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;;; mm-encode.el --- Functions for encoding MIME things -*- lexical-binding: t; -*-
;; Copyright (C) 1998-2025 Free Software Foundation, Inc.
;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
;; MORIOKA Tomohiko <morioka@jaist.ac.jp>
;; This file is part of GNU Emacs.
;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>.
;;; Commentary:
;;; Code:
(eval-when-compile (require 'cl-lib))
(require 'mail-parse)
(autoload 'mailcap-extension-to-mime "mailcap")
(autoload 'mm-body-7-or-8 "mm-bodies")
(autoload 'mm-long-lines-p "mm-bodies")
(defcustom mm-content-transfer-encoding-defaults
'(("text/x-patch" 8bit)
("text/.*" qp-or-base64)
("message/rfc822" 8bit)
("application/emacs-lisp" qp-or-base64)
("application/x-emacs-lisp" qp-or-base64)
("application/x-patch" qp-or-base64)
(".*" base64))
"Alist of regexps that match MIME types and their encodings.
If the encoding is `qp-or-base64', then either quoted-printable
or base64 will be used, depending on what is more efficient.
This list is only consulted when encoding MIME parts in the
bodies -- not for the regular non-MIME-ish messages."
:type '(repeat (list (regexp :tag "MIME type")
(choice :tag "encoding"
(const 7bit)
(const 8bit)
(const qp-or-base64)
(const quoted-printable)
(const base64))))
:group 'mime)
(defcustom mm-sign-option nil
"Option how to create signed parts.
nil, use the default keys without asking;
`guided', let you select signing keys from the menu."
:version "23.2" ;; No Gnus 0.12
:type '(choice (item guided)
(item :tag "default" nil))
:group 'mime-security)
(defcustom mm-encrypt-option nil
"Option how to create encrypted parts.
nil, use the default keys without asking;
`guided', let you select recipients' keys from the menu."
:version "23.2" ;; No Gnus 0.12
:type '(choice (item guided)
(item :tag "default" nil))
:group 'mime-security)
(defvar mm-use-ultra-safe-encoding nil
"If non-nil, use encodings aimed at Procrustean bed survival.
This means that textual parts are encoded as quoted-printable if they
contain lines longer than 76 characters or starting with \"From \" in
the body. Non-7bit encodings (8bit, binary) are generally disallowed.
This is to reduce the probability that a broken MTA or MDA changes the
message.
This variable should never be set directly, but bound before a call to
`mml-generate-mime' or similar functions.")
(defun mm-insert-rfc822-headers (charset encoding)
"Insert text/plain headers with CHARSET and ENCODING."
(insert "MIME-Version: 1.0\n")
(insert "Content-Type: text/plain; charset="
(mail-quote-string (downcase (symbol-name charset))) "\n")
(insert "Content-Transfer-Encoding: "
(downcase (symbol-name encoding)) "\n"))
(defun mm-insert-multipart-headers ()
"Insert multipart/mixed headers."
(let ((boundary "=-=-="))
(insert "MIME-Version: 1.0\n")
(insert "Content-Type: multipart/mixed; boundary=\"" boundary "\"\n")
boundary))
;;;###autoload
(define-obsolete-function-alias 'mm-default-file-encoding
#'mm-default-file-type "28.1") ;Old bad name.
;;;###autoload
(defun mm-default-file-type (file)
"Return a default content type for FILE."
(if (not (string-match "\\.[^.]+\\'" file))
"application/octet-stream"
(mailcap-extension-to-mime (match-string 0 file))))
(defun mm-safer-encoding (encoding &optional type)
"Return an encoding similar to ENCODING but safer than it."
(cond
((eq encoding '7bit) '7bit) ;; 7bit is considered safe.
((memq encoding '(8bit quoted-printable))
;; According to RFC2046, 5.2.1, RFC822 Subtype, "quoted-printable" is not
;; a valid encoding for message/rfc822:
;; No encoding other than "7bit", "8bit", or "binary" is permitted for the
;; body of a "message/rfc822" entity.
