fix: handle context cancellations during instance refresh (#372)

Fixes #370

internal/cloudsql/instance.go

@@ -293,9 +293,17 @@ func (i *Instance) scheduleRefresh(d time.Duration) *refreshOperation {
 		res.md, res.tlsCfg, res.expiry, res.err = i.r.performRefresh(i.ctx, i.connName, i.key, i.RefreshCfg.UseIAMAuthN)
 		close(res.ready)
 
+		select {
+		case <-i.ctx.Done():
+			// instance has been closed, don't schedule anything
+			return
+		default:
+		}
+
 		// Once the refresh is complete, update "current" with working result and schedule a new refresh
 		i.resultGuard.Lock()
 		defer i.resultGuard.Unlock()
+
 		// if failed, scheduled the next refresh immediately
 		if res.err != nil {
 			i.next = i.scheduleRefresh(0)
@@ -308,14 +316,9 @@ func (i *Instance) scheduleRefresh(d time.Duration) *refreshOperation {
 			}
 			return
 		}
+
 		// Update the current results, and schedule the next refresh in the future
 		i.cur = res
-		select {
-		case <-i.ctx.Done():
-			// instance has been closed, don't schedule anything
-			return
-		default:
-		}
 		t := refreshDuration(time.Now(), i.cur.expiry)
 		i.next = i.scheduleRefresh(t)
 	})

internal/cloudsql/instance_test.go

@@ -303,3 +303,32 @@ func TestRefreshDuration(t *testing.T) {
 		})
 	}
 }
+
+func TestContextCancelled(t *testing.T) {
+	ctx := context.Background()
+
+	client, cleanup, err := mock.NewSQLAdminService(ctx)
+	if err != nil {
+		t.Fatalf("%s", err)
+	}
+	defer cleanup()
+
+	// Set up an instance and then close it immediately
+	im, err := NewInstance("my-proj:my-region:my-inst", client, RSAKey, 30, nil, "", RefreshCfg{})
+	if err != nil {
+		t.Fatalf("failed to initialize Instance: %v", err)
+	}
+	im.Close()
+
+	// grab the current value of next before scheduling another refresh
+	next := im.next
+
+	op := im.scheduleRefresh(time.Nanosecond)
+	<-op.ready
+
+	// if scheduleRefresh returns without scheduling another one,
+	// i.next should be untouched and remain the same pointer value
+	if im.next != next {
+		t.Fatalf("refresh did not return after a closed context. next pointer changed: want = %p, got = %p", next, im.next)
+	}
+}