[Tracker] A clean way to add service types

[Ivan Frade <ivan frade nokia com>]

Hi,

 Now it is quite difficult to add new service types in tracker (look at
the Tomboy integration in another thread in the mailing list). Here is
my proposal to simplify it.

 Tracker need to know the service type of a file. When the service type
is known, it can decide to index the contents, extract metadata, etc. 

 Right now, we can assign a mimetype to a service type through .service
files. At the same time, in the code we have some special cases ("Web
History" or "Applications" for instance) where a directory is assigned
to a category (hardcoded!).

 My proposal is to load from configuration files this "directory -
service type" link (extending, not replacing, the current mime
solution). It can be useful to integrate cleanly more applications into
tracker (like tomboy) and to remove the ugly special cases in the code.

 Unfortunately, it is not so easy. Tracker-extract and the filter system
are based in the mimetype to choose the correct extractor/filter. So,
when tracker uses the directory to infer the service type, the real
mimetype of the file could be wrong. For instance, a tomboy note
in .tomboy/ directory have a text/plain mime type.

 One solution could be to use "virtual" mimetypes. For example:

[TomboyNotes]
Parent=Files
Dir=$HOME/.tomboy
VirtualMime=tracker/tomboy
HasFullText=true
HasMetadata=true
HasThumbs=false


 And then tracker will call 
"tracker-extract /home/xxx/.tomboy/12iod3j.note tracker/tomboy"

 and use filter: tracker/tomboy_filter

 I think this could be a good and clean solution to add new applications
in tracker. What do you think?

 Sorry for the long mail. I couldn't use less words.

Ivan