T3083: Add service event-handler

Event-handler allows executing a custom script when detects
some configured "pattern regex"

  set service event-handler event first filter pattern '.*ssh2.*'
  set service event-handler event first script arguments '192.0.2.5'
  set service event-handler event first script environment interface value 'eth0'
  set service event-handler event first script path '/config/scripts/hello.sh'

It is the backport from 1.4

1 files changed, 93 insertions, 0 deletions

diff --git a/src/conf_mode/service_event_handler.py b/src/conf_mode/service_event_handler.py
new file mode 100755
index 000000000..23464120b
--- /dev/null
+++ b/src/conf_mode/service_event_handler.py
@@ -0,0 +1,93 @@
+#!/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
+import json
+from pathlib import Path
+
+from vyos.config import Config
+from vyos.util import call, dict_search
+from vyos import ConfigError
+from vyos import airbag
+
+airbag.enable()
+
+service_name = 'vyos-event-handler'
+service_conf = Path(f'/run/{service_name}.conf')
+
+
+def get_config(config=None):
+    if config:
+        conf = config
+    else:
+        conf = Config()
+
+    base = ['service', 'event-handler', 'event']
+    config = conf.get_config_dict(base,
+                                  get_first_key=True,
+                                  no_tag_node_value_mangle=True)
+
+    return config
+
+
+def verify(config):
+    # bail out early - looks like removal from running config
+    if not config:
+        return None
+
+    for name, event_config in config.items():
+        if not dict_search('filter.pattern', event_config) or not dict_search(
+                'script.path', event_config):
+            raise ConfigError(
+                'Event-handler: both pattern and script path items are mandatory'
+            )
+
+        if dict_search('script.environment.message', event_config):
+            raise ConfigError(
+                'Event-handler: "message" environment variable is reserved for log message text'
+            )
+
+
+def generate(config):
+    if not config:
+        # Remove old config and return
+        if os.path.isfile(service_conf):
+            os.unlink(service_conf)
+        return None
+
+    # Write configuration file
+    conf_json = json.dumps(config, indent=4)
+    service_conf.write_text(conf_json)
+
+    return None
+
+
+def apply(config):
+    if config:
+        call(f'systemctl restart {service_name}.service')
+    else:
+        call(f'systemctl stop {service_name}.service')
+
+
+if __name__ == '__main__':
+    try:
+        c = get_config()
+        verify(c)
+        generate(c)
+        apply(c)
+    except ConfigError as e:
+        print(e)
+        exit(1)