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 Free Software Foundation, Inc.
23 Permission is granted to copy, distribute and/or modify this document
24 under the terms of the GNU Free Documentation License, Version 1.1 or
25 any later version published by the Free Software Foundation; with no
26 Invariant Sections, with the Front-Cover texts being ``A GNU
27 Manual'', and with the Back-Cover Texts as in (a) below. A copy of the
28 license is included in the section entitled ``GNU Free Documentation
29 License'' in the Emacs manual.
31 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
32 this GNU Manual, like GNU software. Copies published by the Free
33 Software Foundation raise funds for GNU development.''
35 This document is part of a collection distributed under the GNU Free
36 Documentation License. If you want to distribute this document
37 separately from the collection, you can do so by adding a copy of the
38 license to the document, as described in section 6 of the license.
44 @title Emacs MIME Manual
46 @author by Lars Magne Ingebrigtsen
49 @vskip 0pt plus 1filll
50 Copyright @copyright{} 1998, 1999, 2000, 2001, 2002 Free Software
53 Permission is granted to copy, distribute and/or modify this document
54 under the terms of the GNU Free Documentation License, Version 1.1 or
55 any later version published by the Free Software Foundation; with the
56 Invariant Sections being none, with the Front-Cover texts being ``A GNU
57 Manual'', and with the Back-Cover Texts as in (a) below. A copy of the
58 license is included in the section entitled ``GNU Free Documentation
59 License'' in the Emacs manual.
61 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
62 this GNU Manual, like GNU software. Copies published by the Free
63 Software Foundation raise funds for GNU development.''
65 This document is part of a collection distributed under the GNU Free
66 Documentation License. If you want to distribute this document
67 separately from the collection, you can do so by adding a copy of the
68 license to the document, as described in section 6 of the license.
77 This manual documents the libraries used to compose and display
80 This manual is directed at users who want to modify the behaviour of
81 the MIME encoding/decoding process or want a more detailed picture of
82 how the Emacs MIME library works, and people who want to write
83 functions and commands that manipulate @sc{mime} elements.
85 @sc{mime} is short for @dfn{Multipurpose Internet Mail Extensions}.
86 This standard is documented in a number of RFCs; mainly RFC2045 (Format
87 of Internet Message Bodies), RFC2046 (Media Types), RFC2047 (Message
88 Header Extensions for Non-ASCII Text), RFC2048 (Registration
89 Procedures), RFC2049 (Conformance Criteria and Examples). It is highly
90 recommended that anyone who intends writing @sc{mime}-compliant software
91 read at least RFC2045 and RFC2047.
94 * Decoding and Viewing:: A framework for decoding and viewing.
95 * Composing:: MML; a language for describing @sc{mime} parts.
96 * Interface Functions:: An abstraction over the basic functions.
97 * Basic Functions:: Utility and basic parsing functions.
98 * Standards:: A summary of RFCs and working documents used.
99 * Index:: Function and variable index.
103 @node Decoding and Viewing
104 @chapter Decoding and Viewing
106 This chapter deals with decoding and viewing @sc{mime} messages on a
109 The main idea is to first analyze a @sc{mime} article, and then allow
110 other programs to do things based on the list of @dfn{handles} that are
111 returned as a result of this analysis.
114 * Dissection:: Analyzing a @sc{mime} message.
115 * Non-MIME:: Analyzing a non-@sc{mime} message.
116 * Handles:: Handle manipulations.
117 * Display:: Displaying handles.
118 * Display Customization:: Variables that affect display.
119 * New Viewers:: How to write your own viewers.
126 The @code{mm-dissect-buffer} is the function responsible for dissecting
127 a @sc{mime} article. If given a multipart message, it will recursively
128 descend the message, following the structure, and return a tree of
129 @sc{mime} handles that describes the structure of the message.
134 Gnus also understands some non-@sc{mime} attachments, such as
135 postscript, uuencode, binhex, yenc, shar, forward, gnatsweb, pgp.
136 Each of these features can be disabled by add an item into
137 @code{mm-uu-configure-list}. For example,
141 (add-to-list 'mm-uu-configure-list '(pgp-signed . disabled))
167 Non-@sc{mime} forwarded message.
175 PGP signed clear text.
178 @findex pgp-encrypted
179 PGP encrypted clear text.
186 @findex emacs-sources
187 Emacs source code. This item works only in the groups matching
188 @code{mm-uu-emacs-sources-regexp}.
195 A @sc{mime} handle is a list that fully describes a @sc{mime}
198 The following macros can be used to access elements in a handle:
201 @item mm-handle-buffer
202 @findex mm-handle-buffer
203 Return the buffer that holds the contents of the undecoded @sc{mime}
207 @findex mm-handle-type
208 Return the parsed @code{Content-Type} of the part.
210 @item mm-handle-encoding
211 @findex mm-handle-encoding
212 Return the @code{Content-Transfer-Encoding} of the part.
214 @item mm-handle-undisplayer
215 @findex mm-handle-undisplayer
216 Return the object that can be used to remove the displayed part (if it
219 @item mm-handle-set-undisplayer
220 @findex mm-handle-set-undisplayer
221 Set the undisplayer object.
223 @item mm-handle-disposition
224 @findex mm-handle-disposition
225 Return the parsed @code{Content-Disposition} of the part.
227 @item mm-handle-disposition
228 @findex mm-handle-disposition
229 Return the description of the part.
231 @item mm-get-content-id
232 Returns the handle(s) referred to by @code{Content-ID}.
240 Functions for displaying, removing and saving.
243 @item mm-display-part
244 @findex mm-display-part
248 @findex mm-remove-part
249 Remove the part (if it has been displayed).
252 @findex mm-inlinable-p
253 Say whether a @sc{mime} type can be displayed inline.
255 @item mm-automatic-display-p
256 @findex mm-automatic-display-p
257 Say whether a @sc{mime} type should be displayed automatically.
259 @item mm-destroy-part
260 @findex mm-destroy-part
261 Free all resources occupied by a part.
265 Offer to save the part in a file.
269 Offer to pipe the part to some process.
271 @item mm-interactively-view-part
272 @findex mm-interactively-view-part
273 Prompt for a mailcap method to use to view the part.
278 @node Display Customization
279 @section Display Customization
283 @item mm-inline-media-tests
284 This is an alist where the key is a @sc{mime} type, the second element
285 is a function to display the part @dfn{inline} (i.e., inside Emacs), and
286 the third element is a form to be @code{eval}ed to say whether the part
287 can be displayed inline.
