;;; rfc2047.el --- functions for encoding and decoding rfc2047 messages

;; Copyright (C) 1998, 1999, 2000, 2002, 2003, 2004,
;;   2005 Free Software Foundation, Inc.

;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
;;	MORIOKA Tomohiko <morioka@jaist.ac.jp>
;; 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 2, 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; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.

;;; Commentary:

;; RFC 2047 is "MIME (Multipurpose Internet Mail Extensions) Part
;; Three:  Message Header Extensions for Non-ASCII Text".

;;; Code:

(eval-when-compile
  (require 'cl)
  (defvar message-posting-charset))

(require 'qp)
(require 'mm-util)
(require 'ietf-drums)
;; Fixme: Avoid this (used for mail-parse-charset) mm dependence on gnus.
(require 'mail-prsvr)
(require 'base64)
(autoload 'mm-body-7-or-8 "mm-bodies")

(defvar rfc2047-header-encoding-alist
  '(("Newsgroups" . nil)
    ("Followup-To" . nil)
    ("Message-ID" . nil)
    ("\\(Resent-\\)?\\(From\\|Cc\\|To\\|Bcc\\|\\(In-\\)?Reply-To\\|Sender\
\\|Mail-Followup-To\\|Mail-Copies-To\\|Approved\\)" . address-mime)
    (t . mime))
  "*Header/encoding method alist.
The list is traversed sequentially.  The keys can either be
header regexps or t.

The values can be:

1) nil, in which case no encoding is done;
2) `mime', in which case the header will be encoded according to RFC2047;
3) `address-mime', like `mime', but takes account of the rules for address
   fields (where quoted strings and comments must be treated separately);
4) a charset, in which case it will be encoded as that charset;
5) `default', in which case the field will be encoded as the rest
   of the article.")

(defvar rfc2047-charset-encoding-alist
  '((us-ascii . nil)
    (iso-8859-1 . Q)
    (iso-8859-2 . Q)
    (iso-8859-3 . Q)
    (iso-8859-4 . Q)
    (iso-8859-5 . B)
    (koi8-r . B)
    (iso-8859-7 . B)
    (iso-8859-8 . B)
    (iso-8859-9 . Q)
    (iso-8859-14 . Q)
    (iso-8859-15 . Q)
    (iso-2022-jp . B)
    (iso-2022-kr . B)
    (gb2312 . B)
    (big5 . B)
    (cn-big5 . B)
    (cn-gb . B)
    (cn-gb-2312 . B)
    (euc-kr . B)
    (iso-2022-jp-2 . B)
    (iso-2022-int-1 . B)
    (viscii . Q))
  "Alist of MIME charsets to RFC2047 encodings.
Valid encodings are nil, `Q' and `B'.  These indicate binary (no) encoding,
quoted-printable and base64 respectively.")

(defvar rfc2047-encode-function-alist
  '((Q . rfc2047-q-encode-string)
    (B . rfc2047-b-encode-string)
    (nil . identity))
  "Alist of RFC2047 encodings to encoding functions.")

(defvar rfc2047-encode-encoded-words t
  "Whether encoded words should be encoded again.")

;;;
;;; Functions for encoding RFC2047 messages
;;;

(defun rfc2047-qp-or-base64 ()
  "Return the type with which to encode the buffer.
This is either `base64' or `quoted-printable'."
  (save-excursion
    (let ((limit (min (point-max) (+ 2000 (point-min))))
	  (n8bit 0))
      (goto-char (point-min))
      (skip-chars-forward "\x20-\x7f\r\n\t" limit)
      (while (< (point) limit)
	(incf n8bit)
	(forward-char 1)
	(skip-chars-forward "\x20-\x7f\r\n\t" limit))
      (if (or (< (* 6 n8bit) (- limit (point-min)))
	      ;; Don't base64, say, a short line with a single
	      ;; non-ASCII char when splitting parts by charset.
	      (= n8bit 1))
	  'quoted-printable
	'base64))))

(defun rfc2047-narrow-to-field ()
  "Narrow the buffer to the header on the current line."
  (beginning-of-line)
  (narrow-to-region
   (point)
   (progn
     (forward-line 1)
     (if (re-search-forward "^[^ \n\t]" nil t)
	 (point-at-bol)
       (point-max))))
  (goto-char (point-min)))

(defun rfc2047-field-value ()
  "Return the value of the field at point."
  (save-excursion
    (save-restriction
      (rfc2047-narrow-to-field)
      (re-search-forward ":[ \t\n]*" nil t)
      (buffer-substring-no-properties (point) (point-max)))))

(defvar rfc2047-encoding-type 'address-mime
  "The type of encoding done by `rfc2047-encode-region'.
This should be dynamically bound around calls to
`rfc2047-encode-region' to either `mime' or `address-mime'.  See
`rfc2047-header-encoding-alist', for definitions.")

