Re: HTTP extensions, semantics and HTTP datagrams / MASQUE / WEBTRANS

Ben Schwartz <bemasc@google.com> Wed, 24 June 2020 18:34 UTC

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References: <54E08031-1892-4CC0-A6CF-0CAA4BFF679B@mnot.net> <02858E1D-C010-4404-ADF3-5EB97D4B32B3@mnot.net>
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From: Ben Schwartz <bemasc@google.com>
Date: Wed, 24 Jun 2020 14:30:11 -0400
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To: Mark Nottingham <mnot@mnot.net>
Cc: "ietf-http-wg@w3.org Group" <ietf-http-wg@w3.org>, David Schinazi <dschinazi.ietf@gmail.com>
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Subject: Re: HTTP extensions, semantics and HTTP datagrams / MASQUE / WEBTRANS
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One direction I think could be interesting is to embrace the Extended
CONNECT as used by WebSocket-H2 (RFC 8441).  If we define ":protocol = tcp"
as a synonym for the old-fashioned CONNECT, then ":protocol = udp" could
represent the basic MASQUE case nicely, and ":protocol = webtransport"
might go naturally as well (if we can't reuse ":protocol = websocket").

The combination of :protocol and transport (H3 vs. H2) might be sufficient
to indicate whether datagrams are allowed.



On Tue, Jun 23, 2020 at 4:49 AM Mark Nottingham <mnot@mnot.net> wrote:

> My personal .02 on this (and I'd be very curious to hear others'
> reactions) --
>
> We don't have a good track record of creating extensions or new
> capabilities that don't map into HTTP semantics. Server Push is probably
> the poster child here. As such, creating a version-specific extension for
> DATAGRAMs without mapping them into a method (or whatever) seems like it's
> leaving an attractive nuisance around; how will it show up in APIs? How
> will it interact with intermediaries? Etc.
>
> We also don't have a lot of precedent for a HTTP version-specific
> extension that does something completely separate to the HTTP interaction
> that's happening on the connection. I'm not sure that it would be something
> we want to encourage.
>
> All that said, we're not the protocol police; I don't think we should
> _stop_ this, but I do think that if we want this to succeed, it might work
> better as something packaged together with CONNECT-UDP (or however it gets
> expressed in HTTP).
>
> AIUI the one big argument for factoring it out into a separate draft is
> that MASQUE might want to use it *without* a method (etc.) for IP proxying.
> So that might be a conversation to have (although that use case has been
> delayed, I think).
>
> Another potential consumer could be a header on CONNECT (or even other
> methods?) that allows unreliable delivery but degrades gracefully to
> reliable delivery on hops that don't provide it. Even then, it seems like
> such a spec could reference the wire formats, etc., in CONNECT-UDP once
> that's defined.
>
> Overall - I have a preference for this to be rolled into a CONNECT-UDP (or
> similar) spec, but can live with it as a separate doc, provided that some
> thought is put into warning potential users about some risks.
>
> What do other folks think?
>
>
> > On 23 Jun 2020, at 9:40 am, Mark Nottingham <mnot@mnot.net> wrote:
> >
> > Hi all,
> >
> > The new MASQUE[1] and WEBTRANS[2] working groups both wish to define new
> protocols using QUIC DATAGRAM frames[3] that are not conveying (existing)
> HTTP semantics, but are intended to be usable over (at least some versions
> of) a HTTP connection.
> >
> > MASQUE's purpose is to proxy UDP and potentially IP (like a VPN) over a
> HTTP/3 connection. For WEBTRANS, the purpose is to create a
> browser-exposed, WebSocket-like protocol that allows unreliable delivery
> (which may also use CONNECT-UDP). These summaries are just my
> understanding; for a more complete picture, see the respective charters and
> related WG discussion.
> >
> > It's not yet clear how or even if these protocols will map into HTTP
> semantics. Some have proposed something like a CONNECT-UDP method; others
> seem to favour negotiating a new protocol using SETTINGS or a similar
> version-specific mechanism directly, avoiding the definition of any generic
> HTTP semantics.
> >
> > So far, the most concrete proposal we have is
> draft-schinazi-quic-h3-datagram,[4] which defines how QUIC DATAGRAM frames
> are surfaced in HTTP/3 without any mapping them into generic HTTP semantics
> (like a method, status code, header, etc.). Thus, a specification using
> them has the choice of defining a generic HTTP extension (like CONNECT-UDP,
> mapping them into HTTP semantics) or a version-specific extension(like
> SETTINGS, bypassing generic semantics).
> >
> > Before these groups get too far down the road, we have an opportunity to
> give them some guidance about how to extend both HTTP's semantics overall,
> and specific versions of HTTP -- keeping in mind recent core
> discussions.[5]
> >
> > The most relevant question is whether new, non-HTTP protocols on a HTTP
> connection should be bootstrapped by generic HTTP semantics (e.g., a
> method), version-specific semantics (e.g., SETTINGS), or something else.
> >
> > There's also a question as to whether something like
> draft-schinazi-h3-datagram is the right approach, or whether it should also
> include generic HTTP semantics "bundled in."
> >
> > Do folks have any thoughts about this?
> >
> > Cheers,
> >
> >
> > 1. <https://datatracker.ietf.org/wg/masque/about/>.
> > 2. <https://datatracker.ietf.org/wg/webtrans/about/>.
> > 3. 'An Unreliable Datagram Extension to QUIC', <
> https://tools.ietf.org/html/draft-ietf-quic-datagram>gt;.
> > 4. <https://tools.ietf.org/html/draft-schinazi-quic-h3-datagram>.
> > 5. <https://github.com/httpwg/http-core/issues/44>.
> >
> > --
> > Mark Nottingham   https://www.mnot.net/
> >
> >
>
> --
> Mark Nottingham   https://www.mnot.net/
>
>
>