[dhcp_relay] Add test case to verify dhcp6relay LLA waiting logic (so…

…nic-net#16494)

What is the motivation for this PR?
We add wait LLA logic in dhcp6relay with sonic-net/sonic-dhcp-relay#52
Current PR is to add test for it to verify dhcp6relay would work well when LLA is missing

How did you do it?
Modify test_interface_binding:

Remove LLA for Vlans
Restart dhcp_relay container
Verify whether sockets for LLA are not established
Add LLA back
Verify whether sockets for LLA are established

How did you verify/test it?
Run test_dhcpv6_relay.py

tests/dhcp_relay/test_dhcpv6_relay.py

@@ -116,6 +116,7 @@ def dut_dhcp_relay_data(duthosts, rand_one_dut_hostname, tbinfo):
     duthost = duthosts[rand_one_dut_hostname]
     dhcp_relay_data_list = []
     down_interface_link_local = ""
+    down_interface_link_local_with_prefix_len = ""
 
     mg_facts = duthost.get_extended_minigraph_facts(tbinfo)
 
@@ -179,18 +180,20 @@ def dut_dhcp_relay_data(duthosts, rand_one_dut_hostname, tbinfo):
                         uplink_interfaces.append(iface_name)
                     uplink_port_indices.append(mg_facts['minigraph_ptf_indices'][iface_name])
         if down_interface_link_local == "":
-            command = "ip addr show {} | grep inet6 | grep 'scope link' | awk '{{print $2}}' | cut -d '/' -f1"\
+            command = "ip addr show {} | grep inet6 | grep 'scope link' | awk '{{print $2}}'"\
                       .format(downlink_vlan_iface['name'])
             res = duthost.shell(command)
             if res['stdout'] != "":
-                down_interface_link_local = res['stdout']
+                down_interface_link_local_with_prefix_len = res['stdout']
+                down_interface_link_local = down_interface_link_local_with_prefix_len.split("/")[0]
 
         dhcp_relay_data = {}
         dhcp_relay_data['downlink_vlan_iface'] = downlink_vlan_iface
         dhcp_relay_data['client_iface'] = client_iface
         dhcp_relay_data['uplink_interfaces'] = uplink_interfaces
         dhcp_relay_data['uplink_port_indices'] = uplink_port_indices
         dhcp_relay_data['down_interface_link_local'] = down_interface_link_local
+        dhcp_relay_data['down_interface_link_local_with_prefix_len'] = down_interface_link_local_with_prefix_len
         dhcp_relay_data['loopback_iface'] = mg_facts['minigraph_lo_interfaces']
         dhcp_relay_data['loopback_ipv6'] = mg_facts['minigraph_lo_interfaces'][1]['addr']
         if 'dualtor' in tbinfo['topo']['name']:
@@ -259,12 +262,56 @@ def test_interface_binding(duthosts, rand_one_dut_hostname, dut_dhcp_relay_data,
         config_reload(duthost)
         wait_critical_processes(duthost)
         pytest_assert(wait_until(120, 5, 0, check_interface_status, duthost))
-    output = duthost.shell("docker exec -t dhcp_relay ss -nlp | grep dhcp6relay")["stdout"]
-    logger.info(output)
-    for dhcp_relay in dut_dhcp_relay_data:
-        assert ("*:{}".format(dhcp_relay['downlink_vlan_iface']['name']) or "*:*" in output,
-                "{} is not found in {}".format("*:{}".format(dhcp_relay['downlink_vlan_iface']['name']), output)) or \
-               ("*:*" in output, "dhcp6relay socket is not properly binded")
+
+    # Cmds to delete LLA for all Vlans
+    delete_cmds = ["ip -6 address del {} dev {}"
+                   .format(data["down_interface_link_local_with_prefix_len"],
+                           data["downlink_vlan_iface"]["name"]) for data in dut_dhcp_relay_data]
+
+    # Cmds to add LLA for all Vlans
+    add_cmds = ["ip -6 address add {} dev {}"
+                .format(data["down_interface_link_local_with_prefix_len"],
+                        data["downlink_vlan_iface"]["name"]) for data in dut_dhcp_relay_data]
+
+    def _check_dhcp6relay_lla_socket(expect_exist):
+        res = {}
+        output = duthost.shell("docker exec -t dhcp_relay ss -nlp | grep dhcp6relay")["stdout"]
+        for dhcp_relay in dut_dhcp_relay_data:
+            key = dhcp_relay['downlink_vlan_iface']['name']
+            res[key] = "{}:547".format(key) in output
+
+        logger.info("_check_dhcp6relay_lla_socket res: {}".format(res))
+
+        # If expect socket exist, then sockets for all vlan should appear
+        if expect_exist:
+            return all(list(res.values()))
+        # If not expect socket exist, then sockets for all vlan shouldn't appear
+        else:
+            return not any(list(res.values()))
+
+    try:
+        duthost.shell_cmds(cmds=delete_cmds)
+        restart_dhcp_service(duthost)
+        time.sleep(10)
+
+        output = duthost.shell("docker exec -t dhcp_relay ss -nlp | grep dhcp6relay")["stdout"]
+        logger.info(output)
+
+        # Raw socket listen all port would startup
+        pytest_assert("*:*" in output, "Raw socket for dhcp6relay is not found")
+
+        # LLA is not ready, hence there should not be sockets listen on LLA
+        pytest_assert(_check_dhcp6relay_lla_socket(False), "LLA sockets are found, which is unexpected")
+
+        duthost.shell_cmds(cmds=add_cmds)
+
+        # Interval for checking lla in dhcp6relay is set as 60s, hence here we expect in worst scenario LLA sould
+        # be ready in 70s
+        # LLAs are ready, hence there should be sockets listen on LLA
+        pytest_assert(wait_until(70, 5, 0, _check_dhcp6relay_lla_socket, True), "Expected LLA sockets are not found")
+    finally:
+        for cmd in add_cmds:
+            duthost.shell(cmd, module_ignore_errors=True)
 
     pytest_assert("Vlan{}".format(new_vlan_id) not in output,
                   "dhcp6relay bind to Vlan{} without dhcpv6_servers configured, which is unexpected"