Internet DRAFT - draft-ietf-cbor-cddl-more-control
draft-ietf-cbor-cddl-more-control
Network Working Group C. Bormann
Internet-Draft Universität Bremen TZI
Intended status: Standards Track 26 February 2024
Expires: 29 August 2024
More Control Operators for CDDL
draft-ietf-cbor-cddl-more-control-03
Abstract
The Concise Data Definition Language (CDDL), standardized in RFC
8610, provides "control operators" as its main language extension
point. RFCs have added to this extension point both in an
application-specific and a more general way.
The present document defines a number of additional generally
applicable control operators for text conversion (Bytes, Integers,
JSON, Printf-style formatting), operations on text, and deterministic
encoding.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://cbor-
wg.github.io/cddl-more-control/. Status information for this
document may be found at https://datatracker.ietf.org/doc/draft-ietf-
cbor-cddl-more-control/.
Discussion of this document takes place on the Concise Binary Object
Representation (CBOR) Maintenance and Extensions Working Group
mailing list (mailto:cbor@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/cbor/. Subscribe at
https://www.ietf.org/mailman/listinfo/cbor/.
Source for this draft and an issue tracker can be found at
https://github.com/cbor-wg/cddl-more-control.
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/.
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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 29 August 2024.
Copyright Notice
Copyright (c) 2024 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 carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Text Conversion . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Byte Strings: Base16 (Hex), Base32, Base45, Base64 . . . 4
2.2. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. Printf-style Formatting . . . . . . . . . . . . . . . . . 6
2.4. JSON Values . . . . . . . . . . . . . . . . . . . . . . . 7
3. Text Processing . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Join . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Deterministic Encoding . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Implementation Status . . . . . . . . . . . . . . . . . . . . 10
7. Security considerations . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . 12
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
The Concise Data Definition Language (CDDL), standardized in
[RFC8610], provides "control operators" as its main language
extension point (Section 3.8 of [RFC8610]). RFCs have added to this
extension point both in an application-specific [RFC9090] and a more
general [RFC9165] way.
The present document defines a number of additional generally
applicable control operators:
+===============+=======================================+
| Name | Purpose |
+===============+=======================================+
| .b64u, .b64c | Base64 representation of byte strings |
+---------------+---------------------------------------+
| .b64u-sloppy, | (sloppy-tolerant variants of the |
| .b64c-sloppy | above) |
+---------------+---------------------------------------+
| .hex, .hexlc, | Base16 representation of byte strings |
| .hexuc | |
+---------------+---------------------------------------+
| .b32, .h32 | Base32 representation of byte strings |
+---------------+---------------------------------------+
| .b45 | Base45 representation of byte strings |
+---------------+---------------------------------------+
| .decimal | Text representation of integer |
| | numbers |
+---------------+---------------------------------------+
| .printf | Printf-formatted text representation |
| | of data items |
+---------------+---------------------------------------+
| .json | Text representation of JSON values |
+---------------+---------------------------------------+
| .join | Building text from array of |
| | components |
+---------------+---------------------------------------+
| .cbordet, | deterministically encoded CBOR data |
| .cborseqdet | items, CBOR sequences |
+---------------+---------------------------------------+
Table 1: New control operators in this document
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1.1. Terminology
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.
Regular expressions mentioned in the text are as defined in
[RFC9485].
This specification uses terminology from [RFC8610]. In particular,
with respect to control operators, "target" refers to the left-hand
side operand, and "controller" to the right-hand side operand.
"Tool" refers to tools along the lines of that described in
Appendix F of [RFC8610]. Note also that the data model underlying
CDDL provides for text strings as well as byte strings as two
separate types, which are then collectively referred to as "strings".
2. Text Conversion
2.1. Byte Strings: Base16 (Hex), Base32, Base45, Base64
A CDDL model often defines data that are byte strings in essence but
need to be transported in various encoded forms, such as base64 or
hex. This section defines a number of control operators to model
these conversions.