289 This variable specifies whether a part @emph{can} be displayed inline,
290 and, if so, how to do it. It does not say whether parts are
291 @emph{actually} displayed inline.
293 @item mm-inlined-types
294 This, on the other hand, says what types are to be displayed inline, if
295 they satisfy the conditions set by the variable above. It's a list of
296 @sc{mime} media types.
298 @item mm-automatic-display
299 This is a list of types that are to be displayed ``automatically'', but
300 only if the above variable allows it. That is, only inlinable parts can
301 be displayed automatically.
303 @item mm-attachment-override-types
304 Some @sc{mime} agents create parts that have a content-disposition of
305 @samp{attachment}. This variable allows overriding that disposition and
306 displaying the part inline. (Note that the disposition is only
307 overridden if we are able to, and want to, display the part inline.)
309 @item mm-discouraged-alternatives
310 List of @sc{mime} types that are discouraged when viewing
311 @samp{multipart/alternative}. Viewing agents are supposed to view the
312 last possible part of a message, as that is supposed to be the richest.
313 However, users may prefer other types instead, and this list says what
314 types are most unwanted. If, for instance, @samp{text/html} parts are
315 very unwanted, and @samp{text/richtech} parts are somewhat unwanted,
316 you could say something like:
319 (setq mm-discouraged-alternatives
320 '("text/html" "text/richtext")
322 (remove "text/html" mm-automatic-display))
325 @item mm-inline-large-images-p
326 When displaying inline images that are larger than the window, XEmacs
327 does not enable scrolling, which means that you cannot see the whole
328 image. To prevent this, the library tries to determine the image size
329 before displaying it inline, and if it doesn't fit the window, the
330 library will display it externally (e.g. with @samp{ImageMagick} or
331 @samp{xv}). Setting this variable to @code{t} disables this check and
332 makes the library display all inline images as inline, regardless of
335 @item mm-inline-override-type
336 @code{mm-inlined-types} may include regular expressions, for example to
337 specify that all @samp{text/.*} parts be displayed inline. If a user
338 prefers to have a type that matches such a regular expression be treated
339 as an attachment, that can be accomplished by setting this variable to a
340 list containing that type. For example assuming @code{mm-inlined-types}
341 includes @samp{text/.*}, then including @samp{text/html} in this
342 variable will cause @samp{text/html} parts to be treated as attachments.
344 @item mm-inline-text-html-renderer
345 This selects the function used to render @sc{html}. The predefined
346 renderers are selected by the symbols @code{w3},
347 @code{w3m}@footnote{See @uref{http://emacs-w3m.namazu.org/} for more
348 information about emacs-w3m}, @code{links}, @code{lynx},
349 @code{w3m-standalone} or @code{html2text}. You can also specify a
350 function, which will be called with a @sc{mime} handle as the
353 @item mm-inline-text-html-with-images
354 Some @sc{html} mails might have the trick of spammers using
355 @samp{<img>} tags. It is likely to be intended to verify whether you
356 have read the mail. You can prevent your personal informations from
357 leaking by setting this option to @code{nil} (which is the default).
358 It is currently ignored by Emacs/w3. For emacs-w3m, you may use the
359 command @kbd{t} on the image anchor to show an image even if it is
360 @code{nil}.@footnote{The command @kbd{T} will load all images. If you
361 have set the option @code{w3m-key-binding} to @code{info}, use @kbd{i}
364 @item mm-inline-text-html-with-w3m-keymap
365 You can use emacs-w3m command keys in the inlined text/html part by
366 setting this option to non-@code{nil}. The default value is @code{t}.
374 Here's an example viewer for displaying @code{text/enriched} inline:
377 (defun mm-display-enriched-inline (handle)
380 (mm-insert-part handle)
381 (save-window-excursion
382 (enriched-decode (point-min) (point-max))
383 (setq text (buffer-string))))
384 (mm-insert-inline handle text)))
387 We see that the function takes a @sc{mime} handle as its parameter. It
388 then goes to a temporary buffer, inserts the text of the part, does some
389 work on the text, stores the result, goes back to the buffer it was
390 called from and inserts the result.
392 The two important helper functions here are @code{mm-insert-part} and
393 @code{mm-insert-inline}. The first function inserts the text of the
394 handle in the current buffer. It handles charset and/or content
395 transfer decoding. The second function just inserts whatever text you
396 tell it to insert, but it also sets things up so that the text can be
397 ``undisplayed' in a convenient manner.
403 @cindex MIME Composing
405 @cindex MIME Meta Language
407 Creating a @sc{mime} message is boring and non-trivial. Therefore, a
408 library called @code{mml} has been defined that parses a language called
409 MML (@sc{mime} Meta Language) and generates @sc{mime} messages.
411 @findex mml-generate-mime
412 The main interface function is @code{mml-generate-mime}. It will
413 examine the contents of the current (narrowed-to) buffer and return a
414 string containing the @sc{mime} message.
417 * Simple MML Example:: An example MML document.
418 * MML Definition:: All valid MML elements.
419 * Advanced MML Example:: Another example MML document.
420 * Encoding Customization:: Variables that affect encoding.
421 * Charset Translation:: How charsets are mapped from @sc{mule} to @sc{mime}.
422 * Conversion:: Going from @sc{mime} to MML and vice versa.
423 * Flowed text:: Soft and hard newlines.
