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

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<mailto: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<mailto:kazuhooku@gmail.com>> wrote:


2025年10月5日(日) 12:48 Mike Bishop <mbishop@evequefou.be<mailto: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<mailto:yrosomakho@zscaler.com>>
Sent: Friday, October 3, 2025 4:42 PM
To: ietf-http-wg@w3.org<mailto:ietf-http-wg@w3.org> <ietf-http-wg@w3.org<mailto:ietf-http-wg@w3.org>>
Cc: David Schinazi <dschinazi.ietf@gmail.com<mailto: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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