Internet DRAFT - draft-kyzivat-case-sensitive-abnf
draft-kyzivat-case-sensitive-abnf
Internet Engineering Task Force P. Kyzivat
Internet-Draft
Updates: 5234 (if approved) September 10, 2014
Intended status: Standards Track
Expires: March 14, 2015
Case-Sensitive String Support in ABNF
draft-kyzivat-case-sensitive-abnf-02
Abstract
This document extends the base definition of ABNF (Augmented Backus-
Naur Form) to include a way to specify ASCII string literals that are
matched in a case-sensitive manner.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Updates to RFC5234 . . . . . . . . . . . . . . . . . . . . . 2
2.1. Terminal values - literal text strings . . . . . . . . . 2
2.2. ABNF Definition of ABNF - char-val . . . . . . . . . . . 4
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. Normative References . . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
The base definition of ABNF (Augmented Backus-Naur Form) supports
ASCII string literals. Matching of these literals is done in a case-
insensitive manner. While this is often the desired behavior, in
some situations case-sensitive matching of string literals is needed.
Literals for case-sensitive matching must be specified using the
numeric representation of those characters. That is inconvenient and
error prone both to write and to read.
This document extends ABNF to have two different types of ASCII
string literals. One type is matched using case-sensitive matching,
while the other is matched using case-insensitive matching. These
types are denoted using type prefixes, similar to the type prefixes
used with numeric values. If no prefix is used, then case-
insensitive matching is used, consistent with previous behavior.
This document is structured as a set of changes to the full ABNF
specification [RFC5234].
2. Updates to RFC5234
This document makes changes to two parts of RFC5234. The two changes
are:
o Replace the last half of section 2.3 of RFC5234 (beginning with
"ABNF permits the specification of literal text strings") with the
contents of Section 2.1 below.
o Replace the <char-val> rule in section 4 of RFC5234 with the
contents of Section 2.2 below.
2.1. Terminal values - literal text strings
ABNF permits the specification of literal text strings directly,
enclosed in quotation marks. Hence:
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command = "command string"
Literal text strings are interpreted as a concatenated set of
printable characters. The character set for these strings is US-
ASCII.
Literal text strings in ABNF may be either case sensitive or case
insensitive. The form of matching used with a literal text string is
denoted by a prefix to the quoted string. The following prefixes are
allowed:
%s = case-sensitive
%i = case-insensitive
To be consistent with prior implementations of ABNF, having no prefix
means that the string is case-insensitive, and is equivalent to
having the "%i" prefix.
Hence:
rulename = %i"aBc"
and:
rulename = "abc"
will both match "abc", "Abc", "aBc", "abC", "ABc", "aBC", "AbC", and
"ABC".
In contrast:
rulename = %s"aBc"
will match only "aBc", and will not match "abc", "Abc", "abC", "ABc",
"aBC", "AbC", or "ABC".
The way that has been used in the past to define a rule that is case
sensitive is to specify the individual characters numerically.
For example:
rulename = %d97 %d98 %d99
or
rulename = %x61.62.63
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will match only the string that comprises only the lowercase
characters, abc. The new way (using a literal text string with a
prefix) has a clear readability advantage over the old way.
2.2. ABNF Definition of ABNF - char-val
char-val = case-insensitive-string /
case-sensitive-string
case-insensitive-string =
[ "%i" ] quoted-string
case-sensitive-string =
"%s" quoted-string
quoted-string = DQUOTE *(%x20-21 / %x23-7E) DQUOTE
; quoted string of SP and VCHAR
; without DQUOTE
3. IANA Considerations
This memo includes no request to IANA.
4. Security Considerations
Security is truly believed to be irrelevant to this document.
5. Normative References
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
Author's Address
Paul Kyzivat
Massachusetts
US
Email: pkyzivat@alum.mit.edu
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