3 @setfilename emacs-mime
4 @settitle Emacs MIME Manual
10 * Emacs MIME: (emacs-mime). The MIME de/composition library.
15 @setchapternewpage odd
19 This file documents the Emacs MIME interface functionality.
21 Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003
22 Free Software Foundation, Inc.
24 Permission is granted to copy, distribute and/or modify this document
25 under the terms of the GNU Free Documentation License, Version 1.1 or
26 any later version published by the Free Software Foundation; with no
27 Invariant Sections, with the Front-Cover texts being ``A GNU
28 Manual'', and with the Back-Cover Texts as in (a) below. A copy of the
29 license is included in the section entitled ``GNU Free Documentation
30 License'' in the Emacs manual.
32 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
33 this GNU Manual, like GNU software. Copies published by the Free
34 Software Foundation raise funds for GNU development.''
36 This document is part of a collection distributed under the GNU Free
37 Documentation License. If you want to distribute this document
38 separately from the collection, you can do so by adding a copy of the
39 license to the document, as described in section 6 of the license.
45 @title Emacs MIME Manual
47 @author by Lars Magne Ingebrigtsen
50 @vskip 0pt plus 1filll
51 Copyright @copyright{} 1998, 1999, 2000, 2001, 2002, 2003 Free Software
54 Permission is granted to copy, distribute and/or modify this document
55 under the terms of the GNU Free Documentation License, Version 1.1 or
56 any later version published by the Free Software Foundation; with the
57 Invariant Sections being none, with the Front-Cover texts being ``A GNU
58 Manual'', and with the Back-Cover Texts as in (a) below. A copy of the
59 license is included in the section entitled ``GNU Free Documentation
60 License'' in the Emacs manual.
62 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
63 this GNU Manual, like GNU software. Copies published by the Free
64 Software Foundation raise funds for GNU development.''
66 This document is part of a collection distributed under the GNU Free
67 Documentation License. If you want to distribute this document
68 separately from the collection, you can do so by adding a copy of the
69 license to the document, as described in section 6 of the license.
78 This manual documents the libraries used to compose and display
81 This manual is directed at users who want to modify the behaviour of
82 the @sc{mime} encoding/decoding process or want a more detailed
83 picture of how the Emacs @sc{mime} library works, and people who want
84 to write functions and commands that manipulate @sc{mime} elements.
86 @sc{mime} is short for @dfn{Multipurpose Internet Mail Extensions}.
87 This standard is documented in a number of RFCs; mainly RFC2045 (Format
88 of Internet Message Bodies), RFC2046 (Media Types), RFC2047 (Message
89 Header Extensions for Non-ASCII Text), RFC2048 (Registration
90 Procedures), RFC2049 (Conformance Criteria and Examples). It is highly
91 recommended that anyone who intends writing @sc{mime}-compliant software
92 read at least RFC2045 and RFC2047.
95 * Decoding and Viewing:: A framework for decoding and viewing.
96 * Composing:: MML; a language for describing @sc{mime} parts.
97 * Interface Functions:: An abstraction over the basic functions.
98 * Basic Functions:: Utility and basic parsing functions.
99 * Standards:: A summary of RFCs and working documents used.
100 * Index:: Function and variable index.
104 @node Decoding and Viewing
105 @chapter Decoding and Viewing
107 This chapter deals with decoding and viewing @sc{mime} messages on a
110 The main idea is to first analyze a @sc{mime} article, and then allow
111 other programs to do things based on the list of @dfn{handles} that are
112 returned as a result of this analysis.
115 * Dissection:: Analyzing a @sc{mime} message.
116 * Non-MIME:: Analyzing a non-@sc{mime} message.
117 * Handles:: Handle manipulations.
118 * Display:: Displaying handles.
119 * Display Customization:: Variables that affect display.
120 * New Viewers:: How to write your own viewers.
127 The @code{mm-dissect-buffer} is the function responsible for dissecting
128 a @sc{mime} article. If given a multipart message, it will recursively
129 descend the message, following the structure, and return a tree of
130 @sc{mime} handles that describes the structure of the message.
134 @vindex mm-uu-configure-list
136 Gnus also understands some non-@sc{mime} attachments, such as
137 postscript, uuencode, binhex, yenc, shar, forward, gnatsweb, pgp.
138 Each of these features can be disabled by add an item into
139 @code{mm-uu-configure-list}. For example,
143 (add-to-list 'mm-uu-configure-list '(pgp-signed . disabled))
169 Non-@sc{mime} forwarded message.
177 PGP signed clear text.
180 @findex pgp-encrypted
181 PGP encrypted clear text.
188 @findex emacs-sources
189 Emacs source code. This item works only in the groups matching
190 @code{mm-uu-emacs-sources-regexp}.
197 A @sc{mime} handle is a list that fully describes a @sc{mime}
200 The following macros can be used to access elements in a handle:
203 @item mm-handle-buffer
204 @findex mm-handle-buffer
205 Return the buffer that holds the contents of the undecoded @sc{mime}
209 @findex mm-handle-type
210 Return the parsed @code{Content-Type} of the part.
212 @item mm-handle-encoding
213 @findex mm-handle-encoding
214 Return the @code{Content-Transfer-Encoding} of the part.
216 @item mm-handle-undisplayer
217 @findex mm-handle-undisplayer
218 Return the object that can be used to remove the displayed part (if it
221 @item mm-handle-set-undisplayer
222 @findex mm-handle-set-undisplayer
223 Set the undisplayer object.
225 @item mm-handle-disposition
226 @findex mm-handle-disposition
227 Return the parsed @code{Content-Disposition} of the part.
229 @item mm-handle-disposition
230 @findex mm-handle-disposition
231 Return the description of the part.
233 @item mm-get-content-id
234 Returns the handle(s) referred to by @code{Content-ID}.
242 Functions for displaying, removing and saving.
245 @item mm-display-part
246 @findex mm-display-part
250 @findex mm-remove-part
251 Remove the part (if it has been displayed).
254 @findex mm-inlinable-p
255 Say whether a @sc{mime} type can be displayed inline.
257 @item mm-automatic-display-p
258 @findex mm-automatic-display-p
259 Say whether a @sc{mime} type should be displayed automatically.
261 @item mm-destroy-part
262 @findex mm-destroy-part
263 Free all resources occupied by a part.
267 Offer to save the part in a file.
271 Offer to pipe the part to some process.
273 @item mm-interactively-view-part
274 @findex mm-interactively-view-part
275 Prompt for a mailcap method to use to view the part.
280 @node Display Customization
281 @section Display Customization
285 @item mm-inline-media-tests
286 @vindex mm-inline-media-tests
287 This is an alist where the key is a @sc{mime} type, the second element
288 is a function to display the part @dfn{inline} (i.e., inside Emacs), and
289 the third element is a form to be @code{eval}ed to say whether the part
290 can be displayed inline.
