Re: How to reset ALTSVC

[Julian Reschke <[e-mail]>]

On 2015-08-26 23:06, Bence Béky wrote:
> Hi,
>
> I noticed that the "clear" keyword was introduced
> <https://github.com/httpwg/http-extensions/commit/68970e3555ba77cd56418c036e601af520b17711>
> to clear alternative service entries for a given origin, but I don't
> seem to find any discussion about this on this mailing list.  Also, I
> was under the impression that when I brought it up at the last meeting,
> there was no objection to advertising an empty string for this purpose.
> I'm just curious what happened.

As the others pointed out, the concern was a) that there are software 
components that do not handle empty values properly, and b) a concern to 
overload the concept of an empty list.

I only finished the edits yesterday and was planning to send an email 
today :-)

> I personally find it still better than the "origin itself" or "bogus
> entry with ma=0" hacks, though not quite as clear and foolproof to
> implement as an empty string.  Alas, I would be interested to hear other
> people's opinions, in case anyone has experience implementing it since
> it was last discussed.
>
> Also, since "clear" clears entries including the ones in the same
> header, why could there be multiple alt-values?  Would instead of
>
> Alt-Svc       = 1#alt-value
> alt-value     = clear / ( alternative *( OWS ";" OWS parameter ) )
>
> the following:
>
> Alt-Svc       = clear / 1#alt-value
> alt-value     = alternative *( OWS ";" OWS parameter )
>
> not make more sense?
> ...

It would, but we are constrained by the HTTP header field semantics. A 
header field value is either list-shaped or it is not. We can't choose 
based on the field contents.

Best regards, Julian