From 337c5d765b21e02aa0476d7a68502bb3febafe26 Mon Sep 17 00:00:00 2001
From: Ben Buzbee <bbuzbee@cloudflare.com>
Date: Wed, 6 Oct 2021 22:40:11 +0000
Subject: [PATCH] Log error if there are no event handlers registered

We see this error all the time
```
no handler registered for event
event.Message=, event.Annotations=, event.Timestamp=0001-01-01T00:00:00Z, event.TaskName=, event.AllocID=, event.TaskID=,
```

So we're handling an even with all default fields. I noted that this can
happen if only err is set as in

```
func (d *driverPluginClient) handleTaskEvents(reqCtx context.Context, ch chan *TaskEvent, stream proto.Driver_TaskEventsClient) {
	defer close(ch)
	for {
		ev, err := stream.Recv()
		if err != nil {
			if err != io.EOF {
				ch <- &TaskEvent{
					Err: grpcutils.HandleReqCtxGrpcErr(err, reqCtx, d.doneCtx),
				}
			}
```

In this case Err fails to be serialized by the logger, see this test

```

	ev := &drivers.TaskEvent{
		Err: fmt.Errorf("errz"),
	}
	i.logger.Warn("ben test", "event", ev)
	i.logger.Warn("ben test2", "event err str", ev.Err.Error())
	i.logger.Warn("ben test3", "event err", ev.Err)
	ev.Err = nil
	i.logger.Warn("ben test4", "nil error", ev.Err)

2021-10-06T22:37:56.736Z INFO nomad.stdout {"@level":"warn","@message":"ben test","@module":"client.driver_mgr","@timestamp":"2021-10-06T22:37:56.643900Z","driver":"mock_driver","event":{"TaskID":"","TaskName":"","AllocID":"","Timestamp":"0001-01-01T00:00:00Z","Message":"","Annotations":null,"Err":{}}}
2021-10-06T22:37:56.736Z INFO nomad.stdout {"@level":"warn","@message":"ben test2","@module":"client.driver_mgr","@timestamp":"2021-10-06T22:37:56.644226Z","driver":"mock_driver","event err str":"errz"}
2021-10-06T22:37:56.736Z INFO nomad.stdout {"@level":"warn","@message":"ben test3","@module":"client.driver_mgr","@timestamp":"2021-10-06T22:37:56.644240Z","driver":"mock_driver","event err":"errz"}
2021-10-06T22:37:56.736Z INFO nomad.stdout {"@level":"warn","@message":"ben test4","@module":"client.driver_mgr","@timestamp":"2021-10-06T22:37:56.644252Z","driver":"mock_driver","nil error":null}
```

Note in the first example err is set to an empty object and the error is
lost.

What we want is the last two examples which call out the err field
explicitly so we can see what it is in this case
---
 .changelog/11280.txt                           | 3 +++
 client/pluginmanager/drivermanager/instance.go | 3 ++-
 2 files changed, 5 insertions(+), 1 deletion(-)
 create mode 100644 .changelog/11280.txt

diff --git a/.changelog/11280.txt b/.changelog/11280.txt
new file mode 100644
index 000000000000..583f0232d969
--- /dev/null
+++ b/.changelog/11280.txt
@@ -0,0 +1,3 @@
+```release-note:improvement
+client/plugins/drivermanager: log if there is an error in a driver event
+```
\ No newline at end of file
diff --git a/client/pluginmanager/drivermanager/instance.go b/client/pluginmanager/drivermanager/instance.go
index 863fb649217a..9167a512affd 100644
--- a/client/pluginmanager/drivermanager/instance.go
+++ b/client/pluginmanager/drivermanager/instance.go
@@ -481,5 +481,6 @@ func (i *instanceManager) handleEvent(ev *drivers.TaskEvent) {
 		return
 	}
 
-	i.logger.Warn("no handler registered for event", "event", ev)
+	i.logger.Warn("no handler registered for event", "event", ev, "error", ev.Err)
+
 }