292 This variable specifies whether a part @emph{can} be displayed inline,
293 and, if so, how to do it. It does not say whether parts are
294 @emph{actually} displayed inline.
296 @item mm-inlined-types
297 @vindex mm-inlined-types
298 This, on the other hand, says what types are to be displayed inline, if
299 they satisfy the conditions set by the variable above. It's a list of
300 @sc{mime} media types.
302 @item mm-automatic-display
303 @vindex mm-automatic-display
304 This is a list of types that are to be displayed ``automatically'', but
305 only if the above variable allows it. That is, only inlinable parts can
306 be displayed automatically.
308 @item mm-automatic-external-display
309 @vindex mm-automatic-external-display
310 This is a list of types that will be displayed automatically in an
313 @item mm-keep-viewer-alive-types
314 @vindex mm-keep-viewer-alive-types
315 This is a list of media types for which the external viewer will not
316 be killed when selecting a different article.
318 @item mm-attachment-override-types
319 @vindex mm-attachment-override-types
320 Some @sc{mime} agents create parts that have a content-disposition of
321 @samp{attachment}. This variable allows overriding that disposition and
322 displaying the part inline. (Note that the disposition is only
323 overridden if we are able to, and want to, display the part inline.)
325 @item mm-discouraged-alternatives
326 @vindex mm-discouraged-alternatives
327 List of @sc{mime} types that are discouraged when viewing
328 @samp{multipart/alternative}. Viewing agents are supposed to view the
329 last possible part of a message, as that is supposed to be the richest.
330 However, users may prefer other types instead, and this list says what
331 types are most unwanted. If, for instance, @samp{text/html} parts are
332 very unwanted, and @samp{text/richtext} parts are somewhat unwanted,
333 you could say something like:
336 (setq mm-discouraged-alternatives
337 '("text/html" "text/richtext")
339 (remove "text/html" mm-automatic-display))
342 @item mm-inline-large-images
343 @vindex mm-inline-large-images
344 When displaying inline images that are larger than the window, XEmacs
345 does not enable scrolling, which means that you cannot see the whole
346 image. To prevent this, the library tries to determine the image size
347 before displaying it inline, and if it doesn't fit the window, the
348 library will display it externally (e.g. with @samp{ImageMagick} or
349 @samp{xv}). Setting this variable to @code{t} disables this check and
350 makes the library display all inline images as inline, regardless of
353 @item mm-inline-override-types
354 @vindex mm-inline-override-types
355 @code{mm-inlined-types} may include regular expressions, for example to
356 specify that all @samp{text/.*} parts be displayed inline. If a user
357 prefers to have a type that matches such a regular expression be treated
358 as an attachment, that can be accomplished by setting this variable to a
359 list containing that type. For example assuming @code{mm-inlined-types}
360 includes @samp{text/.*}, then including @samp{text/html} in this
361 variable will cause @samp{text/html} parts to be treated as attachments.
363 @item mm-text-html-renderer
364 @vindex mm-text-html-renderer
365 This selects the function used to render @sc{html}. The predefined
366 renderers are selected by the symbols @code{w3},
367 @code{w3m}@footnote{See @uref{http://emacs-w3m.namazu.org/} for more
368 information about emacs-w3m}, @code{links}, @code{lynx},
369 @code{w3m-standalone} or @code{html2text}. If @code{nil} use an
370 external viewer. You can also specify a function, which will be
371 called with a @sc{mime} handle as the argument.
373 @item mm-inline-text-html-with-images
374 @vindex mm-inline-text-html-with-images
375 Some @sc{html} mails might have the trick of spammers using
376 @samp{<img>} tags. It is likely to be intended to verify whether you
377 have read the mail. You can prevent your personal informations from
378 leaking by setting this option to @code{nil} (which is the default).
379 It is currently ignored by Emacs/w3. For emacs-w3m, you may use the
380 command @kbd{t} on the image anchor to show an image even if it is
381 @code{nil}.@footnote{The command @kbd{T} will load all images. If you
382 have set the option @code{w3m-key-binding} to @code{info}, use @kbd{i}
385 @item mm-w3m-safe-url-regexp
386 @vindex mm-w3m-safe-url-regexp
387 A regular expression that matches safe URL names, i.e. URLs that are
388 unlikely to leak personal information when rendering @sc{html} email
389 (the default value is @samp{\\`cid:}). If @code{nil} consider all
392 @item mm-inline-text-html-with-w3m-keymap
393 @vindex mm-inline-text-html-with-w3m-keymap
394 You can use emacs-w3m command keys in the inlined text/html part by
395 setting this option to non-@code{nil}. The default value is @code{t}.
397 @item mm-external-terminal-program
398 @vindex mm-external-terminal-program
399 The program used to start an external terminal.
407 Here's an example viewer for displaying @code{text/enriched} inline:
410 (defun mm-display-enriched-inline (handle)
413 (mm-insert-part handle)
414 (save-window-excursion
415 (enriched-decode (point-min) (point-max))
416 (setq text (buffer-string))))
417 (mm-insert-inline handle text)))
420 We see that the function takes a @sc{mime} handle as its parameter. It
421 then goes to a temporary buffer, inserts the text of the part, does some
422 work on the text, stores the result, goes back to the buffer it was
423 called from and inserts the result.
425 The two important helper functions here are @code{mm-insert-part} and
426 @code{mm-insert-inline}. The first function inserts the text of the
427 handle in the current buffer. It handles charset and/or content
428 transfer decoding. The second function just inserts whatever text you
429 tell it to insert, but it also sets things up so that the text can be
430 ``undisplayed' in a convenient manner.
