LGTM2
On 4/27/22 2:33 AM, Yoav Weiss wrote:
LGTM1
I'm excited about this work as it unlocks many potential wins in terms
of loading performance. Interest from Mozilla as well as support from
leading CDNs is also promising in terms of activation and usage.
Thanks for working on this!!
On Wed, Apr 27, 2022 at 7:49 AM Daisuke Enomoto
<[email protected]> wrote:
Hi
Any other questions or concerns?
Thanks!
On Thu, Apr 21, 2022 at 5:23 PM Kenichi Ishibashi
<[email protected]> wrote:
Hi Yoav,
On Thu, Apr 21, 2022 at 3:26 PM Yoav Weiss
<[email protected]> wrote:
On Thu, Apr 21, 2022 at 4:13 AM Kenichi Ishibashi
<[email protected]> wrote:
Contact emails
[email protected], [email protected]
Explainer
https://github.com/bashi/early-hints-explainer/blob/main/explainer.md
<https://github.com/bashi/early-hints-explainer/blob/main/explainer.md>
Specification
https://tools.ietf.org/html/rfc8297
<https://tools.ietf.org/html/rfc8297>
https://html.spec.whatwg.org/#early-hints
Design docs
https://docs.google.com/document/d/1gCh_CnfrJq_VL7aGoq6skc7sn4yn5pKsM0gkHe5B9go/edit?usp=sharing
<https://docs.google.com/document/d/1gCh_CnfrJq_VL7aGoq6skc7sn4yn5pKsM0gkHe5B9go/edit?usp=sharing>
Summary
Support 103 Early Hints informational responses during
top-level frame navigation. When a 103 response
includes link headers Chromium tries to preload
specified resources (including modulepreload) or
preconnect to specified origins before the final
response is received. This gives Web developers a way
to optimize Core Web Vitals such as Largest Contentful
Paint (LCP).
Blink component
Internals>Preload
<https://bugs.chromium.org/p/chromium/issues/list?q=component:Internals%3EPreload>
TAG review
https://github.com/w3ctag/design-reviews/issues/638
<https://github.com/w3ctag/design-reviews/issues/638>
TAG review status
Issues addressed
Risks
Interoperability and Compatibility
Browsers may not understand a 103 response but they
are expected
<https://www.ietf.org/archive/id/draft-ietf-httpbis-semantics-19.html#name-informational-1xx>to
ignore 1xx responses if they don’t understand 1xx
responses. Firefox is implementing 103 support.
Proxies may not understand a 103 response. They may
treat the 103 response as a part of the final response
when the response is sent over HTTP/1.1. The problem
is less likely to happen over HTTP/2 and HTTP/3 thanks
to their frame format. Chromium only handles 103
responses over HTTP/2 and HTTP/3.
The HTML and Fetch standards have been updated to
handle preload link headers in 103 responses for
navigations (whatwg/html#7675
<https://github.com/whatwg/html/pull/7675>,
whatwg/fetch#1404
<https://github.com/whatwg/fetch/pull/1404>). For
preconnect there are ongoing efforts to specify the
behavior. See “Anticipated spec changes” section below
for more information.
Gecko: In development
<https://bugzilla.mozilla.org/show_bug.cgi?id=1407355>.
Can you ask for an official position?
https://bit.ly/blink-signals
I should have put the link to the official position. They said
it's worth prototyping
<https://github.com/mozilla/standards-positions/issues/134> and
IIUC it's under development.
WebKit: No signal
<https://lists.webkit.org/pipermail/webkit-dev/2021-May/031861.html>.
Web developers: Positive. Positive interest and intent
of support by popular CDNs (Fastly
<https://www.fastly.com/blog/faster-websites-early-priority-hints>,
Cloudflare
<https://blog.cloudflare.com/early-hints/>). We've
been collaborating with partners to evaluate the
impact of Early Hints and we observed significant
improvements on page loading metrics such as FCP.
Ergonomics
The primary usage of this feature is to send link
headers to preload resources or preconnect to servers
to improve page load performance. Due to potential
security concerns Chromium only handles the first 103
response for the top-frame navigation.
