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} or
349 @code{html2text}. You can also specify a function, which will be
350 called with a @sc{mime} handle as the argument.
352 @item mm-inline-text-html-with-images
353 Some @sc{html} mails might have the trick of spammers using
354 @samp{<img>} tags. It is likely to be intended to verify whether you
355 have read the mail. You can prevent your personal informations from
356 leaking by setting this option to @code{nil} (which is the default).
357 It is currently ignored by Emacs/w3. For emacs-w3m, you may use the
358 command @kbd{t} on the image anchor to show an image even if it is
359 @code{nil}.@footnote{The command @kbd{T} will load all images. If you
360 have set the option @code{w3m-key-binding} to @code{info}, use @kbd{i}
363 @item mm-inline-text-html-with-w3m-keymap
364 You can use emacs-w3m command keys in the inlined text/html part by
365 setting this option to non-@code{nil}. The default value is @code{t}.
373 Here's an example viewer for displaying @code{text/enriched} inline:
376 (defun mm-display-enriched-inline (handle)
379 (mm-insert-part handle)
380 (save-window-excursion
381 (enriched-decode (point-min) (point-max))
382 (setq text (buffer-string))))
383 (mm-insert-inline handle text)))
386 We see that the function takes a @sc{mime} handle as its parameter. It
387 then goes to a temporary buffer, inserts the text of the part, does some
388 work on the text, stores the result, goes back to the buffer it was
389 called from and inserts the result.
391 The two important helper functions here are @code{mm-insert-part} and
392 @code{mm-insert-inline}. The first function inserts the text of the
393 handle in the current buffer. It handles charset and/or content
394 transfer decoding. The second function just inserts whatever text you
395 tell it to insert, but it also sets things up so that the text can be
396 ``undisplayed' in a convenient manner.
402 @cindex MIME Composing
404 @cindex MIME Meta Language
406 Creating a @sc{mime} message is boring and non-trivial. Therefore, a
407 library called @code{mml} has been defined that parses a language called
408 MML (@sc{mime} Meta Language) and generates @sc{mime} messages.
410 @findex mml-generate-mime
411 The main interface function is @code{mml-generate-mime}. It will
412 examine the contents of the current (narrowed-to) buffer and return a
413 string containing the @sc{mime} message.
416 * Simple MML Example:: An example MML document.
417 * MML Definition:: All valid MML elements.
418 * Advanced MML Example:: Another example MML document.
419 * Encoding Customization:: Variables that affect encoding.
420 * Charset Translation:: How charsets are mapped from @sc{mule} to @sc{mime}.
421 * Conversion:: Going from @sc{mime} to MML and vice versa.
422 * Flowed text:: Soft and hard newlines.
426 @node Simple MML Example
427 @section Simple MML Example
429 Here's a simple @samp{multipart/alternative}:
432 <#multipart type=alternative>
433 This is a plain text part.
434 <#part type=text/enriched>
435 <center>This is a centered enriched part</center>
439 After running this through @code{mml-generate-mime}, we get this:
442 Content-Type: multipart/alternative; boundary="=-=-="
448 This is a plain text part.
451 Content-Type: text/enriched
454 <center>This is a centered enriched part</center>
461 @section MML Definition
463 The MML language is very simple. It looks a bit like an SGML
464 application, but it's not.
466 The main concept of MML is the @dfn{part}. Each part can be of a
467 different type or use a different charset. The way to delineate a part
468 is with a @samp{<#part ...>} tag. Multipart parts can be introduced
469 with the @samp{<#multipart ...>} tag. Parts are ended by the
470 @samp{<#/part>} or @samp{<#/multipart>} tags. Parts started with the
471 @samp{<#part ...>} tags are also closed by the next open tag.
473 There's also the @samp{<#external ...>} tag. These introduce
474 @samp{external/message-body} parts.
476 Each tag can contain zero or more parameters on the form
477 @samp{parameter=value}. The values may be enclosed in quotation marks,
478 but that's not necessary unless the value contains white space. So
479 @samp{filename=/home/user/#hello$^yes} is perfectly valid.
481 The following parameters have meaning in MML; parameters that have no
482 meaning are ignored. The MML parameter names are the same as the
483 @sc{mime} parameter names; the things in the parentheses say which
484 header it will be used in.
488 The @sc{mime} type of the part (@code{Content-Type}).
491 Use the contents of the file in the body of the part
492 (@code{Content-Disposition}).
495 The contents of the body of the part are to be encoded in the character
496 set speficied (@code{Content-Type}). @xref{Charset Translation}.
499 Might be used to suggest a file name if the part is to be saved
500 to a file (@code{Content-Type}).
503 Valid values are @samp{inline} and @samp{attachment}
504 (@code{Content-Disposition}).
