do not try encode None, always return a string from get_primary_interface (#287)

azurelinuxagent/common/osutil/default.py

@@ -500,6 +500,10 @@ class DefaultOSUtil(object):
                     if primary is None or metric < primary_metric:
                         primary = iface
                         primary_metric = metric
+
+        if primary is None:
+            primary = ''
+
         logger.info('primary interface is [{0}]'.format(primary))
         return primary
 

tests/common/osutil/test_default.py

@@ -106,6 +106,17 @@ class TestOSUtil(AgentTestCase):
             self.assertFalse(osutil.DefaultOSUtil().is_primary_interface('nflg'))
             self.assertFalse(osutil.DefaultOSUtil().is_primary_interface('invalid'))
 
+    def test_no_primary_does_not_throw(self):
+        with patch.object(osutil.DefaultOSUtil, 'get_primary_interface') \
+                as patch_primary:
+            exception = False
+            patch_primary.return_value = ''
+            try:
+                osutil.DefaultOSUtil().get_first_if()[0]
+            except Exception as e:
+                exception = True
+            self.assertFalse(exception)
+
     def test_dhcp_lease_default(self):
         self.assertTrue(osutil.DefaultOSUtil().get_dhcp_lease_endpoint() is None)