Internet DRAFT - draft-ietf-jsonpath-iregexp
draft-ietf-jsonpath-iregexp
Network Working Group C. Bormann
Internet-Draft Universität Bremen TZI
Intended status: Standards Track T. Bray
Expires: 31 December 2023 Textuality
29 June 2023
I-Regexp: An Interoperable Regexp Format
draft-ietf-jsonpath-iregexp-08
Abstract
This document specifies I-Regexp, a flavor of regular expressions
that is limited in scope with the goal of interoperation across many
different regular-expression libraries.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-jsonpath-iregexp/.
Discussion of this document takes place on the JSONPath Working Group
mailing list (mailto:JSONPath@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/JSONPath/. Subscribe at
https://www.ietf.org/mailman/listinfo/JSONPath/.
Source for this draft and an issue tracker can be found at
https://github.com/ietf-wg-jsonpath/iregexp.
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 31 December 2023.
Bormann & Bray Expires 31 December 2023 [Page 1]
Internet-Draft I-Regexp June 2023
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
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
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Objectives . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. I-Regexp Syntax . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Checking Implementations . . . . . . . . . . . . . . . . 5
4. I-Regexp Semantics . . . . . . . . . . . . . . . . . . . . . 5
5. Mapping I-Regexp to Regexp Dialects . . . . . . . . . . . . . 5
5.1. Multi-Character Escapes . . . . . . . . . . . . . . . . . 6
5.2. XSD Regexps . . . . . . . . . . . . . . . . . . . . . . . 6
5.3. ECMAScript Regexps . . . . . . . . . . . . . . . . . . . 6
5.4. PCRE, RE2, Ruby Regexps . . . . . . . . . . . . . . . . . 7
6. Motivation and Background . . . . . . . . . . . . . . . . . . 7
6.1. Implementing I-Regexp . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Security considerations . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. Regexps and Similar Constructs in Recent Published
RFCs . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
This specification describes an interoperable regular expression
("regexp") flavor, I-Regexp.
I-Regexp does not provide advanced regular expression features such
as capture groups, lookahead, or backreferences. It supports only a
Boolean matching capability, i.e., testing whether a given regular
expression matches a given piece of text.
Bormann & Bray Expires 31 December 2023 [Page 2]
Internet-Draft I-Regexp June 2023
I-Regexp supports the entire repertoire of Unicode characters
(Unicode scalar values); both the I-Regexp strings themselves and the
strings they are matched against are sequences of Unicode scalar
values (often represented in UTF-8 encoding form [STD63] for
interchange).
I-Regexp is a subset of XSD regular expressions [XSD-2].
This document includes guidance for converting I-Regexps for use with
several well-known regular expression idioms.
The development of I-Regexp was motivated by the work of the JSONPath
Working Group. The Working Group wanted to include in its
specification [I-D.ietf-jsonpath-base] support for the use of regular
expressions in JSONPath filters, but was unable to find a useful
specification for regular expressions which would be interoperable
across the popular libraries.
1.1. Terminology
This document uses the abbreviation "regexp" for what are usually
called regular expressions in programming. "I-Regexp" is used as a
noun meaning a character string (sequence of Unicode scalar values)
that conforms to the requirements in this specification; the plural
is "I-Regexps".
This specification uses Unicode terminology. A good entry point into
that is provided by [UNICODE-GLOSSARY].
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.
The grammatical rules in this document are to be interpreted as ABNF,
as described in [RFC5234] and [RFC7405], where the "characters" of
Section 2.3 of [RFC5234] are Unicode scalar values.
2. Objectives
I-Regexps should handle the vast majority of practical cases where a
matching regexp is needed in a data model specification or a query
language expression.
Bormann & Bray Expires 31 December 2023 [Page 3]
Internet-Draft I-Regexp June 2023
The editors of this document conducted a survey of the regexp syntax
used in published RFCs. All examples found there should be covered
by I-Regexps, both syntactically and with their intended semantics.
The exception is the use of multi-character escapes, for which
workaround guidance is provided in Section 5.
