Persistent data with KDED (or KIOD) and a KIO Slave?

[Mark Gaiser]

Hi,

I'm about to experiment a bit with a KIO slave idea [1] I've been having
for a while.

I get how a KIO slave works, that's not an issue.

What i don't get fully is how a KIO slave with persistent storage works
(say like baloo or stash) where a KIOD/KDED module is required to read from
the storage.

How would i make a module that:
* starts on-demand and stays running for the session lifetime once it's
started. It should only stop if the session stops or if i tell it to stop.
I'm guessing this is with "X-KDE-Kded-phase" at 2, but then i still don't
get where that module is registered, how kded knows about it and - most
importantly! - what needs to be done to get KDED or KIOD to start it? Is
that some sort of spacial dbus signal?...
* We have KDED and KIOD, i think i would like to use KIOD for the reduced
dependency, but is that possible with the requirements of the point above
this one?
* For persistent storage (or session persistent like for instance the stash
plugin), what is the best way to get data from the module into the KIO
slave? DBus? Protobuf? shared memory?

[1] At this moment it's for a KIO slave dedicated to tag support backed by
either a JSON or YAML file and does not require file monitoring at all to
work. I know about Baloo and it's tag support, this is not for that. It's
merely a "hey, this would be cool, could it work?" experiment.

Cheers,
Mark
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