[sysName]: Implement sysName OID (sonic-net#185)

[sysName]: Add sysName OID implementation in snmpagent.
sysName OID is currently supported by snmpd. Override this
implementation to make sure the latest hostname is taken
from config db.
Add a new MIB class to support retrieving sysName from config_db
Add unit-test to test sysName OID.

src/sonic_ax_impl/main.py

@@ -24,6 +24,7 @@
 class SonicMIB(
     rfc1213.InterfacesMIB,
     rfc1213.IpMib,
+    rfc1213.SysNameMIB,
     rfc2737.PhysicalTableMIB,
     rfc3433.PhysicalSensorTableMIB,
     rfc2863.InterfaceMIBObjects,

src/sonic_ax_impl/mibs/ietf/rfc1213.py

@@ -1,5 +1,6 @@
 import ipaddress
 import python_arptable
+import socket
 from enum import unique, Enum
 from bisect import bisect_right
 
@@ -673,3 +674,31 @@ class InterfacesMIB(metaclass=MIBMeta, prefix='.1.3.6.1.2.1.2'):
     # FIXME Placeholder
     ifSpecific = \
         SubtreeMIBEntry('2.1.22', if_updater, ValueType.OBJECT_IDENTIFIER, lambda sub_id: ObjectIdentifier.null_oid())
+
+class sysNameUpdater(MIBUpdater):
+    def __init__(self):
+        super().__init__()
+        self.db_conn = mibs.init_db()
+        self.hostname = socket.gethostname()
+
+    def reinit_data(self):
+        self.db_conn.connect(self.db_conn.CONFIG_DB)
+        device_metadata = self.db_conn.get_all(self.db_conn.CONFIG_DB, "DEVICE_METADATA|localhost")
+
+        if device_metadata and device_metadata.get('hostname'):
+            self.hostname = device_metadata['hostname']
+
+    def update_data(self):
+        return
+
+    def get_sys_name(self):
+        """
+        Subclass update interface information
+        """
+        return self.hostname
+
+
+class SysNameMIB(metaclass=MIBMeta, prefix='.1.3.6.1.2.1.1.5'):
+    updater = sysNameUpdater()
+
+    sysName = MIBEntry('0', ValueType.OCTET_STRING, updater.get_sys_name)

tests/mock_tables/config_db.json

@@ -14,5 +14,9 @@
     "admin_status": "up",
     "alias": "mgmt2",
     "speed": 1000
+  },
+  "DEVICE_METADATA|localhost": {
+    "chassis_serial_number": "SAMPLETESTSN",
+    "hostname" : "test_hostname"
   }
 }

tests/mock_tables/global_db/config_db.json

@@ -14,5 +14,9 @@
     "admin_status": "up",
     "alias": "mgmt2",
     "speed": 1000
+  },
+  "DEVICE_METADATA|localhost": {
+    "chassis_serial_number": "SAMPLETESTSN",
+    "hostname" : "namespace_hostname"
   }
 }

tests/namespace/test_sysname.py

@@ -0,0 +1,44 @@
+import os
+import sys
+import importlib
+from unittest import TestCase
+
+from ax_interface import ValueType
+from ax_interface.pdu_implementations import GetPDU, GetNextPDU
+from ax_interface.encodings import ObjectIdentifier
+from ax_interface.constants import PduTypes
+from ax_interface.pdu import PDU, PDUHeader
+from ax_interface.mib import MIBTable
+from sonic_ax_impl.mibs.ietf import rfc1213
+import tests.mock_tables.dbconnector
+
+class TestGetNextPDU(TestCase):
+    @classmethod
+    def setUpClass(cls):
+        tests.mock_tables.dbconnector.load_namespace_config()
+        importlib.reload(rfc1213)
+        cls.lut = MIBTable(rfc1213.SysNameMIB)
+        for updater in cls.lut.updater_instances:
+            updater.reinit_data()
+            updater.update_data()
+
+    def test_getpdu_sysname(self):
+        oid = ObjectIdentifier(9, 0, 0, 0, (1, 3, 6, 1, 2, 1, 1, 5, 0))
+        get_pdu = GetPDU(
+            header=PDUHeader(1, PduTypes.GET, 16, 0, 42, 0, 0, 0),
+            oids=[oid]
+        )
+
+        encoded = get_pdu.encode()
+        response = get_pdu.make_response(self.lut)
+        print(response)
+
+        n = len(response.values)
+        value0 = response.values[0]
+        self.assertEqual(value0.type_, ValueType.OCTET_STRING)
+        self.assertEqual(str(value0.name), str(ObjectIdentifier(9, 0, 0, 0, (1, 3, 6, 1, 2, 1, 1, 5, 0))))
+        self.assertEqual(str(value0.data), 'namespace_hostname')
+
+    @classmethod
+    def tearDownClass(cls):
+        tests.mock_tables.dbconnector.clean_up_config()

tests/test_sysname.py

@@ -0,0 +1,38 @@
+import os
+import sys
+from unittest import TestCase
+
+from unittest import TestCase
+
+from ax_interface import ValueType
+from ax_interface.pdu_implementations import GetPDU, GetNextPDU
+from ax_interface.encodings import ObjectIdentifier
+from ax_interface.constants import PduTypes
+from ax_interface.pdu import PDU, PDUHeader
+from ax_interface.mib import MIBTable
+from sonic_ax_impl.mibs.ietf import rfc1213
+
+class TestGetNextPDU(TestCase):
+    @classmethod
+    def setUpClass(cls):
+        cls.lut = MIBTable(rfc1213.SysNameMIB)
+        for updater in cls.lut.updater_instances:
+            updater.reinit_data()
+            updater.update_data()
+
+    def test_getpdu_sysname(self):
+        oid = ObjectIdentifier(9, 0, 0, 0, (1, 3, 6, 1, 2, 1, 1, 5, 0))
+        get_pdu = GetPDU(
+            header=PDUHeader(1, PduTypes.GET, 16, 0, 42, 0, 0, 0),
+            oids=[oid]
+        )
+
+        encoded = get_pdu.encode()
+        response = get_pdu.make_response(self.lut)
+        print(response)
+
+        n = len(response.values)
+        value0 = response.values[0]
+        self.assertEqual(value0.type_, ValueType.OCTET_STRING)
+        self.assertEqual(str(value0.name), str(ObjectIdentifier(9, 0, 0, 0, (1, 3, 6, 1, 2, 1, 1, 5, 0))))
+        self.assertEqual(str(value0.data), 'test_hostname')