Stopping the Avahi service and return a list of elements

Question

Following this example I want to stop the service when I get all elements and return them in a list.

To stop the infinite loop is to call gobject.MainLoop().quit(), but do not know when or where to call. Thanks

Answer 1

You'll want to listen to the AllForNow signal as well. Consider CacheExhausted and Failure as well. The interface for org.freedesktop.Avahi.ServiceBrowser is declared here.

Running the following on my machine returns in about a second and prints:

browsing ...
cache exhausted
New service: name = Lexmark X264dn; address = 10.9.0.93; port = 80
that's all for now
done
0:00:01.004258

Hope it helps!

---

from _dbus_glib_bindings import DBusGMainLoop
import dbus, avahi
import gobject

class ServiceBrowser():
    def __init__(self, service):
        loop = DBusGMainLoop(set_as_default=True)

        bus = dbus.SystemBus(mainloop=loop)

        self._server = dbus.Interface(bus.get_object(avahi.DBUS_NAME, avahi.DBUS_PATH_SERVER), avahi.DBUS_INTERFACE_SERVER)

        browser = self._server.ServiceBrowserNew(avahi.IF_UNSPEC, avahi.PROTO_INET, service, '', 0)
        listener = dbus.Interface(bus.get_object(avahi.DBUS_NAME, browser), avahi.DBUS_INTERFACE_SERVICE_BROWSER)

        listener.connect_to_signal("ItemNew", self.item_new_handler)
        listener.connect_to_signal("ItemRemove", self.item_remove_handler)
        listener.connect_to_signal("AllForNow", self.all_for_now_handler)
        listener.connect_to_signal("CacheExhausted", self.cache_exhausted_handler)
        listener.connect_to_signal("Failure", self.failure_handler)

        self._mainloop = gobject.MainLoop()


    def service_resolved(self, *args):
        print 'New service: name = %s; address = %s; port = %s' % (args[2], args[7], args[8])


    def print_error(self, *args):
        print 'error_handler'
        print args[0]

    def item_new_handler(self, interface, protocol, name, stype, domain, flags):
        self._server.ResolveService(interface, protocol, name, stype, domain, avahi.PROTO_UNSPEC, dbus.UInt32(0), reply_handler=self.service_resolved, error_handler=self.print_error)


    def item_remove_handler(self, interface, protocol, name, stype, domain, flags):
        print "Removed service: %s" % name


    def all_for_now_handler(self):
        print "that's all for now"
        self._mainloop.quit()


    def cache_exhausted_handler(self):
        print "cache exhausted"


    def failure_handler(self, error):
        print "failure: %s" % error


    def browse(self):
        self._mainloop.run()


def browse_avahi(service):
    browser = ServiceBrowser(service)
    browser.browse()

def main():
    t0 = datetime.utcnow()
    print "browsing ..."
    browse_avahi('_http._tcp')
    print "done"
    print datetime.utcnow()-t0

if __name__ == '__main__':
    main()

Answer 2

You'll want to stop the service browsing when the last service for now has arrived. This will give you a snapshot of the current available services.

There is a flag in the C layer allowing you to inspect whether more services are comming shortly. It's called AVAHI_BROWSER_ALL_FOR_NOW. I'm not familiar with the python bindings, but perhaps this flag can be inspected somehow in the stype or flags arguments of the callback?

When you see this flag is set - call gobject.MainLoop().quit()