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Prevent logging context going missing on federation request timeout (#10810)
In `MatrixFederationHttpClient._send_request()`, we make a HTTP request using an `Agent`, wrap that request in a timeout and await the resulting `Deferred`. On its own, the `Agent` performing the HTTP request correctly stashes and restores the logging context while waiting. The addition of the timeout introduces a path where the logging context is not restored when execution resumes. To address this, we wrap the timeout `Deferred` in a `make_deferred_yieldable()` to stash the logging context and restore it on completion of the `await`. However this is not sufficient, since by the time we construct the timeout `Deferred`, the `Agent` has already stashed and cleared the logging context when using `make_deferred_yieldable()` to produce its `Deferred` for the request. Hence, we wrap the `Agent` request in a `run_in_background()` to "fork" and preserve the logging context so that we can stash and restore it when `await`ing the timeout `Deferred`. This approach is similar to the one used with `defer.gatherResults`. Note that the code is still not fully correct. When a timeout occurs, the request remains running in the background (existing behavior which is nothing to do with the new call to `run_in_background`) and may re-start the logging context after it has finished.
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2 changed files with 14 additions and 4 deletions
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changelog.d/10810.bugfix
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changelog.d/10810.bugfix
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Fix a case where logging contexts would go missing when federation requests time out.
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@ -66,7 +66,7 @@ from synapse.http.client import (
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)
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from synapse.http.federation.matrix_federation_agent import MatrixFederationAgent
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from synapse.logging import opentracing
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from synapse.logging.context import make_deferred_yieldable
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from synapse.logging.context import make_deferred_yieldable, run_in_background
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from synapse.logging.opentracing import set_tag, start_active_span, tags
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from synapse.types import JsonDict
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from synapse.util import json_decoder
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@ -553,20 +553,29 @@ class MatrixFederationHttpClient:
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with Measure(self.clock, "outbound_request"):
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# we don't want all the fancy cookie and redirect handling
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# that treq.request gives: just use the raw Agent.
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request_deferred = self.agent.request(
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# To preserve the logging context, the timeout is treated
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# in a similar way to `defer.gatherResults`:
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# * Each logging context-preserving fork is wrapped in
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# `run_in_background`. In this case there is only one,
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# since the timeout fork is not logging-context aware.
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# * The `Deferred` that joins the forks back together is
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# wrapped in `make_deferred_yieldable` to restore the
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# logging context regardless of the path taken.
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request_deferred = run_in_background(
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self.agent.request,
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method_bytes,
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url_bytes,
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headers=Headers(headers_dict),
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bodyProducer=producer,
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)
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request_deferred = timeout_deferred(
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request_deferred,
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timeout=_sec_timeout,
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reactor=self.reactor,
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)
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response = await request_deferred
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response = await make_deferred_yieldable(request_deferred)
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except DNSLookupError as e:
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raise RequestSendFailed(e, can_retry=retry_on_dns_fail) from e
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except Exception as e:
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