1 ;;; utf7.el --- UTF-7 encoding/decoding for Emacs -*-coding: iso-8859-1;-*-
3 ;; Copyright (C) 1999, 2000, 2002, 2003, 2004,
4 ;; 2005 Free Software Foundation, Inc.
6 ;; Author: Jon K Hellan <hellan@acm.org>
7 ;; Maintainer: bugs@gnus.org
10 ;; This file is part of GNU Emacs.
12 ;; GNU Emacs is free software; you can redistribute it and/or modify
13 ;; it under the terms of the GNU General Public License as published by
14 ;; the Free Software Foundation; either version 2, or (at your option)
17 ;; GNU Emacs is distributed in the hope that it will be useful,
18 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
19 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 ;; GNU General Public License for more details.
22 ;; You should have received a copy of the GNU General Public License
23 ;; along with GNU Emacs; see the file COPYING. If not, write to
24 ;; the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
25 ;; Boston, MA 02110-1301, USA.
29 ;; UTF-7 - A Mail-Safe Transformation Format of Unicode - RFC 2152
30 ;; This is a transformation format of Unicode that contains only 7-bit
31 ;; ASCII octets and is intended to be readable by humans in the limiting
32 ;; case that the document consists of characters from the US-ASCII
34 ;; In short, runs of characters outside US-ASCII are encoded as base64
36 ;; A variation of UTF-7 is specified in IMAP 4rev1 (RFC 2060) as the way
37 ;; to represent characters outside US-ASCII in mailbox names in IMAP.
38 ;; This library supports both variants, but the IMAP variation was the
40 ;; The routines convert UTF-7 -> UTF-16 (16 bit encoding of Unicode)
41 ;; -> current character set, and vice versa.
42 ;; However, until Emacs supports Unicode, the only Emacs character set
43 ;; supported here is ISO-8859.1, which can trivially be converted to/from
45 ;; When decoding results in a character outside the Emacs character set,
46 ;; an error is thrown. It is up to the application to recover.
48 ;; UTF-7 should be done by providing a coding system. Mule-UCS does
49 ;; already, but I don't know if it does the IMAP version and it's not
50 ;; clear whether that should really be a coding system. The UTF-16
51 ;; part of the conversion can be done with coding systems available
52 ;; with Mule-UCS or some versions of Emacs. Unfortunately these were
53 ;; done wrongly (regarding handling of byte-order marks and how the
54 ;; variants were named), so we don't have a consistent name for the
55 ;; necessary coding system. The code below doesn't seem to DTRT
58 ;; (utf7-encode "a+£")
61 ;; $ echo "a+£"|iconv -f iso-8859-1 -t utf-7
70 (eval-when-compile (require 'cl
))
73 (defconst utf7-direct-encoding-chars
" -%'-*,-[]-}"
74 "Character ranges which do not need escaping in UTF-7.")
76 (defconst utf7-imap-direct-encoding-chars
77 (concat utf7-direct-encoding-chars
"+\\~")
78 "Character ranges which do not need escaping in the IMAP variant of UTF-7.")
80 (defconst utf7-utf-16-coding-system
81 (cond ((mm-coding-system-p 'utf-16-be-no-signature
) ; Mule-UCS
82 'utf-16-be-no-signature
)
83 ((and (mm-coding-system-p 'utf-16-be
) ; Emacs 22.1
84 ;; Avoid versions with BOM.
85 (= 2 (length (encode-coding-string "a" 'utf-16-be
))))
87 ((mm-coding-system-p 'utf-16-be-nosig
) ; ?
89 "Coding system which encodes big endian UTF-16 without a BOM signature.")
91 (defsubst utf7-imap-get-pad-length
(len modulus
)
92 "Return required length of padding for IMAP modified base64 fragment."
93 (mod (- len
) modulus
))
95 (defun utf7-encode-internal (&optional for-imap
)
96 "Encode text in (temporary) buffer as UTF-7.
97 Use IMAP modification if FOR-IMAP is non-nil."
98 (let ((start (point-min))
100 (narrow-to-region start end
)
102 (let* ((esc-char (if for-imap ?
& ?
+))
103 (direct-encoding-chars
104 (if for-imap utf7-imap-direct-encoding-chars
105 utf7-direct-encoding-chars
))
106 (not-direct-encoding-chars (concat "^" direct-encoding-chars
)))
108 (skip-chars-forward direct-encoding-chars
)
112 (fc (following-char))
114 (skip-chars-forward not-direct-encoding-chars
)))
115 (if (and (= fc esc-char
)
116 (= run-length
1)) ; Lone esc-char?