(defun rfc2047-encode-message-header ()
  "Encode the message header according to `rfc2047-header-encoding-alist'.
Should be called narrowed to the head of the message."
  (interactive "*")
  (save-excursion
    (goto-char (point-min))
    (let (alist elem method)
      (while (not (eobp))
	(save-restriction
	  (rfc2047-narrow-to-field)
	  (if (not (rfc2047-encodable-p))
	      (prog1
		  (if (and (eq (mm-body-7-or-8) '8bit)
			   (mm-multibyte-p)
			   (mm-coding-system-p
			    (car message-posting-charset)))
		      ;; 8 bit must be decoded.
		      (mm-encode-coding-region
		       (point-min) (point-max)
		       (mm-charset-to-coding-system
			(car message-posting-charset))))
		;; No encoding necessary, but folding is nice
		(when nil
		  (rfc2047-fold-region
		   (save-excursion
		     (goto-char (point-min))
		     (skip-chars-forward "^:")
		     (when (looking-at ": ")
		       (forward-char 2))
		     (point))
		   (point-max))))
	    ;; We found something that may perhaps be encoded.
	    (setq method nil
		  alist rfc2047-header-encoding-alist)
	    (while (setq elem (pop alist))
	      (when (or (and (stringp (car elem))
			     (looking-at (car elem)))
			(eq (car elem) t))
		(setq alist nil
		      method (cdr elem))))
	    (re-search-forward "^[^:]+: *" nil t)
	    (cond
	     ((eq method 'address-mime)
	      (rfc2047-encode-region (point) (point-max)))
	     ((eq method 'mime)
	      (let ((rfc2047-encoding-type 'mime))
		(rfc2047-encode-region (point) (point-max))))
	     ((eq method 'default)
	      (if (and (featurep 'mule)
		       (if (boundp 'default-enable-multibyte-characters)
			   default-enable-multibyte-characters)
		       mail-parse-charset)
		  (mm-encode-coding-region (point) (point-max)
					   mail-parse-charset)))
	     ;; We get this when CC'ing messsages to newsgroups with
	     ;; 8-bit names.  The group name mail copy just got
	     ;; unconditionally encoded.  Previously, it would ask
	     ;; whether to encode, which was quite confusing for the
	     ;; user.  If the new behaviour is wrong, tell me. I have
	     ;; left the old code commented out below.
	     ;; -- Per Abrahamsen <abraham@dina.kvl.dk> Date: 2001-10-07.
	     ;; Modified by Dave Love, with the commented-out code changed
	     ;; in accordance with changes elsewhere.
	     ((null method)
	      (rfc2047-encode-region (point) (point-max)))
;;; 	     ((null method)
;;; 	      (if (or (message-options-get
;;; 		       'rfc2047-encode-message-header-encode-any)
;;; 		      (message-options-set
;;; 		       'rfc2047-encode-message-header-encode-any
;;; 		       (y-or-n-p
;;; 			"Some texts are not encoded. Encode anyway?")))
;;; 		  (rfc2047-encode-region (point-min) (point-max))
;;; 		(error "Cannot send unencoded text")))
	     ((mm-coding-system-p method)
	      (if (and (featurep 'mule)
		       (if (boundp 'default-enable-multibyte-characters)
			   default-enable-multibyte-characters))
		  (mm-encode-coding-region (point) (point-max) method)))
	     ;; Hm.
	     (t)))
	  (goto-char (point-max)))))))

;; Fixme: This, and the require below may not be the Right Thing, but
;; should be safe just before release.  -- fx 2001-02-08
(eval-when-compile (defvar message-posting-charset))

(defun rfc2047-encodable-p ()
  "Return non-nil if any characters in current buffer need encoding in headers.
The buffer may be narrowed."
  (require 'message)			; for message-posting-charset
  (let ((charsets
	 (mm-find-mime-charset-region (point-min) (point-max))))
    (goto-char (point-min))
    (or (and rfc2047-encode-encoded-words
	     (prog1
		 (search-forward "=?" nil t)
	       (goto-char (point-min))))
	(and charsets
	     (not (equal charsets (list (car message-posting-charset))))))))

;; Use this syntax table when parsing into regions that may need
;; encoding.  Double quotes are string delimiters, backslash is
;; character quoting, and all other RFC 2822 special characters are
;; treated as punctuation so we can use forward-sexp/forward-word to
;; skip to the end of regions appropriately.  Nb. ietf-drums does
;; things differently.
(defconst rfc2047-syntax-table
  ;; (make-char-table 'syntax-table '(2)) only works in Emacs.
  (let ((table (make-syntax-table)))
    ;; The following is done to work for setting all elements of the table
    ;; in Emacs 21 and 22 and XEmacs; it appears to be the cleanest way.
    ;; Play safe and don't assume the form of the word syntax entry --
    ;; copy it from ?a.
    (if (fboundp 'set-char-table-range)	; Emacs
	(funcall (intern "set-char-table-range")
		 table t (aref (standard-syntax-table) ?a))
      (if (fboundp 'put-char-table)
	  (if (fboundp 'get-char-table)	; warning avoidance
	      (put-char-table t (get-char-table ?a (standard-syntax-table))
			      table))))
    (modify-syntax-entry ?\\ "\\" table)
    (modify-syntax-entry ?\" "\"" table)
    (modify-syntax-entry ?\( "(" table)
    (modify-syntax-entry ?\) ")" table)
    (modify-syntax-entry ?\< "." table)
    (modify-syntax-entry ?\> "." table)
    (modify-syntax-entry ?\[ "." table)
    (modify-syntax-entry ?\] "." table)
    (modify-syntax-entry ?: "." table)
    (modify-syntax-entry ?\; "." table)
    (modify-syntax-entry ?, "." table)
    (modify-syntax-entry ?@ "." table)
    table))

