Multipart Content-Format for the Constrained Application Protocol (CoAP)
RFC 8710

Document Type RFC - Proposed Standard (February 2020; No errata)
Authors Thomas Fossati  , Klaus Hartke  , Carsten Bormann 
Last updated 2020-09-10
Replaces draft-fossati-core-multipart-ct, draft-bormann-core-maybe
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Internet Engineering Task Force (IETF)                        T. Fossati
Request for Comments: 8710                                           ARM
Category: Standards Track                                      K. Hartke
ISSN: 2070-1721                                                 Ericsson
                                                              C. Bormann
                                                  Universit├Ąt Bremen TZI
                                                           February 2020

Multipart Content-Format for the Constrained Application Protocol (CoAP)

Abstract

   This memo defines application/multipart-core, an application-
   independent media type that can be used to combine representations of
   zero or more different media types (each with a Constrained
   Application Protocol (CoAP) Content-Format identifier) into a single
   representation, with minimal framing overhead.

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
   https://www.rfc-editor.org/info/rfc8710.

Copyright Notice

   Copyright (c) 2020 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
   (https://trustee.ietf.org/license-info) 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.  Requirements Language
   2.  Multipart Content-Format Encoding
   3.  Usage Example: Observing Resources
   4.  Implementation Hints
   5.  IANA Considerations
     5.1.  Registration of Media Type application/multipart-core
     5.2.  Registration of a Content-Format Identifier for
           application/multipart-core
   6.  Security Considerations
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   This memo defines application/multipart-core, an application-
   independent media type that can be used to combine representations of
   zero or more different media types (each with a CoAP Content-Format
   identifier [RFC7252]) into a single representation, with minimal
   framing overhead.

   This simple and efficient binary framing mechanism can be employed to
   create application-specific message bodies that build on multiple
   already existing media types.

   As the name of the media type suggests, application/multipart-core
   was inspired by the multipart media types initially defined in the
   original set of MIME specifications [RFC2046] and later.  However,
   while those needed to focus on the syntactic aspects of integrating
   multiple representations into one email, transfer protocols providing
   full data transparency such as CoAP as well as readily available
   encoding formats such as the Concise Binary Object Representation
   (CBOR) [RFC7049] shift the focus towards the intended use of the
   combined representations.  In this respect, the basic intent of the
   application/multipart-core media type is like that of multipart/mixed
   (Section 5.1.3 of [RFC2046]); however, the semantics are relaxed to
   allow for both ordered and unordered collections of media types.

      Historical Note: Experience with multipart/mixed in email has
      shown that recipients that care about order of included body parts
      will process them in the order they are listed inside multipart/
      mixed, and recipients that don't care about the order will ignore
      it anyway.  The media type multipart/parallel that was intended
      for unordered collections didn't deploy.

   The detailed semantics of the representations are refined by the
   context established by the application in the accompanying request
   parameters, e.g., the resource URI and any further options (header
   fields), but three usage scenarios are envisioned:

   In one case, the individual representations in an application/
   multipart-core message body occur in a sequence, which may be
   employed by an application where such a sequence is natural, e.g.,
   for a number of audio snippets in various formats to be played out in
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