507 Valid values are @samp{7bit}, @samp{8bit}, @samp{quoted-printable} and
508 @samp{base64} (@code{Content-Transfer-Encoding}). @xref{Charset
512 A description of the part (@code{Content-Description}).
515 RFC822 date when the part was created (@code{Content-Disposition}).
517 @item modification-date
518 RFC822 date when the part was modified (@code{Content-Disposition}).
521 RFC822 date when the part was read (@code{Content-Disposition}).
524 Who to encrypt/sign the part to. This field is used to override any
525 auto-detection based on the To/CC headers.
528 The size (in octets) of the part (@code{Content-Disposition}).
531 What technology to sign this MML part with (@code{smime}, @code{pgp}
535 What technology to encrypt this MML part with (@code{smime},
536 @code{pgp} or @code{pgpmime})
540 Parameters for @samp{application/octet-stream}:
544 Type of the part; informal---meant for human readers
545 (@code{Content-Type}).
548 Parameters for @samp{message/external-body}:
552 A word indicating the supported access mechanism by which the file may
553 be obtained. Values include @samp{ftp}, @samp{anon-ftp}, @samp{tftp},
554 @samp{localfile}, and @samp{mailserver}. (@code{Content-Type}.)
557 The RFC822 date after which the file may no longer be fetched.
558 (@code{Content-Type}.)
561 The size (in octets) of the file. (@code{Content-Type}.)
564 Valid values are @samp{read} and @samp{read-write}
565 (@code{Content-Type}).
569 Parameters for @samp{sign=smime}:
574 File containing key and certificate for signer.
578 Parameters for @samp{encrypt=smime}:
583 File containing certificate for recipient.
588 @node Advanced MML Example
589 @section Advanced MML Example
591 Here's a complex multipart message. It's a @samp{multipart/mixed} that
592 contains many parts, one of which is a @samp{multipart/alternative}.
595 <#multipart type=mixed>
596 <#part type=image/jpeg filename=~/rms.jpg disposition=inline>
597 <#multipart type=alternative>
598 This is a plain text part.
599 <#part type=text/enriched name=enriched.txt>
600 <center>This is a centered enriched part</center>
602 This is a new plain text part.
603 <#part disposition=attachment>
604 This plain text part is an attachment.
608 And this is the resulting @sc{mime} message:
611 Content-Type: multipart/mixed; boundary="=-=-="
619 Content-Type: image/jpeg;
621 Content-Disposition: inline;
623 Content-Transfer-Encoding: base64
625 /9j/4AAQSkZJRgABAQAAAQABAAD/2wBDAAgGBgcGBQgHBwcJCQgKDBQNDAsLDBkSEw8UHRof
626 Hh0aHBwgJC4nICIsIxwcKDcpLDAxNDQ0Hyc5PTgyPC4zNDL/wAALCAAwADABAREA/8QAHwAA
627 AQUBAQEBAQEAAAAAAAAAAAECAwQFBgcICQoL/8QAtRAAAgEDAwIEAwUFBAQAAAF9AQIDAAQR
628 BRIhMUEGE1FhByJxFDKBkaEII0KxwRVS0fAkM2JyggkKFhcYGRolJicoKSo0NTY3ODk6Q0RF
629 RkdISUpTVFVWV1hZWmNkZWZnaGlqc3R1dnd4eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ip
630 qrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uHi4+Tl5ufo6erx8vP09fb3+Pn6/9oACAEB
