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   1 ;;; mm-encode.el --- Functions for encoding MIME things
   2
   3 ;; Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004,
   4 ;;   2005, 2006, 2007, 2008 Free Software Foundation, Inc.
   5
   6 ;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
   7 ;;      MORIOKA Tomohiko <morioka@jaist.ac.jp>
   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, or (at your option)
  13 ;; 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; see the file COPYING.  If not, write to the
  22 ;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  23 ;; Boston, MA 02110-1301, USA.
  24
  25 ;;; Commentary:
  26
  27 ;;; Code:
  28
  29 (eval-when-compile (require 'cl))
  30 (require 'mail-parse)
  31 (require 'mailcap)
  32 (eval-and-compile
  33   (autoload 'mm-body-7-or-8 "mm-bodies")
  34   (autoload 'mm-long-lines-p "mm-bodies"))
  35
  36 (defcustom mm-content-transfer-encoding-defaults
  37   '(("text/x-patch" 8bit)
  38     ("text/.*" qp-or-base64)
  39     ("message/rfc822" 8bit)
  40     ("application/emacs-lisp" qp-or-base64)
  41     ("application/x-emacs-lisp" qp-or-base64)
  42     ("application/x-patch" qp-or-base64)
  43     (".*" base64))
  44   "Alist of regexps that match MIME types and their encodings.
  45 If the encoding is `qp-or-base64', then either quoted-printable
  46 or base64 will be used, depending on what is more efficient.
  47
  48 `qp-or-base64' has another effect.  It will fold long lines so that
  49 MIME parts may not be broken by MTA.  So do `quoted-printable' and
  50 `base64'.
  51
  52 Note: It affects body encoding only when a part is a raw forwarded
  53 message (which will be made by `gnus-summary-mail-forward' with the
  54 arg 2 for example) or is neither the text/* type nor the message/*
  55 type.  Even though in those cases, you can use the `encoding' MML tag
  56 to specify encoding of non-ASCII MIME parts."
  57   :type '(repeat (list (regexp :tag "MIME type")
  58                        (choice :tag "encoding"
  59                                (const 7bit)
  60                                (const 8bit)
  61                                (const qp-or-base64)
  62                                (const quoted-printable)
  63                                (const base64))))
  64   :group 'mime)
  65
  66 (defvar mm-use-ultra-safe-encoding nil
  67   "If non-nil, use encodings aimed at Procrustean bed survival.
  68
  69 This means that textual parts are encoded as quoted-printable if they
  70 contain lines longer than 76 characters or starting with \"From \" in
  71 the body.  Non-7bit encodings (8bit, binary) are generally disallowed.
  72 This is to reduce the probability that a broken MTA or MDA changes the
  73 message.
  74
  75 This variable should never be set directly, but bound before a call to
  76 `mml-generate-mime' or similar functions.")
  77
  78 (defun mm-insert-rfc822-headers (charset encoding)
  79   "Insert text/plain headers with CHARSET and ENCODING."
  80   (insert "MIME-Version: 1.0\n")
  81   (insert "Content-Type: text/plain; charset="
  82           (mail-quote-string (downcase (symbol-name charset))) "\n")
  83   (insert "Content-Transfer-Encoding: "
  84           (downcase (symbol-name encoding)) "\n"))
  85
  86 (defun mm-insert-multipart-headers ()
  87   "Insert multipart/mixed headers."
  88   (let ((boundary "=-=-="))
  89     (insert "MIME-Version: 1.0\n")
  90     (insert "Content-Type: multipart/mixed; boundary=\"" boundary "\"\n")
  91     boundary))
  92
  93 (defun mm-default-file-encoding (file)
  94   "Return a default encoding for FILE."
  95   (if (not (string-match "\\.[^.]+$" file))
  96       "application/octet-stream"
  97     (mailcap-extension-to-mime (match-string 0 file))))
  98
  99 (defun mm-safer-encoding (encoding &optional type)
 100   "Return an encoding similar to ENCODING but safer than it."
 101   (cond
 102    ((eq encoding '7bit) '7bit) ;; 7bit is considered safe.
 103    ((memq encoding '(8bit quoted-printable))
 104     ;; According to RFC2046, 5.2.1, RFC822 Subtype, "quoted-printable" is not
 105     ;; a valid encoding for message/rfc822:
 106     ;; No encoding other than "7bit", "8bit", or "binary" is permitted for the
 107     ;; body of a "message/rfc822" entity.
 108     (if (string= type "message/rfc822") '8bit 'quoted-printable))
 109    ;; The remaining encodings are binary and base64 (and perhaps some
 110    ;; non-standard ones), which are both turned into base64.
