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[emacs.git] / lisp / gnus / utf7.el
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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
8 ;; Keywords: mail
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)
15 ;; any later version.
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.
27 ;;; Commentary:
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
33 ;; repertoire.
34 ;; In short, runs of characters outside US-ASCII are encoded as base64
35 ;; inside delimiters.
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
39 ;; reason I wrote it.
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
44 ;; Unicode.
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
56 ;; generally. E.g.:
58 ;; (utf7-encode "a+£")
59 ;; => "a+ACsAow-"
61 ;; $ echo "a+£"|iconv -f iso-8859-1 -t utf-7
62 ;; a+-+AKM
64 ;; -- fx
67 ;;; Code:
69 (require 'base64)
70 (eval-when-compile (require 'cl))
71 (require 'mm-util)
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))))
86 'utf-16-be)
87 ((mm-coding-system-p 'utf-16-be-nosig) ; ?
88 '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))
99 (end (point-max)))
100 (narrow-to-region start end)
101 (goto-char start)
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)))
107 (while (not (eobp))
108 (skip-chars-forward direct-encoding-chars)
109 (unless (eobp)
110 (insert esc-char)
111 (let ((p (point))
112 (fc (following-char))
113 (run-length
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))
119 (insert "-")))))))
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."
124 (save-restriction
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)))
129 (goto-char start)
130 (let ((pm (point-max)))
131 (when for-imap
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))
141 (end (point-max)))
142 (goto-char start)
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 ?, ?/)))))
146 (while (not (eobp))
147 (skip-chars-forward esc-pattern)
148 (unless (eobp)
149 (forward-char)
150 (let ((p (point))
151 (run-length (skip-chars-forward base64-chars)))
152 (when (and (not (eobp)) (= (following-char) ?-))
153 (delete-char 1))
154 (unless (= run-length 0) ; Encoded lone esc-char?
155 (save-excursion
156 (utf7-fragment-decode p (point) for-imap)
157 (goto-char p)
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."
163 (save-restriction
164 (narrow-to-region start end)
165 (when for-imap
166 (goto-char start)
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)
177 (lambda ()
178 (encode-coding-region (point-min) (point-max)
179 utf7-utf-16-coding-system))
180 (lambda ()
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))
194 (while (not (eobp))
195 (insert 0)
196 (forward-char)))
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))
202 (while (not (eobp))
203 (if (= 0 (following-char))
204 (delete-char 1)
205 (error "Unable to convert from Unicode"))
206 (forward-char))
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))
213 (with-temp-buffer
214 (insert string)
215 (utf7-encode-internal for-imap)
216 (buffer-string))))
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))
221 (with-temp-buffer
222 (insert string)
223 (utf7-decode-internal for-imap)
224 (mm-enable-multibyte)
225 (buffer-string))))
227 (provide 'utf7)
229 ;;; arch-tag: 96078b55-85c7-4161-aed2-932c24b282c7
230 ;;; utf7.el ends here