631 AAA/AO/rifFHjldNuGsrDa0qcSSHkA+gHrXKw+LtWLrMb+RgTyhbr+HSug07xNqV9fQtZrNI
632 AyiaE/NuBPOOOP0rvRNE880KOC8TbXXGCv1FPqjrF4LDR7u5L7SkTFT/ALWOP1xXgTuXfc7E
633 sx6nua6rwp4IvvEM8chCxWxOdzn7wz6V9AaB4S07w9p5itow0rDLSY5Pt9K43xO66P4xs71m
634 2QXiGCbA4yOVJ9+1aYORkdK434lyNH4ahCnG66VT9Nj15JFbPdX0MS43M4VQf5/yr2vSpLnw
635 5ZW8dlCZ8KFXjOPX0/mK6rSPEGt3Angu44fNEReHYNvIH3TzXDeKNO8RX+kSX2ouZkicTIOc
636 L+g7E810ulFjpVtv3bwgB3HJyK5L4quY/C9sVxk3ij/xx6850u7t1mtp/wDlpEw3An3Jr3Dw
637 34gsbWza4nBlhC5LDsaW6+IFgupQyCF3iHH7gA7c9R9ay7zx6t7aX9jHC4smhfBkGCvHGfrm
638 tLQ7hbnRrV1GPkAP1x1/Hr+Ncr8Vzjwrbf8AX6v/AKA9eQRyYlQk8Yx9K6XTNbkgia2ciSIn
639 7p5Ga9Atte0LTLKO6it4i7dVRFJDcZ4PvXN+JvEMF9bILVGXJLSZ4zkjivRPDaeX4b08HOTC
640 pOffmua+KkbS+GLVUGT9tT/0B68eeIpIFYjB70+OOVXyoOM9+M1eaWeCLzHPyHGO/NVWvJJm
641 jQ8KGH1NfQWhXSXmh2c8eArRLwO3HSv/2Q==
644 Content-Type: multipart/alternative; boundary="==-=-="
650 This is a plain text part.
653 Content-Type: text/enriched;
657 <center>This is a centered enriched part</center>
663 This is a new plain text part.
666 Content-Disposition: attachment
669 This plain text part is an attachment.
674 @node Encoding Customization
675 @section Encoding Customization
679 @item mm-body-charset-encoding-alist
680 @vindex mm-body-charset-encoding-alist
681 Mapping from MIME charset to encoding to use. This variable is
682 usually used except, e.g., when other requirements force a specific
683 encoding (digitally signed messages require 7bit encodings). The
684 default is @code{((iso-2022-jp . 7bit) (iso-2022-jp-2 . 7bit))}. As
685 an example, if you do not want to have ISO-8859-1 characters
686 quoted-printable encoded, you may add @code{(iso-8859-1 . 8bit)} to
687 this variable. You can override this setting on a per-message basis
688 by using the @code{encoding} MML tag (@pxref{MML Definition}).
690 @item mm-coding-system-priorities
691 @vindex mm-coding-system-priorities
692 Prioritize coding systems to use for outgoing messages. The default
693 is nil, which means to use the defaults in Emacs. It is a list of
694 coding system symbols (aliases of coding systems does not work, use
695 @kbd{M-x describe-coding-system} to make sure you are not specifying
696 an alias in this variable). For example, if you have configured Emacs
697 to use prefer UTF-8, but wish that outgoing messages should be sent in
698 ISO-8859-1 if possible, you can set this variable to
699 @code{(iso-latin-1)}. You can override this setting on a per-message
700 basis by using the @code{charset} MML tag (@pxref{MML Definition}).
702 @item mm-content-transfer-encoding-defaults
703 @vindex mm-content-transfer-encoding-defaults
704 Mapping from MIME types to encoding to use. This variable is usually
705 used except, e.g., when other requirements force a safer encoding
706 (digitally signed messages require 7bit encoding). Besides the normal
707 MIME encodings, @code{qp-or-base64} may be used to indicate that for
708 each case the most efficient of quoted-printable and base64 should be
709 used. You can override this setting on a per-message basis by using
710 the @code{encoding} MML tag (@pxref{MML Definition}).
712 @item mm-use-ultra-safe-encoding
713 @vindex mm-use-ultra-safe-encoding
714 When this is non-nil, it means that textual parts are encoded as
715 quoted-printable if they contain lines longer than 76 characters or
716 starting with "From " in the body. Non-7bit encodings (8bit, binary)
717 are generally disallowed. This reduce the probability that a non-8bit
718 clean MTA or MDA changes the message. This should never be set
719 directly, but bound by other functions when necessary (e.g., when
720 encoding messages that are to be digitally signed).
724 @node Charset Translation
725 @section Charset Translation
728 During translation from MML to @sc{mime}, for each @sc{mime} part which
729 has been composed inside Emacs, an appropriate charset has to be chosen.
731 @vindex mail-parse-charset
732 If you are running a non-@sc{mule} Emacs, this process is simple: If the
733 part contains any non-ASCII (8-bit) characters, the @sc{mime} charset
734 given by @code{mail-parse-charset} (a symbol) is used. (Never set this
735 variable directly, though. If you want to change the default charset,
736 please consult the documentation of the package which you use to process
738 @xref{Various Message Variables, , Various Message Variables, message,
739 Message Manual}, for example.)
740 If there are only ASCII characters, the @sc{mime} charset US-ASCII is
746 @vindex mm-mime-mule-charset-alist
747 Things are slightly more complicated when running Emacs with @sc{mule}
748 support. In this case, a list of the @sc{mule} charsets used in the
749 part is obtained, and the @sc{mule} charsets are translated to @sc{mime}
750 charsets by consulting the variable @code{mm-mime-mule-charset-alist}.
751 If this results in a single @sc{mime} charset, this is used to encode
752 the part. But if the resulting list of @sc{mime} charsets contains more
753 than one element, two things can happen: If it is possible to encode the
754 part via UTF-8, this charset is used. (For this, Emacs must support
755 the @code{utf-8} coding system, and the part must consist entirely of
756 characters which have Unicode counterparts.) If UTF-8 is not available
757 for some reason, the part is split into several ones, so that each one
758 can be encoded with a single @sc{mime} charset. The part can only be
759 split at line boundaries, though---if more than one @sc{mime} charset is
760 required to encode a single line, it is not possible to encode the part.