427 @node Simple MML Example
428 @section Simple MML Example
430 Here's a simple @samp{multipart/alternative}:
433 <#multipart type=alternative>
434 This is a plain text part.
435 <#part type=text/enriched>
436 <center>This is a centered enriched part</center>
440 After running this through @code{mml-generate-mime}, we get this:
443 Content-Type: multipart/alternative; boundary="=-=-="
449 This is a plain text part.
452 Content-Type: text/enriched
455 <center>This is a centered enriched part</center>
462 @section MML Definition
464 The MML language is very simple. It looks a bit like an SGML
465 application, but it's not.
467 The main concept of MML is the @dfn{part}. Each part can be of a
468 different type or use a different charset. The way to delineate a part
469 is with a @samp{<#part ...>} tag. Multipart parts can be introduced
470 with the @samp{<#multipart ...>} tag. Parts are ended by the
471 @samp{<#/part>} or @samp{<#/multipart>} tags. Parts started with the
472 @samp{<#part ...>} tags are also closed by the next open tag.
474 There's also the @samp{<#external ...>} tag. These introduce
475 @samp{external/message-body} parts.
477 Each tag can contain zero or more parameters on the form
478 @samp{parameter=value}. The values may be enclosed in quotation marks,
479 but that's not necessary unless the value contains white space. So
480 @samp{filename=/home/user/#hello$^yes} is perfectly valid.
482 The following parameters have meaning in MML; parameters that have no
483 meaning are ignored. The MML parameter names are the same as the
484 @sc{mime} parameter names; the things in the parentheses say which
485 header it will be used in.
489 The @sc{mime} type of the part (@code{Content-Type}).
492 Use the contents of the file in the body of the part
493 (@code{Content-Disposition}).
496 The contents of the body of the part are to be encoded in the character
497 set speficied (@code{Content-Type}). @xref{Charset Translation}.
500 Might be used to suggest a file name if the part is to be saved
501 to a file (@code{Content-Type}).
504 Valid values are @samp{inline} and @samp{attachment}
505 (@code{Content-Disposition}).
508 Valid values are @samp{7bit}, @samp{8bit}, @samp{quoted-printable} and
509 @samp{base64} (@code{Content-Transfer-Encoding}). @xref{Charset
513 A description of the part (@code{Content-Description}).
516 RFC822 date when the part was created (@code{Content-Disposition}).
518 @item modification-date
519 RFC822 date when the part was modified (@code{Content-Disposition}).
522 RFC822 date when the part was read (@code{Content-Disposition}).
525 Who to encrypt/sign the part to. This field is used to override any
526 auto-detection based on the To/CC headers.
529 The size (in octets) of the part (@code{Content-Disposition}).
532 What technology to sign this MML part with (@code{smime}, @code{pgp}
536 What technology to encrypt this MML part with (@code{smime},
537 @code{pgp} or @code{pgpmime})
541 Parameters for @samp{application/octet-stream}:
545 Type of the part; informal---meant for human readers
546 (@code{Content-Type}).
549 Parameters for @samp{message/external-body}:
553 A word indicating the supported access mechanism by which the file may
554 be obtained. Values include @samp{ftp}, @samp{anon-ftp}, @samp{tftp},
555 @samp{localfile}, and @samp{mailserver}. (@code{Content-Type}.)
558 The RFC822 date after which the file may no longer be fetched.
559 (@code{Content-Type}.)
562 The size (in octets) of the file. (@code{Content-Type}.)
565 Valid values are @samp{read} and @samp{read-write}
566 (@code{Content-Type}).
570 Parameters for @samp{sign=smime}:
575 File containing key and certificate for signer.
579 Parameters for @samp{encrypt=smime}:
584 File containing certificate for recipient.
589 @node Advanced MML Example
590 @section Advanced MML Example
592 Here's a complex multipart message. It's a @samp{multipart/mixed} that
593 contains many parts, one of which is a @samp{multipart/alternative}.
596 <#multipart type=mixed>
597 <#part type=image/jpeg filename=~/rms.jpg disposition=inline>
598 <#multipart type=alternative>
599 This is a plain text part.
600 <#part type=text/enriched name=enriched.txt>
601 <center>This is a centered enriched part</center>
603 This is a new plain text part.
604 <#part disposition=attachment>
605 This plain text part is an attachment.
609 And this is the resulting @sc{mime} message:
612 Content-Type: multipart/mixed; boundary="=-=-="
620 Content-Type: image/jpeg;
622 Content-Disposition: inline;
624 Content-Transfer-Encoding: base64
626 /9j/4AAQSkZJRgABAQAAAQABAAD/2wBDAAgGBgcGBQgHBwcJCQgKDBQNDAsLDBkSEw8UHRof
627 Hh0aHBwgJC4nICIsIxwcKDcpLDAxNDQ0Hyc5PTgyPC4zNDL/wAALCAAwADABAREA/8QAHwAA
628 AQUBAQEBAQEAAAAAAAAAAAECAwQFBgcICQoL/8QAtRAAAgEDAwIEAwUFBAQAAAF9AQIDAAQR
629 BRIhMUEGE1FhByJxFDKBkaEII0KxwRVS0fAkM2JyggkKFhcYGRolJicoKSo0NTY3ODk6Q0RF
630 RkdISUpTVFVWV1hZWmNkZWZnaGlqc3R1dnd4eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ip
631 qrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uHi4+Tl5ufo6erx8vP09fb3+Pn6/9oACAEB
