Fix: zero route may have empty nexthop (sonic-net#276)

**- What I did**
Fix: zero route may have empty nexthop. Improve code robustness.

**- How I did it**

**- How to verify it**
Manual test:
1. manipulate ApplDB default route: remove nexthop field and value
2. recover
3. manipulate ApplDB default route: remove ifname field and value
4. recover

Also add unit test.

src/sonic_ax_impl/mibs/ietf/rfc1213.py

@@ -152,7 +152,10 @@ def update_data(self):
                 ipn = ipaddress.ip_network(ipnstr)
                 ent = Namespace.dbs_get_all(self.db_conn, mibs.APPL_DB, routestr, blocking=False)
                 if ent:
-                    nexthops = ent["nexthop"]
+                    nexthops = ent.get("nexthop", None)
+                    if nexthops is None:
+                        mibs.logger.warning("Route has no nexthop: {} {}".format(routestr, str(ent)))
+                        continue
                     for nh in nexthops.split(','):
                         # TODO: if ipn contains IP range, create more sub_id here
                         sub_id = ip2byte_tuple(ipn.network_address)

src/sonic_ax_impl/mibs/ietf/rfc4292.py

@@ -67,8 +67,14 @@ def update_data(self):
             ent = db_conn.get_all(mibs.APPL_DB, route_str, blocking=False)
             if not ent:
                 continue
-            nexthops = ent["nexthop"]
-            ifnames = ent["ifname"]
+            nexthops = ent.get("nexthop", None)
+            if nexthops is None:
+                mibs.logger.warning("Route has no nexthop: {} {}".format(route_str, str(ent)))
+                continue
+            ifnames = ent.get("ifname", None)
+            if ifnames is None:
+                mibs.logger.warning("Route has no ifname: {} {}".format(route_str, str(ent)))
+                continue
             for nh, ifn in zip(nexthops.split(','), ifnames.split(',')):
                 ## Ignore non front panel interfaces
                 ## TODO: non front panel interfaces should not be in APPL_DB at very beginning

tests/test_rfc1213.py

@@ -0,0 +1,45 @@
+import os
+import sys
+from unittest import TestCase
+
+if sys.version_info.major == 3:
+    from unittest import mock
+else:
+    import mock
+
+modules_path = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+sys.path.insert(0, os.path.join(modules_path, 'src'))
+
+from sonic_ax_impl.mibs.ietf.rfc1213 import NextHopUpdater
+
+class TestNextHopUpdater(TestCase):
+
+    @mock.patch('sonic_ax_impl.mibs.Namespace.dbs_keys', mock.MagicMock(return_value=(["ROUTE_TABLE:0.0.0.0/0"])))
+    @mock.patch('sonic_ax_impl.mibs.Namespace.dbs_get_all', mock.MagicMock(return_value=({"nexthop": "10.0.0.1,10.0.0.3", "ifname": "Ethernet0,Ethernet4"})))
+    def test_NextHopUpdater_route_has_next_hop(self):
+        updater = NextHopUpdater()
+
+        with mock.patch('sonic_ax_impl.mibs.logger.warning') as mocked_warning:
+            updater.update_data()
+
+            # check warning
+            mocked_warning.assert_not_called()
+
+        self.assertTrue(len(updater.route_list) == 1)
+        self.assertTrue(updater.route_list[0] == (0,0,0,0))
+
+    @mock.patch('sonic_ax_impl.mibs.Namespace.dbs_keys', mock.MagicMock(return_value=(["ROUTE_TABLE:0.0.0.0/0"])))
+    @mock.patch('sonic_ax_impl.mibs.Namespace.dbs_get_all', mock.MagicMock(return_value=({"ifname": "Ethernet0,Ethernet4"})))
+    def test_NextHopUpdater_route_no_next_hop(self):
+        updater = NextHopUpdater()
+
+        with mock.patch('sonic_ax_impl.mibs.logger.warning') as mocked_warning:
+            updater.update_data()
+
+            # check warning
+            expected = [
+                mock.call("Route has no nexthop: ROUTE_TABLE:0.0.0.0/0 {'ifname': 'Ethernet0,Ethernet4'}")
+            ]
+            mocked_warning.assert_has_calls(expected)
+
+        self.assertTrue(len(updater.route_list) == 0)

tests/test_rfc4292.py

@@ -0,0 +1,61 @@
+import os
+import sys
+from unittest import TestCase
+
+if sys.version_info.major == 3:
+    from unittest import mock
+else:
+    import mock
+
+modules_path = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+sys.path.insert(0, os.path.join(modules_path, 'src'))
+
+from sonic_ax_impl.mibs.ietf.rfc4292 import RouteUpdater
+
+class TestRouteUpdater(TestCase):
+
+    @mock.patch('sonic_py_common.multi_asic.get_all_namespaces', mock.MagicMock(return_value=({"front_ns": ['']})))
+    @mock.patch('swsscommon.swsscommon.SonicV2Connector.get_all', mock.MagicMock(return_value=({"nexthop": "10.0.0.1", "ifname": "Ethernet0"})))
+    def test_RouteUpdater_route_has_next_hop_and_iframe(self):
+        updater = RouteUpdater()
+
+        with mock.patch('sonic_ax_impl.mibs.logger.warning') as mocked_warning:
+            updater.update_data()
+
+            # check warning
+            mocked_warning.assert_not_called()
+
+        self.assertTrue(len(updater.route_dest_list) == 1)
+        self.assertTrue(updater.route_dest_list[0] == (0, 0, 0, 0, 0, 0, 0, 0, 0, 10, 0, 0, 1))
+
+    @mock.patch('sonic_py_common.multi_asic.get_all_namespaces', mock.MagicMock(return_value=({"front_ns": ['']})))
+    @mock.patch('swsscommon.swsscommon.SonicV2Connector.get_all', mock.MagicMock(return_value=({"ifname": "Ethernet0"})))
+    def test_RouteUpdater_route_no_next_hop(self):
+        updater = RouteUpdater()
+
+        with mock.patch('sonic_ax_impl.mibs.logger.warning') as mocked_warning:
+            updater.update_data()
+
+            # check warning
+            expected = [
+                mock.call("Route has no nexthop: ROUTE_TABLE:0.0.0.0/0 {'ifname': 'Ethernet0'}")
+            ]
+            mocked_warning.assert_has_calls(expected)
+
+        self.assertTrue(len(updater.route_dest_list) == 0)
+
+    @mock.patch('sonic_py_common.multi_asic.get_all_namespaces', mock.MagicMock(return_value=({"front_ns": ['']})))
+    @mock.patch('swsscommon.swsscommon.SonicV2Connector.get_all', mock.MagicMock(return_value=({"nexthop": "10.0.0.1"})))
+    def test_RouteUpdater_route_no_iframe(self):
+        updater = RouteUpdater()
+
+        with mock.patch('sonic_ax_impl.mibs.logger.warning') as mocked_warning:
+            updater.update_data()
+
+            # check warning
+            expected = [
+                mock.call("Route has no ifname: ROUTE_TABLE:0.0.0.0/0 {'nexthop': '10.0.0.1'}")
+            ]
+            mocked_warning.assert_has_calls(expected)
+
+        self.assertTrue(len(updater.route_dest_list) == 0)