Intent to Extend Origin Trial: Subresource prefetching+loading via Signed HTTP Exchange

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Tsuyoshi Horo

Mar 18, 2020, 6:07:28 AM3/18/20
to blink-dev

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Support signed exchange subresource prefetching and loading by extending the HTTP link header.

An Origin Trial for Subresource prefetching+loading via Signed HTTP Exchange started in Chrome 78 and is scheduled to end in Chrome 82. We have received some feedback from developers like this. But getting adoption of this feature takes time because it requires both article publisher’s adoption and article aggregator’s adoption. So we intend to extend the Origin Trial until Chrome 86.

Link to “Intent to Implement” blink-dev discussion!topic/blink-dev/zdvJLcditVA

Goals for experimentation

The main goal is to measure the performance benefit of alternative subresource signed exchange prefetch. And also, this feature requires participation of both content publishers and distributors. So we would like to know whether this API design and mechanism works or not. 

Experimental timeline

M78 - M86 

Any risks when the experiment finishes?

After the OriginTrial expires, Chrome will not prefetch the alternative subresource signed exchanges, but will prefetch the original subresources written in the inner link header.

Ongoing technical constraints



DevTools shows the information about signed exchange subresource prefetching and loading in the Network tab.

Will this feature be supported on all five Blink platforms supported by Origin Trials (Windows, Mac, Linux, Chrome OS, and Android)?


Link to entry on the feature dashboard

Mar 19, 2020, 3:24:52 PM3/19/20
to blink-dev,
Hey Horo-san:

The API OWNERS discussed this at today's meeting and, while there was general support for allowing an extension of this OT, we have concerns about the total end-to-end length of the trial. To reduce those concerns, I'm wondering if it might be possible to get the feedback you need with a shorter extension. If not, can you perhaps outline changes you're anticipating to the design of the feature in the near future? Also, if we go with a longer trial, we'd also appreciate updates on usage rate in an ongoing way.


Tsuyoshi Horo

Mar 24, 2020, 11:08:21 PM3/24/20
to Alex Russell, blink-dev

Sorry for the delayed response.
It took time to communicate with developers who are planning to use this feature.

We had expected that at least one partner would be testing this but it hasn't happened yet.
I understand that extending the OT until Chrome 86 is too long.
We talked to the developers, and it looks like some of them can be ready to test this during about M83-M84 timeframe.
Does it make sense to extend this to Chrome 84?

Thank you.

Yoav Weiss

Mar 25, 2020, 12:34:08 PM3/25/20
to Tsuyoshi Horo, Alex Russell, blink-dev
Extending till M84 is one reasonable option.
Alternatively, if your OT partners won't start testing until M83, maybe it's better to turn off the OT in M81 and restart it in M83? That might give you a larger window for the actual testing (as then it would be easier to extend the OT beyond 84 if needed)

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Tsuyoshi Horo

Mar 25, 2020, 9:17:48 PM3/25/20
to Yoav Weiss, Alex Russell, blink-dev
Thank you for your suggestion.

It is OK for us to stop the OT in M81.
But according to the announcement, M82 release was skipped.
So I think stopping the OT in M81 and restarting in M83 is the same as just extending the OT.

Chris Harrelson

Mar 31, 2020, 7:51:21 PM3/31/20
to Tsuyoshi Horo, Yoav Weiss, Alex Russell, blink-dev
Extending the origin trial to M84 (without stopping in M81) LGTM.

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