762 When running Emacs with @sc{mule} support, the preferences for which
763 coding system to use is inherited from Emacs itself. This means that
764 if Emacs is set up to prefer UTF-8, it will be used when encoding
765 messages. You can modify this by altering the
766 @code{mm-coding-system-priorities} variable though (@pxref{Encoding
769 The charset to be used can be overriden by setting the @code{charset}
770 MML tag (@pxref{MML Definition}) when composing the message.
772 The encoding of characters (quoted-printable, 8bit etc) is orthogonal
773 to the discussion here, and is controlled by the variables
774 @code{mm-body-charset-encoding-alist} and
775 @code{mm-content-transfer-encoding-defaults} (@pxref{Encoding
782 A (multipart) @sc{mime} message can be converted to MML with the
783 @code{mime-to-mml} function. It works on the message in the current
784 buffer, and substitutes MML markup for @sc{mime} boundaries.
785 Non-textual parts do not have their contents in the buffer, but instead
786 have the contents in separate buffers that are referred to from the MML
790 An MML message can be converted back to @sc{mime} by the
791 @code{mml-to-mime} function.
793 These functions are in certain senses ``lossy''---you will not get back
794 an identical message if you run @sc{mime-to-mml} and then
795 @sc{mml-to-mime}. Not only will trivial things like the order of the
796 headers differ, but the contents of the headers may also be different.
797 For instance, the original message may use base64 encoding on text,
798 while @sc{mml-to-mime} may decide to use quoted-printable encoding, and
801 In essence, however, these two functions should be the inverse of each
802 other. The resulting contents of the message should remain equivalent,
808 @cindex format=flowed
810 The Emacs @sc{mime} library will respect the @code{use-hard-newlines}
811 variable (@pxref{Hard and Soft Newlines, ,Hard and Soft Newlines,
812 emacs, Emacs Manual}) when encoding a message, and the
813 ``format=flowed'' Content-Type parameter when decoding a message.
815 On encoding text, lines terminated by soft newline characters are
816 filled together and wrapped after the column decided by
817 @code{fill-flowed-encode-column}. This variable controls how the text
818 will look in a client that does not support flowed text, the default
819 is to wrap after 66 characters. If hard newline characters are not
820 present in the buffer, no flow encoding occurs.
822 On decoding flowed text, lines with soft newline characters are filled
823 together and wrapped after the column decided by
824 @code{fill-flowed-display-column}. The default is to wrap after
830 @node Interface Functions
831 @chapter Interface Functions
832 @cindex interface functions
835 The @code{mail-parse} library is an abstraction over the actual
836 low-level libraries that are described in the next chapter.
838 Standards change, and so programs have to change to fit in the new
839 mold. For instance, RFC2045 describes a syntax for the
840 @code{Content-Type} header that only allows ASCII characters in the
841 parameter list. RFC2231 expands on RFC2045 syntax to provide a scheme
842 for continuation headers and non-ASCII characters.
844 The traditional way to deal with this is just to update the library
845 functions to parse the new syntax. However, this is sometimes the wrong
846 thing to do. In some instances it may be vital to be able to understand
847 both the old syntax as well as the new syntax, and if there is only one
848 library, one must choose between the old version of the library and the
849 new version of the library.
851 The Emacs @sc{mime} library takes a different tack. It defines a
852 series of low-level libraries (@file{rfc2047.el}, @file{rfc2231.el}
853 and so on) that parses strictly according to the corresponding
854 standard. However, normal programs would not use the functions
855 provided by these libraries directly, but instead use the functions
856 provided by the @code{mail-parse} library. The functions in this
857 library are just aliases to the corresponding functions in the latest
858 low-level libraries. Using this scheme, programs get a consistent
859 interface they can use, and library developers are free to create
860 write code that handles new standards.
862 The following functions are defined by this library:
865 @item mail-header-parse-content-type
866 @findex mail-header-parse-content-type
867 Parse a @code{Content-Type} header and return a list on the following
872 (attribute1 . value1)
873 (attribute2 . value2)
880 (mail-header-parse-content-type
881 "image/gif; name=\"b980912.gif\"")
882 @result{} ("image/gif" (name . "b980912.gif"))
885 @item mail-header-parse-content-disposition
886 @findex mail-header-parse-content-disposition
887 Parse a @code{Content-Disposition} header and return a list on the same
888 format as the function above.
890 @item mail-content-type-get
891 @findex mail-content-type-get
892 Takes two parameters---a list on the format above, and an attribute.
893 Returns the value of the attribute.
896 (mail-content-type-get
897 '("image/gif" (name . "b980912.gif")) 'name)
898 @result{} "b980912.gif"
901 @item mail-header-encode-parameter
902 @findex mail-header-encode-parameter
903 Takes a parameter string and returns an encoded version of the string.
904 This is used for parameters in headers like @code{Content-Type} and
905 @code{Content-Disposition}.