(defun rfc2047-encode-region (b e)
  "Encode words in region B to E that need encoding.
By default, the region is treated as containing RFC2822 addresses.
Dynamically bind `rfc2047-encoding-type' to change that."
  (save-restriction
    (narrow-to-region b e)
    (let ((encodable-regexp (if rfc2047-encode-encoded-words
				"[^\000-\177]+\\|=\\?"
			      "[^\000-\177]+"))
	  start				; start of current token
	  end begin csyntax
	  ;; Whether there's an encoded word before the current token,
	  ;; either immediately or separated by space.
	  last-encoded
	  (orig-text (buffer-substring-no-properties b e)))
      (if (eq 'mime rfc2047-encoding-type)
	  ;; Simple case.  Continuous words in which all those contain
	  ;; non-ASCII characters are encoded collectively.  Encoding
	  ;; ASCII words, including `Re:' used in Subject headers, is
	  ;; avoided for interoperability with non-MIME clients and
	  ;; for making it easy to find keywords.
	  (progn
	    (goto-char (point-min))
	    (while (progn (skip-chars-forward " \t\n")
			  (not (eobp)))
	      (setq start (point))
	      (while (and (looking-at "[ \t\n]*\\([^ \t\n]+\\)")
			  (progn
			    (setq end (match-end 0))
			    (re-search-forward encodable-regexp end t)))
		(goto-char end))
	      (if (> (point) start)
		  (rfc2047-encode start (point))
		(goto-char end))))
	;; `address-mime' case -- take care of quoted words, comments.
	(with-syntax-table rfc2047-syntax-table
	  (goto-char (point-min))
	  (condition-case err		; in case of unbalanced quotes
	      ;; Look for rfc2822-style: sequences of atoms, quoted
	      ;; strings, specials, whitespace.  (Specials mustn't be
	      ;; encoded.)
	      (while (not (eobp))
		;; Skip whitespace.
		(skip-chars-forward " \t\n")
		(setq start (point))
		(cond
		 ((not (char-after)))	; eob
		 ;; else token start
		 ((eq ?\" (setq csyntax (char-syntax (char-after))))
		  ;; Quoted word.
		  (forward-sexp)
		  (setq end (point))
		  ;; Does it need encoding?
		  (goto-char start)
		  (if (re-search-forward encodable-regexp end 'move)
		      ;; It needs encoding.  Strip the quotes first,
		      ;; since encoded words can't occur in quotes.
		      (progn
			(goto-char end)
			(delete-backward-char 1)
			(goto-char start)
			(delete-char 1)
			(when last-encoded
			  ;; There was a preceding quoted word.  We need
			  ;; to include any separating whitespace in this
			  ;; word to avoid it getting lost.
			  (skip-chars-backward " \t")
			  ;; A space is needed between the encoded words.
			  (insert ? )
			  (setq start (point)
				end (1+ end)))
			;; Adjust the end position for the deleted quotes.
			(rfc2047-encode start (- end 2))
			(setq last-encoded t)) ; record that it was encoded
		    (setq last-encoded  nil)))
		 ((eq ?. csyntax)
		  ;; Skip other delimiters, but record that they've
		  ;; potentially separated quoted words.
		  (forward-char)
		  (setq last-encoded nil))
		 ((eq ?\) csyntax)
		  (error "Unbalanced parentheses"))
		 ((eq ?\( csyntax)
		  ;; Look for the end of parentheses.
		  (forward-list)
		  ;; Encode text as an unstructured field.
		  (let ((rfc2047-encoding-type 'mime))
		    (rfc2047-encode-region (1+ start) (1- (point))))
		  (skip-chars-forward ")"))
		 (t		    ; normal token/whitespace sequence
		  ;; Find the end.
		  ;; Skip one ASCII word, or encode continuous words
		  ;; in which all those contain non-ASCII characters.
		  (setq end nil)
		  (while (not (or end (eobp)))
		    (when (looking-at "[\000-\177]+")
		      (setq begin (point)
			    end (match-end 0))
		      (when (progn
			      (while (and (or (re-search-forward
					       "[ \t\n]\\|\\Sw" end 'move)
					      (setq end nil))
					  (eq ?\\ (char-syntax (char-before))))
				;; Skip backslash-quoted characters.
				(forward-char))
			      end)
			(setq end (match-beginning 0))
			(if rfc2047-encode-encoded-words
			    (progn
			      (goto-char begin)
			      (when (search-forward "=?" end 'move)
				(goto-char (match-beginning 0))
				(setq end nil)))
			  (goto-char end))))
		    ;; Where the value nil of `end' means there may be
		    ;; text to have to be encoded following the point.
		    ;; Otherwise, the point reached to the end of ASCII
		    ;; words separated by whitespace or a special char.
		    (unless end
		      (when (looking-at encodable-regexp)
			(goto-char (setq begin (match-end 0)))
			(while (and (looking-at "[ \t\n]+\\([^ \t\n]+\\)")
				    (setq end (match-end 0))
				    (progn
				      (while (re-search-forward
					      encodable-regexp end t))
				      (< begin (point)))
				    (goto-char begin)
				    (or (not (re-search-forward "\\Sw" end t))
					(progn
					  (goto-char (match-beginning 0))
					  nil)))
			  (goto-char end))
			(when (looking-at "[^ \t\n]+")
			  (setq end (match-end 0))
			  (if (re-search-forward "\\Sw+" end t)
			      ;; There are special characters better
			      ;; to be encoded so that MTAs may parse
			      ;; them safely.
			      (cond ((= end (point)))
				    ((looking-at (concat "\\sw*\\("
							 encodable-regexp
							 "\\)"))
				     (setq end nil))
				    (t
				     (goto-char (1- (match-end 0)))
				     (unless (= (point) (match-beginning 0))
				       ;; Separate encodable text and
				       ;; delimiter.
				       (insert " "))))
			    (goto-char end)
			    (skip-chars-forward " \t\n")
			    (if (and (looking-at "[^ \t\n]+")
				     (string-match encodable-regexp
						   (match-string 0)))
				(setq end nil)
			      (goto-char end)))))))
		  (skip-chars-backward " \t\n")
		  (setq end (point))
		  (goto-char start)
		  (if (re-search-forward encodable-regexp end 'move)
		      (progn
			(unless (memq (char-before start) '(nil ?\t ? ))
			  (if (progn
				(goto-char start)
				(skip-chars-backward "^ \t\n")
				(and (looking-at "\\Sw+")
				     (= (match-end 0) start)))
			      ;; Also encode bogus delimiters.
			      (setq start (point))
			    ;; Separate encodable text and delimiter.
			    (goto-char start)
			    (insert " ")
			    (setq start (1+ start)
				  end (1+ end))))
			(rfc2047-encode start end)
			(setq last-encoded t))
		    (setq last-encoded nil)))))
	    (error
	     (if (or debug-on-quit debug-on-error)
		 (signal (car err) (cdr err))
	       (error "Invalid data for rfc2047 encoding: %s"
		      (mm-replace-in-string orig-text "[ \t\n]+" " "))))))))
    (rfc2047-fold-region b (point))
    (goto-char (point-max))))

