Compression Dictionaries for HTTP/2
draft-vkrasnov-h2-compression-dictionaries-02

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Network Working Group                                         V. Krasnov
Internet-Draft                                           Cloudflare Inc.
Intended status: Informational                            March 13, 2017
Expires: September 14, 2017

                  Compression Dictionaries for HTTP/2
               draft-vkrasnov-h2-compression-dictionaries-02

Abstract

   This document specifies a new HTTP/2 frame type and new HTTP/2
   settings values that would enable the use of previously transferred
   data as compression dictionaries, significantly improving overall
   compression ratio for a given connection.

   In addition, this document proposes to define a set of industry
   standard, static, dictionaries to be used with any Lempel-Ziv based
   compression for the common textual MIME types prevalent on the web.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on September 14, 2017.

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
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   (http://trustee.ietf.org/license-info) in effect on the date of
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   carefully, as they describe your rights and restrictions with respect
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Krasnov                Expires September 14, 2017               [Page 1]
Internet-Draft     Compression Dictionaries for HTTP/2        March 2017

   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.  Conventions and Terminology . . . . . . . . . . . . . . .   3
   2.  HTTP/2 Extension  . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Extension Settings  . . . . . . . . . . . . . . . . . . .   3
     2.2.  Extension Frames  . . . . . . . . . . . . . . . . . . . .   4
       2.2.1.  The SET_COMPRESSION_CONTEXT . . . . . . . . . . . . .   4
       2.2.2.  The SET_DICTIONARY Frame  . . . . . . . . . . . . . .   4
       2.2.3.  The USE_DICTIONARY Frame  . . . . . . . . . . . . . .   5
     2.3.  Static Dictionaries . . . . . . . . . . . . . . . . . . .   5
   3.  Dictionary State  . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Server Behavior . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Client Behavior . . . . . . . . . . . . . . . . . . . . .   7
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   5.  HTTP/1.1 Mappings . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  The mapping . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The HTTP/2 [RFC7540] protocol encourages the use of many small assets
   for CSS/JS/HTML, due to its multiplexed nature.  Prior to HTTP/2,
   asset inlining was encouraged, resulting in fewer, larger assets per
   website.

   The HTTP/2 protocol also allows for transmitted data to be compressed
   with a lossless compression format.  The format used is specified in
   the "Content-Encoding" (see [RFC2616], section 14.11) header field.
   For example, "Content-Encoding: br" means the data was compressed
   using the Brotli format.

   The nature of the compression algorithms, such as DEFLATE [RFC1951]
   and Brotli [RFC7932], used with HTTP in practice, require a certain
   "window" of data to perform backward matching.  Therefore, larger
   files have much better compression ratio.  To improve compression for
   smaller files, these algorithms allow to use a chunk of arbitrary
   data as a "Custom Dictionary" and function as the initial sliding
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