Add specific exception for qubesd communication error

qubesmgmt/base.py

@@ -69,6 +69,11 @@ class PropertyHolder(object):
         In case of success, return actual data. In case of error,
         raise appropriate exception.
         '''
+
+        if len(response_data) == 0:
+            raise qubesmgmt.exc.QubesDaemonNoResponseError(
+                'Got empty response from qubesd')
+
         if response_data[0:2] == b'\x30\x00':
             return response_data[2:]
         elif response_data[0:2] == b'\x32\x00':
@@ -89,7 +94,8 @@ class PropertyHolder(object):
             # TODO: handle traceback if given
             raise exc_class(format_string, *args)
         else:
-            raise qubesmgmt.exc.QubesException('Invalid response format')
+            raise qubesmgmt.exc.QubesDaemonCommunicationError(
+                'Invalid response format')
 
     def property_list(self):
         '''

qubesmgmt/exc.py

@@ -101,3 +101,13 @@ class BackupCancelledError(QubesException):
 
 class QubesMemoryError(QubesException, MemoryError):
     '''Cannot start domain, because not enough memory is available'''
+
+
+class QubesDaemonCommunicationError(QubesException, IOError):
+    '''Error while communicating with qubesd, may mean insufficient
+    permissions, as well'''
+
+
+# pylint: disable=too-many-ancestors
+class QubesDaemonNoResponseError(QubesDaemonCommunicationError):
+    '''Got empty response from qubesd'''

qubesmgmt/tests/errors.py

@@ -51,8 +51,9 @@ class TC_00_Errors(qubesmgmt.tests.QubesTestCase):
         self.assertEqual(str(context.exception), 'An error occurred: 1, 2')
 
     def test_010_empty(self):
-        self.app.expected_calls[('dom0', 'mgmt.vm.List', None, None)] = b''\
-        # FIXME: change to appropriate exception when defined
-        with self.assertRaises(qubesmgmt.exc.QubesException) as context:
+        self.app.expected_calls[('dom0', 'mgmt.vm.List', None, None)] = b''
+        with self.assertRaises(qubesmgmt.exc.QubesDaemonNoResponseError) \
+                as context:
             vms = list(self.app.domains)
-        self.assertEqual(str(context.exception), 'Invalid response format')
+        self.assertEqual(str(context.exception),
+            'Got empty response from qubesd')