632 AAA/AO/rifFHjldNuGsrDa0qcSSHkA+gHrXKw+LtWLrMb+RgTyhbr+HSug07xNqV9fQtZrNI
633 AyiaE/NuBPOOOP0rvRNE880KOC8TbXXGCv1FPqjrF4LDR7u5L7SkTFT/ALWOP1xXgTuXfc7E
634 sx6nua6rwp4IvvEM8chCxWxOdzn7wz6V9AaB4S07w9p5itow0rDLSY5Pt9K43xO66P4xs71m
635 2QXiGCbA4yOVJ9+1aYORkdK434lyNH4ahCnG66VT9Nj15JFbPdX0MS43M4VQf5/yr2vSpLnw
636 5ZW8dlCZ8KFXjOPX0/mK6rSPEGt3Angu44fNEReHYNvIH3TzXDeKNO8RX+kSX2ouZkicTIOc
637 L+g7E810ulFjpVtv3bwgB3HJyK5L4quY/C9sVxk3ij/xx6850u7t1mtp/wDlpEw3An3Jr3Dw
638 34gsbWza4nBlhC5LDsaW6+IFgupQyCF3iHH7gA7c9R9ay7zx6t7aX9jHC4smhfBkGCvHGfrm
639 tLQ7hbnRrV1GPkAP1x1/Hr+Ncr8Vzjwrbf8AX6v/AKA9eQRyYlQk8Yx9K6XTNbkgia2ciSIn
640 7p5Ga9Atte0LTLKO6it4i7dVRFJDcZ4PvXN+JvEMF9bILVGXJLSZ4zkjivRPDaeX4b08HOTC
641 pOffmua+KkbS+GLVUGT9tT/0B68eeIpIFYjB70+OOVXyoOM9+M1eaWeCLzHPyHGO/NVWvJJm
642 jQ8KGH1NfQWhXSXmh2c8eArRLwO3HSv/2Q==
645 Content-Type: multipart/alternative; boundary="==-=-="
651 This is a plain text part.
654 Content-Type: text/enriched;
658 <center>This is a centered enriched part</center>
664 This is a new plain text part.
667 Content-Disposition: attachment
670 This plain text part is an attachment.
675 @node Encoding Customization
676 @section Encoding Customization
680 @item mm-body-charset-encoding-alist
681 @vindex mm-body-charset-encoding-alist
682 Mapping from MIME charset to encoding to use. This variable is
683 usually used except, e.g., when other requirements force a specific
684 encoding (digitally signed messages require 7bit encodings). The
685 default is @code{((iso-2022-jp . 7bit) (iso-2022-jp-2 . 7bit))}. As
686 an example, if you do not want to have ISO-8859-1 characters
687 quoted-printable encoded, you may add @code{(iso-8859-1 . 8bit)} to
688 this variable. You can override this setting on a per-message basis
689 by using the @code{encoding} MML tag (@pxref{MML Definition}).
691 @item mm-coding-system-priorities
692 @vindex mm-coding-system-priorities
693 Prioritize coding systems to use for outgoing messages. The default
694 is nil, which means to use the defaults in Emacs. It is a list of
695 coding system symbols (aliases of coding systems does not work, use
696 @kbd{M-x describe-coding-system} to make sure you are not specifying
697 an alias in this variable). For example, if you have configured Emacs
698 to use prefer UTF-8, but wish that outgoing messages should be sent in
699 ISO-8859-1 if possible, you can set this variable to
700 @code{(iso-latin-1)}. You can override this setting on a per-message
701 basis by using the @code{charset} MML tag (@pxref{MML Definition}).
703 @item mm-content-transfer-encoding-defaults
704 @vindex mm-content-transfer-encoding-defaults
705 Mapping from MIME types to encoding to use. This variable is usually
706 used except, e.g., when other requirements force a safer encoding
707 (digitally signed messages require 7bit encoding). Besides the normal
708 MIME encodings, @code{qp-or-base64} may be used to indicate that for
709 each case the most efficient of quoted-printable and base64 should be
710 used. You can override this setting on a per-message basis by using
711 the @code{encoding} MML tag (@pxref{MML Definition}).
713 @item mm-use-ultra-safe-encoding
714 @vindex mm-use-ultra-safe-encoding
715 When this is non-nil, it means that textual parts are encoded as
716 quoted-printable if they contain lines longer than 76 characters or
717 starting with "From " in the body. Non-7bit encodings (8bit, binary)
718 are generally disallowed. This reduce the probability that a non-8bit
719 clean MTA or MDA changes the message. This should never be set
720 directly, but bound by other functions when necessary (e.g., when
721 encoding messages that are to be digitally signed).
725 @node Charset Translation
726 @section Charset Translation
729 During translation from MML to @sc{mime}, for each @sc{mime} part which
730 has been composed inside Emacs, an appropriate charset has to be chosen.
732 @vindex mail-parse-charset
733 If you are running a non-@sc{mule} Emacs, this process is simple: If the
734 part contains any non-ASCII (8-bit) characters, the @sc{mime} charset
735 given by @code{mail-parse-charset} (a symbol) is used. (Never set this
736 variable directly, though. If you want to change the default charset,
737 please consult the documentation of the package which you use to process
739 @xref{Various Message Variables, , Various Message Variables, message,
740 Message Manual}, for example.)
741 If there are only ASCII characters, the @sc{mime} charset US-ASCII is
747 @vindex mm-mime-mule-charset-alist
748 Things are slightly more complicated when running Emacs with @sc{mule}
749 support. In this case, a list of the @sc{mule} charsets used in the
750 part is obtained, and the @sc{mule} charsets are translated to @sc{mime}
751 charsets by consulting the variable @code{mm-mime-mule-charset-alist}.
752 If this results in a single @sc{mime} charset, this is used to encode
753 the part. But if the resulting list of @sc{mime} charsets contains more
754 than one element, two things can happen: If it is possible to encode the
755 part via UTF-8, this charset is used. (For this, Emacs must support
756 the @code{utf-8} coding system, and the part must consist entirely of
757 characters which have Unicode counterparts.) If UTF-8 is not available
758 for some reason, the part is split into several ones, so that each one
759 can be encoded with a single @sc{mime} charset. The part can only be
760 split at line boundaries, though---if more than one @sc{mime} charset is
761 required to encode a single line, it is not possible to encode the part.
