Alt-Svc special value "clear" clarification

Hi all,

The HTTP Alternative Services RFC (7838) specifies that the "Alt-Svc"
header field can contain one of two values - either a list of
alternative services or the keyword "clear". From section 3 of the RFC:

> A field value containing the special value "clear" indicates that the
> origin requests all alternatives for that origin to be invalidated
> (including those specified in the same response, in case of an
> invalid reply containing both "clear" and alternative services).

My question is thus: What should the client do if an alternative service
returns an "Alt-Svc: clear" header? In particular, which endpoints
should be invalidated?

For example: The client makes a request to $origin, which in it's
response advertises alternative services $alt1 and $alt2. The client
then makes a subsequent request for $alt1, which then returns (either on
purpose or by accident) the "Alt-Svc: clear" header.

Given that $alt1 specified the clear and the RFC states that "all
alternatives" should be invalidated, and $origin is effectively an
alternative service for $alt1, should both $origin and $alt2 be
invalidated? Or should $alt1 and $alt2 be invalidated, even though
it was $alt1 that caused the action to be taken?


Received on Wednesday, 29 March 2017 10:43:23 UTC