[bpt/emacs.git] / lisp / gnus / utf7.el

;;; utf7.el --- UTF-7 encoding/decoding for Emacs   -*-coding: utf-8;-*-

;; Copyright (C) 1999-2013 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
Commit	Line	Data
c38e0c97	1	;;; utf7.el --- UTF-7 encoding/decoding for Emacs --coding: utf-8;--
e84b4b86	2
ab422c4d	3	;; Copyright (C) 1999-2013 Free Software Foundation, Inc.
c113de23 GM	4
c113de23 GM	5	;; Author: Jon K Hellan <hellan@acm.org>
23f87bed	6	;; Maintainer: bugs@gnus.org
c113de23 GM	7	;; Keywords: mail
	8
	9	;; This file is part of GNU Emacs.
	10
5e809f55	11	;; GNU Emacs is free software: you can redistribute it and/or modify
c113de23	12	;; it under the terms of the GNU General Public License as published by
5e809f55 GM	13	;; the Free Software Foundation, either version 3 of the License, or
5e809f55 GM	14	;; (at your option) any later version.
c113de23 GM	15
	16	;; GNU Emacs is distributed in the hope that it will be useful,
	17	;; but WITHOUT ANY WARRANTY; without even the implied warranty of
	18	;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	19	;; GNU General Public License for more details.
	20
	21	;; You should have received a copy of the GNU General Public License
5e809f55	22	;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>.
c113de23 GM	23
c113de23 GM	24	;;; Commentary:
23f87bed MB	25
	26	;; UTF-7 - A Mail-Safe Transformation Format of Unicode - RFC 2152
	27	;; This is a transformation format of Unicode that contains only 7-bit
	28	;; ASCII octets and is intended to be readable by humans in the limiting
	29	;; case that the document consists of characters from the US-ASCII
	30	;; repertoire.
	31	;; In short, runs of characters outside US-ASCII are encoded as base64
	32	;; inside delimiters.
	33	;; A variation of UTF-7 is specified in IMAP 4rev1 (RFC 2060) as the way
	34	;; to represent characters outside US-ASCII in mailbox names in IMAP.
	35	;; This library supports both variants, but the IMAP variation was the
	36	;; reason I wrote it.
	37	;; The routines convert UTF-7 -> UTF-16 (16 bit encoding of Unicode)
	38	;; -> current character set, and vice versa.
	39	;; However, until Emacs supports Unicode, the only Emacs character set
	40	;; supported here is ISO-8859.1, which can trivially be converted to/from
	41	;; Unicode.
	42	;; When decoding results in a character outside the Emacs character set,
	43	;; an error is thrown. It is up to the application to recover.
	44
	45	;; UTF-7 should be done by providing a coding system. Mule-UCS does
	46	;; already, but I don't know if it does the IMAP version and it's not
	47	;; clear whether that should really be a coding system. The UTF-16
	48	;; part of the conversion can be done with coding systems available
	49	;; with Mule-UCS or some versions of Emacs. Unfortunately these were
	50	;; done wrongly (regarding handling of byte-order marks and how the
	51	;; variants were named), so we don't have a consistent name for the
	52	;; necessary coding system. The code below doesn't seem to DTRT
	53	;; generally. E.g.:
	54	;;
c38e0c97	55	;; (utf7-encode "a+£")
23f87bed MB	56	;; => "a+ACsAow-"
23f87bed MB	57	;;
c38e0c97	58	;; $ echo "a+£"\|iconv -f utf-8 -t utf-7
23f87bed MB	59	;; a+-+AKM
23f87bed MB	60	;;
bf247b6e	61	;; -- fx
23f87bed	62
c113de23 GM	63
	64	;;; Code:
	65
	66	(require 'base64)
5ce3df57	67	(eval-when-compile (require 'cl))
23f87bed	68	(require 'mm-util)
c113de23	69
23f87bed	70	(defconst utf7-direct-encoding-chars " -%'-*,-[]-}"
c113de23 GM	71	"Character ranges which do not need escaping in UTF-7.")
c113de23 GM	72
23f87bed	73	(defconst utf7-imap-direct-encoding-chars
c113de23 GM	74	(concat utf7-direct-encoding-chars "+\\~")
	75	"Character ranges which do not need escaping in the IMAP variant of UTF-7.")
