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

1 files changed, 120 insertions, 0 deletions

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)