Question

I’m building an Python application that has to connect and disconnect from Wifi on linux box. I’m using NetworkManager layer, through the nice networkmanager lib found in cnetworkmanager (a python CLI for NetworkManager http://vidner.net/martin/software/cnetworkmanager/ thanx to Martin Vidner), in a daemon (named stationd).
This daemon runs a gobject.MainLoop. Once a timeout_add_seconds awake (triggers by a action of user in GUI), I have to disconnect current running Wifi and connect to a new one:

from dbus.mainloop.glib import DBusGMainLoop
DBusGMainLoop(set_as_default=True)

from networkmanager import NetworkManager
import networkmanager.applet.settings as settings
from networkmanager.applet import USER_SERVICE 
from networkmanager.applet.service import NetworkManagerUserSettings, NetworkManagerSettings
import time
import memcache

import gobject
loop = gobject.MainLoop()

nm = NetworkManager()

dummy_handler = lambda *args: None

cache = memcache.Client(['127.0.0.1:11211',] )


def get_device(dev_spec, hint):
    candidates = []
    devs = NetworkManager().GetDevices()
    for dev in devs:
        if dev._settings_type() == hint:
            candidates.append(dev)
    if len(candidates) == 1:
        return candidates[0]
    for dev in devs:
        if dev["Interface"] == dev_spec:
            return dev
    print "Device '%s' not found" % dev_spec
    return None

def kill_allconnections():
    connections=nm['ActiveConnections']
    for c in connections:
        print c.object_path
        nm.DeactivateConnection(c.object_path)

class Wifi(object):

    def connect(self, ssid, security="open", password=None):
        "Connects to given Wifi network"
        c=None # connection settings
        us = NetworkManagerUserSettings([])
        if security=="open":
            c = settings.WiFi(ssid)
        elif security=="wep":
            c = settings.Wep(ssid, password)
        elif security=="wpa":
            c = settings.WpaPsk(ssid, password)
        else:
            raise AttributeError("invalid security model '%s'"%security)
        svc = USER_SERVICE
        svc_conn = us.addCon(c.conmap)
        hint = svc_conn.settings["connection"]["type"]
        dev = get_device("", hint)
        appath = "/"
        nm.ActivateConnection(svc, svc_conn, dev, appath, reply_handler=dummy_handler, error_handler=dummy_handler)


def change_network_settings():
    key="station:network:change"
    change=cache.get(key)
    if change is not None:
        print "DISCONNECT"
        kill_allconnections()
        print "CHANGE SETTINGS"
        wifi=cache.get(key+':wifi')
        if wifi is not None:
            ssid=cache.get(key+':wifi:ssid')
            security=cache.get(key+':wifi:security')
            password=cache.get(key+':wifi:password')
            print "SWITCHING TO %s"%ssid
            Wifi().connect(ssid, security, password)
        cache.delete(key)
    return True    

def mainloop():
   gobject.timeout_add_seconds(1, change_network_settings)
   try:
      loop.run()
   except KeyboardInterrupt:
      loop.quit()

if __name__=="__main__":
    mainloop()

This runs perfectly for a first connection (read : the box is not connected, daemon is ran and box connects flawlessly to Wifi). Issue is when I try to connect to another Wifi : kill_allconnections() is ran silently, and connect method raises an exception on nm.ActivateConnection:

Traceback (most recent call last):
  File "stationd.py", line 40, in change_network_settings
    Wifi().connect(ssid, security, password)
  File "/home/biopredictive/station/lib/network.py", line 88, in connect
    us = NetworkManagerUserSettings([])
  File "/home/biopredictive/station/lib/networkmanager/applet/service/__init__.py", line 71, in __init__
    super(NetworkManagerUserSettings, self).__init__(conmaps, USER_SERVICE)
  File "/home/biopredictive/station/lib/networkmanager/applet/service/__init__.py", line 33, in __init__
    dbus.service.Object.__init__(self, bus, opath, bus_name)
  File "/usr/lib/pymodules/python2.6/dbus/service.py", line 480, in __init__
    self.add_to_connection(conn, object_path)
  File "/usr/lib/pymodules/python2.6/dbus/service.py", line 571, in add_to_connection
    self._fallback)
KeyError: "Can't register the object-path handler for '/org/freedesktop/NetworkManagerSettings': there is already a handler"

It looks like my former connection didn’t release all its resources ?
I’m very new to gobject/dbus programming. Would you please help ?

Answer 1

I have answered on the D-Bus mailing list. Quoting here for the archive:

class Wifi(...):
    def connect(...):
        ...
        us = NetworkManagerUserSettings([]) 

NetworkManagerUserSettings is a server, not a client. (It’s a design
quirk of NM which was eliminated in NM 0.9)
You should create only one for the daemon, not for each conection
attempt.