That restriction is specified, right? AFAICT, "process
early hints headers
<https://html.spec.whatwg.org/multipage/semantics.html#process-early-hint-headers>"
is only called from "process a navigate response
<https://html.spec.whatwg.org/multipage/browsing-the-web.html#navigating-across-documents:process-early-hint-headers>".
Yes, you're right. Sorry for the confusion. Chromium has these
restrictions to follow the specification.
See this document
<https://chromium.googlesource.com/chromium/src/+/master/docs/early-hints.md>for
details of restrictions. These restrictions may be
relaxed in the future.
Activation
Popular HTTP servers and CDNs provide configurations
or options to send Early Hints responses.
Security
Request mode
<https://fetch.spec.whatwg.org/#concept-request-mode>and
credentials mode
<https://fetch.spec.whatwg.org/#concept-request-credentials-mode>are
calculated the same as normal preload and preconnect.
Preloads triggered by a 103 response follow policies
specified in the same 103 response. Chromium only
handles the first 103 response and ignores following
103 responses to avoid contradiction policies between
these responses and the final response. Chromium
doesn’t use preloaded resources triggered by a 103
response when there are conflicting policies between a
103 response and the final response. See the security
considerations section
<https://docs.google.com/document/d/1gCh_CnfrJq_VL7aGoq6skc7sn4yn5pKsM0gkHe5B9go/edit#heading=h.fhq04xt0tah6>of
the design doc for more information.
Is that specified?
Yes. These behaviors are specified in "process a navigate
fetch
<https://html.spec.whatwg.org/multipage/browsing-the-web.html#process-a-navigate-fetch>"
and "process early hint headers
<https://html.spec.whatwg.org/multipage/semantics.html#process-early-hint-headers>".
WebView application risks
We don’t expect WebView specific problems with this
feature.
Debuggability
If a resource is preloaded by Early Hints, the
corresponding PerformanceResourceTiming object reports
that its initiatorType is "early-hints".
When the document doesn’t use resources preloaded by
Early Hints within a few seconds from the window’s
load event Chromium will show warning messages (this
is under review now).
DevTools lack Early Hints support and we consider
adding Early Hints support in DevTools in the future.
In the meanwhile developers can use NetLog
<https://www.chromium.org/for-testers/providing-network-details/>,
WebPageTest, or network protocol analyzers such as
Wireshark for debugging.
Is this feature fully tested by
web-platform-tests
<https://chromium.googlesource.com/chromium/src/+/master/docs/testing/web_platform_tests.md>?
Yes
<https://github.com/web-platform-tests/wpt/tree/master/loading/early-hints>
Flag name
EarlyHintsPreloadForNavigation
Requires code in //chrome?
False
Tracking bug
https://crbug.com/671310 <https://crbug.com/671310>
Launch bug
https://crbug.com/1197989 <https://crbug.com/1197989>
Sample links
https://early-hints.fastlylabs.com/
<https://early-hints.fastlylabs.com/>
Estimated milestones
We would like to ship this feature in M103.
Anticipated spec changes
Historically preconnect hasn’t been specified well
(whatwg/html#4224
<https://github.com/whatwg/html/issues/4224>). There
are ongoing efforts to specify the behavior. For
example whatwg/html#7814
<https://github.com/whatwg/html/pull/7814>specified
the behavior of <link rel=preconnect>.
whatwg/html#7835
<https://github.com/whatwg/html/pull/7835>will specify
preconnect in link headers and it will cover 103
responses.
Great to see those PRs have landed!
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/5207422375297024
<https://chromestatus.com/feature/5207422375297024>
Links to previous Intent discussions
Intent to Experiment:
https://groups.google.com/u/1/a/chromium.org/g/blink-dev/c/xb_NHDS3twY
<https://groups.google.com/u/1/a/chromium.org/g/blink-dev/c/xb_NHDS3twY>
This intent message was generated by Chrome Platform
Status <https://chromestatus.com/>.
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