From 838f19b9ff900d3d9ded7b121c64ab182532a698 Mon Sep 17 00:00:00 2001
From: Shaunak Kashyap <ycombinator@gmail.com>
Date: Wed, 4 Oct 2023 17:48:23 -0700
Subject: [PATCH] Immediately notify observer when registered

---
 .../application/upgrade/details/details.go    | 19 ++++++++++++-------
 .../upgrade/details/details_test.go           |  4 +++-
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/internal/pkg/agent/application/upgrade/details/details.go b/internal/pkg/agent/application/upgrade/details/details.go
index e31f570b44f..7a09763b786 100644
--- a/internal/pkg/agent/application/upgrade/details/details.go
+++ b/internal/pkg/agent/application/upgrade/details/details.go
@@ -62,13 +62,14 @@ func (d *Details) Fail(err error) {
 }
 
 // RegisterObserver allows an interested consumer of Details to register
-// themselves as an Observer. When NotifyObservers is called, all registered
-// observers are sent the current upgrade details.
+// themselves as an Observer. The registered observer is immediately notified
+// of the current upgrade details.
 func (d *Details) RegisterObserver(observer Observer) {
 	d.mu.Lock()
 	defer d.mu.Unlock()
 
 	d.observers = append(d.observers, observer)
+	d.notifyObserver(observer)
 }
 
 // NotifyObservers sends the current upgrade details to all registered
@@ -81,10 +82,14 @@ func (d *Details) NotifyObservers() {
 
 func (d *Details) notifyObservers() {
 	for _, observer := range d.observers {
-		if d.State == StateCompleted {
-			observer(nil)
-		} else {
-			observer(d)
-		}
+		d.notifyObserver(observer)
+	}
+}
+
+func (d *Details) notifyObserver(observer Observer) {
+	if d.State == StateCompleted {
+		observer(nil)
+	} else {
+		observer(d)
 	}
 }
diff --git a/internal/pkg/agent/application/upgrade/details/details_test.go b/internal/pkg/agent/application/upgrade/details/details_test.go
index 4c45e062070..92fd0a47eaf 100644
--- a/internal/pkg/agent/application/upgrade/details/details_test.go
+++ b/internal/pkg/agent/application/upgrade/details/details_test.go
@@ -44,9 +44,11 @@ func TestDetailsObserver(t *testing.T) {
 
 	var observedDetails *Details
 	obs := func(updatedDetails *Details) { observedDetails = updatedDetails }
+
 	det.RegisterObserver(obs)
-	require.Nil(t, observedDetails)
 	require.Len(t, det.observers, 1)
+	require.NotNil(t, observedDetails)
+	require.Equal(t, StateRequested, observedDetails.State)
 
 	det.SetState(StateDownloading)
 	require.Equal(t, StateDownloading, det.State)