mailcap MIME type handlers

mailcap MIME type handlers

[Ben Bacarisse]

Short version:

How can I get Emacs (specifically mailcap.el) to prioritise my system's
or my personal mailcap settings?

Gnus, for example, opens PDF files in doc-view-mode rather than using
the program specified in /etc/mailcap or ~/.mailcap.

In more detail...

From an quick examination of mailcap.el it seems that an initial set of
mailcap data, given an explicit list assigned to mailcap-mime-data, is
augmented by reading the system's mailcap files along with the user's
mailcap.  However, the initial data do not simply provide a default
back-stop because many of them use Emacs modes that are, for most
people, to be preferred.  This is achieved by sorting the list of
possible matches with a predicate that favours Lisp symbols over strings
(mailcap-viewer-lessp).  Thus '(viewer doc-view-mode) will win over
'(viewer "/usr/bin/mupdf %s") or, indeed, over any setting from the
parsed files.

I have a crude solution.  If, after mailcap is loaded, I manually
execute

  (setq mailcap-mime-data nil)
  (mailcap-parse-mailcaps nil t)

only the parsed entries will be seen as the initial value of
mailcap-mime-data is lost.  But this is not a good solution not least
because I may want some of these "built-in" handlers -- I haven't
checked them all.

What is the proper way to deal with this?

If there isn't a neat solution, maybe I can hook into the mailcap system
to get the behaviour I want.  What's the best way to do that?  Do I need
to resort to advice-add?

-- 
Ben.

Re: mailcap MIME type handlers

[Teemu Likonen]

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Ben Bacarisse [2018-09-23 03:52:03+01] wrote:

> How can I get Emacs (specifically mailcap.el) to prioritise my
> system's or my personal mailcap settings?
>
> Gnus, for example, opens PDF files in doc-view-mode rather than using
> the program specified in /etc/mailcap or ~/.mailcap.

Use variable mailcap-user-mime-data:

    (setq mailcap-user-mime-data
          '(((type . "application/pdf")
             (viewer . "my-viewer %s"))))

-- 
/// Teemu Likonen   - .-..   <https://keybase.io/tlikonen> //
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Re: mailcap MIME type handlers

[Ben Bacarisse]

Teemu Likonen <tlikonen@iki.fi> writes:

> Ben Bacarisse [2018-09-23 03:52:03+01] wrote:
>
>> How can I get Emacs (specifically mailcap.el) to prioritise my
>> system's or my personal mailcap settings?
>>
>> Gnus, for example, opens PDF files in doc-view-mode rather than using
>> the program specified in /etc/mailcap or ~/.mailcap.
>
> Use variable mailcap-user-mime-data:
>
>     (setq mailcap-user-mime-data
>           '(((type . "application/pdf")
>              (viewer . "my-viewer %s"))))

Thanks, but that's a bit of a sledge hammer!  It looses all the other
settings, and duplicates where I specify the viewer.

I'd like mailcap.el to get the setting from ~/.mailcap.  My current
work-around is to

  (require 'mailcap)
  (setq mailcap-mime-data nil)
  (mailcap-parse-mailcaps nil t)

in .emacs, but that's also rather crude because it loses the default
settings from mailcap-user-mime-data, some of which may be useful (I
have not looked at them all).  Not to mention doing all the work twice.

-- 
Ben.