62 lines
2.2 KiB
Python
62 lines
2.2 KiB
Python
# vim: tabstop=4 shiftwidth=4 softtabstop=4
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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from oslo.config import cfg
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from keystone.contrib.kds.common import exception
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CONF = cfg.CONF
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# NOTE(jamielennox): This class is a direct copy from nova, glance, heat and
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# a bunch of other projects. It has been submitted to OSLO
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# https://review.openstack.org/#/c/67002/ and should be synced when available.
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class LazyPluggable(object):
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"""A pluggable backend loaded lazily based on some value."""
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def __init__(self, pivot, config_group=None, **backends):
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self.__backends = backends
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self.__pivot = pivot
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self.__backend = None
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self.__config_group = config_group
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def __get_backend(self):
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if not self.__backend:
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if self.__config_group is None:
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backend_name = CONF[self.__pivot]
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else:
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backend_name = CONF[self.__config_group][self.__pivot]
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if backend_name not in self.__backends:
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allowed = ', '.join(self.__backends.iterkeys())
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raise exception.BackendException(backend=backend_name,
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allowed=allowed)
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backend = self.__backends[backend_name]
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if isinstance(backend, tuple):
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name = backend[0]
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fromlist = backend[1]
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else:
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name = backend
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fromlist = backend
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self.__backend = __import__(name=name, globals=None,
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locals=None, fromlist=fromlist)
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return self.__backend
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def __getattr__(self, key):
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backend = self.__get_backend()
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return getattr(backend, key)
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