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![Jorik Schellekens](/assets/img/avatar_default.png)
* Opentracing survival guide * Update decorator names in doc * Doc cleanup These are all alterations as a result of comments in #5703, it includes mostly typos and clarifications. The most interesting changes are: - Split developer and user docs into two sections - Add a high level description of OpenTracing * newsfile * Move contributer specific info to docstring. * Sample config. * Trailing whitespace. * Update 5703.misc * Apply suggestions from code review Mostly just rewording parts of the docs for clarity. Co-Authored-By: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
484 lines
15 KiB
Python
484 lines
15 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2019 The Matrix.org Foundation C.I.C.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.import opentracing
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# NOTE
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# This is a small wrapper around opentracing because opentracing is not currently
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# packaged downstream (specifically debian). Since opentracing instrumentation is
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# fairly invasive it was awkward to make it optional. As a result we opted to encapsulate
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# all opentracing state in these methods which effectively noop if opentracing is
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# not present. We should strongly consider encouraging the downstream distributers
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# to package opentracing and making opentracing a full dependency. In order to facilitate
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# this move the methods have work very similarly to opentracing's and it should only
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# be a matter of few regexes to move over to opentracing's access patterns proper.
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"""
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============================
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Using OpenTracing in Synapse
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============================
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Python-specific tracing concepts are at https://opentracing.io/guides/python/.
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Note that Synapse wraps OpenTracing in a small module (this one) in order to make the
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OpenTracing dependency optional. That means that the access patterns are
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different to those demonstrated in the OpenTracing guides. However, it is
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still useful to know, especially if OpenTracing is included as a full dependency
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in the future or if you are modifying this module.
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OpenTracing is encapsulated so that
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no span objects from OpenTracing are exposed in Synapse's code. This allows
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OpenTracing to be easily disabled in Synapse and thereby have OpenTracing as
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an optional dependency. This does however limit the number of modifiable spans
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at any point in the code to one. From here out references to `opentracing`
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in the code snippets refer to the Synapses module.
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Tracing
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-------
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In Synapse it is not possible to start a non-active span. Spans can be started
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using the ``start_active_span`` method. This returns a scope (see
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OpenTracing docs) which is a context manager that needs to be entered and
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exited. This is usually done by using ``with``.
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.. code-block:: python
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from synapse.logging.opentracing import start_active_span
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with start_active_span("operation name"):
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# Do something we want to tracer
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Forgetting to enter or exit a scope will result in some mysterious and grievous log
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context errors.
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At anytime where there is an active span ``opentracing.set_tag`` can be used to
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set a tag on the current active span.
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Tracing functions
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-----------------
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Functions can be easily traced using decorators. There is a decorator for
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'normal' function and for functions which are actually deferreds. The name of
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the function becomes the operation name for the span.
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.. code-block:: python
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from synapse.logging.opentracing import trace, trace_deferred
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# Start a span using 'normal_function' as the operation name
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@trace
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def normal_function(*args, **kwargs):
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# Does all kinds of cool and expected things
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return something_usual_and_useful
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# Start a span using 'deferred_function' as the operation name
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@trace_deferred
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@defer.inlineCallbacks
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def deferred_function(*args, **kwargs):
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# We start
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yield we_wait
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# we finish
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defer.returnValue(something_usual_and_useful)
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Operation names can be explicitly set for functions by using
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``trace_using_operation_name`` and
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``trace_deferred_using_operation_name``
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.. code-block:: python
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from synapse.logging.opentracing import (
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trace_using_operation_name,
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trace_deferred_using_operation_name
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)
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@trace_using_operation_name("A *much* better operation name")
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def normal_function(*args, **kwargs):
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# Does all kinds of cool and expected things
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return something_usual_and_useful
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@trace_deferred_using_operation_name("Another exciting operation name!")
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@defer.inlineCallbacks
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def deferred_function(*args, **kwargs):
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# We start
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yield we_wait
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# we finish
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defer.returnValue(something_usual_and_useful)
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Contexts and carriers
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---------------------
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There are a selection of wrappers for injecting and extracting contexts from
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carriers provided. Unfortunately OpenTracing's three context injection
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techniques are not adequate for our inject of OpenTracing span-contexts into
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Twisted's http headers, EDU contents and our database tables. Also note that
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the binary encoding format mandated by OpenTracing is not actually implemented
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by jaeger_client v4.0.0 - it will silently noop.
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Please refer to the end of ``logging/opentracing.py`` for the available
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injection and extraction methods.
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Homeserver whitelisting
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-----------------------
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Most of the whitelist checks are encapsulated in the modules's injection
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and extraction method but be aware that using custom carriers or crossing
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unchartered waters will require the enforcement of the whitelist.
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``logging/opentracing.py`` has a ``whitelisted_homeserver`` method which takes
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in a destination and compares it to the whitelist.
