HTTP/3 and Alt-svc

[Dimitri]

A site can tell a client browser that it supports HTTP/3 by adding the following server header

alt-svc: h3-xx=":yyyy"

(with x and y replaced by the appropriate values, of-course).

Now, I would like to know, if, when the request is made through HTTP/3, we should still add the "alt-svc: h3" header? I can't find information on this subject.

To me, this is useless and counter productive to add a header saying there is an alternative service, when this is already this alternative service which is being used. However, when I look at site like Google, or other big tech, they add the alt-svc header all the time, even when the connection is established in HTTP/3.

[lucy24]

This may be another case where it is simpler to stick on the header all the time, even when it’s redundant, rather than take the time to check if it’s needed. By analogy, consider the Upgrade-Insecure-Requests header, which is routinely sent by browsers even when the request is already HTTPS anyway.

[Dimitri]

I see, thank you!

I turned on HTTP/3 at all my sites, so I was trying to perfect it :)

HTTP/3 still does not have a final draft, but most browsers are supporting draft 29, so I thought it was time to activate it.