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# Copyright 2014, 2015 OpenMarket Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from twisted.internet import defer
import threading
import logging
logger = logging.getLogger(__name__)
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 __str__(self):
return "sentinel"
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:
if self.thread_local.current_context is self.sentinel:
logger.debug("Expected logging context %s has been lost", self)
else:
logger.warn(
"Current logging context %s is not 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()
LoggingContext.thread_local.current_context = LoggingContext.sentinel
def __exit__(self, type, value, traceback):
"""Restores the current logging context"""
LoggingContext.thread_local.current_context = self.current_context
if self.current_context is not LoggingContext.sentinel:
if self.current_context.parent_context is None:
logger.warn(
"Restoring dead context: %s",
self.current_context,
)
class _PreservingContextDeferred(defer.Deferred):
"""A deferred that ensures that all callbacks and errbacks are called with
the given logging context.
"""
def __init__(self, context):
self._log_context = context
defer.Deferred.__init__(self)
def addCallbacks(self, callback, errback=None,
callbackArgs=None, callbackKeywords=None,
errbackArgs=None, errbackKeywords=None):
callback = self._wrap_callback(callback)
errback = self._wrap_callback(errback)
return defer.Deferred.addCallbacks(
self, callback,
errback=errback,
callbackArgs=callbackArgs,
callbackKeywords=callbackKeywords,
errbackArgs=errbackArgs,
errbackKeywords=errbackKeywords,
)
def _wrap_callback(self, f):
def g(res, *args, **kwargs):
with PreserveLoggingContext():
LoggingContext.thread_local.current_context = self._log_context
res = f(res, *args, **kwargs)
return res
return g
def preserve_context_over_fn(fn, *args, **kwargs):
"""Takes a function and invokes it with the given arguments, but removes
and restores the current logging context while doing so.
If the result is a deferred, call preserve_context_over_deferred before
returning it.
"""
with PreserveLoggingContext():
res = fn(*args, **kwargs)
if isinstance(res, defer.Deferred):
return preserve_context_over_deferred(res)
else:
return res
def preserve_context_over_deferred(deferred):
"""Given a deferred wrap it such that any callbacks added later to it will
be invoked with the current context.
"""
current_context = LoggingContext.current_context()
d = _PreservingContextDeferred(current_context)
deferred.chainDeferred(d)
return d
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