[Trivial] Refactor libvirt inspector connection & uri

libvirt inpsector has an attribute called `uri`, which only used
when connecting to libvirtd. There is no such need to do so, a
local variable can do it as well.

Meanwhile, we initialize connection by calling a method
`_get_connection`, and there is an attribute ``connection`` holds
the returned value. This method can be replaced with a property
`connection`, to shorten typing and avoid function calling style.

Change-Id: I8604d00c9298f56009c579fd23adc2c93ad44f8c

2 files changed, 23 insertions, 30 deletions

diff --git a/ceilometer/compute/virt/libvirt/inspector.py b/ceilometer/compute/virt/libvirt/inspector.py
index 8220d997..28be2cac 100644
--- a/ceilometer/compute/virt/libvirt/inspector.py
+++ b/ceilometer/compute/virt/libvirt/inspector.py
@@ -68,32 +68,31 @@ class LibvirtInspector(virt_inspector.Inspector):
     per_type_uris = dict(uml='uml:///system', xen='xen:///', lxc='lxc:///')
 
     def __init__(self):
-        self.uri = self._get_uri()
-        self.connection = None
+        self._connection = None
 
-    def _get_uri(self):
-        return CONF.libvirt_uri or self.per_type_uris.get(CONF.libvirt_type,
-                                                          'qemu:///system')
-
-    def _get_connection(self):
-        if not self.connection:
+    @property
+    def connection(self):
+        if not self._connection:
             global libvirt
             if libvirt is None:
                 libvirt = __import__('libvirt')
-            LOG.debug('Connecting to libvirt: %s', self.uri)
-            self.connection = libvirt.openReadOnly(self.uri)
 
-        return self.connection
+            uri = (CONF.libvirt_uri or
+                   self.per_type_uris.get(CONF.libvirt_type, 'qemu:///system'))
+            LOG.debug('Connecting to libvirt: %s', uri)
+            self._connection = libvirt.openReadOnly(uri)
+
+        return self._connection
 
     def check_sanity(self):
-        if not self._get_connection():
+        if not self.connection:
             raise virt_inspector.NoSanityException()
 
     @retry_on_disconnect
     def _lookup_by_uuid(self, instance):
         instance_name = util.instance_name(instance)
         try:
-            return self._get_connection().lookupByUUIDString(instance.id)
+            return self.connection.lookupByUUIDString(instance.id)
         except Exception as ex:
             if not libvirt or not isinstance(ex, libvirt.libvirtError):
                 raise virt_inspector.InspectorException(six.text_type(ex))
diff --git a/ceilometer/tests/unit/compute/virt/libvirt/test_inspector.py b/ceilometer/tests/unit/compute/virt/libvirt/test_inspector.py
index 16220cfa..f622e372 100644
--- a/ceilometer/tests/unit/compute/virt/libvirt/test_inspector.py
+++ b/ceilometer/tests/unit/compute/virt/libvirt/test_inspector.py
@@ -41,7 +41,6 @@ class TestLibvirtInspection(base.BaseTestCase):
             name = 'instance-00000001'
         self.instance = VMInstance
         self.inspector = libvirt_inspector.LibvirtInspector()
-        self.inspector.connection = mock.Mock()
         libvirt_inspector.libvirt = mock.Mock()
         libvirt_inspector.libvirt.VIR_DOMAIN_SHUTOFF = 5
         libvirt_inspector.libvirt.libvirtError = self.fakeLibvirtError
@@ -338,15 +337,11 @@ class TestLibvirtInspectionWithError(base.BaseTestCase):
         self.inspector = libvirt_inspector.LibvirtInspector()
         self.useFixture(fixtures.MonkeyPatch(
             'ceilometer.compute.virt.libvirt.inspector.'
-            'LibvirtInspector._get_connection',
-            self._dummy_get_connection))
+            'LibvirtInspector.connection',
+            mock.MagicMock(side_effect=Exception('dummy'))))
         libvirt_inspector.libvirt = mock.Mock()
         libvirt_inspector.libvirt.libvirtError = self.fakeLibvirtError
 
-    @staticmethod
-    def _dummy_get_connection(*args, **kwargs):
-        raise Exception('dummy')
-
     def test_inspect_unknown_error(self):
         self.assertRaises(virt_inspector.InspectorException,
                           self.inspector.inspect_cpus, 'foo')
@@ -359,16 +354,15 @@ class TestLibvirtInitWithError(base.BaseTestCase):
         self.inspector = libvirt_inspector.LibvirtInspector()
         libvirt_inspector.libvirt = mock.Mock()
 
-    @mock.patch('ceilometer.compute.virt.libvirt.inspector.'
-                'LibvirtInspector._get_connection',
-                mock.Mock(return_value=None))
     def test_init_error(self):
-        self.assertRaises(virt_inspector.NoSanityException,
-                          self.inspector.check_sanity)
+        with mock.patch.object(libvirt_inspector.libvirt,
+                               'openReadOnly',
+                               return_value=None):
+            self.assertRaises(virt_inspector.NoSanityException,
+                              self.inspector.check_sanity)
 
-    @mock.patch('ceilometer.compute.virt.libvirt.inspector.'
-                'LibvirtInspector._get_connection',
-                mock.Mock(side_effect=virt_inspector.NoDataException))
     def test_init_exception(self):
-        self.assertRaises(virt_inspector.NoDataException,
-                          self.inspector.check_sanity)
+        with mock.patch.object(libvirt_inspector.libvirt,
+                               'openReadOnly',
+                               side_effect=ImportError):
+            self.assertRaises(ImportError, self.inspector.check_sanity)