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=======
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Gotchas
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=======
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- Checking whitelists on span propagation
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- Inserting pii
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- Forgetting to enter or exit a scope
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- Span source: make sure that the span you expect to be active across a
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function call really will be that one. Does the current function have more
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than one caller? Will all of those calling functions have be in a context
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with an active span?
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"""
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import contextlib
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import logging
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import re
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from functools import wraps
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from twisted.internet import defer
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from synapse.config import ConfigError
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try:
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import opentracing
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except ImportError:
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opentracing = None
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try:
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from jaeger_client import Config as JaegerConfig
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from synapse.logging.scopecontextmanager import LogContextScopeManager
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except ImportError:
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JaegerConfig = None
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LogContextScopeManager = None
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logger = logging.getLogger(__name__)
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class _DumTagNames(object):
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"""wrapper of opentracings tags. We need to have them if we
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want to reference them without opentracing around. Clearly they
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should never actually show up in a trace. `set_tags` overwrites
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these with the correct ones."""
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INVALID_TAG = "invalid-tag"
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COMPONENT = INVALID_TAG
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DATABASE_INSTANCE = INVALID_TAG
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DATABASE_STATEMENT = INVALID_TAG
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DATABASE_TYPE = INVALID_TAG
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DATABASE_USER = INVALID_TAG
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ERROR = INVALID_TAG
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HTTP_METHOD = INVALID_TAG
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HTTP_STATUS_CODE = INVALID_TAG
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HTTP_URL = INVALID_TAG
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MESSAGE_BUS_DESTINATION = INVALID_TAG
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PEER_ADDRESS = INVALID_TAG
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PEER_HOSTNAME = INVALID_TAG
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PEER_HOST_IPV4 = INVALID_TAG
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PEER_HOST_IPV6 = INVALID_TAG
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PEER_PORT = INVALID_TAG
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PEER_SERVICE = INVALID_TAG
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SAMPLING_PRIORITY = INVALID_TAG
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SERVICE = INVALID_TAG
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SPAN_KIND = INVALID_TAG
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SPAN_KIND_CONSUMER = INVALID_TAG
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SPAN_KIND_PRODUCER = INVALID_TAG
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SPAN_KIND_RPC_CLIENT = INVALID_TAG
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SPAN_KIND_RPC_SERVER = INVALID_TAG
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def only_if_tracing(func):
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"""Executes the function only if we're tracing. Otherwise return.
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Assumes the function wrapped may return None"""
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@wraps(func)
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def _only_if_tracing_inner(*args, **kwargs):
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if opentracing:
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return func(*args, **kwargs)
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else:
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return
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return _only_if_tracing_inner
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# A regex which matches the server_names to expose traces for.
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# None means 'block everything'.
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_homeserver_whitelist = None
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tags = _DumTagNames
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def init_tracer(config):
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"""Set the whitelists and initialise the JaegerClient tracer
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Args:
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config (HomeserverConfig): The config used by the homeserver
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"""
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global opentracing
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if not config.opentracer_enabled:
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# We don't have a tracer
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opentracing = None
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return
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if not opentracing or not JaegerConfig:
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raise ConfigError(
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"The server has been configured to use opentracing but opentracing is not "
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"installed."
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)
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# Include the worker name
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name = config.worker_name if config.worker_name else "master"
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set_homeserver_whitelist(config.opentracer_whitelist)
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jaeger_config = JaegerConfig(
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config={"sampler": {"type": "const", "param": 1}, "logging": True},
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service_name="{} {}".format(config.server_name, name),
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scope_manager=LogContextScopeManager(config),
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)
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jaeger_config.initialize_tracer()
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# Set up tags to be opentracing's tags
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global tags
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tags = opentracing.tags
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@contextlib.contextmanager
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def _noop_context_manager(*args, **kwargs):
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"""Does absolutely nothing really well. Can be entered and exited arbitrarily.
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Good substitute for an opentracing scope."""
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yield
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# Could use kwargs but I want these to be explicit
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def start_active_span(
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operation_name,
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child_of=None,
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references=None,
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tags=None,
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start_time=None,
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ignore_active_span=False,
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finish_on_close=True,
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):
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"""Starts an active opentracing span. Note, the scope doesn't become active
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until it has been entered, however, the span starts from the time this
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message is called.