763 When running Emacs with @sc{mule} support, the preferences for which
764 coding system to use is inherited from Emacs itself. This means that
765 if Emacs is set up to prefer UTF-8, it will be used when encoding
766 messages. You can modify this by altering the
767 @code{mm-coding-system-priorities} variable though (@pxref{Encoding
770 The charset to be used can be overriden by setting the @code{charset}
771 MML tag (@pxref{MML Definition}) when composing the message.
773 The encoding of characters (quoted-printable, 8bit etc) is orthogonal
774 to the discussion here, and is controlled by the variables
775 @code{mm-body-charset-encoding-alist} and
776 @code{mm-content-transfer-encoding-defaults} (@pxref{Encoding
783 A (multipart) @sc{mime} message can be converted to MML with the
784 @code{mime-to-mml} function. It works on the message in the current
785 buffer, and substitutes MML markup for @sc{mime} boundaries.
786 Non-textual parts do not have their contents in the buffer, but instead
787 have the contents in separate buffers that are referred to from the MML
791 An MML message can be converted back to @sc{mime} by the
792 @code{mml-to-mime} function.
794 These functions are in certain senses ``lossy''---you will not get back
795 an identical message if you run @sc{mime-to-mml} and then
796 @sc{mml-to-mime}. Not only will trivial things like the order of the
797 headers differ, but the contents of the headers may also be different.
798 For instance, the original message may use base64 encoding on text,
799 while @sc{mml-to-mime} may decide to use quoted-printable encoding, and
802 In essence, however, these two functions should be the inverse of each
803 other. The resulting contents of the message should remain equivalent,
809 @cindex format=flowed
811 The Emacs @sc{mime} library will respect the @code{use-hard-newlines}
812 variable (@pxref{Hard and Soft Newlines, ,Hard and Soft Newlines,
813 emacs, Emacs Manual}) when encoding a message, and the
814 ``format=flowed'' Content-Type parameter when decoding a message.
816 On encoding text, lines terminated by soft newline characters are
817 filled together and wrapped after the column decided by
818 @code{fill-flowed-encode-column}. This variable controls how the text
819 will look in a client that does not support flowed text, the default
820 is to wrap after 66 characters. If hard newline characters are not
821 present in the buffer, no flow encoding occurs.
823 On decoding flowed text, lines with soft newline characters are filled
824 together and wrapped after the column decided by
825 @code{fill-flowed-display-column}. The default is to wrap after
831 @node Interface Functions
832 @chapter Interface Functions
833 @cindex interface functions
836 The @code{mail-parse} library is an abstraction over the actual
837 low-level libraries that are described in the next chapter.
839 Standards change, and so programs have to change to fit in the new
840 mold. For instance, RFC2045 describes a syntax for the
841 @code{Content-Type} header that only allows ASCII characters in the
842 parameter list. RFC2231 expands on RFC2045 syntax to provide a scheme
843 for continuation headers and non-ASCII characters.
845 The traditional way to deal with this is just to update the library
846 functions to parse the new syntax. However, this is sometimes the wrong
847 thing to do. In some instances it may be vital to be able to understand
848 both the old syntax as well as the new syntax, and if there is only one
849 library, one must choose between the old version of the library and the
850 new version of the library.
852 The Emacs @sc{mime} library takes a different tack. It defines a
853 series of low-level libraries (@file{rfc2047.el}, @file{rfc2231.el}
854 and so on) that parses strictly according to the corresponding
855 standard. However, normal programs would not use the functions
856 provided by these libraries directly, but instead use the functions
857 provided by the @code{mail-parse} library. The functions in this
858 library are just aliases to the corresponding functions in the latest
859 low-level libraries. Using this scheme, programs get a consistent
860 interface they can use, and library developers are free to create
861 write code that handles new standards.
863 The following functions are defined by this library:
866 @item mail-header-parse-content-type
867 @findex mail-header-parse-content-type
868 Parse a @code{Content-Type} header and return a list on the following
873 (attribute1 . value1)
874 (attribute2 . value2)
881 (mail-header-parse-content-type
882 "image/gif; name=\"b980912.gif\"")
883 @result{} ("image/gif" (name . "b980912.gif"))
886 @item mail-header-parse-content-disposition
887 @findex mail-header-parse-content-disposition
888 Parse a @code{Content-Disposition} header and return a list on the same
889 format as the function above.
891 @item mail-content-type-get
892 @findex mail-content-type-get
893 Takes two parameters---a list on the format above, and an attribute.
894 Returns the value of the attribute.
897 (mail-content-type-get
898 '("image/gif" (name . "b980912.gif")) 'name)
899 @result{} "b980912.gif"
902 @item mail-header-encode-parameter
903 @findex mail-header-encode-parameter
904 Takes a parameter string and returns an encoded version of the string.
905 This is used for parameters in headers like @code{Content-Type} and
906 @code{Content-Disposition}.
908 @item mail-header-remove-comments
909 @findex mail-header-remove-comments
910 Return a comment-free version of a header.
913 (mail-header-remove-comments
914 "Gnus/5.070027 (Pterodactyl Gnus v0.27) (Finnish Landrace)")
915 @result{} "Gnus/5.070027 "
918 @item mail-header-remove-whitespace
919 @findex mail-header-remove-whitespace
920 Remove linear white space from a header. Space inside quoted strings
921 and comments is preserved.
924 (mail-header-remove-whitespace
925 "image/gif; name=\"Name with spaces\"")
926 @result{} "image/gif;name=\"Name with spaces\""
929 @item mail-header-get-comment
930 @findex mail-header-get-comment
931 Return the last comment in a header.
934 (mail-header-get-comment
935 "Gnus/5.070027 (Pterodactyl Gnus v0.27) (Finnish Landrace)")
936 @result{} "Finnish Landrace"
939 @item mail-header-parse-address
940 @findex mail-header-parse-address
941 Parse an address and return a list containing the mailbox and the
945 (mail-header-parse-address
946 "Hrvoje Niksic <hniksic@@srce.hr>")
947 @result{} ("hniksic@@srce.hr" . "Hrvoje Niksic")
950 @item mail-header-parse-addresses
951 @findex mail-header-parse-addresses
952 Parse a string with list of addresses and return a list of elements like
953 the one described above.