436 @cindex MIME Composing
438 @cindex MIME Meta Language
440 Creating a @sc{mime} message is boring and non-trivial. Therefore, a
441 library called @code{mml} has been defined that parses a language called
442 MML (@sc{mime} Meta Language) and generates @sc{mime} messages.
444 @findex mml-generate-mime
445 The main interface function is @code{mml-generate-mime}. It will
446 examine the contents of the current (narrowed-to) buffer and return a
447 string containing the @sc{mime} message.
450 * Simple MML Example:: An example MML document.
451 * MML Definition:: All valid MML elements.
452 * Advanced MML Example:: Another example MML document.
453 * Encoding Customization:: Variables that affect encoding.
454 * Charset Translation:: How charsets are mapped from @sc{mule} to @sc{mime}.
455 * Conversion:: Going from @sc{mime} to MML and vice versa.
456 * Flowed text:: Soft and hard newlines.
460 @node Simple MML Example
461 @section Simple MML Example
463 Here's a simple @samp{multipart/alternative}:
466 <#multipart type=alternative>
467 This is a plain text part.
468 <#part type=text/enriched>
469 <center>This is a centered enriched part</center>
473 After running this through @code{mml-generate-mime}, we get this:
476 Content-Type: multipart/alternative; boundary="=-=-="
482 This is a plain text part.
485 Content-Type: text/enriched
488 <center>This is a centered enriched part</center>
495 @section MML Definition
497 The MML language is very simple. It looks a bit like an SGML
498 application, but it's not.
500 The main concept of MML is the @dfn{part}. Each part can be of a
501 different type or use a different charset. The way to delineate a part
502 is with a @samp{<#part ...>} tag. Multipart parts can be introduced
503 with the @samp{<#multipart ...>} tag. Parts are ended by the
504 @samp{<#/part>} or @samp{<#/multipart>} tags. Parts started with the
505 @samp{<#part ...>} tags are also closed by the next open tag.
507 There's also the @samp{<#external ...>} tag. These introduce
508 @samp{external/message-body} parts.
510 Each tag can contain zero or more parameters on the form
511 @samp{parameter=value}. The values may be enclosed in quotation marks,
512 but that's not necessary unless the value contains white space. So
513 @samp{filename=/home/user/#hello$^yes} is perfectly valid.
515 The following parameters have meaning in MML; parameters that have no
516 meaning are ignored. The MML parameter names are the same as the
517 @sc{mime} parameter names; the things in the parentheses say which
518 header it will be used in.
522 The @sc{mime} type of the part (@code{Content-Type}).
525 Use the contents of the file in the body of the part
526 (@code{Content-Disposition}).
529 The contents of the body of the part are to be encoded in the character
530 set speficied (@code{Content-Type}). @xref{Charset Translation}.
533 Might be used to suggest a file name if the part is to be saved
534 to a file (@code{Content-Type}).
537 Valid values are @samp{inline} and @samp{attachment}
538 (@code{Content-Disposition}).
541 Valid values are @samp{7bit}, @samp{8bit}, @samp{quoted-printable} and
542 @samp{base64} (@code{Content-Transfer-Encoding}). @xref{Charset
546 A description of the part (@code{Content-Description}).
549 RFC822 date when the part was created (@code{Content-Disposition}).
551 @item modification-date
552 RFC822 date when the part was modified (@code{Content-Disposition}).
555 RFC822 date when the part was read (@code{Content-Disposition}).
558 Who to encrypt/sign the part to. This field is used to override any
559 auto-detection based on the To/CC headers.
562 The size (in octets) of the part (@code{Content-Disposition}).
565 What technology to sign this MML part with (@code{smime}, @code{pgp}
569 What technology to encrypt this MML part with (@code{smime},
570 @code{pgp} or @code{pgpmime})
574 Parameters for @samp{application/octet-stream}:
578 Type of the part; informal---meant for human readers
579 (@code{Content-Type}).
582 Parameters for @samp{message/external-body}:
586 A word indicating the supported access mechanism by which the file may
587 be obtained. Values include @samp{ftp}, @samp{anon-ftp}, @samp{tftp},
588 @samp{localfile}, and @samp{mailserver}. (@code{Content-Type}.)
591 The RFC822 date after which the file may no longer be fetched.
592 (@code{Content-Type}.)
595 The size (in octets) of the file. (@code{Content-Type}.)
598 Valid values are @samp{read} and @samp{read-write}
599 (@code{Content-Type}).
603 Parameters for @samp{sign=smime}:
608 File containing key and certificate for signer.
612 Parameters for @samp{encrypt=smime}:
617 File containing certificate for recipient.
622 @node Advanced MML Example
623 @section Advanced MML Example
625 Here's a complex multipart message. It's a @samp{multipart/mixed} that
626 contains many parts, one of which is a @samp{multipart/alternative}.
