import threading import logging class LoggingContext(object): """Additional context for log formatting. Contexts are scoped within a "with" block. Contexts inherit the state of their parent contexts. Args: name (str): Name for the context for debugging. """ __slots__ = ["parent_context", "name", "__dict__"] thread_local = threading.local() class Sentinel(object): """Sentinel to represent the root context""" __slots__ = [] def copy_to(self, record): pass sentinel = Sentinel() def __init__(self, name=None): self.parent_context = None self.name = name def __str__(self): return "%s@%x" % (self.name, id(self)) @classmethod def current_context(cls): """Get the current logging context from thread local storage""" return getattr(cls.thread_local, "current_context", cls.sentinel) def __enter__(self): """Enters this logging context into thread local storage""" if self.parent_context is not None: raise Exception("Attempt to enter logging context multiple times") self.parent_context = self.current_context() self.thread_local.current_context = self return self def __exit__(self, type, value, traceback): """Restore the logging context in thread local storage to the state it was before this context was entered. Returns: None to avoid suppressing any exeptions that were thrown. """ if self.thread_local.current_context is not self: logging.error( "Current logging context %s is not the expected context %s", self.thread_local.current_context, self ) self.thread_local.current_context = self.parent_context self.parent_context = None def __getattr__(self, name): """Delegate member lookup to parent context""" return getattr(self.parent_context, name) def copy_to(self, record): """Copy fields from this context and its parents to the record""" if self.parent_context is not None: self.parent_context.copy_to(record) for key, value in self.__dict__.items(): setattr(record, key, value) class LoggingContextFilter(logging.Filter): """Logging filter that adds values from the current logging context to each record. Args: **defaults: Default values to avoid formatters complaining about missing fields """ def __init__(self, **defaults): self.defaults = defaults def filter(self, record): """Add each fields from the logging contexts to the record. Returns: True to include the record in the log output. """ context = LoggingContext.current_context() for key, value in self.defaults.items(): setattr(record, key, value) context.copy_to(record) return True class PreserveLoggingContext(object): """Captures the current logging context and restores it when the scope is exited. Used to restore the context after a function using @defer.inlineCallbacks is resumed by a callback from the reactor.""" __slots__ = ["current_context"] def __enter__(self): """Captures the current logging context""" self.current_context = LoggingContext.current_context() def __exit__(self, type, value, traceback): """Restores the current logging context""" LoggingContext.thread_local.current_context = self.current_context