Re: Lifting HTTP/3 Features into Extensions

I like the idea of mandatory-to-implement extensions, because it means we
can still replace them later.

Regarding trailers, "the core remit of the protocol" - but the protocol in
that sentence is HTTP/2, not HTTP/3. When HTTP/2 was standardized, it
dropped support for a the Upgrade header, which you could consider core
remit of HTTP/1.1, so we have a precedent for removing features because we
believed we had something better. We have an opportunity to make HTTP/3
better, do we really need to bring everything in from HTTP/2 just because
it was there then? And going back to trailers, I'm not suggesting they
should not exist, I'm suggesting demoting them to an extension so it
becomes possible to iterate on that extension without changing the version
number of the mapping.

David

On Wed, Dec 12, 2018 at 2:07 PM Mike Bishop <mbishop@evequefou.be> wrote:

> Trailers aren’t an extension, no more than QPACK is.  They’re required to
> transfer HTTP semantics, which is the core remit of the protocol.
>
>
>
> *From:* David Schinazi <dschinazi.ietf@gmail.com>
> *Sent:* Wednesday, December 12, 2018 1:13 PM
> *To:* Mike Bishop <mbishop@evequefou.be>
> *Cc:* Ian Swett <ianswett@google.com>; ianswett=
> 40google.com@dmarc.ietf.org; fenix@fb.com; Ryan Hamilton <rch@google.com>;
> jri.ietf@gmail.com; ietf-http-wg@w3.org; Lucas Pardue <
> lucaspardue.24.7@gmail.com>; QUIC <quic@ietf.org>; Martin Thomson <
> martin.thomson@gmail.com>; kazuhooku@gmail.com
> *Subject:* Re: Lifting HTTP/3 Features into Extensions
>
>
>
> I think there is value in moving some features to extensions. I don't see
> anything in the charter preventing us from moving specific work items to
> extensions, especially if we believe it'll accelerate us shipping v1, and
> allow experimentations that could produce a better prioritization scheme.
> From what I heard from people involved in the HTTP/2 standardization
> efforts, some things about prioritization and push could have been done
> differently, and most likely would have if they had been standardized as
> extensions. It would be great for us to gain this flexibility in HTTP/3.
> Moving trailers to an extension would allow us to remove the length from
> DATA.
>
>
>
> David
>
>
>
> On Wed, Dec 12, 2018 at 10:43 AM Mike Bishop <mbishop@evequefou.be> wrote:
>
> To preface, this is really a separate discussion, linked to this one only
> by what is effectively whataboutism.  We don’t have consensus to do this
> complicating thing that optimizes for a common case, so why did we achieve
> consensus to do those other complicated things that optimize for uncommon
> cases?  But that consensus was achieved in HTTP/2, and my personal reading
> of the charter leads me to believe we’re prohibited from wholesale removal
> of H2 features in HTTP/3; we try to keep the same general spirit unless
> things are fundamentally incompatible with running over QUIC.
>
>
>
> Moving everything post-DATA to a separate stream is a fairly dramatic
> change, and I’m having trouble seeing exactly how that would work.  And it
> suffers the same liability that it’s likely to be an under-exercised code
> path.
>
>
>
> Priority and push were both controversial pieces of H2 for various
> reasons.  Unlike in HTTP/2, they are more decoupled from the stream state
> model in HTTP/3, and either or both could easily could become an
> extension.  I find the argument more persuasive for priority than for push,
> because one could very reasonably choose to experiment with several
> independent priority schemes – the pseudo-7540-style we have now, the
> three-bit SPDY-style priorities, a varint fixed priority, the
> weighted-group
> <https://lists.w3.org/Archives/Public/ietf-http-wg/2014JanMar/0396.html>,
> etc.
>
>
>
> *From:* Ian Swett <ianswett@google.com>
> *Sent:* Wednesday, December 12, 2018 9:27 AM
> *To:* ianswett=40google.com@dmarc.ietf.org; Roberto Peon <fenix@fb.com>;
> Ryan Hamilton <rch@google.com>; Jana Iyengar <jri.ietf@gmail.com>; Mike
> Bishop <mbishop@evequefou.be>; HTTP Working Group <ietf-http-wg@w3.org>;
> Lucas Pardue <lucaspardue.24.7@gmail.com>; IETF QUIC WG <quic@ietf.org>;
> Martin Thomson <martin.thomson@gmail.com>; Kazuho Oku <kazuhooku@gmail.com
> >
> *Subject:* Re: Final DATA frames
>
>
>
> From a technical perspective, yes.  But from a goals/process perspective,
> I think they related.  We've spent a lot of time on very complex work in
> the QUIC WG, and I realize everyone has a different perspective, but I'm
> confused by the amount of pushback this got relative to all the work we
> have done to make PUSH and something approximating(since they're actually
> different) H2 priorities work on top of QUIC.
>
>
>
> If I remember correctly, your main argument against this framing change
> was that the existing DATA frame with a length becomes largely useless and
> might be under-exercised.  That makes me feel like we've over-optimized for
> the complex special cases and made a design error or two at least one step
> prior to this proposal.
>
>
>
> To make a specific and relevant suggestion, maybe DATA should never have a
> length and if we want features that most requests don't
> use(trailers/PUSH_PROMISE/etc) we should put them on a separate
> unidirectional stream?
>
>
>
>
>
>
>
> On Wed, Dec 12, 2018 at 12:02 PM Dmitri Tikhonov <
> dtikhonov@litespeedtech.com> wrote:
>
> But you would agree that these are completely different discussions?
>
> One is whether to modify HTTP/3 framing mechanism.  The other is
> changing HTTP/3 feature set.
>
> My point is that it is unjustified to to say that since we have
> decided not to change the framing mechanism we should consider
> dropping prioritization and push promises.
>
> On Wed, Dec 12, 2018 at 11:38:09AM -0500, Ian Swett wrote:
> > I don't want to derail this too much(probably too late for that), and no
> > one has a PR anywhere close to landing, but I do think we should start
> > thinking of these as potential extensions.  I disagree that they're
> > HTTP/2's primary features, both due to lack of use and lack of measurable
> > benefits years after standardization.  Push might actually benefit from
> > being an extension, because then potential improvements(ie: cache-digest)
> > could be integrated into the extension more quickly.
> >
> > On the other hand, QPACK is relatively complex but we have clearer
> > demonstrations of it's benefit.
> >
> > On Wed, Dec 12, 2018 at 9:00 AM Dmitri Tikhonov <
> dtikhonov@litespeedtech.com>
> > wrote:
> >
> > > On Tue, Dec 11, 2018 at 09:02:01PM -0500, Ian Swett wrote:
> > > > TLDR: If the focus is on shipping v1 and making sure we don't
> introduce
> > > > premature optimizations into HTTP/3, I thInk we should seriously
> consider
> > > > moving PUSH and the existing priorities to an extension.
> > >
> > > The EOS DATA frame and HTTP prioritization and push promises are not
> > > equivalent.  One is simply fiddling with the way data is framed and
> > > is not visible to the application.  The others are HTTP/2's primary
> > > features.
> > >
> > >   - Dmitri.
> > >
>
>