Add is_extension_supported to neutron_lib

This enables a plugin to determine if a specific extension is
enabled.

Change-Id: I721cb63e9163304422684d683e62e24de01796be

neutron_lib/api/extensions.py

@@ -17,6 +17,16 @@ import abc
 import six
 
 
+def is_extension_supported(plugin, alias):
+    """Validate that the extension is supported.
+
+    :param plugin: The plugin class.
+    :param alias: The alias to check.
+    :returns: True if the alias is supported else False.
+    """
+    return alias in getattr(plugin, "supported_extension_aliases", [])
+
+
 @six.add_metaclass(abc.ABCMeta)
 class ExtensionDescriptor(object):
     """Base class that defines the contract for extensions."""

neutron_lib/tests/unit/api/test_extensions.py

@@ -14,6 +14,7 @@
 #    under the License.
 
 from neutron_lib.api import extensions
+from neutron_lib.services import base as service_base
 from neutron_lib.tests import _base as base
 
 
@@ -81,3 +82,29 @@ class TestExtensionDescriptor(base.BaseTestCase):
         extension_description.update_attributes_map(self.extended_attributes)
         self.assertEqual(self.extension_attrs_map,
                          {'resource_one': {'three': 'third'}})
+
+
+class DummyPlugin(service_base.ServicePluginBase):
+
+    supported_extension_aliases = ['flash']
+
+    def get_plugin_type(self):
+        return 'Flash Gordon'
+
+    def get_plugin_description(self):
+        return 'Legend!'
+
+
+class TestExtensionIsSupported(base.BaseTestCase):
+
+    def setUp(self):
+        super(TestExtensionIsSupported, self).setUp()
+        self._plugin = DummyPlugin()
+
+    def test_extension_exists(self):
+        self.assertTrue(extensions.is_extension_supported(self._plugin,
+                                                          "flash"))
+
+    def test_extension_does_not_exist(self):
+        self.assertFalse(extensions.is_extension_supported(self._plugin,
+                                                           "gordon"))

releasenotes/notes/add-extension-supported-be6f7069856d2891.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Rehome the validation for checking if an extension is supported by the
+    plugin. The method ``is_extension_supported`` will now be part of
+    ``neutron_lib.api.extensions``.