907 @item mail-header-remove-comments
908 @findex mail-header-remove-comments
909 Return a comment-free version of a header.
912 (mail-header-remove-comments
913 "Gnus/5.070027 (Pterodactyl Gnus v0.27) (Finnish Landrace)")
914 @result{} "Gnus/5.070027 "
917 @item mail-header-remove-whitespace
918 @findex mail-header-remove-whitespace
919 Remove linear white space from a header. Space inside quoted strings
920 and comments is preserved.
923 (mail-header-remove-whitespace
924 "image/gif; name=\"Name with spaces\"")
925 @result{} "image/gif;name=\"Name with spaces\""
928 @item mail-header-get-comment
929 @findex mail-header-get-comment
930 Return the last comment in a header.
933 (mail-header-get-comment
934 "Gnus/5.070027 (Pterodactyl Gnus v0.27) (Finnish Landrace)")
935 @result{} "Finnish Landrace"
938 @item mail-header-parse-address
939 @findex mail-header-parse-address
940 Parse an address and return a list containing the mailbox and the
944 (mail-header-parse-address
945 "Hrvoje Niksic <hniksic@@srce.hr>")
946 @result{} ("hniksic@@srce.hr" . "Hrvoje Niksic")
949 @item mail-header-parse-addresses
950 @findex mail-header-parse-addresses
951 Parse a string with list of addresses and return a list of elements like
952 the one described above.
955 (mail-header-parse-addresses
956 "Hrvoje Niksic <hniksic@@srce.hr>, Steinar Bang <sb@@metis.no>")
957 @result{} (("hniksic@@srce.hr" . "Hrvoje Niksic")
958 ("sb@@metis.no" . "Steinar Bang"))
961 @item mail-header-parse-date
962 @findex mail-header-parse-date
963 Parse a date string and return an Emacs time structure.
965 @item mail-narrow-to-head
966 @findex mail-narrow-to-head
967 Narrow the buffer to the header section of the buffer. Point is placed
968 at the beginning of the narrowed buffer.
970 @item mail-header-narrow-to-field
971 @findex mail-header-narrow-to-field
972 Narrow the buffer to the header under point. Understands continuation
975 @item mail-header-fold-field
976 @findex mail-header-fold-field
977 Fold the header under point.
979 @item mail-header-unfold-field
980 @findex mail-header-unfold-field
981 Unfold the header under point.
983 @item mail-header-field-value
984 @findex mail-header-field-value
985 Return the value of the field under point.
987 @item mail-encode-encoded-word-region
988 @findex mail-encode-encoded-word-region
989 Encode the non-ASCII words in the region. For instance,
990 @samp{Naïve} is encoded as @samp{=?iso-8859-1?q?Na=EFve?=}.
992 @item mail-encode-encoded-word-buffer
993 @findex mail-encode-encoded-word-buffer
994 Encode the non-ASCII words in the current buffer. This function is
995 meant to be called narrowed to the headers of a message.
997 @item mail-encode-encoded-word-string
998 @findex mail-encode-encoded-word-string
999 Encode the words that need encoding in a string, and return the result.
1002 (mail-encode-encoded-word-string
1003 "This is naïve, baby")
1004 @result{} "This is =?iso-8859-1?q?na=EFve,?= baby"
1007 @item mail-decode-encoded-word-region
1008 @findex mail-decode-encoded-word-region
1009 Decode the encoded words in the region.
1011 @item mail-decode-encoded-word-string
1012 @findex mail-decode-encoded-word-string
1013 Decode the encoded words in the string and return the result.
1016 (mail-decode-encoded-word-string
1017 "This is =?iso-8859-1?q?na=EFve,?= baby")
1018 @result{} "This is naïve, baby"
1023 Currently, @code{mail-parse} is an abstraction over @code{ietf-drums},
1024 @code{rfc2047}, @code{rfc2045} and @code{rfc2231}. These are documented
1025 in the subsequent sections.
1029 @node Basic Functions
1030 @chapter Basic Functions
1032 This chapter describes the basic, ground-level functions for parsing and
1033 handling. Covered here is parsing @code{From} lines, removing comments
1034 from header lines, decoding encoded words, parsing date headers and so
1035 on. High-level functionality is dealt with in the next chapter
1036 (@pxref{Decoding and Viewing}).
1039 * rfc2045:: Encoding @code{Content-Type} headers.
1040 * rfc2231:: Parsing @code{Content-Type} headers.
1041 * ietf-drums:: Handling mail headers defined by RFC822bis.
1042 * rfc2047:: En/decoding encoded words in headers.
1043 * time-date:: Functions for parsing dates and manipulating time.
1044 * qp:: Quoted-Printable en/decoding.
1045 * base64:: Base64 en/decoding.
1046 * binhex:: Binhex decoding.
1047 * uudecode:: Uuencode decoding.
1048 * yenc:: Yenc decoding.
1049 * rfc1843:: Decoding HZ-encoded text.
