Re: How to reset ALTSVC

On Wed, Apr 1, 2015 at 5:17 PM, Mark Nottingham <mnot@mnot.net> wrote:

>
> > On 2 Apr 2015, at 10:02 am, Ryan Hamilton <rch@google.com> wrote:
> >
> > On Wed, Apr 1, 2015 at 9:24 AM, Martin Thomson <martin.thomson@gmail.com>
> wrote:
> > On 1 April 2015 at 05:11, Bence Béky <bnc@chromium.org> wrote:
> > > I think the simplest way to say "the alternative services for this
> > > origin is the following list: {empty list}" is to say "{empty list}"
> > > instead of "{one item identical to origin, which is understood to have
> > > the special meaning that it's an empty list}" or "{one item with valid
> > > but arbitrary port and a special, otherwise unused value for ma, which
> > > is understood to have the special meaning that it's an empty list}".
> >
> > That argument only makes sense if you don't consider the origin to be
> > a validate alternative.  That it's implicit and always present isn't
> > of much consequence.
> >
> > That's surprising to me. As I read the spec, Alt-Svc is all about
> specifying different ways to reach a server:
> >
> >    ...document specifies "alternative services" for HTTP, which allow
> >    an origin's resources to be authoritatively available at a separate
> >    network location
> >
> >
> > To me, that does not imply that the origin is present in the list of
> alternatives. If the origin is implicitly in that list, should Alt-Svc-Used
> be sent when using it? That doesn't seem reasonable to me, which makes me
> think that the origin really isn't implicitly part of the Alt-Svc list.
> >
> > Am I thinking about this the wrong way?
>
> Well, literally speaking it’s not an alternative; it’s the authority (the
> thing that alt-svc provides alternatives *to*).
>

​Yes, exactly. But since Alt-Svc lists alternatives, not authorities, it
doesn't make sense to think that the authority is implicitly in the
alternatives list.​


​So if we're thinking about how to clear any alt-svc mappings that a client
might have stored, it seems perplexing to propose that be accomplished by
saying:

Alt-Svc: <scheme>:<origin>​

Further, consider the case of an https:// origin which uses ALPN to
optionally negotiate HTTP/2 but supports HTTP/1 for legacy clients. Does it
need to list both h2 and http1?

Sure seems more explicit to say:

Alt-Svc:

It *is* in the list of “places I can get stuff for this origin from”,
> however.
>

​Agreed!

​Cheers,

Ryan
​