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'

4 files changed, 180 insertions, 0 deletions

diff --git a/data/templates/event-handler/systemd_event_handler_service.j2 b/data/templates/event-handler/systemd_event_handler_service.j2
new file mode 100644
index 000000000..da35a51c4
--- /dev/null
+++ b/data/templates/event-handler/systemd_event_handler_service.j2
@@ -0,0 +1,11 @@
+[Unit]
+Description=Event handler
+After=network.target
+
+[Service]
+Type=simple
+Restart=always
+ExecStart=/usr/bin/python3 /usr/libexec/vyos/vyos-event-handler.py --config /run/vyos-event-handler.conf
+
+[Install]
+WantedBy=multi-user.target
diff --git a/interface-definitions/system-event-handler.xml.in b/interface-definitions/system-event-handler.xml.in
new file mode 100644
index 000000000..f5d8afabd
--- /dev/null
+++ b/interface-definitions/system-event-handler.xml.in
@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<interfaceDefinition>
+  <node name="system">
+    <children>
+      <tagNode name="event-handler" owner="${vyos_conf_scripts_dir}/system_event_handler.py">
+        <properties>
+          <help>Event handler name</help>
+        </properties>
+        <children>
+          <leafNode name="pattern">
+            <properties>
+              <help>Match pattern (regex)</help>
+            </properties>
+          </leafNode>
+          <leafNode name="script">
+            <properties>
+              <help>Event handler script file</help>
+              <constraint>
+                <validator name="script"/>
+              </constraint>
+            </properties>
+          </leafNode>
+        </children>
+      </tagNode>
+    </children>
+  </node>
+</interfaceDefinition>
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)
diff --git a/src/helpers/vyos-event-handler.py b/src/helpers/vyos-event-handler.py
new file mode 100755
index 000000000..018a752f4
--- /dev/null
+++ b/src/helpers/vyos-event-handler.py
@@ -0,0 +1,55 @@
+#!/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 argparse
+import select
+import re
+import json
+
+from sys import argv
+from os import getpid
+from systemd import journal
+from vyos.util import call
+
+
+parser = argparse.ArgumentParser()
+parser.add_argument("-c", "--config", action="store", help="Path to even-handler configuration", required=True)
+
+args = parser.parse_args()
+config = args.config
+data = journal.Reader()
+data.seek_tail()
+data.get_previous()
+p = select.poll()
+p.register(data, data.get_events())
+my_pid = getpid()
+
+with open(config, 'r') as f:
+    config = json.load(f)
+
+
+if __name__ == '__main__':
+    while p.poll():
+        if data.process() != journal.APPEND:
+            continue
+        for entry in data:
+            message = entry['MESSAGE']
+            for name, event_config in config.items():
+                pattern = re.compile(rf'{event_config["pattern"]}')
+                script = event_config['script']
+                if message != "" and entry['_PID'] != my_pid and pattern.match(message):
+                    call(script)
+                    journal.send(f'Pattern found: {event_config["pattern"]}, script executed: {script}')