lisp/mail/flow-fill.el

   1 ;;; flow-fill.el --- interpret RFC2646 "flowed" text  -*- lexical-binding:t -*-
   2
   3 ;; Copyright (C) 2000-2018 Free Software Foundation, Inc.
   4
   5 ;; Author: Simon Josefsson <jas@pdc.kth.se>
   6 ;; Keywords: mail
   7
   8 ;; This file is part of GNU Emacs.
   9
  10 ;; GNU Emacs is free software: you can redistribute it and/or modify
  11 ;; it under the terms of the GNU General Public License as published by
  12 ;; the Free Software Foundation, either version 3 of the License, or
  13 ;; (at your option) any later version.
  14
  15 ;; GNU Emacs is distributed in the hope that it will be useful,
  16 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 ;; GNU General Public License for more details.
  19
  20 ;; You should have received a copy of the GNU General Public License
  21 ;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
  22
  23 ;;; Commentary:
  24
  25 ;; This implement decoding of RFC2646 formatted text, including the
  26 ;; quoted-depth wins rules.
  27
  28 ;; Theory of operation: search for lines ending with SPC, save quote
  29 ;; length of line, remove SPC and concatenate line with the following
  30 ;; line if quote length of following line matches current line.
  31
  32 ;; When no further concatenations are possible, we've found a
  33 ;; paragraph and we let `fill-region' fill the long line into several
  34 ;; lines with the quote prefix as `fill-prefix'.
  35
  36 ;; Todo: implement basic `fill-region' (Emacs and XEmacs
  37 ;;       implementations differ..)
  38
  39 ;;; History:
  40
  41 ;; 2000-02-17  posted on ding mailing list
  42 ;; 2000-02-19  use `point-at-{b,e}ol' in XEmacs
  43 ;; 2000-03-11  no compile warnings for point-at-bol stuff
  44 ;; 2000-03-26  committed to gnus cvs
  45 ;; 2000-10-23  don't flow "-- " lines, make "quote-depth wins" rule
  46 ;;             work when first line is at level 0.
  47 ;; 2002-01-12  probably incomplete encoding support
  48 ;; 2003-12-08  started working on test harness.
  49
  50 ;;; Code:
  51
  52
  53 (defcustom fill-flowed-display-column 'fill-column
  54   "Column beyond which format=flowed lines are wrapped, when displayed.
  55 This can be a Lisp expression or an integer."
  56   :version "22.1"
  57   :group 'mime-display
  58   :type '(choice (const :tag "Standard `fill-column'" fill-column)
  59                  (const :tag "Fit Window" (- (window-width) 5))
  60                  (sexp)
  61                  (integer)))
  62
  63 (defcustom fill-flowed-encode-column 66
  64   "Column beyond which format=flowed lines are wrapped, in outgoing messages.
  65 This can be a Lisp expression or an integer.
  66 RFC 2646 suggests 66 characters for readability."
  67   :version "22.1"
  68   :group 'mime-display
  69   :type '(choice (const :tag "Standard fill-column" fill-column)
  70                  (const :tag "RFC 2646 default (66)" 66)
  71                  (sexp)
  72                  (integer)))
  73
  74 ;;;###autoload
  75 (defun fill-flowed-encode (&optional buffer)
  76   (with-current-buffer (or buffer (current-buffer))
  77     ;; No point in doing this unless hard newlines is used.
  78     (when use-hard-newlines
  79       (let ((start (point-min)) end)
  80         ;; Go through each paragraph, filling it and adding SPC
  81         ;; as the last character on each line.
  82         (while (setq end (text-property-any start (point-max) 'hard 't))
  83           (save-restriction
  84             (narrow-to-region start end)
  85             (let ((fill-column (eval fill-flowed-encode-column)))
  86               (fill-flowed-fill-buffer))
  87             (goto-char (point-min))
  88             (while (re-search-forward "\n" nil t)
  89               (replace-match " \n" t t))
  90             (goto-char (setq start (1+ (point-max)))))))
  91       t)))
  92
  93 (defun fill-flowed-fill-buffer ()
  94   (let ((prefix nil)
  95         (prev-prefix nil)
  96         (start (point-min)))
  97     (goto-char (point-min))
  98     (while (not (eobp))
  99       (setq prefix (and (looking-at "[> ]+")
 100                         (match-string 0)))
 101       (if (equal prefix prev-prefix)
 102           (forward-line 1)
 103         (save-restriction
 104           (narrow-to-region start (point))
 105           (let ((fill-prefix prev-prefix))
 106             (fill-region (point-min) (point-max) t 'nosqueeze 'to-eop))
 107           (goto-char (point-max)))
 108         (setq prev-prefix prefix
 109               start (point))))
 110     (save-restriction
 111       (narrow-to-region start (point))
 112       (let ((fill-prefix prev-prefix))
 113         (fill-region (point-min) (point-max) t 'nosqueeze 'to-eop)))))
 114
 115 ;;;###autoload
 116 (defun fill-flowed (&optional buffer delete-space)
 117   (with-current-buffer (or (current-buffer) buffer)
 118     (goto-char (point-min))
 119     ;; Remove space stuffing.