(if (string= type "message/rfc822") '8bit 'quoted-printable))
;; The remaining encodings are binary and base64 (and perhaps some
;; non-standard ones), which are both turned into base64.
(t (if (string= type "message/rfc822") 'binary 'base64))))
(defun mm-encode-content-transfer-encoding (encoding &optional type)
"Encode the current buffer with ENCODING for MIME type TYPE.
ENCODING can be: nil (do nothing); one of `quoted-printable', `base64';
`7bit', `8bit' or `binary' (all do nothing); a function to do the encoding."
(cond
((eq encoding 'quoted-printable)
;; This used to try to make a multibyte buffer unibyte. That's
;; completely wrong, since you'd get QP-encoded emacs-mule. If
;; this gets run on multibyte text it's an error that needs
;; fixing, and the encoding function will signal an error.
;; Likewise base64 below.
(quoted-printable-encode-region (point-min) (point-max) t))
((eq encoding 'base64)
(when (string-match "\\`text/" type)
(goto-char (point-min))
(while (search-forward "\n" nil t)
(replace-match "\r\n" t t)))
(base64-encode-region (point-min) (point-max)))
((memq encoding '(7bit 8bit binary))
;; Do nothing.
)
((null encoding)
;; Do nothing.
)
;; Fixme: Ignoring errors here looks bogus.
((functionp encoding)
(ignore-errors (funcall encoding (point-min) (point-max))))
(t
(error "Unknown encoding %s" encoding))))
(defun mm-encode-buffer (type &optional encoding)
"Encode the buffer which contains data of MIME type TYPE by ENCODING.
TYPE is a string or a list of the components.
The optional ENCODING overrides the encoding determined according to
TYPE and `mm-content-transfer-encoding-defaults'.
The encoding used is returned."
(let ((mime-type (if (stringp type) type (car type))))
(mm-encode-content-transfer-encoding
(or encoding
(setq encoding (or (and (listp type)
(cadr (assq 'encoding type)))
(mm-content-transfer-encoding mime-type))))
mime-type)
encoding))
(defun mm-insert-headers (type encoding &optional file)
"Insert headers for TYPE."
(insert "Content-Type: " type)
(when file
(insert ";\n\tname=\"" (file-name-nondirectory file) "\""))
(insert "\n")
(insert (format "Content-Transfer-Encoding: %s\n" encoding))
(insert "Content-Disposition: inline")
(when file
(insert ";\n\tfilename=\"" (file-name-nondirectory file) "\""))
(insert "\n")
(insert "\n"))
(defun mm-content-transfer-encoding (type)
"Return a CTE suitable for TYPE to encode the current buffer."
(let ((rules mm-content-transfer-encoding-defaults))
(catch 'found
(while rules
(when (string-match (caar rules) type)
(throw 'found
(let ((encoding
(if (eq (cadr (car rules)) 'qp-or-base64)
(mm-qp-or-base64)
(cadr (car rules)))))
(if mm-use-ultra-safe-encoding
(mm-safer-encoding encoding type)
encoding))))
(pop rules)))))
(defun mm-qp-or-base64 ()
"Return the type with which to encode the buffer.
This is either `base64' or `quoted-printable'."
(if (equal mm-use-ultra-safe-encoding '(sign . "pgp"))
;; perhaps not always accurate?
'quoted-printable
(save-excursion
(let ((limit (min (point-max) (+ 2000 (point-min))))
(n8bit 0))
(goto-char (point-min))
(skip-chars-forward "\x20-\x7f\r\n\t" limit)
(while (< (point) limit)
(cl-incf n8bit)
(forward-char 1)
(skip-chars-forward "\x20-\x7f\r\n\t" limit))
(if (or (< (* 6 n8bit) (- limit (point-min)))
;; Don't base64, say, a short line with a single
;; non-ASCII char when splitting parts by charset.
(= n8bit 1))
'quoted-printable
'base64)))))
(provide 'mm-encode)
;;; mm-encode.el ends here
|