	76
23f87bed MB	77	(defconst utf7-utf-16-coding-system
	78	(cond ((mm-coding-system-p 'utf-16-be-no-signature) ; Mule-UCS
	79	'utf-16-be-no-signature)
0c43b6f8	80	((and (mm-coding-system-p 'utf-16-be) ; Emacs
23f87bed MB	81	;; Avoid versions with BOM.
	82	(= 2 (length (encode-coding-string "a" 'utf-16-be))))
	83	'utf-16-be)
	84	((mm-coding-system-p 'utf-16-be-nosig) ; ?
	85	'utf-16-be-nosig))
	86	"Coding system which encodes big endian UTF-16 without a BOM signature.")
	87
c113de23 GM	88	(defsubst utf7-imap-get-pad-length (len modulus)
	89	"Return required length of padding for IMAP modified base64 fragment."
	90	(mod (- len) modulus))
	91
	92	(defun utf7-encode-internal (&optional for-imap)
	93	"Encode text in (temporary) buffer as UTF-7.
	94	Use IMAP modification if FOR-IMAP is non-nil."
	95	(let ((start (point-min))
	96	(end (point-max)))
	97	(narrow-to-region start end)
	98	(goto-char start)
23f87bed MB	99	(let* ((esc-char (if for-imap ?& ?+))
	100	(direct-encoding-chars
	101	(if for-imap utf7-imap-direct-encoding-chars
	102	utf7-direct-encoding-chars))
	103	(not-direct-encoding-chars (concat "^" direct-encoding-chars)))
c113de23 GM	104	(while (not (eobp))
	105	(skip-chars-forward direct-encoding-chars)
	106	(unless (eobp)
	107	(insert esc-char)
	108	(let ((p (point))
	109	(fc (following-char))
	110	(run-length
23f87bed	111	(skip-chars-forward not-direct-encoding-chars)))
c113de23 GM	112	(if (and (= fc esc-char)
c113de23 GM	113	(= run-length 1)) ; Lone esc-char?
d355a0b7	114	(delete-char -1) ; Now there's one too many
c113de23 GM	115	(utf7-fragment-encode p (point) for-imap))
	116	(insert "-")))))))
	117
	118	(defun utf7-fragment-encode (start end &optional for-imap)
	119	"Encode text from START to END in buffer as UTF-7 escape fragment.
	120	Use IMAP modification if FOR-IMAP is non-nil."
	121	(save-restriction
	122	(narrow-to-region start end)
	123	(funcall (utf7-get-u16char-converter 'to-utf-16))
23f87bed MB	124	(mm-with-unibyte-current-buffer
23f87bed MB	125	(base64-encode-region start (point-max)))
c113de23 GM	126	(goto-char start)
	127	(let ((pm (point-max)))
	128	(when for-imap
	129	(while (search-forward "/" nil t)
	130	(replace-match ",")))
	131	(skip-chars-forward "^= \t\n" pm)
	132	(delete-region (point) pm))))
	133
	134	(defun utf7-decode-internal (&optional for-imap)
	135	"Decode UTF-7 text in (temporary) buffer.
	136	Use IMAP modification if FOR-IMAP is non-nil."
	137	(let ((start (point-min))
	138	(end (point-max)))
	139	(goto-char start)
	140	(let* ((esc-pattern (concat "^" (char-to-string (if for-imap ?& ?+))))
	141	(base64-chars (concat "A-Za-z0-9+"
	142	(char-to-string (if for-imap ?, ?/)))))
	143	(while (not (eobp))
	144	(skip-chars-forward esc-pattern)
	145	(unless (eobp)
	146	(forward-char)
	147	(let ((p (point))
	148	(run-length (skip-chars-forward base64-chars)))
	149	(when (and (not (eobp)) (= (following-char) ?-))
	150	(delete-char 1))
	151	(unless (= run-length 0) ; Encoded lone esc-char?
