Re: Proposal Towards Universal HTTP/3, with a polyfill of QUIC for TCP (Fwd: New Version Notification for draft-kazuho-httpbis-http3-on-streams-00.txt)

[Hugo Landau <[e-mail]>]

On Sat, Feb 17, 2024 at 08:39:18AM +0900, Kazuho Oku wrote:
> 2024年2月16日(金) 18:00 Hugo Landau <[e-mail]>:
> >
> > > Hello QUIC and HTTP enthusiasts,
> > >
> > > We, Lucas and I, have submitted two drafts aimed at broadening the reach of
> > > HTTP/3 - yes, making it available over TCP as well. We are eager to hear
> > > your thoughts on these:
> > >
> > > QUIC on Streams: A polyfill for operating QUIC on top of TCP.
> > > https://datatracker.ietf.org/doc/html/draft-kazuho-quic-quic-on-streams
> > >
> > > HTTP/3 on Streams: How to run HTTP/3 unmodified over TCP, utilizing QUIC on
> > > Streams.
> > > https://datatracker.ietf.org/doc/html/draft-kazuho-httpbis-http3-on-streams
> > >
> > > As the co-author of the two drafts, let me explain why we have submitted
> > > these.
> > >
> > > The rationale behind our proposal is the complexity of having two major
> > > HTTP versions (HTTP/2 and HTTP/3), both actively used and extended. This
> > > might not be the situation that we want to be in.
> > >
> > > HTTP/2 is showing its age. We discussed its challenges at the IETF 118 side
> > > meeting in Prague.
> > >
> > > Despite these challenges, we are still trying to extend HTTP/2, as seen
> > > with WebTransport. WebTransport extends both HTTP/3 and HTTP/2, but it does
> > > so differently for each, due to the inherent differences between the HTTP
> > > versions.
> > >
> > > Why are we doing this?
> > >
> > > Because HTTP/3 works only on QUIC. Given that UDP is not as universally
> > > accessible as TCP, we find ourselves in a position where we need to
> > > maintain and extend not only HTTP/3 but also HTTP/2 as a backstop protocol.
> > >
> > > This effort comes with its costs, which we have been attempting to manage.
> > >
> > > However, if we could create a polyfill for QUIC that operates on top of
> > > TCP, and then use it to run HTTP/3 over TCP, do we still need to invest in
> > > HTTP/2?
> > >
> > > Of course, HTTP/2 won’t disappear overnight.
> > >
> > > Yet, by making HTTP/3 more universally usable, we can at least stop
> > > extending HTTP/2.
> > >
> > > By focusing our new efforts solely on HTTP/3, we can conserve energy.
> > >
> > > By making HTTP/3 universally accessible, and by having new extensions
> > > solely to HTTP/3, we can expect a shift of traffic towards HTTP/3.
> > >
> > > This shift would reduce the necessity to modify our HTTP/2 stacks (we’d be
> > > less concerned about performance issues), and provide us with a better
> > > chance to phase out HTTP/2 sooner.
> > >
> > > Some might argue that implementing a polyfill of QUIC comes with its own
> > > set of costs. However, it is my understanding that many QUIC stacks already
> > > have the capability to read QUIC frames other than from QUIC packets,
> > > primarily for testing purposes. This suggests that the effort would be more
> > > about leveraging existing code paths rather than writing new code from
> > > scratch. Furthermore, a QUIC polyfill would extend its benefits beyond just
> > > HTTP, by aiding other application protocols that aim to be built on top of
> > > QUIC, providing them accessibility over TCP.
> > >
> > > Please let us know what you think. Best regards,
> > It's an interesting proposal. Looks fairly sensible.
> > I could see a lot of other uses also for having a mapping of the QUIC
> > application-level semantics without QUIC itself, such as for diagnostic
> > use or intra-DC backhaul of incoming traffic.
> >
> > I question the utility of implicit length signalling. Unless there's a
> > real use for this (maybe there is and I'm just not seeing it) I would
> > probably just prohibit these encodings. The max_frame_size transport
> > parameter proposed here cannot be reduced below 16384. So you're saving
> > at most 3 bytes (to encode 16384) for every 16384 bytes. That would seem
> > to yield an efficiency increase of 0.018%. For larger max_frame_size
> > values this obviously gets even smaller.
> >
> > Is there a rationale to supporting this I'm not seeing?
> 
> Thank you for your comments!
> 
> Regarding your question, in the initial draft, we attempted to limit
> changes to the way frames are communicated, while preserving the frame
> encoding of QUIC v1 unchanged. The purpose of this approach is to
> maximize code reuse between QUIC v1 and QUIC over Streams.
> 
> For STREAM frames that lack length fields, we considered two options:
> a) defining a method to deduce the length from another source, or
> b) prohibiting the use of such frames.
> 
> We opted for option (a) for consistency, under the assumption that it
> would not be more complex to implementations than (b).
> 
> However, it was a narrow decision. I acknowledge that opting for (b)
> would also be straightforward to implement, especially since STREAM
> frames lacking length fields are identified by specific frame types
> (namely, 0x08, 0x09, 0x0c, 0x0d), and considering we're already
> restricting the use of certain QUIC v1 frames.
Yeah. I would strongly support (b) without a very clear motivating use
case otherwise.