629 <#multipart type=mixed>
630 <#part type=image/jpeg filename=~/rms.jpg disposition=inline>
631 <#multipart type=alternative>
632 This is a plain text part.
633 <#part type=text/enriched name=enriched.txt>
634 <center>This is a centered enriched part</center>
636 This is a new plain text part.
637 <#part disposition=attachment>
638 This plain text part is an attachment.
642 And this is the resulting @sc{mime} message:
645 Content-Type: multipart/mixed; boundary="=-=-="
653 Content-Type: image/jpeg;
655 Content-Disposition: inline;
657 Content-Transfer-Encoding: base64
659 /9j/4AAQSkZJRgABAQAAAQABAAD/2wBDAAgGBgcGBQgHBwcJCQgKDBQNDAsLDBkSEw8UHRof
660 Hh0aHBwgJC4nICIsIxwcKDcpLDAxNDQ0Hyc5PTgyPC4zNDL/wAALCAAwADABAREA/8QAHwAA
661 AQUBAQEBAQEAAAAAAAAAAAECAwQFBgcICQoL/8QAtRAAAgEDAwIEAwUFBAQAAAF9AQIDAAQR
662 BRIhMUEGE1FhByJxFDKBkaEII0KxwRVS0fAkM2JyggkKFhcYGRolJicoKSo0NTY3ODk6Q0RF
663 RkdISUpTVFVWV1hZWmNkZWZnaGlqc3R1dnd4eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ip
664 qrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uHi4+Tl5ufo6erx8vP09fb3+Pn6/9oACAEB
665 AAA/AO/rifFHjldNuGsrDa0qcSSHkA+gHrXKw+LtWLrMb+RgTyhbr+HSug07xNqV9fQtZrNI
666 AyiaE/NuBPOOOP0rvRNE880KOC8TbXXGCv1FPqjrF4LDR7u5L7SkTFT/ALWOP1xXgTuXfc7E
667 sx6nua6rwp4IvvEM8chCxWxOdzn7wz6V9AaB4S07w9p5itow0rDLSY5Pt9K43xO66P4xs71m
668 2QXiGCbA4yOVJ9+1aYORkdK434lyNH4ahCnG66VT9Nj15JFbPdX0MS43M4VQf5/yr2vSpLnw
669 5ZW8dlCZ8KFXjOPX0/mK6rSPEGt3Angu44fNEReHYNvIH3TzXDeKNO8RX+kSX2ouZkicTIOc
670 L+g7E810ulFjpVtv3bwgB3HJyK5L4quY/C9sVxk3ij/xx6850u7t1mtp/wDlpEw3An3Jr3Dw
671 34gsbWza4nBlhC5LDsaW6+IFgupQyCF3iHH7gA7c9R9ay7zx6t7aX9jHC4smhfBkGCvHGfrm
672 tLQ7hbnRrV1GPkAP1x1/Hr+Ncr8Vzjwrbf8AX6v/AKA9eQRyYlQk8Yx9K6XTNbkgia2ciSIn
673 7p5Ga9Atte0LTLKO6it4i7dVRFJDcZ4PvXN+JvEMF9bILVGXJLSZ4zkjivRPDaeX4b08HOTC
674 pOffmua+KkbS+GLVUGT9tT/0B68eeIpIFYjB70+OOVXyoOM9+M1eaWeCLzHPyHGO/NVWvJJm
675 jQ8KGH1NfQWhXSXmh2c8eArRLwO3HSv/2Q==
678 Content-Type: multipart/alternative; boundary="==-=-="
684 This is a plain text part.
687 Content-Type: text/enriched;
691 <center>This is a centered enriched part</center>
697 This is a new plain text part.
700 Content-Disposition: attachment
703 This plain text part is an attachment.
708 @node Encoding Customization
709 @section Encoding Customization
713 @item mm-body-charset-encoding-alist
714 @vindex mm-body-charset-encoding-alist
715 Mapping from @sc{mime} charset to encoding to use. This variable is
716 usually used except, e.g., when other requirements force a specific
717 encoding (digitally signed messages require 7bit encodings). The
718 default is @code{((iso-2022-jp . 7bit) (iso-2022-jp-2 . 7bit))}. As
719 an example, if you do not want to have ISO-8859-1 characters
720 quoted-printable encoded, you may add @code{(iso-8859-1 . 8bit)} to
721 this variable. You can override this setting on a per-message basis
722 by using the @code{encoding} MML tag (@pxref{MML Definition}).
724 @item mm-coding-system-priorities
725 @vindex mm-coding-system-priorities
726 Prioritize coding systems to use for outgoing messages. The default
727 is @code{nil}, which means to use the defaults in Emacs. It is a list of
728 coding system symbols (aliases of coding systems does not work, use
729 @kbd{M-x describe-coding-system} to make sure you are not specifying
730 an alias in this variable). For example, if you have configured Emacs
731 to use prefer UTF-8, but wish that outgoing messages should be sent in
732 ISO-8859-1 if possible, you can set this variable to
733 @code{(iso-latin-1)}. You can override this setting on a per-message
734 basis by using the @code{charset} MML tag (@pxref{MML Definition}).
736 @item mm-content-transfer-encoding-defaults
737 @vindex mm-content-transfer-encoding-defaults
738 Mapping from @sc{mime} types to encoding to use. This variable is usually
739 used except, e.g., when other requirements force a safer encoding
740 (digitally signed messages require 7bit encoding). Besides the normal
741 @sc{mime} encodings, @code{qp-or-base64} may be used to indicate that for
742 each case the most efficient of quoted-printable and base64 should be
743 used. You can override this setting on a per-message basis by using
744 the @code{encoding} MML tag (@pxref{MML Definition}).
746 @item mm-use-ultra-safe-encoding
747 @vindex mm-use-ultra-safe-encoding
748 When this is non-@code{nil}, it means that textual parts are encoded as
749 quoted-printable if they contain lines longer than 76 characters or
750 starting with "From " in the body. Non-7bit encodings (8bit, binary)
751 are generally disallowed. This reduce the probability that a non-8bit
752 clean MTA or MDA changes the message. This should never be set
753 directly, but bound by other functions when necessary (e.g., when
754 encoding messages that are to be digitally signed).
758 @node Charset Translation
759 @section Charset Translation
762 During translation from MML to @sc{mime}, for each @sc{mime} part which
763 has been composed inside Emacs, an appropriate charset has to be chosen.
765 @vindex mail-parse-charset
766 If you are running a non-@sc{mule} Emacs, this process is simple: If the
767 part contains any non-ASCII (8-bit) characters, the @sc{mime} charset
768 given by @code{mail-parse-charset} (a symbol) is used. (Never set this
769 variable directly, though. If you want to change the default charset,
770 please consult the documentation of the package which you use to process
772 @xref{Various Message Variables, , Various Message Variables, message,
773 Message Manual}, for example.)
774 If there are only ASCII characters, the @sc{mime} charset US-ASCII is
780 @vindex mm-mime-mule-charset-alist
781 Things are slightly more complicated when running Emacs with @sc{mule}
782 support. In this case, a list of the @sc{mule} charsets used in the
783 part is obtained, and the @sc{mule} charsets are translated to @sc{mime}
784 charsets by consulting the variable @code{mm-mime-mule-charset-alist}.
