T6350: CGNAT add op-mode to show allocation

Add op-mode command `show nat cgnat allocation` to get CGNAT
allocations (internal address, external address, port-range)

data/op-mode-standardized.json

@@ -3,6 +3,7 @@
 "bgp.py",
 "bonding.py",
 "bridge.py",
+"cgnat.py",
 "config_mgmt.py",
 "conntrack.py",
 "container.py",

op-mode-definitions/nat.xml.in

@@ -7,6 +7,19 @@
           <help>Show IPv4 Network Address Translation (NAT) information</help>
         </properties>
         <children>
+          <node name="cgnat">
+            <properties>
+              <help>Show Carrier-Grade Network Address Translation (CGNAT)</help>
+            </properties>
+            <children>
+              <node name="allocation">
+                <properties>
+                  <help>Show allocated CGNAT parameters</help>
+                </properties>
+                <command>sudo ${vyos_op_scripts_dir}/cgnat.py show_allocation</command>
+              </node>
+            </children>
+          </node>
           <node name="source">
             <properties>
               <help>Show source IPv4 to IPv4 Network Address Translation (NAT) information</help>

src/op_mode/cgnat.py

@@ -0,0 +1,75 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2024 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 json
+import sys
+import typing
+
+from tabulate import tabulate
+
+import vyos.opmode
+
+from vyos.configquery import ConfigTreeQuery
+from vyos.utils.process import cmd
+
+CGNAT_TABLE = 'cgnat'
+
+
+def _get_raw_data():
+    """ Get CGNAT dictionary
+    """
+    cmd_output = cmd(f'nft --json list table ip {CGNAT_TABLE}')
+    data = json.loads(cmd_output)
+    return data
+
+
+def _get_formatted_output(data):
+    elements = data['nftables'][2]['map']['elem']
+    allocations = []
+    for elem in elements:
+        internal = elem[0]  # internal
+        external = elem[1]['concat'][0]  # external
+        start_port = elem[1]['concat'][1]['range'][0]
+        end_port = elem[1]['concat'][1]['range'][1]
+        port_range = f'{start_port}-{end_port}'
+        allocations.append((internal, external, port_range))
+
+    headers = ['Internal IP', 'External IP', 'Port range']
+    output = tabulate(allocations, headers, numalign="left")
+    return output
+
+
+def show_allocation(raw: bool):
+    config = ConfigTreeQuery()
+    if not config.exists('nat cgnat'):
+        raise vyos.opmode.UnconfiguredSubsystem('CGNAT is not configured')
+
+    if raw:
+        return _get_raw_data()
+
+    else:
+        raw_data = _get_raw_data()
+        return _get_formatted_output(raw_data)
+
+
+if __name__ == '__main__':
+    try:
+        res = vyos.opmode.run(sys.modules[__name__])
+        if res:
+            print(res)
+    except (ValueError, vyos.opmode.Error) as e:
+        print(e)
+        sys.exit(1)