dhcpv6-client: T2590: fix vyos-hostsd update for nameserver and search domains

After migrating from ISC DHCLIENT for IPv6 to wide-dhcp-client the logic which
was present to update /etc/resolv.conf with the DHCP specified nameservers and
also the search domain list was no longer present.

This commit adds a per interface rendered script to inform vyos-hostsd about
the received IPv6 nameservers and search domains.

(cherry picked from commit ece425f0191762638b7c967097accd8739e9103d)

4 files changed, 44 insertions, 20 deletions

diff --git a/data/templates/dhcp-client/dhcp6c-script.j2 b/data/templates/dhcp-client/dhcp6c-script.j2
new file mode 100644
index 000000000..14fb25cf6
--- /dev/null
+++ b/data/templates/dhcp-client/dhcp6c-script.j2
@@ -0,0 +1,31 @@
+#!/bin/sh
+# Update DNS information for DHCPv6 clients
+# should be used only if vyos-hostsd is running
+
+if /usr/bin/systemctl -q is-active vyos-hostsd; then
+    hostsd_client="/usr/bin/vyos-hostsd-client"
+    hostsd_changes=
+
+    if [ -n "$new_domain_name" ]; then
+        logmsg info "Deleting search domains with tag \"dhcpv6-{{ ifname }}\" via vyos-hostsd-client"
+        $hostsd_client --delete-search-domains --tag "dhcpv6-{{ ifname }}"
+        logmsg info "Adding domain name \"$new_domain_name\" as search domain with tag \"dhcpv6-{{ ifname }}\" via vyos-hostsd-client"
+        $hostsd_client --add-search-domains "$new_domain_name" --tag "dhcpv6-{{ ifname }}"
+        hostsd_changes=y
+    fi
+
+    if [ -n "$new_domain_name_servers" ]; then
+        logmsg info "Deleting nameservers with tag \"dhcpv6-{{ ifname }}\" via vyos-hostsd-client"
+        $hostsd_client --delete-name-servers --tag "dhcpv6-{{ ifname }}"
+        logmsg info "Adding nameservers \"$new_domain_name_servers\" with tag \"dhcpv6-{{ ifname }}\" via vyos-hostsd-client"
+        $hostsd_client --add-name-servers $new_domain_name_servers --tag "dhcpv6-{{ ifname }}"
+        hostsd_changes=y
+    fi
+
+    if [ $hostsd_changes ]; then
+        logmsg info "Applying changes via vyos-hostsd-client"
+        $hostsd_client --apply
+    else
+        logmsg info "No changes to apply via vyos-hostsd-client"
+    fi
+fi
diff --git a/data/templates/dhcp-client/ipv6.tmpl b/data/templates/dhcp-client/ipv6.tmpl
index c292664e9..348ac1f22 100644
--- a/data/templates/dhcp-client/ipv6.tmpl
+++ b/data/templates/dhcp-client/ipv6.tmpl
@@ -23,6 +23,7 @@ interface {{ ifname }} {
     send ia-pd {{ pd }}; # prefix delegation #{{ pd }}
 {%   endfor %}
 {% endif %}
+    script "{{ dhcp6_script_file }}";
 };
 
 {% if address is defined and 'dhcpv6' in address %}
diff --git a/python/vyos/ifconfig/interface.py b/python/vyos/ifconfig/interface.py
index 6b19f12a2..778c601ee 100644
--- a/python/vyos/ifconfig/interface.py
+++ b/python/vyos/ifconfig/interface.py
@@ -1,4 +1,4 @@
-# Copyright 2019-2021 VyOS maintainers and contributors <maintainers@vyos.io>
+# Copyright 2019-2024 VyOS maintainers and contributors <maintainers@vyos.io>
 #
 # This library is free software; you can redistribute it and/or
 # modify it under the terms of the GNU Lesser General Public
@@ -1186,12 +1186,18 @@ class Interface(Control):
 
         ifname = self.ifname
         config_file = f'/run/dhcp6c/dhcp6c.{ifname}.conf'
+        script_file = f'/etc/wide-dhcpv6/dhcp6c.{ifname}.script' # can not live under /run b/c of noexec mount option
         systemd_override_file = f'/run/systemd/system/dhcp6c@{ifname}.service.d/10-override.conf'
         systemd_service = f'dhcp6c@{ifname}.service'
 
