From 14b8c0476f93ea2ed3134e75733e45aa0ab6f5a5 Mon Sep 17 00:00:00 2001
From: Sean Quah <8349537+squahtx@users.noreply.github.com>
Date: Tue, 14 Sep 2021 13:01:30 +0100
Subject: 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.
---
 changelog.d/10810.bugfix | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/10810.bugfix

(limited to 'changelog.d')

diff --git a/changelog.d/10810.bugfix b/changelog.d/10810.bugfix
new file mode 100644
index 0000000000..43e91f1f51
--- /dev/null
+++ b/changelog.d/10810.bugfix
@@ -0,0 +1 @@
+Fix a case where logging contexts would go missing when federation requests time out.
-- 
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