Updating HTTP Caching Policy in Trailers
draft-nottingham-cache-trailers-00
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The most recent (often, unpublished) draft is at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
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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 9 September 2021.
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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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