Internet DRAFT - draft-rundgren-cotx
draft-rundgren-cotx
Network Working Group A. Rundgren, Ed.
Internet-Draft Independent
Intended status: Informational 3 September 2023
Expires: 6 March 2024
CBOR Object Type Extension (COTX)
draft-rundgren-cotx-05
Abstract
This document describes a CBOR tag for augmenting CBOR data items
with type identifiers in the form of arbitrary CBOR text strings.
This design enables type identifiers to optionally be expressed as
URLs, potentially pointing to Web pages holding related descriptions
in human readable form, as well as being compatible with established
methods for adding type information to JSON and XML data.
Status of This Memo
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Copyright Notice
Copyright (c) 2023 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Specification . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Sample . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Normative References . . . . . . . . . . . . . . . . . . 5
5.2. Informative References . . . . . . . . . . . . . . . . . 5
Appendix A. URI and URL Identifiers . . . . . . . . . . . . . . 6
A.1. Registering a Dedicated Domain . . . . . . . . . . . . . 6
A.2. Using a Sub-domain . . . . . . . . . . . . . . . . . . . 6
A.3. The 'tag' URI Scheme . . . . . . . . . . . . . . . . . . 6
Appendix B. URN Identifiers . . . . . . . . . . . . . . . . . . 6
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 7
Document History . . . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
This specification introduces a method for augmenting data expressed
in the CBOR [RFC8949] notation, with a type identifier mechanism
based on CBOR text strings.
The primary purposes of the text based type identifier tag described
in this document are:
* Enabling developers defining application specific type identifiers
without necessarily having to go through an external registration
process.
* By supporting URLs [URL] as type identifiers, related human
readable information may (through dereferencing), be provided for
usage with Web browsers. Since URLs are compatible with firmly
established methods for adding type information to JSON and XML
data, this design may simplify a switch to CBOR. See also
Appendix A.
This specification is also intended to provide a path for ISO using
CBOR as a possible alternative to XML by supporting their current URN
[RFC8141] based type identifier naming scheme. See also Appendix B.
By applying the typing scheme to top level CBOR objects, additional
functionality is enabled including:
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* Support for embedding CBOR objects in other CBOR and non-CBOR
constructs, as well as storage in databases, without being forced
adding information about the object.
* Remove the need for application specific media types. In many
cases "application/cbor" would suffice.
1.1. Terminology
In this document the term CBOR "object" is used interchangeably with
the CBOR [RFC8949] "data item".
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.
2. Specification
This specification builds on the CBOR [RFC8949] tag feature (major
type 6), by defining a fixed tag with the preliminary decimal value
of 1010. See also Section 3.
This tag MUST in turn enclose a CBOR array (major type 4) with two
elements, where the first element MUST contain a type identifier in
textual format indicating the definition of a CBOR object, while the
second element MUST hold an instance of the associated object itself.
The type identifier MUST be a valid CBOR text string (major type 3),
while the only constraint on the targeted object is that it MUST be a
valid CBOR object.
The syntax expressed in CBOR diagnostic notation (section 8 of
[RFC8949]) would read as:
1010([_Object Type Identifier_, _Object Instance Data_])
Note that real-world usages will typically impose constraints like
requiring type identifiers to be expressed as HTTPS URLs etc.
2.1. Sample
Consider the following sample:
1010(["https://example.com/myobject", {
1: "data",
2: "more data"
}])
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Converting the sample above to CBOR expressed in hexadecimal notation
(here shown with embedded comments as well), should result in the
following output:
D9 03F2 # tag(1010)
82 # array(2)
78 1C # text(28)
68747470733A2F2F6578616D706C652E636F6D2F6D796F626A656374
# "https://example.com/myobject"
A2 # map(2)
01 # unsigned(1)
64 # text(4)
64617461 # "data"
02 # unsigned(2)
69 # text(9)
6D6F72652064617461 # "more data"
In a typical implementation "https://example.com/myobject" would also
serve as a hyper-link to human readable information about the
identifier, accessed through a Web browser.
3. IANA Considerations
In the registry [IANA.cbor-tags], IANA is requested to allocate the
tag defined in Table 1.
