Re: [External⚠️] Re: Unbound DATA frames in HTTP/3 proposal

The intent of the capsule protocol was to carry information mostly
untouched through intermediaries. For that reason, we landed on a design
that just uses the data stream - a concept that's defined for all versions
of HTTP [1] - and works if intermediaries just shovel bytes like they do
for unextended CONNECT.

I don't think we should move capsules to a separate frame or a separate
stream, because that significantly complicates things. Now you can encode
them in multiple ways, and receivers have to deal with ordering if you
receive them on both (or erroring out if that's not allowed), and hit all
the pitfalls of asynchronous signalling.

The goal of UNBOUND_DATA was to be the simplest possible solution to the
issue of repeatedly making chunks when the semantic you want is "keep
going until I'm done". And if we combine this with a similar solution at
the capsule layer [2] then you can run connect-tcp directly on raw QUIC
STREAM frames.

Thanks Mike for finding the 2018 discussion on this topic, I had vague
memories of those conversations but had forgotten most of the details. I
still don't quite understand the strong opposition here - I absolutely
agree that there exist many cases where using UNBOUND_DATA is not suitable,
but in those cases just don't use it. I could see not wanting this feature
in the base protocol because the base protocol was intended to be as
general purpose as possible, and that change would have required all
receivers to implement it, but this is an extension that not every
implementation needs to support.

David

[1] https://www.rfc-editor.org/rfc/rfc9297#section-3.1
[2] https://github.com/DavidSchinazi/draft-schinazi-masque-9297bis/issues/4

On Tue, Oct 7, 2025 at 6:36 AM Ben Schwartz <bemasc@meta.com> wrote:

