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;;; utf-7.el --- utf-7 coding system
;; Copyright (C) 2003-2021 Free Software Foundation, Inc.
;; Author: Dave Love <fx@gnu.org>
;; Keywords: i18n, 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 <https://www.gnu.org/licenses/>.
;;; Commentary:
;; Defines a coding system for UTF-7, defined in RFC 2152. Non-ASCII
;; segments are encoded as base64-encoded big endian UTF-16. Also
;; defines a variation required for IMAP (RFC 2060).
;; The encoding and decoding was originally taken from Jon K Hellan's
;; implementation in Gnus, but has been substantially re-done.
;; This probably needs more attention. In particular, it's not
;; completely consistent with iconv's behavior. It's arguable
;; whether the IMAP version should be a coding system since it's
;; apparently only used for IMAP mailbox names, so it's commented out.
;;; Code:
(defun utf-7-decode (len imap)
"Decode LEN bytes of UTF-7 at point.
IMAP non-nil means use the IMAP version."
(save-excursion
(save-restriction
(narrow-to-region (point) (+ (point) len))
(let ((not-esc (if imap "^&" "^+"))
(skip-chars (if imap "A-Za-z0-9+," "A-Za-z0-9+/")))
(while (not (eobp))
(skip-chars-forward not-esc)
(unless (eobp)
(forward-char)
(let ((p (point))
(run-length (skip-chars-forward skip-chars)))
(if (eq ?- (char-after))
(delete-char 1))
(unless (= run-length 0) ; encoded lone esc-char
(let ((pl (mod (- run-length) 4)))
(insert-char ?= pl)
(if imap
(subst-char-in-region p (point) ?, ?/))
(base64-decode-region p (point)))
(decode-coding-region p (point) 'utf-16be)
(save-excursion
(goto-char p)
(delete-char -1)))))))
(- (point-max) (point-min)))))
;;;###autoload
(defun utf-7-post-read-conversion (len)
(utf-7-decode len nil))
;;;###autoload
(defun utf-7-imap-post-read-conversion (len)
(utf-7-decode len t))
(defun utf-7-encode (from to imap)
"Encode bytes between FROM and TO to UTF-7.
ESC and SKIP-CHARS are adjusted for the normal and IMAP versions."
(let* ((old-buf (current-buffer))
(esc (if imap ?& ?+))
;; These are characters which can be encoded asis.
(skip-chars (if imap
"\t\n\r\x20-\x25\x27-\x7e" ; rfc2060
;; This includes the rfc2152 optional set.
;; Perhaps it shouldn't (like iconv).
"\t\n\r -*,-[]-}"))
(not-skip-chars (format "^%s%c" skip-chars esc)))
(set-buffer (generate-new-buffer " *temp*"))
(if (stringp from)
(insert from)
(insert-buffer-substring old-buf from to))
(goto-char (point-min))
(while (not (eobp))
(skip-chars-forward skip-chars)
(if (eq esc (char-after))
(progn (forward-char)
(insert ?-))
(unless (eobp)
(insert esc)
(let ((p (point)))
(skip-chars-forward not-skip-chars)
(save-restriction
;; encode-coding-region doesn't preserve point
(narrow-to-region p (point))
(encode-coding-region p (point-max) 'utf-16be)
(base64-encode-region p (point-max))
(if imap
(subst-char-in-region p (point-max) ?/ ?,))
(goto-char p)
;; As I read the RFC, this isn't correct, but it's
;; consistent with iconv, at least regarding `='.
(skip-chars-forward "^= \t\n")
(delete-region (point) (point-max))))
;; RFC2060 stipulates that all names MUST end in US-ASCII (i.e.
;; a name that ends with a Unicode octet MUST end with a "-").
(if (or imap (not (eobp)))
(insert ?-)))))
nil))
;;;###autoload
(defun utf-7-pre-write-conversion (from to)
(utf-7-encode from to nil))
;;;###autoload
(defun utf-7-imap-pre-write-conversion (from to)
(utf-7-encode from to t))
(provide 'utf-7)
;;; utf-7.el ends here
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