Updating HTTP Caching Policy in Trailers
draft-nottingham-cache-trailers-00

Document Type Active Internet-Draft (individual)
Authors Mark Nottingham  , James Snell 
Last updated 2021-03-07
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Network Working Group                                      M. Nottingham
Internet-Draft                                                          
Intended status: Standards Track                                J. Snell
Expires: 9 September 2021                                   8 March 2021

                Updating HTTP Caching Policy in Trailers
                   draft-nottingham-cache-trailers-00

Abstract

   This specification defines how to update caching policy for a
   response in HTTP trailer fields, after the content has been sent.

Note to Readers

   _RFC EDITOR: please remove this section before publication_

   The issues list for this draft can be found at
   https://github.com/mnot/I-D/labels/cache-trailers
   (https://github.com/mnot/I-D/labels/cache-trailers).

   The most recent (often, unpublished) draft is at
   https://mnot.github.io/I-D/cache-trailers/ (https://mnot.github.io/I-
   D/cache-trailers/).

   Recent changes are listed at https://github.com/mnot/I-D/commits/gh-
   pages/cache-trailers (https://github.com/mnot/I-D/commits/gh-pages/
   cache-trailers).

   See also the draft's current status in the IETF datatracker, at
   https://datatracker.ietf.org/doc/draft-nottingham-cache-trailers/
   (https://datatracker.ietf.org/doc/draft-nottingham-cache-trailers/).

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on 9 September 2021.

Copyright Notice

   Copyright (c) 2021 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
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  The "trailer-update" HTTP Cache Directive . . . . . . . . . .   3
     2.1.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   Web content that is "dynamically" generated -- i.e., with the
   response body streamed by the server to the client as it is created
   -- is often assumed to be uncacheable.  In practice, though, there
   are some scenarios where caching is beneficial; for example, when a
   private cache might be able to reuse a personalised, dynamic response
   for a period, or when such a response can be shared by a number of
   clients.

   A server choosing a caching policy for such a response faces a
   conundrum: if an error or other unforeseen condition happens during
   the generation of the response, that caching policy might be too
   liberal.  Currently, the only available solutions are to:

   1.  prevent or severely curtail downstream caching, or

   2.  buffer the response until a caching policy can be confidently
       assigned.

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   In both cases, performance suffers; in the former, caching efficiency
   is less than it could be in the common case, In the latter, the
   server consumes additional resources and delays the response.

   This specification provides a third solution: updating the caching
   policy in HTTP trailer fields, after the content has been sent.
   Doing so allows content to be streamed, while caching policy can be
   determined after the content is actually generated.

1.1.  Notational Conventions
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