130 lines
4.2 KiB
EmacsLisp
130 lines
4.2 KiB
EmacsLisp
;;; utf-7.el --- utf-7 coding system -*- lexical-binding: t; -*-
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;; Copyright (C) 2003-2024 Free Software Foundation, Inc.
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;; Author: Dave Love <fx@gnu.org>
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;; Keywords: i18n, mail
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;; This file is part of GNU Emacs.
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;; GNU Emacs is free software: you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation, either version 3 of the License, or
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;; (at your option) any later version.
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;; GNU Emacs is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;; You should have received a copy of the GNU General Public License
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;; along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>.
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;;; Commentary:
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;; Defines a coding system for UTF-7, defined in RFC 2152. Non-ASCII
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;; segments are encoded as base64-encoded big endian UTF-16. Also
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;; defines a variation required for IMAP (RFC 2060).
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;; The encoding and decoding was originally taken from Jon K Hellan's
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;; implementation in Gnus, but has been substantially re-done.
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;; This probably needs more attention. In particular, it's not
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;; completely consistent with iconv's behavior. It's arguable
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;; whether the IMAP version should be a coding system since it's
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;; apparently only used for IMAP mailbox names, so it's commented out.
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;;; Code:
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(defun utf-7-decode (len imap)
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"Decode LEN bytes of UTF-7 at point.
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IMAP non-nil means use the IMAP version."
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(save-excursion
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(save-restriction
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(narrow-to-region (point) (+ (point) len))
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(let ((not-esc (if imap "^&" "^+"))
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(skip-chars (if imap "A-Za-z0-9+," "A-Za-z0-9+/")))
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(while (not (eobp))
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(skip-chars-forward not-esc)
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(unless (eobp)
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(forward-char)
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(let ((p (point))
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(run-length (skip-chars-forward skip-chars)))
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(if (eq ?- (char-after))
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(delete-char 1))
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(unless (= run-length 0) ; encoded lone esc-char
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(let ((pl (mod (- run-length) 4)))
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(insert-char ?= pl)
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(if imap
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(subst-char-in-region p (point) ?, ?/))
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(base64-decode-region p (point)))
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(decode-coding-region p (point) 'utf-16be)
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(save-excursion
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(goto-char p)
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(delete-char -1)))))))
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(- (point-max) (point-min)))))
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;;;###autoload
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(defun utf-7-post-read-conversion (len)
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(utf-7-decode len nil))
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;;;###autoload
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(defun utf-7-imap-post-read-conversion (len)
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(utf-7-decode len t))
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(defun utf-7-encode (from to imap)
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"Encode bytes between FROM and TO to UTF-7.
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ESC and SKIP-CHARS are adjusted for the normal and IMAP versions."
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(let* ((old-buf (current-buffer))
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(esc (if imap ?& ?+))
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;; These are characters which can be encoded asis.
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(skip-chars (if imap
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"\t\n\r\x20-\x25\x27-\x7e" ; rfc2060
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;; This includes the rfc2152 optional set.
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;; Perhaps it shouldn't (like iconv).
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"\t\n\r -*,-[]-}"))
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(not-skip-chars (format "^%s%c" skip-chars esc)))
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(set-buffer (generate-new-buffer " *temp*"))
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(if (stringp from)
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(insert from)
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(insert-buffer-substring old-buf from to))
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(goto-char (point-min))
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(while (not (eobp))
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(skip-chars-forward skip-chars)
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(if (eq esc (char-after))
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(progn (forward-char)
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(insert ?-))
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(unless (eobp)
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(insert esc)
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(let ((p (point)))
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(skip-chars-forward not-skip-chars)
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(save-restriction
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;; encode-coding-region doesn't preserve point
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(narrow-to-region p (point))
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(encode-coding-region p (point-max) 'utf-16be)
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(base64-encode-region p (point-max))
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(if imap
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(subst-char-in-region p (point-max) ?/ ?,))
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(goto-char p)
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;; As I read the RFC, this isn't correct, but it's
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;; consistent with iconv, at least regarding `='.
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(skip-chars-forward "^= \t\n")
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(delete-region (point) (point-max))))
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;; RFC2060 stipulates that all names MUST end in US-ASCII (i.e.
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;; a name that ends with a Unicode octet MUST end with a "-").
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(if (or imap (not (eobp)))
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(insert ?-)))))
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nil))
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;;;###autoload
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(defun utf-7-pre-write-conversion (from to)
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(utf-7-encode from to nil))
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;;;###autoload
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(defun utf-7-imap-pre-write-conversion (from to)
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(utf-7-encode from to t))
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(provide 'utf-7)
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;;; utf-7.el ends here
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