(defun rfc2047-encode-string (string)
  "Encode words in STRING.
By default, the string is treated as containing addresses (see
`rfc2047-encoding-type')."
  (mm-with-multibyte-buffer
    (insert string)
    (rfc2047-encode-region (point-min) (point-max))
    (buffer-string)))

(defvar rfc2047-encode-max-chars 76
  "Maximum characters of each header line that contain encoded-words.
If it is nil, encoded-words will not be folded.  Too small value may
cause an error.  Don't change this for no particular reason.")

(defun rfc2047-encode-1 (column string cs encoder start crest tail
				&optional eword)
  "Subroutine used by `rfc2047-encode'."
  (cond ((string-equal string "")
	 (or eword ""))
	((not rfc2047-encode-max-chars)
	 (concat start
		 (funcall encoder (if cs
				      (mm-encode-coding-string string cs)
				    string))
		 "?="))
	((>= column rfc2047-encode-max-chars)
	 (when eword
	   (cond ((string-match "\n[ \t]+\\'" eword)
		  ;; Reomove a superfluous empty line.
		  (setq eword (substring eword 0 (match-beginning 0))))
		 ((string-match "(+\\'" eword)
		  ;; Break the line before the open parenthesis.
		  (setq crest (concat crest (match-string 0 eword))
			eword (substring eword 0 (match-beginning 0))))))
	 (rfc2047-encode-1 (length crest) string cs encoder start " " tail
			   (concat eword "\n" crest)))
	(t
	 (let ((index 0)
	       (limit (1- (length string)))
	       (prev "")
	       next len)
	   (while (and prev
		       (<= index limit))
	     (setq next (concat start
				(funcall encoder
					 (if cs
					     (mm-encode-coding-string
					      (substring string 0 (1+ index))
					      cs)
					   (substring string 0 (1+ index))))
				"?=")
		   len (+ column (length next)))
	     (if (> len rfc2047-encode-max-chars)
		 (setq next prev
		       prev nil)
	       (if (or (< index limit)
		       (<= (+ len (or (string-match "\n" tail)
				      (length tail)))
			   rfc2047-encode-max-chars))
		   (setq prev next
			 index (1+ index))
		 (if (string-match "\\`)+" tail)
		     ;; Break the line after the close parenthesis.
		     (setq tail (concat (substring tail 0 (match-end 0))
					"\n "
					(substring tail (match-end 0)))
			   prev next
			   index (1+ index))
		   (setq next prev
			 prev nil)))))
	   (if (> index limit)
	       (concat eword next tail)
	     (if (= 0 index)
		 (if (and eword
			  (string-match "(+\\'" eword))
		     (setq crest (concat crest (match-string 0 eword))
			   eword (substring eword 0 (match-beginning 0)))
		   (setq eword (concat eword next)))
	       (setq crest " "
		     eword (concat eword next)))
	     (when (string-match "\n[ \t]+\\'" eword)
	       ;; Reomove a superfluous empty line.
	       (setq eword (substring eword 0 (match-beginning 0))))
	     (rfc2047-encode-1 (length crest) (substring string index)
			       cs encoder start " " tail
			       (concat eword "\n" crest)))))))

