lisp/mail/flow-fill.el

   1 ;;; flow-fill.el --- interpret RFC2646 "flowed" text
   2
   3 ;; Copyright (C) 2000-2017 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 (eval-when-compile (require 'cl))
  53
  54 (defcustom fill-flowed-display-column 'fill-column
  55   "Column beyond which format=flowed lines are wrapped, when displayed.
  56 This can be a Lisp expression or an integer."
  57   :version "22.1"
  58   :group 'mime-display
  59   :type '(choice (const :tag "Standard `fill-column'" fill-column)
  60                  (const :tag "Fit Window" (- (window-width) 5))
  61                  (sexp)
  62                  (integer)))
  63
  64 (defcustom fill-flowed-encode-column 66
  65   "Column beyond which format=flowed lines are wrapped, in outgoing messages.
  66 This can be a Lisp expression or an integer.
  67 RFC 2646 suggests 66 characters for readability."
  68   :version "22.1"
  69   :group 'mime-display
  70   :type '(choice (const :tag "Standard fill-column" fill-column)
  71                  (const :tag "RFC 2646 default (66)" 66)
  72                  (sexp)
  73                  (integer)))
  74
  75 ;;;###autoload
  76 (defun fill-flowed-encode (&optional buffer)
  77   (with-current-buffer (or buffer (current-buffer))
  78     ;; No point in doing this unless hard newlines is used.
  79     (when use-hard-newlines
  80       (let ((start (point-min)) end)
  81         ;; Go through each paragraph, filling it and adding SPC
  82         ;; as the last character on each line.
  83         (while (setq end (text-property-any start (point-max) 'hard 't))
  84           (save-restriction
  85             (narrow-to-region start end)
  86             (let ((fill-column (eval fill-flowed-encode-column)))
  87               (fill-flowed-fill-buffer))
  88             (goto-char (point-min))
  89             (while (re-search-forward "\n" nil t)
  90               (replace-match " \n" t t))
  91             (goto-char (setq start (1+ (point-max)))))))
  92       t)))
  93
  94 (defun fill-flowed-fill-buffer ()
  95   (let ((prefix nil)
  96         (prev-prefix nil)
  97         (start (point-min)))
  98     (goto-char (point-min))
  99     (while (not (eobp))
 100       (setq prefix (and (looking-at "[> ]+")
 101                         (match-string 0)))
 102       (if (equal prefix prev-prefix)
 103           (forward-line 1)
 104         (save-restriction
 105           (narrow-to-region start (point))
 106           (let ((fill-prefix prev-prefix))
 107             (fill-region (point-min) (point-max) t 'nosqueeze 'to-eop))
 108           (goto-char (point-max)))
 109         (setq prev-prefix prefix
 110               start (point))))
 111     (save-restriction
 112       (narrow-to-region start (point))
 113       (let ((fill-prefix prev-prefix))
 114         (fill-region (point-min) (point-max) t 'nosqueeze 'to-eop)))))
 115
 116 ;;;###autoload
 117 (defun fill-flowed (&optional buffer delete-space)
 118   (with-current-buffer (or (current-buffer) buffer)
 119     (goto-char (point-min))
 120     ;; Remove space stuffing.
 121     (while (re-search-forward "^\\( \\|>+ $\\)" nil t)
 122       (delete-char -1)
 123       (forward-line 1))
 124     (goto-char (point-min))
 125     (while (re-search-forward " $" nil t)
 126       (when (save-excursion
 127               (beginning-of-line)
 128               (looking-at "^\\(>*\\)\\( ?\\)"))
 129         (let ((quote (match-string 1))
 130               sig)
 131           (if (string= quote "")
 132               (setq quote nil))
 133           (when (and quote (string= (match-string 2) ""))
 134             (save-excursion
 135               ;; insert SP after quote for pleasant reading of quoted lines
 136               (beginning-of-line)
 137               (when (> (skip-chars-forward ">") 0)
 138                 (insert " "))))
 139           ;; XXX slightly buggy handling of "-- "
 140           (while (and (save-excursion
 141                         (ignore-errors (backward-char 3))
 142                         (setq sig (looking-at "-- "))
 143                         (looking-at "[^-][^-] "))
 144                       (save-excursion
 145                         (unless (eobp)
 146                           (forward-char 1)
 147                           (looking-at (format "^\\(%s\\)\\([^>\n\r]\\)"
 148                                               (or quote " ?"))))))
