path: root/iconvdata/utf-7.c

/* Conversion module for UTF-7.
   Copyright (C) 2000-2023 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

/* UTF-7 is a legacy encoding used for transmitting Unicode within the
   ASCII character set, used primarily by mail agents.  New programs
   are encouraged to use UTF-8 instead.

   UTF-7 is specified in RFC 2152 (and old RFC 1641, RFC 1642).  The
   original Base64 encoding is defined in RFC 2045.  */

#include <dlfcn.h>
#include <gconv.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>


enum variant
{
  UTF7,
  UTF_7_IMAP
};

/* Must be in the same order as enum variant above.  */
static const char names[] =
  "UTF-7//\0"
  "UTF-7-IMAP//\0"
  "\0";

static uint32_t
shift_character (enum variant const var)
{
  if (var == UTF7)
    return '+';
  else if (var == UTF_7_IMAP)
    return '&';
  else
    abort ();
}

static bool
between (uint32_t const ch,
	 uint32_t const lower_bound, uint32_t const upper_bound)
{
  return (ch >= lower_bound && ch <= upper_bound);
}

/* The set of "direct characters":
   A-Z a-z 0-9 ' ( ) , - . / : ? space tab lf cr
   FOR UTF-7-IMAP
   A-Z a-z 0-9 ' ( ) , - . / : ? space
   ! " # $ % + * ; < = > @ [ \ ] ^ _ ` { | } ~
*/

static bool
isdirect (uint32_t ch, enum variant var)
{
  if (var == UTF7)
    return (between (ch, 'A', 'Z')
	    || between (ch, 'a', 'z')
	    || between (ch, '0', '9')
	    || ch == '\'' || ch == '(' || ch == ')'
	    || between (ch, ',', '/')
	    || ch == ':' || ch == '?'
	    || ch == ' ' || ch == '\t' || ch == '\n' || ch == '\r');
  else if (var == UTF_7_IMAP)
    return (ch != '&' && between (ch, ' ', '~'));
  abort ();
}


/* The set of "direct and optional direct characters":
   A-Z a-z 0-9 ' ( ) , - . / : ? space tab lf cr
   (UTF-7 only)
   ! " # $ % & * ; < = > @ [ ] ^ _ ` { | }
*/

static bool
isxdirect (uint32_t ch, enum variant var)
{
  if (isdirect (ch, var))
    return true;
  if (var != UTF7)
    return false;
  return between (ch, '!', '&')
    || ch == '*'
    || between (ch, ';', '@')
    || (between (ch, '[', '`') && ch != '\\')
    || between (ch, '{', '}');
}


/* Characters which needs to trigger an explicit shift back to US-ASCII (UTF-7
   only): Modified base64 + '-' (shift back character)
   A-Z a-z 0-9 + / -
*/

static