The control operators generally are of a form that could be used like
this:
signature-for-json = text .b64u signature
signature = bytes .cbor COSE_Sign1
The specification of these control operators is complicated by the
large number of transformations in use. Inspired by Section 8 of RFC
8949 [STD94], we use representations defined in [RFC4648] with the
following names:
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+==============+=======================+========================+
| name | meaning | reference |
+==============+=======================+========================+
| .b64u | Base64URL, no padding | Section 5 of [RFC4648] |
+--------------+-----------------------+------------------------+
| .b64u-sloppy | Base64URL, no | Section 5 of [RFC4648] |
| | padding, sloppy | |
+--------------+-----------------------+------------------------+
| .b64c | Base64 classic, | Section 4 of [RFC4648] |
| | padding | |
+--------------+-----------------------+------------------------+
| .b64c-sloppy | Base64 classic, | Section 4 of [RFC4648] |
| | padding, sloppy | |
+--------------+-----------------------+------------------------+
| .b32 | Base32, no padding | Section 6 of [RFC4648] |
+--------------+-----------------------+------------------------+
| .h32 | Base32/hex alphabet, | Section 7 of [RFC4648] |
| | no padding | |
+--------------+-----------------------+------------------------+
| .hex | Base16 (hex), either | Section 8 of [RFC4648] |
| | case | |
+--------------+-----------------------+------------------------+
| .hexlc | Base16 (hex), lower | Section 8 of [RFC4648] |
| | case | |
+--------------+-----------------------+------------------------+
| .hexuc | Base16 (hex), upper | Section 8 of [RFC4648] |
| | case | |
+--------------+-----------------------+------------------------+
| .b45 | Base45 | [RFC9285] |
+--------------+-----------------------+------------------------+
Table 2: Control Operators for Text Conversion of byte strings
Note that this specification is somewhat opinionated here: It does
not provide base64url, base32 or base32hex encoding with padding, or
base64 classic without padding. Experience indicates that these
combinations only ever occur in error, so the usability of CDDL is
increased by not providing them in the first place. Also, adding "c"
makes sure that any decision for classic base64 is actively taken.
The additional designation "sloppy" indicates that the text string is
not validated for any additional bits being zero, in variance to what
is specified in the paragraph behind table 1 in Section 4 of
[RFC4648]. Note that the present specification is opinionated again
in not specifying a sloppy variant of base32 or base32/hex, as no
legacy use of sloppy base32(/hex) was known at the time of writing.
Base45 is known to be suboptimal for use in environments with limited
data transparency (such as URLs), but is included because of its
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close relationship to QR codes and its wide use in health informatics
(note that base45 is at least strongly specified not to allow sloppy
forms of encoding).
2.2. Numbers
+==========+=================+===========+
| name | meaning | reference |
+==========+=================+===========+
| .decimal | Decimal Integer | --- |
+----------+-----------------+-----------+
Table 3: Control Operator for Text
Conversion of Integers
The control operator .decimal allows the modeling of text strings
that carry numeric information in decimal form, such as in the
uint64/int64 formats of YANG-JSON [RFC7951].
yang-json-sid = text .decimal (0..9223372036854775807)
Again, the specification is opinionated by only providing integer
numbers without leading zeros, i.e., the decimal numbers match the
regular expression 0|-?[1-9][0-9]* (of course, further restricted by
the control type). See the next section for more flexibility, and
for octal, hexadecimal, or binary conversions.
2.3. Printf-style Formatting
+=========+===================================+===========+
| name | meaning | reference |
+=========+===================================+===========+
| .printf | Printf-formatting of data item(s) | --- |
+---------+-----------------------------------+-----------+
Table 4: Control Operator for Printf-formatting of data
item(s)
The control operator .printf allows the modeling of text strings that
carry various formatted information, as long as the format can be
represented in Printf-style formatting strings as they are used in
the C language (see Section 7.21.6.1 of [C]).