 149             (save-excursion
 150               (replace-match (if (string= (match-string 2) " ")
 151                                  "" "\\2")))
 152             (backward-delete-char -1)
 153             (when delete-space
 154               (delete-char -1))
 155             (end-of-line))
 156           (unless sig
 157             (condition-case nil
 158                 (let ((fill-prefix (when quote (concat quote " ")))
 159                       (fill-column (eval fill-flowed-display-column))
 160                       adaptive-fill-mode)
 161                   (fill-region (point-at-bol)
 162                                (min (1+ (point-at-eol))
 163                                     (point-max))
 164                                'left 'nosqueeze))
 165               (error
 166                (forward-line 1)
 167                nil))))))))
 168
 169 ;; Test vectors.
 170
 171 (defvar show-trailing-whitespace)
 172
 173 (defvar fill-flowed-encode-tests
 174   `(
 175     ;; The syntax of each list element is:
 176     ;; (INPUT . EXPECTED-OUTPUT)
 177     (,(concat
 178        "> Thou villainous ill-breeding spongy dizzy-eyed \n"
 179        "> reeky elf-skinned pigeon-egg! \n"
 180        ">> Thou artless swag-bellied milk-livered \n"
 181        ">> dismal-dreaming idle-headed scut!\n"
 182        ">>> Thou errant folly-fallen spleeny reeling-ripe \n"
 183        ">>> unmuzzled ratsbane!\n"
 184        ">>>> Henceforth, the coding style is to be strictly \n"
 185        ">>>> enforced, including the use of only upper case.\n"
 186        ">>>>> I've noticed a lack of adherence to the coding \n"
 187        ">>>>> styles, of late.\n"
 188        ">>>>>> Any complaints?")
 189      .
 190      ,(concat
 191        "> Thou villainous ill-breeding spongy dizzy-eyed reeky elf-skinned\n"
 192        "> pigeon-egg! \n"
 193        ">> Thou artless swag-bellied milk-livered dismal-dreaming idle-headed\n"
 194        ">> scut!\n"
 195        ">>> Thou errant folly-fallen spleeny reeling-ripe unmuzzled ratsbane!\n"
 196        ">>>> Henceforth, the coding style is to be strictly enforced,\n"
 197        ">>>> including the use of only upper case.\n"
 198        ">>>>> I've noticed a lack of adherence to the coding styles, of late.\n"
 199        ">>>>>> Any complaints?\n"
 200        ))
 201     ;; (,(concat
 202     ;;    "\n"
 203     ;;    "> foo\n"
 204     ;;    "> \n"
 205     ;;    "> \n"
 206     ;;    "> bar\n")
 207     ;;  .
 208     ;;  ,(concat
 209     ;;    "\n"
 210     ;;    "> foo bar\n"))
 211     ))
 212
 213 (defun fill-flowed-test ()
 214   (interactive "")
 215   (switch-to-buffer (get-buffer-create "*Format=Flowed test output*"))
 216   (erase-buffer)
 217   (setq show-trailing-whitespace t)
 218   (dolist (test fill-flowed-encode-tests)
 219     (let (start output)
 220       (insert "***** BEGIN TEST INPUT *****\n")
 221       (insert (car test))
 222       (insert "***** END TEST INPUT *****\n\n")
 223       (insert "***** BEGIN TEST OUTPUT *****\n")
 224       (setq start (point))
 225       (insert (car test))
 226       (save-restriction
 227         (narrow-to-region start (point))
 228         (fill-flowed))
 229       (setq output (buffer-substring start (point-max)))
 230       (insert "***** END TEST OUTPUT *****\n")
 231       (unless (string= output (cdr test))
 232         (insert "\n***** BEGIN TEST EXPECTED OUTPUT *****\n")
 233         (insert (cdr test))
 234         (insert "***** END TEST EXPECTED OUTPUT *****\n"))
 235       (insert "\n\n")))
 236   (goto-char (point-max)))
 237
 238 (provide 'flow-fill)
 239
 240 ;;; flow-fill.el ends here