Client Hint Reliability
draft-davidben-http-client-hint-reliability-02
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David Benjamin
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2020-11-30
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HTTP D. Benjamin
Internet-Draft Google LLC
Updates: ietf-httpbis-client-hints (if approved) 30 November 2020
Intended status: Experimental
Expires: 3 June 2021
Client Hint Reliability
draft-davidben-http-client-hint-reliability-02
Abstract
This document defines the Critical-CH HTTP response header, and the
ACCEPT_CH HTTP/2 and HTTP/3 frames to allow HTTP servers to reliably
specify their Client Hint preferences, with minimal performance
overhead.
Discussion Venues
This note is to be removed before publishing as an RFC.
Source for this draft and an issue tracker can be found at
https://github.com/davidben/http-client-hint-reliability.
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."
This Internet-Draft will expire on 3 June 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
Benjamin Expires 3 June 2021 [Page 1]
Internet-Draft Client Hint Reliability November 2020
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 Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. The Critical-CH Response Header Field . . . . . . . . . . . . 3
3.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. The ACCEPT_CH Frame . . . . . . . . . . . . . . . . . . . . . 5
4.1. HTTP/2 ACCEPT_CH Frame . . . . . . . . . . . . . . . . . 5
4.2. HTTP/3 ACCEPT_CH Frame . . . . . . . . . . . . . . . . . 6
4.3. Processing ACCEPT_CH Frames . . . . . . . . . . . . . . . 7
4.4. Interaction with Critical-CH . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . 12
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
[I-D.ietf-httpbis-client-hints] defines a response header, Accept-CH,
for servers to advertise a set of request headers used for proactive
content negotiation. This allows user agents to send request headers
only when used, improving their performance overhead as well as
reducing passive fingerprinting surface.
However, on the first HTTP request to a server, the user agent will
not have received the Accept-CH header and may not take the server
preferences into account. More generally, the server's configuration
may have changed since the most recent HTTP request to the server.
This document defines a pair of mechanisms to resolve this:
1. an HTTP response header, Critical-CH, for the server to instruct
the user agent to retry the request
2. an alternate delivery mechanism for Accept-CH in HTTP/2 [RFC7540]
and HTTP/3 [I-D.ietf-quic-http], which can avoid the performance
hit of a retry in most cases
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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
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