+======+===================+=============+========================+
| Tag | Data Item | Semantics | Reference |
+======+===================+=============+========================+
| 1010 | array: [id: text | Object type | draft-rundgren-cotx-04 |
| | string, obj: any] | identifier | |
+------+-------------------+-------------+------------------------+
Table 1: Values for Tag Numbers
This request has been granted.
4. Security Considerations
This specification inherits all the security considerations of CBOR
[RFC8949].
URL-based type identifiers MUST NOT be used for automatically
downloading CBOR schema data like CDDL [RFC8610] to CBOR processors,
since this introduces potential vulnerabilities.
The availability of type information does in no way limit the need
for input data validation.
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For signed CBOR objects, it is RECOMMENDED to include the object type
identifier extension in the signature calculation as well. The same
considerations apply to encryption using AEAD algorithms.
5. References
5.1. Normative References
[IANA.cbor-tags]
IANA, "Concise Binary Object Representation (CBOR) Tags",
19 September 2013,
<https://www.iana.org/assignments/cbor-tags>.
[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>.
[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>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
5.2. Informative References
[RFC4151] Kindberg, T. and S. Hawke, "The 'tag' URI Scheme",
RFC 4151, DOI 10.17487/RFC4151, October 2005,
<https://www.rfc-editor.org/info/rfc4151>.
[RFC5141] Goodwin, J. and H. Apel, "A Uniform Resource Name (URN)
Namespace for the International Organization for
Standardization (ISO)", RFC 5141, DOI 10.17487/RFC5141,
March 2008, <https://www.rfc-editor.org/info/rfc5141>.
[RFC8141] Saint-Andre, P. and J. Klensin, "Uniform Resource Names
(URNs)", RFC 8141, DOI 10.17487/RFC8141, April 2017,
<https://www.rfc-editor.org/info/rfc8141>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
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[URL] What WG, "Living Standard — Last Updated 3 May 2022",
<https://url.spec.whatwg.org/>.
[XSD] W3C, "XML Schema Definition Language (XSD) 1.1 Part 1:
Structures", <http://www.w3.org/TR/xmlschema11-1/>.
Appendix A. URI and URL Identifiers
The primary reason for using URI or URL [URL] based type identifiers
is for maintaining a single name-space for the entire specification
of a system. Note that the referenced URL specification does not
distinguish between URIs and URLs.
This non-normative section describes different methods for dealing
with type identifiers expressed as URIs or URLs.
A.1. Registering a Dedicated Domain
A core issue with identifiers depending on domain (DNS) names is that
domain names may not necessarily remain valid during the anticipated
life-time of an identifier. The owner of a domain name may due to
organizational changes, neglect, lack of interest, or even death,
lose control over its use, effectively leaving associated identifiers
orphaned.
A.2. Using a Sub-domain
An alternative is using a dedicated sub-domain belonging to an entity
that is likely to survive for the foreseeable future. With the
advent of public repositories like GitHub, this appears to be a
simpler, cheaper, and more robust solution than maintaining dedicated
domain names.
A.3. The 'tag' URI Scheme
For applications where strict control over the name-space is hard to
achieve, the 'tag' URI scheme [RFC4151] may be used.
Appendix B. URN Identifiers
ISO currently use URN [RFC8141] [RFC5141] based type identifiers like
"urn:iso:std:iso:20022:tech:xsd:pain.001.001.10" for data definitions
using XML schema [XSD]. This method could be applied to CBOR and
CDDL [RFC8610] as well.
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Acknowledgements
People who have contributed with valuable feedback to this
specification include Christian Amsüss, Carsten Bormann, and Joe
Hildebrand.
Document History
[[ This section to be removed by the RFC Editor before publication as
an RFC ]]
Version 00:
* Initial publication.
Version 01:
* IANA reference update.
Version 02:
* Made type identifier a CBOR text string.
* Wordsmithing.
Version 03:
* Cleaner abstract and intro.
Version 04:
* Type identifier throughout the spec.
Version 05:
* IANA have granted the regitration.
Author's Address
Anders Rundgren (editor)
Independent
Montpellier
France
Email: anders.rundgren.net@gmail.com
URI: https://www.linkedin.com/in/andersrundgren/
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