[sugar] Issues with the presence service

[Marco Pesenti Gritti]

> So how about this for a flow?
>
> - PS sees new "_tamtam._tcp" service advertised, sends ServiceAppeared
> signal
>
> - Home Page receives ServiceAppeared signal, looks through it's registry
> for Activities that can handle "_tamtam._tcp"
>
> - Home Page finds the TamTam activity can handle it, and asks some
> TamTam code to thumbnail and display the activity on the Home Page
>
> My point is that on the activities _themselves_ can know what service
> types the can handle, and how to handle those types.  We don't need a
> "default type" passed through the PS, because the local activity knows
> how to handle it.  For example, the browser uses "_web_olpc._udp" and
> "_olpc_model._tcp".  The Browser activity already knows that the
> _web_olpc._udp service is the "default" service for a browser activity,
> and it can tell the Home Page that without the PS getting involved.
>   

Ah! I had forgot the default type is just the name of the default 
service... I need a new brain.

>   
>>>> - There seem to be no way to join an activity other than manually 
>>>> duplicate the service. Also should we provide this rather than have 
>>>> every activity to reimplement it? In sugar.activity.Activity or maybe 
>>>> even directly in the shell...
>>>>     
>>>>         
>>> Well, we _have_ to create a new service when we join the activity, since
>>> we need to change the source address for the service anyway.  Even if we
>>> receive a service from the network from somebody else, that service is
>>> "somebody else's" service, and _not_ ours.  We have to create a new
>>> service, cloned from the original service, and publish that instead,
>>> because that uses our local information
>>>       
>> Right, my point was more than we need convenient way to do it (and one 
>> that doesn't need a comment to clarify what is going on)...
>>
>>                 # Ok, there's an existing chat service that we copy
>>                 # parameters and such from
>>                 addr = service.get_address()
>>                 port = service.get_port()
>>                 self._chat_service = 
>> self._pservice.share_activity(self._activity,
>>                                 stype=ActivityChat.SERVICE_TYPE, 
>> address=addr, port=port)
>>     
>
> Hmm, maybe we should make the Activity base class handle the sharing?
> Because Activity objects already know their default service type, 

I think we should do that.
Btw there is join_activity/joinActivity in shell/PresenceService which 
seem to be unused?

> and we
> shouldn't be using "share_activity" to publish anything _except_ the
> default service type.
>
>   

I think that's not the case at the moment... so we should fix it.

There are probably other cases where you will want to "clone and 
republish" a service. That might not be frequent enough to deserve a 
specific API though, not sure.

> I wanted to get away from having create_service()/create_activity()
> calls that just create the service/activity and then wait for you to do
> something with it.  That's pretty useless and encourages bad habits.
> When you create a service, it should be published automatically because
> there's no legitimate reason I can think of that it shouldn't be
> published automatically.
>   

Yeah, that make sense.

Seems like we covered pretty much everything. We just need to go through 
this thread and fix up stuff...

Thanks,
Marco