> UNBOUNDED_DATA achieves reduced framing overhead at the cost of a semantic
> constraint: it is no longer possible to send other frame types on this
> request.  This means that UNBOUNDED_DATA is not purely an optimization; it
> "leaks" up through the HTTP abstract interface.  As a result, it cannot be
> used transparently by an HTTP engine on arbitrary requests, because the
> HTTP engine doesn't know if the application may require other frame types
> later.
>
> Some of the comments from 2018 hint at an alternative approach that is
> closer to transparent.  For example, imagine a frame like:
>
> DELEGATE_DATA {
>   Type (i)
>   Length (i)
>   Stream ID (i)
> }
>
> This means "all future DATA frame contents on this stream are delegated to
> the indicated, unframed, unidirectional stream".  The original request
> stream can continue to carry frame types other than DATA.
>
> The ordering of the other frame types relative to the data stream is lost,
> but this is acceptable.  There are currently two other frame types in use
> on request streams: HEADERS and PRIORITY_UPDATE.  HEADERS are defined to
> occur only at the beginning or end of the stream, so their relative
> position is unambiguous.  PRIORITY_UPDATE is not sensitive to the ordering
> relative to the data stream.
>
> --Ben
>
> ------------------------------
> *From:* Kazuho Oku <kazuhooku@gmail.com>
> *Sent:* Tuesday, October 7, 2025 2:54 AM
> *To:* Yaroslav Rosomakho <yrosomakho@zscaler.com>
> *Cc:* Mike Bishop <mbishop@evequefou.be>; ietf-http-wg@w3.org <
> ietf-http-wg@w3.org>; David Schinazi <dschinazi.ietf@gmail.com>
> *Subject:* Re: [External⚠️] Re: Unbound DATA frames in HTTP/3 proposal
>
> 2025年10月7日(火) 14: 43 Yaroslav Rosomakho <yrosomakho@ zscaler. com>: I
> think there's an important distinction here between an optional capability
> that endpoints can negotiate for potential performance improvements and
> what’s defined as
>
>
> 2025年10月7日(火) 14:43 Yaroslav Rosomakho <yrosomakho@zscaler.com>:
>
> I think there's an important distinction here between an optional
> capability that endpoints can negotiate for potential performance
> improvements and what’s defined as part of the base protocol. The earlier
> "zero-length DATA means unbounded" proposal would have changed the core
> framing semantics for all HTTP/3 traffic; in contrast, UNBOUND_DATA is a
> negotiated extension that endpoints can explicitly opt into.
>
> While a dedicated CAPSULE frame type could indeed simplify capsule-based
> protocols, the motivation for UNBOUND_DATA goes beyond Capsules. The
> immediate driver for me is the standard CONNECT method where the data is
> already opaque, and the additional HTTP/3 DATA framing layer introduces
> unnecessary per-frame overhead and can, in some implementations, trigger an
> extra memory copy.
>
>
> I see, thank you for the clarification.
>
> I'm not sure if we want to spend time optimizing traditional CONNECT when
> we are developing an improved version: draft-ietf-httpbis-connect-tcp.
>
> And FWIW, draft-ietf-httpbis-connect-tcp does depend on Capsules. IIRC, we
> discussed if the dependency should be optional due to performance concerns,
> and agreed that it is acceptable.
>
> To paraphrase, there has been a consensus that having a new layer of TLV
> encoding is fine. So the question is, now that there is a proposal to
> eliminate one layer of TLV encoding, do we need to redo the discussion?
>
> Maybe that is a long way to state that it might be more productive to
> spend time optimizing how Capsules are conveyed.
>
>
> The goal here is not to change generic HTTP semantics, but to provide an
> optional optimisation for cases where framing boundaries have no semantic
> value. It can also be used unidirectionally: an endpoint can advertise
> support for receiving unbound data without ever sending it itself.
>
>
> Yeah I get the argument, but outside of new tunneling mechanisms, I'm not
> sure how much new information we have to reconsider.
>
>
> Best Regards,
> Yaroslav
>
> On Tue, Oct 7, 2025 at 2:00 AM Kazuho Oku <kazuhooku@gmail.com> wrote:
>
>
>
> 2025年10月5日(日) 12:48 Mike Bishop <mbishop@evequefou.be>:
>
> It's been a while and I didn't recall details, so I did a bit of
> spelunking for the history. There was a proposal
> <https://github.com/quicwg/base-drafts/pull/2098> to allow DATA frames
> with length==0 to behave this way, extending to the end of the data stream,
> for all the reasons you cite.  It was merged, but then Martin observed that
> all the discussion of it had been on GitHub, rather than the list, so
> deciding that there had been consensus to merge was improper. We did
> discuss it on the list
> <https://urldefense.com/v3/__https://mailarchive.ietf.org/arch/msg/quic/3v2fwQJeWO8m7wYazBPxwRDWl88/__;!!Bt8RZUm9aw!6K3UbM5hk54HvWsHdiCCqKVJUTgtx2g0qLmAARnOERmZEwws6AthNcGWdyCLQgAGz2cAddFBIWJi-g$>,
> and subsequently reverted it.
>
> This isn't an argument for or against your extension, but do page in the
