From faca9953c0d412944a23dfbc62e5634a509c51e8 Mon Sep 17 00:00:00 2001
From: Zane Bitter <zbitter@redhat.com>
Date: Tue, 27 Nov 2012 15:41:57 +0100
Subject: [PATCH] Add a module for dynamically loading plugins

Change-Id: I662b5989941b467c78a392098db0cd19ff86201c
Signed-off-by: Zane Bitter <zbitter@redhat.com>
---
 heat/common/plugin_loader.py     | 64 +++++++++++++++++++++++++++++
 heat/tests/test_plugin_loader.py | 70 ++++++++++++++++++++++++++++++++
 2 files changed, 134 insertions(+)
 create mode 100644 heat/common/plugin_loader.py
 create mode 100644 heat/tests/test_plugin_loader.py

diff --git a/heat/common/plugin_loader.py b/heat/common/plugin_loader.py
new file mode 100644
index 0000000000..325d560492
--- /dev/null
+++ b/heat/common/plugin_loader.py
@@ -0,0 +1,64 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+#
+#    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.
+
+import pkgutil
+import sys
+import types
+
+from heat.openstack.common import log as logging
+
+logger = logging.getLogger(__name__)
+
+
+def _module_name(*components):
+    return '.'.join(components)
+
+
+def create_subpackage(path, parent_package_name, subpackage_name="plugins"):
+    package_name = _module_name(parent_package_name, subpackage_name)
+
+    package = types.ModuleType(package_name)
+    package.__path__ = [path] if isinstance(path, basestring) else list(path)
+    sys.modules[package_name] = package
+
+    return package
+
+
+def _import_module(importer, module_name, package):
+    fullname = _module_name(package.__name__, module_name)
+    if fullname in sys.modules:
+        return sys.modules[fullname]
+
+    loader = importer.find_module(fullname)
+    if loader is None:
+        return None
+
+    module = loader.load_module(fullname)
+    setattr(package, module_name, module)
+    return module
+
+
+def load_modules(package, ignore_error=False):
+    path = package.__path__
+    for importer, module_name, is_package in pkgutil.walk_packages(path):
+        try:
+            module = _import_module(importer, module_name, package)
+        except ImportError as ex:
+            logger.error(_('Failed to import module %s') % module_name)
+            if not ignore_error:
+                raise
+        else:
+            if module is not None:
+                yield module
diff --git a/heat/tests/test_plugin_loader.py b/heat/tests/test_plugin_loader.py
new file mode 100644
index 0000000000..d458d32493
--- /dev/null
+++ b/heat/tests/test_plugin_loader.py
@@ -0,0 +1,70 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+#    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.
+
+
+import nose
+import pkgutil
+import sys
+import unittest
+from nose.plugins.attrib import attr
+
+import heat.engine
+from heat.common import plugin_loader
+
+
+@attr(tag=['unit', 'plugin_loader'])
+@attr(speed='fast')
+class PluginLoaderTest(unittest.TestCase):
+    def test_module_name(self):
+        self.assertEqual(plugin_loader._module_name('foo.bar', 'blarg.wibble'),
+                         'foo.bar.blarg.wibble')
+
+    def test_create_subpackage_single_path(self):
+        pkg_name = 'heat.engine.test_single_path'
+        self.assertFalse(pkg_name in sys.modules)
+        pkg = plugin_loader.create_subpackage('/tmp',
+                                              'heat.engine',
+                                              'test_single_path')
+        self.assertTrue(pkg_name in sys.modules)
+        self.assertEqual(sys.modules[pkg_name], pkg)
+        self.assertEqual(pkg.__path__, ['/tmp'])
+        self.assertEqual(pkg.__name__, pkg_name)
+
+    def test_create_subpackage_path_list(self):
+        path_list = ['/tmp']
+        pkg_name = 'heat.engine.test_path_list'
+        self.assertFalse(pkg_name in sys.modules)
+        pkg = plugin_loader.create_subpackage('/tmp',
+                                              'heat.engine',
+                                              'test_path_list')
+        self.assertTrue(pkg_name in sys.modules)
+        self.assertEqual(sys.modules[pkg_name], pkg)
+        self.assertEqual(pkg.__path__, path_list)
+        self.assertFalse(pkg.__path__ is path_list)
+        self.assertEqual(pkg.__name__, pkg_name)
+
+    def test_import_module_existing(self):
+        import heat.engine.service
+        importer = pkgutil.ImpImporter(heat.engine.__path__[0])
+        loaded = plugin_loader._import_module(importer,
+                                              'service',
+                                              heat.engine)
+        self.assertTrue(loaded is heat.engine.service)
+
+    def test_import_module_garbage(self):
+        importer = pkgutil.ImpImporter(heat.engine.__path__[0])
+        self.assertEqual(plugin_loader._import_module(importer,
+                                                      'wibble',
+                                                      heat.engine),
+                         None)