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The controller (right-hand side) of the .printf control is an array
of one Printf-style format string and zero or more data items that
fit the individual conversion specifications in the format string.
The construct matches a text string representing the textual output
of an equivalent C-language printf function call that is given the
format string and the data items following it in the array.
From the printf specification in the C language, length modifiers
(paragraph 7) are not used and MUST NOT be included in the format
string. The 's' conversion specifier (paragraph 8) is used to
interpolate a text string in UTF-8 form. The 'c' conversion
specifier (paragraph 8) represents a single Unicode scalar value as a
UTF-8 character. The 'p' and 'n' conversion specifiers (paragraph 8)
are not used and MUST NOT be included in the format string.
In the following example, my_alg_19 matches the text string "0x0013":
my_alg_19 = hexlabel<19>
hexlabel<K> = text .printf (["0x%04x", K])
The data items in the controller array do not need to be literals, as
for example in:
any_alg = hexlabel<1..20>
hexlabel<K> = text .printf (["0x%04x", K])
Here, any_alg matches the text strings "0x0013" or "0x0001" but not
"0x1234".
2.4. JSON Values
Some applications store complete JSON texts into text strings, the
JSON value for which can easily be defined in CDDL. This is
supported by a control operator similar to .cbor in Section 3.8.4 of
[RFC8610].
+=======+=========+===========+
| name | meaning | reference |
+=======+=========+===========+
| .json | JSON | [STD90] |
+-------+---------+-----------+
Table 5: Control Operator
for Text Conversion of JSON
values
embedded-claims = text .json claims
claims = {iss: text, exp: text}
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Note that a .jsonseq is not provided, as no use case is known yet.
There is no way to constrain the use of blank space in data items to
be validated; variants (e.g, not providing for any blank space) could
be defined.
3. Text Processing
3.1. Join
Often, text strings need to be constructed out of parts that can best
be modeled as an array.
+=======+==================================+===========+
| name | meaning | reference |
+=======+==================================+===========+
| .join | concatenate elements of an array | --- |
+-------+----------------------------------+-----------+
Table 6: Control Operator for Text Generation from
Arrays
In general, this control operator is hard to validate as it would
require full parser functionality. It is therefore recommended to
only use it in simple cases, and leave full parsing to ABNF (see
Section 3 of [RFC9165]) or similar.
legacy-ip-address = text .join [bytetext, ".", bytetext,
".", bytetext, ".", bytetext]
bytetext = text .decimal byte
byte = 0..255
4. Deterministic Encoding
[RFC8610] and [RFC8742] specify the control operators .cbor and
.cborseq to indicate that the value of a byte string should be an
encoded CBOR data item or a CBOR sequence.
This specification provides complementary control operators .cbordet
and .cborseqdet that indicate that these data items/sequences need to
be encoded in accordance to Sections 4.2.1 and 4.2.2 of RFC 8949
[STD94].
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+=============+=========================+===========+
| name | meaning | reference |
+=============+=========================+===========+
| .cbordet | deterministically | [RFC8610] |
| | encoded CBOR data item | |
+-------------+-------------------------+-----------+
| .cborseqdet | CBOR sequence made from | [RFC8742] |
| | deterministically | |
| | encoded CBOR data items | |
+-------------+-------------------------+-----------+
Table 7: Control Operator for Deterministically
Encoded Data Items and Sequences
Note that considerations of deterministic representation at the
application level can often be expressed in the CDDL definition of
the right-hand side and then do not need additional control
operators.
5. IANA Considerations
// RFC Editor: please replace RFC-XXXX with the RFC number of this
// RFC and remove this note.
