Internet DRAFT - draft-hurst-quic-http-data-offset-frame
draft-hurst-quic-http-data-offset-frame
Network Working Group S. Hurst
Internet-Draft BBC Research & Development
Intended status: Experimental 4 July 2022
Expires: 5 January 2023
An Offset Extension Frame For HTTP/3 Data
draft-hurst-quic-http-data-offset-frame-02
Abstract
This document specifies an optional extension frame type for HTTP/3
that extends the functionality of the DATA frame type to include an
offset for the HTTP message payload. This is useful in situations
where the HTTP/3 exchange is taking place over an unreliable
transport mechanism.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 5 January 2023.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
3. DATA_WITH_OFFSET Extension Frame . . . . . . . . . . . . . . 3
4. Realising HTTP Multipart Range Responses With HTTP/3 Binary
Framing . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Response Headers . . . . . . . . . . . . . . . . . . . . 4
4.2. Usage of DATA_WITH_OFFSET frame with HTTP Range
Responses . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Negotiating Support For The DATA_WITH_OFFSET Frame . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8
Appendix B. Changelog . . . . . . . . . . . . . . . . . . . . . 8
B.1. Changes since
draft-hurst-quic-http-data-offset-frame-01 . . . . . . . 8
B.2. Changes since
draft-hurst-quic-http-data-offset-frame-00 . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
HTTP/3 [RFC9114] supports the transfer of HTTP semantics over the
QUIC transport protocol [RFC9000]. In a conventional HTTP/3 message
exchange, messages consist of a header field section sent as a single
HEADERS frame, an optional HTTP message payload sent as a series of
DATA frames, followed optionally by a trailer field section sent as a
single HEADERS frame. Each DATA frame does not describe its position
within the HTTP message payload; rather this is calculated from the
position within the QUIC stream minus the overhead from HTTP/3 frame
headers and the contents of the header field section.
In the case where the message exchange is taking place across a
partially reliable or unreliable profile of [RFC9000], packet loss
could result in a lack of synchronisation in the receiver between the
perceived HTTP/3 DATA frame offset and the QUIC STREAM frame offset,
potentially resulting in a corrupt HTTP representation at the
receiver.
In addition, there are other use cases, such as HTTP multipart range
requests, where the HTTP/3 payload offset has no direct mapping to
the value calculated by the method described above.
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This document introduces an extension frame type DATA_WITH_OFFSET
which can be used to explicitly signal the offset in the original
representation of the data being conveyed within the frame.
2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document uses the variable-length integer encoding from
[RFC9000]. The packet and frame diagrams in this document use the
bespoke format specified in [RFC9000].
3. DATA_WITH_OFFSET Extension Frame
Based on the DATA frame defined in [RFC9114], the DATA_WITH_OFFSET
frame conveys arbitrary, variable-length sequences of bytes at a
defined offset of an HTTP representation. By carrying an explicit
payload offset in the HTTP/3 frame header, the HTTP message payload
offset is decoupled from the QUIC STREAM frame header offset value.
The additional payload offset field takes the form of a variable-
length integer, as shown in Figure 1 below.
DATA_WITH_OFFSET Frame {
Type (i) = 0xd00,
Length (i),
Offset (i),
Data (..),
}
Figure 1: DATA_WITH_OFFSET Frame
If its peer has indicated support for the DATA_WITH_OFFSET extension
frame type (as described in Section 5 below) a sender MAY choose to
use either DATA frames or DATA_WITH_OFFSET frames to transmit an HTTP
representation. Senders MUST NOT mix the use of DATA and
DATA_WITH_OFFSET frames on the same QUIC stream (i.e. in the same
HTTP message).
*Author's Note:* The author welcomes comments about relaxation of
the requirement to not mix the usage of DATA and DATA_WITH_OFFSET
frames in the same HTTP message.
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[RFC9114] defines three stream types: control stream, request stream
and push stream. The DATA_WITH_OFFSET frame is only permitted to
appear on request streams and push streams. A DATA_WITH_OFFSET frame
MUST NOT appear on control streams. If a DATA_WITH_OFFSET frame is
received on a control stream, the recipient MUST respond with a
connection error of type H3_FRAME_UNEXPECTED, as described in
[RFC9114].
