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137 lines
5 KiB
Python
137 lines
5 KiB
Python
"""Registers functions to be called if an exception or signal occurs."""
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import functools
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import logging
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import os
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import signal
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import traceback
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from certbot import errors
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logger = logging.getLogger(__name__)
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# _SIGNALS stores the signals that will be handled by the ErrorHandler. These
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# signals were chosen as their default handler terminates the process and could
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# potentially occur from inside Python. Signals such as SIGILL were not
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# included as they could be a sign of something devious and we should terminate
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# immediately.
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_SIGNALS = [signal.SIGTERM]
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if os.name != "nt":
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for signal_code in [signal.SIGHUP, signal.SIGQUIT,
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signal.SIGXCPU, signal.SIGXFSZ]:
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# Adding only those signals that their default action is not Ignore.
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# This is platform-dependent, so we check it dynamically.
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if signal.getsignal(signal_code) != signal.SIG_IGN:
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_SIGNALS.append(signal_code)
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class ErrorHandler(object):
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"""Context manager for running code that must be cleaned up on failure.
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The context manager allows you to register functions that will be called
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when an exception (excluding SystemExit) or signal is encountered. Usage:
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handler = ErrorHandler(cleanup1_func, *cleanup1_args, **cleanup1_kwargs)
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handler.register(cleanup2_func, *cleanup2_args, **cleanup2_kwargs)
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with handler:
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do_something()
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Or for one cleanup function:
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with ErrorHandler(func, args, kwargs):
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do_something()
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If an exception is raised out of do_something, the cleanup functions will
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be called in last in first out order. Then the exception is raised.
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Similarly, if a signal is encountered, the cleanup functions are called
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followed by the previously received signal handler.
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Each registered cleanup function is called exactly once. If a registered
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function raises an exception, it is logged and the next function is called.
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Signals received while the registered functions are executing are
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deferred until they finish.
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"""
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def __init__(self, func=None, *args, **kwargs):
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self.body_executed = False
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self.funcs = []
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self.prev_handlers = {}
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self.received_signals = []
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if func is not None:
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self.register(func, *args, **kwargs)
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def __enter__(self):
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self.body_executed = False
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self._set_signal_handlers()
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def __exit__(self, exec_type, exec_value, trace):
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self.body_executed = True
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retval = False
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# SystemExit is ignored to properly handle forks that don't exec
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if exec_type in (None, SystemExit):
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return retval
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elif exec_type is errors.SignalExit:
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logger.debug("Encountered signals: %s", self.received_signals)
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retval = True
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else:
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logger.debug("Encountered exception:\n%s", "".join(
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traceback.format_exception(exec_type, exec_value, trace)))
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self._call_registered()
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self._reset_signal_handlers()
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self._call_signals()
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return retval
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def register(self, func, *args, **kwargs):
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"""Sets func to be called with *args and **kwargs during cleanup
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:param function func: function to be called in case of an error
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"""
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self.funcs.append(functools.partial(func, *args, **kwargs))
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def _call_registered(self):
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"""Calls all registered functions"""
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logger.debug("Calling registered functions")
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while self.funcs:
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try:
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self.funcs[-1]()
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except Exception as error: # pylint: disable=broad-except
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logger.error("Encountered exception during recovery")
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logger.exception(error)
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self.funcs.pop()
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def _set_signal_handlers(self):
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"""Sets signal handlers for signals in _SIGNALS."""
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for signum in _SIGNALS:
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prev_handler = signal.getsignal(signum)
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# If prev_handler is None, the handler was set outside of Python
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if prev_handler is not None:
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self.prev_handlers[signum] = prev_handler
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signal.signal(signum, self._signal_handler)
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def _reset_signal_handlers(self):
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"""Resets signal handlers for signals in _SIGNALS."""
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for signum in self.prev_handlers:
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signal.signal(signum, self.prev_handlers[signum])
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self.prev_handlers.clear()
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def _signal_handler(self, signum, unused_frame):
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"""Replacement function for handling recieved signals.
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Store the recieved signal. If we are executing the code block in
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the body of the context manager, stop by raising signal exit.
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:param int signum: number of current signal
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"""
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self.received_signals.append(signum)
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if not self.body_executed:
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raise errors.SignalExit
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def _call_signals(self):
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"""Finally call the deferred signals."""
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for signum in self.received_signals:
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logger.debug("Calling signal %s", signum)
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os.kill(os.getpid(), signum)
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