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#!/opt/cloudlinux/venv/bin/python3 -bb
# coding=utf-8
#
# Copyright © Cloud Linux GmbH & Cloud Linux Software, Inc 2010-2019 All Rights Reserved
#
# Licensed under CLOUD LINUX LICENSE AGREEMENT
# http://cloudlinux.com/docs/LICENSE.TXT
import syslog
import types # NOQA
from traceback import format_exc
class Event:
"""
Event is an object that can have several listeners.
Register new handler using '.register()' method.
When you call '.throw_event(*a, **kw)' , class notifies all registered listeners.
This class is logging his actions to syslog.
Exceptions happened in hooks are logged as warnings, all
other messages have debug level. For debug purposes you can
manually change syslog level in /etc/rsyslog.conf file.
"""
# messages with level 'DEBUG' needed only for developers
# so hide them by default in order not to confuse clients
WRITE_DEBUG_TO_SYSLOG = False
def __init__(self):
self._listeners = set()
@classmethod
def _log_message(cls, level, message):
# type: (int, str) -> None
if level == syslog.LOG_DEBUG and not cls.WRITE_DEBUG_TO_SYSLOG:
return
syslog.syslog(level, message)
# noinspection PyBroadException
def _run_or_log_exception(self, func, *args, **kwargs):
# type: (types.FunctionType, list, dict) -> None
"""Run callable object func and forward exceptions to syslog"""
try:
func(*args, **kwargs)
except BaseException:
footprint = self._get_function_footprint(func)
message = (
"WARNING: An error occurred while notifying handler "
f"{footprint} with ({args}, {kwargs}). Following error raised: {format_exc()}."
"Please, contact CloudLinux support if it happens again."
)
self._log_message(syslog.LOG_WARNING, message)
else:
message = f"DEBUG: Handler {func} notified with params: ({args}, {kwargs})"
self._log_message(syslog.LOG_DEBUG, message)
@staticmethod
def _get_function_footprint(func):
# type: (types.FunctionType) -> str
return func.__name__ + ':' + func.__module__
# TODO: add arguments match validation here
def register(self, func):
# type: (types.FunctionType) -> types.FunctionType
self._listeners.add(func)
self._log_message(
syslog.LOG_DEBUG,
f"DEBUG: Registered new handler {self._get_function_footprint(func)}."
)
# return func here in order to be able to use multiple decorators at once
# otherwise, decorated function becomes 'None'
return func
def unregister(self, func):
# type: (types.FunctionType) -> None
if func in self._listeners:
self._listeners.remove(func)
self._log_message(
syslog.LOG_DEBUG,
f"DEBUG: Unregister handler {self._get_function_footprint(func)}."
)
def throw_event(self, *args, **kwargs):
# type: (list, dict) -> None
for func in self._listeners:
self._run_or_log_exception(func, *args, **kwargs)