success.html>
>             and navigator.getInstalledRelatedApps
>             <https://cs.chromium.org/chromium/src/third_party/WebKit/LayoutTests/installedapp/getinstalledrelatedapps.html> layout
>             tests (which currently use an explicit mock of calls to
>             the Mojo service) to a standard fake interface. Since my
>             APIs are significantly simpler than Bluetooth, I might
>             give it a shot and report back to this group. (Note though
>             that they aren't standardised yet so I'm not sure if
>             they'd be includeable in TestHarness. Still would serve as
>             a useful case study.)
>             On Fri, 10 Mar 2017 at 14:52 Giovanni Ortuño
>             <ortuno@chromium.org <mailto:ortuno@chromium.org>> wrote:
>                 Hi all,
>                 Some context: We, the Web Bluetooth team, are looking
>                 into upstreaming our Chromium Layout Tests to Web
>                 Platform Tests. In order to test the Web Bluetooth
>                 API, we are introducing a Test API that accompanies
>                 the spec and allows our tests to fake Bluetooth
>                 Devices: Web Bluetooth Test
>                 <https://docs.google.com/document/d/1Nhv_oVDCodd1pEH_jj9k8gF4rPGb_84VYaZ9IG8M_WY/edit#heading=h.ap8dnjfog4qc>.
>                 Parts of this API are implemented in JS. These parts
>                 are Chromium specific, e.g. how to talk with our IPC
>                 system, so it wouldn't make sense to include them as
>                 resources.
>                 To that extent, we would like to add a file called
>                 "web-bluetooth-test.js" which would be similar to
>                 "testharnessreport.js" to the testharness repo. On the
>                 main repo that file would be empty but on the Chromium
>                 repo that file would have the necessary code to fake
>                 devices in Chromium.
>                 There are many APIs that follow a similar pattern:
>                 they define a Test API surface that they use to fake
>                 behavior. Some examples include Geolocation
>                 <https://cs.chromium.org/chromium/src/third_party/WebKit/LayoutTests/geolocation-api/error.html?type=cs&q=mojo-helpers+file:%5Esrc/third_party/WebKit/LayoutTests/geolocation-api/+package:%5Echromium$&l=17>,
>                 Vibration
>                 <https://cs.chromium.org/chromium/src/third_party/WebKit/LayoutTests/vibration/vibration-durations.html?l=13>,
>                 NFC
>                 <https://cs.chromium.org/chromium/src/third_party/WebKit/LayoutTests/nfc/push.html?l=73>,
>                 Sensors
>                 <https://cs.chromium.org/chromium/src/third_party/WebKit/LayoutTests/sensor/accelerometer.html?l=45>,
>                 etc. So we think it would make sense to add a folder
>                 to include all of these Test APIs in, straw-man
>                 proposal: platform-fakes.
>                 ./
>                 ./testharness.js
>                 ./testharnessreport.js
>                 ./platform-fakes/web-bluetooth-test.js
>                 ./platform-fakes/geolocation-test.js
>                 ...
>                 Do y'all think this is a good approach?
>                 Let me know what you think,
>                 Gio
Received on Monday, 3 April 2017 14:43:26 UTC

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