Internet DRAFT - draft-peon-httpbis-h2-priority-one-less
draft-peon-httpbis-h2-priority-one-less
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
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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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