[avahi] Subtypes

[Lennart Poettering]

On Tue, 21.08.07 14:25, Zachary Loafman (zml+avahi at zml.net) wrote:

Hi!

> > 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?

The latter. Subtypes may only be used as query "keys". They are never
part of a query "result".

> 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)?

Avahi caches every RR it receives. However, it refreshes only RRs
which a local client looks for.

> 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).

No, this is not possible. There is no API for this. As mentioned, the
intended usage for subtypes is additional query keys for a subset of
services. 

Lennart

-- 
Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net         ICQ# 11060553
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