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Versions: 00 draft-ietf-core-multipart-ct

CoRE Working Group                                            C. Bormann
Internet-Draft                                   Universitaet Bremen TZI
Intended status: Informational                            March 18, 2018
Expires: September 19, 2018


                    The application/maybe media type
                      draft-bormann-core-maybe-00

Abstract

   Many media types may be used in situations where it may beneficial to
   indicate that the object represented in this media type is not yet
   (or no longer) present.

   The Observe option introduced in Observing Resources in the
   Constrained Application Protocol (CoAP) (RFC7641) requires sequences
   of responses (notifications) to carry the same Content-Format.

   The application/maybe media type provides a way to use a single media
   type (and thus Content-Format) to express presence or absence of
   information in a specific media type.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 19, 2018.

Copyright Notice

   Copyright (c) 2018 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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  The application/maybe media type  . . . . . . . . . . . . . .   2
   3.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Implementation hints  . . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   (See Abstract.)

1.1.  Terminology

   This memo uses terms from [RFC7252], [RFC7641] and [RFC7049].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.  These words may also appear in this
   document in lower case as plain English words, absent their normative
   meanings.

   The term "byte", abbreviated by "B", is used in its now customary
   sense as a synonym for "octet".

2.  The application/maybe media type

   An application/maybe object either indicates the absence of the
   underlying media type or its presence together with an object of that
   media type.





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   This is represented by a CBOR [RFC7049] object structured as follows
   (illustrated in CDDL [I-D.ietf-cbor-cddl]):

   maybe = [
     ? (
       content-format: uint,
       content: bstr
     )
   ]

3.  Discussion

   The position for indicating a content-format could also provide an
   alternative for indicating a media type represented as a string.

   maybe1 = [
     ? (
       (content-format: uint // media-type: tstr),
       content: bstr
     )
   ]

   This would make the application/maybe media type easier to use with
   media types that do not have a content-format registered yet.

4.  Implementation hints

   This section describes the serialization for readers that may be new
   to CBOR.  It does not contain any new information.

   An absent object is represented by an empty CBOR array, which is
   serialized as a single byte with the value 0x80.

   A present object is represented by a two-element CBOR array, which is
   serialized as 0x82 followed by the two elements.  The first element
   is an unsigned integer for the Content-Format value, which is
   represented as described in Table 1.  The second element is the
   object as a byte string, which is represented as a length as
   described in Table 2 followed by the bytes of the object.












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                      +----------------+------------+
                      | Serialization  | Value      |
                      +----------------+------------+
                      | 0x00..0x17     | 0..23      |
                      |                |            |
                      | 0x18 0xnn      | 24..255    |
                      |                |            |
                      | 0x19 0xnn 0xnn | 256..66535 |
                      +----------------+------------+

                 Table 1: Serialization of content-format

            +-----------------------------+-------------------+
            | Serialization               | Length            |
            +-----------------------------+-------------------+
            | 0x40..0x57                  | 0..23             |
            |                             |                   |
            | 0x58 0xnn                   | 24..255           |
            |                             |                   |
            | 0x59 0xnn 0xnn              | 256..66535        |
            |                             |                   |
            | 0x5a 0xnn 0xnn 0xnn 0xnn    | 66536..4294967295 |
            |                             |                   |
            | 0x5b 0xnn .. 0xnn (8 bytes) | 4294967296..      |
            +-----------------------------+-------------------+

                  Table 2: Serialization of object length

   For example, a present text/plain object (content-format 0) of value
   "Hello World" (11 characters) would be serialized as

      0x82 0x00 0x4b H e l l o 0x20 w o r l d

   In effect, the serialization is done by prefixing the object with
   information about its content-format.

5.  IANA Considerations

   TBD (add in the obvious template information).

6.  Security Considerations

   TBD








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7.  Acknowledgements

   The potential need for an application/maybe media type was suggested
   by Klaus Hartke.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

8.2.  Informative References

   [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.

   [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>.

   [RFC7641]  Hartke, K., "Observing Resources in the Constrained
              Application Protocol (CoAP)", RFC 7641,
              DOI 10.17487/RFC7641, September 2015,
              <https://www.rfc-editor.org/info/rfc7641>.

Author's Address










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

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











































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