[avahi] Subtypes

[Zachary Loafman]

(If this message somehow reaches twice, I apologize. It looks like my
first message was smallowed somewhere along the way, probably because
the "From" was different.)

I'm a little confused about DNS-SD subtypes.

I'm working on an application that's not unlike one previously
discussed at http://lists.freedesktop.org/archives/avahi/2006-May/000730.html:

> The main service should bear a name like:
>
>   bittorrent at foobar
>
> and a type of
>
>   _bittorrent._tcp
>
> The subservice for the bt hash
> 32f17bbf96bdc77de85bb91ff8d56f124e817c0a should be:
>
>   _32f17bbf96bdc77de85bb91ff8d56f124e817c0a._sub._bittorrent._tcp
>
> You may include the peer-id in the TXT records if you think that makes
> sense.

I want to use a similar gooblety-gook subtype so that our resolver can
find an exact instance of the application amongst a set of machines.
However, I have a few questions:

1) If the host X publishes a record for _bittorrent._tcp, will host Y
also see the subtype along with it, or is this only possible through a
query from host Y for the specific subtype?

2) Does avahi-daemon cache the subtypes along with the type? If the
answer to #1 is "no," does this caching occur only on query? (i.e. if
Y keeps looking for _foo._sub._bittorrent._tcp, does avahi-daemon
cache where to find the sub-type)?

3) Is there any way to browse subtypes? (I guess this also depends on
#1, though you could imagine being able to browse the
previously-cached values).

...Zach