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Thomson 3 Internet-Draft Mozilla 4 Updates: 7540 (if approved) R. Peon 5 Intended status: Standards Track July 25, 2019 6 Expires: January 26, 2020 8 Deprecation of HTTP/2 Priority Signaling Hints 9 draft-peon-httpbis-h2-priority-one-less-00 11 Abstract 13 This document deprecates HTTP/2 priority signaling hints. 15 Status of This Memo 17 This Internet-Draft is submitted in full conformance with the 18 provisions of BCP 78 and BCP 79. 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF). Note that other groups may also distribute 22 working documents as Internet-Drafts. The list of current Internet- 23 Drafts is at https://datatracker.ietf.org/drafts/current/. 25 Internet-Drafts are draft documents valid for a maximum of six months 26 and may be updated, replaced, or obsoleted by other documents at any 27 time. It is inappropriate to use Internet-Drafts as reference 28 material or to cite them other than as "work in progress." 30 This Internet-Draft will expire on January 26, 2020. 32 Copyright Notice 34 Copyright (c) 2019 IETF Trust and the persons identified as the 35 document authors. All rights reserved. 37 This document is subject to BCP 78 and the IETF Trust's Legal 38 Provisions Relating to IETF Documents 39 (https://trustee.ietf.org/license-info) in effect on the date of 40 publication of this document. Please review these documents 41 carefully, as they describe your rights and restrictions with respect 42 to this document. Code Components extracted from this document must 43 include Simplified BSD License text as described in Section 4.e of 44 the Trust Legal Provisions and are provided without warranty as 45 described in the Simplified BSD License. 47 Table of Contents 49 1. Deprecation of HTTP/2 Priority Signaling Hints . . . . . . . 2 50 2. Security and Privacy Considerations . . . . . . . . . . . . . 3 51 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 52 4. References . . . . . . . . . . . . . . . . . . . . . . . . . 3 53 4.1. Normative References . . . . . . . . . . . . . . . . . . 3 54 4.2. Informative References . . . . . . . . . . . . . . . . . 3 55 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 3 57 1. Deprecation of HTTP/2 Priority Signaling Hints 59 An important feature of any implementation of a protocol that 60 provides multiplexing is the ability to prioritize the sending of 61 information. This was an important realization in the design of 62 HTTP/2 [HTTP2]. Prioritization is a difficult problem, so it will 63 always be suboptimal, particularly if one endpoint operates in 64 ignorance of the needs of its peer. 66 HTTP/2 introduced a complex prioritization signaling scheme that used 67 a combination of dependencies and weights, formed into an unbalanced 68 tree. That scheme also depends on in-order delivery, so it is 69 unsuitable for use in protocols like HTTP/3 [HTTP3], which attempts 70 to avoid global ordering. 72 Furthermore, though this scheme is rich in some ways, it has proven 73 to be inadequate in several others. It is not well suited to major 74 use cases like live video delivery and it cannot be used to carry 75 hints from servers. 77 This prioritization scheme suffers from poor deployment and 78 interoperability. Most server implementations do not include support 79 for this scheme, some favoring instead bespoke schemes based on 80 heuristics and other hints, like the content type of resources and 81 the order in which requests arrive. 83 Consequently, the priority hints defined in HTTP/2 cannot be used 84 across different HTTP versions. So either we define richer schemes 85 that might support translation between versions, or we suffer 86 information loss if multiple versions are in use. 88 Retaining the HTTP/2 priority scheme increases the complexity of the 89 entire system without any evidence that the value it provides offsets 90 that complexity. 92 This document formally deprecates the priority scheme defined in 93 HTTP/2, acknowledging the lack of wide interoperability and its lack 94 of suitability for new protocol versions and current use cases. 96 HTTP/2 servers were never obligated to use the information provided 97 by clients in HTTP/2 PRIORITY (and HEADERS) frames. This document 98 encourages servers to ignore those frames. Similarly, HTTP/2 clients 99 are encouraged not to send priority information in HTTP/2. 101 2. Security and Privacy Considerations 103 HTTP/2 prioritization signaling was always optional. Processing of 104 priority information could be used as a denial of service vector by 105 adversaries. Ignoring priority information removes this vector. 107 3. IANA Considerations 109 This document makes no request of IANA. 111 4. References 113 4.1. Normative References 115 [HTTP2] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext 116 Transfer Protocol Version 2 (HTTP/2)", RFC 7540, 117 DOI 10.17487/RFC7540, May 2015, 118 . 120 4.2. Informative References 122 [HTTP3] Bishop, M., "Hypertext Transfer Protocol Version 3 123 (HTTP/3)", draft-ietf-quic-http-22 (work in progress), 124 July 2019. 126 Authors' Addresses 128 Martin Thomson 129 Mozilla 131 Email: mt@lowentropy.net 133 Roberto Peon 135 Email: grmocg@gmail.com