An HTTP Extension Framework
RFC 2774

Document Type RFC - Experimental (February 2000; No errata)
Last updated 2013-03-02
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Network Working Group                                          H. Nielsen
Request for Comments: 2774                                       P. Leach
Category: Experimental                                          Microsoft
                                                              S. Lawrence
                                                          Agranat Systems
                                                            February 2000

                      An HTTP Extension Framework

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

IESG Note

   This document was originally requested for Proposed Standard status.
   However, due to mixed reviews during Last Call and within the HTTP
   working group, it is being published as an Experimental document.
   This is not necessarily an indication of technical flaws in the
   document; rather, there is a more general concern about whether this
   document actually represents community consensus regarding the
   evolution of HTTP.  Additional study and discussion are needed before
   this can be determined.

   Note also that when HTTP is used as a substrate for other protocols,
   it may be necessary or appropriate to use other extension mechanisms
   in addition to, or instead of, those defined here.  This document
   should therefore not be taken as a blueprint for adding extensions to
   HTTP, but it defines mechanisms that might be useful in such
   circumstances.

Nielsen, et al.               Experimental                      [Page 1]
RFC 2774              An HTTP Extension Framework          February 2000

Abstract

   A wide range of applications have proposed various extensions of the
   HTTP protocol. Current efforts span an enormous range, including
   distributed authoring, collaboration, printing, and remote procedure
   call mechanisms. These HTTP extensions are not coordinated, since
   there has been no standard framework for defining extensions and
   thus, separation of concerns. This document describes a generic
   extension mechanism for HTTP, which is designed to address the
   tension between private agreement and public specification and to
   accommodate extension of applications using HTTP clients, servers,
   and proxies.  The proposal associates each extension with a globally
   unique identifier, and uses HTTP header fields to carry the extension
   identifier and related information between the parties involved in
   the extended communication.

Table of Contents

   1.  Introduction ...............................................3
   2.  Notational Conventions .....................................3
   3.  Extension Declarations .....................................4
    3.1   Header Field Prefixes ...................................5
   4.  Extension Header Fields ....................................6
    4.1   End-to-End Extensions ...................................7
    4.2   Hop-by-Hop Extensions ...................................7
    4.3   Extension Response Header Fields ........................8
   5.  Mandatory HTTP Requests ....................................8
    5.1   Fulfilling a Mandatory Request .........................10
   6.  Mandatory HTTP Responses ..................................11
   7.  510 Not Extended ..........................................11
   8.  Publishing an Extension ...................................11
   9.  Caching Considerations ....................................12
   10. Security Considerations ...................................13
   11. References ................................................13
   12. Acknowledgements ..........................................14
   13. Authors' Addresses ........................................14
   14. Summary of Protocol Interactions ..........................15
   15. Examples ..................................................16
    15.1  User Agent to Origin Server ............................16
    15.2  User Agent to Origin Server via HTTP/1.1 Proxy .........17
    15.3  User Agent to Origin Server via HTTP/1.0 Proxy .........18
   Full Copyright Statement ......................................20

Nielsen, et al.               Experimental                      [Page 2]
RFC 2774              An HTTP Extension Framework          February 2000

1. Introduction

   This proposal is designed to address the tension between private
   agreement and public specification; and to accommodate dynamic
   extension of HTTP clients and servers by software components. The
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