956 (mail-header-parse-addresses
957 "Hrvoje Niksic <hniksic@@srce.hr>, Steinar Bang <sb@@metis.no>")
958 @result{} (("hniksic@@srce.hr" . "Hrvoje Niksic")
959 ("sb@@metis.no" . "Steinar Bang"))
962 @item mail-header-parse-date
963 @findex mail-header-parse-date
964 Parse a date string and return an Emacs time structure.
966 @item mail-narrow-to-head
967 @findex mail-narrow-to-head
968 Narrow the buffer to the header section of the buffer. Point is placed
969 at the beginning of the narrowed buffer.
971 @item mail-header-narrow-to-field
972 @findex mail-header-narrow-to-field
973 Narrow the buffer to the header under point. Understands continuation
976 @item mail-header-fold-field
977 @findex mail-header-fold-field
978 Fold the header under point.
980 @item mail-header-unfold-field
981 @findex mail-header-unfold-field
982 Unfold the header under point.
984 @item mail-header-field-value
985 @findex mail-header-field-value
986 Return the value of the field under point.
988 @item mail-encode-encoded-word-region
989 @findex mail-encode-encoded-word-region
990 Encode the non-ASCII words in the region. For instance,
991 @samp{Naïve} is encoded as @samp{=?iso-8859-1?q?Na=EFve?=}.
993 @item mail-encode-encoded-word-buffer
994 @findex mail-encode-encoded-word-buffer
995 Encode the non-ASCII words in the current buffer. This function is
996 meant to be called narrowed to the headers of a message.
998 @item mail-encode-encoded-word-string
999 @findex mail-encode-encoded-word-string
1000 Encode the words that need encoding in a string, and return the result.
1003 (mail-encode-encoded-word-string
1004 "This is naïve, baby")
1005 @result{} "This is =?iso-8859-1?q?na=EFve,?= baby"
1008 @item mail-decode-encoded-word-region
1009 @findex mail-decode-encoded-word-region
1010 Decode the encoded words in the region.
1012 @item mail-decode-encoded-word-string
1013 @findex mail-decode-encoded-word-string
1014 Decode the encoded words in the string and return the result.
1017 (mail-decode-encoded-word-string
1018 "This is =?iso-8859-1?q?na=EFve,?= baby")
1019 @result{} "This is naïve, baby"
1024 Currently, @code{mail-parse} is an abstraction over @code{ietf-drums},
1025 @code{rfc2047}, @code{rfc2045} and @code{rfc2231}. These are documented
1026 in the subsequent sections.
1030 @node Basic Functions
1031 @chapter Basic Functions
1033 This chapter describes the basic, ground-level functions for parsing and
1034 handling. Covered here is parsing @code{From} lines, removing comments
1035 from header lines, decoding encoded words, parsing date headers and so
1036 on. High-level functionality is dealt with in the next chapter
1037 (@pxref{Decoding and Viewing}).
1040 * rfc2045:: Encoding @code{Content-Type} headers.
1041 * rfc2231:: Parsing @code{Content-Type} headers.
1042 * ietf-drums:: Handling mail headers defined by RFC822bis.
1043 * rfc2047:: En/decoding encoded words in headers.
1044 * time-date:: Functions for parsing dates and manipulating time.
1045 * qp:: Quoted-Printable en/decoding.
1046 * base64:: Base64 en/decoding.
1047 * binhex:: Binhex decoding.
1048 * uudecode:: Uuencode decoding.
1049 * yenc:: Yenc decoding.
1050 * rfc1843:: Decoding HZ-encoded text.
1051 * mailcap:: How parts are displayed is specified by the @file{.mailcap} file
1058 RFC2045 is the ``main'' @sc{mime} document, and as such, one would
1059 imagine that there would be a lot to implement. But there isn't, since
1060 most of the implementation details are delegated to the subsequent
1063 So @file{rfc2045.el} has only a single function:
1066 @item rfc2045-encode-string
1067 @findex rfc2045-encode-string
1068 Takes a parameter and a value and returns a @samp{PARAM=VALUE} string.
1069 @var{value} will be quoted if there are non-safe characters in it.
1076 RFC2231 defines a syntax for the @code{Content-Type} and
1077 @code{Content-Disposition} headers. Its snappy name is @dfn{MIME
1078 Parameter Value and Encoded Word Extensions: Character Sets, Languages,
1081 In short, these headers look something like this:
1084 Content-Type: application/x-stuff;
1085 title*0*=us-ascii'en'This%20is%20even%20more%20;
1086 title*1*=%2A%2A%2Afun%2A%2A%2A%20;
1090 They usually aren't this bad, though.
1092 The following functions are defined by this library:
1095 @item rfc2231-parse-string
1096 @findex rfc2231-parse-string
1097 Parse a @code{Content-Type} header and return a list describing its
1101 (rfc2231-parse-string
1102 "application/x-stuff;
1103 title*0*=us-ascii'en'This%20is%20even%20more%20;
1104 title*1*=%2A%2A%2Afun%2A%2A%2A%20;
1105 title*2=\"isn't it!\"")
1106 @result{} ("application/x-stuff"
1107 (title . "This is even more ***fun*** isn't it!"))
1110 @item rfc2231-get-value
1111 @findex rfc2231-get-value
1112 Takes one of the lists on the format above and returns
1113 the value of the specified attribute.
1115 @item rfc2231-encode-string
1116 @findex rfc2231-encode-string
1117 Encode a parameter in headers likes @code{Content-Type} and
1118 @code{Content-Disposition}.
1126 @dfn{drums} is an IETF working group that is working on the replacement
1129 The functions provided by this library include:
1132 @item ietf-drums-remove-comments
1133 @findex ietf-drums-remove-comments
1134 Remove the comments from the argument and return the results.
1136 @item ietf-drums-remove-whitespace
1137 @findex ietf-drums-remove-whitespace
1138 Remove linear white space from the string and return the results.
1139 Spaces inside quoted strings and comments are left untouched.
1141 @item ietf-drums-get-comment
1142 @findex ietf-drums-get-comment
1143 Return the last most comment from the string.
1145 @item ietf-drums-parse-address
1146 @findex ietf-drums-parse-address
1147 Parse an address string and return a list that contains the mailbox and
1148 the plain text name.
