Re: [DISCUSSION, default settings] Using mailcap as default handler for opening file links

[Max Nikulin]

> On 04/06/2022 20:42, Ihor Radchenko wrote:
> > Should we change the default file handlers to Emacs globally (unless
> > user customizes otherwise)? Should we continue efforts to work around
> > mailcap issues? Maybe there is yet another alternative generic way to
> > open files?

Ihor, back to your patch introducing invocation of the "file" utility. 
To get consistent behavior it should be done much earlier, when it 
becomes known that the file is not a remote one, not only as a part of 
mailcap code path (perhaps as a fallback for a file with no extension). 
Unfortunately it requires more work since Emacs mostly uses file 
suffixes, not MIME types, so the determined type should be converted to 
file extension to query e.g. auto-mode-alist.

Ideally both MIME type and file suffix should be taken into account 
since e.g. .xpi mozilla extensions are recognized as regular zip archives.

Ihor Radchenko. [PATCH v3] Re: Bug in 9.5.3 org--file-default-apps. Mon, 
30 May 2022 22:00:27 +0800. 
https://list.orgmode.org/8735gr15ok.fsf@localhost
> ((remote . emacs)
>  (system . mailcap)
>  (t . mailcap))
>
> So, is (3) following what you would expect from mailcap (regardless
> whether it is incorrectly configured or not)? Wrong configuration of
> mailcap is none of Org business - we need not to be "smart" and fix user
> "errors". They may be deliberate.

I was trying to say that mailcap.el has some predefined associations 
that are intended to handle some file types by Emacs instead of external 
handlers configured in mailcap files, unless `mailcap-user-mime-data' or 
`mailcap-prefer-mailcap-viewers' prescribes another behavior.

> Max Nikulin writes:
> > I read implementation of `org-open-file' once more and now I see that 
> > currently remote files can not be processed by mailcap code path even 
> > with custom `org-file-apps', so thank you for explanation. In some cases 
> > it may be handy to launch remote viewer from a host accessed through 
> > ssh, but let's leave it aside.
>
> This is exactly why you can always customize org-file-apps. 

Have I missed something of `org-file-apps' are ignored for remote files?

P.S. Earlier it was discussed whether run-mailcap inspects file content 
or relies solely on file suffix. A side note: originally mailcap 
processes parts of mail messages and MIME type is specified by the 
Cotntent-Type header. So handling of standalone files with no original 
MIME type is not a really native way to use mailcap. On the other hand 
sometimes there is no better way than reusing existing database.