117 (delete-backward-char 1) ; Now there's one too many
118 (utf7-fragment-encode p
(point) for-imap
))
121 (defun utf7-fragment-encode (start end
&optional for-imap
)
122 "Encode text from START to END in buffer as UTF-7 escape fragment.
123 Use IMAP modification if FOR-IMAP is non-nil."
125 (narrow-to-region start end
)
126 (funcall (utf7-get-u16char-converter 'to-utf-16
))
127 (mm-with-unibyte-current-buffer
128 (base64-encode-region start
(point-max)))
130 (let ((pm (point-max)))
132 (while (search-forward "/" nil t
)
133 (replace-match ",")))
134 (skip-chars-forward "^= \t\n" pm
)
135 (delete-region (point) pm
))))
137 (defun utf7-decode-internal (&optional for-imap
)
138 "Decode UTF-7 text in (temporary) buffer.
139 Use IMAP modification if FOR-IMAP is non-nil."
140 (let ((start (point-min))
143 (let* ((esc-pattern (concat "^" (char-to-string (if for-imap ?
& ?
+))))
144 (base64-chars (concat "A-Za-z0-9+"
145 (char-to-string (if for-imap ?
, ?
/)))))
147 (skip-chars-forward esc-pattern
)
151 (run-length (skip-chars-forward base64-chars
)))
152 (when (and (not (eobp)) (= (following-char) ?-
))
154 (unless (= run-length
0) ; Encoded lone esc-char?
156 (utf7-fragment-decode p
(point) for-imap
)
158 (delete-backward-char 1)))))))))
160 (defun utf7-fragment-decode (start end
&optional for-imap
)
161 "Decode base64 encoded fragment from START to END of UTF-7 text in buffer.
162 Use IMAP modification if FOR-IMAP is non-nil."
164 (narrow-to-region start end
)
167 (while (search-forward "," nil
'move-to-end
) (replace-match "/")))
168 (let ((pl (utf7-imap-get-pad-length (- end start
) 4)))
169 (insert (make-string pl ?
=))
170 (base64-decode-region start
(+ end pl
)))
171 (funcall (utf7-get-u16char-converter 'from-utf-16
))))
173 (defun utf7-get-u16char-converter (which-way)
174 "Return a function to convert between UTF-16 and current character set."
175 (if utf7-utf-16-coding-system
176 (if (eq which-way
'to-utf-16
)
178 (encode-coding-region (point-min) (point-max)
179 utf7-utf-16-coding-system
))
181 (decode-coding-region (point-min) (point-max)
182 utf7-utf-16-coding-system
)))
183 ;; Add test to check if we are really Latin-1.
184 (if (eq which-way
'to-utf-16
)
185 'utf7-latin1-u16-char-converter
186 'utf7-u16-latin1-char-converter
)))
188 (defun utf7-latin1-u16-char-converter ()
189 "Convert latin 1 (ISO-8859.1) characters to 16 bit Unicode.
190 Characters are converted to raw byte pairs in narrowed buffer."
191 (mm-encode-coding-region (point-min) (point-max) 'iso-8859-1
)
192 (mm-disable-multibyte)
193 (goto-char (point-min))
198 (defun utf7-u16-latin1-char-converter ()
199 "Convert 16 bit Unicode characters to latin 1 (ISO-8859.1).
200 Characters are in raw byte pairs in narrowed buffer."
201 (goto-char (point-min))
203 (if (= 0 (following-char))
205 (error "Unable to convert from Unicode"))
207 (mm-decode-coding-region (point-min) (point-max) 'iso-8859-1
)
208 (mm-enable-multibyte))
210 (defun utf7-encode (string &optional for-imap
)
211 "Encode UTF-7 STRING. Use IMAP modification if FOR-IMAP is non-nil."
212 (let ((default-enable-multibyte-characters t
))
215 (utf7-encode-internal for-imap
)
218 (defun utf7-decode (string &optional for-imap
)
219 "Decode UTF-7 STRING. Use IMAP modification if FOR-IMAP is non-nil."
220 (let ((default-enable-multibyte-characters nil
))
223 (utf7-decode-internal for-imap
)
224 (mm-enable-multibyte)
229 ;;; arch-tag: 96078b55-85c7-4161-aed2-932c24b282c7
230 ;;; utf7.el ends here