-        if enable and 'disable' not in self.config:
-            render(systemd_override_file, 'dhcp-client/ipv6.override.conf.j2', self.config)
-            render(config_file, 'dhcp-client/ipv6.tmpl', self.config)
+        # Rendered client configuration files require additional settings
+        config = deepcopy(self.config)
+        config['dhcp6_script_file'] = script_file
+
+        if enable and 'disable' not in config:
+            render(systemd_override_file, 'dhcp-client/ipv6.override.conf.j2', config)
+            render(config_file, 'dhcp-client/ipv6.tmpl', config)
+            render(script_file, 'dhcp-client/dhcp6c-script.j2', config, permission=0o755)
 
             # Reload systemd unit definitons as some options are dynamically generated
             self._cmd('systemctl daemon-reload')
@@ -1204,6 +1210,8 @@ class Interface(Control):
                 self._cmd(f'systemctl stop {systemd_service}')
             if os.path.isfile(config_file):
                 os.remove(config_file)
+            if os.path.isfile(script_file):
+                os.remove(script_file)
 
     def set_mirror(self):
         # Please refer to the document for details
diff --git a/src/etc/dhcp/dhclient-enter-hooks.d/04-vyos-resolvconf b/src/etc/dhcp/dhclient-enter-hooks.d/04-vyos-resolvconf
index 518abeaec..9a8a53bfd 100644
--- a/src/etc/dhcp/dhclient-enter-hooks.d/04-vyos-resolvconf
+++ b/src/etc/dhcp/dhclient-enter-hooks.d/04-vyos-resolvconf
@@ -14,14 +14,6 @@ if /usr/bin/systemctl -q is-active vyos-hostsd; then
             hostsd_changes=y
         fi
 
-        if [ -n "$new_dhcp6_domain_search" ]; then
-            logmsg info "Deleting search domains with tag \"dhcpv6-$interface\" via vyos-hostsd-client"
-            $hostsd_client --delete-search-domains --tag "dhcpv6-$interface"
-            logmsg info "Adding search domain \"$new_dhcp6_domain_search\" with tag \"dhcpv6-$interface\" via vyos-hostsd-client"
-            $hostsd_client --add-search-domains "$new_dhcp6_domain_search" --tag "dhcpv6-$interface"
-            hostsd_changes=y
-        fi
-
         if [ -n "$new_domain_name_servers" ]; then
             logmsg info "Deleting nameservers with tag \"dhcp-$interface\" via vyos-hostsd-client"
             $hostsd_client --delete-name-servers --tag "dhcp-$interface"
@@ -30,14 +22,6 @@ if /usr/bin/systemctl -q is-active vyos-hostsd; then
             hostsd_changes=y
         fi
 
-        if [ -n "$new_dhcp6_name_servers" ]; then
-            logmsg info "Deleting nameservers with tag \"dhcpv6-$interface\" via vyos-hostsd-client"
-            $hostsd_client --delete-name-servers --tag "dhcpv6-$interface"
-            logmsg info "Adding nameservers \"$new_dhcp6_name_servers\" with tag \"dhcpv6-$interface\" via vyos-hostsd-client"
-            $hostsd_client --add-name-servers $new_dhcp6_name_servers --tag "dhcpv6-$interface"
-            hostsd_changes=y
-        fi
-
         if [ $hostsd_changes ]; then
             logmsg info "Applying changes via vyos-hostsd-client"
             $hostsd_client --apply