HTTP Header Common Structure

Document Type Active Internet-Draft (httpbis WG)
Last updated 2017-04-25
Replaces draft-ietf-httpbis-jfv
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HTTP Working Group                                             P-H. Kamp
Internet-Draft                                 The Varnish Cache Project
Intended status: Standards Track                          April 24, 2017
Expires: October 26, 2017

                      HTTP Header Common Structure


   An abstract data model for HTTP headers, "Common Structure", and a
   HTTP/1 serialization of it, generalized from current HTTP headers.

Note to Readers

   Discussion of this draft takes place on the HTTP working group
   mailing list (, which is archived at .

   Working Group information can be found at ;
   source code and issues list for this draft can be found at .

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on October 26, 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
   Provisions Relating to IETF Documents

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   ( in effect on the date of
   publication of this document.  Please review these documents
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1.  Introduction

   The HTTP protocol does not impose any structure or datamodel on the
   information in HTTP headers, the HTTP/1 serialization is the
   datamodel: An ASCII string without control characters.

   HTTP header definitions specify how the string must be formatted and
   while families of similar headers exist, it still requires an
   uncomfortable large number of bespoke parser and validation routines
   to process HTTP traffic correctly.

   In order to improve performance HTTP/2 and HPACK uses naive text-
   compression, which incidentally decoupled the on-the-wire
   serialization from the data model.

   During the development of HPACK it became evident that significantly
   bigger gains were available if semantic compression could be used,
   most notably with timestamps.  However, the lack of a common data
   structure for HTTP headers would make semantic compression one long
   list of special cases.

   Parallel to this, various proposals for how to fulfill data-
   transportation needs, and to a lesser degree to impose some kind of
   order on HTTP headers, at least going forward, were floated.

   All of these proposals, JSON, CBOR etc. run into the same basic
   problem: Their serialization is incompatible with RFC 7230's
   [RFC7230] ABNF definition of 'field-value'.

   For binary formats, such as CBOR, a wholesale base64/85
   reserialization would be needed, with negative results for both
   debugability and bandwidth.

   For textual formats, such as JSON, the format must first be neutered
   to not violate field-value's ABNF, and then workarounds added to
   reintroduce the features just lost, for instance UNICODE strings.

   The post-surgery format is no longer JSON, and it experience
   indicates that almost-but-not-quite compatibility is worse than no

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   This proposal starts from the other end, and builds and generalizes a
   data structure definition from existing HTTP headers, which means
   that HTTP/1 serialization and 'field-value' compatibility is built

   If all future HTTP headers are defined to fit into this Common
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