T2898: add ndp-proxy service

VyOS CLI command
  set service ndp-proxy interface eth0 prefix 2001:db8::/64 mode 'static'

Will generate the following NDP proxy configuration

  $ cat /run/ndppd/ndppd.conf
  # autogenerated by service_ndp-proxy.py

  # This tells 'ndppd' how often to reload the route file /proc/net/ipv6_route
  route-ttl 30000

  # This sets up a listener, that will listen for any Neighbor Solicitation
  # messages, and respond to them according to a set of rules
  proxy eth0 {
      # Turn on or off the router flag for Neighbor Advertisements
      router no
      # Control how long to wait for a Neighbor Advertisment message before invalidating the entry (milliseconds)
      timeout 500
      # Control how long a valid or invalid entry remains in the cache (milliseconds)
      ttl 30000

      # This is a rule that the target address is to match against. If no netmask
      # is provided, /128 is assumed. You may have several rule sections, and the
      # addresses may or may not overlap.
      rule 2001:db8::/64 {
          static
      }
  }

3 files changed, 153 insertions, 11 deletions

diff --git a/src/conf_mode/nat66.py b/src/conf_mode/nat66.py
index 0ba08aef3..dee1551fe 100755
--- a/src/conf_mode/nat66.py
+++ b/src/conf_mode/nat66.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python3
 #
-# Copyright (C) 2020-2021 VyOS maintainers and contributors
+# Copyright (C) 2020-2023 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
@@ -36,7 +36,6 @@ airbag.enable()
 k_mod = ['nft_nat', 'nft_chain_nat']
 
 nftables_nat66_config = '/run/nftables_nat66.nft'
-ndppd_config = '/run/ndppd/ndppd.conf'
 
 def get_config(config=None):
     if config:
@@ -101,7 +100,6 @@ def generate(nat):
         nat['first_install'] = True
 
     render(nftables_nat66_config, 'firewall/nftables-nat66.j2', nat, permission=0o755)
-    render(ndppd_config, 'ndppd/ndppd.conf.j2', nat, permission=0o755)
     return None
 
 def apply(nat):
@@ -109,14 +107,6 @@ def apply(nat):
         return None
 
     cmd(f'nft -f {nftables_nat66_config}')
-
-    if 'deleted' in nat or not dict_search('source.rule', nat):
-        cmd('systemctl stop ndppd')
-        if os.path.isfile(ndppd_config):
-            os.unlink(ndppd_config)
-    else:
-        cmd('systemctl restart ndppd')
-
     call_dependents()
 
     return None
diff --git a/src/conf_mode/service_ndp-proxy.py b/src/conf_mode/service_ndp-proxy.py
new file mode 100755
index 000000000..aa2374f4c
--- /dev/null
+++ b/src/conf_mode/service_ndp-proxy.py
@@ -0,0 +1,91 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2023 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
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import os
+
+from sys import exit
+
+from vyos.config import Config
+from vyos.configverify import verify_interface_exists
+from vyos.utils.process import call
+from vyos.template import render
+from vyos import ConfigError
+from vyos import airbag
+airbag.enable()
+
+systemd_service = 'ndppd.service'
+ndppd_config = '/run/ndppd/ndppd.conf'
+
+def get_config(config=None):
+    if config:
+        conf = config
+    else:
+        conf = Config()
+    base = ['service', 'ndp-proxy']
+    if not conf.exists(base):
+        return None
+
+    ndpp = conf.get_config_dict(base, key_mangling=('-', '_'),
+                                get_first_key=True,
+                                with_recursive_defaults=True)
+
+    return ndpp
+
+def verify(ndpp):
+    if not ndpp:
+        return None
+
+    if 'interface' in ndpp:
+        for interface, interface_config in ndpp['interface'].items():
+            verify_interface_exists(interface)
+
+            if 'rule' in interface_config:
+                for rule, rule_config in interface_config['rule'].items():
+                    if rule_config['mode'] == 'interface' and 'interface' not in rule_config:
+                        raise ConfigError(f'Rule "{rule}" uses interface mode but no interface defined!')
+
+                    if rule_config['mode'] != 'interface' and 'interface' in rule_config:
+                        if interface_config['mode'] != 'interface' and 'interface' in interface_config:
+                            raise ConfigError(f'Rule "{rule}" does not use interface mode, thus interface can not be defined!')
+
+    return None
+
+def generate(ndpp):
+    if not ndpp:
+        return None
+
+    render(ndppd_config, 'ndppd/ndppd.conf.j2', ndpp)
+    return None
+
+def apply(ndpp):
+    if not ndpp:
+        call(f'systemctl stop {systemd_service}')
+        if os.path.isfile(ndppd_config):
+            os.unlink(ndppd_config)
+        return None
+
+    call(f'systemctl reload-or-restart {systemd_service}')
+    return None
+
+if __name__ == '__main__':
+    try:
+        c = get_config()
+        verify(c)
+        generate(c)
+        apply(c)
+    except ConfigError as e:
+        print(e)
+        exit(1)
diff --git a/src/migration-scripts/nat66/2-to-3 b/src/migration-scripts/nat66/2-to-3
new file mode 100755
index 000000000..f34f170b3
--- /dev/null
+++ b/src/migration-scripts/nat66/2-to-3
@@ -0,0 +1,61 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2023 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
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+from sys import argv,exit
+from vyos.configtree import ConfigTree
+
+if len(argv) < 2:
+    print("Must specify file name!")
+    exit(1)
+
+file_name = argv[1]
+
+with open(file_name, 'r') as f:
+    config_file = f.read()
+
+base = ['nat66', 'source']
+new_base = ['service', 'ndp-proxy', 'interface']
+
+config = ConfigTree(config_file)
+if not config.exists(base):
+    # Nothing to do
+    exit(0)
+
+for rule in config.list_nodes(base + ['rule']):
+    base_rule = base + ['rule', rule]
+
+    interface = None
+    if config.exists(base_rule + ['outbound-interface', 'name']):
+        interface = config.return_value(base_rule + ['outbound-interface', 'name'])
+    else:
+        continue
+
+    prefix_base = base_rule + ['source', 'prefix']
+    if config.exists(prefix_base):
+        prefix = config.return_value(prefix_base)
+        config.set(new_base + [interface, 'prefix', prefix, 'mode'], value='static')
+        config.set_tag(new_base)
+        config.set_tag(new_base + [interface, 'prefix'])
+
+        if config.exists(base_rule + ['disable']):
+            config.set(new_base + [interface, 'prefix', prefix, 'disable'])
+
+try:
+    with open(file_name, 'w') as f:
+        f.write(config.to_string())
+except OSError as e:
+    print("Failed to save the modified config: {}".format(e))
+    exit(1)