1150 @item ietf-drums-parse-addresses
1151 @findex ietf-drums-parse-addresses
1152 Parse a string that contains any number of comma-separated addresses and
1153 return a list that contains mailbox/plain text pairs.
1155 @item ietf-drums-parse-date
1156 @findex ietf-drums-parse-date
1157 Parse a date string and return an Emacs time structure.
1159 @item ietf-drums-narrow-to-header
1160 @findex ietf-drums-narrow-to-header
1161 Narrow the buffer to the header section of the current buffer.
1169 RFC2047 (Message Header Extensions for Non-ASCII Text) specifies how
1170 non-ASCII text in headers are to be encoded. This is actually rather
1171 complicated, so a number of variables are necessary to tweak what this
1174 The following variables are tweakable:
1177 @item rfc2047-default-charset
1178 @vindex rfc2047-default-charset
1179 Characters in this charset should not be decoded by this library.
1180 This defaults to @code{iso-8859-1}.
1182 @item rfc2047-header-encoding-list
1183 @vindex rfc2047-header-encoding-list
1184 This is an alist of header / encoding-type pairs. Its main purpose is
1185 to prevent encoding of certain headers.
1187 The keys can either be header regexps, or @code{t}.
1189 The values can be either @code{nil}, in which case the header(s) in
1190 question won't be encoded, or @code{mime}, which means that they will be
1193 @item rfc2047-charset-encoding-alist
1194 @vindex rfc2047-charset-encoding-alist
1195 RFC2047 specifies two forms of encoding---@code{Q} (a
1196 Quoted-Printable-like encoding) and @code{B} (base64). This alist
1197 specifies which charset should use which encoding.
1199 @item rfc2047-encoding-function-alist
1200 @vindex rfc2047-encoding-function-alist
1201 This is an alist of encoding / function pairs. The encodings are
1202 @code{Q}, @code{B} and @code{nil}.
1204 @item rfc2047-q-encoding-alist
1205 @vindex rfc2047-q-encoding-alist
1206 The @code{Q} encoding isn't quite the same for all headers. Some
1207 headers allow a narrower range of characters, and that is what this
1208 variable is for. It's an alist of header regexps / allowable character
1211 @item rfc2047-encoded-word-regexp
1212 @vindex rfc2047-encoded-word-regexp
1213 When decoding words, this library looks for matches to this regexp.
1217 Those were the variables, and these are this functions:
1220 @item rfc2047-narrow-to-field
1221 @findex rfc2047-narrow-to-field
1222 Narrow the buffer to the header on the current line.
1224 @item rfc2047-encode-message-header
1225 @findex rfc2047-encode-message-header
1226 Should be called narrowed to the header of a message. Encodes according
1227 to @code{rfc2047-header-encoding-alist}.
1229 @item rfc2047-encode-region
1230 @findex rfc2047-encode-region
1231 Encodes all encodable words in the region specified.
1233 @item rfc2047-encode-string
1234 @findex rfc2047-encode-string
1235 Encode a string and return the results.
1237 @item rfc2047-decode-region
1238 @findex rfc2047-decode-region
1239 Decode the encoded words in the region.
1241 @item rfc2047-decode-string
1242 @findex rfc2047-decode-string
1243 Decode a string and return the results.
1251 While not really a part of the @sc{mime} library, it is convenient to
1252 document this library here. It deals with parsing @code{Date} headers
1253 and manipulating time. (Not by using tesseracts, though, I'm sorry to
1256 These functions convert between five formats: A date string, an Emacs
1257 time structure, a decoded time list, a second number, and a day number.
1259 Here's a bunch of time/date/second/day examples:
1262 (parse-time-string "Sat Sep 12 12:21:54 1998 +0200")
1263 @result{} (54 21 12 12 9 1998 6 nil 7200)
1265 (date-to-time "Sat Sep 12 12:21:54 1998 +0200")
1266 @result{} (13818 19266)
1268 (time-to-seconds '(13818 19266))
1269 @result{} 905595714.0
1271 (seconds-to-time 905595714.0)
1272 @result{} (13818 19266 0)
1274 (time-to-days '(13818 19266))
1277 (days-to-time 729644)
1278 @result{} (961933 65536)
1280 (time-since '(13818 19266))
1283 (time-less-p '(13818 19266) '(13818 19145))
1286 (subtract-time '(13818 19266) '(13818 19145))
1289 (days-between "Sat Sep 12 12:21:54 1998 +0200"
1290 "Sat Sep 07 12:21:54 1998 +0200")
1293 (date-leap-year-p 2000)
1296 (time-to-day-in-year '(13818 19266))
1299 (time-to-number-of-days
1301 (date-to-time "Mon, 01 Jan 2001 02:22:26 GMT")))
1302 @result{} 4.146122685185185
1305 And finally, we have @code{safe-date-to-time}, which does the same as
1306 @code{date-to-time}, but returns a zero time if the date is
1307 syntactically malformed.
1309 The five data representations used are the following:
1313 An RFC822 (or similar) date string. For instance: @code{"Sat Sep 12
1314 12:21:54 1998 +0200"}.
1317 An internal Emacs time. For instance: @code{(13818 26466)}.
1320 A floating point representation of the internal Emacs time. For
1321 instance: @code{905595714.0}.
1324 An integer number representing the number of days since 00000101. For
1325 instance: @code{729644}.
1328 A list of decoded time. For instance: @code{(54 21 12 12 9 1998 6 t
1332 All the examples above represent the same moment.
1334 These are the functions available:
1338 Take a date and return a time.
1340 @item time-to-seconds
1341 Take a time and return seconds.
1343 @item seconds-to-time
1344 Take seconds and return a time.
1347 Take a time and return days.
1350 Take days and return a time.
1353 Take a date and return days.
1355 @item time-to-number-of-days
1356 Take a time and return the number of days that represents.
1358 @item safe-date-to-time
1359 Take a date and return a time. If the date is not syntactically valid,
1360 return a "zero" date.
