lisp/gnus/mm-encode.el

   1 ;;; mm-encode.el --- functions for encoding MIME things
   2 ;; Copyright (C) 1998, 1999, 2000 Free Software Foundation, Inc.
   3
   4 ;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
   5 ;;      MORIOKA Tomohiko <morioka@jaist.ac.jp>
   6 ;; This file is part of GNU Emacs.
   7
   8 ;; GNU Emacs is free software; you can redistribute it and/or modify
   9 ;; it under the terms of the GNU General Public License as published by
  10 ;; the Free Software Foundation; either version 2, or (at your option)
  11 ;; any later version.
  12
  13 ;; GNU Emacs is distributed in the hope that it will be useful,
  14 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16 ;; GNU General Public License for more details.
  17
  18 ;; You should have received a copy of the GNU General Public License
  19 ;; along with GNU Emacs; see the file COPYING.  If not, write to the
  20 ;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  21 ;; Boston, MA 02111-1307, USA.
  22
  23 ;;; Commentary:
  24
  25 ;;; Code:
  26
  27 (eval-when-compile (require 'cl))
  28 (require 'mail-parse)
  29 (require 'mailcap)
  30 (eval-and-compile
  31   (autoload 'mm-body-7-or-8 "mm-bodies"))
  32
  33 (defvar mm-content-transfer-encoding-defaults
  34   '(("text/x-patch" 8bit)
  35     ("text/.*" qp-or-base64)
  36     ("message/rfc822" 8bit)
  37     ("application/emacs-lisp" 8bit)
  38     ("application/x-patch" 8bit)
  39     (".*" qp-or-base64))
  40   "Alist of regexps that match MIME types and their encodings.
  41 If the encoding is `qp-or-base64', then either quoted-printable
  42 or base64 will be used, depending on what is more efficient.")
  43
  44 (defvar mm-use-ultra-safe-encoding nil
  45   "If non-nil, use encodings aimed at Procrustean bed survival.
  46
  47 This means that textual parts are encoded as quoted-printable if they
  48 contain lines longer than 76 characters or starting with \"From \" in
  49 the body.  Non-7bit encodings (8bit, binary) are generally disallowed.
  50 This is to reduce the probability that a broken MTA or MDA changes the
  51 message.
  52
  53 This variable should never be set directly, but bound before a call to
  54 `mml-generate-mime' or similar functions.")
  55
  56 (defun mm-insert-rfc822-headers (charset encoding)
  57   "Insert text/plain headers with CHARSET and ENCODING."
  58   (insert "MIME-Version: 1.0\n")
  59   (insert "Content-Type: text/plain; charset="
  60           (mail-quote-string (downcase (symbol-name charset))) "\n")
  61   (insert "Content-Transfer-Encoding: "
  62           (downcase (symbol-name encoding)) "\n"))
  63
  64 (defun mm-insert-multipart-headers ()
  65   "Insert multipart/mixed headers."
  66   (let ((boundary "=-=-="))
  67     (insert "MIME-Version: 1.0\n")
  68     (insert "Content-Type: multipart/mixed; boundary=\"" boundary "\"\n")
  69     boundary))
  70
  71 (defun mm-default-file-encoding (file)
  72   "Return a default encoding for FILE."
  73   (if (not (string-match "\\.[^.]+$" file))
  74       "application/octet-stream"
  75     (mailcap-extension-to-mime (match-string 0 file))))
  76
  77 (defun mm-safer-encoding (encoding)
  78   "Return a safer but similar encoding."
  79   (cond
  80    ((memq encoding '(7bit 8bit quoted-printable)) 'quoted-printable)
  81    ;; The remaing encodings are binary and base64 (and perhaps some
  82    ;; non-standard ones), which are both turned into base64.
  83    (t 'base64)))
  84
  85 (defun mm-encode-content-transfer-encoding (encoding &optional type)
  86   (cond
  87    ((eq encoding 'quoted-printable)
  88     (quoted-printable-encode-region (point-min) (point-max) t))
  89    ((eq encoding 'base64)
  90     (when (equal type "text/plain")
  91       (goto-char (point-min))
  92       (while (search-forward "\n" nil t)
  93         (replace-match "\r\n" t t)))
  94     (condition-case error
  95         (base64-encode-region (point-min) (point-max))
  96       (error
  97        (message "Error while decoding: %s" error)
  98        nil)))
  99    ((memq encoding '(7bit 8bit binary))
 100     ;; Do nothing.
 101     )
 102    ((null encoding)
 103     ;; Do nothing.
 104     )
 105    ((functionp encoding)
 106     (ignore-errors (funcall encoding (point-min) (point-max))))
 107    (t
 108     (message "Unknown encoding %s; defaulting to 8bit" encoding))))
 109
 110 (defun mm-encode-buffer (type)
 111   "Encode the buffer which contains data of TYPE.
 112 The encoding used is returned."
 113   (let* ((mime-type (if (stringp type) type (car type)))
 114          (encoding
 115           (or (and (listp type)
 116                    (cadr (assq 'encoding type)))
 117               (mm-content-transfer-encoding mime-type)))
 118          (bits (mm-body-7-or-8)))
 119     ;; We force buffers that are 7bit to be unencoded, no matter
 120     ;; what the preferred encoding is.
 121     (when (eq bits '7bit)
 122       (setq encoding bits))
 123     (mm-encode-content-transfer-encoding encoding mime-type)
 124     encoding))
 125
 126 (defun mm-insert-headers (type encoding &optional file)
 127   "Insert headers for TYPE."
 128   (insert "Content-Type: " type)
 129   (when file
 130     (insert ";\n\tname=\"" (file-name-nondirectory file) "\""))
 131   (insert "\n")
 132   (insert (format "Content-Transfer-Encoding: %s\n" encoding))
 133   (insert "Content-Disposition: inline")
 134   (when file
 135     (insert ";\n\tfilename=\"" (file-name-nondirectory file) "\""))
 136   (insert "\n")
 137   (insert "\n"))
 138
 139 (defun mm-content-transfer-encoding (type)
 140   "Return a CTE suitable for TYPE to encode the current buffer."
 141   (let ((rules mm-content-transfer-encoding-defaults))
 142     (catch 'found
 143       (while rules
 144         (when (string-match (caar rules) type)
 145           (throw 'found
 146                  (let ((encoding
 147                         (if (eq (cadr (car rules)) 'qp-or-base64)
 148                             (mm-qp-or-base64)
 149                           (cadr (car rules)))))
 150                    (if mm-use-ultra-safe-encoding
 151                        (mm-safer-encoding encoding)
 152                      encoding))))
 153         (pop rules)))))
 154
 155 (defun mm-qp-or-base64 ()
 156   (save-excursion
 157     (let ((limit (min (point-max) (+ 2000 (point-min))))
 158           (n8bit 0))
 159       (goto-char (point-min))
 160       (skip-chars-forward "\x20-\x7f\r\n\t" limit)
 161       (while (< (point) limit)
 162         (incf n8bit)
 163         (forward-char 1)
 164         (skip-chars-forward "\x20-\x7f\r\n\t" limit))
 165       (if (or (< (* 6 n8bit) (- limit (point-min)))
 166               ;; Don't base64, say, a short line with a single
 167               ;; non-ASCII char when splitting parts by charset.
 168               (= n8bit 1))
 169           'quoted-printable
 170         'base64))))
 171
 172 (provide 'mm-encode)
 173
 174 ;;; mm-encode.el ends here