3. I-Regexp Syntax
An I-Regexp MUST conform to the ABNF specification in Figure 1.
i-regexp = branch *( "|" branch )
branch = *piece
piece = atom [ quantifier ]
quantifier = ( "*" / "+" / "?" ) / range-quantifier
range-quantifier = "{" QuantExact [ "," [ QuantExact ] ] "}"
QuantExact = 1*%x30-39 ; '0'-'9'
atom = NormalChar / charClass / ( "(" i-regexp ")" )
NormalChar = ( %x00-27 / "," / "-" / %x2F-3E ; '/'-'>'
/ %x40-5A ; '@'-'Z'
/ %x5E-7A ; '^'-'z'
/ %x7E-10FFFF )
charClass = "." / SingleCharEsc / charClassEsc / charClassExpr
SingleCharEsc = "\" ( %x28-2B ; '('-'+'
/ "-" / "." / "?" / %x5B-5E ; '['-'^'
/ %s"n" / %s"r" / %s"t" / %x7B-7D ; '{'-'}'
)
charClassEsc = catEsc / complEsc
charClassExpr = "[" [ "^" ] ( "-" / CCE1 ) *CCE1 [ "-" ] "]"
CCE1 = ( CCchar [ "-" CCchar ] ) / charClassEsc
CCchar = ( %x00-2C / %x2E-5A ; '.'-'Z'
/ %x5E-10FFFF ) / SingleCharEsc
catEsc = %s"\p{" charProp "}"
complEsc = %s"\P{" charProp "}"
charProp = IsCategory
IsCategory = Letters / Marks / Numbers / Punctuation / Separators /
Symbols / Others
Letters = %s"L" [ ( %s"l" / %s"m" / %s"o" / %s"t" / %s"u" ) ]
Marks = %s"M" [ ( %s"c" / %s"e" / %s"n" ) ]
Numbers = %s"N" [ ( %s"d" / %s"l" / %s"o" ) ]
Punctuation = %s"P" [ ( %x63-66 ; 'c'-'f'
/ %s"i" / %s"o" / %s"s" ) ]
Separators = %s"Z" [ ( %s"l" / %s"p" / %s"s" ) ]
Symbols = %s"S" [ ( %s"c" / %s"k" / %s"m" / %s"o" ) ]
Others = %s"C" [ ( %s"c" / %s"f" / %s"n" / %s"o" ) ]
Figure 1: I-Regexp Syntax in ABNF
Bormann & Bray Expires 31 December 2023 [Page 4]
Internet-Draft I-Regexp June 2023
As an additional restriction, charClassExpr is not allowed to match
[^], which according to this grammar would parse as a positive
character class containing the single character ^.
This is essentially XSD regexp without character class subtraction,
without multi-character escapes such as \s, \S, and \w, and without
Unicode blocks.
An I-Regexp implementation MUST be a complete implementation of this
limited subset. In particular, full support for the Unicode
functionality defined in this specification is REQUIRED; the
implementation MUST NOT limit itself to 7- or 8-bit character sets
such as ASCII and MUST support the Unicode character property set in
character classes.
3.1. Checking Implementations
A _checking_ I-Regexp implementation is one that checks a supplied
regexp for compliance with this specification and reports any
problems. Checking implementations give their users confidence that
they didn't accidentally insert non-interoperable syntax, so checking
is RECOMMENDED. Exceptions to this rule may be made for low-effort
implementations that map I-Regexp to another regexp library by simple
steps such as performing the mapping operations discussed in
Section 5; here, the effort needed to do full checking may dwarf the
rest of the implementation effort. Implementations SHOULD document
whether they are checking or not.
Specifications that employ I-Regexp may want to define in which cases
their implementations can work with a non-checking I-Regexp
implementation and when full checking is needed, possibly in the
process of defining their own implementation classes.
4. I-Regexp Semantics
This syntax is a subset of that of [XSD-2]. Implementations which
interpret I-Regexps MUST yield Boolean results as specified in
[XSD-2]. (See also Section 5.2.)
5. Mapping I-Regexp to Regexp Dialects
The material in this section is non-normative, provided as guidance
to developers who want to use I-Regexps in the context of other
regular expression dialects.
Bormann & Bray Expires 31 December 2023 [Page 5]
Internet-Draft I-Regexp June 2023
5.1. Multi-Character Escapes
Common multi-character escapes (MCEs), and character classes built
around them, which are not supported in I-Regexp, can usually be
replaced as shown for example in Table 1.
+===========+==============+
| MCE/class | Replace with |
+===========+==============+
| \S | [^ \t\n\r] |
+-----------+--------------+
| [\S ] | [^\t\n\r] |
+-----------+--------------+
| \d | [0-9] |
+-----------+--------------+
Table 1: Example
substitutes for multi-
character escapes
Note that the semantics of \d in XSD regular expressions is that of
\p{Nd}; however, this would include all Unicode characters that are
digits in various writing systems, which is almost certainly not what
is required in IETF publications.
The construct \p{IsBasicLatin} is essentially a reference to legacy
ASCII, it can be replaced by the character class [\u0000-\u007f].
