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
      }
  }

1 files changed, 91 insertions, 0 deletions

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)