The purpose of the DATA_WITH_OFFSET frame is only to assist in
locating a particular slice of data carried as part of an HTTP
message payload, and not as a means to send data out of order.
Senders MUST send data in order, i.e. with increasing values in the
Offset field. In cases where the underlying transport does not
guarantee in-order delivery of HTTP/3 frames, the receiver MUST be
prepared to deal with out-of-order reception of DATA_WITH_OFFSET
frames.
4. Realising HTTP Multipart Range Responses With HTTP/3 Binary Framing
HTTP Range Requests, described in [RFC9110], is an optional feature
of HTTP that allows a client to request transfer of one or more
subranges of a given representation. Despite the move to binary
framing for HTTP in [RFC7540] and subsequently [RFC9114], multiple
part HTTP Range Requests still rely on textual encoding - including
boundary strings - which is inefficient. These boundary strings then
preface additional HTTP headers for each body part, which always
carry a Content-Range field, and may additionally carry a Content-
Type field which is likely to be repeated across every body part. It
is not possible to compress these headers using [RFC9204].
By using the DATA_WITH_OFFSET frame described in Section 3, the
network efficiency of multiple part range requests is improved by no
longer needing to encode a boundary string into the representation
response. Instead, the offset of each part of a representation is
simply encoded in the header of a fresh HTTP DATA_WITH_OFFSET frame.
4.1. Response Headers
[RFC9110] specifies how a server may respond to an HTTP multipart
range request using the 206 (Partial Content) status code. The
response message carries a Content-Type response header indicating
the multipart/byteranges media type with its required boundary
parameter. This boundary parameter allows each body part to carry
its own header area containing a Content-Range header to describe
what range of the selected representation this body part conveys, as
well as a Content-Type header (if applicable) which describes the
actual media type of the selected representation.
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(Note that section 14.2 of [RFC9110] describes several reasons why a
server may choose to deliver a different selection of parts than what
the client originally requested.)
Because a selected representation may only contain a single Content-
Type header field with a single value, repeating this header field in
every body part is highly inefficient. Moreover, the unbounded
length of the boundary parameter further reduces transmission
efficiency.
This specification modifies the syntax of the Content-Range header
and explicitly defines it as a list-based field as per section 5.6.1
of [RFC9110] that is carried in the first HEADERS block sent as part
of an HTTP/3 response. In addition, when used on the same QUIC
stream as DATA_WITH_OFFSET frames, this specification permits the
Content-Range and Content-Type HTTP headers to appear in the HEADERS
frame of a 206 (Partial Content) response, enabling it to indicate
the MIME media type of the whole representation without needing to
duplicate it for each body part.
Content-Range = 1#range-item
range-item = range-unit SP
( range-resp / unsatisfied-range )
range-resp = incl-range "/" ( complete-length / "*" )
incl-range = first-pos "-" last-pos
unsatisfied-range = "*/" complete-length
complete-length = 1*DIGIT
Figure 2: ABNF for extended Content-Range
:status = 206
content-type = video/mp4
content-range = bytes 10000-17999/18879543, bytes 24000-41999/18879543
Figure 3: Range-Response header example
Implementations advertising support for the DATA_WITH_OFFSET frame as
described in Section 5 MUST be able to consume this overloaded form
of the Content-Range HTTP response header.
A server MAY continue to use the method described in [RFC9110] even
if a client has expressed support for the DATA_WITH_OFFSET frame.
*Author's Note:* Is it possibly worth splitting this out into its
own HTTP setting value?
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4.2. Usage of DATA_WITH_OFFSET frame with HTTP Range Responses
The DATA_WITH_OFFSET frame may be used in conjunction with HTTP Range
Requests, as described in [RFC9110]. When carrying data for a byte
range response, the Offset field in the frame header MUST reflect the
starting byte position of the frame's payload in the HTTP
representation and not the offset within the HTTP/3 exchange. For
example, for an HTTP/3 range request made with a request header of
range: bytes=1000-1999, the first DATA_WITH_OFFSET frame in the
response MUST carry the value 1000 in the Offset field of the frame
header.
