Got positive signal from Safari.
On Wednesday, January 15, 2025 at 5:25:48 PM UTC+1 Chris
Harrelson wrote:
Please also fill out the various reviews in your chromestatus
entry (privacy, security, enterprise, debuggability, testing).
On Tue, Jan 14, 2025 at 2:43 PM 'Liang Zhao (REDMOND)' via
blink-dev <blin...@chromium.org> wrote:
*From:*Mike Taylor <mike...@chromium.org>
*Sent:* Tuesday, January 14, 2025 7:10 AM
*To:* Liang Zhao (REDMOND) <liang...@microsoft.com>;
blin...@chromium.org
*Cc:* hiro...@chromium.org; mk...@chromium.org
*Subject:* [EXTERNAL] Re: [blink-dev] Intent to Ship:
Fire error event instead of throwing for CSP blocked worker
You don't often get email from mike...@chromium.org.
Learn why this is important
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On 1/13/25 5:19 PM, 'Liang Zhao (REDMOND)' via blink-dev
wrote:
*Contact emails*
lz...@microsoft.com
*Explainer*
None
I think an explainer (or even an inline text explaining the
change, providing an example, etc) would have significantly
helped folks understand what it is that you're trying to ship.
Could you write something to that effect?
When the url is blocked by Content Security Policy, script code
“new Worker(url)” and “new SharedWorker(url)” currently throws
exception. According to spec, the CSP check is done as part of
fetch which happens asynchronously and the constructor should not
throw. Instead an error event should fire after the object is
returned.
This feature aligns Chromium behavior with spec.
*Specification*
https://fetch.spec.whatwg.org/#concept-main-fetch
This points at a relatively long algorithm. Can you point out the
specific steps that are relevant here?
Step 7 of the linked “main fetch” section. Updated the spec link
in chromestatus to https://www.w3.org/TR/CSP3/#fetch-integration,
which is a better place to understand that CSP check is part of
fetch instead of details of how fetch is done in the fetch spec.
*Summary*
When blocked by CSP, Chromium currently throws
SecurityError from constructor. Spec requires CSP to
be checked as part of fetch and fires error event
asynchronously. This aims to make Chromium spec
conformant, which is not throwing during constructor
and fires error event asynchronously.
Which constructor?
The constructor of Worker and SharedWorker objects. Also
updated the chromestatus so that it is clear.
An example demonstrating where developers need to catch those
exceptions now would be helpful IMO.
Before the change if developer wants to handle the worker being
blocked failure, the code would be something like this:
try {
var worker = new Worker(url);
…
} catch (e) {
// error handling code
}
After the change, the code would be something like this:
var worker = new Worker(url);
worker.addEventListener('error', function(event) {
// error handling code
});
…
*Blink component*
Blink>SecurityFeature>ContentSecurityPolicy
<https://issues.chromium.org/issues?q=customfield1222907:%22Blink%3ESecurityFeature%3EContentSecurityPolicy%22>
*TAG review*
None
*TAG review status*
Not applicable
*Risks*
*Interoperability and Compatibility*
Are you able to expand on the compatibility implications
for this change, i.e., do we know if Firefox has any site
breakage as a result of their behavior? What scenarios
might surprise developers who are relying on Chrome's
current behavior, etc?
We are not aware of any site breakage for Firefox due to
its behavior. If a site has a worker that is blocked by
CSP and has code after "new Worker()", those code
currently does not run in Chrome or Safari, but runs in
Firefox. After the change, those code would run in Chrome.
Also, if sites are doing something as a result of catching a CSP
failure exception, that would stop working (unless they shift to
start listening to the relevant event), right?
That is correct. If a site has code that runs upon catching
SecurityError exception during new Worker()/SharedWorker(), those
code would not run. Instead. if the site has error event
listener, that event listener will run.
Currently Firefox works as spec-ed while Safari works
the same as Chrome. With the wrong test code in WPT
tests, Firefox is failing the tests:
https://wpt.fyi/results/content-security-policy/worker-src/dedicated-worker-src-child-fallback-blocked.sub.html?label=experimental&label=master&aligned
<https://wpt.fyi/results/content-security-policy/worker-src/dedicated-worker-src-child-fallback-blocked.sub.html?label=experimental&label=master&aligned>
https://wpt.fyi/results/content-security-policy/worker-src/shared-worker-src-child-fallback-blocked.sub.html?label=experimental&label=master&aligned
<https://wpt.fyi/results/content-security-policy/worker-src/shared-worker-src-child-fallback-blocked.sub.html?label=experimental&label=master&aligned>
After updating Chrome code and WPT tests, Firefox
passes the tests while Safari fails the tests.
Can you explain what you mean by wrong test code?
The current WPT test code expects exception to throw,
which is not what’s required by the spec. The test code
has a TODO comment states that the test code is wrong
with a link to https://crbug.com/663298,
/Gecko/: Shipped/Shipping
/WebKit/: No signal
Have we asked for a signal from WebKit folks?
Filed an issue at
https://github.com/WebKit/standards-positions/issues/451.
Positive signal from
https://github.com/WebKit/standards-positions/issues/451: “As
such I suggest we mark this as position: support one week from now.”
/Web developers/: No signals
/Other signals/: This changes the behavior the same
as Firefox.
*WebView application risks*
/Does this intent deprecate or change behavior of
existing APIs, such that it has potentially high risk
for Android WebView-based applications?/
*Debuggability*
When worker is blocked by CSP, there is DevTools
message logged about the blocking by CSP. This
behavior is not changed.
*Will this feature be supported on all six Blink
platforms (Windows, Mac, Linux, ChromeOS, Android,
and Android WebView)?*
Yes
*Is this feature fully tested by web-platform-tests
<https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>?*
Yes
https://wpt.fyi/results/content-security-policy/worker-src/dedicated-worker-src-child-fallback-blocked.sub.html?label=experimental&label=master&aligned
<https://wpt.fyi/results/content-security-policy/worker-src/dedicated-worker-src-child-fallback-blocked.sub.html?label=experimental&label=master&aligned>
https://wpt.fyi/results/content-security-policy/worker-src/shared-worker-src-child-fallback-blocked.sub.html?label=experimental&label=master&aligned
<https://wpt.fyi/results/content-security-policy/worker-src/shared-worker-src-child-fallback-blocked.sub.html?label=experimental&label=master&aligned>
Note that the test code currently has the wrong
expectation and will be updated as part of this
feature work.
*Flag name on about://flags*
None
*Finch feature name*
None
*Non-finch justification*
This is a simple change of behavior for uncommon
scenario where worker is blocked by CSP, and the
changed behavior is the same as Firefox and spec
aligned. It is unlikely that a site depends on the
current behavior of throwing exception for blocked
worker.
Can we back up "it is unlikely" with some data? Absent
that, I would strongly suggest we put this behind a flag.
Changed the plan to put this new behavior behind
NoThrowForCSPBlockedWorker feature flag. Also updated the
chromestatus.
*Requires code in //chrome?*
False
*Tracking bug*
https://issues.chromium.org/issues/41285169
*Estimated milestones*
Shipping on desktop
134
DevTrial on desktop
134
Shipping on Android
134
DevTrial on Android
134
Shipping on WebView
134
*Anticipated spec changes*
/Open questions about a feature may be a source of
future web compat or interop issues. Please list open
issues (e.g. links to known github issues in the
project for the feature specification) whose
resolution may introduce web compat/interop risk
(e.g., changing to naming or structure of the API in
a non-backward-compatible way)./
None
*Link to entry on the Chrome Platform Status*
https://chromestatus.com/feature/5177205656911872?gate=5108732671033344
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