1363 Take two times and say whether the first time is less (i. e., earlier)
1364 than the second time.
1367 Take a time and return a time saying how long it was since that time.
1370 Take two times and subtract the second from the first. I. e., return
1371 the time between the two times.
1374 Take two days and return the number of days between those two days.
1376 @item date-leap-year-p
1377 Take a year number and say whether it's a leap year.
1379 @item time-to-day-in-year
1380 Take a time and return the day number within the year that the time is
1389 This library deals with decoding and encoding Quoted-Printable text.
1391 Very briefly explained, qp encoding means translating all 8-bit
1392 characters (and lots of control characters) into things that look like
1393 @samp{=EF}; that is, an equal sign followed by the byte encoded as a hex
1396 The following functions are defined by the library:
1399 @item quoted-printable-decode-region
1400 @findex quoted-printable-decode-region
1401 QP-decode all the encoded text in the specified region.
1403 @item quoted-printable-decode-string
1404 @findex quoted-printable-decode-string
1405 Decode the QP-encoded text in a string and return the results.
1407 @item quoted-printable-encode-region
1408 @findex quoted-printable-encode-region
1409 QP-encode all the encodable characters in the specified region. The third
1410 optional parameter @var{fold} specifies whether to fold long lines.
1411 (Long here means 72.)
1413 @item quoted-printable-encode-string
1414 @findex quoted-printable-encode-string
1415 QP-encode all the encodable characters in a string and return the
1425 Base64 is an encoding that encodes three bytes into four characters,
1426 thereby increasing the size by about 33%. The alphabet used for
1427 encoding is very resistant to mangling during transit.
1429 The following functions are defined by this library:
1432 @item base64-encode-region
1433 @findex base64-encode-region
1434 base64 encode the selected region. Return the length of the encoded
1435 text. Optional third argument @var{no-line-break} means do not break
1436 long lines into shorter lines.
1438 @item base64-encode-string
1439 @findex base64-encode-string
1440 base64 encode a string and return the result.
1442 @item base64-decode-region
1443 @findex base64-decode-region
1444 base64 decode the selected region. Return the length of the decoded
1445 text. If the region can't be decoded, return @code{nil} and don't
1448 @item base64-decode-string
1449 @findex base64-decode-string
1450 base64 decode a string and return the result. If the string can't be
1451 decoded, @code{nil} is returned.
1462 @code{binhex} is an encoding that originated in Macintosh environments.
1463 The following function is supplied to deal with these:
1466 @item binhex-decode-region
1467 @findex binhex-decode-region
1468 Decode the encoded text in the region. If given a third parameter, only
1469 decode the @code{binhex} header and return the filename.
1479 @code{uuencode} is probably still the most popular encoding of binaries
1480 used on Usenet, although @code{base64} rules the mail world.
1482 The following function is supplied by this package:
1485 @item uudecode-decode-region
1486 @findex uudecode-decode-region
1487 Decode the text in the region.
1495 @code{yenc} is used for encoding binaries on Usenet. The following
1496 function is supplied by this package:
1499 @item yenc-decode-region
1500 @findex yenc-decode-region
1501 Decode the encoded text in the region.
1512 RFC1843 deals with mixing Chinese and ASCII characters in messages. In
1513 essence, RFC1843 switches between ASCII and Chinese by doing this:
1516 This sentence is in ASCII.
1517 The next sentence is in GB.~@{<:Ky2;S@{#,NpJ)l6HK!#~@}Bye.
1520 Simple enough, and widely used in China.
1522 The following functions are available to handle this encoding:
1525 @item rfc1843-decode-region
1526 Decode HZ-encoded text in the region.
1528 @item rfc1843-decode-string
1529 Decode a HZ-encoded string and return the result.
1537 The @file{~/.mailcap} file is parsed by most @sc{mime}-aware message
1538 handlers and describes how elements are supposed to be displayed.
1539 Here's an example file:
1543 audio/wav; wavplayer %s
1544 application/msword; catdoc %s ; copiousoutput ; nametemplate=%s.doc
1547 This says that all image files should be displayed with @code{gimp},
1548 that WAVE audio files should be played by @code{wavplayer}, and that
1549 MS-WORD files should be inlined by @code{catdoc}.
1551 The @code{mailcap} library parses this file, and provides functions for
1555 @item mailcap-mime-data
1556 @vindex mailcap-mime-data
1557 This variable is an alist of alists containing backup viewing rules.
1561 Interface functions:
1564 @item mailcap-parse-mailcaps
1565 @findex mailcap-parse-mailcaps
1566 Parse the @code{~/.mailcap} file.
1568 @item mailcap-mime-info
1569 Takes a @sc{mime} type as its argument and returns the matching viewer.
1579 The Emacs @sc{mime} library implements handling of various elements
1580 according to a (somewhat) large number of RFCs, drafts and standards
1581 documents. This chapter lists the relevant ones. They can all be
1582 fetched from @uref{http://quimby.gnus.org/notes/}.
1587 Standard for the Format of ARPA Internet Text Messages.
1590 Standard for Interchange of USENET Messages
1593 Format of Internet Message Bodies
1599 Message Header Extensions for Non-ASCII Text
1602 Registration Procedures
1605 Conformance Criteria and Examples
1608 @sc{mime} Parameter Value and Encoded Word Extensions: Character Sets,
1609 Languages, and Continuations
1612 HZ - A Data Format for Exchanging Files of Arbitrarily Mixed Chinese and
1615 @item draft-ietf-drums-msg-fmt-05.txt
1616 Draft for the successor of RFC822
1619 The @sc{mime} Multipart/Related Content-type
1622 The Multipart/Report Content Type for the Reporting of Mail System
1623 Administrative Messages
1626 Communicating Presentation Information in Internet Messages: The
1627 Content-Disposition Header Field
1630 Documentation of the text/plain format parameter for flowed text.
1646 @c coding: iso-8859-1