lisp/gnus/mm-encode.el

   1 ;;; mm-encode.el --- Functions for encoding MIME things
   2
   3 ;; Copyright (C) 1998-2016 Free Software Foundation, Inc.
   4
   5 ;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
   6 ;;      MORIOKA Tomohiko <morioka@jaist.ac.jp>
   7 ;; This file is part of GNU Emacs.
   8
   9 ;; GNU Emacs is free software: you can redistribute it and/or modify
  10 ;; it under the terms of the GNU General Public License as published by
  11 ;; the Free Software Foundation, either version 3 of the License, or
  12 ;; (at your option) any later version.
  13
  14 ;; GNU Emacs is distributed in the hope that it will be useful,
  15 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  16 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17 ;; GNU General Public License for more details.
  18
  19 ;; You should have received a copy of the GNU General Public License
  20 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  21
  22 ;;; Commentary:
  23
  24 ;;; Code:
  25
  26 (eval-when-compile (require 'cl))
  27 (require 'mail-parse)
  28 (autoload 'mailcap-extension-to-mime "mailcap")
  29 (autoload 'mm-body-7-or-8 "mm-bodies")
  30 (autoload 'mm-long-lines-p "mm-bodies")
  31
  32 (defcustom mm-content-transfer-encoding-defaults
  33   '(("text/x-patch" 8bit)
  34     ("text/.*" qp-or-base64)
  35     ("message/rfc822" 8bit)
  36     ("application/emacs-lisp" qp-or-base64)
  37     ("application/x-emacs-lisp" qp-or-base64)
  38     ("application/x-patch" qp-or-base64)
  39     (".*" 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 This list is only consulted when encoding MIME parts in the
  45 bodies -- not for the regular non-MIME-ish messages."
  46   :type '(repeat (list (regexp :tag "MIME type")
  47                        (choice :tag "encoding"
  48                                (const 7bit)
  49                                (const 8bit)
  50                                (const qp-or-base64)
  51                                (const quoted-printable)
  52                                (const base64))))
  53   :group 'mime)
  54
  55 (defcustom mm-sign-option nil
  56   "Option how to create signed parts.
  57 nil, use the default keys without asking;
  58 `guided', let you select signing keys from the menu."
  59   :version "23.2" ;; No Gnus 0.12
  60   :type '(choice (item guided)
  61                  (item :tag "default" nil))
  62   :group 'mime-security)
  63
  64 (defcustom mm-encrypt-option nil
  65   "Option how to create encrypted parts.
  66 nil, use the default keys without asking;
  67 `guided', let you select recipients' keys from the menu."
  68   :version "23.2" ;; No Gnus 0.12
  69   :type '(choice (item guided)
  70                  (item :tag "default" nil))
  71   :group 'mime-security)
  72
  73 (defvar mm-use-ultra-safe-encoding nil
  74   "If non-nil, use encodings aimed at Procrustean bed survival.
  75
  76 This means that textual parts are encoded as quoted-printable if they
  77 contain lines longer than 76 characters or starting with \"From \" in
  78 the body.  Non-7bit encodings (8bit, binary) are generally disallowed.
  79 This is to reduce the probability that a broken MTA or MDA changes the
  80 message.
  81
  82 This variable should never be set directly, but bound before a call to
  83 `mml-generate-mime' or similar functions.")
  84
  85 (defun mm-insert-rfc822-headers (charset encoding)
  86   "Insert text/plain headers with CHARSET and ENCODING."
  87   (insert "MIME-Version: 1.0\n")
  88   (insert "Content-Type: text/plain; charset="
  89           (mail-quote-string (downcase (symbol-name charset))) "\n")
  90   (insert "Content-Transfer-Encoding: "
  91           (downcase (symbol-name encoding)) "\n"))
  92
  93 (defun mm-insert-multipart-headers ()
  94   "Insert multipart/mixed headers."
  95   (let ((boundary "=-=-="))
  96     (insert "MIME-Version: 1.0\n")
  97     (insert "Content-Type: multipart/mixed; boundary=\"" boundary "\"\n")
  98     boundary))
  99
 100 ;;;###autoload
 101 (defun mm-default-file-encoding (file)
 102   "Return a default encoding for FILE."
 103   (if (not (string-match "\\.[^.]+$" file))
 104       "application/octet-stream"
 105     (mailcap-extension-to-mime (match-string 0 file))))
 106
 107 (defun mm-safer-encoding (encoding &optional type)
 108   "Return an encoding similar to ENCODING but safer than it."
 109   (cond
 110    ((eq encoding '7bit) '7bit) ;; 7bit is considered safe.
 111    ((memq encoding '(8bit quoted-printable))
 112     ;; According to RFC2046, 5.2.1, RFC822 Subtype, "quoted-printable" is not
 113     ;; a valid encoding for message/rfc822:
 114     ;; No encoding other than "7bit", "8bit", or "binary" is permitted for the
 115     ;; body of a "message/rfc822" entity.
