#!/bin/env python

# Copyright 2015 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

import dbus

SHILL_SERVICE_NAME = 'org.chromium.flimflam'

INTERFACE_MANAGER = 'org.chromium.flimflam.Manager'
INTERFACE_SERVICE = 'org.chromium.flimflam.Service'

STATIC_IP_CONFIG_KEY = 'StaticIPConfig'
SAVED_IP_CONFIG_KEY = 'SavedIPConfig'
NAME_SERVERS_KEY = 'NameServers'

LOCAL_NAME_SERVER = '127.0.0.1'

def main():
  bus = dbus.SystemBus()
  manager = bus.get_object(SHILL_SERVICE_NAME, '/')
  i_manager = dbus.Interface(manager, INTERFACE_MANAGER)
  ethernet_path = i_manager.FindMatchingService({'Type': 'ethernet'})
  ethernet_service = bus.get_object(SHILL_SERVICE_NAME, ethernet_path)
  i_ethernet_service = dbus.Interface(ethernet_service, INTERFACE_SERVICE)
  properties = i_ethernet_service.GetProperties()

  # We must merge the nameservers received over DHCP with the extra nameserver
  # we want to install.
  static_ip_config = properties.get(STATIC_IP_CONFIG_KEY, {})
  static_name_servers = static_ip_config.get(NAME_SERVERS_KEY, [])
  saved_ip_config = properties.get(SAVED_IP_CONFIG_KEY, {})
  saved_name_servers = saved_ip_config.get(NAME_SERVERS_KEY, [])
  # By keeping LOCAL_NAME_SERVER first, dnsmasq can forward requests to any
  # number of entries below. OTOH, if we keep the local nameserver last, there's
  # a chance that we'll hit the maximum number of entries allowed in
  # resolv.conf, and never make it to the local nameserver.
  merged_name_servers = [dbus.String(LOCAL_NAME_SERVER)] + saved_name_servers


  # NB: Careful now -- this script is usually launched by an upstart job every
  # time shill connects. This means that by toggling shill's connection state,
  # we're eventually relaunching this script. Therefore, we must ensure that we
  # don't keep toggling shill when no new changes are made to the nameservers.
  if set(merged_name_servers) == set(static_name_servers):
    print('List of static nameservers is up-to-date. Exiting early.')
    return

  static_ip_config[NAME_SERVERS_KEY] = merged_name_servers
  i_ethernet_service.SetProperty(STATIC_IP_CONFIG_KEY, static_ip_config)
  # If we updated the nameservers, we need to toggle the service connection to
  # pick up the new nameservers.
  try:
    i_ethernet_service.Disconnect()
  finally:
    i_ethernet_service.Connect()


if __name__ == '__main__':
  main()