(defun rfc2047-encode (b e)
  "Encode the word(s) in the region B to E.
Point moves to the end of the region."
  (let ((mime-charset (or (mm-find-mime-charset-region b e) (list 'us-ascii)))
	cs encoding tail crest eword)
    (cond ((> (length mime-charset) 1)
	   (error "Can't rfc2047-encode `%s'"
		  (buffer-substring-no-properties b e)))
	  ((= (length mime-charset) 1)
	   (setq mime-charset (car mime-charset)
		 cs (mm-charset-to-coding-system mime-charset))
	   (unless (and (mm-multibyte-p)
			(mm-coding-system-p cs))
	     (setq cs nil))
	   (save-restriction
	     (narrow-to-region b e)
	     (setq encoding
		   (or (cdr (assq mime-charset
				  rfc2047-charset-encoding-alist))
		       ;; For the charsets that don't have a preferred
		       ;; encoding, choose the one that's shorter.
		       (if (eq (rfc2047-qp-or-base64) 'base64)
			   'B
			 'Q)))
	     (widen)
	     (goto-char e)
	     (skip-chars-forward "^ \t\n")
	     ;; `tail' may contain a close parenthesis.
	     (setq tail (buffer-substring-no-properties e (point)))
	     (goto-char b)
	     (setq b (point-marker)
		   e (set-marker (make-marker) e))
	     (rfc2047-fold-region (point-at-bol) b)
	     (goto-char b)
	     (skip-chars-backward "^ \t\n")
	     (unless (= 0 (skip-chars-backward " \t"))
	       ;; `crest' may contain whitespace and an open parenthesis.
	       (setq crest (buffer-substring-no-properties (point) b)))
	     (setq eword (rfc2047-encode-1
			  (- b (point-at-bol))
			  (mm-replace-in-string
			   (buffer-substring-no-properties b e)
			   "\n\\([ \t]?\\)" "\\1")
			  cs
			  (or (cdr (assq encoding
					 rfc2047-encode-function-alist))
			      'identity)
			  (concat "=?" (downcase (symbol-name mime-charset))
				  "?" (upcase (symbol-name encoding)) "?")
			  (or crest " ")
			  tail))
	     (delete-region (if (eq (aref eword 0) ?\n)
				(if (bolp)
				    ;; The line was folded before encoding.
				    (1- (point))
				  (point))
			      (goto-char b))
			    (+ e (length tail)))
	     ;; `eword' contains `crest' and `tail'.
	     (insert eword)
	     (set-marker b nil)
	     (set-marker e nil)
	     (unless (or (/= 0 (length tail))
			 (eobp)
			 (looking-at "[ \t\n)]"))
	       (insert " "))))
	  (t
	   (goto-char e)))))

(defun rfc2047-fold-field ()
  "Fold the current header field."
  (save-excursion
    (save-restriction
      (rfc2047-narrow-to-field)
      (rfc2047-fold-region (point-min) (point-max)))))

