wdiff rfc7405.original rfc7405.txt


Internet Engineering Task Force (IETF)                        P. Kyzivat
Internet-Draft
Request for Comments: 7405                                 November 2014
Updates: 5234 (if approved)                           September 10, 2014
Intended status:
Category: Standards Track
Expires: March 14, 2015
ISSN: 2070-1721

                 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 US-ASCII string literals that
   are matched in a case-sensitive manner.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on March 14, 2015.
   http://www.rfc-editor.org/info/rfc7405.

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   Copyright (c) 2014 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Updates to RFC5234 RFC 5234 . . . . . . . . . . . . . . . . . . . . .   2
     2.1.  Terminal values Values - literal text strings Literal Text Strings  . . . . . . . . .   2   3
     2.2.  ABNF Definition of ABNF - char-val  . . . . . . . . . . .   4
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.
   4.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4   5

1.  Introduction

   The base definition of ABNF (Augmented Backus-Naur Form) supports US-
   ASCII string literals.  Matching  The matching of these literals is done in a case-
   insensitive
   case-insensitive manner.  While this is often the desired behavior,
   in some situations 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 characters, which is inconvenient
   and error prone both to write and to read.

   This document extends ABNF to have two different types of ASCII US-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, prefixes similar to the type prefixes
   used with numeric values.  If no prefix is used, then case-
   insensitive matching is used, used (as is consistent with previous behavior.
   behavior).

   This document is structured as a set of changes to the full ABNF
   specification [RFC5234].

2.  Updates to RFC5234 RFC 5234

   This document makes changes to two parts of RFC5234. [RFC5234].  The two
   changes
   are: are as follows:

   o  Replace the last half of section Section 2.3 of RFC5234 [RFC5234] (beginning with
      "ABNF permits the specification of literal text strings") with the
      contents of Section 2.1 below. 2.1.

   o  Replace the <char-val> rule in section Section 4 of RFC5234 [RFC5234] with the
      contents of Section 2.2 below. 2.2.

2.1.  Terminal values Values - literal text strings Literal Text Strings

   ABNF permits the specification of literal text strings directly,
   enclosed in quotation marks.  Hence:

         command     =  "command string"

   Literal text strings are interpreted as a concatenated set of
   printable characters.

   NOTE:

   The character set for these strings is US-
   ASCII. 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, 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", "aBc" and will not match "abc", "Abc", "abC", "ABc",
   "aBC", "AbC", or "ABC".

   The way that has been used in

   In the past to define a rule that is case
   sensitive is to specify past, the numerical specification of individual characters numerically. was
   used to define a case-sensitive rule.

   For example:

         rulename    =  %d97 %d98 %d99

   or

         rulename    =  %x61.62.63

   will match only the string that comprises only the lowercase
   characters, abc.  The new way (using  Using a literal text string with a
   prefix) 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.

4.  Normative References

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008. 2008,
              <http:/www.rfc-editor.org/info/rfc5234>.

Author's Address

   Paul Kyzivat
   Massachusetts
   US

   Email:
   United States

   EMail: pkyzivat@alum.mit.edu