Internet DRAFT - draft-richter-cbor-error-tag
draft-richter-cbor-error-tag
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
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This Internet-Draft will expire on August 3, 2019.
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Copyright Notice
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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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