(defun rfc2047-fold-region (b e)
  "Fold long lines in region B to E."
  (save-restriction
    (narrow-to-region b e)
    (goto-char (point-min))
    (let ((break nil)
	  (qword-break nil)
	  (first t)
	  (bol (save-restriction
		 (widen)
		 (point-at-bol))))
      (while (not (eobp))
	(when (and (or break qword-break)
		   (> (- (point) bol) 76))
	  (goto-char (or break qword-break))
	  (setq break nil
		qword-break nil)
	  (skip-chars-backward " \t")
	  (if (looking-at "[ \t]")
	      (insert ?\n)
	    (insert "\n "))
	  (setq bol (1- (point)))
	  ;; Don't break before the first non-LWSP characters.
	  (skip-chars-forward " \t")
	  (unless (eobp)
	    (forward-char 1)))
	(cond
	 ((eq (char-after) ?\n)
	  (forward-char 1)
	  (setq bol (point)
		break nil
		qword-break nil)
	  (skip-chars-forward " \t")
	  (unless (or (eobp) (eq (char-after) ?\n))
	    (forward-char 1)))
	 ((eq (char-after) ?\r)
	  (forward-char 1))
	 ((memq (char-after) '(?  ?\t))
	  (skip-chars-forward " \t")
	  (unless first ;; Don't break just after the header name.
	    (setq break (point))))
	 ((not break)
	  (if (not (looking-at "=\\?[^=]"))
	      (if (eq (char-after) ?=)
		  (forward-char 1)
		(skip-chars-forward "^ \t\n\r="))
	    ;; Don't break at the start of the field.
	    (unless (= (point) b)
	      (setq qword-break (point)))
	    (skip-chars-forward "^ \t\n\r")))
	 (t
	  (skip-chars-forward "^ \t\n\r")))
	(setq first nil))
      (when (and (or break qword-break)
		 (> (- (point) bol) 76))
	(goto-char (or break qword-break))
	(setq break nil
	      qword-break nil)
	(if (or (> 0 (skip-chars-backward " \t"))
		(looking-at "[ \t]"))
	    (insert ?\n)
	  (insert "\n "))
	(setq bol (1- (point)))
	;; Don't break before the first non-LWSP characters.
	(skip-chars-forward " \t")
	(unless (eobp)
	  (forward-char 1))))))

(defun rfc2047-unfold-field ()
  "Fold the current line."
  (save-excursion
    (save-restriction
      (rfc2047-narrow-to-field)
      (rfc2047-unfold-region (point-min) (point-max)))))

(defun rfc2047-unfold-region (b e)
  "Unfold lines in region B to E."
  (save-restriction
    (narrow-to-region b e)
    (goto-char (point-min))
    (let ((bol (save-restriction
		 (widen)
		 (point-at-bol)))
	  (eol (point-at-eol)))
      (forward-line 1)
      (while (not (eobp))
	(if (and (looking-at "[ \t]")
		 (< (- (point-at-eol) bol) 76))
	    (delete-region eol (progn
				 (goto-char eol)
				 (skip-chars-forward "\r\n")
				 (point)))
	  (setq bol (point-at-bol)))
	(setq eol (point-at-eol))
	(forward-line 1)))))

(defun rfc2047-b-encode-string (string)
  "Base64-encode the header contained in STRING."
  (base64-encode-string string t))

(defun rfc2047-q-encode-string (string)
  "Quoted-printable-encode the header in STRING."
  (mm-with-unibyte-buffer
    (insert string)
    (quoted-printable-encode-region
     (point-min) (point-max) nil
     ;; = (\075), _ (\137), ? (\077) are used in the encoded word.
     ;; Avoid using 8bit characters.
     ;; This list excludes `especials' (see the RFC2047 syntax),
     ;; meaning that some characters in non-structured fields will
     ;; get encoded when they con't need to be.  The following is
     ;; what it used to be.
     ;;;  ;; Equivalent to "^\000-\007\011\013\015-\037\200-\377=_?"
     ;;;  "\010\012\014\040-\074\076\100-\136\140-\177")
     "-\b\n\f !#-'*+0-9A-Z\\^`-~\d")
    (subst-char-in-region (point-min) (point-max) ?  ?_)
    (buffer-string)))

(defun rfc2047-encode-parameter (param value)
  "Return and PARAM=VALUE string encoded in the RFC2047-like style.
This is a replacement for the `rfc2231-encode-string' function.

When attaching files as MIME parts, we should use the RFC2231 encoding
to specify the file names containing non-ASCII characters.  However,
many mail softwares don't support it in practice and recipients won't
be able to extract files with correct names.  Instead, the RFC2047-like
encoding is acceptable generally.  This function provides the very
RFC2047-like encoding, resigning to such a regrettable trend.  To use
it, put the following line in your ~/.gnus.el file:

\(defalias 'mail-header-encode-parameter 'rfc2047-encode-parameter)
"
  (let* ((rfc2047-encoding-type 'mime)
	 (rfc2047-encode-max-chars nil)
	 (string (rfc2047-encode-string value)))
    (if (string-match (concat "[" ietf-drums-tspecials "]") string)
	(format "%s=%S" param string)
      (concat param "=" string))))

;;;
;;; Functions for decoding RFC2047 messages
;;;

(eval-and-compile
  (defconst rfc2047-encoded-word-regexp
    "=\\?\\([^][\000-\040()<>@,\;:*\\\"/?.=]+\\)\\(?:\\*[^?]+\\)?\
\\?\\(B\\|Q\\)\\?\\([!->@-~ ]*\\)\\?="))

(defvar rfc2047-quote-decoded-words-containing-tspecials nil
  "If non-nil, quote decoded words containing special characters.")

