From b9dda0ff224e4c3c332e5aefd761834f09c96433 Mon Sep 17 00:00:00 2001
From: Eric Eastwood <erice@element.io>
Date: Thu, 13 Nov 2025 09:57:56 -0600
Subject: [PATCH] Restore printing `sentinel` for `log_record.request` (#19172)

This was unintentionally changed in
https://github.com/element-hq/synapse/pull/19068.

There is no real bug here. Without this PR, we just printed an empty
string for the `sentinel` logcontext whereas the prior art behavior was
to print `sentinel` which this PR restores.

Found while staring at the logs in
https://github.com/element-hq/synapse/issues/19165


### Reproduction strategy

1. Configure Synapse with
[logging](https://github.com/element-hq/synapse/blob/df802882bb2ec7d52d5c064c20531fe5a5b263b1/docs/sample_log_config.yaml)
1. Start Synapse: `poetry run synapse_homeserver --config-path
homeserver.yaml`
1. Notice the `asyncio - 64 - DEBUG - - Using selector: EpollSelector`
log line (notice empty string `- -`)
1. With this PR, the log line will be `asyncio - 64 - DEBUG - sentinel -
Using selector: EpollSelector` (notice `sentinel`)
---
 changelog.d/19172.misc     |  1 +
 synapse/logging/context.py | 29 +++++++++++++++++------------
 2 files changed, 18 insertions(+), 12 deletions(-)
 create mode 100644 changelog.d/19172.misc

diff --git a/changelog.d/19172.misc b/changelog.d/19172.misc
new file mode 100644
index 000000000..4792f8b56
--- /dev/null
+++ b/changelog.d/19172.misc
@@ -0,0 +1 @@
+Restore printing `sentinel` for the log record `request` when no logcontext is active.
diff --git a/synapse/logging/context.py b/synapse/logging/context.py
index 2410d9572..b6535be38 100644
--- a/synapse/logging/context.py
+++ b/synapse/logging/context.py
@@ -619,19 +619,24 @@ class LoggingContextFilter(logging.Filter):
             True to include the record in the log output.
         """
         context = current_context()
-        record.request = self._default_request
-
-        # Avoid overwriting an existing `server_name` on the record. This is running in
-        # the context of a global log record filter so there may be 3rd-party code that
-        # adds their own `server_name` and we don't want to interfere with that
-        # (clobber).
-        if not hasattr(record, "server_name"):
-            record.server_name = "unknown_server_from_no_logcontext"
-
-        # context should never be None, but if it somehow ends up being, then
-        # we end up in a death spiral of infinite loops, so let's check, for
+        # type-ignore: `context` should never be `None`, but if it somehow ends up
+        # being, then we end up in a death spiral of infinite loops, so let's check, for
         # robustness' sake.
-        if context is not None:
+        #
+        # Add some default values to avoid log formatting errors.
+        if context is None:
+            record.request = self._default_request  # type: ignore[unreachable]
+
+            # Avoid overwriting an existing `server_name` on the record. This is running in
+            # the context of a global log record filter so there may be 3rd-party code that
+            # adds their own `server_name` and we don't want to interfere with that
+            # (clobber).
+            if not hasattr(record, "server_name"):
+                record.server_name = "unknown_server_from_no_logcontext"
+
+        # Otherwise, in the normal, expected case, fill in the log record attributes
+        # from the logcontext.
+        else:
 
             def safe_set(attr: str, value: Any) -> None:
                 """