T6948: Smoketest for DHCP server leases sync with hostd records

The test `test_dhcp_hostsd_lease_sync` validates
DHCP server leases in sync with hostd records.

Since the DHCP server running in smoketest environment
might not have actual clients to lease IP addresses,
we simulate the lease creation and deletion using
kea helper functions (kea_add_lease and kea_delete_lease).

smoketest/scripts/cli/test_service_dhcp-server.py

@@ -1,6 +1,6 @@
 #!/usr/bin/env python3
 #
-# Copyright (C) 2020-2024 VyOS maintainers and contributors
+# Copyright (C) 2020-2025 VyOS maintainers and contributors
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 2 or later as
@@ -15,13 +15,18 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 import os
+import re
 import unittest
 
 from json import loads
 
 from base_vyostest_shim import VyOSUnitTestSHIM
+from time import sleep
 
 from vyos.configsession import ConfigSessionError
+from vyos.kea import kea_add_lease
+from vyos.kea import kea_delete_lease
+from vyos.utils.process import cmd
 from vyos.utils.process import process_named_running
 from vyos.utils.file import read_file
 from vyos.template import inc_ip
@@ -31,6 +36,7 @@
 CTRL_PROCESS_NAME = 'kea-ctrl-agent'
 KEA4_CONF = '/run/kea/kea-dhcp4.conf'
 KEA4_CTRL = '/run/kea/dhcp4-ctrl-socket'
+HOSTSD_CLIENT = '/usr/bin/vyos-hostsd-client'
 base_path = ['service', 'dhcp-server']
 interface = 'dum8765'
 subnet = '192.0.2.0/25'
@@ -842,6 +848,79 @@ def test_dhcp_on_interface_with_vrf(self):
         self.cli_delete(['vrf', 'name', 'SMOKE-DHCP'])
         self.cli_commit()
 
+    def test_dhcp_hostsd_lease_sync(self):
+        shared_net_name = 'SMOKE-LEASE-SYNC'
+        domain_name = 'sync.private'
+
+        client_range = range(1, 4)
+        subnet_range_start = inc_ip(subnet, 10)
+        subnet_range_stop  = inc_ip(subnet, 20)
+
+        def internal_cleanup():
+            for seq in client_range:
+                ip_addr = inc_ip(subnet, seq)
+                kea_delete_lease(4, ip_addr)
+                cmd(f'{HOSTSD_CLIENT} --delete-hosts --tag dhcp-server-{ip_addr} --apply')
+
+        self.addClassCleanup(internal_cleanup)
+
+        pool = base_path + ['shared-network-name', shared_net_name, 'subnet', subnet]
+        self.cli_set(pool + ['subnet-id', '1'])
+        self.cli_set(pool + ['option', 'domain-name', domain_name])
+        self.cli_set(pool + ['range', '0', 'start', subnet_range_start])
+        self.cli_set(pool + ['range', '0', 'stop', subnet_range_stop])
+
+        # commit changes
+        self.cli_commit()
+
+        config = read_file(KEA4_CONF)
+        obj = loads(config)
+
+        self.verify_config_value(obj, ['Dhcp4', 'shared-networks'], 'name', shared_net_name)
+        self.verify_config_value(obj, ['Dhcp4', 'shared-networks', 0, 'subnet4'], 'subnet', subnet)
+        self.verify_config_value(obj, ['Dhcp4', 'shared-networks', 0, 'subnet4'], 'id', 1)
+
+        # Verify options
+        self.verify_config_object(
+                obj,
+                ['Dhcp4', 'shared-networks', 0, 'subnet4', 0, 'option-data'],
+                {'name': 'domain-name', 'data': domain_name})
+        self.verify_config_object(
+                obj,
+                ['Dhcp4', 'shared-networks', 0, 'subnet4', 0, 'pools'],
+                {'pool': f'{subnet_range_start} - {subnet_range_stop}'})
+
+        # Check for running process
+        self.assertTrue(process_named_running(PROCESS_NAME))
+
+        # All up and running, now test vyos-hostsd store
+
+        # 1. Inject leases into kea
+        for seq in client_range:
+            client = f'client{seq}'
+            mac = f'00:50:00:00:00:{seq:02}'
+            ip = inc_ip(subnet, seq)
+            kea_add_lease(4, ip, host_name=client, mac_address=mac)
+
+        # 2. Verify that leases are not available in vyos-hostsd
+        tag_regex = re.escape(f'dhcp-server-{subnet.rsplit(".", 1)[0]}')
+        host_json = cmd(f'{HOSTSD_CLIENT} --get-hosts {tag_regex}')
+        self.assertFalse(host_json.strip('{}'))
+
+        # 3. Restart the service to trigger vyos-hostsd sync and wait for it to start
+        self.op_mode(['restart', 'dhcp', 'server'])
+        count = 0
+        while count < 30:
+            is_running = process_named_running(PROCESS_NAME)
+            if is_running:
+                break
+            count += 1
+            sleep(1)
+
+        # 4. Verify that leases are synced and available in vyos-hostsd
+        tag_regex = re.escape(f'dhcp-server-{subnet.rsplit(".", 1)[0]}')
+        host_json = cmd(f'{HOSTSD_CLIENT} --get-hosts {tag_regex}')
+        self.assertTrue(host_json)
 
 if __name__ == '__main__':
     unittest.main(verbosity=2)