> history before re-attempting something we decided against previously.
>
>
> IMO, the arguments against stands today too, for generic HTTP.
>
> At the same time, I share the pain of Yaroslav and David. Because Capsules
> is a TLV format nested on top of HTTP, when using Capsules, we have three
> layers of TLV now, i.e., QUIC STREAM frames, HTTP/3 DATA frames, and
> Capsules.
>
> The complexity does not necessarily come from that they are layered, but
> from the fact that the TLV structures do not share the same boundary. An
> HTTP/3 DATA frame might extend beyond a QUIC STREAM frames and end in the
> middle of the next STREAM frame. Similarly, a Capsule might extend beyond a
> HTTP/3 DATA frame and end in the middle of the next DATA frame.
>
> This disagreement of boundary leads to buffering in each layer,
> speculative or incremental decoding, that are either heavyweight and/or
> complex.
>
> Considering these aspects, I wonder if the middle ground would be to
> specify a HTTP/3 CAPSULE frame that carries one capsule.
>
> It can look like below.
>
> CAPSULE Frame {
>   Type (i) = 0xTBD, // this is HTTP/3 frame type
>   Capsule Type (i), // the type of the capsule
>   Length (i),
>   Data (..),
> }
>
> Admittedly there will be one byte overhead (or one quicint overhead)
> compared to the original proposal, but the benefit is that the design is
> consistent with generic HTTP/3 and therefore would not be a disruptive
> change.
>
> WDYT?
>
>
> ------------------------------
> *From:* Yaroslav Rosomakho <yrosomakho@zscaler.com>
> *Sent:* Friday, October 3, 2025 4:42 PM
> *To:* ietf-http-wg@w3.org <ietf-http-wg@w3.org>
> *Cc:* David Schinazi <dschinazi.ietf@gmail.com>
> *Subject:* Unbound DATA frames in HTTP/3 proposal
>
> Dear HTTP Working Group,
>
> While HTTP/3 streams are very efficient for long-term connections such as
> CONNECT, WebSockets and WebTransport, the requirement to encapsulate
> everything into finite-length DATA frames reduces potential performance and
> flexibility. Best case scenario it introduces few extra unnecessary bytes
> on the wire, worst case scenario it can cause an extra memory copy.
>
> David and I would like to propose an optional extension, UNBOUND_DATA
> frame. This frame indicates that the remainder of the stream is data. This
> reduces framing overhead and simplifies transmission of long-lived or
> indeterminate-length payloads.
>
> Feedback and suggestions are very welcome.
>
> Best Regards,
> Yaroslav
>
> ---------- Forwarded message ---------
> A new version of Internet-Draft
> draft-rosomakho-httpbis-h3-unbound-data-00.txt
> has been successfully submitted by Yaroslav Rosomakho and posted to the
> IETF repository.
>
> Name:     draft-rosomakho-httpbis-h3-unbound-data
> Revision: 00
> Title:    Unbound DATA Frames in HTTP/3
> Date:     2025-10-03
> Group:    Individual Submission
> Pages:    8
> URL:
> https://www.ietf.org/archive/id/draft-rosomakho-httpbis-h3-unbound-data-00.txt
> <https://urldefense.com/v3/__https://www.ietf.org/archive/id/draft-rosomakho-httpbis-h3-unbound-data-00.txt__;!!Bt8RZUm9aw!6K3UbM5hk54HvWsHdiCCqKVJUTgtx2g0qLmAARnOERmZEwws6AthNcGWdyCLQgAGz2cAddHZJIE5og$>
> Status:
> https://datatracker.ietf.org/doc/draft-rosomakho-httpbis-h3-unbound-data/
> <https://urldefense.com/v3/__https://datatracker.ietf.org/doc/draft-rosomakho-httpbis-h3-unbound-data/__;!!Bt8RZUm9aw!6K3UbM5hk54HvWsHdiCCqKVJUTgtx2g0qLmAARnOERmZEwws6AthNcGWdyCLQgAGz2cAddFNhSZBwQ$>
> HTML:
> https://www.ietf.org/archive/id/draft-rosomakho-httpbis-h3-unbound-data-00.html
> <https://urldefense.com/v3/__https://www.ietf.org/archive/id/draft-rosomakho-httpbis-h3-unbound-data-00.html__;!!Bt8RZUm9aw!6K3UbM5hk54HvWsHdiCCqKVJUTgtx2g0qLmAARnOERmZEwws6AthNcGWdyCLQgAGz2cAddETma0iFQ$>
> HTMLized:
> https://datatracker.ietf.org/doc/html/draft-rosomakho-httpbis-h3-unbound-data
> <https://urldefense.com/v3/__https://datatracker.ietf.org/doc/html/draft-rosomakho-httpbis-h3-unbound-data__;!!Bt8RZUm9aw!6K3UbM5hk54HvWsHdiCCqKVJUTgtx2g0qLmAARnOERmZEwws6AthNcGWdyCLQgAGz2cAddHGhRWbCg$>
>
>
> Abstract:
>
>    This document defines a new HTTP/3 frame type, UNBOUND_DATA, and a
>    corresponding SETTINGS parameter that enables endpoints to negotiate
>    its use.  When an endpoint sends an UNBOUND_DATA frame on a request
>    or response stream, it indicates that all subsequent octets on that
>    stream are interpreted as data.  This applies both to message body
>    data and to octets transmitted after CONNECT or extended CONNECT.
>    The use of UNBOUND_DATA removes the need to encapsulate each portion
>    of the data in DATA frames, reducing framing overhead and simplifying
>    transmission of long-lived or indeterminate-length payloads.
>
>
>
> The IETF Secretariat
>
>
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>
> --
> Kazuho Oku
>
>
>
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> --
> Kazuho Oku
>