785 If this results in a single @sc{mime} charset, this is used to encode
786 the part. But if the resulting list of @sc{mime} charsets contains more
787 than one element, two things can happen: If it is possible to encode the
788 part via UTF-8, this charset is used. (For this, Emacs must support
789 the @code{utf-8} coding system, and the part must consist entirely of
790 characters which have Unicode counterparts.) If UTF-8 is not available
791 for some reason, the part is split into several ones, so that each one
792 can be encoded with a single @sc{mime} charset. The part can only be
793 split at line boundaries, though---if more than one @sc{mime} charset is
794 required to encode a single line, it is not possible to encode the part.
796 When running Emacs with @sc{mule} support, the preferences for which
797 coding system to use is inherited from Emacs itself. This means that
798 if Emacs is set up to prefer UTF-8, it will be used when encoding
799 messages. You can modify this by altering the
800 @code{mm-coding-system-priorities} variable though (@pxref{Encoding
803 The charset to be used can be overriden by setting the @code{charset}
804 MML tag (@pxref{MML Definition}) when composing the message.
806 The encoding of characters (quoted-printable, 8bit etc) is orthogonal
807 to the discussion here, and is controlled by the variables
808 @code{mm-body-charset-encoding-alist} and
809 @code{mm-content-transfer-encoding-defaults} (@pxref{Encoding
816 A (multipart) @sc{mime} message can be converted to MML with the
817 @code{mime-to-mml} function. It works on the message in the current
818 buffer, and substitutes MML markup for @sc{mime} boundaries.
819 Non-textual parts do not have their contents in the buffer, but instead
820 have the contents in separate buffers that are referred to from the MML
824 An MML message can be converted back to @sc{mime} by the
825 @code{mml-to-mime} function.
827 These functions are in certain senses ``lossy''---you will not get back
828 an identical message if you run @sc{mime-to-mml} and then
829 @sc{mml-to-mime}. Not only will trivial things like the order of the
830 headers differ, but the contents of the headers may also be different.
831 For instance, the original message may use base64 encoding on text,
832 while @sc{mml-to-mime} may decide to use quoted-printable encoding, and
835 In essence, however, these two functions should be the inverse of each
836 other. The resulting contents of the message should remain equivalent,
842 @cindex format=flowed
844 The Emacs @sc{mime} library will respect the @code{use-hard-newlines}
845 variable (@pxref{Hard and Soft Newlines, ,Hard and Soft Newlines,
846 emacs, Emacs Manual}) when encoding a message, and the
847 ``format=flowed'' Content-Type parameter when decoding a message.
849 On encoding text, lines terminated by soft newline characters are
850 filled together and wrapped after the column decided by
851 @code{fill-flowed-encode-column}. This variable controls how the text
852 will look in a client that does not support flowed text, the default
853 is to wrap after 66 characters. If hard newline characters are not
854 present in the buffer, no flow encoding occurs.
856 On decoding flowed text, lines with soft newline characters are filled
857 together and wrapped after the column decided by
858 @code{fill-flowed-display-column}. The default is to wrap after
864 @node Interface Functions
865 @chapter Interface Functions
866 @cindex interface functions
869 The @code{mail-parse} library is an abstraction over the actual
870 low-level libraries that are described in the next chapter.
872 Standards change, and so programs have to change to fit in the new
873 mold. For instance, RFC2045 describes a syntax for the
874 @code{Content-Type} header that only allows ASCII characters in the
875 parameter list. RFC2231 expands on RFC2045 syntax to provide a scheme
876 for continuation headers and non-ASCII characters.
878 The traditional way to deal with this is just to update the library
879 functions to parse the new syntax. However, this is sometimes the wrong
880 thing to do. In some instances it may be vital to be able to understand
881 both the old syntax as well as the new syntax, and if there is only one
882 library, one must choose between the old version of the library and the
883 new version of the library.
885 The Emacs @sc{mime} library takes a different tack. It defines a
886 series of low-level libraries (@file{rfc2047.el}, @file{rfc2231.el}
887 and so on) that parses strictly according to the corresponding
888 standard. However, normal programs would not use the functions
889 provided by these libraries directly, but instead use the functions
890 provided by the @code{mail-parse} library. The functions in this
891 library are just aliases to the corresponding functions in the latest
892 low-level libraries. Using this scheme, programs get a consistent
893 interface they can use, and library developers are free to create
894 write code that handles new standards.
896 The following functions are defined by this library:
899 @item mail-header-parse-content-type
900 @findex mail-header-parse-content-type
901 Parse a @code{Content-Type} header and return a list on the following
906 (attribute1 . value1)
907 (attribute2 . value2)
914 (mail-header-parse-content-type
915 "image/gif; name=\"b980912.gif\"")
916 @result{} ("image/gif" (name . "b980912.gif"))
919 @item mail-header-parse-content-disposition
920 @findex mail-header-parse-content-disposition
921 Parse a @code{Content-Disposition} header and return a list on the same
922 format as the function above.
924 @item mail-content-type-get
925 @findex mail-content-type-get
926 Takes two parameters---a list on the format above, and an attribute.
927 Returns the value of the attribute.
930 (mail-content-type-get
931 '("image/gif" (name . "b980912.gif")) 'name)
932 @result{} "b980912.gif"
935 @item mail-header-encode-parameter
936 @findex mail-header-encode-parameter
937 Takes a parameter string and returns an encoded version of the string.
938 This is used for parameters in headers like @code{Content-Type} and
939 @code{Content-Disposition}.
941 @item mail-header-remove-comments
942 @findex mail-header-remove-comments
943 Return a comment-free version of a header.
946 (mail-header-remove-comments
947 "Gnus/5.070027 (Pterodactyl Gnus v0.27) (Finnish Landrace)")
948 @result{} "Gnus/5.070027 "
951 @item mail-header-remove-whitespace
952 @findex mail-header-remove-whitespace
953 Remove linear white space from a header. Space inside quoted strings
954 and comments is preserved.
957 (mail-header-remove-whitespace
958 "image/gif; name=\"Name with spaces\"")
959 @result{} "image/gif;name=\"Name with spaces\""
962 @item mail-header-get-comment
963 @findex mail-header-get-comment
964 Return the last comment in a header.
967 (mail-header-get-comment
968 "Gnus/5.070027 (Pterodactyl Gnus v0.27) (Finnish Landrace)")
969 @result{} "Finnish Landrace"
972 @item mail-header-parse-address
973 @findex mail-header-parse-address
974 Parse an address and return a list containing the mailbox and the
978 (mail-header-parse-address
979 "Hrvoje Niksic <hniksic@@srce.hr>")
980 @result{} ("hniksic@@srce.hr" . "Hrvoje Niksic")
983 @item mail-header-parse-addresses
984 @findex mail-header-parse-addresses
985 Parse a string with list of addresses and return a list of elements like
986 the one described above.
