HTTP L. Pardue Internet-Draft Cloudflare Intended status: Standards Track 26 March 2023 Expires: 27 September 2023 HTTP priority order extension draft-pardue-httpbis-priority-order-00 Abstract The send-order parameter for the HTTP extensible prioritization scheme allows explicit ordering indication independent of request order. This can be used to as an additional input signal to scheduling decisions, to support alternative sending behaviors. About This Document This note is to be removed before publishing as an RFC. The latest revision of this draft can be found at https://LPardue.github.io/draft-pardue-httpbis-priority-order/draft- pardue-httpbis-priority-order.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft- pardue-httpbis-priority-order/. Discussion of this document takes place on the HTTP Working Group mailing list (mailto:ietf-http-wg@w3.org), which is archived at https://lists.w3.org/Archives/Public/ietf-http-wg/. Source for this draft and an issue tracker can be found at https://github.com/LPardue/draft-pardue-httpbis-priority-order. 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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." Pardue Expires 27 September 2023 [Page 1] Internet-Draft HTTP priority order March 2023 This Internet-Draft will expire on 27 September 2023. Copyright Notice Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 3. The send-order parameter . . . . . . . . . . . . . . . . . . 4 4. Server Scheduling . . . . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. Normative References . . . . . . . . . . . . . . . . . . . . 7 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction The extensible prioritization scheme for HTTP provides guidance for servers using priority signals to schedule the sending of stream data; Section 10 of [RFC9218]. It recommends that when there are multiple items with the same urgency servers choose how to allocate bandwidth by considering the stream ID and incremental parameter, and possibly other signals. Pardue Expires 27 September 2023 [Page 2] Internet-Draft HTTP priority order March 2023 In web use cases, an HTML document can include other resources and user agents tend to issue requests in an ordered sequence that matches the actions of HTML or HTTP receiver processing. Requests are made using ascending stream IDs where lower-numbered streams typically relate to objects that were discovered earlier than higher- numbered streams. Because stream IDs represent an ordering that closely matches the receiver processing needs, the scheduling guidance in [RFC9218] can be effectively used to send data that is optimal for this consumption pattern. As a simple example, a client that issues non-incremental requests of the same urgency on streams 0, 4, 8 and 12 would expect a server , that is following Section 10 of [RFC9218], to serve the response in the order 0, 4, 8 and 12. A strictly singular serving order is unlikely to meet the needs of HTTP-based applications. The urgency and incremental parameters augment stream ID, urgency allows more important resources (from a processing perspective) to be sent ahead of less important resources, while incremental streams share bandwidth among resources that can be effectively loaded in parallel. There are other use cases where the user agent may not be able to influence the order of request emission in the most optimal sequence, or may discover an important resource late on and would like the response to "jump the queue" of other streams within a single urgency level. The send-order parameter defined by this document can be used in these situations. While it might be possible to achieve a similar outcome by careful use of the urgency parameter, such as reserving an urgency level, the limited number of levels can make this approach difficult in practice. Alternatively, rebalancing or reprioritization of concurrent stream urgencies might also achieve these goals but encounters issues related to churn and responsiveness due to the latency of reprioritization signals. 2. Conventions and Definitions 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 following terminology from Section 3 of [STRUCTURED-FIELDS] to specify syntax and parsing: Boolean, Dictionary, and Integer. Example HTTP requests and responses use the HTTP/2-style formatting from [HTTP/2]. Pardue Expires 27 September 2023 [Page 3] Internet-Draft HTTP priority order March 2023 This document uses the variable-length integer encoding from [QUIC]. 3. The send-order parameter The send-order (bikeshed-order-name) parameter value is Integer (see Section 3.3.1 of [STRUCTURED-FIELDS]), between 0 and 2^32. The range is ascending, higher values have precedence over lower values. Endpoints use send-order to communicate an ordering precedence that is independent of the request order. There is no default value, omission of the parameter means that there is no additional ordering preference. The send-order parameter satisfies the urgency and incremental parameter compatibility requirements in Section 4.3 of [RFC9218]. The following example shows an HTTP/3 client issuing multiple requests on the same connection, without the send-order parameter, and responses sent by a server following the guidance in Section 10 of [RFC9218]. Pardue Expires 27 September 2023 [Page 4] Internet-Draft HTTP priority order March 2023 Client Server HEADERS (stream 0) :method = GET :scheme = https :authority = example.net :path = /image1.jpg priority = u=1 HEADERS (stream 4) :method = GET :scheme = https :authority = example.net :path = /image2.jpg priority = u=1 HEADERS (stream 8) :method = GET :scheme = https :authority = example.net :path = /image3.jpg priority = u=1 HEADERS (stream 0) :status = 200 content-type = image/jpeg DATA (stream 0) {binary data} HEADERS (stream 4) :status = 200 content-type = image/jpeg DATA (stream 4) {binary data} HEADERS (stream 8) :status = 200 content-type = image/jpeg DATA (stream 8) {binary data} The following example shows an HTTP/3 client issuing multiple requests on the same connection, without the send-order parameter, and responses sent by a server following the guidance in Section 4. Pardue Expires 27 September 2023 [Page 5] Internet-Draft HTTP priority order March 2023 Client Server HEADERS (stream 0) :method = GET :scheme = https :authority = example.net :path = /image1.jpg priority = u=1 HEADERS (stream 4) :method = GET :scheme = https :authority = example.net :path = /image2.jpg priority = u=1,bikeshed-order-name=25 HEADERS (stream 8) :method = GET :scheme = https :authority = example.net :path = /image3.jpg priority = u=1,bikeshed-order-name=15 HEADERS (stream 4) :status = 200 content-type = image/jpeg DATA (stream 4) {binary data} HEADERS (stream 8) :status = 200 content-type = image/jpeg DATA (stream 8) {binary data} HEADERS (stream 0) :status = 200 content-type = image/jpeg DATA (stream 0) {binary data} 4. Server Scheduling This document updates the scheduling guidance in Section 10 of [RFC9218]. Pardue Expires 27 September 2023 [Page 6] Internet-Draft HTTP priority order March 2023 Non-incremental responses of the same urgency SHOULD be served by prioritizing bandwidth allocation in ascending order of send-order. If there are no responses with a send-order, allocation SHOULD use ascending order of stream ID. Incremental responses of the same urgency are not affected by send- order. 5. Security Considerations The considerations in [RFC9218] apply. There are not believed to be any additional considerations. 6. IANA Considerations TODO 7. Normative References [HTTP/2] Thomson, M., Ed. and C. Benfield, Ed., "HTTP/2", RFC 9113, DOI 10.17487/RFC9113, June 2022, . [QUIC] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, May 2021, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC9218] Oku, K. and L. Pardue, "Extensible Prioritization Scheme for HTTP", RFC 9218, DOI 10.17487/RFC9218, June 2022, . [STRUCTURED-FIELDS] Nottingham, M. and P-H. Kamp, "Structured Field Values for HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021, . Pardue Expires 27 September 2023 [Page 7] Internet-Draft HTTP priority order March 2023 Acknowledgments TODO acknowledge. Author's Address Lucas Pardue Cloudflare Email: lucaspardue.24.7@gmail.com Pardue Expires 27 September 2023 [Page 8]