1050 * mailcap:: How parts are displayed is specified by the @file{.mailcap} file
1057 RFC2045 is the ``main'' @sc{mime} document, and as such, one would
1058 imagine that there would be a lot to implement. But there isn't, since
1059 most of the implementation details are delegated to the subsequent
1062 So @file{rfc2045.el} has only a single function:
1065 @item rfc2045-encode-string
1066 @findex rfc2045-encode-string
1067 Takes a parameter and a value and returns a @samp{PARAM=VALUE} string.
1068 @var{value} will be quoted if there are non-safe characters in it.
1075 RFC2231 defines a syntax for the @code{Content-Type} and
1076 @code{Content-Disposition} headers. Its snappy name is @dfn{MIME
1077 Parameter Value and Encoded Word Extensions: Character Sets, Languages,
1080 In short, these headers look something like this:
1083 Content-Type: application/x-stuff;
1084 title*0*=us-ascii'en'This%20is%20even%20more%20;
1085 title*1*=%2A%2A%2Afun%2A%2A%2A%20;
1089 They usually aren't this bad, though.
1091 The following functions are defined by this library:
1094 @item rfc2231-parse-string
1095 @findex rfc2231-parse-string
1096 Parse a @code{Content-Type} header and return a list describing its
1100 (rfc2231-parse-string
1101 "application/x-stuff;
1102 title*0*=us-ascii'en'This%20is%20even%20more%20;
1103 title*1*=%2A%2A%2Afun%2A%2A%2A%20;
1104 title*2=\"isn't it!\"")
1105 @result{} ("application/x-stuff"
1106 (title . "This is even more ***fun*** isn't it!"))
1109 @item rfc2231-get-value
1110 @findex rfc2231-get-value
1111 Takes one of the lists on the format above and returns
1112 the value of the specified attribute.
1114 @item rfc2231-encode-string
1115 @findex rfc2231-encode-string
1116 Encode a parameter in headers likes @code{Content-Type} and
1117 @code{Content-Disposition}.
1125 @dfn{drums} is an IETF working group that is working on the replacement
1128 The functions provided by this library include:
1131 @item ietf-drums-remove-comments
1132 @findex ietf-drums-remove-comments
1133 Remove the comments from the argument and return the results.
1135 @item ietf-drums-remove-whitespace
1136 @findex ietf-drums-remove-whitespace
1137 Remove linear white space from the string and return the results.
1138 Spaces inside quoted strings and comments are left untouched.
1140 @item ietf-drums-get-comment
1141 @findex ietf-drums-get-comment
1142 Return the last most comment from the string.
1144 @item ietf-drums-parse-address
1145 @findex ietf-drums-parse-address
1146 Parse an address string and return a list that contains the mailbox and
1147 the plain text name.
1149 @item ietf-drums-parse-addresses
1150 @findex ietf-drums-parse-addresses
1151 Parse a string that contains any number of comma-separated addresses and
1152 return a list that contains mailbox/plain text pairs.
1154 @item ietf-drums-parse-date
1155 @findex ietf-drums-parse-date
1156 Parse a date string and return an Emacs time structure.
1158 @item ietf-drums-narrow-to-header
1159 @findex ietf-drums-narrow-to-header
1160 Narrow the buffer to the header section of the current buffer.
1168 RFC2047 (Message Header Extensions for Non-ASCII Text) specifies how
1169 non-ASCII text in headers are to be encoded. This is actually rather
1170 complicated, so a number of variables are necessary to tweak what this
1173 The following variables are tweakable:
1176 @item rfc2047-default-charset
1177 @vindex rfc2047-default-charset
1178 Characters in this charset should not be decoded by this library.
1179 This defaults to @code{iso-8859-1}.
1181 @item rfc2047-header-encoding-list
1182 @vindex rfc2047-header-encoding-list
1183 This is an alist of header / encoding-type pairs. Its main purpose is
1184 to prevent encoding of certain headers.
1186 The keys can either be header regexps, or @code{t}.
1188 The values can be either @code{nil}, in which case the header(s) in
1189 question won't be encoded, or @code{mime}, which means that they will be
1192 @item rfc2047-charset-encoding-alist
1193 @vindex rfc2047-charset-encoding-alist
1194 RFC2047 specifies two forms of encoding---@code{Q} (a
1195 Quoted-Printable-like encoding) and @code{B} (base64). This alist
1196 specifies which charset should use which encoding.
1198 @item rfc2047-encoding-function-alist
1199 @vindex rfc2047-encoding-function-alist
1200 This is an alist of encoding / function pairs. The encodings are
1201 @code{Q}, @code{B} and @code{nil}.