989 (mail-header-parse-addresses
990 "Hrvoje Niksic <hniksic@@srce.hr>, Steinar Bang <sb@@metis.no>")
991 @result{} (("hniksic@@srce.hr" . "Hrvoje Niksic")
992 ("sb@@metis.no" . "Steinar Bang"))
995 @item mail-header-parse-date
996 @findex mail-header-parse-date
997 Parse a date string and return an Emacs time structure.
999 @item mail-narrow-to-head
1000 @findex mail-narrow-to-head
1001 Narrow the buffer to the header section of the buffer. Point is placed
1002 at the beginning of the narrowed buffer.
1004 @item mail-header-narrow-to-field
1005 @findex mail-header-narrow-to-field
1006 Narrow the buffer to the header under point. Understands continuation
1009 @item mail-header-fold-field
1010 @findex mail-header-fold-field
1011 Fold the header under point.
1013 @item mail-header-unfold-field
1014 @findex mail-header-unfold-field
1015 Unfold the header under point.
1017 @item mail-header-field-value
1018 @findex mail-header-field-value
1019 Return the value of the field under point.
1021 @item mail-encode-encoded-word-region
1022 @findex mail-encode-encoded-word-region
1023 Encode the non-ASCII words in the region. For instance,
1024 @samp{Naïve} is encoded as @samp{=?iso-8859-1?q?Na=EFve?=}.
1026 @item mail-encode-encoded-word-buffer
1027 @findex mail-encode-encoded-word-buffer
1028 Encode the non-ASCII words in the current buffer. This function is
1029 meant to be called narrowed to the headers of a message.
1031 @item mail-encode-encoded-word-string
1032 @findex mail-encode-encoded-word-string
1033 Encode the words that need encoding in a string, and return the result.
1036 (mail-encode-encoded-word-string
1037 "This is naïve, baby")
1038 @result{} "This is =?iso-8859-1?q?na=EFve,?= baby"
1041 @item mail-decode-encoded-word-region
1042 @findex mail-decode-encoded-word-region
1043 Decode the encoded words in the region.
1045 @item mail-decode-encoded-word-string
1046 @findex mail-decode-encoded-word-string
1047 Decode the encoded words in the string and return the result.
1050 (mail-decode-encoded-word-string
1051 "This is =?iso-8859-1?q?na=EFve,?= baby")
1052 @result{} "This is naïve, baby"
1057 Currently, @code{mail-parse} is an abstraction over @code{ietf-drums},
1058 @code{rfc2047}, @code{rfc2045} and @code{rfc2231}. These are documented
1059 in the subsequent sections.
1063 @node Basic Functions
1064 @chapter Basic Functions
1066 This chapter describes the basic, ground-level functions for parsing and
1067 handling. Covered here is parsing @code{From} lines, removing comments
1068 from header lines, decoding encoded words, parsing date headers and so
1069 on. High-level functionality is dealt with in the next chapter
1070 (@pxref{Decoding and Viewing}).
1073 * rfc2045:: Encoding @code{Content-Type} headers.
1074 * rfc2231:: Parsing @code{Content-Type} headers.
1075 * ietf-drums:: Handling mail headers defined by RFC822bis.
1076 * rfc2047:: En/decoding encoded words in headers.
1077 * time-date:: Functions for parsing dates and manipulating time.
1078 * qp:: Quoted-Printable en/decoding.
1079 * base64:: Base64 en/decoding.
1080 * binhex:: Binhex decoding.
1081 * uudecode:: Uuencode decoding.
1082 * yenc:: Yenc decoding.
1083 * rfc1843:: Decoding HZ-encoded text.
1084 * mailcap:: How parts are displayed is specified by the @file{.mailcap} file
1091 RFC2045 is the ``main'' @sc{mime} document, and as such, one would
1092 imagine that there would be a lot to implement. But there isn't, since
1093 most of the implementation details are delegated to the subsequent
1096 So @file{rfc2045.el} has only a single function:
1099 @item rfc2045-encode-string
1100 @findex rfc2045-encode-string
1101 Takes a parameter and a value and returns a @samp{PARAM=VALUE} string.
1102 @var{value} will be quoted if there are non-safe characters in it.
1109 RFC2231 defines a syntax for the @code{Content-Type} and
1110 @code{Content-Disposition} headers. Its snappy name is @dfn{MIME
1111 Parameter Value and Encoded Word Extensions: Character Sets, Languages,
1114 In short, these headers look something like this:
1117 Content-Type: application/x-stuff;
1118 title*0*=us-ascii'en'This%20is%20even%20more%20;
1119 title*1*=%2A%2A%2Afun%2A%2A%2A%20;
1123 They usually aren't this bad, though.
1125 The following functions are defined by this library:
1128 @item rfc2231-parse-string
1129 @findex rfc2231-parse-string
1130 Parse a @code{Content-Type} header and return a list describing its
1134 (rfc2231-parse-string
1135 "application/x-stuff;
1136 title*0*=us-ascii'en'This%20is%20even%20more%20;
1137 title*1*=%2A%2A%2Afun%2A%2A%2A%20;
1138 title*2=\"isn't it!\"")
1139 @result{} ("application/x-stuff"
1140 (title . "This is even more ***fun*** isn't it!"))
1143 @item rfc2231-get-value
1144 @findex rfc2231-get-value
1145 Takes one of the lists on the format above and returns
1146 the value of the specified attribute.
1148 @item rfc2231-encode-string
1149 @findex rfc2231-encode-string
1150 Encode a parameter in headers likes @code{Content-Type} and
1151 @code{Content-Disposition}.