(defvar rfc2047-allow-incomplete-encoded-text t
  "*Non-nil means allow incomplete encoded-text in successive encoded-words.
Dividing of encoded-text in the place other than character boundaries
violates RFC2047 section 5, while we have a capability to decode it.
If it is non-nil, the decoder will decode B- or Q-encoding in each
encoded-word, concatenate them, and decode it by charset.  Otherwise,
the decoder will fully decode each encoded-word before concatenating
them.")

(defun rfc2047-charset-to-coding-system (charset)
  "Return coding-system corresponding to MIME CHARSET.
If your Emacs implementation can't decode CHARSET, return nil."
  (when (stringp charset)
    (setq charset (intern (downcase charset))))
  (when (or (not charset)
	    (eq 'gnus-all mail-parse-ignored-charsets)
	    (memq 'gnus-all mail-parse-ignored-charsets)
	    (memq charset mail-parse-ignored-charsets))
    (setq charset mail-parse-charset))
  (let ((cs (mm-coding-system-p (mm-charset-to-coding-system charset))))
    (cond ((eq cs 'ascii)
	   (setq cs (or (mm-charset-to-coding-system mail-parse-charset)
			'raw-text)))
	  (cs)
	  ((and charset
		(listp mail-parse-ignored-charsets)
		(memq 'gnus-unknown mail-parse-ignored-charsets))
	   (setq cs (mm-charset-to-coding-system mail-parse-charset))))
    (if (eq cs 'ascii)
	'raw-text
      cs)))

(defun rfc2047-decode-encoded-words (words)
  "Decode successive encoded-words in WORDS and return a decoded string.
Each element of WORDS looks like (CHARSET ENCODING ENCODED-TEXT
ENCODED-WORD)."
  (let (word charset cs encoding text rest)
    (while words
      (setq word (pop words))
      (if (and (or (setq cs (rfc2047-charset-to-coding-system
			     (setq charset (car word))))
		   (progn
		     (message "Unknown charset: %s" charset)
		     nil))
	       (condition-case code
		   (cond ((char-equal ?B (nth 1 word))
			  (setq text (base64-decode-string
				      (rfc2047-pad-base64 (nth 2 word)))))
			 ((char-equal ?Q (nth 1 word))
			  (setq text (quoted-printable-decode-string
				      (mm-subst-char-in-string
				       ?_ ?  (nth 2 word) t)))))
		 (error
		  (message "%s" (error-message-string code))
		  nil)))
	  (if (and rfc2047-allow-incomplete-encoded-text
		   (eq cs (caar rest)))
	      ;; Concatenate text of which the charset is the same.
	      (setcdr (car rest) (concat (cdar rest) text))
	    (push (cons cs text) rest))
	;; Don't decode encoded-word.
	(push (cons nil (nth 3 word)) rest)))
    (while rest
      (setq words (concat
		   (or (and (setq cs (caar rest))
			    (condition-case code
				(mm-decode-coding-string (cdar rest) cs)
			      (error
			       (message "%s" (error-message-string code))
			       nil)))
		       (concat (when (cdr rest) " ")
			       (cdar rest)
			       (when (and words
					  (not (eq (string-to-char words) ? )))
				 " ")))
		   words)
	    rest (cdr rest)))
    words))

;; Fixme: This should decode in place, not cons intermediate strings.
;; Also check whether it needs to worry about delimiting fields like
;; encoding.

;; In fact it's reported that (invalid) encoding of mailboxes in
;; addr-specs is in use, so delimiting fields might help.  Probably
;; not decoding a word which isn't properly delimited is good enough
;; and worthwhile (is it more correct or not?), e.g. something like
;; `=?iso-8859-1?q?foo?=@'.

