Add rpc to openstack-common.

Implements blueprint common-rpc.

This patch imports nova.rpc to openstack-common.  All of the necessary
changes to the core code to make it compatible with openstack-common
have been done in nova, so the only changes made here are to imports.

There are more changes made to the tests, but nothing that changes the
core functionality of the tests.

Change-Id: I17330aa4adfd0f22c449a2376833c7fe9dfd0cf1

1 files changed, 105 insertions, 0 deletions

diff --git a/openstack/common/rpc/dispatcher.py b/openstack/common/rpc/dispatcher.py
new file mode 100644
index 0000000..7319eb2
--- /dev/null
+++ b/openstack/common/rpc/dispatcher.py
@@ -0,0 +1,105 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright 2012 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.
+
+"""
+Code for rpc message dispatching.
+
+Messages that come in have a version number associated with them.  RPC API
+version numbers are in the form:
+
+    Major.Minor
+
+For a given message with version X.Y, the receiver must be marked as able to
+handle messages of version A.B, where:
+
+    A = X
+
+    B >= Y
+
+The Major version number would be incremented for an almost completely new API.
+The Minor version number would be incremented for backwards compatible changes
+to an existing API.  A backwards compatible change could be something like
+adding a new method, adding an argument to an existing method (but not
+requiring it), or changing the type for an existing argument (but still
+handling the old type as well).
+
+The conversion over to a versioned API must be done on both the client side and
+server side of the API at the same time.  However, as the code stands today,
+there can be both versioned and unversioned APIs implemented in the same code
+base.
+"""
+
+from openstack.common.rpc import common as rpc_common
+
+
+class RpcDispatcher(object):
+    """Dispatch rpc messages according to the requested API version.
+
+    This class can be used as the top level 'manager' for a service.  It
+    contains a list of underlying managers that have an API_VERSION attribute.
+    """
+
+    def __init__(self, callbacks):
+        """Initialize the rpc dispatcher.
+
+        :param callbacks: List of proxy objects that are an instance
+                          of a class with rpc methods exposed.  Each proxy
+                          object should have an RPC_API_VERSION attribute.
+        """
+        self.callbacks = callbacks
+        super(RpcDispatcher, self).__init__()
+
+    @staticmethod
+    def _is_compatible(mversion, version):
+        """Determine whether versions are compatible.
+
+        :param mversion: The API version implemented by a callback.
+        :param version: The API version requested by an incoming message.
+        """
+        version_parts = version.split('.')
+        mversion_parts = mversion.split('.')
+        if int(version_parts[0]) != int(mversion_parts[0]):  # Major
+            return False
+        if int(version_parts[1]) > int(mversion_parts[1]):  # Minor
+            return False
+        return True
+
+    def dispatch(self, ctxt, version, method, **kwargs):
+        """Dispatch a message based on a requested version.
+
+        :param ctxt: The request context
+        :param version: The requested API version from the incoming message
+        :param method: The method requested to be called by the incoming
+                       message.
+        :param kwargs: A dict of keyword arguments to be passed to the method.
+
+        :returns: Whatever is returned by the underlying method that gets
+                  called.
+        """
+        if not version:
+            version = '1.0'
+
+        for proxyobj in self.callbacks:
+            if hasattr(proxyobj, 'RPC_API_VERSION'):
+                rpc_api_version = proxyobj.RPC_API_VERSION
+            else:
+                rpc_api_version = '1.0'
+            if not hasattr(proxyobj, method):
+                continue
+            if self._is_compatible(rpc_api_version, version):
+                return getattr(proxyobj, method)(ctxt, **kwargs)
+
+        raise rpc_common.UnsupportedRpcVersion(version=version)