PATCH and FETCH Methods for the Constrained Application Protocol (CoAP)
RFC 8132

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Internet Engineering Task Force (IETF)                   P. van der Stok
Request for Comments: 8132                                    Consultant
Category: Standards Track                                     C. Bormann
ISSN: 2070-1721                                  Universitaet Bremen TZI
                                                               A. Sehgal
                                                            NAVOMI, Inc.
                                                              April 2017

PATCH and FETCH Methods for the Constrained Application Protocol (CoAP)

Abstract

   The methods defined in RFC 7252 for the Constrained Application
   Protocol (CoAP) only allow access to a complete resource, not to
   parts of a resource.  In case of resources with larger or complex
   data, or in situations where resource continuity is required,
   replacing or requesting the whole resource is undesirable.  Several
   applications using CoAP need to access parts of the resources.

   This specification defines the new CoAP methods, FETCH, PATCH, and
   iPATCH, which are used to access and update parts of a resource.

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
   http://www.rfc-editor.org/info/rfc8132.

van der Stok, et al.         Standards Track                    [Page 1]
RFC 8132                    CoAP FETCH PATCH                  April 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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   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  FETCH . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  PATCH and iPATCH  . . . . . . . . . . . . . . . . . . . .   4
     1.3.  Requirements Language . . . . . . . . . . . . . . . . . .   5
     1.4.  Terminology and Acronyms  . . . . . . . . . . . . . . . .   5
   2.  FETCH Method  . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Response Codes  . . . . . . . . . . . . . . . . . . . . .   6
     2.2.  Error Handling  . . . . . . . . . . . . . . . . . . . . .   6
     2.3.  Option Numbers  . . . . . . . . . . . . . . . . . . . . .   7
       2.3.1.  The Content-Format Option . . . . . . . . . . . . . .   7
       2.3.2.  The ETag Option . . . . . . . . . . . . . . . . . . .   8
     2.4.  Working with Observe  . . . . . . . . . . . . . . . . . .   8
     2.5.  Working with Block  . . . . . . . . . . . . . . . . . . .   8
     2.6.  Building FETCH Requests . . . . . . . . . . . . . . . . .   8
     2.7.  A Simple Example for FETCH  . . . . . . . . . . . . . . .   8
   3.  PATCH and iPATCH Methods  . . . . . . . . . . . . . . . . . .   9
     3.1.  Simple Examples for PATCH and iPATCH  . . . . . . . . . .  12
     3.2.  Response Codes  . . . . . . . . . . . . . . . . . . . . .  14
     3.3.  Option Numbers  . . . . . . . . . . . . . . . . . . . . .  14
     3.4.  Error Handling  . . . . . . . . . . . . . . . . . . . . .  15
   4.  The New Set of CoAP Methods . . . . . . . . . . . . . . . . .  16
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  19
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

van der Stok, et al.         Standards Track                    [Page 2]
RFC 8132                    CoAP FETCH PATCH                  April 2017

1.  Introduction

   Similar to HTTP, the GET method defined in [RFC7252] for the
   Constrained Application Protocol (CoAP) only allows the specification
   of a URI and request parameters in CoAP options, not the transfer of