Pairing and replication does not work if Avahi is down

[Roman Yepishev]

Replication does not work when Avahi is not running:

~/.cache/desktop-couch/log/desktop-couch-replication.log:
2010-01-12 16:04:26,178 DEBUG found 1 self_identity records
2010-01-12 16:04:26,265 ERROR We seem to be running already, or can't publish our zeroconf advert. org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.Avahi was not provided by any .service files

I was asked to try desktopcouch-pair tool by aquarius:

rtg@buzz:~/.cache/desktop-couch/log$ desktopcouch-pair
2010-01-12 21:52:16,619 [11437] root:DEBUG: starting couchdb pairing tool
2010-01-12 21:52:22,477 [11437] root:DEBUG: found 1 self_identity records
2010-01-12 21:52:22,478 [11437] root:DEBUG: paired back-connecting machine count is 0
2010-01-12 21:52:22,478 [11437] root:DEBUG: exiting couchdb pairing tool
Traceback (most recent call last):
  File "/usr/bin/desktopcouch-pair", line 908, in <module>
    main(sys.argv)
  File "/usr/bin/desktopcouch-pair", line 897, in main
    pick_or_listen = PickOrListen()
  File "/usr/bin/desktopcouch-pair", line 763, in __init__
    self.pick_pane = self.create_pick_pane(top_vbox)
  File "/usr/bin/desktopcouch-pair", line 558, in create_pick_pane
    remove_service_from_list, show_local=False)
  File "/usr/lib/python2.6/dist-packages/desktopcouch/pair/couchdb_pairing/dbus_io.py", line 239, in discover_services
    bus, server = get_dbus_bus_server()
  File "/usr/lib/python2.6/dist-packages/desktopcouch/pair/couchdb_pairing/dbus_io.py", line 54, in get_dbus_bus_server
    root_name = bus.get_object(avahi.DBUS_NAME, avahi.DBUS_PATH_SERVER)
  File "/usr/lib/pymodules/python2.6/dbus/bus.py", line 244, in get_object
    follow_name_owner_changes=follow_name_owner_changes)
  File "/usr/lib/pymodules/python2.6/dbus/proxies.py", line 241, in __init__
    self._named_service = conn.activate_name_owner(bus_name)
  File "/usr/lib/pymodules/python2.6/dbus/bus.py", line 183, in activate_name_owner
    self.start_service_by_name(bus_name)
  File "/usr/lib/pymodules/python2.6/dbus/bus.py", line 281, in start_service_by_name
    'su', (bus_name, flags)))
  File "/usr/lib/pymodules/python2.6/dbus/connection.py", line 620, in call_blocking
    message, timeout)
dbus.exceptions.DBusException: org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.Avahi was not provided by any .service files

So,
<aquarius> hahaha. So desktopcouch-pair *and* desktopcouch itself both assume that avahi works. Oops.

[Joshua Blount (jblount)]

Adjusting to "low" priority since we probably just need an error message that says as much.

[Roman Yepishev (rye)]

Avahi may be down for various reasons:
 * ISP which likes to break mDNS
 * not being able to block .local resolution on their routers if ISP assigns this zone.
 * no need for Avahi in LAN at all.

Since desktopcouch replication to ubuntuone has a static mapping and does not really need Avahi and it should work even without it, i think this bug needs to have at least 'Medium' importance.

The meaningful message about inability of advertise the presence on mDNS is also welcomed.