1 ;;; utf7.el --- UTF-7 encoding/decoding for Emacs
2 ;; Copyright (C) 1999 Free Software Foundation, Inc.
4 ;; Author: Jon K Hellan <hellan@acm.org>
7 ;; This file is part of GNU Emacs, but the same permissions apply
9 ;; GNU Emacs is free software; you can redistribute it and/or modify
10 ;; it under the terms of the GNU General Public License as published by
11 ;; the Free Software Foundation; either version 2, or (at your option)
14 ;; GNU Emacs is distributed in the hope that it will be useful,
15 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
16 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 ;; GNU General Public License for more details.
19 ;; You should have received a copy of the GNU General Public License
20 ;; along with GNU Emacs; see the file COPYING. If not, write to
21 ;; the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
22 ;; Boston, MA 02111-1307, USA.
25 ;;; UTF-7 - A Mail-Safe Transformation Format of Unicode - RFC 2152
26 ;;; This is a transformation format of Unicode that contains only 7-bit
27 ;;; ASCII octets and is intended to be readable by humans in the limiting
28 ;;; case that the document consists of characters from the US-ASCII
30 ;;; In short, runs of characters outside US-ASCII are encoded as base64
31 ;;; inside delimiters.
32 ;;; A variation of UTF-7 is specified in IMAP 4rev1 (RFC 2060) as the way
33 ;;; to represent characters outside US-ASCII in mailbox names in IMAP.
34 ;;; This library supports both variants, but the IMAP variation was the
35 ;;; reason I wrote it.
36 ;;; The routines convert UTF-7 -> UTF-16 (16 bit encoding of Unicode)
37 ;;; -> current character set, and vice versa.
38 ;;; However, until Emacs supports Unicode, the only Emacs character set
39 ;;; supported here is ISO-8859.1, which can trivially be converted to/from
41 ;;; When decoding results in a character outside the Emacs character set,
42 ;;; an error is thrown. It is up to the application to recover.
48 (defvar utf7-direct-encoding-chars " -%'-*,-[]-}"
49 "Characters ranges which do not need escaping in UTF-7")
51 (defvar utf7-imap-direct-encoding-chars
52 (concat utf7-direct-encoding-chars "+\\~")
53 "Characters ranges which do not need escaping in the IMAP variant of UTF-7")
55 (defsubst utf7-imap-get-pad-length (len modulus)
56 "Return required length of padding for IMAP modified base64 fragment."
57 (mod (- len) modulus))
59 (defun utf7-encode-internal (&optional for-imap)
60 "Encode text in (temporary) buffer as UTF-7.
61 Use IMAP modification if FOR-IMAP is non-nil."
62 (let ((start (point-min))
64 (narrow-to-region start end)
66 (let ((esc-char (if for-imap ?& ?+))
67 (direct-encoding-chars
68 (if for-imap utf7-imap-direct-encoding-chars
69 utf7-direct-encoding-chars)))
71 (skip-chars-forward direct-encoding-chars)
77 (skip-chars-forward (concat "^" direct-encoding-chars))))
78 (if (and (= fc esc-char)
79 (= run-length 1)) ; Lone esc-char?
80 (delete-backward-char 1) ; Now there's one too many
81 (utf7-fragment-encode p (point) for-imap))
84 (defun utf7-fragment-encode (start end &optional for-imap)
85 "Encode text from START to END in buffer as UTF-7 escape fragment.
86 Use IMAP modification if FOR-IMAP is non-nil."
88 (narrow-to-region start end)
89 (funcall (utf7-get-u16char-converter 'to-utf-16))
90 (base64-encode-region start (point-max))
92 (let ((pm (point-max)))
94 (while (search-forward "/" nil t)
96 (skip-chars-forward "^= \t\n" pm)
97 (delete-region (point) pm))))
99 (defun utf7-decode-internal (&optional for-imap)
100 "Decode UTF-7 text in (temporary) buffer.
101 Use IMAP modification if FOR-IMAP is non-nil."
102 (let ((start (point-min))
105 (let* ((esc-pattern (concat "^" (char-to-string (if for-imap ?& ?+))))
106 (base64-chars (concat "A-Za-z0-9+"
107 (char-to-string (if for-imap ?, ?/)))))
109 (skip-chars-forward esc-pattern)
113 (run-length (skip-chars-forward base64-chars)))
114 (when (and (not (eobp)) (= (following-char) ?-))
116 (unless (= run-length 0) ; Encoded lone esc-char?
118 (utf7-fragment-decode p (point) for-imap)
120 (delete-backward-char 1)))))))))
122 (defun utf7-fragment-decode (start end &optional for-imap)
123 "Decode base64 encoded fragment from START to END of UTF-7 text in buffer.
124 Use IMAP modification if FOR-IMAP is non-nil."
126 (narrow-to-region start end)
129 (while (search-forward "," nil 'move-to-end) (replace-match "/")))
130 (let ((pl (utf7-imap-get-pad-length (- end start) 4)))
131 (insert (make-string pl ?=))
132 (base64-decode-region start (+ end pl)))
133 (funcall (utf7-get-u16char-converter 'from-utf-16))))
135 (defun utf7-get-u16char-converter (which-way)
136 "Return a function to convert between UTF-16 and current character set."
137 ;; Add test to check if we are really Latin-1.
138 ;; Support other character sets once Emacs groks Unicode.
139 (if (eq which-way 'to-utf-16)
140 'utf7-latin1-u16-char-converter
141 'utf7-u16-latin1-char-converter))
143 (defun utf7-latin1-u16-char-converter ()
144 "Convert latin 1 (ISO-8859.1) characters to 16 bit Unicode.
145 Characters are converted to raw byte pairs in narrowed buffer."
146 (goto-char (point-min))
151 (defun utf7-u16-latin1-char-converter ()
152 "Convert 16 bit Unicode characters to latin 1 (ISO-8859.1).
153 Characters are in raw byte pairs in narrowed buffer."
154 (goto-char (point-min))
156 (if (= 0 (following-char))
158 (error "Unable to convert from Unicode"))
161 (defun utf7-encode (string &optional for-imap)
162 "Encode UTF-7 string. Use IMAP modification if FOR-IMAP is non-nil."
163 (let ((default-enable-multibyte-characters nil))
166 (utf7-encode-internal for-imap)
169 (defun utf7-decode (string &optional for-imap)
170 "Decode UTF-7 string. Use IMAP modification if FOR-IMAP is non-nil."
171 (let ((default-enable-multibyte-characters nil))
174 (utf7-decode-internal for-imap)
179 ;;; utf7.el ends here