1;;; mm-encode.el --- Functions for encoding MIME things
2
3;; Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004,
4;;   2005, 2006, 2007 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 2, 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.
45If the encoding is `qp-or-base64', then either quoted-printable
46or 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
49MIME parts may not be broken by MTA.  So do `quoted-printable' and
50`base64'.
51
52Note: It affects body encoding only when a part is a raw forwarded
53message (which will be made by `gnus-summary-mail-forward' with the
54arg 2 for example) or is neither the text/* type nor the message/*
55type.  Even though in those cases, you can use the `encoding' MML tag
56to 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
69This means that textual parts are encoded as quoted-printable if they
70contain lines longer than 76 characters or starting with \"From \" in
71the body.  Non-7bit encodings (8bit, binary) are generally disallowed.
72This is to reduce the probability that a broken MTA or MDA changes the
73message.
74
75This 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)
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)) 'quoted-printable)
104   ;; The remaining encodings are binary and base64 (and perhaps some
105   ;; non-standard ones), which are both turned into base64.
106   (t 'base64)))
107
108(defun mm-encode-content-transfer-encoding (encoding &optional type)
109  "Encode the current buffer with ENCODING for MIME type TYPE.
110ENCODING can be: nil (do nothing); one of `quoted-printable', `base64';
111`7bit', `8bit' or `binary' (all do nothing); a function to do the encoding."
112  (cond
113   ((eq encoding 'quoted-printable)
114    ;; This used to try to make a multibyte buffer unibyte.  That's
115    ;; completely wrong, since you'd get QP-encoded emacs-mule.  If
116    ;; this gets run on multibyte text it's an error that needs
117    ;; fixing, and the encoding function will signal an error.
118    ;; Likewise base64 below.
119    (quoted-printable-encode-region (point-min) (point-max) t))
120   ((eq encoding 'base64)
121    (when (string-match "\\`text/" type)
122      (goto-char (point-min))
123      (while (search-forward "\n" nil t)
124	(replace-match "\r\n" t t)))
125    (base64-encode-region (point-min) (point-max)))
126   ((memq encoding '(7bit 8bit binary))
127    ;; Do nothing.
128    )
129   ((null encoding)
130    ;; Do nothing.
131    )
132   ;; Fixme: Ignoring errors here looks bogus.
133   ((functionp encoding)
134    (ignore-errors (funcall encoding (point-min) (point-max))))
135   (t
136    (error "Unknown encoding %s" encoding))))
137
138(defun mm-encode-buffer (type)
139  "Encode the buffer which contains data of MIME type TYPE.
140TYPE is a string or a list of the components.
141The encoding used is returned."
142  (let* ((mime-type (if (stringp type) type (car type)))
143	 (encoding
144	  (or (and (listp type)
145		   (cadr (assq 'encoding type)))
146	      (mm-content-transfer-encoding mime-type)))
147	 (bits (mm-body-7-or-8)))
148    ;; We force buffers that are 7bit to be unencoded, no matter
149    ;; what the preferred encoding is.
150    ;; Only if the buffers don't contain lone lines.
151    (when (and (eq bits '7bit) (not (mm-long-lines-p 76)))
152      (setq encoding bits))
153    (mm-encode-content-transfer-encoding encoding mime-type)
154    encoding))
155
156(defun mm-insert-headers (type encoding &optional file)
157  "Insert headers for TYPE."
158  (insert "Content-Type: " type)
159  (when file
160    (insert ";\n\tname=\"" (file-name-nondirectory file) "\""))
161  (insert "\n")
162  (insert (format "Content-Transfer-Encoding: %s\n" encoding))
163  (insert "Content-Disposition: inline")
164  (when file
165    (insert ";\n\tfilename=\"" (file-name-nondirectory file) "\""))
166  (insert "\n")
167  (insert "\n"))
168
169(defun mm-content-transfer-encoding (type)
170  "Return a CTE suitable for TYPE to encode the current buffer."
171  (let ((rules mm-content-transfer-encoding-defaults))
172    (catch 'found
173      (while rules
174	(when (string-match (caar rules) type)
175	  (throw 'found
176		 (let ((encoding
177			(if (eq (cadr (car rules)) 'qp-or-base64)
178			    (mm-qp-or-base64)
179			  (cadr (car rules)))))
180		   (if mm-use-ultra-safe-encoding
181		       (mm-safer-encoding encoding)
182		     encoding))))
183	(pop rules)))))
184
185(defun mm-qp-or-base64 ()
186  "Return the type with which to encode the buffer.
187This is either `base64' or `quoted-printable'."
188  (if (equal mm-use-ultra-safe-encoding '(sign . "pgp"))
189      ;; perhaps not always accurate?
190      'quoted-printable
191    (save-excursion
192      (let ((limit (min (point-max) (+ 2000 (point-min))))
193	    (n8bit 0))
194	(goto-char (point-min))
195	(skip-chars-forward "\x20-\x7f\r\n\t" limit)
196	(while (< (point) limit)
197	  (incf n8bit)
198	  (forward-char 1)
199	  (skip-chars-forward "\x20-\x7f\r\n\t" limit))
200	(if (or (< (* 6 n8bit) (- limit (point-min)))
201		;; Don't base64, say, a short line with a single
202		;; non-ASCII char when splitting parts by charset.
203		(= n8bit 1))
204	    'quoted-printable
205	  'base64)))))
206
207(provide 'mm-encode)
208
209;;; arch-tag: 7d01bba4-d469-4851-952b-dc863f84ed66
210;;; mm-encode.el ends here
211