1203 @item rfc2047-q-encoding-alist
1204 @vindex rfc2047-q-encoding-alist
1205 The @code{Q} encoding isn't quite the same for all headers. Some
1206 headers allow a narrower range of characters, and that is what this
1207 variable is for. It's an alist of header regexps / allowable character
1210 @item rfc2047-encoded-word-regexp
1211 @vindex rfc2047-encoded-word-regexp
1212 When decoding words, this library looks for matches to this regexp.
1216 Those were the variables, and these are this functions:
1219 @item rfc2047-narrow-to-field
1220 @findex rfc2047-narrow-to-field
1221 Narrow the buffer to the header on the current line.
1223 @item rfc2047-encode-message-header
1224 @findex rfc2047-encode-message-header
1225 Should be called narrowed to the header of a message. Encodes according
1226 to @code{rfc2047-header-encoding-alist}.
1228 @item rfc2047-encode-region
1229 @findex rfc2047-encode-region
1230 Encodes all encodable words in the region specified.
1232 @item rfc2047-encode-string
1233 @findex rfc2047-encode-string
1234 Encode a string and return the results.
1236 @item rfc2047-decode-region
1237 @findex rfc2047-decode-region
1238 Decode the encoded words in the region.
1240 @item rfc2047-decode-string
1241 @findex rfc2047-decode-string
1242 Decode a string and return the results.
1250 While not really a part of the @sc{mime} library, it is convenient to
1251 document this library here. It deals with parsing @code{Date} headers
1252 and manipulating time. (Not by using tesseracts, though, I'm sorry to
1255 These functions convert between five formats: A date string, an Emacs
1256 time structure, a decoded time list, a second number, and a day number.
1258 Here's a bunch of time/date/second/day examples:
1261 (parse-time-string "Sat Sep 12 12:21:54 1998 +0200")
1262 @result{} (54 21 12 12 9 1998 6 nil 7200)
1264 (date-to-time "Sat Sep 12 12:21:54 1998 +0200")
1265 @result{} (13818 19266)
1267 (time-to-seconds '(13818 19266))
1268 @result{} 905595714.0
1270 (seconds-to-time 905595714.0)
1271 @result{} (13818 19266 0)
1273 (time-to-days '(13818 19266))
1276 (days-to-time 729644)
1277 @result{} (961933 65536)
1279 (time-since '(13818 19266))
1282 (time-less-p '(13818 19266) '(13818 19145))
1285 (subtract-time '(13818 19266) '(13818 19145))
1288 (days-between "Sat Sep 12 12:21:54 1998 +0200"
1289 "Sat Sep 07 12:21:54 1998 +0200")
1292 (date-leap-year-p 2000)
1295 (time-to-day-in-year '(13818 19266))
1298 (time-to-number-of-days
1300 (date-to-time "Mon, 01 Jan 2001 02:22:26 GMT")))
1301 @result{} 4.146122685185185
1304 And finally, we have @code{safe-date-to-time}, which does the same as
1305 @code{date-to-time}, but returns a zero time if the date is
1306 syntactically malformed.
1308 The five data representations used are the following:
1312 An RFC822 (or similar) date string. For instance: @code{"Sat Sep 12
1313 12:21:54 1998 +0200"}.
1316 An internal Emacs time. For instance: @code{(13818 26466)}.
1319 A floating point representation of the internal Emacs time. For
1320 instance: @code{905595714.0}.
1323 An integer number representing the number of days since 00000101. For
1324 instance: @code{729644}.
1327 A list of decoded time. For instance: @code{(54 21 12 12 9 1998 6 t
1331 All the examples above represent the same moment.
1333 These are the functions available:
1337 Take a date and return a time.
1339 @item time-to-seconds
1340 Take a time and return seconds.
1342 @item seconds-to-time
1343 Take seconds and return a time.
1346 Take a time and return days.
1349 Take days and return a time.
1352 Take a date and return days.
1354 @item time-to-number-of-days
1355 Take a time and return the number of days that represents.
1357 @item safe-date-to-time
1358 Take a date and return a time. If the date is not syntactically valid,
1359 return a "zero" date.
1362 Take two times and say whether the first time is less (i. e., earlier)
1363 than the second time.
1366 Take a time and return a time saying how long it was since that time.
1369 Take two times and subtract the second from the first. I. e., return
1370 the time between the two times.
1373 Take two days and return the number of days between those two days.
1375 @item date-leap-year-p
1376 Take a year number and say whether it's a leap year.
1378 @item time-to-day-in-year
1379 Take a time and return the day number within the year that the time is
1388 This library deals with decoding and encoding Quoted-Printable text.
1390 Very briefly explained, qp encoding means translating all 8-bit
1391 characters (and lots of control characters) into things that look like
1392 @samp{=EF}; that is, an equal sign followed by the byte encoded as a hex
1395 The following functions are defined by the library:
1398 @item quoted-printable-decode-region
1399 @findex quoted-printable-decode-region
1400 QP-decode all the encoded text in the specified region.
1402 @item quoted-printable-decode-string
1403 @findex quoted-printable-decode-string
1404 Decode the QP-encoded text in a string and return the results.
1406 @item quoted-printable-encode-region
1407 @findex quoted-printable-encode-region
1408 QP-encode all the encodable characters in the specified region. The third
1409 optional parameter @var{fold} specifies whether to fold long lines.