1159 @dfn{drums} is an IETF working group that is working on the replacement
1162 The functions provided by this library include:
1165 @item ietf-drums-remove-comments
1166 @findex ietf-drums-remove-comments
1167 Remove the comments from the argument and return the results.
1169 @item ietf-drums-remove-whitespace
1170 @findex ietf-drums-remove-whitespace
1171 Remove linear white space from the string and return the results.
1172 Spaces inside quoted strings and comments are left untouched.
1174 @item ietf-drums-get-comment
1175 @findex ietf-drums-get-comment
1176 Return the last most comment from the string.
1178 @item ietf-drums-parse-address
1179 @findex ietf-drums-parse-address
1180 Parse an address string and return a list that contains the mailbox and
1181 the plain text name.
1183 @item ietf-drums-parse-addresses
1184 @findex ietf-drums-parse-addresses
1185 Parse a string that contains any number of comma-separated addresses and
1186 return a list that contains mailbox/plain text pairs.
1188 @item ietf-drums-parse-date
1189 @findex ietf-drums-parse-date
1190 Parse a date string and return an Emacs time structure.
1192 @item ietf-drums-narrow-to-header
1193 @findex ietf-drums-narrow-to-header
1194 Narrow the buffer to the header section of the current buffer.
1202 RFC2047 (Message Header Extensions for Non-ASCII Text) specifies how
1203 non-ASCII text in headers are to be encoded. This is actually rather
1204 complicated, so a number of variables are necessary to tweak what this
1207 The following variables are tweakable:
1210 @item rfc2047-default-charset
1211 @vindex rfc2047-default-charset
1212 Characters in this charset should not be decoded by this library.
1213 This defaults to @code{iso-8859-1}.
1215 @item rfc2047-header-encoding-alist
1216 @vindex rfc2047-header-encoding-alist
1217 This is an alist of header / encoding-type pairs. Its main purpose is
1218 to prevent encoding of certain headers.
1220 The keys can either be header regexps, or @code{t}.
1222 The values can be either @code{nil}, in which case the header(s) in
1223 question won't be encoded, or @code{mime}, which means that they will be
1226 @item rfc2047-charset-encoding-alist
1227 @vindex rfc2047-charset-encoding-alist
1228 RFC2047 specifies two forms of encoding---@code{Q} (a
1229 Quoted-Printable-like encoding) and @code{B} (base64). This alist
1230 specifies which charset should use which encoding.
1232 @item rfc2047-encoding-function-alist
1233 @vindex rfc2047-encoding-function-alist
1234 This is an alist of encoding / function pairs. The encodings are
1235 @code{Q}, @code{B} and @code{nil}.
1237 @item rfc2047-q-encoding-alist
1238 @vindex rfc2047-q-encoding-alist
1239 The @code{Q} encoding isn't quite the same for all headers. Some
1240 headers allow a narrower range of characters, and that is what this
1241 variable is for. It's an alist of header regexps / allowable character
1244 @item rfc2047-encoded-word-regexp
1245 @vindex rfc2047-encoded-word-regexp
1246 When decoding words, this library looks for matches to this regexp.
1250 Those were the variables, and these are this functions:
1253 @item rfc2047-narrow-to-field
1254 @findex rfc2047-narrow-to-field
1255 Narrow the buffer to the header on the current line.
1257 @item rfc2047-encode-message-header
1258 @findex rfc2047-encode-message-header
1259 Should be called narrowed to the header of a message. Encodes according
1260 to @code{rfc2047-header-encoding-alist}.
1262 @item rfc2047-encode-region
1263 @findex rfc2047-encode-region
1264 Encodes all encodable words in the region specified.
1266 @item rfc2047-encode-string
1267 @findex rfc2047-encode-string
1268 Encode a string and return the results.
1270 @item rfc2047-decode-region
1271 @findex rfc2047-decode-region
1272 Decode the encoded words in the region.
1274 @item rfc2047-decode-string
1275 @findex rfc2047-decode-string
1276 Decode a string and return the results.
1284 While not really a part of the @sc{mime} library, it is convenient to
1285 document this library here. It deals with parsing @code{Date} headers
1286 and manipulating time. (Not by using tesseracts, though, I'm sorry to
1289 These functions convert between five formats: A date string, an Emacs
1290 time structure, a decoded time list, a second number, and a day number.
1292 Here's a bunch of time/date/second/day examples:
1295 (parse-time-string "Sat Sep 12 12:21:54 1998 +0200")
1296 @result{} (54 21 12 12 9 1998 6 nil 7200)
1298 (date-to-time "Sat Sep 12 12:21:54 1998 +0200")
1299 @result{} (13818 19266)
1301 (time-to-seconds '(13818 19266))
1302 @result{} 905595714.0
1304 (seconds-to-time 905595714.0)
1305 @result{} (13818 19266 0)
1307 (time-to-days '(13818 19266))
1310 (days-to-time 729644)
1311 @result{} (961933 65536)
1313 (time-since '(13818 19266))
1316 (time-less-p '(13818 19266) '(13818 19145))
1319 (subtract-time '(13818 19266) '(13818 19145))
1322 (days-between "Sat Sep 12 12:21:54 1998 +0200"
1323 "Sat Sep 07 12:21:54 1998 +0200")
1326 (date-leap-year-p 2000)
1329 (time-to-day-in-year '(13818 19266))
1332 (time-to-number-of-days
1334 (date-to-time "Mon, 01 Jan 2001 02:22:26 GMT")))
1335 @result{} 4.146122685185185
1338 And finally, we have @code{safe-date-to-time}, which does the same as
1339 @code{date-to-time}, but returns a zero time if the date is
1340 syntactically malformed.
1342 The five data representations used are the following:
1346 An RFC822 (or similar) date string. For instance: @code{"Sat Sep 12
1347 12:21:54 1998 +0200"}.
1350 An internal Emacs time. For instance: @code{(13818 26466)}.
1353 A floating point representation of the internal Emacs time. For
1354 instance: @code{905595714.0}.
1357 An integer number representing the number of days since 00000101. For
1358 instance: @code{729644}.
