T913: DHCP relay service XML/Python rewrite for IPv4

1 files changed, 158 insertions, 0 deletions

diff --git a/src/conf_mode/dhcp_relay.py b/src/conf_mode/dhcp_relay.py
new file mode 100755
index 000000000..f757491e0
--- /dev/null
+++ b/src/conf_mode/dhcp_relay.py
@@ -0,0 +1,158 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2018 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 sys
+import os
+import jinja2
+
+from vyos.config import Config
+from vyos import ConfigError
+
+config_file = r'/etc/default/isc-dhcp-relay'
+
+# Please be careful if you edit the template.
+config_tmpl = """
+### Autogenerated by dhcp_relay.py ###
+
+# Defaults for isc-dhcp-relay initscript
+# sourced by /etc/init.d/isc-dhcp-relay
+
+#
+# This is a POSIX shell fragment
+#
+
+# What servers should the DHCP relay forward requests to?
+SERVERS="{{ server | join(' ') }}"
+
+# On what interfaces should the DHCP relay (dhrelay) serve DHCP requests?
+INTERFACES="{{ interface | join(' ') }}"
+
+# Additional options that are passed to the DHCP relay daemon?
+OPTIONS="-4 -p {{ port }} {{ options | join(' ') }}"
+"""
+
+default_config_data = {
+    'interface': [],
+    'server': [],
+    'options': [],
+    'port': '67',
+    'hop_count': '10',
+    'relay_agent_packets': 'forward'
+}
+
+def get_config():
+    relay = default_config_data
+    conf = Config()
+    if not conf.exists('service dhcp-relay'):
+        return None
+    else:
+        conf.set_level('service dhcp-relay')
+
+    # Network interfaces to listen on
+    if conf.exists('interface'):
+        relay['interface'] = conf.return_values('interface')
+
+    # Servers equal to the address of the DHCP server(s)
+    if conf.exists('server'):
+        relay['server'] = conf.return_values('server')
+
+    conf.set_level('service dhcp-relay relay-options')
+
+    if conf.exists('hop-count'):
+        count = '-c ' + conf.return_value('hop-count')
+        relay['options'].append(count)
+
+    # Specify the maximum packet size to send to a DHCPv4/BOOTP server.
+    # This might be done to allow sufficient space for addition of relay agent
+    # options while still fitting into the Ethernet MTU size.
+    #
+    # Available in DHCPv4 mode only:
+    if conf.exists('max-size'):
+        size = '-A ' + conf.return_value('max-size')
+        relay['options'].append(size)
+
+    # Listen and transmit on port <xy>. This is mostly useful for debugging
+    # purposes. Default is port 67 for DHCPv4/BOOTP, or port 547 for DHCPv6.
+    if conf.exists('port'):
+        relay['port'] = conf.return_value('port')
+
+    # Control the handling of incoming DHCPv4 packets which already contain
+    # relay agent options. If such a packet does not have giaddr set in its
+    # header, the DHCP standard requires that the packet be discarded. However,
+    # if giaddr is set, the relay agent may handle the situation in four ways:
+    # It may append its own set of relay options to the packet, leaving the
+    # supplied option field intact; it may replace the existing agent option
+    # field; it may forward the packet unchanged; or, it may discard it.
+    #
+    # Available in DHCPv4 mode only:
+    if conf.exists('relay-agents-packets'):
+        pkt = '-m ' + conf.return_value('relay-agents-packets')
+        relay['options'].append(pkt)
+
+    return relay
+
+def verify(relay):
+    # bail out early - looks like removal from running config
+    if relay is None:
+        return None
+
+    if len(relay['interface']) < 2:
+        # We can only issue a warning otherwise old configurations might break
+        print('WARNING: At least two interfaces are required for DHCP relay\n' \
+              'to work\n')
+
+    if 'lo' in relay['interface']:
+        raise ConfigError('DHCP relay does not support the loopback interface.')
+
+    if len(relay['server']) == 0:
+        raise ConfigError('No DHCP relay server(s) configured.\n' \
+                          'At least one DHCP relay server required.')
+
+    return None
+
+def generate(relay):
+    # bail out early - looks like removal from running config
+    if relay is None:
+        return None
+
+    tmpl = jinja2.Template(config_tmpl)
+    config_text = tmpl.render(relay)
+    with open(config_file, 'w') as f:
+        f.write(config_text)
+
+    return None
+
+def apply(relay):
+    if relay is not None:
+        os.system('sudo systemctl restart isc-dhcp-relay.service')
+    else:
+        # DHCP relay support is removed in the commit
+        os.system('sudo systemctl stop isc-dhcp-relay.service')
+        os.unlink(config_file)
+
+    return None
+
+if __name__ == '__main__':
+    try:
+        c = get_config()
+        verify(c)
+        generate(c)
+        apply(c)
+    except ConfigError as e:
+        print(e)
+        sys.exit(1)