An HTTP Status Code for Indicating Hints
RFC 8297
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Document |
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RFC - Experimental
(December 2017; No errata)
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Author |
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Kazuho Oku
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Last updated |
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2017-12-19
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IETF
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plain text
html
pdf
htmlized
bibtex
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Reviews |
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Stream |
WG state
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Submitted to IESG for Publication
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Document shepherd |
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Mark Nottingham
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Shepherd write-up |
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Show
(last changed 2017-06-20)
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IESG |
IESG state |
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RFC 8297 (Experimental)
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Consensus Boilerplate |
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Yes
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Telechat date |
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Responsible AD |
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Alexey Melnikov
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Send notices to |
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Mark Nottingham <mnot@mnot.net>
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IANA |
IANA review state |
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Version Changed - Review Needed
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IANA action state |
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RFC-Ed-Ack
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Internet Engineering Task Force (IETF) K. Oku
Request for Comments: 8297 Fastly
Category: Experimental December 2017
ISSN: 2070-1721
An HTTP Status Code for Indicating Hints
Abstract
This memo introduces an informational HTTP status code that can be
used to convey hints that help a client make preparations for
processing the final response.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for examination, experimental implementation, and
evaluation.
This document defines an Experimental Protocol for the Internet
community. This document is a product of the Internet Engineering
Task Force (IETF). It represents the consensus of the IETF
community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents approved by the IESG are a candidate for any level of
Internet Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8297.
Copyright Notice
Copyright (c) 2017 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 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.
Oku Experimental [Page 1]
RFC 8297 Early Hints December 2017
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. HTTP Status Code 103: Early Hints . . . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Normative References . . . . . . . . . . . . . . . . . . 6
5.2. Informative References . . . . . . . . . . . . . . . . . 6
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
It is common for HTTP responses to contain links to external
resources that need to be fetched prior to their use, for example,
rendering HTML by a web browser. Having such links available to the
client as early as possible helps to minimize perceived latency.
The "preload" [Preload] link relation can be used to convey such
links in the Link header field of an HTTP response. However, it is
not always possible for an origin server to generate the header block
of a final response immediately after receiving a request. For
example, the origin server might delegate a request to an upstream
HTTP server running at a distant location, or the status code might
depend on the result of a database query.
The dilemma here is that even though it is preferable for an origin
server to send some header fields as soon as it receives a request,
it cannot do so until the status code and the full header fields of
the final HTTP response are determined.
HTTP/2 [RFC7540] server push can accelerate the delivery of
resources, but only resources for which the server is authoritative.
The other limitation of server push is that the response will be
transmitted regardless of whether the client has the response cached.
At the cost of spending one extra round trip compared to server push
in the worst case, delivering Link header fields in a timely fashion
is more flexible and might consume less bandwidth.
This memo defines a status code for sending an informational response
([RFC7231], Section 6.2) that contains header fields that are likely
to be included in the final response. A server can send the
informational response containing some of the header fields to help
the client start making preparations for processing the final
response, and then run time-consuming operations to generate the
Oku Experimental [Page 2]
RFC 8297 Early Hints December 2017
final response. The informational response can also be used by an
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