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HTTPBIS                                                       M. Thomson
Internet-Draft                                                   Mozilla
Updates: 7540 (if approved)                                      R. Peon
Intended status: Standards Track                           July 25, 2019
Expires: January 26, 2020


             Deprecation of HTTP/2 Priority Signaling Hints
               draft-peon-httpbis-h2-priority-one-less-00

Abstract

   This document deprecates HTTP/2 priority signaling hints.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on January 26, 2020.

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   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Deprecation of HTTP/2 Priority Signaling Hints  . . . . . . .   2
   2.  Security and Privacy Considerations . . . . . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   4.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Normative References  . . . . . . . . . . . . . . . . . .   3
     4.2.  Informative References  . . . . . . . . . . . . . . . . .   3
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   3

1.  Deprecation of HTTP/2 Priority Signaling Hints

   An important feature of any implementation of a protocol that
   provides multiplexing is the ability to prioritize the sending of
   information.  This was an important realization in the design of
   HTTP/2 [HTTP2].  Prioritization is a difficult problem, so it will
   always be suboptimal, particularly if one endpoint operates in
   ignorance of the needs of its peer.

   HTTP/2 introduced a complex prioritization signaling scheme that used
   a combination of dependencies and weights, formed into an unbalanced
   tree.  That scheme also depends on in-order delivery, so it is
   unsuitable for use in protocols like HTTP/3 [HTTP3], which attempts
   to avoid global ordering.

   Furthermore, though this scheme is rich in some ways, it has proven
   to be inadequate in several others.  It is not well suited to major
   use cases like live video delivery and it cannot be used to carry
   hints from servers.

   This prioritization scheme suffers from poor deployment and
   interoperability.  Most server implementations do not include support
   for this scheme, some favoring instead bespoke schemes based on
   heuristics and other hints, like the content type of resources and
   the order in which requests arrive.

   Consequently, the priority hints defined in HTTP/2 cannot be used
   across different HTTP versions.  So either we define richer schemes
   that might support translation between versions, or we suffer
   information loss if multiple versions are in use.

   Retaining the HTTP/2 priority scheme increases the complexity of the
   entire system without any evidence that the value it provides offsets
   that complexity.

   This document formally deprecates the priority scheme defined in
   HTTP/2, acknowledging the lack of wide interoperability and its lack
   of suitability for new protocol versions and current use cases.



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   HTTP/2 servers were never obligated to use the information provided
   by clients in HTTP/2 PRIORITY (and HEADERS) frames.  This document
   encourages servers to ignore those frames.  Similarly, HTTP/2 clients
   are encouraged not to send priority information in HTTP/2.

2.  Security and Privacy Considerations

   HTTP/2 prioritization signaling was always optional.  Processing of
   priority information could be used as a denial of service vector by
   adversaries.  Ignoring priority information removes this vector.

3.  IANA Considerations

   This document makes no request of IANA.

4.  References

4.1.  Normative References

   [HTTP2]    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>.

4.2.  Informative References

   [HTTP3]    Bishop, M., "Hypertext Transfer Protocol Version 3
              (HTTP/3)", draft-ietf-quic-http-22 (work in progress),
              July 2019.

Authors' Addresses

   Martin Thomson
   Mozilla

   Email: mt@lowentropy.net


   Roberto Peon

   Email: grmocg@gmail.com










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