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# vim: tabstop=4 shiftwidth=4 softtabstop=4
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# Copyright 2012 Red Hat, Inc.
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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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# http://www.apache.org/licenses/LICENSE-2.0
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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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Code for rpc message dispatching.
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Messages that come in have a version number associated with them. RPC API
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version numbers are in the form:
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For a given message with version X.Y, the receiver must be marked as able to
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handle messages of version A.B, where:
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The Major version number would be incremented for an almost completely new API.
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The Minor version number would be incremented for backwards compatible changes
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to an existing API. A backwards compatible change could be something like
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adding a new method, adding an argument to an existing method (but not
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requiring it), or changing the type for an existing argument (but still
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handling the old type as well).
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The conversion over to a versioned API must be done on both the client side and
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server side of the API at the same time. However, as the code stands today,
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there can be both versioned and unversioned APIs implemented in the same code
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from nova.rpc import common as rpc_common
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class RpcDispatcher(object):
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"""Dispatch rpc messages according to the requested API version.
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This class can be used as the top level 'manager' for a service. It
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contains a list of underlying managers that have an API_VERSION attribute.
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def __init__(self, callbacks):
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"""Initialize the rpc dispatcher.
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:param callbacks: List of proxy objects that are an instance
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of a class with rpc methods exposed. Each proxy
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object should have an RPC_API_VERSION attribute.
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self.callbacks = callbacks
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super(RpcDispatcher, self).__init__()
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def _is_compatible(mversion, version):
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"""Determine whether versions are compatible.
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:param mversion: The API version implemented by a callback.
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:param version: The API version requested by an incoming message.
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version_parts = version.split('.')
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mversion_parts = mversion.split('.')
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if int(version_parts[0]) != int(mversion_parts[0]): # Major
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if int(version_parts[1]) > int(mversion_parts[1]): # Minor
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def dispatch(self, ctxt, version, method, **kwargs):
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"""Dispatch a message based on a requested version.
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:param ctxt: The request context
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:param version: The requested API version from the incoming message
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:param method: The method requested to be called by the incoming
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:param kwargs: A dict of keyword arguments to be passed to the method.
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:returns: Whatever is returned by the underlying method that gets
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for proxyobj in self.callbacks:
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if hasattr(proxyobj, 'RPC_API_VERSION'):
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rpc_api_version = proxyobj.RPC_API_VERSION
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rpc_api_version = '1.0'
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if not hasattr(proxyobj, method):
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if self._is_compatible(rpc_api_version, version):
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return getattr(proxyobj, method)(ctxt, **kwargs)
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raise rpc_common.UnsupportedRpcVersion(version=version)
added
removed
nova/rpc/dispatcher.py
