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Versions: 00 01 02 03 04 05 draft-ietf-core-multipart-ct

CoRE                                                          C. Bormann
Internet-Draft                                   Universitaet Bremen TZI
Intended status: Standards Track                           June 05, 2018
Expires: December 7, 2018


                   Multipart Content-Format for CoAP
                   draft-fossati-core-multipart-ct-04

Abstract

   This memo defines multipart/core, an application-independent media-
   type that can be used to combine (even recursively) several different
   media types into a single CoAP message-body with minimal framing
   overhead, along with a CoAP Content-Format identifier.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 7, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Multipart Content-Format Encoding . . . . . . . . . . . . . .   2
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Registration of media type multipart/core . . . . . . . .   3
     3.2.  Registration of a Content-Format identifier for
           multipart/core  . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   This memo defines multipart/core, an application-independent media-
   type that can be used to combine several different media types into a
   single CoAP [RFC7252] message-body with minimal framing overhead,
   along with a CoAP Content-Format identifier.

   This simple and efficient binary framing mechanism can be employed to
   create application specific request and response bodies which build
   on multiple already existing media types.

   Applications using the multipart/core Content-Format define the
   internal structure of the multipart/core representation.  Optionally,
   they might also register a new media type and an associated Content-
   Format identifier -- typically one in the range 10000-64999.

   One way to structure the sub-types specific to a multipart/core
   container is to always include them at the same fixed position.  This
   specification allows to indicate that an optional part is not present
   by substituting a null value for the representation of the part.

2.  Multipart Content-Format Encoding

   A representation of media-type multipart/core contains a collection
   of zero or more representations, each along with their respective
   content format.

   The collection is encoded as a CBOR [RFC7049] array with an even
   number of elements.  The second, fourth, sixth, etc. element is a
   byte string containing a representation, or the value "null" if an
   optional part is indicated as not given.  The first, third, fifth,
   etc. element is an unsigned integer specifying the content format ID
   of the representation following it.



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   For example, a collection containing two representations, one with
   content format ID 42 and one with content format ID 0, looks like
   this in CBOR diagnostic notation:

      [42, h'0123456789abcdef', 0, h'3031323334']

   For illustration, the structure of a multipart/core representation
   can be described by the CDDL [I-D.ietf-cbor-cddl] specification in
   Figure 1:

   multipart-core = [* multipart-part]
   multipart-part = (type: uint .size 2, part: bytes / null)

                     Figure 1: CDDL for multipart/core

3.  IANA Considerations

3.1.  Registration of media type multipart/core

   IANA is requested to register the following media type [RFC6838]:

   Type name:  multipart

   Subtype name:  core

   Required parameters:  N/A

   Optional parameters:  N/A

   Encoding considerations:  binary

   Security considerations:  See the Security Considerations Section of
      RFCthis

   Interoperability considerations:  N/A

   Published specification:  RFCthis

   Applications that use this media type:  Applications that need to
      combine representations of potentially several media types into
      one, e.g.  EST-CoAP [I-D.ietf-ace-coap-est]

   Fragment identifier considerations:  N/A

   Additional information:

      Deprecated alias names for this type:  N/A




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      Magic number(s):  N/A

      File extension(s):  N/A

      Macintosh file type code(s):  N/A

   Person & email address to contact for further information:
      iesg&ietf.org

   Intended usage:  COMMON

   Restrictions on usage:  N/A

   Author:  CoRE WG

   Change controller:  IESG

   Provisional registration? (standards tree only):  no

3.2.  Registration of a Content-Format identifier for multipart/core

   IANA is requested to register the following Content-Format to the
   "CoAP Content-Formats" subregistry, within the "Constrained RESTful
   Environments (CoRE) Parameters" registry, from the IETF Review space
   (specifically, 256..999):

              +----------------+----------+-----+-----------+
              | Media Type     | Encoding | ID  | Reference |
              +----------------+----------+-----+-----------+
              | multipart/core | --       | TBD | RFCthis   |
              +----------------+----------+-----+-----------+

4.  Security Considerations

   The security considerations of [RFC7049] apply.  In particular,
   resource exhaustion attacks may emply large values for the byte
   string size fields, or deeply nested structures of recursively
   embedded multipart/core representations.

5.  References

5.1.  Normative References

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <https://www.rfc-editor.org/info/rfc7049>.





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   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/info/rfc7252>.

5.2.  Informative References

   [I-D.ietf-ace-coap-est]
              Stok, P., Kampanakis, P., Kumar, S., Richardson, M.,
              Furuhed, M., and S. Raza, "EST over secure CoAP (EST-
              coaps)", draft-ietf-ace-coap-est-00 (work in progress),
              February 2018.

   [I-D.ietf-cbor-cddl]
              Birkholz, H., Vigano, C., and C. Bormann, "Concise data
              definition language (CDDL): a notational convention to
              express CBOR data structures", draft-ietf-cbor-cddl-02
              (work in progress), February 2018.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <https://www.rfc-editor.org/info/rfc6838>.

Acknowledgements

   Most of the text in this draft is from earlier contributions by
   Thomas Fossati and Klaus Hartke.  The re-mix in this document is
   based on the requirements in [I-D.ietf-ace-coap-est].

Author's Address

   Carsten Bormann
   Universitaet Bremen TZI
   Postfach 330440
   Bremen  D-28359
   Germany

   Phone: +49-421-218-63921
   Email: cabo@tzi.org











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