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Versions: 00 01 02 RFC 7405

Internet Engineering Task Force                               P. Kyzivat
Internet-Draft
Updates: 5234 (if approved)                              August 18, 2014
Intended status: Standards Track
Expires: February 19, 2015


                 Case-Sensitive String Support in ABNF
                  draft-kyzivat-case-sensitive-abnf-01

Abstract

   This document extends the base definition of ABNF (Augmented Mackus-
   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
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   This Internet-Draft will expire on February 19, 2015.

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   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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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 Mackus-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

   If no prefix is present then the string is case-insensitive.

   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

   will match only the string that comprises only the lowercase
   characters, abc.  This mechanism has a clear readability




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   disadvantage, with respect to using a literal text string with a
   prefix, and new the prefix mechanism is preferred.

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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