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 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 http://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 March 14, 2015. Copyright Notice Copyright (c) 2014 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 (http://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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Kyzivat Expires March 14, 2015 [Page 1] Internet-Draft Case-Sensitive String Support in ABNF September 2014 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 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: Kyzivat Expires March 14, 2015 [Page 2] Internet-Draft Case-Sensitive String Support in ABNF September 2014 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 Kyzivat Expires March 14, 2015 [Page 3] Internet-Draft Case-Sensitive String Support in ABNF September 2014 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 Kyzivat Expires March 14, 2015 [Page 4]