event-handler: T3083: Optimized event-handler

* Removed dynamic generating for systemd unit
* Optimized configuration file deleting process
* Added exceptions handlers to event-handler script to protect service
from most obvious potential troubles
* Improved logging
* Moved pattern compilation outside a messages loop to avoid extra operations
* Added signal handlers for proper systemd integration

5 files changed, 158 insertions, 96 deletions

diff --git a/data/templates/event-handler/systemd_event_handler_service.j2 b/data/templates/event-handler/systemd_event_handler_service.j2
deleted file mode 100644
index da35a51c4..000000000
--- a/data/templates/event-handler/systemd_event_handler_service.j2
+++ /dev/null
@@ -1,11 +0,0 @@
-[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/src/conf_mode/system_event_handler.py b/src/conf_mode/system_event_handler.py
index 8efc816cb..9f91e99fc 100755
--- a/src/conf_mode/system_event_handler.py
+++ b/src/conf_mode/system_event_handler.py
@@ -15,22 +15,17 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 import json
-import os
+from pathlib import Path
 
 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()
 
+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'
+service_name = 'vyos-event-handler'
+service_conf = Path(f'/run/{service_name}.conf')
 
 
 def get_config(config=None):
@@ -40,41 +35,43 @@ def get_config(config=None):
         conf = Config()
 
     base = ['system', 'event-handler']
-    event = conf.get_config_dict(base, get_first_key=True, no_tag_node_value_mangle=True)
+    config = conf.get_config_dict(base,
+                                  get_first_key=True,
+                                  no_tag_node_value_mangle=True)
 
-    return event
+    return config
 
-def verify(event):
+
+def verify(config):
     # bail out early - looks like removal from running config
-    if not event:
+    if not config:
         return None
 
-    for name, event_config in event.items():
+    for name, event_config in config.items():
         if 'pattern' not in event_config or 'script' not in event_config:
-            raise ConfigError(f'Event-handler "pattern and script" are mandatory!')
+            raise ConfigError(
+                'Event-handler: both pattern and script items 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)
+def generate(config):
+    if not config:
+        # Remove old config and return
+        service_conf.unlink(missing_ok=True)
+        return None
 
-    render(service_path, 'event-handler/systemd_event_handler_service.j2', event)
+    # Write configuration file
+    conf_json = json.dumps(config, indent=4)
+    service_conf.write_text(conf_json)
 
     return None
 
-def apply(event):
-    call('systemctl daemon-reload')
-    if event:
-        call(f'systemctl restart {systemd_service}.service')
+
+def apply(config):
+    if config:
+        call(f'systemctl restart {service_name}.service')
     else:
-        call(f'systemctl stop {systemd_service}.service')
+        call(f'systemctl stop {service_name}.service')
 
-        for f in [service_path, event_conf]:
-            if os.path.isfile(f):
-                os.unlink(f)
 
 if __name__ == '__main__':
     try:
diff --git a/src/helpers/vyos-event-handler.py b/src/helpers/vyos-event-handler.py
deleted file mode 100755
index 018a752f4..000000000
--- a/src/helpers/vyos-event-handler.py
+++ /dev/null
@@ -1,55 +0,0 @@
-#!/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}')
diff --git a/src/system/vyos-event-handler.py b/src/system/vyos-event-handler.py
new file mode 100755
index 000000000..f4b793dbe
--- /dev/null
+++ b/src/system/vyos-event-handler.py
@@ -0,0 +1,120 @@
+#!/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 os import getpid
+from pathlib import Path
+from signal import signal, SIGTERM, SIGINT
+from systemd import journal
+from sys import exit
+from vyos.util import call
+
+# Identify this script
+my_pid = getpid()
+my_name = Path(__file__).stem
+
+
+# handle termination signal
+def handle_signal(signal_type, frame):
+    if signal_type == SIGTERM:
+        journal.send('Received SIGTERM signal, stopping normally',
+                     SYSLOG_IDENTIFIER=my_name)
+    if signal_type == SIGINT:
+        journal.send('Received SIGINT signal, stopping normally',
+                     SYSLOG_IDENTIFIER=my_name)
+    exit(0)
+
+
+# Execute script safely
+def script_run(pattern: str, script_path: str) -> None:
+    try:
+        call(script_path)
+        journal.send(
+            f'Pattern found: "{pattern}", script executed: "{script_path}"',
+            SYSLOG_IDENTIFIER=my_name)
+    except Exception as err:
+        journal.send(
+            f'Pattern found: "{pattern}", failed to execute script "{script_path}": {err}',
+            SYSLOG_IDENTIFIER=my_name)
+
+
+# iterate trough regexp items
+def analyze_message(message: str, regex_patterns: dict) -> None:
+    for pattern_compiled, pattern_config in regex_patterns.items():
+        if pattern_compiled.match(message):
+            script_run(pattern_config['pattern_raw'],
+                       pattern_config['pattern_script'])
+
+
+if __name__ == '__main__':
+    # Parse command arguments and get config
+    parser = argparse.ArgumentParser()
+    parser.add_argument('-c',
+                        '--config',
+                        action='store',
+                        help='Path to even-handler configuration',
+                        required=True,
+                        type=Path)
+
+    args = parser.parse_args()
+    try:
+        config_path = Path(args.config)
+        config = json.loads(config_path.read_text())
+    except Exception as err:
+        print(
+            f'Configuration file "{config_path}" does not exist or malformed: {err}'
+        )
+        exit(1)
+
+    # Prepare for proper exitting
+    signal(SIGTERM, handle_signal)
+    signal(SIGINT, handle_signal)
+
+    # Set up journal connection
+    data = journal.Reader()
+    data.seek_tail()
+    data.get_previous()
+    p = select.poll()
+    p.register(data, data.get_events())
+
+    # Prepare compiled regex objects
+    patterns = {}
+    for name, event_config in config.items():
+        pattern_raw = f'{event_config["pattern"]}'
+        pattern_compiled = re.compile(rf'{event_config["pattern"]}')
+        pattern_config = {
+            pattern_compiled: {
+                'pattern_raw': pattern_raw,
+                'pattern_script': event_config['script']
+            }
+        }
+        patterns.update(pattern_config)
+
+    journal.send(f'Started with configuration: {config}',
+                 SYSLOG_IDENTIFIER=my_name)
+
+    while p.poll():
+        if data.process() != journal.APPEND:
+            continue
+        for entry in data:
+            message = entry['MESSAGE']
+            pid = entry['_PID']
+            # Skip empty messages and messages from this process
+            if message and pid != my_pid:
+                analyze_message(message, patterns)
diff --git a/src/systemd/vyos-event-handler.service b/src/systemd/vyos-event-handler.service
new file mode 100644
index 000000000..6afe4f95b
--- /dev/null
+++ b/src/systemd/vyos-event-handler.service
@@ -0,0 +1,11 @@
+[Unit]
+Description=VyOS event handler
+After=network.target vyos-router.service
+
+[Service]
+Type=simple
+Restart=always
+ExecStart=/usr/bin/python3 /usr/libexec/vyos/system/vyos-event-handler.py --config /run/vyos-event-handler.conf
+
+[Install]
+WantedBy=multi-user.target