An HTTP Status Code for Indicating Hints
draft-ietf-httpbis-early-hints-00

Document Type Active Internet-Draft (httpbis WG)
Last updated 2017-02-08
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HTTP Working Group                                                K. Oku
Internet-Draft                                            DeNA Co., Ltd.
Intended status: Experimental                           February 8, 2017
Expires: August 12, 2017

                An HTTP Status Code for Indicating Hints
                   draft-ietf-httpbis-early-hints-00

Abstract

   This memo introduces an informational status code for HTTP that can
   be used for indicating hints to help a client start making
   preparations for processing the final response.

Note to Readers

   Discussion of this draft takes place on the HTTP working group
   mailing list (ietf-http-wg@w3.org), which is archived at
   https://lists.w3.org/Archives/Public/ietf-http-wg/ .

   Working Group information can be found at https://httpwg.github.io/ ;
   source code and issues list for this draft can be found at
   https://github.com/httpwg/http-extensions/labels/early-hints .

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 http://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 August 12, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://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
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  103 Early Hints . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   Most if not all of the web pages processed by a web browser contain
   links to external resources that need to be fetched prior to
   rendering the documents.  Therefore, it is beneficial to send such
   links as early as possible in order to minimize the time spent until
   the browser becomes possible to render the document.  Link header of
   type "preload" ([Preload]) can be used to indicate such links within
   the response headers of an HTTP response.

   However, it is not always possible for an origin server to send a
   response immediately after receiving a request.  In fact, it is often
   the contrary.  There are many deployments in which an origin server
   needs to query a database before generating a response.  It is also
   not unusual for an origin server to delegate a request to an upstream
   HTTP server running at a distant location.

   The dilemma here is that even though it is preferable for an origin
   server to send some headers as soon as it receives a request, it
   cannot do so until the status code and the headers of the final HTTP
   response is determined.

   HTTP/2 ([RFC7540]) push can be used as a solution to the issue, but
   has its own limitations.  The resources that can be pushed using
   HTTP/2 are limited to those belonging to the same origin.  Also, it

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