 116     (if (string= type "message/rfc822") '8bit 'quoted-printable))
 117    ;; The remaining encodings are binary and base64 (and perhaps some
 118    ;; non-standard ones), which are both turned into base64.
 119    (t (if (string= type "message/rfc822") 'binary 'base64))))
 120
 121 (defun mm-encode-content-transfer-encoding (encoding &optional type)
 122   "Encode the current buffer with ENCODING for MIME type TYPE.
 123 ENCODING can be: nil (do nothing); one of `quoted-printable', `base64';
 124 `7bit', `8bit' or `binary' (all do nothing); a function to do the encoding."
 125   (cond
 126    ((eq encoding 'quoted-printable)
 127     ;; This used to try to make a multibyte buffer unibyte.  That's
 128     ;; completely wrong, since you'd get QP-encoded emacs-mule.  If
 129     ;; this gets run on multibyte text it's an error that needs
 130     ;; fixing, and the encoding function will signal an error.
 131     ;; Likewise base64 below.
 132     (quoted-printable-encode-region (point-min) (point-max) t))
 133    ((eq encoding 'base64)
 134     (when (string-match "\\`text/" type)
 135       (goto-char (point-min))
 136       (while (search-forward "\n" nil t)
 137         (replace-match "\r\n" t t)))
 138     (base64-encode-region (point-min) (point-max)))
 139    ((memq encoding '(7bit 8bit binary))
 140     ;; Do nothing.
 141     )
 142    ((null encoding)
 143     ;; Do nothing.
 144     )
 145    ;; Fixme: Ignoring errors here looks bogus.
 146    ((functionp encoding)
 147     (ignore-errors (funcall encoding (point-min) (point-max))))
 148    (t
 149     (error "Unknown encoding %s" encoding))))
 150
 151 (defun mm-encode-buffer (type &optional encoding)
 152   "Encode the buffer which contains data of MIME type TYPE by ENCODING.
 153 TYPE is a string or a list of the components.
 154 The optional ENCODING overrides the encoding determined according to
 155 TYPE and `mm-content-transfer-encoding-defaults'.
 156 The encoding used is returned."
 157   (let ((mime-type (if (stringp type) type (car type))))
 158     (mm-encode-content-transfer-encoding
 159      (or encoding
 160          (setq encoding (or (and (listp type)
 161                                  (cadr (assq 'encoding type)))
 162                             (mm-content-transfer-encoding mime-type))))
 163      mime-type)
 164     encoding))
 165
 166 (defun mm-insert-headers (type encoding &optional file)
 167   "Insert headers for TYPE."
 168   (insert "Content-Type: " type)
 169   (when file
 170     (insert ";\n\tname=\"" (file-name-nondirectory file) "\""))
 171   (insert "\n")
 172   (insert (format "Content-Transfer-Encoding: %s\n" encoding))
 173   (insert "Content-Disposition: inline")
 174   (when file
 175     (insert ";\n\tfilename=\"" (file-name-nondirectory file) "\""))
 176   (insert "\n")
 177   (insert "\n"))
 178
 179 (defun mm-content-transfer-encoding (type)
 180   "Return a CTE suitable for TYPE to encode the current buffer."
 181   (let ((rules mm-content-transfer-encoding-defaults))
 182     (catch 'found
 183       (while rules
 184         (when (string-match (caar rules) type)
 185           (throw 'found
 186                  (let ((encoding
 187                         (if (eq (cadr (car rules)) 'qp-or-base64)
 188                             (mm-qp-or-base64)
 189                           (cadr (car rules)))))
 190                    (if mm-use-ultra-safe-encoding
 191                        (mm-safer-encoding encoding type)
 192                      encoding))))
 193         (pop rules)))))
 194
 195 (defun mm-qp-or-base64 ()
 196   "Return the type with which to encode the buffer.
 197 This is either `base64' or `quoted-printable'."
 198   (if (equal mm-use-ultra-safe-encoding '(sign . "pgp"))
 199       ;; perhaps not always accurate?
 200       'quoted-printable
 201     (save-excursion
 202       (let ((limit (min (point-max) (+ 2000 (point-min))))
 203             (n8bit 0))
 204         (goto-char (point-min))
 205         (skip-chars-forward "\x20-\x7f\r\n\t" limit)
 206         (while (< (point) limit)
 207           (incf n8bit)
 208           (forward-char 1)
 209           (skip-chars-forward "\x20-\x7f\r\n\t" limit))
 210         (if (or (< (* 6 n8bit) (- limit (point-min)))
 211                 ;; Don't base64, say, a short line with a single
 212                 ;; non-ASCII char when splitting parts by charset.
 213                 (= n8bit 1))
 214             'quoted-printable
 215           'base64)))))
 216
 217 (provide 'mm-encode)
 218
 219 ;;; mm-encode.el ends here