5.2. XSD Regexps
Any I-Regexp also is an XSD Regexp [XSD-2], so the mapping is an
identity function.
Note that a few errata for [XSD-2] have been fixed in [XSD11-2],
which is therefore also included as a normative reference. XSD 1.1
is less widely implemented than XSD 1.0, and implementations of XSD
1.0 are likely to include these bugfixes, so for the intents and
purposes of this specification an implementation of XSD 1.0 regexps
is equivalent to an implementation of XSD 1.1 regexps.
5.3. ECMAScript Regexps
Perform the following steps on an I-Regexp to obtain an ECMAScript
regexp [ECMA-262]:
* For any unescaped dots (.) outside character classes (first
alternative of charClass production): replace dot by [^\n\r].
Bormann & Bray Expires 31 December 2023 [Page 6]
Internet-Draft I-Regexp June 2023
* Envelope the result in ^(?: and )$.
The ECMAScript regexp is to be interpreted as a Unicode pattern ("u"
flag; see Section 21.2.2 "Pattern Semantics" of [ECMA-262]).
Note that where a regexp literal is required, the actual regexp needs
to be enclosed in /.
5.4. PCRE, RE2, Ruby Regexps
Perform the same steps as in Section 5.3 to obtain a valid regexp in
PCRE [PCRE2], the Go programming language [RE2], and the Ruby
programming language, except that the last step is:
* Enclose the regexp in \A(?: and )\z.
6. Motivation and Background
While regular expressions originally were intended to describe a
formal language to support a Boolean matching function, they have
been enhanced with parsing functions that support the extraction and
replacement of arbitrary portions of the matched text. With this
accretion of features, parsing regexp libraries have become more
susceptible to bugs and surprising performance degradations which can
be exploited in Denial of Service attacks by an attacker who controls
the regexp submitted for processing. I-Regexp is designed to offer
interoperability, and to be less vulnerable to such attacks, with the
trade-off that its only function is to offer a boolean response as to
whether a character sequence is matched by a regexp.
6.1. Implementing I-Regexp
XSD regexps are relatively easy to implement or map to widely
implemented parsing regexp dialects, with these notable exceptions:
* Character class subtraction. This is a very useful feature in
many specifications, but it is unfortunately mostly absent from
parsing regexp dialects. Thus, it is omitted from I-Regexp.
* Multi-character escapes. \d, \w, \s and their uppercase
complement classes exhibit a large amount of variation between
regexp flavors. Thus, they are omitted from I-Regexp.
Bormann & Bray Expires 31 December 2023 [Page 7]
Internet-Draft I-Regexp June 2023
* Not all regexp implementations support accesses to Unicode tables
that enable executing constructs such as \p{Nd}, although the
\p/\P feature in general is now quite widely available. While in
principle it is possible to translate these into character-class
matches, this also requires access to those tables. Thus, regexp
libraries in severely constrained environments may not be able to
support I-Regexp conformance.
7. IANA Considerations
This document makes no requests of IANA.
8. Security considerations
While technically out of scope of this specification, Section 10
(Security Considerations) of [STD63] applies to implementations.
Particular note needs to be taken of the last paragraph of Section 3
(UTF-8 definition) of [STD63]; an I-Regexp implementation may need to
mitigate limitations of the platform implementation in this regard.
As discussed in Section 6, more complex regexp libraries may contain
exploitable bugs leading to crashes and remote code execution. There
is also the problem that such libraries often have hard-to-predict
performance characteristics, leading to attacks that overload an
implementation by matching against an expensive attacker-controlled
regexp.
I-Regexps have been designed to allow implementation in a way that is
resilient to both threats; this objective needs to be addressed
throughout the implementation effort. Non-checking implementations
(see Section 3.1) are likely to expose security limitations of any
regexp engine they use, which may be less problematic if that engine
has been built with security considerations in mind (e.g., [RE2]); a
checking implementation is still RECOMMENDED.
Implementations that specifically implement the I-Regexp subset can,
with care, be designed to generally run in linear time and space in
the input, and to detect when that would not be the case (see below).
Existing regexp engines should be able to easily handle most
I-Regexps (after the adjustments discussed in Section 5), but may
consume excessive resources for some types of I-Regexps or outright
reject them because they cannot guarantee efficient execution. (Note
that different versions of the same regexp library may be more or
less vulnerable to excessive resource consumption for these cases.)
Bormann & Bray Expires 31 December 2023 [Page 8]
Internet-Draft I-Regexp June 2023
Specifically, range quantifiers (as in a{2,4}) provide particular
challenges for both existing and I-Regexp focused implementations.
