Add client hint docs: Downlink, ECT, RTT

[hamishwillee]

This header is in the Network Information spec here: https://wicg.github.io/netinfo/#rtt-request-header-field

There is not all that much information, but you can see it is associated with the NetworkInformation.rtt and there is some useful general guidance in https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/client-hints.

Spec update is in mdn/browser-compat-data#10951

This is another part of #1408

[github-actions]

Preview URLs

• https://pr5883.content.dev.mdn.mozit.cloud/en-US/docs/Glossary/Effective_connection_type
• https://pr5883.content.dev.mdn.mozit.cloud/en-US/docs/Glossary/Client_hints
• https://pr5883.content.dev.mdn.mozit.cloud/en-US/docs/Web/API/NetworkInformation/rtt
• https://pr5883.content.dev.mdn.mozit.cloud/en-US/docs/Web/API/NetworkInformation/downlink
• https://pr5883.content.dev.mdn.mozit.cloud/en-US/docs/Web/API/NetworkInformation/saveData
• https://pr5883.content.dev.mdn.mozit.cloud/en-US/docs/Web/API/NetworkInformation/effectiveType
• https://pr5883.content.dev.mdn.mozit.cloud/en-US/docs/Web/HTTP/Headers
• https://pr5883.content.dev.mdn.mozit.cloud/en-US/docs/Web/HTTP/Headers/ECT
• https://pr5883.content.dev.mdn.mozit.cloud/en-US/docs/Web/HTTP/Headers/RTT
• https://pr5883.content.dev.mdn.mozit.cloud/en-US/docs/Web/HTTP/Headers/Save-Data
• https://pr5883.content.dev.mdn.mozit.cloud/en-US/docs/Web/HTTP/Headers/Accept-CH-Lifetime
• https://pr5883.content.dev.mdn.mozit.cloud/en-US/docs/Web/HTTP/Headers/Accept-CH
• https://pr5883.content.dev.mdn.mozit.cloud/en-US/docs/Web/HTTP/Headers/Downlink

Flaws

Note! 11 documents with no flaws that don't need to be listed. 🎉

URL: /en-US/docs/Web/API/NetworkInformation/downlink
Title: NetworkInformation.downlink
on GitHub
Flaw count: 1

• macros:
  • /en-US/docs/Web/JavaScript/Reference/double does not exist

---

URL: /en-US/docs/Web/HTTP/Headers
Title: HTTP headers
on GitHub
Flaw count: 4

• macros:
  • /en-US/docs/Glossary/COEP does not exist
  • /en-US/docs/Glossary/COOP does not exist
  • /en-US/docs/Glossary/CORP does not exist
• broken_links:
  • Can't resolve /en-US/docs/Web/API/Save_Data_API

External URLs

URL: /en-US/docs/Glossary/Effective_connection_type
Title: Effective connection type
on GitHub

No new external URLs

---

URL: /en-US/docs/Glossary/Client_hints
Title: Client hints
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/API/NetworkInformation/rtt
Title: NetworkInformation.rtt
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/API/NetworkInformation/downlink
Title: NetworkInformation.downlink
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/API/NetworkInformation/saveData
Title: NetworkInformation.saveData
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/API/NetworkInformation/effectiveType
Title: NetworkInformation.effectiveType
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/HTTP/Headers
Title: HTTP headers
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/HTTP/Headers/ECT
Title: ECT
on GitHub

• https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/client-hints (1 time) (Note! This may be a new URL 👀)

---

URL: /en-US/docs/Web/HTTP/Headers/RTT
Title: RTT
on GitHub

• https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/client-hints (1 time) (Note! This may be a new URL 👀)

---

URL: /en-US/docs/Web/HTTP/Headers/Save-Data
Title: Save-Data
on GitHub

• https://css-tricks.com/help-users-save-data/ (1 time) (Note! This may be a new URL 👀)
• https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/client-hints (1 time) (Note! This may be a new URL 👀)
• https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/save-data/ (1 time) (Note! This may be a new URL 👀)

---

URL: /en-US/docs/Web/HTTP/Headers/Accept-CH-Lifetime
Title: Accept-CH-Lifetime
on GitHub

• https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-client-hints-08 (1 time) (Note! This may be a new URL 👀)

---

URL: /en-US/docs/Web/HTTP/Headers/Accept-CH
Title: Accept-CH
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/HTTP/Headers/Downlink
Title: Downlink
on GitHub

• https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/client-hints (1 time) (Note! This may be a new URL 👀)

(this comment was updated 2021-06-18 01:54:46.742637)

[hamishwillee]

@Elchi3 OK, this got bigger

• I added the missing network headers ECT and Downlink
• Updated Save-Data to better cross link.
• Cross linked all of these to the equivalent web API
• Added sections for client headers in both the main headers page and in the client headers page.

I think this is a good place to stop for now. In future though it might be worth having a client headers guide much like https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/client-hints and cut back the glossary entry. This gives us a structure to work with now though.

Can you please review again :-)

[Elchi3]

Thanks for your work! Some comments.

[hamishwillee]

@Elchi3 Thanks for the detailed review - I seem to have injected more errors than usual :-(.

I accepted all changes, added directives sections, reverted the specifications section. Note that I kept the specifications macro for the new header docs. Yes they show missing info now, but I'm hoping that the spec issue will be resolved soon and don't think it worth adding the manual table while we wait. Happy to add a manual table if you think this is a "requirement".

[Elchi3]

Note that I kept the specifications macro for the new header docs. Yes they show missing info now, but I'm hoping that the spec issue will be resolved soon and don't think it worth adding the manual table while we wait. Happy to add a manual table if you think this is a "requirement".

This was the correct call! These headers use https://wicg.github.io/netinfo/ which does in fact work as soon as the latest BCD is on MDN production in a few hours. What doesn't work right now is HTTP features that reference IETF specs. You can follow w3c/browser-specs#280 to be notified when it's available upstream.

[Elchi3]

Thanks Hamish, fantastic work! 👍