 111    (t (if (string= type "message/rfc822") 'binary 'base64))))
 112
 113 (defun mm-encode-content-transfer-encoding (encoding &optional type)
 114   "Encode the current buffer with ENCODING for MIME type TYPE.
 115 ENCODING can be: nil (do nothing); one of `quoted-printable', `base64';
 116 `7bit', `8bit' or `binary' (all do nothing); a function to do the encoding."
 117   (cond
 118    ((eq encoding 'quoted-printable)
 119     ;; This used to try to make a multibyte buffer unibyte.  That's
 120     ;; completely wrong, since you'd get QP-encoded emacs-mule.  If
 121     ;; this gets run on multibyte text it's an error that needs
 122     ;; fixing, and the encoding function will signal an error.
 123     ;; Likewise base64 below.
 124     (quoted-printable-encode-region (point-min) (point-max) t))
 125    ((eq encoding 'base64)
 126     (when (string-match "\\`text/" type)
 127       (goto-char (point-min))
 128       (while (search-forward "\n" nil t)
 129         (replace-match "\r\n" t t)))
 130     (base64-encode-region (point-min) (point-max)))
 131    ((memq encoding '(7bit 8bit binary))
 132     ;; Do nothing.
 133     )
 134    ((null encoding)
 135     ;; Do nothing.
 136     )
 137    ;; Fixme: Ignoring errors here looks bogus.
 138    ((functionp encoding)
 139     (ignore-errors (funcall encoding (point-min) (point-max))))
 140    (t
 141     (error "Unknown encoding %s" encoding))))
 142
 143 (defun mm-encode-buffer (type)
 144   "Encode the buffer which contains data of MIME type TYPE.
 145 TYPE is a string or a list of the components.
 146 The encoding used is returned."
 147   (let* ((mime-type (if (stringp type) type (car type)))
 148          (encoding
 149           (or (and (listp type)
 150                    (cadr (assq 'encoding type)))
 151               (mm-content-transfer-encoding mime-type)))
 152          (bits (mm-body-7-or-8)))
 153     ;; We force buffers that are 7bit to be unencoded, no matter
 154     ;; what the preferred encoding is.
 155     ;; Only if the buffers don't contain lone lines.
 156     (when (and (eq bits '7bit) (not (mm-long-lines-p 76)))
 157       (setq encoding bits))
 158     (mm-encode-content-transfer-encoding encoding mime-type)
 159     encoding))
 160
 161 (defun mm-insert-headers (type encoding &optional file)
 162   "Insert headers for TYPE."
 163   (insert "Content-Type: " type)
 164   (when file
 165     (insert ";\n\tname=\"" (file-name-nondirectory file) "\""))
 166   (insert "\n")
 167   (insert (format "Content-Transfer-Encoding: %s\n" encoding))
 168   (insert "Content-Disposition: inline")
 169   (when file
 170     (insert ";\n\tfilename=\"" (file-name-nondirectory file) "\""))
 171   (insert "\n")
 172   (insert "\n"))
 173
 174 (defun mm-content-transfer-encoding (type)
 175   "Return a CTE suitable for TYPE to encode the current buffer."
 176   (let ((rules mm-content-transfer-encoding-defaults))
 177     (catch 'found
 178       (while rules
 179         (when (string-match (caar rules) type)
 180           (throw 'found
 181                  (let ((encoding
 182                         (if (eq (cadr (car rules)) 'qp-or-base64)
 183                             (mm-qp-or-base64)
 184                           (cadr (car rules)))))
 185                    (if mm-use-ultra-safe-encoding
 186                        (mm-safer-encoding encoding type)
 187                      encoding))))
 188         (pop rules)))))
 189
 190 (defun mm-qp-or-base64 ()
 191   "Return the type with which to encode the buffer.
 192 This is either `base64' or `quoted-printable'."
 193   (if (equal mm-use-ultra-safe-encoding '(sign . "pgp"))
 194       ;; perhaps not always accurate?
 195       'quoted-printable
 196     (save-excursion
 197       (let ((limit (min (point-max) (+ 2000 (point-min))))
 198             (n8bit 0))
 199         (goto-char (point-min))
 200         (skip-chars-forward "\x20-\x7f\r\n\t" limit)
 201         (while (< (point) limit)
 202           (incf n8bit)
 203           (forward-char 1)
 204           (skip-chars-forward "\x20-\x7f\r\n\t" limit))
 205         (if (or (< (* 6 n8bit) (- limit (point-min)))
 206                 ;; Don't base64, say, a short line with a single
 207                 ;; non-ASCII char when splitting parts by charset.
 208                 (= n8bit 1))
 209             'quoted-printable
 210           'base64)))))
 211
 212 (provide 'mm-encode)
 213
 214 ;; arch-tag: 7d01bba4-d469-4851-952b-dc863f84ed66
 215 ;;; mm-encode.el ends here