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-;;; utf7.el --- UTF-7 encoding/decoding for Emacs -*-coding: utf-8;-*-
-
-;; Copyright (C) 1999-2016 Free Software Foundation, Inc.
-
-;; Author: Jon K Hellan <hellan@acm.org>
-;; Maintainer: bugs@gnus.org
-;; Keywords: mail
-
-;; This file is part of GNU Emacs.
-
-;; 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 3 of the License, 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. If not, see <http://www.gnu.org/licenses/>.
-
-;;; 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.
-
-;; UTF-7 should be done by providing a coding system. Mule-UCS does
-;; already, but I don't know if it does the IMAP version and it's not
-;; clear whether that should really be a coding system. The UTF-16
-;; part of the conversion can be done with coding systems available
-;; with Mule-UCS or some versions of Emacs. Unfortunately these were
-;; done wrongly (regarding handling of byte-order marks and how the
-;; variants were named), so we don't have a consistent name for the
-;; necessary coding system. The code below doesn't seem to DTRT
-;; generally. E.g.:
-;;
-;; (utf7-encode "a+£")
-;; => "a+ACsAow-"
-;;
-;; $ echo "a+£"|iconv -f utf-8 -t utf-7
-;; a+-+AKM
-;;
-;; -- fx
-
-
-;;; Code:
-
-(require 'base64)
-(eval-when-compile (require 'cl))
-(require 'mm-util)
-
-(defconst utf7-direct-encoding-chars " -%'-*,-[]-}"
- "Character ranges which do not need escaping in UTF-7.")
-
-(defconst utf7-imap-direct-encoding-chars
- (concat utf7-direct-encoding-chars "+\\~")
- "Character ranges which do not need escaping in the IMAP variant of UTF-7.")
-
-(defconst utf7-utf-16-coding-system
- (cond ((mm-coding-system-p 'utf-16-be-no-signature) ; Mule-UCS
- 'utf-16-be-no-signature)
- ((and (mm-coding-system-p 'utf-16-be) ; Emacs
- ;; Avoid versions with BOM.
- (= 2 (length (encode-coding-string "a" 'utf-16-be))))
- 'utf-16-be)
- ((mm-coding-system-p 'utf-16-be-nosig) ; ?
- 'utf-16-be-nosig))
- "Coding system which encodes big endian UTF-16 without a BOM signature.")
-
-(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))
- (not-direct-encoding-chars (concat "^" 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 not-direct-encoding-chars)))
- (if (and (= fc esc-char)
- (= run-length 1)) ; Lone esc-char?
- (delete-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))
- (mm-with-unibyte-current-buffer
- (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-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."
- (if utf7-utf-16-coding-system
- (if (eq which-way 'to-utf-16)
- (lambda ()
- (encode-coding-region (point-min) (point-max)
- utf7-utf-16-coding-system))
- (lambda ()
- (decode-coding-region (point-min) (point-max)
- utf7-utf-16-coding-system)))
- ;; Add test to check if we are really Latin-1.
- (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."
- (mm-encode-coding-region (point-min) (point-max) 'iso-8859-1)
- (mm-disable-multibyte)
- (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))
- (mm-decode-coding-region (point-min) (point-max) 'iso-8859-1)
- (mm-enable-multibyte))
-
-;;;###autoload
-(defun utf7-encode (string &optional for-imap)
- "Encode UTF-7 STRING. Use IMAP modification if FOR-IMAP is non-nil."
- (if (and (coding-system-p 'utf-7) (coding-system-p 'utf-7-imap))
- ;; Emacs 23 with proper support for IMAP
- (encode-coding-string string (if for-imap 'utf-7-imap 'utf-7))
- (mm-with-multibyte-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."
- (if (and (coding-system-p 'utf-7) (coding-system-p 'utf-7-imap))
- ;; Emacs 23 with proper support for IMAP
- (decode-coding-string string (if for-imap 'utf-7-imap 'utf-7))
- (mm-with-unibyte-buffer
- (insert string)
- (utf7-decode-internal for-imap)
- (mm-enable-multibyte)
- (buffer-string))))
-
-(provide 'utf7)
-
-;;; utf7.el ends here
generated by cgit v1.2.3 (git 2.39.1) at 2025-04-08 12:21:12 +0000