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# -*- test-case-name: twisted.logger.test.test_observer -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
Basic log observers.
"""
from typing import Callable, Optional
from zope.interface import implementer
from twisted.python.failure import Failure
from ._interfaces import ILogObserver, LogEvent
from ._logger import Logger
OBSERVER_DISABLED = (
"Temporarily disabling observer {observer} due to exception: {log_failure}"
)
@implementer(ILogObserver)
class LogPublisher:
"""
I{ILogObserver} that fans out events to other observers.
Keeps track of a set of L{ILogObserver} objects and forwards
events to each.
"""
def __init__(self, *observers: ILogObserver) -> None:
self._observers = list(observers)
self.log = Logger(observer=self)
def addObserver(self, observer: ILogObserver) -> None:
"""
Registers an observer with this publisher.
@param observer: An L{ILogObserver} to add.
"""
if not callable(observer):
raise TypeError(f"Observer is not callable: {observer!r}")
if observer not in self._observers:
self._observers.append(observer)
def removeObserver(self, observer: ILogObserver) -> None:
"""
Unregisters an observer with this publisher.
@param observer: An L{ILogObserver} to remove.
"""
try:
self._observers.remove(observer)
except ValueError:
pass
def __call__(self, event: LogEvent) -> None:
"""
Forward events to contained observers.
"""
if "log_trace" not in event:
trace: Optional[Callable[[ILogObserver], None]] = None
else:
def trace(observer: ILogObserver) -> None:
"""
Add tracing information for an observer.
@param observer: an observer being forwarded to
"""
event["log_trace"].append((self, observer))
brokenObservers = []
for observer in self._observers:
if trace is not None:
trace(observer)
try:
observer(event)
except Exception:
brokenObservers.append((observer, Failure()))
for brokenObserver, failure in brokenObservers:
errorLogger = self._errorLoggerForObserver(brokenObserver)
errorLogger.failure(
OBSERVER_DISABLED,
failure=failure,
observer=brokenObserver,
)
def _errorLoggerForObserver(self, observer: ILogObserver) -> Logger:
"""
Create an error-logger based on this logger, which does not contain the
given bad observer.
@param observer: The observer which previously had an error.
@return: A L{Logger} without the given observer.
"""
errorPublisher = LogPublisher(
*(obs for obs in self._observers if obs is not observer)
)
return Logger(observer=errorPublisher)
@implementer(ILogObserver)
def bitbucketLogObserver(event: LogEvent) -> None:
"""
I{ILogObserver} that does nothing with the events it sees.
"""
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