(defun rfc2047-decode-region (start end)
  "Decode MIME-encoded words in region between START and END."
  (interactive "r")
  (let ((case-fold-search t)
	(eword-regexp (eval-when-compile
			;; Ignore whitespace between encoded-words.
			(concat "[\n\t ]*\\(" rfc2047-encoded-word-regexp
				"\\)")))
	b e match words)
    (save-excursion
      (save-restriction
	(narrow-to-region start end)
	(goto-char (setq b start))
	;; Look for the encoded-words.
	(while (setq match (re-search-forward eword-regexp nil t))
	  (setq e (match-beginning 1)
		end (match-end 0)
		words nil)
	  (while match
	    (push (list (match-string 2) ;; charset
			(char-after (match-beginning 3)) ;; encoding
			(match-string 4) ;; encoded-text
			(match-string 1)) ;; encoded-word
		  words)
	    ;; Look for the subsequent encoded-words.
	    (when (setq match (looking-at eword-regexp))
	      (goto-char (setq end (match-end 0)))))
	  ;; Replace the encoded-words with the decoded one.
	  (delete-region e end)
	  (insert (rfc2047-decode-encoded-words (nreverse words)))
	  (save-restriction
	    (narrow-to-region e (point))
	    (goto-char e)
	    ;; Remove newlines between decoded words, though such
	    ;; things essentially must not be there.
	    (while (re-search-forward "[\n\r]+" nil t)
	      (replace-match " "))
	    ;; Quote decoded words if there are special characters
	    ;; which might violate RFC2822.
	    (when (and rfc2047-quote-decoded-words-containing-tspecials
		       (let ((regexp (car (rassq
					   'address-mime
					   rfc2047-header-encoding-alist))))
			 (when regexp
			   (save-restriction
			     (widen)
			     (beginning-of-line)
			     (while (and (memq (char-after) '(?  ?\t))
					 (zerop (forward-line -1))))
			     (looking-at regexp)))))
	      (let (quoted)
		(goto-char e)
		(skip-chars-forward " \t")
		(setq start (point))
		(setq quoted (eq (char-after) ?\"))
		(goto-char (point-max))
		(skip-chars-backward " \t")
		(if (setq quoted (and quoted
				      (> (point) (1+ start))
				      (eq (char-before) ?\")))
		    (progn
		      (backward-char)
		      (setq start (1+ start)
			    end (point-marker)))
		  (setq end (point-marker)))
		(goto-char start)
		(while (search-forward "\"" end t)
		  (when (prog2
			    (backward-char)
			    (zerop (% (skip-chars-backward "\\\\") 2))
			  (goto-char (match-beginning 0)))
		    (insert "\\"))
		  (forward-char))
		(when (and (not quoted)
			   (progn
			     (goto-char start)
			     (re-search-forward
			      (concat "[" ietf-drums-tspecials "]")
			      end t)))
		  (goto-char start)
		  (insert "\"")
		  (goto-char end)
		  (insert "\""))
		(set-marker end nil)))
	    (goto-char (point-max)))
	  (when (and (mm-multibyte-p)
		     mail-parse-charset
		     (not (eq mail-parse-charset 'us-ascii))
		     (not (eq mail-parse-charset 'gnus-decoded)))
	    (mm-decode-coding-region b e mail-parse-charset))
	  (setq b (point)))
	(when (and (mm-multibyte-p)
		   mail-parse-charset
		   (not (eq mail-parse-charset 'us-ascii))
		   (not (eq mail-parse-charset 'gnus-decoded)))
	  (mm-decode-coding-region b (point-max) mail-parse-charset))))))

(defun rfc2047-decode-string (string)
  "Decode the quoted-printable-encoded STRING and return the results."
  (let ((m (mm-multibyte-p)))
    (if (string-match "=\\?" string)
	(with-temp-buffer
	  ;; Fixme: This logic is wrong, but seems to be required by
	  ;; Gnus summary buffer generation.  The value of `m' depends
	  ;; on the current buffer, not global multibyteness or that
	  ;; of the string.  Also the string returned should always be
	  ;; multibyte in a multibyte session, i.e. the buffer should
	  ;; be multibyte before `buffer-string' is called.
	  (when m
	    (mm-enable-multibyte))
	  (insert string)
	  (inline
	    (rfc2047-decode-region (point-min) (point-max)))
	  (buffer-string))
      ;; Fixme: As above, `m' here is inappropriate.
      (if (and m
	       mail-parse-charset
	       (not (eq mail-parse-charset 'us-ascii))
	       (not (eq mail-parse-charset 'gnus-decoded)))
	  ;; `decode-coding-string' in Emacs offers a third optional
	  ;; arg NOCOPY to avoid consing a new string if the decoding
	  ;; is "trivial".  Unfortunately it currently doesn't
	  ;; consider anything else than a `nil' coding system
	  ;; trivial.
	  ;; `rfc2047-decode-string' is called multiple times for each
	  ;; article during summary buffer generation, and we really
	  ;; want to avoid unnecessary consing.  So we bypass
	  ;; `decode-coding-string' if the string is purely ASCII.
	  (if (and (fboundp 'detect-coding-string)
		   ;; string is purely ASCII
		   (eq (detect-coding-string string t) 'undecided))
	      string
	    (mm-decode-coding-string string mail-parse-charset))
	(mm-string-as-multibyte string)))))

(defun rfc2047-pad-base64 (string)
  "Pad STRING to quartets."
  ;; Be more liberal to accept buggy base64 strings. If
  ;; base64-decode-string accepts buggy strings, this function could
  ;; be aliased to identity.
  (if (= 0 (mod (length string) 4))
      string
    (when (string-match "=+$" string)
      (setq string (substring string 0 (match-beginning 0))))
    (case (mod (length string) 4)
      (0 string)
      (1 string) ;; Error, don't pad it.
      (2 (concat string "=="))
      (3 (concat string "=")))))

(provide 'rfc2047)

;;; arch-tag: a07fe3d4-22b5-4c4a-bd89-b1f82d5d36f6
;;; rfc2047.el ends here