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# Copyright 2012 OpenStack Foundation
#
# 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.
import functools
from oslo_log import log
from oslo_log import versionutils
from oslo_utils import importutils
import stevedore
LOG = log.getLogger(__name__)
def response_truncated(f):
"""Truncate the list returned by the wrapped function.
This is designed to wrap Manager list_{entity} methods to ensure that
any list limits that are defined are passed to the driver layer. If a
hints list is provided, the wrapper will insert the relevant limit into
the hints so that the underlying driver call can try and honor it. If the
driver does truncate the response, it will update the 'truncated' attribute
in the 'limit' entry in the hints list, which enables the caller of this
function to know if truncation has taken place. If, however, the driver
layer is unable to perform truncation, the 'limit' entry is simply left in
the hints list for the caller to handle.
A _get_list_limit() method is required to be present in the object class
hierarchy, which returns the limit for this backend to which we will
truncate.
If a hints list is not provided in the arguments of the wrapped call then
any limits set in the config file are ignored. This allows internal use
of such wrapped methods where the entire data set is needed as input for
the calculations of some other API (e.g. get role assignments for a given
project).
"""
@functools.wraps(f)
def wrapper(self, *args, **kwargs):
if kwargs.get('hints') is None:
return f(self, *args, **kwargs)
list_limit = self.driver._get_list_limit()
if list_limit:
kwargs['hints'].set_limit(list_limit)
return f(self, *args, **kwargs)
return wrapper
def load_driver(namespace, driver_name, *args):
try:
driver_manager = stevedore.DriverManager(namespace,
driver_name,
invoke_on_load=True,
invoke_args=args)
return driver_manager.driver
except RuntimeError as e:
LOG.debug('Failed to load %r using stevedore: %s', driver_name, e)
# Ignore failure and continue on.
@versionutils.deprecated(as_of=versionutils.deprecated.LIBERTY,
in_favor_of='entrypoints',
what='direct import of driver')
def _load_using_import(driver_name, *args):
return importutils.import_object(driver_name, *args)
# For backwards-compatibility, an unregistered class reference can
# still be used.
return _load_using_import(driver_name, *args)
class Manager(object):
"""Base class for intermediary request layer.
The Manager layer exists to support additional logic that applies to all
or some of the methods exposed by a service that are not specific to the
HTTP interface.
It also provides a stable entry point to dynamic backends.
An example of a probable use case is logging all the calls.
"""
driver_namespace = None
def __init__(self, driver_name):
self.driver = load_driver(self.driver_namespace, driver_name)
def __getattr__(self, name):
"""Forward calls to the underlying driver."""
f = getattr(self.driver, name)
setattr(self, name, f)
return f
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