text: #
  # Copyright 2013 Red Hat, Inc.
  #
  #    Licensed under the Apache License, Version 2.0 (the "License"); you may
  #    not use this file except in compliance with the License. You may obtain
  #    a copy of the License at
  #
  #         http://www.apache.org/licenses/LICENSE-2.0
  #
  #    Unless required by applicable law or agreed to in writing, software
  #    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  #    License for the specific language governing permissions and limitations
  #    under the License.
  #
  
  """
  Base RPC client and server common to all services.
  """
  
  from oslo.config import cfg
  
  from nova.openstack.common import jsonutils
  from nova.openstack.common import rpc
  import nova.openstack.common.rpc.proxy as rpc_proxy
  
  
  CONF = cfg.CONF
  rpcapi_cap_opt = cfg.StrOpt('baseapi',
          help='Set a version cap for messages sent to the base api in any '
               'service')
  CONF.register_opt(rpcapi_cap_opt, 'upgrade_levels')
  
  _NAMESPACE = 'baseapi'
  
  
  class BaseAPI(rpc_proxy.RpcProxy):
      """Client side of the base rpc API.
  
      API version history:
  
          1.0 - Initial version.
          1.1 - Add get_backdoor_port
      """
  
      #
      # NOTE(russellb): This is the default minimum version that the server
      # (manager) side must implement unless otherwise specified using a version
      # argument to self.call()/cast()/etc. here.  It should be left as X.0 where
      # X is the current major API version (1.0, 2.0, ...).  For more information
      # about rpc API versioning, see the docs in
      # openstack/common/rpc/dispatcher.py.
      #
      BASE_RPC_API_VERSION = '1.0'
  
      VERSION_ALIASES = {
          # baseapi was added in havana
      }
  
      def __init__(self, topic):
          version_cap = self.VERSION_ALIASES.get(CONF.upgrade_levels.baseapi,
                                                 CONF.upgrade_levels.baseapi)
          super(BaseAPI, self).__init__(topic=topic,
                  default_version=self.BASE_RPC_API_VERSION,
                  version_cap=version_cap)
          self.namespace = _NAMESPACE
  
      def ping(self, context, arg, timeout=None):
          arg_p = jsonutils.to_primitive(arg)
          msg = self.make_namespaced_msg('ping', self.namespace, arg=arg_p)
          return self.call(context, msg, timeout=timeout)
  
      def get_backdoor_port(self, context, host):
          msg = self.make_namespaced_msg('get_backdoor_port', self.namespace)
          return self.call(context, msg,
                           topic=rpc.queue_get_for(context, self.topic, host),
                           version='1.1')
  
  
  class BaseRPCAPI(object):
      """Server side of the base RPC API."""
  
      RPC_API_NAMESPACE = _NAMESPACE
      RPC_API_VERSION = '1.1'
  
      def __init__(self, service_name, backdoor_port):
          self.service_name = service_name
          self.backdoor_port = backdoor_port
  
      def ping(self, context, arg):
          resp = {'service': self.service_name, 'arg': arg}
          return jsonutils.to_primitive(resp)
  
      def get_backdoor_port(self, context):
          return self.backdoor_port
  