event-handler: T3083: Add simple event-handler

Event-handler allows executing a custom script when in logs it
detects configured "pattern"
A simple implemenation

set system event-handler first pattern '.*ssh2.*'
set system event-handler first script '/config/scripts/hello.sh'

1 files changed, 87 insertions, 0 deletions

diff --git a/src/conf_mode/system_event_handler.py b/src/conf_mode/system_event_handler.py
new file mode 100755
index 000000000..8efc816cb
--- /dev/null
+++ b/src/conf_mode/system_event_handler.py
@@ -0,0 +1,87 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2022 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 os
+
+from vyos.config import Config
+from vyos.configdict import node_changed
+from vyos.util import cmd
+from vyos.util import call
+from vyos.template import render
+from vyos import ConfigError
+from vyos import airbag
+airbag.enable()
+
+
+systemd_dir = '/etc/systemd/system'
+systemd_service = 'vyos-event-handler'
+service_path = f'{systemd_dir}/{systemd_service}.service'
+event_conf = '/run/vyos-event-handler.conf'
+
+
+def get_config(config=None):
+    if config:
+        conf = config
+    else:
+        conf = Config()
+
+    base = ['system', 'event-handler']
+    event = conf.get_config_dict(base, get_first_key=True, no_tag_node_value_mangle=True)
+
+    return event
+
+def verify(event):
+    # bail out early - looks like removal from running config
+    if not event:
+        return None
+
+    for name, event_config in event.items():
+        if 'pattern' not in event_config or 'script' not in event_config:
+            raise ConfigError(f'Event-handler "pattern and script" are mandatory!')
+
+def generate(event):
+    if not event:
+        return None
+
+    conf_json = json.dumps(event, indent = 4)
+    with open(event_conf, 'w') as f:
+        f.write(conf_json)
+
+    render(service_path, 'event-handler/systemd_event_handler_service.j2', event)
+
+    return None
+
+def apply(event):
+    call('systemctl daemon-reload')
+    if event:
+        call(f'systemctl restart {systemd_service}.service')
+    else:
+        call(f'systemctl stop {systemd_service}.service')
+
+        for f in [service_path, event_conf]:
+            if os.path.isfile(f):
+                os.unlink(f)
+
+if __name__ == '__main__':
+    try:
+        c = get_config()
+        verify(c)
+        generate(c)
+        apply(c)
+    except ConfigError as e:
+        print(e)
+        exit(1)