This document requests IANA to register the contents of Table 8 into
the registry "CDDL Control Operators" of [IANA.cddl]:
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+==============+============+
| Name | Reference |
+==============+============+
| .b64u | [RFC-XXXX] |
+--------------+------------+
| .b64u-sloppy | [RFC-XXXX] |
+--------------+------------+
| .b64c | [RFC-XXXX] |
+--------------+------------+
| .b64c-sloppy | [RFC-XXXX] |
+--------------+------------+
| .b45 | [RFC-XXXX] |
+--------------+------------+
| .b32 | [RFC-XXXX] |
+--------------+------------+
| .h32 | [RFC-XXXX] |
+--------------+------------+
| .hex | [RFC-XXXX] |
+--------------+------------+
| .hexlc | [RFC-XXXX] |
+--------------+------------+
| .hexuc | [RFC-XXXX] |
+--------------+------------+
| .decimal | [RFC-XXXX] |
+--------------+------------+
| .printf | [RFC-XXXX] |
+--------------+------------+
| .json | [RFC-XXXX] |
+--------------+------------+
| .join | [RFC-XXXX] |
+--------------+------------+
| .cbordet | [RFC-XXXX] |
+--------------+------------+
| .cborseqdet | [RFC-XXXX] |
+--------------+------------+
Table 8: New control
operators to be
registered
6. Implementation Status
This section is to be removed before publishing as an RFC.
In the CDDL tool described in Appendix F of [RFC8610], the control
operators defined in the present revision of this specification are
implemented as of version 0.10.4.
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7. Security considerations
The security considerations of [RFC8610] apply.
8. References
8.1. Normative References
[C] International Organization for Standardization,
"Information technology — Programming languages — C",
Fourth Edition, ISO/IEC 9899:2018, June 2018,
<https://www.iso.org/standard/74528.html>. Technically
equivalent specification text is available at
https://web.archive.org/web/20181230041359if_/
http://www.open- std.org/jtc1/sc22/wg14/www/abq/
c17_updated_proposed_fdis.pdf
(https://web.archive.org/web/20181230041359if_/
http://www.open- std.org/jtc1/sc22/wg14/www/abq/
c17_updated_proposed_fdis.pdf)
[IANA.cddl]
IANA, "Concise Data Definition Language (CDDL)",
<https://www.iana.org/assignments/cddl>.
[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/rfc/rfc2119>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/rfc/rfc4648>.
[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/rfc/rfc8174>.
[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/rfc/rfc8610>.
[RFC8742] Bormann, C., "Concise Binary Object Representation (CBOR)
Sequences", RFC 8742, DOI 10.17487/RFC8742, February 2020,
<https://www.rfc-editor.org/rfc/rfc8742>.
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[RFC9165] Bormann, C., "Additional Control Operators for the Concise
Data Definition Language (CDDL)", RFC 9165,
DOI 10.17487/RFC9165, December 2021,
<https://www.rfc-editor.org/rfc/rfc9165>.
[RFC9285] Fältström, P., Ljunggren, F., and D.W. van Gulik, "The
Base45 Data Encoding", RFC 9285, DOI 10.17487/RFC9285,
August 2022, <https://www.rfc-editor.org/rfc/rfc9285>.
[RFC9485] Bormann, C. and T. Bray, "I-Regexp: An Interoperable
Regular Expression Format", RFC 9485,
DOI 10.17487/RFC9485, October 2023,
<https://www.rfc-editor.org/rfc/rfc9485>.
[STD90] Internet Standard 90,
<https://www.rfc-editor.org/info/std90>.
At the time of writing, this STD comprises the following:
Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[STD94] Internet Standard 94,
<https://www.rfc-editor.org/info/std94>.
At the time of writing, this STD comprises the following:
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>.
8.2. Informative References
[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG",
RFC 7951, DOI 10.17487/RFC7951, August 2016,
<https://www.rfc-editor.org/rfc/rfc7951>.
[RFC9090] Bormann, C., "Concise Binary Object Representation (CBOR)
Tags for Object Identifiers", RFC 9090,
DOI 10.17487/RFC9090, July 2021,
<https://www.rfc-editor.org/rfc/rfc9090>.
Acknowledgements
Henk Birkholz suggested the need for many of the control operators
defined here.
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Author's Address
Carsten Bormann
Universität Bremen TZI
Postfach 330440
D-28359 Bremen
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
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