emacs/lisp/mail/mail-utils.el

;;; mail-utils.el --- utility functions used both by rmail and rnews  -*- lexical-binding: t -*-

;; Copyright (C) 1985, 2001-2025 Free Software Foundation, Inc.

;; Maintainer: emacs-devel@gnu.org
;; Keywords: mail, news

;; 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:

;; Utility functions for mail and netnews handling.  These handle fine
;; points of header parsing.

;;; Code:

;;;###autoload
(defcustom mail-use-rfc822 nil
  "If non-nil, use a full, hairy RFC 822 (or later) parser on mail addresses.
Otherwise, (the default) use a smaller, somewhat faster, and
often correct parser."
  :type 'boolean
  :group 'mail)

;;;###autoload
(defcustom mail-dont-reply-to-names nil
  "Regexp specifying addresses to prune from a reply message.
If this is nil, it is set the first time you compose a reply, to
a value which excludes your own email address.

Matching addresses are excluded from the Cc field in replies, and
also the To field, unless this would leave an empty To field."
  :type '(choice regexp (const :tag "Your Name" nil))
  :group 'mail)

(defun mail--wrap-re-regexp (re)
  (concat "\\`[ \t]*"
          "\\("
          re
          ; Re(1) or Re[1] or Re^1
          "\\(([0-9]+)\\|\\[[0-9]+\\]\\|\\^[0-9]+\\)?"
          ; SPC/NBSP followed by various colon variants and TAB/SPC
          " ?\u00a0*"
          "[" password-colon-equivalents "]"
          "[ \t]*"
          ; Handle repetition, eg "Re[1]: Re[2]:"
          "\\)*"
          "[ \t]*"))

;;;###autoload
(defcustom mail-re-regexps
  '("RE" "R\u00c9\\.?" "FWD?" "رد" "回复" "回覆" "SV" "Antw\\.?"
  "VS" "REF" "AW" "ΑΠ" "ΣΧΕΤ" "השב" "Vá" "R" "RIF" "BLS" "RES"
  "Odp" "YNT" "ATB")
  "List of localized \"Re\" abbreviations in various languages.
Each component can be a regular expression or a simple string.  Matching
is done case-insensitively.  Used to initialize the legacy
`rmail-re-abbrevs' and `message-subject-re-regexp' user options."
  :type '(repeat regexp)
  :set (lambda (sym val)
         (custom-set-default sym val)
         (dolist (sym '(rmail-re-abbrevs
                        message-subject-re-regexp))
           (when (get sym 'standard-value)
             (custom-reevaluate-setting sym))))
  :group 'mail
  :version "31.1")

(defvar epa-inhibit)
;; Returns t if file FILE is an Rmail file.
;;;###autoload
(defun mail-file-babyl-p (file)
  "Return non-nil if FILE is a Babyl file."
  (let ((epa-inhibit t))
    (with-temp-buffer
      (insert-file-contents file nil 0 100)
      (looking-at "BABYL OPTIONS:"))))

(defun mail-string-delete (string start end)
  "Return a string containing all of STRING except the part
from START (inclusive) to END (exclusive)."
  (declare (obsolete substring "29.1"))
  (if (null end) (substring string 0 start)
    (concat (substring string 0 start)
	    (substring string end nil))))

;;;###autoload
(defun mail-quote-printable (string &optional wrapper)
  "Convert a string to the \"quoted printable\" Q encoding if necessary.
If the string contains only ASCII characters and no troublesome ones,
we return it unconverted.

If the optional argument WRAPPER is non-nil,
we add the wrapper characters =?ISO-8859-1?Q?....?=."
  (let ((i 0) (result ""))
    (save-match-data
      (while (or (string-match "[?=\"]" string i)
		 (string-match "[^\000-\177]" string i))
	(setq result
	      (concat result (substring string i (match-beginning 0))
		      (upcase (format "=%02x"
				      (aref string (match-beginning 0))))))
	(setq i (match-end 0)))
      (if wrapper
	  (concat "=?ISO-8859-1?Q?"
		  result (substring string i)
		  "?=")
	(concat result (substring string i))))))

