Expose contentEncoding in resourceTiming

[guohuideng2024]

こんにちは TAG-さん!

I'm requesting a TAG review of exposing contentEncoding in resourceTiming.

Propose that we add an explicit .contentEncoding in resourceTiming.
contentEncoding value has been very helpful for web apps and CDN in monitoring and optimization. As more compressions are deployed, it's no longer practical to infer such value. Therefore, it's desirable to explicitly expose it.

• Explainer¹:
  https://github.com/guohuideng2024/resource-timing/blob/gh-pages/Explainers/Content_Encoding.md
• Specification:
  Return a content-encoding header for resource timing and more whatwg/fetch#1796
  Expose a filtered content-encoding value to resource timing  w3c/resource-timing#411
• WPT Tests:
  https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/web_tests/external/wpt/resource-timing/content-encoding.https.html
• User research: Here.
• Security and Privacy self-review²: Here.
• GitHub repo:
  https://github.com/w3c/resource-timing
• Primary contacts:
  @guohuideng2024, Microsoft
• Organization/project driving the specification: Microsoft
• Multi-stakeholder support³:
  • Chromium comments: Already implemented behind a feature flag.
  • Mozilla comments: Expose contentEncoding in resourceTiming mozilla/standards-positions#1189
  • WebKit comments: expose contentEncoding in resourceTiming WebKit/standards-positions#467
• Status/issue trackers for implementations⁴:
  https://chromestatus.com/feature/4818080273006592
  Expose Content-Encoding to ResourceTiming w3c/resource-timing#381

Further details:

• I have reviewed the TAG's Web Platform Design Principles
• The group where the work on this specification is currently being done: WebPerfWG
• The group where standardization of this work is intended to be done (if different from the current group): WebPerfWG
• Major unresolved issues with or opposition to this specification: None.
• This work is being funded by: Microsoft

[torgo]

Just a quick request - can you please amend the explainer to be clearer about the user need? This explainer jumps right in and describes the technology but doesn't describe what user need it's trying to service. If there is a security issue we are trying to protect users from here, what is it and how would users normally encounter it? Then describe how this technology fixes that problem... See https://tag.w3.org/explainers/ for more info on writing explainers.

[martinthomson]

Thanks for sharing this with us. Aside from @torgo's comment about explainers and user needs (which are indirect for this API generally, but still worth writing down), the feature is worthwhile. Compression encoding in particular has a material effect on performance and being able to split performance reports by the choice of encoding makes a lot of sense. We don't see any other major problems.

A couple of notes about your security and privacy questionnaire:

1. You answered negatively about question 7 (information about the browser platform), which is incorrect. It reveals which content codings are supported by the browser. This is acceptable because that information is already exposed through other means and - more importantly - it is browser-specific rather than user-specific. You include this in your analysis already, but it's worth getting the questionnaire correct.
2. Question 21 saying "not directly" is troubling. I can't see how this would reveal anything about the use of assistive technology. If it does, that would be cause for concern and some further analysis. Can you say more?