proposal request: virtual MIME types unknown in time of installation

[Stanislav Brabec]

Stanislav Brabec wrote in Wed Nov 16, 2005 at 14:41 +0100: 

> As a package maintainer, I meet often with two calls for MIME type
> virtualization.
> 
> 1) Application uses back-end for file operations.
> 
> E.g. eog can open everything, what can provide gdk-pixbuf-loader
> subsystem.
> 
> Using hardwired MIME type list in the eog.desktop is an ugly
> work-around.
> 
> 2) Application can open more MIME types using plug-ins.
> 
> E.g. gimp can open image/x-dcraw only if RAW photo plugin is installed.
> 
> Using hardwired MIME type list with MIME types for all plugins and
> adding MIME type description XML file to plug-in is an ugly work-around.

> Proposal:
> 
> eog.desktop:
> MimeType=virtual/gdk-pixbuf-loader

I have just revived my old proposal and tried to look at keywords available in the current spec.

I found following ways to define them, changing or not changing spec.
Please look at it and let me know, what looks better.

First additionally adds sub-class-of virtual/foo to the image MIME type,
second one defines new keyword and adds and extends definition of
virtual/foo.


1) Keep current spec, change implementation:

With current implementation, it is possible to define:

/usr/share/mime/packages/gdk-pixbuf.xml:

<?xml version="1.0" encoding="UTF-8"?>
<mime-info xmlns="http://www.freedesktop.org/standards/shared-mime-info">
  <mime-type type="image/png">
    <sub-class-of type="virtual/gdk-pixbuf-loader"/>
  </mime-type>
</mime-info>

It does nearly what we need and surprisingly it works with
update-mime-database and does not break MIME type definition (only
issues warning).

But looking at implementation in Nautilus, it does not exactly, what we
expect: Nautilus interprets sub-class MIME types as low priority
candidates for opening MIME type - it offers them in sub-menu, but not
as default. This behavior seems to be correct (because nobody wants to
open SVG in the XML or text editor as a default application).

Additionally, it seems that Nautilus offers only applications coming
with the first sub-class-of line.

We can work-around this problem saying, that virtual/* MIME types are
special and candidates offered by this way are good candidates.

Pro:
No spec change needed

Con:
Needs change in implementation


2) Define new keyword into spec.

Proposed keyword is logically reversed, but not reversed in
functionality, I don't propose name "super-class-of", but name
"provides":

> <?xml version="1.0" encoding="UTF-8"?>
> <mime-info
> xmlns="http://www.freedesktop.org/standards/shared-mime-info">
>   <mime-type type="virtual/gdk-pixbuf-loader">
>     <provides type="image/x-dcraw"/>
>   </mime-type>
> </mime-info>

Pro:
Looks more logical.
No "hijacking" of existing definitions.

Con:
Needs change in spec.
Needs change in implementation.

-- 
Best Regards / S pozdravem,

Stanislav Brabec
software developer
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