From ffc6a0f36edda396a8421cf7a3c0feb88be20d0b Mon Sep 17 00:00:00 2001
From: Inphi <mlaw2501@gmail.com>
Date: Sun, 22 Oct 2023 11:37:56 -0400
Subject: [PATCH] event: fix Resubscribe deadlock when unsubscribing after
 inner sub ends (#28359)

A goroutine is used to manage the lifetime of subscriptions managed by
resubscriptions. When the subscription ends with no error, the resub
goroutine ends as well. However, the resub goroutine needs to live
long enough to read from the unsub channel. Otheriwse, an Unsubscribe
call deadlocks when writing to the unsub channel.

This is fixed by adding a buffer to the unsub channel.
---
 event/subscription.go      |  2 +-
 event/subscription_test.go | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/event/subscription.go b/event/subscription.go
index 6c6287471..07e059c6d 100644
--- a/event/subscription.go
+++ b/event/subscription.go
@@ -120,7 +120,7 @@ func ResubscribeErr(backoffMax time.Duration, fn ResubscribeErrFunc) Subscriptio
 		backoffMax: backoffMax,
 		fn:         fn,
 		err:        make(chan error),
-		unsub:      make(chan struct{}),
+		unsub:      make(chan struct{}, 1),
 	}
 	go s.loop()
 	return s
diff --git a/event/subscription_test.go b/event/subscription_test.go
index ba081705c..743d0bf67 100644
--- a/event/subscription_test.go
+++ b/event/subscription_test.go
@@ -154,3 +154,27 @@ func TestResubscribeWithErrorHandler(t *testing.T) {
 		t.Fatalf("unexpected subscription errors %v, want %v", subErrs, expectedSubErrs)
 	}
 }
+
+func TestResubscribeWithCompletedSubscription(t *testing.T) {
+	t.Parallel()
+
+	quitProducerAck := make(chan struct{})
+	quitProducer := make(chan struct{})
+
+	sub := ResubscribeErr(100*time.Millisecond, func(ctx context.Context, lastErr error) (Subscription, error) {
+		return NewSubscription(func(unsubscribed <-chan struct{}) error {
+			select {
+			case <-quitProducer:
+				quitProducerAck <- struct{}{}
+				return nil
+			case <-unsubscribed:
+				return nil
+			}
+		}), nil
+	})
+
+	// Ensure producer has started and exited before Unsubscribe
+	close(quitProducer)
+	<-quitProducerAck
+	sub.Unsubscribe()
+}