Driver registry

Uses automatic dependency injection to provide controllers with driver
interfaces (identity_api, token_api, etc).

See tests/test_injection.py for a self-contained example.

Change-Id: I255087de534292fbf57a45b19f97488f831f607c

2 files changed, 70 insertions, 7 deletions

diff --git a/keystone/common/controller.py b/keystone/common/controller.py
index 5f351411..ee7ce5b5 100644
--- a/keystone/common/controller.py
+++ b/keystone/common/controller.py
@@ -1,6 +1,7 @@
 import uuid
 import functools
 
+from keystone.common import dependency
 from keystone.common import logging
 from keystone.common import wsgi
 from keystone import exception
@@ -55,15 +56,10 @@ def protected(f):
     return wrapper
 
 
+@dependency.requires('identity_api', 'policy_api', 'token_api')
 class V2Controller(wsgi.Application):
     """Base controller class for Identity API v2."""
-
-    def __init__(self, catalog_api, identity_api, policy_api, token_api):
-        self.catalog_api = catalog_api
-        self.identity_api = identity_api
-        self.policy_api = policy_api
-        self.token_api = token_api
-        super(V2Controller, self).__init__()
+    pass
 
 
 class V3Controller(V2Controller):
diff --git a/keystone/common/dependency.py b/keystone/common/dependency.py
new file mode 100644
index 00000000..dc3e4ac4
--- /dev/null
+++ b/keystone/common/dependency.py
@@ -0,0 +1,67 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright 2012 OpenStack LLC
+#
+# 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.
+
+REGISTRY = {}
+
+
+class UnresolvableDependencyException(Exception):
+    def __init__(self, name):
+        msg = 'Unregistered dependency: %s' % name
+        super(UnresolvableDependencyException, self).__init__(msg)
+
+
+def provider(name):
+    """Register the wrapped dependency provider under the specified name."""
+    def wrapper(cls):
+        def wrapped(init):
+            def __wrapped_init__(self, *args, **kwargs):
+                """Initialize the wrapped object and add it to the registry."""
+                init(self, *args, **kwargs)
+                REGISTRY[name] = self
+
+            return __wrapped_init__
+
+        cls.__init__ = wrapped(cls.__init__)
+        return cls
+
+    return wrapper
+
+
+def requires(*dependencies):
+    """Inject specified dependencies from the registry into the instance."""
+    def wrapper(self, *args, **kwargs):
+        """Inject each dependency from the registry."""
+        self.__wrapped_init__(*args, **kwargs)
+
+        for dependency in self._dependencies:
+            if dependency not in REGISTRY:
+                raise UnresolvableDependencyException(dependency)
+            setattr(self, dependency, REGISTRY[dependency])
+
+    def wrapped(cls):
+        """Note the required dependencies on the object for later injection.
+
+        The dependencies of the parent class are combined with that of the
+        child class to create a new set of dependencies.
+        """
+        existing_dependencies = getattr(cls, '_dependencies', set())
+        cls._dependencies = existing_dependencies.union(dependencies)
+        if not hasattr(cls, '__wrapped_init__'):
+            cls.__wrapped_init__ = cls.__init__
+            cls.__init__ = wrapper
+        return cls
+
+    return wrapped