Adds ability to inherit wsgi extensions

Needed for blueprint disable-server-extensions

It is possible to create a wsgi resource that extends another
resource by using the same controller, but any extensions that
have been applied to the original resource will have no affect.

This adds a new parameter to ResourceExtension that allows it
to inherit extensions from another resource. This is necessary
because we are moving key funcionality of the /servers resource
into extensions, and some other resources (like create-server-ext)
extend that functionality. This way we can keep the functionality
of the other extensions.

Change-Id: I21b4c2569c35d59c1f466642355564084a277aea

3 files changed, 30 insertions, 4 deletions

diff --git a/nova/api/openstack/__init__.py b/nova/api/openstack/__init__.py
index e84353df9..6baa6be91 100644
--- a/nova/api/openstack/__init__.py
+++ b/nova/api/openstack/__init__.py
@@ -132,7 +132,13 @@ class APIRouter(base_wsgi.Router):
             LOG.debug(_('Extended resource: %s'),
                       resource.collection)
 
-            wsgi_resource = wsgi.Resource(resource.controller)
+            inherits = None
+            if resource.inherits:
+                inherits = self.resources.get(resource.inherits)
+                if not resource.controller:
+                    resource.controller = inherits.controller
+            wsgi_resource = wsgi.Resource(resource.controller,
+                                          inherits=inherits)
             self.resources[resource.collection] = wsgi_resource
             kargs = dict(
                 controller=wsgi_resource,
diff --git a/nova/api/openstack/extensions.py b/nova/api/openstack/extensions.py
index da2157ad8..d8a3edb4b 100644
--- a/nova/api/openstack/extensions.py
+++ b/nova/api/openstack/extensions.py
@@ -289,9 +289,9 @@ class ControllerExtension(object):
 class ResourceExtension(object):
     """Add top level resources to the OpenStack API in nova."""
 
-    def __init__(self, collection, controller, parent=None,
+    def __init__(self, collection, controller=None, parent=None,
                  collection_actions=None, member_actions=None,
-                 custom_routes_fn=None):
+                 custom_routes_fn=None, inherits=None):
         if not collection_actions:
             collection_actions = {}
         if not member_actions:
@@ -302,6 +302,7 @@ class ResourceExtension(object):
         self.collection_actions = collection_actions
         self.member_actions = member_actions
         self.custom_routes_fn = custom_routes_fn
+        self.inherits = inherits
 
 
 def wrap_errors(fn):
diff --git a/nova/api/openstack/wsgi.py b/nova/api/openstack/wsgi.py
index 229783d54..3ea7c1c7c 100644
--- a/nova/api/openstack/wsgi.py
+++ b/nova/api/openstack/wsgi.py
@@ -660,11 +660,16 @@ class Resource(wsgi.Application):
 
     """
 
-    def __init__(self, controller, action_peek=None, **deserializers):
+    def __init__(self, controller, action_peek=None, inherits=None,
+                 **deserializers):
         """
         :param controller: object that implement methods created by routes lib
         :param action_peek: dictionary of routines for peeking into an action
                             request body to determine the desired action
+        :param inherits: another resource object that this resource should
+                         inherit extensions from. Any action extensions that
+                         are applied to the parent resource will also apply
+                         to this resource.
         """
 
         self.controller = controller
@@ -689,6 +694,7 @@ class Resource(wsgi.Application):
         # Save a mapping of extensions
         self.wsgi_extensions = {}
         self.wsgi_action_extensions = {}
+        self.inherits = inherits
 
     def register_actions(self, controller):
         """Registers controller actions with this resource."""
@@ -944,6 +950,19 @@ class Resource(wsgi.Application):
         return response
 
     def get_method(self, request, action, content_type, body):
+        meth, extensions = self._get_method(request,
+                                            action,
+                                            content_type,
+                                            body)
+        if self.inherits:
+            _meth, parent_ext = self.inherits.get_method(request,
+                                                         action,
+                                                         content_type,
+                                                         body)
+            extensions.extend(parent_ext)
+        return meth, extensions
+
+    def _get_method(self, request, action, content_type, body):
         """Look up the action-specific method and its extensions."""
 
         # Look up the method