 120     (while (re-search-forward "^\\( \\|>+ $\\)" nil t)
 121       (delete-char -1)
 122       (forward-line 1))
 123     (goto-char (point-min))
 124     (while (re-search-forward " $" nil t)
 125       (when (save-excursion
 126               (beginning-of-line)
 127               (looking-at "^\\(>*\\)\\( ?\\)"))
 128         (let ((quote (match-string 1))
 129               sig)
 130           (if (string= quote "")
 131               (setq quote nil))
 132           (when (and quote (string= (match-string 2) ""))
 133             (save-excursion
 134               ;; insert SP after quote for pleasant reading of quoted lines
 135               (beginning-of-line)
 136               (when (> (skip-chars-forward ">") 0)
 137                 (insert " "))))
 138           ;; XXX slightly buggy handling of "-- "
 139           (while (and (save-excursion
 140                         (ignore-errors (backward-char 3))
 141                         (setq sig (looking-at "-- "))
 142                         (looking-at "[^-][^-] "))
 143                       (save-excursion
 144                         (unless (eobp)
 145                           (forward-char 1)
 146                           (looking-at (format "^\\(%s\\)\\([^>\n\r]\\)"
 147                                               (or quote " ?"))))))
 148             (save-excursion
 149               (replace-match (if (string= (match-string 2) " ")
 150                                  "" "\\2")))
 151             (backward-delete-char -1)
 152             (when delete-space
 153               (delete-char -1))
 154             (end-of-line))
 155           (unless sig
 156             (condition-case nil
 157                 (let ((fill-prefix (when quote (concat quote " ")))
 158                       (fill-column (eval fill-flowed-display-column))
 159                       adaptive-fill-mode)
 160                   (fill-region (point-at-bol)
 161                                (min (1+ (point-at-eol))
 162                                     (point-max))
 163                                'left 'nosqueeze))
 164               (error
 165                (forward-line 1)
 166                nil))))))))
 167
 168 ;; Test vectors.
 169
 170 (defvar show-trailing-whitespace)
 171
 172 (defvar fill-flowed-encode-tests
 173   `(
 174     ;; The syntax of each list element is:
 175     ;; (INPUT . EXPECTED-OUTPUT)
 176     (,(concat
 177        "> Thou villainous ill-breeding spongy dizzy-eyed \n"
 178        "> reeky elf-skinned pigeon-egg! \n"
 179        ">> Thou artless swag-bellied milk-livered \n"
 180        ">> dismal-dreaming idle-headed scut!\n"
 181        ">>> Thou errant folly-fallen spleeny reeling-ripe \n"
 182        ">>> unmuzzled ratsbane!\n"
 183        ">>>> Henceforth, the coding style is to be strictly \n"
 184        ">>>> enforced, including the use of only upper case.\n"
 185        ">>>>> I've noticed a lack of adherence to the coding \n"
 186        ">>>>> styles, of late.\n"
 187        ">>>>>> Any complaints?")
 188      .
 189      ,(concat
 190        "> Thou villainous ill-breeding spongy dizzy-eyed reeky elf-skinned\n"
 191        "> pigeon-egg! \n"
 192        ">> Thou artless swag-bellied milk-livered dismal-dreaming idle-headed\n"
 193        ">> scut!\n"
 194        ">>> Thou errant folly-fallen spleeny reeling-ripe unmuzzled ratsbane!\n"
 195        ">>>> Henceforth, the coding style is to be strictly enforced,\n"
 196        ">>>> including the use of only upper case.\n"
 197        ">>>>> I've noticed a lack of adherence to the coding styles, of late.\n"
 198        ">>>>>> Any complaints?\n"
 199        ))
 200     ;; (,(concat
 201     ;;    "\n"
 202     ;;    "> foo\n"
 203     ;;    "> \n"
 204     ;;    "> \n"
 205     ;;    "> bar\n")
 206     ;;  .
 207     ;;  ,(concat
 208     ;;    "\n"
 209     ;;    "> foo bar\n"))
 210     ))
 211
 212 (defun fill-flowed-test ()
 213   (interactive "")
 214   (switch-to-buffer (get-buffer-create "*Format=Flowed test output*"))
 215   (erase-buffer)
 216   (setq show-trailing-whitespace t)
 217   (dolist (test fill-flowed-encode-tests)
 218     (let (start output)
 219       (insert "***** BEGIN TEST INPUT *****\n")
 220       (insert (car test))
 221       (insert "***** END TEST INPUT *****\n\n")
 222       (insert "***** BEGIN TEST OUTPUT *****\n")
 223       (setq start (point))
 224       (insert (car test))
 225       (save-restriction
 226         (narrow-to-region start (point))
 227         (fill-flowed))
 228       (setq output (buffer-substring start (point-max)))
 229       (insert "***** END TEST OUTPUT *****\n")
 230       (unless (string= output (cdr test))
 231         (insert "\n***** BEGIN TEST EXPECTED OUTPUT *****\n")
 232         (insert (cdr test))
 233         (insert "***** END TEST EXPECTED OUTPUT *****\n"))
 234       (insert "\n\n")))
 235   (goto-char (point-max)))
 236
 237 (provide 'flow-fill)
 238
 239 ;;; flow-fill.el ends here