;;; flow-fill.el --- interpret RFC2646 "flowed" text -*- lexical-binding:t -*-
;; Copyright (C) 2000-2022 Free Software Foundation, Inc.
;; Author: Simon Josefsson <jas@pdc.kth.se>
;; 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 <https://www.gnu.org/licenses/>.
;;; Commentary:
;; This implement decoding of RFC2646 formatted text, including the
;; quoted-depth wins rules.
;; Theory of operation: search for lines ending with SPC, save quote
;; length of line, remove SPC and concatenate line with the following
;; line if quote length of following line matches current line.
;; When no further concatenations are possible, we've found a
;; paragraph and we let `fill-region' fill the long line into several
;; lines with the quote prefix as `fill-prefix'.
;; Todo: implement basic `fill-region'
;;; History:
;; 2000-02-17 posted on ding mailing list
;; 2000-02-19 use `point-at-{b,e}ol' in XEmacs
;; 2000-03-11 no compile warnings for point-at-bol stuff
;; 2000-03-26 committed to gnus cvs
;; 2000-10-23 don't flow "-- " lines, make "quote-depth wins" rule
;; work when first line is at level 0.
;; 2002-01-12 probably incomplete encoding support
;; 2003-12-08 started working on test harness.
;;; Code:
(defcustom fill-flowed-display-column 'fill-column
"Column beyond which format=flowed lines are wrapped, when displayed.
This can be a Lisp expression or an integer."
:version "22.1"
:group 'mime-display
:type '(choice (const :tag "Standard `fill-column'" fill-column)
(const :tag "Fit Window" (- (window-width) 5))
(sexp)
(integer)))
(defcustom fill-flowed-encode-column 66
"Column beyond which format=flowed lines are wrapped, in outgoing messages.
This can be a Lisp expression or an integer.
RFC 2646 suggests 66 characters for readability."
:version "22.1"
:group 'mime-display
:type '(choice (const :tag "Standard fill-column" fill-column)
(const :tag "RFC 2646 default (66)" 66)
(sexp)
(integer)))
;;;###autoload
(defun fill-flowed-encode (&optional buffer)
(with-current-buffer (or buffer (current-buffer))
;; No point in doing this unless hard newlines is used.
(when use-hard-newlines
(let ((start (point-min)) end)
;; Go through each paragraph, filling it and adding SPC
;; as the last character on each line.
(while (setq end (text-property-any start (point-max) 'hard 't))
(save-restriction
(narrow-to-region start end)
(let ((fill-column (eval fill-flowed-encode-column t)))
(fill-flowed-fill-buffer))
(goto-char (point-min))
(while (re-search-forward "\n" nil t)
(replace-match " \n" t t))
(goto-char (setq start (1+ (point-max)))))))
t)))
(defun fill-flowed-fill-buffer ()
(let ((prefix nil)
(prev-prefix nil)
(start (point-min)))
(goto-char (point-min))
(while (not (eobp))
(setq prefix (and (looking-at "[> ]+")
(match-string 0)))
(if (equal prefix prev-prefix)
(forward-line 1)
(save-restriction
(narrow-to-region start (point))
(let ((fill-prefix prev-prefix))
(fill-region (point-min) (point-max) t 'nosqueeze 'to-eop))
(goto-char (point-max)))
(setq prev-prefix prefix
start (point))))
(save-restriction
(narrow-to-region start (point))
(let ((fill-prefix prev-prefix))
(fill-region (point-min) (point-max) t 'nosqueeze 'to-eop)))))
;;;###autoload
(defun fill-flowed (&optional buffer delete-space)
"Apply RFC2646 decoding to BUFFER.
If BUFFER is nil, default to the current buffer.
If DELETE-SPACE, delete RFC2646 spaces padding at the end of
lines."
(with-current-buffer (or buffer (current-buffer))
(let ((fill-column (eval fill-flowed-display-column t)))
(goto-char (point-min))
(while (not (eobp))
(cond
((and (looking-at "^>+")
(eq (char-before (line-end-position)) ?\s))
(let ((prefix (match-string 0)))
;; Insert a space character after the quote signs for more
;; pleasant reading of quoted lines.
(goto-char (match-end 0))
(unless (looking-at " ")
(insert " "))
(while (and (eq (char-before (line-end-position)) ?\s)
(not (eobp))
(save-excursion
(forward-line 1)
(looking-at (format "\\(%s ?\\)[^>]" prefix))))
(end-of-line)
(when (and (not (eobp))
(save-excursion
(forward-line 1)
(looking-at (format "\\(%s ?\\)[^>]" prefix))))
;; Delete the newline and the quote at the start of the
;; next line.
(delete-region (point) (match-end 1))))
(ignore-errors
(let ((fill-prefix (concat prefix " "))
adaptive-fill-mode)
(fill-region (line-beginning-position)
(line-end-position)
'left 'nosqueeze)))))
(t
;; Delete the newline.
(when (eq (following-char) ?\s)
(delete-char 1))
;; Hack: Don't do the flowing on the signature line.
(when (and (not (looking-at "-- $"))
(eq (char-before (line-end-position)) ?\s))
(while (and (not (eobp))
(eq (char-before (line-end-position)) ?\s))
(end-of-line)
(when delete-space
(delete-char -1))
(delete-char 1))
(ignore-errors
(let ((fill-prefix ""))
(fill-region (line-beginning-position)
(line-end-position)
'left 'nosqueeze))))))
(forward-line 1)))))
(make-obsolete-variable 'fill-flowed-encode-tests nil "27.1")
(defvar fill-flowed-encode-tests)
(defun fill-flowed-test ()
(declare (obsolete nil "27.1"))
(interactive "")
(user-error (concat "This function is obsolete. Please see "
"test/lisp/mail/flow-fill-tests.el "
"in the Emacs source tree")))
(provide 'flow-fill)
;;; flow-fill.el ends here