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Args:
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See opentracing.tracer
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Returns:
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scope (Scope) or noop_context_manager
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"""
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if opentracing is None:
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return _noop_context_manager()
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else:
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# We need to enter the scope here for the logcontext to become active
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return opentracing.tracer.start_active_span(
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operation_name,
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child_of=child_of,
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references=references,
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tags=tags,
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start_time=start_time,
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ignore_active_span=ignore_active_span,
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finish_on_close=finish_on_close,
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)
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@only_if_tracing
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def close_active_span():
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"""Closes the active span. This will close it's logcontext if the context
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was made for the span"""
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opentracing.tracer.scope_manager.active.__exit__(None, None, None)
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@only_if_tracing
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def set_tag(key, value):
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"""Set's a tag on the active span"""
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opentracing.tracer.active_span.set_tag(key, value)
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@only_if_tracing
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def log_kv(key_values, timestamp=None):
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"""Log to the active span"""
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opentracing.tracer.active_span.log_kv(key_values, timestamp)
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# Note: we don't have a get baggage items because we're trying to hide all
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# scope and span state from synapse. I think this method may also be useless
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# as a result
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@only_if_tracing
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def set_baggage_item(key, value):
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"""Attach baggage to the active span"""
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opentracing.tracer.active_span.set_baggage_item(key, value)
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@only_if_tracing
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def set_operation_name(operation_name):
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"""Sets the operation name of the active span"""
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opentracing.tracer.active_span.set_operation_name(operation_name)
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@only_if_tracing
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def set_homeserver_whitelist(homeserver_whitelist):
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"""Sets the whitelist
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Args:
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homeserver_whitelist (iterable of strings): regex of whitelisted homeservers
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"""
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global _homeserver_whitelist
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if homeserver_whitelist:
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# Makes a single regex which accepts all passed in regexes in the list
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_homeserver_whitelist = re.compile(
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"({})".format(")|(".join(homeserver_whitelist))
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)
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@only_if_tracing
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def whitelisted_homeserver(destination):
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"""Checks if a destination matches the whitelist
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Args:
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destination (String)"""
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if _homeserver_whitelist:
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return _homeserver_whitelist.match(destination)
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return False
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def start_active_span_from_context(
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headers,
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operation_name,
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references=None,
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tags=None,
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start_time=None,
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ignore_active_span=False,
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finish_on_close=True,
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):
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"""
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Extracts a span context from Twisted Headers.
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args:
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headers (twisted.web.http_headers.Headers)
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returns:
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span_context (opentracing.span.SpanContext)
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"""
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# Twisted encodes the values as lists whereas opentracing doesn't.
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# So, we take the first item in the list.
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# Also, twisted uses byte arrays while opentracing expects strings.
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if opentracing is None:
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return _noop_context_manager()
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header_dict = {k.decode(): v[0].decode() for k, v in headers.getAllRawHeaders()}
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context = opentracing.tracer.extract(opentracing.Format.HTTP_HEADERS, header_dict)
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return opentracing.tracer.start_active_span(
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operation_name,
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child_of=context,
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references=references,
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tags=tags,
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start_time=start_time,
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ignore_active_span=ignore_active_span,
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finish_on_close=finish_on_close,
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)
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@only_if_tracing
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def inject_active_span_twisted_headers(headers, destination):
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"""
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Injects a span context into twisted headers inplace
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Args:
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headers (twisted.web.http_headers.Headers)
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span (opentracing.Span)
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Returns:
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Inplace modification of headers
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Note:
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The headers set by the tracer are custom to the tracer implementation which
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should be unique enough that they don't interfere with any headers set by
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synapse or twisted. If we're still using jaeger these headers would be those
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here:
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https://github.com/jaegertracing/jaeger-client-python/blob/master/jaeger_client/constants.py
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"""
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if not whitelisted_homeserver(destination):
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return
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span = opentracing.tracer.active_span
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carrier = {}
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opentracing.tracer.inject(span, opentracing.Format.HTTP_HEADERS, carrier)
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for key, value in carrier.items():
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headers.addRawHeaders(key, value)
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@only_if_tracing
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def inject_active_span_byte_dict(headers, destination):
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"""
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Injects a span context into a dict where the headers are encoded as byte
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strings
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Args:
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headers (dict)
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span (opentracing.Span)
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Returns:
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Inplace modification of headers
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Note:
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The headers set by the tracer are custom to the tracer implementation which
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should be unique enough that they don't interfere with any headers set by
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synapse or twisted. If we're still using jaeger these headers would be those
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here:
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https://github.com/jaegertracing/jaeger-client-python/blob/master/jaeger_client/constants.py
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"""
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if not whitelisted_homeserver(destination):
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return
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span = opentracing.tracer.active_span
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carrier = {}
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opentracing.tracer.inject(span, opentracing.Format.HTTP_HEADERS, carrier)
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for key, value in carrier.items():
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headers[key.encode()] = [value.encode()]
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def trace_servlet(servlet_name, func):
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"""Decorator which traces a serlet. It starts a span with some servlet specific
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tags such as the servlet_name and request information"""
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@wraps(func)
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@defer.inlineCallbacks
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def _trace_servlet_inner(request, *args, **kwargs):
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with start_active_span_from_context(
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request.requestHeaders,
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"incoming-client-request",
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tags={
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"request_id": request.get_request_id(),
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tags.SPAN_KIND: tags.SPAN_KIND_RPC_SERVER,
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tags.HTTP_METHOD: request.get_method(),
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tags.HTTP_URL: request.get_redacted_uri(),
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tags.PEER_HOST_IPV6: request.getClientIP(),
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"servlet_name": servlet_name,
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},
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):
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result = yield defer.maybeDeferred(func, request, *args, **kwargs)
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defer.returnValue(result)
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return _trace_servlet_inner
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