1361 A list of decoded time. For instance: @code{(54 21 12 12 9 1998 6 t
1365 All the examples above represent the same moment.
1367 These are the functions available:
1371 Take a date and return a time.
1373 @item time-to-seconds
1374 Take a time and return seconds.
1376 @item seconds-to-time
1377 Take seconds and return a time.
1380 Take a time and return days.
1383 Take days and return a time.
1386 Take a date and return days.
1388 @item time-to-number-of-days
1389 Take a time and return the number of days that represents.
1391 @item safe-date-to-time
1392 Take a date and return a time. If the date is not syntactically valid,
1393 return a "zero" date.
1396 Take two times and say whether the first time is less (i. e., earlier)
1397 than the second time.
1400 Take a time and return a time saying how long it was since that time.
1403 Take two times and subtract the second from the first. I. e., return
1404 the time between the two times.
1407 Take two days and return the number of days between those two days.
1409 @item date-leap-year-p
1410 Take a year number and say whether it's a leap year.
1412 @item time-to-day-in-year
1413 Take a time and return the day number within the year that the time is
1422 This library deals with decoding and encoding Quoted-Printable text.
1424 Very briefly explained, qp encoding means translating all 8-bit
1425 characters (and lots of control characters) into things that look like
1426 @samp{=EF}; that is, an equal sign followed by the byte encoded as a hex
1429 The following functions are defined by the library:
1432 @item quoted-printable-decode-region
1433 @findex quoted-printable-decode-region
1434 QP-decode all the encoded text in the specified region.
1436 @item quoted-printable-decode-string
1437 @findex quoted-printable-decode-string
1438 Decode the QP-encoded text in a string and return the results.
1440 @item quoted-printable-encode-region
1441 @findex quoted-printable-encode-region
1442 QP-encode all the encodable characters in the specified region. The third
1443 optional parameter @var{fold} specifies whether to fold long lines.
1444 (Long here means 72.)
1446 @item quoted-printable-encode-string
1447 @findex quoted-printable-encode-string
1448 QP-encode all the encodable characters in a string and return the
1458 Base64 is an encoding that encodes three bytes into four characters,
1459 thereby increasing the size by about 33%. The alphabet used for
1460 encoding is very resistant to mangling during transit.
1462 The following functions are defined by this library:
1465 @item base64-encode-region
1466 @findex base64-encode-region
1467 base64 encode the selected region. Return the length of the encoded
1468 text. Optional third argument @var{no-line-break} means do not break
1469 long lines into shorter lines.
1471 @item base64-encode-string
1472 @findex base64-encode-string
1473 base64 encode a string and return the result.
1475 @item base64-decode-region
1476 @findex base64-decode-region
1477 base64 decode the selected region. Return the length of the decoded
1478 text. If the region can't be decoded, return @code{nil} and don't
1481 @item base64-decode-string
1482 @findex base64-decode-string
1483 base64 decode a string and return the result. If the string can't be
1484 decoded, @code{nil} is returned.
1495 @code{binhex} is an encoding that originated in Macintosh environments.
1496 The following function is supplied to deal with these:
1499 @item binhex-decode-region
1500 @findex binhex-decode-region
1501 Decode the encoded text in the region. If given a third parameter, only
1502 decode the @code{binhex} header and return the filename.
1511 @code{uuencode} is probably still the most popular encoding of binaries
1512 used on Usenet, although @code{base64} rules the mail world.
1514 The following function is supplied by this package:
1517 @item uudecode-decode-region
1518 @findex uudecode-decode-region
1519 Decode the text in the region.
1527 @code{yenc} is used for encoding binaries on Usenet. The following
1528 function is supplied by this package:
1531 @item yenc-decode-region
1532 @findex yenc-decode-region
1533 Decode the encoded text in the region.
1544 RFC1843 deals with mixing Chinese and ASCII characters in messages. In
1545 essence, RFC1843 switches between ASCII and Chinese by doing this:
1548 This sentence is in ASCII.
1549 The next sentence is in GB.~@{<:Ky2;S@{#,NpJ)l6HK!#~@}Bye.
1552 Simple enough, and widely used in China.
1554 The following functions are available to handle this encoding:
1557 @item rfc1843-decode-region
1558 Decode HZ-encoded text in the region.
1560 @item rfc1843-decode-string
1561 Decode a HZ-encoded string and return the result.
1569 The @file{~/.mailcap} file is parsed by most @sc{mime}-aware message
1570 handlers and describes how elements are supposed to be displayed.
1571 Here's an example file:
1575 audio/wav; wavplayer %s
1576 application/msword; catdoc %s ; copiousoutput ; nametemplate=%s.doc
1579 This says that all image files should be displayed with @code{gimp},
1580 that WAVE audio files should be played by @code{wavplayer}, and that
1581 MS-WORD files should be inlined by @code{catdoc}.
1583 The @code{mailcap} library parses this file, and provides functions for
1587 @item mailcap-mime-data
1588 @vindex mailcap-mime-data
1589 This variable is an alist of alists containing backup viewing rules.
1593 Interface functions:
1596 @item mailcap-parse-mailcaps
1597 @findex mailcap-parse-mailcaps
1598 Parse the @file{~/.mailcap} file.
1600 @item mailcap-mime-info
1601 Takes a @sc{mime} type as its argument and returns the matching viewer.
1611 The Emacs @sc{mime} library implements handling of various elements
1612 according to a (somewhat) large number of RFCs, drafts and standards
1613 documents. This chapter lists the relevant ones. They can all be
1614 fetched from @uref{http://quimby.gnus.org/notes/}.
1619 Standard for the Format of ARPA Internet Text Messages.
1622 Standard for Interchange of USENET Messages
1625 Format of Internet Message Bodies
1631 Message Header Extensions for Non-ASCII Text
1634 Registration Procedures
1637 Conformance Criteria and Examples
1640 @sc{mime} Parameter Value and Encoded Word Extensions: Character Sets,
1641 Languages, and Continuations
1644 HZ - A Data Format for Exchanging Files of Arbitrarily Mixed Chinese and
1647 @item draft-ietf-drums-msg-fmt-05.txt
1648 Draft for the successor of RFC822
1651 The @sc{mime} Multipart/Related Content-type
1654 The Multipart/Report Content Type for the Reporting of Mail System
1655 Administrative Messages
1658 Communicating Presentation Information in Internet Messages: The
1659 Content-Disposition Header Field
1662 Documentation of the text/plain format parameter for flowed text.
1678 @c coding: iso-8859-1