Function: utf-7-decode

utf-7-decode is a byte-compiled function defined in utf-7.el.gz.

Signature

(utf-7-decode LEN IMAP)

Documentation

Decode LEN bytes of UTF-7 at point.

IMAP non-nil means use the IMAP version.

Source Code

;; Defined in /usr/src/emacs/lisp/international/utf-7.el.gz
;;; utf-7.el --- utf-7 coding system  -*- lexical-binding: t; -*-

;; Copyright (C) 2003-2025 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)))))