These may therefore limit range quantifiers in composability
(disallowing nested range quantifiers such as (a{2,4}){2,4}) or range
(disallowing very large ranges such as a{20,200000}), or detect and
reject any excessive resource consumption caused by them.
I-Regexp implementations that are used to evaluate regexps from
untrusted sources need to be robust to these cases. Implementers
using existing regexp libraries are encouraged to check their
documentation to see if mitigations are configurable, such as limits
in resource consumption, and to document their own degree of
robustness resulting from employing such mitigations.
9. References
9.1. 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/rfc/rfc2119>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/rfc/rfc5234>.
[RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF",
RFC 7405, DOI 10.17487/RFC7405, December 2014,
<https://www.rfc-editor.org/rfc/rfc7405>.
[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>.
[XSD-2] Malhotra, A., Ed. and P. V. Biron, Ed., "XML Schema Part
2: Datatypes Second Edition", W3C REC REC-xmlschema-
2-20041028, W3C REC-xmlschema-2-20041028, 28 October 2004,
<https://www.w3.org/TR/2004/REC-xmlschema-2-20041028/>.
[XSD11-2] Malhotra, A., Ed., Peterson, D., Ed., Thompson, H., Ed.,
Sperberg-McQueen, M., Ed., Biron, P. V., Ed., and S. Gao,
Ed., "W3C XML Schema Definition Language (XSD) 1.1 Part 2:
Datatypes", W3C REC REC-xmlschema11-2-20120405, W3C REC-
xmlschema11-2-20120405, 5 April 2012,
<https://www.w3.org/TR/2012/REC-xmlschema11-2-20120405/>.
Bormann & Bray Expires 31 December 2023 [Page 9]
Internet-Draft I-Regexp June 2023
9.2. Informative References
[ECMA-262] Ecma International, "ECMAScript 2020 Language
Specification", ECMA Standard ECMA-262, 11th Edition, June
2020, <https://www.ecma-international.org/wp-
content/uploads/ECMA-262.pdf>.
[I-D.ietf-jsonpath-base]
Gössner, S., Normington, G., and C. Bormann, "JSONPath:
Query expressions for JSON", Work in Progress, Internet-
Draft, draft-ietf-jsonpath-base-14, 10 June 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-
jsonpath-base-14>.
[PCRE2] "Perl-compatible Regular Expressions (revised API:
PCRE2)", n.d., <http://pcre.org/current/doc/html/>.
[RE2] "RE2 is a fast, safe, thread-friendly alternative to
backtracking regular expression engines like those used in
PCRE, Perl, and Python. It is a C++ library.", n.d.,
<https://github.com/google/re2>.
[RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
DOI 10.17487/RFC7493, March 2015,
<https://www.rfc-editor.org/rfc/rfc7493>.
[STD63] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/rfc/rfc3629>.
[UNICODE-GLOSSARY]
Unicode, Inc., "Glossary of Unicode Terms",
<https://unicode.org/glossary/>.
Appendix A. Regexps and Similar Constructs in Recent Published RFCs
This section is to be removed before publishing as an RFC.
This appendix contains a number of regular expressions that have been
extracted from some recently published RFCs based on some ad-hoc
matching. Multi-line constructions were not included. With the
exception of some (often surprisingly dubious) usage of multi-
character escapes and a reference to the IsBasicLatin Unicode block,
all regular expressions validate against the ABNF in Figure 1.
Bormann & Bray Expires 31 December 2023 [Page 10]
Internet-Draft I-Regexp June 2023
rfc6021.txt 459 (([0-1](\.[1-3]?[0-9]))|(2\.(0|([1-9]\d*))))
rfc6021.txt 513 \d*(\.\d*){1,127}
rfc6021.txt 529 \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(\.\d+)?
rfc6021.txt 631 ([0-9a-fA-F]{2}(:[0-9a-fA-F]{2})*)?
rfc6021.txt 647 [0-9a-fA-F]{2}(:[0-9a-fA-F]{2}){5}
rfc6021.txt 933 ((:|[0-9a-fA-F]{0,4}):)([0-9a-fA-F]{0,4}:){0,5}
rfc6021.txt 938 (([^:]+:){6}(([^:]+:[^:]+)|(.*\..*)))|
rfc6021.txt 1026 ((:|[0-9a-fA-F]{0,4}):)([0-9a-fA-F]{0,4}:){0,5}
rfc6021.txt 1031 (([^:]+:){6}(([^:]+:[^:]+)|(.*\..*)))|
rfc6020.txt 6647 [0-9a-fA-F]*
rfc6095.txt 2544 \S(.*\S)?