	152	(save-excursion
	153	(utf7-fragment-decode p (point) for-imap)
	154	(goto-char p)
d355a0b7	155	(delete-char -1)))))))))
c113de23 GM	156
	157	(defun utf7-fragment-decode (start end &optional for-imap)
	158	"Decode base64 encoded fragment from START to END of UTF-7 text in buffer.
	159	Use IMAP modification if FOR-IMAP is non-nil."
	160	(save-restriction
	161	(narrow-to-region start end)
	162	(when for-imap
	163	(goto-char start)
	164	(while (search-forward "," nil 'move-to-end) (replace-match "/")))
	165	(let ((pl (utf7-imap-get-pad-length (- end start) 4)))
	166	(insert (make-string pl ?=))
	167	(base64-decode-region start (+ end pl)))
	168	(funcall (utf7-get-u16char-converter 'from-utf-16))))
	169
	170	(defun utf7-get-u16char-converter (which-way)
	171	"Return a function to convert between UTF-16 and current character set."
23f87bed MB	172	(if utf7-utf-16-coding-system
	173	(if (eq which-way 'to-utf-16)
	174	(lambda ()
	175	(encode-coding-region (point-min) (point-max)
	176	utf7-utf-16-coding-system))
	177	(lambda ()
	178	(decode-coding-region (point-min) (point-max)
	179	utf7-utf-16-coding-system)))
	180	;; Add test to check if we are really Latin-1.
	181	(if (eq which-way 'to-utf-16)
	182	'utf7-latin1-u16-char-converter
	183	'utf7-u16-latin1-char-converter)))
c113de23 GM	184
	185	(defun utf7-latin1-u16-char-converter ()
	186	"Convert latin 1 (ISO-8859.1) characters to 16 bit Unicode.
	187	Characters are converted to raw byte pairs in narrowed buffer."
23f87bed MB	188	(mm-encode-coding-region (point-min) (point-max) 'iso-8859-1)
23f87bed MB	189	(mm-disable-multibyte)
c113de23 GM	190	(goto-char (point-min))
	191	(while (not (eobp))
	192	(insert 0)
	193	(forward-char)))
	194
	195	(defun utf7-u16-latin1-char-converter ()
	196	"Convert 16 bit Unicode characters to latin 1 (ISO-8859.1).
	197	Characters are in raw byte pairs in narrowed buffer."
	198	(goto-char (point-min))
	199	(while (not (eobp))
	200	(if (= 0 (following-char))
	201	(delete-char 1)
	202	(error "Unable to convert from Unicode"))
23f87bed MB	203	(forward-char))
	204	(mm-decode-coding-region (point-min) (point-max) 'iso-8859-1)
	205	(mm-enable-multibyte))
c113de23	206
20a673b2	207	;;;###autoload
c113de23 GM	208	(defun utf7-encode (string &optional for-imap)
c113de23 GM	209	"Encode UTF-7 STRING. Use IMAP modification if FOR-IMAP is non-nil."
f21470ef RS	210	(if (and (coding-system-p 'utf-7) (coding-system-p 'utf-7-imap))
	211	;; Emacs 23 with proper support for IMAP
	212	(encode-coding-string string (if for-imap 'utf-7-imap 'utf-7))
5f3710a2 GM	213	(mm-with-multibyte-buffer
	214	(insert string)
	215	(utf7-encode-internal for-imap)
	216	(buffer-string))))
c113de23 GM	217
	218	(defun utf7-decode (string &optional for-imap)
	219	"Decode UTF-7 STRING. Use IMAP modification if FOR-IMAP is non-nil."
f21470ef RS	220	(if (and (coding-system-p 'utf-7) (coding-system-p 'utf-7-imap))
	221	;; Emacs 23 with proper support for IMAP
	222	(decode-coding-string string (if for-imap 'utf-7-imap 'utf-7))
5f3710a2 GM	223	(mm-with-unibyte-buffer
	224	(insert string)
	225	(utf7-decode-internal for-imap)
	226	(mm-enable-multibyte)
	227	(buffer-string))))
c113de23 GM	228
	229	(provide 'utf7)
	230
	231	;;; utf7.el ends here