;;;###autoload
(defun mail-quote-printable-region (beg end &optional wrapper)
  "Convert the region to the \"quoted printable\" Q encoding.
If the optional argument WRAPPER is non-nil,
we add the wrapper characters =?ISO-8859-1?Q?....?=."
  (interactive "r\nP")
  (save-match-data
    (save-excursion
      (goto-char beg)
      (save-restriction
	(narrow-to-region beg end)
	(while (re-search-forward "[?=\"\200-\377]" nil t)
	  (replace-match (upcase (format "=%02x" (preceding-char)))
			 t t))
	(when wrapper
	  (goto-char beg)
	  (insert "=?ISO-8859-1?Q?")
	  (goto-char end)
	  (insert "?="))))))

(defun mail-unquote-printable-hexdigit (char)
  (setq char (upcase char))
  (if (>= char ?A)
      (+ (- char ?A) 10)
    (- char ?0)))

;;;###autoload
(defun mail-unquote-printable (string &optional wrapper)
  "Undo the \"quoted printable\" encoding.
If the optional argument WRAPPER is non-nil,
we expect to find and remove the wrapper characters =?ISO-8859-1?Q?....?=."
  (save-match-data
    (and wrapper
	 (string-match "\\`=\\?ISO-8859-1\\?Q\\?\\([^?]*\\)\\?" string)
	 (setq string (match-string 1 string)))
    (let ((i 0) strings)
      (while (string-match "=\\(..\\|\n\\)" string i)
	(setq strings (cons (substring string i (match-beginning 0)) strings))
	(unless (= (aref string (match-beginning 1)) ?\n)
	  (setq strings
		(cons (make-string 1
				   (+ (* 16 (mail-unquote-printable-hexdigit
					     (aref string (match-beginning 1))))
				      (mail-unquote-printable-hexdigit
				       (aref string (1+ (match-beginning 1))))))
		      strings)))
	(setq i (match-end 0)))
      (apply #'concat (nreverse (cons (substring string i) strings))))))

;; FIXME Gnus for some reason has `quoted-printable-decode-region' in qp.el.
;;;###autoload
(defun mail-unquote-printable-region (beg end &optional wrapper noerror
					  unibyte)
  "Undo the \"quoted printable\" encoding in buffer from BEG to END.
If the optional argument WRAPPER is non-nil,
we expect to find and remove the wrapper characters =?ISO-8859-1?Q?....?=.
On encountering malformed quoted-printable text, exits with an error,
unless NOERROR is non-nil, in which case it continues, and returns nil
when finished.  Returns non-nil on successful completion.
If UNIBYTE is non-nil, insert converted characters as unibyte.
That is useful if you are going to character code decoding afterward,
as Rmail does."
  ;; FIXME: `unibyte' should always be non-nil, and the iso-latin-1
  ;; specific handling should be removed (or moved elsewhere and generalized).
  (interactive "r\nP")
  (let (failed)
    (save-match-data
      (save-excursion
	(save-restriction
	  (narrow-to-region beg end)
	  (goto-char (point-min))
	  (when (and wrapper
		     (looking-at "\\`=\\?ISO-8859-1\\?Q\\?\\([^?]*\\)\\?"))
	    (delete-region (match-end 1) end)
	    (delete-region (point) (match-beginning 1)))
	  (while (re-search-forward "=\\(\\([0-9A-F][0-9A-F]\\)\\|[=\n]\\|..\\)" nil t)
	    (goto-char (match-end 0))
	    (cond ((= (char-after (match-beginning 1)) ?\n)
		   (replace-match ""))
		  ((= (char-after (match-beginning 1)) ?=)
		   (replace-match "="))
		  ((match-beginning 2)
		   (let ((char (+ (* 16 (mail-unquote-printable-hexdigit
					 (char-after (match-beginning 2))))
				  (mail-unquote-printable-hexdigit
				   (char-after (1+ (match-beginning 2)))))))
		     (if unibyte
			 (progn
			   (replace-match "")
			   ;; insert-byte will insert this as a
			   ;; corresponding eight-bit character.
			   (insert-byte char 1))
		       (replace-match (make-string 1 char) t t))))
		  (noerror
		   (setq failed t))
		  (t
		   (error "Malformed MIME quoted-printable message"))))
	  (not failed))))))

(autoload 'rfc822-addresses "rfc822")

