Re: [Evolution-hackers] PIM server synchronization and Evolution online/offline state

Am Dienstag 03 April 2012, um 18:05:33 schrieb Matthew Barnes:
> On Tue, 2012-04-03 at 17:29 +0200, Christian Hilberg wrote:
> > Seems to me that opening a connection in order to find out whether I could
> > open a connection is more than evo-kolab would need. Unless the "service-available"
> > check would be really cheap, it seems to me that "host-reachable" would
> > suffice. Once I actually try to connect and fail, I know that I cannot
> > connect. Nothing lost. ;-) (What's more, if "service-available" was TRUE half
> > an hour ago, when the check was made, that does not automatically mean that
> > it is still TRUE when I want to actually *use* the connection half an hour
> > later - so, not sure whether a "service-available" check would help much).
> Perhaps then simply rename the "online" property to "host-reachable" to
> clarify it's meaning as a first step?  "Online" seems like too nebulous
> a term in this context anyway.

That may be worth it, especially since it is GNetworkMonitor setting this
flag and it is networking-related.

> Beyond that you can probably tell I'm flailing around for a coherent
> story.  What I had in mind for "service-available" was a way to notify
> the client app to just disable certain actions for that account to avoid
> repeated "Service Unavailable" error messages.

Sure, if my backend already knows that the service in question is
not reachable, then no need to try to connect - it could act as if
in "offline" state and just store the PIM object in the local offline
cache. That's all.

> But then two questions spring to mind:
> 1) If a backend can queue up changes offline to be synchronized with
>    a remote server later when it's available again, does that imply its
>    "service-available" flag should remain TRUE always?

Not necessarily - the only bit the backend needs to know is whether it is
*supposed* to queue up changes and not try to spool them up onto the server (this
exactly comprises an "offline" mode, though networking may still be available).

If "network-available" is FALSE, this implies "service-available" to be FALSE -
unless, of course, the service is local, but I do not think you will run a
groupware server on your local client machine with networking down...

If "network-available" changes from FALSE to TRUE, then I think "service-available"
needs to be re-checked and the flag set accordingly.

> 2) If a backend CANNOT queue up changes offline, how then should it
>    determine when the remote server becomes available again?  Poll?
>    Allow the user to say "try again"?
> I think I'm lacking insight here, so advice is appreciated.

How about the "service-available" to be set much like the to-be "network-available",
through GNetworkMonitor, as an EBackend property, which, when changed, emits a signal?

Just rough thinking, nothing elaborate as yet - I'll be meditating this. :)

Kind regards,


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