Structured Field Values for HTTP
RFC 8941

Document Type RFC - Proposed Standard (February 2021; No errata)
Authors Mark Nottingham  , Poul-Henning Kamp 
Last updated 2021-02-08
Replaces draft-nottingham-structured-headers, draft-ietf-httpbis-jfv, draft-kamp-httpbis-structure
Stream Internent Engineering Task Force (IETF)
Formats plain text html xml pdf htmlized (tools) htmlized bibtex
Stream WG state Submitted to IESG for Publication (wg milestone: - Submit Structured He... )
Document shepherd Tommy Pauly
Shepherd write-up Show (last changed 2020-04-08)
IESG IESG state RFC 8941 (Proposed Standard)
Action Holders
Consensus Boilerplate Yes
Telechat date
Responsible AD Barry Leiba
Send notices to Tommy Pauly <>
IANA IANA review state Version Changed - Review Needed
IANA action state No IANA Actions

Internet Engineering Task Force (IETF)                     M. Nottingham
Request for Comments: 8941                                        Fastly
Category: Standards Track                                      P-H. Kamp
ISSN: 2070-1721                                The Varnish Cache Project
                                                           February 2021

                    Structured Field Values for HTTP


   This document describes a set of data types and associated algorithms
   that are intended to make it easier and safer to define and handle
   HTTP header and trailer fields, known as "Structured Fields",
   "Structured Headers", or "Structured Trailers".  It is intended for
   use by specifications of new HTTP fields that wish to use a common
   syntax that is more restrictive than traditional HTTP field values.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

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
   ( 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
     1.1.  Intentionally Strict Processing
     1.2.  Notational Conventions
   2.  Defining New Structured Fields
   3.  Structured Data Types
     3.1.  Lists
       3.1.1.  Inner Lists
       3.1.2.  Parameters
     3.2.  Dictionaries
     3.3.  Items
       3.3.1.  Integers
       3.3.2.  Decimals
       3.3.3.  Strings
       3.3.4.  Tokens
       3.3.5.  Byte Sequences
       3.3.6.  Booleans
   4.  Working with Structured Fields in HTTP
     4.1.  Serializing Structured Fields
       4.1.1.  Serializing a List
       4.1.2.  Serializing a Dictionary
       4.1.3.  Serializing an Item
       4.1.4.  Serializing an Integer
       4.1.5.  Serializing a Decimal
       4.1.6.  Serializing a String
       4.1.7.  Serializing a Token
       4.1.8.  Serializing a Byte Sequence
       4.1.9.  Serializing a Boolean
     4.2.  Parsing Structured Fields
       4.2.1.  Parsing a List
       4.2.2.  Parsing a Dictionary
       4.2.3.  Parsing an Item
       4.2.4.  Parsing an Integer or Decimal
       4.2.5.  Parsing a String
       4.2.6.  Parsing a Token
       4.2.7.  Parsing a Byte Sequence
       4.2.8.  Parsing a Boolean
   5.  IANA Considerations
   6.  Security Considerations
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Appendix A.  Frequently Asked Questions
     A.1.  Why Not JSON?
   Appendix B.  Implementation Notes
   Authors' Addresses

1.  Introduction

   Specifying the syntax of new HTTP header (and trailer) fields is an
   onerous task; even with the guidance in Section 8.3.1 of [RFC7231],
   there are many decisions -- and pitfalls -- for a prospective HTTP
   field author.

   Once a field is defined, bespoke parsers and serializers often need
   to be written, because each field value has a slightly different
   handling of what looks like common syntax.

   This document introduces a set of common data structures for use in
   definitions of new HTTP field values to address these problems.  In
   particular, it defines a generic, abstract model for them, along with
   a concrete serialization for expressing that model in HTTP [RFC7230]
   header and trailer fields.

   An HTTP field that is defined as a "Structured Header" or "Structured
   Trailer" (if the field can be either, it is a "Structured Field")
   uses the types defined in this specification to define its syntax and
   basic handling rules, thereby simplifying both its definition by
   specification writers and handling by implementations.

   Additionally, future versions of HTTP can define alternative
   serializations of the abstract model of these structures, allowing
   fields that use that model to be transmitted more efficiently without
   being redefined.

   Note that it is not a goal of this document to redefine the syntax of
   existing HTTP fields; the mechanisms described herein are only
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