(defun mail-strip-quoted-names (address)
  "Delete comments and quoted strings in an address list ADDRESS.
Also delete leading/trailing whitespace and replace FOO <BAR> with just BAR.
Return a modified address list."
  (when address
    (if mail-use-rfc822
	(mapconcat #'identity (rfc822-addresses address) ", ")
      (let (pos)

        ;; Strip comments.
        (while (setq pos (string-match
                          "[ \t]*(\\([^()\\]\\|\\\\.\\|\\\\\n\\)*)"
                          address))
          (setq address (replace-match "" nil nil address 0)))

        ;; strip surrounding whitespace
        (string-match "\\`[ \t\n]*" address)
        (setq address (substring address
                                 (match-end 0)
                                 (string-match "[ \t\n]*\\'" address
                                               (match-end 0))))

        ;; strip `quoted' names (This is supposed to hack `"Foo Bar" <bar@host>')
        (setq pos 0)
        (while (setq pos (string-match
                          "\\([ \t]?\\)\\([ \t]*\"\\([^\"\\]\\|\\\\.\\|\\\\\n\\)*\"[ \t\n]*\\)"
			  address pos))
          ;; If the next thing is "@", we have "foo bar"@host.  Leave it.
          (if (and (> (length address) (match-end 0))
                   (= (aref address (match-end 0)) ?@))
              (setq pos (match-end 0))
            ;; Otherwise discard the "..." part.
            (setq address (replace-match "" nil nil address 2))))
        ;; If this address contains <...>, replace it with just
        ;; the part between the <...>.
        (while (setq pos (string-match "\\(,\\s-*\\|\\`\\)\\([^,]*<\\([^>,:]*\\)>[^,]*\\)\\(\\s-*,\\|\\'\\)"
                                       address))
          (setq address (replace-match (match-string 3 address)
                                       nil 'literal address 2)))
        address))))

(defun mail-dont-reply-to (destinations)
  "Prune addresses from DESTINATIONS, a list of recipient addresses.
Remove all addresses matching `mail-dont-reply-to-names' from the
comma-separated list, and return the pruned list."
  ;; FIXME this (setting a user option the first time a command is used)
  ;; is somewhat strange.  Normally one would never set the option,
  ;; but instead fall back to the default so long as it was nil.
  ;; Or just set the default directly in the defcustom.
  (if (null mail-dont-reply-to-names)
      (setq mail-dont-reply-to-names
            (if (> (length user-mail-address) 0)
                (concat "\\`" (regexp-quote user-mail-address) "\\'"))))
  ;; Split up DESTINATIONS and match each element separately.
  (let ((start-pos 0) (cur-pos 0)
	(case-fold-search t))
    (while start-pos
      (setq cur-pos (string-match "[,\"]" destinations cur-pos))
      (if (and cur-pos (equal (match-string 0 destinations) "\""))
	  ;; Search for matching quote.
	  (let ((next-pos (string-search "\"" destinations (1+ cur-pos))))
	    (if next-pos
		(setq cur-pos (1+ next-pos))
	      ;; If the open-quote has no close-quote,
	      ;; delete the open-quote to get something well-defined.
	      ;; This case is not valid, but it can happen if things
	      ;; are weird elsewhere.
	      (setq destinations (concat (substring destinations 0 cur-pos)
				    (substring destinations (1+ cur-pos))))
	      (setq cur-pos start-pos)))
	(let* ((address (substring destinations start-pos cur-pos))
	       (naked-address (mail-strip-quoted-names address)))
	  (if (and mail-dont-reply-to-names
		   (string-match mail-dont-reply-to-names naked-address))
	      (setq destinations (concat (substring destinations 0 start-pos)
				    (and cur-pos (substring destinations
							    (1+ cur-pos))))
		    cur-pos start-pos)
	    (setq cur-pos (and cur-pos (1+ cur-pos))
		  start-pos cur-pos))))))
  ;; get rid of any trailing commas
  (let ((pos (string-match "[ ,\t\n]*\\'" destinations)))
    (if pos
        (setq destinations (substring destinations 0 pos))))
  ;; remove leading spaces. they bother me.
  (if (string-match "\\(\\s \\|,\\)*" destinations)
      (substring destinations (match-end 0))
    destinations))


