diff --git a/synapse/util/logcontext.py b/synapse/util/logcontext.py
new file mode 100644
index 0000000000..13176b05ce
--- /dev/null
+++ b/synapse/util/logcontext.py
@@ -0,0 +1,108 @@
+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
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