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Network Working Group                                         J. Richter
Internet-Draft                               pdv Financial Software GmbH
Intended status: Informational                                C. Bormann
Expires: August 3, 2019                          Universitaet Bremen TZI
                                                        January 30, 2019


 Concise Binary Object Representation (CBOR) Tag for Error Indications
                    draft-richter-cbor-error-tag-01

Abstract

   The Concise Binary Object Representation (CBOR, RFC 7049) is a data
   format whose design goals include the possibility of extremely small
   code size, fairly small message size, and extensibility without the
   need for version negotiation.

   In CBOR, one point of extensibility is the definition of CBOR tags.
   While CBOR defines representations for null values and for an
   undefined value, there is no convention for expressing errors or
   exceptions in data structures, where the actual value desired could
   not be calculated due to an error.  The present specification defines
   a tag for such error indications, enabling the addition of varying
   levels of detail.

Note to Readers

   Please discuss this draft on the mailing list cbor@ietf.org -
   subscribe at https://www.ietf.org/mailman/listinfo/cbor to follow the
   discussions.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 August 3, 2019.




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Copyright Notice

   Copyright (c) 2019 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
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   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
   2.  Error Format  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  CDDL typenames  . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The Concise Binary Object Representation (CBOR, [RFC7049]) provides
   for the interchange of structured data without a requirement for a
   pre-agreed schema.  RFC 7049 defines a basic set of data types, as
   well as a tagging mechanism that enables extending the set of data
   types supported via an IANA registry.

   In CBOR, one point of extensibility is the definition of CBOR tags.
   While CBOR defines representations for null values and for an
   undefine value, there is no convention for expressing errors or
   exceptions in data structures.  The present specification defines a
   tag for such error indications, enabling varying levels of detail.










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2.  Error Format

   An error value is indicated by CBOR tag TBD101, which tags a data
   item that may contain additional information about the error value:

   o  If no further information is provided, the data item is the CBOR
      value null.

   o  If a diagnostic text string is provided, the data item is that
      text string.

   o  If more detailed information is provided, the data item is a map
      (CBOR major type 5), with text string or integer keys and values
      as defined by the application.

   This specification does not further define what keys and values
   should be used in a map that is used as the tagged item for this tag.
   However, to maximize interoperability, the following keys and values
   are suggested for use whenever they are appropriate for an
   application (the keys are text strings, suggested value types are
   indicated in the table with CDDL names):

   +---------+--------------------------------------------------+------+
   | key     | value                                            | type |
   +---------+--------------------------------------------------+------+
   | name    | a formal name for the kind of error amenable to  | text |
   |         | program processing, maybe a class name or a URI  |      |
   | code    | a number assigned for the kind of error, e.g. an | int  |
   |         | HTTP-style error code such as 404                |      |
   | message | human-readable description; what would be in the | text |
   |         | diagnostic text string if only that were         |      |
   |         | provided                                         |      |
   | file    | indicating location of error in program: file    | text |
   |         | name                                             |      |
   | line    | indicating location of error in program: line    | uint |
   |         | number                                           |      |
   | column  | indicating location of error in program: column  | uint |
   |         | number                                           |      |
   +---------+--------------------------------------------------+------+

   Note that these suggestions have been somewhat inspired by the
   JavaScript "Error" object (Section 19.5 of [ECMA262])), except that
   two-word forms of keys have been shortened to single words.  There is
   no intention that the details of the JavaScript "Error" object are
   normative for the present specification.  More generally, there is no
   intention to limit the use of the Tag defined here to those
   applications that would employ the JavaScript "Error" object.




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   (Discussion: changing lineNumber into line sounds like a good idea.
   Changing fileName into file is suboptimal, but reallu the problem is
   that neither says "source file".  I was thinking about using "source"
   in place of "file".)















































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3.  CDDL typenames

   For the use with the CBOR Data Definition Language, CDDL
   [I-D.ietf-cbor-cddl], the type names defined in Figure 1 are
   recommended:

   error = error-of<(null / text / {* (int/text) => any})>
   error-of<T> = #6.101(T)

                 Figure 1: Recommended type names for CDDL

4.  IANA Considerations

   In the registry [IANA.cbor-tags], IANA is requested to allocate the
   tag in Table 1 from the FCFS space, with the present document as the
   specification reference.

         +--------+-----------------+----------------------------+
         |    Tag | Data Item       | Semantics                  |
         +--------+-----------------+----------------------------+
         | TBD101 | null, text, map | [RFCthis] error indication |
         +--------+-----------------+----------------------------+

                         Table 1: Values for Tags

5.  Security Considerations

   The security considerations of RFC 7049 apply.

   Error/diagnostic information provided by a system can disclose
   internals of that to an attacker; care should be taken with the tag
   introduced here that its use does not facilitate attacks in this way.



















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6.  References

6.1.  Normative References

   [I-D.ietf-cbor-cddl]
              Birkholz, H., Vigano, C., and C. Bormann, "Concise data
              definition language (CDDL): a notational convention to
              express CBOR and JSON data structures", draft-ietf-cbor-
              cddl-06 (work in progress), November 2018.

   [IANA.cbor-tags]
              IANA, "Concise Binary Object Representation (CBOR) Tags",
              <http://www.iana.org/assignments/cbor-tags>.

   [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>.

6.2.  Informative References

   [ECMA262]  Ecma International, "ECMAScript 2018 Language
              Specification", ECMA Standard ECMA-262, 9th Edition, June
              2018, <https://www.ecma-
              international.org/publications/files/ECMA-ST/
              Ecma-262.pdf>.

Acknowledgements

Authors' Addresses

   Joerg Richter
   pdv Financial Software GmbH
   Dorotheenstr. 64
   Hamburg  D-22301
   Germany

   Email: joerg.richter@pdv-fs.de


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

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




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