;;;###autoload
(defun mail-fetch-field (field-name &optional last all list delete)
  "Return the value of the header field whose type is FIELD-NAME.
If second arg LAST is non-nil, use the last field of type FIELD-NAME.
If third arg ALL is non-nil, concatenate all such fields with commas between.
If 4th arg LIST is non-nil, return a list of all such fields.
If 5th arg DELETE is non-nil, delete all header lines that are
included in the result.
The buffer should be narrowed to just the header, else false
matches may be returned from the message body."
  (save-excursion
    (goto-char (point-min))
    (let ((case-fold-search t)
	  (name (concat "^" (regexp-quote field-name) "[ \t]*:[ \t]*")))
      (if (or all list)
	  (let ((value (if all "")))
	    (while (re-search-forward name nil t)
	      (let ((opoint (point)))
		(while (progn (forward-line 1)
			      (looking-at "[ \t]")))
		;; Back up over newline, then trailing spaces or tabs
		(forward-char -1)
		(skip-chars-backward " \t" opoint)
		(if list
		    (setq value (cons (buffer-substring-no-properties
				       opoint (point))
				      value))
		  (setq value (concat value
				      (if (string= value "") "" ", ")
				      (buffer-substring-no-properties
				       opoint (point)))))
                (if delete
                    (delete-region (line-beginning-position) (point)))))
	    (if list
		value
	      (and (not (string= value "")) value)))
	(if (re-search-forward name nil t)
	    (progn
	      (if last (while (re-search-forward name nil t)))
	      (let ((opoint (point)))
		(while (progn (forward-line 1)
			      (looking-at "[ \t]")))
		;; Back up over newline, then trailing spaces or tabs
		(forward-char -1)
		(skip-chars-backward " \t" opoint)
                (prog1
                    (buffer-substring-no-properties opoint (point))
                  (if delete
                      (delete-region (line-beginning-position)
                                     (1+ (point))))))))))))

;; Parse a list of tokens separated by commas.
;; It runs from point to the end of the visible part of the buffer.
;; Whitespace before or after tokens is ignored,
;; but whitespace within tokens is kept.
(defun mail-parse-comma-list ()
  (let (accumulated
	beg)
    (skip-chars-forward " \t\n")
    (while (not (eobp))
      (setq beg (point))
      (skip-chars-forward "^,")
      (skip-chars-backward " \t\n")
      (setq accumulated
	    (cons (buffer-substring-no-properties beg (point))
		  accumulated))
      (skip-chars-forward "^,")
      (skip-chars-forward ", \t\n"))
    accumulated))

(defun mail-comma-list-regexp (labels)
  (let (pos)
    (setq pos (or (string-match "[^ \t]" labels) 0))
    ;; Remove leading and trailing whitespace.
    (setq labels (substring labels pos (string-match "[ \t]*$" labels pos)))
    ;; Change each comma to \|, and flush surrounding whitespace.
    (while (setq pos (string-match "[ \t]*,[ \t]*" labels))
      (setq labels
	    (concat (substring labels 0 pos)
		    "\\|"
		    (substring labels (match-end 0))))))
  labels)

(defun mail-rfc822-time-zone (time)
  (declare (obsolete format-time-string "29.1"))
  (format-time-string "%z" time))

(defun mail-rfc822-date ()
  (let ((system-time-locale "C"))
    (format-time-string "%-d %b %Y %T %z")))

(defun mail-mbox-from ()
  "Return an mbox \"From \" line for the current message.
The buffer should be narrowed to just the header."
  (let* ((from (mail-strip-quoted-names (or (mail-fetch-field "from")
					    (mail-fetch-field "really-from")
					    (mail-fetch-field "sender")
					    (mail-fetch-field "return-path")
					    "unknown")))
	 (date (mail-fetch-field "date"))
	 ;; A From: header can contain multiple addresses, a "From "
	 ;; line must contain only one.  (Bug#7760)
	 ;; See, e.g., RFC 5322, 3.6.2. Originator Fields.
	 (end (string-match "[ \t]*[,\n]" from)))
    (format "From %s %s\n" (if end
			       (substring from 0 end)
			     from)
	    (or (and date
		     (ignore-errors
		      (current-time-string (date-to-time date))))
		(current-time-string)))))

(provide 'mail-utils)

;;; mail-utils.el ends here