1410 (Long here means 72.)
1412 @item quoted-printable-encode-string
1413 @findex quoted-printable-encode-string
1414 QP-encode all the encodable characters in a string and return the
1424 Base64 is an encoding that encodes three bytes into four characters,
1425 thereby increasing the size by about 33%. The alphabet used for
1426 encoding is very resistant to mangling during transit.
1428 The following functions are defined by this library:
1431 @item base64-encode-region
1432 @findex base64-encode-region
1433 base64 encode the selected region. Return the length of the encoded
1434 text. Optional third argument @var{no-line-break} means do not break
1435 long lines into shorter lines.
1437 @item base64-encode-string
1438 @findex base64-encode-string
1439 base64 encode a string and return the result.
1441 @item base64-decode-region
1442 @findex base64-decode-region
1443 base64 decode the selected region. Return the length of the decoded
1444 text. If the region can't be decoded, return @code{nil} and don't
1447 @item base64-decode-string
1448 @findex base64-decode-string
1449 base64 decode a string and return the result. If the string can't be
1450 decoded, @code{nil} is returned.
1461 @code{binhex} is an encoding that originated in Macintosh environments.
1462 The following function is supplied to deal with these:
1465 @item binhex-decode-region
1466 @findex binhex-decode-region
1467 Decode the encoded text in the region. If given a third parameter, only
1468 decode the @code{binhex} header and return the filename.
1478 @code{uuencode} is probably still the most popular encoding of binaries
1479 used on Usenet, although @code{base64} rules the mail world.
1481 The following function is supplied by this package:
1484 @item uudecode-decode-region
1485 @findex uudecode-decode-region
1486 Decode the text in the region.
1494 @code{yenc} is used for encoding binaries on Usenet. The following
1495 function is supplied by this package:
1498 @item yenc-decode-region
1499 @findex yenc-decode-region
1500 Decode the encoded text in the region.
1511 RFC1843 deals with mixing Chinese and ASCII characters in messages. In
1512 essence, RFC1843 switches between ASCII and Chinese by doing this:
1515 This sentence is in ASCII.
1516 The next sentence is in GB.~@{<:Ky2;S@{#,NpJ)l6HK!#~@}Bye.
1519 Simple enough, and widely used in China.
1521 The following functions are available to handle this encoding:
1524 @item rfc1843-decode-region
1525 Decode HZ-encoded text in the region.
1527 @item rfc1843-decode-string
1528 Decode a HZ-encoded string and return the result.
1536 The @file{~/.mailcap} file is parsed by most @sc{mime}-aware message
1537 handlers and describes how elements are supposed to be displayed.
1538 Here's an example file:
1542 audio/wav; wavplayer %s
1543 application/msword; catdoc %s ; copiousoutput ; nametemplate=%s.doc
1546 This says that all image files should be displayed with @code{gimp},
1547 that WAVE audio files should be played by @code{wavplayer}, and that
1548 MS-WORD files should be inlined by @code{catdoc}.
1550 The @code{mailcap} library parses this file, and provides functions for
1554 @item mailcap-mime-data
1555 @vindex mailcap-mime-data
1556 This variable is an alist of alists containing backup viewing rules.
1560 Interface functions:
1563 @item mailcap-parse-mailcaps
1564 @findex mailcap-parse-mailcaps
1565 Parse the @code{~/.mailcap} file.
1567 @item mailcap-mime-info
1568 Takes a @sc{mime} type as its argument and returns the matching viewer.
1578 The Emacs @sc{mime} library implements handling of various elements
1579 according to a (somewhat) large number of RFCs, drafts and standards
1580 documents. This chapter lists the relevant ones. They can all be
1581 fetched from @uref{http://quimby.gnus.org/notes/}.
1586 Standard for the Format of ARPA Internet Text Messages.
1589 Standard for Interchange of USENET Messages
1592 Format of Internet Message Bodies
1598 Message Header Extensions for Non-ASCII Text
1601 Registration Procedures
1604 Conformance Criteria and Examples
1607 @sc{mime} Parameter Value and Encoded Word Extensions: Character Sets,
1608 Languages, and Continuations
1611 HZ - A Data Format for Exchanging Files of Arbitrarily Mixed Chinese and
1614 @item draft-ietf-drums-msg-fmt-05.txt
1615 Draft for the successor of RFC822
1618 The @sc{mime} Multipart/Related Content-type
1621 The Multipart/Report Content Type for the Reporting of Mail System
1622 Administrative Messages
1625 Communicating Presentation Information in Internet Messages: The
1626 Content-Disposition Header Field
1629 Documentation of the text/plain format parameter for flowed text.
1645 @c coding: iso-8859-1