--- /dev/null
+;;; utf7.el --- UTF-7 encoding/decoding for Emacs
+;; Copyright (C) 1999 Free Software Foundation, Inc.
+
+;; Author: Jon K Hellan <hellan@item.ntnu.no>
+;; Keywords: mail
+
+;; This file is part of GNU Emacs, but the same permissions apply
+
+;; GNU Emacs is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 2, or (at your option)
+;; any later version.
+
+;; GNU Emacs 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 General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs; see the file COPYING. If not, write to
+;; the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+;; Boston, MA 02111-1307, USA.
+
+;;; Commentary:
+;;; UTF-7 - A Mail-Safe Transformation Format of Unicode - RFC 2152
+;;; This is a transformation format of Unicode that contains only 7-bit
+;;; ASCII octets and is intended to be readable by humans in the limiting
+;;; case that the document consists of characters from the US-ASCII
+;;; repertoire.
+;;; In short, runs of characters outside US-ASCII are encoded as base64
+;;; inside delimiters.
+;;; A variation of UTF-7 is specified in IMAP 4rev1 (RFC 2060) as the way
+;;; to represent characters outside US-ASCII in mailbox names in IMAP.
+;;; This library supports both variants, but the IMAP variation was the
+;;; reason I wrote it.
+;;; The routines convert UTF-7 -> UTF-16 (16 bit encoding of Unicode)
+;;; -> current character set, and vice versa.
+;;; However, until Emacs supports Unicode, the only Emacs character set
+;;; supported here is ISO-8859.1, which can trivially be converted to/from
+;;; Unicode.
+;;; When decoding results in a character outside the Emacs character set,
+;;; an error is thrown. It is up to the application to recover.
+
+;;; Code:
+
+(require 'base64)
+
+(defvar utf7-direct-encoding-chars " -%'-*,-[]-}"
+ "Characters ranges which do not need escaping in UTF-7")
+
+(defvar utf7-imap-direct-encoding-chars
+ (concat utf7-direct-encoding-chars "+\\~")
+ "Characters ranges which do not need escaping in the IMAP variant of UTF-7")
+
+(defsubst utf7-imap-get-pad-length (len modulus)
+ "Return required length of padding for IMAP modified base64 fragment."
+ (mod (- len) modulus))
+
+(defun utf7-encode-internal (&optional for-imap)
+ "Encode text in (temporary) buffer as UTF-7.
+Use IMAP modification if FOR-IMAP is non-nil."
+ (let ((start (point-min))
+ (end (point-max)))
+ (narrow-to-region start end)
+ (goto-char start)
+ (let ((esc-char (if for-imap ?& ?+))
+ (direct-encoding-chars
+ (if for-imap utf7-imap-direct-encoding-chars
+ utf7-direct-encoding-chars)))
+ (while (not (eobp))
+ (skip-chars-forward direct-encoding-chars)
+ (unless (eobp)
+ (insert esc-char)
+ (let ((p (point))
+ (fc (following-char))
+ (run-length
+ (skip-chars-forward (concat "^" direct-encoding-chars))))
+ (if (and (= fc esc-char)
+ (= run-length 1)) ; Lone esc-char?
+ (delete-backward-char 1) ; Now there's one too many
+ (utf7-fragment-encode p (point) for-imap))
+ (insert "-")))))))
+
+(defun utf7-fragment-encode (start end &optional for-imap)
+ "Encode text from START to END in buffer as UTF-7 escape fragment.
+Use IMAP modification if FOR-IMAP is non-nil."
+ (save-restriction
+ (narrow-to-region start end)
+ (funcall (utf7-get-u16char-converter 'to-utf-16))
+ (base64-encode-region start (point-max))
+ (goto-char start)
+ (let ((pm (point-max)))
+ (when for-imap
+ (while (search-forward "/" nil t)
+ (replace-match ",")))
+ (skip-chars-forward "^= \t\n" pm)
+ (delete-region (point) pm))))
+
+(defun utf7-decode-internal (&optional for-imap)
+ "Decode UTF-7 text in (temporary) buffer.
+Use IMAP modification if FOR-IMAP is non-nil."
+ (let ((start (point-min))
+ (end (point-max)))
+ (goto-char start)
+ (let* ((esc-pattern (concat "^" (char-to-string (if for-imap ?& ?+))))
+ (base64-chars (concat "A-Za-z0-9+"
+ (char-to-string (if for-imap ?, ?/)))))
+ (while (not (eobp))
+ (skip-chars-forward esc-pattern)
+ (unless (eobp)
+ (forward-char)
+ (let ((p (point))
+ (run-length (skip-chars-forward base64-chars)))
+ (when (and (not (eobp)) (= (following-char) ?-))
+ (delete-char 1))
+ (unless (= run-length 0) ; Encoded lone esc-char?
+ (save-excursion
+ (utf7-fragment-decode p (point) for-imap)
+ (goto-char p)
+ (delete-backward-char 1)))))))))
+
+(defun utf7-fragment-decode (start end &optional for-imap)
+ "Decode base64 encoded fragment from START to END of UTF-7 text in buffer.
+Use IMAP modification if FOR-IMAP is non-nil."
+ (save-restriction
+ (narrow-to-region start end)
+ (when for-imap
+ (goto-char start)
+ (while (search-forward "," nil 'move-to-end) (replace-match "/")))
+ (let ((pl (utf7-imap-get-pad-length (- end start) 4)))
+ (insert (make-string pl ?=))
+ (base64-decode-region start (+ end pl)))
+ (funcall (utf7-get-u16char-converter 'from-utf-16))))
+
+(defun utf7-get-u16char-converter (which-way)
+ "Return a function to convert between UTF-16 and current character set."
+ ;; Add test to check if we are really Latin-1.
+ ;; Support other character sets once Emacs groks Unicode.
+ (if (eq which-way 'to-utf-16)
+ 'utf7-latin1-u16-char-converter
+ 'utf7-u16-latin1-char-converter))
+
+(defun utf7-latin1-u16-char-converter ()
+ "Convert latin 1 (ISO-8859.1) characters to 16 bit Unicode.
+Characters are converted to raw byte pairs in narrowed buffer."
+ (goto-char (point-min))
+ (while (not (eobp))
+ (insert 0)
+ (forward-char)))
+
+(defun utf7-u16-latin1-char-converter ()
+ "Convert 16 bit Unicode characters to latin 1 (ISO-8859.1).
+Characters are in raw byte pairs in narrowed buffer."
+ (goto-char (point-min))
+ (while (not (eobp))
+ (if (= 0 (following-char))
+ (delete-char 1)
+ (error "Unable to convert from Unicode"))
+ (forward-char)))
+
+(defun utf7-encode (string &optional for-imap)
+ "Encode UTF-7 string. Use IMAP modification if FOR-IMAP is non-nil."
+ (let ((default-enable-multibyte-characters nil))
+ (with-temp-buffer
+ (insert string)
+ (utf7-encode-internal for-imap)
+ (buffer-string))))
+
+(defun utf7-decode (string &optional for-imap)
+ "Decode UTF-7 string. Use IMAP modification if FOR-IMAP is non-nil."
+ (let ((default-enable-multibyte-characters nil))
+ (with-temp-buffer
+ (insert string)
+ (utf7-decode-internal for-imap)
+ (buffer-string))))
+
+(provide 'utf7)
+
+;;; utf7.el ends here
projects / gnus / commitdiff