rfc6110.txt 1583 [aeiouy]*
rfc6110.txt 3222 [A-Z][a-z]*
rfc6536.txt 1583 \*
rfc6536.txt 1632 [^\*].*
rfc6643.txt 524 \p{IsBasicLatin}{0,255}
rfc6728.txt 3480 \S+
rfc6728.txt 3500 \S(.*\S)?
rfc6991.txt 477 (([0-1](\.[1-3]?[0-9]))|(2\.(0|([1-9]\d*))))
rfc6991.txt 525 \d*(\.\d*){1,127}
rfc6991.txt 541 [a-zA-Z_][a-zA-Z0-9\-_.]*
rfc6991.txt 542 .|..|[^xX].*|.[^mM].*|..[^lL].*
rfc6991.txt 571 \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(\.\d+)?
rfc6991.txt 665 ([0-9a-fA-F]{2}(:[0-9a-fA-F]{2})*)?
rfc6991.txt 693 [0-9a-fA-F]{2}(:[0-9a-fA-F]{2}){5}
rfc6991.txt 725 ([0-9a-fA-F]{2}(:[0-9a-fA-F]{2})*)?
rfc6991.txt 743 [0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-
rfc6991.txt 1041 ((:|[0-9a-fA-F]{0,4}):)([0-9a-fA-F]{0,4}:){0,5}
rfc6991.txt 1046 (([^:]+:){6}(([^:]+:[^:]+)|(.*\..*)))|
rfc6991.txt 1099 [0-9\.]*
rfc6991.txt 1109 [0-9a-fA-F:\.]*
rfc6991.txt 1164 ((:|[0-9a-fA-F]{0,4}):)([0-9a-fA-F]{0,4}:){0,5}
rfc6991.txt 1169 (([^:]+:){6}(([^:]+:[^:]+)|(.*\..*)))|
rfc7407.txt 933 ([0-9a-fA-F]){2}(:([0-9a-fA-F]){2}){0,254}
rfc7407.txt 1494 ([0-9a-fA-F]){2}(:([0-9a-fA-F]){2}){4,31}
rfc7758.txt 703 \d{2}:\d{2}:\d{2}(\.\d+)?
rfc7758.txt 1358 \d{2}:\d{2}:\d{2}(\.\d+)?
rfc7895.txt 349 \d{4}-\d{2}-\d{2}
rfc7950.txt 8323 [0-9a-fA-F]*
rfc7950.txt 8355 [a-zA-Z_][a-zA-Z0-9\-_.]*
rfc7950.txt 8356 [xX][mM][lL].*
rfc8040.txt 4713 \d{4}-\d{2}-\d{2}
rfc8049.txt 6704 [A-Z]{2}
rfc8194.txt 629 \*
rfc8194.txt 637 [0-9]{8}\.[0-9]{6}
rfc8194.txt 905 Z|[\+\-]\d{2}:\d{2}
rfc8194.txt 963 (2((2[4-9])|(3[0-9]))\.).*
rfc8194.txt 974 (([fF]{2}[0-9a-fA-F]{2}):).*
Bormann & Bray Expires 31 December 2023 [Page 11]
Internet-Draft I-Regexp June 2023
rfc8299.txt 7986 [A-Z]{2}
rfc8341.txt 1878 \*
rfc8341.txt 1927 [^\*].*
rfc8407.txt 1723 [0-9\.]*
rfc8407.txt 1749 [a-zA-Z_][a-zA-Z0-9\-_.]*
rfc8407.txt 1750 .|..|[^xX].*|.[^mM].*|..[^lL].*
rfc8525.txt 550 \d{4}-\d{2}-\d{2}
rfc8776.txt 838 /?([a-zA-Z0-9\-_.]+)(/[a-zA-Z0-9\-_.]+)*
rfc8776.txt 874 ([a-zA-Z0-9\-_.]+:)*
rfc8819.txt 311 [\S ]+
rfc8944.txt 596 [0-9a-fA-F]{2}(:[0-9a-fA-F]{2}){7}
Figure 2: Example regular expressions extracted from RFCs
Acknowledgements
This specification has been motivated by the discussion in the IETF
JSONPATH WG about whether to include a regexp mechanism into the
JSONPath query expression specification, as well as by previous
discussions about the YANG pattern and CDDL .regexp features.
The basic approach for this specification was inspired by The I-JSON
Message Format [RFC7493].
Authors' Addresses
Carsten Bormann
Universität Bremen TZI
Postfach 330440
D-28359 Bremen
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
Tim Bray
Textuality
Canada
Email: tbray@textuality.com
Bormann & Bray Expires 31 December 2023 [Page 12]
