URL and application handling/registration standard

[Yfrwlf]

The association of applications to file types and URLs are handled in 
different ways by different desktop environments (DEs) currently.  It is 
understandable as to how this system evolved, because you want file:// 
to be associated with Dolphin in KDE, and with Nautilus in Gnome.  
However, this leaves programs broken which try to register with specific 
DEs which the user doesn't use. Developers  are not able to work with 
every DE's proprietary registration system because doing so is 
impossible.  This helps create a detrimental environment for the open 
source ecosystem. There should be standards for setting default 
applications for file and URL handlers if none currently exist, and they 
need to address the issue of DE-specific needs as well as default 
settings for all DEs.

Does anyone know if such standards exist yet?  If not, we need to create 
them.  Here is an example of the logic that could be used. The first two 
columns specify what application is the *default/primary* application to 
run when the user calls a certain file or URL type, and the 3rd column 
gives the corresponding action that should be used to decide which one 
to run.

DE-Wide 	DE-Specific
	Resulting Selection while running Specific DE
	Action upon installing
none specified
	none specified 	prompt user for program or do nothing
	Change both DE-Wide and DE-Specific
nautilus
	none specified 	run nautilus
	Change only DE-Specific
none specified 	nautilus
	run nautilus
	Could prompt user, change DE-Wide
nautilus
	dolphin
	run dolphin
	Could prompt user



The "Action upon installing" column refers to when a program is being 
installed or run for the first time and attempts update the 
association.  If a program finds an existing setting, it could either 
ask the user if they want to change it or make the change anyway or do 
nothing.  In turn, that choice could, ideally, depend on a DE or global 
setting as well so that users could avoid all prompts like that in order 
to further create a uniform desktop experience.  Regardless, the 
installer/program would always at least add itself to a list of 
applications which can be used to handle that file type or URL, so there 
would be a default app setting and a path to that app as well as a list 
of all apps capable of handling the request.

Examples:
When installing applications such as torrent clients, they should 
register "magnet://" to call them, no matter the DE.
When installing web browsers, "url://" should be associated to them, no 
matter the DE.
When installing a chat client, programs should register themselves for 
each "aim://", "yahoo://", "xmpp://" etc URL type, and possibly prompt 
user for changing the defaults for those if one already exists.

Implementation:
What would be the best way to implement this standard?  What existing 
standards are being used for these types of things, if any?  I know that 
Gnome has gconf and has what amounts to basically a registry for Gnome, 
but the problem is that it is just for Gnome and so not a true standard 
that all DEs and programs can use. Perhaps if Gnome's registry is done 
well, a similar system could be placed in ~/.config, which seems to be 
the standard for all user configuration data which many apps are 
currently choosing to use.

Thoughts, ideas, and suggestions please!
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