For HTTP response messages carrying a set of byte ranges, a
DATA_WITH_OFFSET frame MUST NOT carry data for more than one
contiguous byte range within that set. An individual byte range MAY
be carried over multiple instances of the DATA_WITH_OFFSET frame.
5. Negotiating Support For The DATA_WITH_OFFSET Frame
The DATA_WITH_OFFSET frame described in Section 3 is an optional
extension to the regular HTTP/3 protocol specification and, as such,
usage of the frame type must be negotiated as described in section 9
of [RFC9114]. For a conventional HTTP/3 connection, this is done
using HTTP/3 SETTINGS frames carried on the control streams.
This specification defines the following setting:
SETTINGS_ENABLE_DATA_WITH_OFFSET_FRAME (0xd00): A boolean value with
a default value of 0 (false). Any non-zero value is true.
*Author's Note:* It is intended that the value of the H3 SETTINGS
frame should mirror the value of the frame to indicate which
version of the DATA_WITH_OFFSET frame it understands, should
subsequent revisions of this draft change the frame type.
An endpoint that implements this specification SHOULD send a
SETTINGS_ENABLE_DATA_WITH_OFFSET_FRAME setting at the beginning of
the connection to indicate that it is able to process
DATA_WITH_OFFSET frames from its peer.
An endpoint MUST NOT send a DATA_WITH_OFFSET frame unless it has
received a positive (i.e. non-zero)
SETTINGS_ENABLE_DATA_WITH_OFFSET_FRAME setting from its peer.
6. Security Considerations
This document introduces no new security considerations beyond those
discussed in [RFC9114].
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7. IANA Considerations
This specification registers a new frame type in the "HTTP/3 Frame
Type" registry ([RFC9114]).
+==================+=======+===============+
| Frame Type | Value | Specification |
+==================+=======+===============+
| DATA_WITH_OFFSET | 0xd00 | Section 3 |
+------------------+-------+---------------+
Table 1: Registered HTTP/3 Frame Type
*Author's Note:* The final, intended value of the frame type is
0xd0f, but in order to allow for this extension to naturally
evolve and allow for the frame format to change, it starts at
0xd00 and subsequent revisions of this extension can take
incrementally higher frame type values between 0xd00 and 0xd0e.
This specification registers a new setting in the "HTTP/3 Settings"
registry ([RFC9114]).
+=======================================+=====+=============+=======+
|Setting |Value|Specification|Default|
+=======================================+=====+=============+=======+
|SETTINGS_ENABLE_DATA_WITH_OFFSET_FRAME |0xd00|Section 5 |0 |
+---------------------------------------+-----+-------------+-------+
Table 2: Registered HTTP/3 Settings
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/info/rfc9110>.
[RFC9114] Bishop, M., Ed., "HTTP/3", RFC 9114, DOI 10.17487/RFC9114,
June 2022, <https://www.rfc-editor.org/info/rfc9114>.
8.2. Informative References
[RFC9204] Krasic, C., Bishop, M., and A. Frindell, Ed., "QPACK:
Field Compression for HTTP/3", RFC 9204,
DOI 10.17487/RFC9204, June 2022,
<https://www.rfc-editor.org/info/rfc9204>.
Appendix A. Acknowledgements
The author would like to thank the following for their contributions
to the design described in the present document: Lucas Pardue,
Richard Bradbury and David Waring.
I am also grateful for Chris Poole's helpful review comments.
Appendix B. Changelog
*RFC Editor's Note:* Please remove this section prior to
publication of a final version of this document.
B.1. Changes since draft-hurst-quic-http-data-offset-frame-01
* Update HTTP/3 reference to the published [RFC9114]
* Update QPACK reference to the published [RFC9204]
* Update httpbis-semantics reference to the published [RFC9110]
B.2. Changes since draft-hurst-quic-http-data-offset-frame-00
* Update reference to QUIC transport I-D to [RFC9000].
* Update reference to draft-ietf-httpbis-semantics I-D.
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Author's Address
Sam Hurst
BBC Research & Development
Email: sam.hurst@bbc.co.uk
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