CloseNotifier: return pointer instead of value

pkg/middlewares/metrics/metrics_test.go

@@ -7,6 +7,7 @@ import (
 	"testing"
 
 	"github.com/go-kit/kit/metrics"
+	"github.com/stretchr/testify/assert"
 )
 
 // CollectingCounter is a metrics.Counter implementation that enables access to the CounterValue and LastLabelValues.
@@ -56,3 +57,44 @@ func newCollectingRetryMetrics() *collectingRetryMetrics {
 func (m *collectingRetryMetrics) ServiceRetriesCounter() metrics.Counter {
 	return m.retriesCounter
 }
+
+type rwWithCloseNotify struct {
+	*httptest.ResponseRecorder
+}
+
+func (r *rwWithCloseNotify) CloseNotify() <-chan bool {
+	panic("implement me")
+}
+
+func TestCloseNotifier(t *testing.T) {
+	testCases := []struct {
+		rw                      http.ResponseWriter
+		desc                    string
+		implementsCloseNotifier bool
+	}{
+		{
+			rw:                      httptest.NewRecorder(),
+			desc:                    "does not implement CloseNotifier",
+			implementsCloseNotifier: false,
+		},
+		{
+			rw:                      &rwWithCloseNotify{httptest.NewRecorder()},
+			desc:                    "implements CloseNotifier",
+			implementsCloseNotifier: true,
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			_, ok := test.rw.(http.CloseNotifier)
+			assert.Equal(t, test.implementsCloseNotifier, ok)
+
+			rw := newResponseRecorder(test.rw)
+			_, impl := rw.(http.CloseNotifier)
+			assert.Equal(t, test.implementsCloseNotifier, impl)
+		})
+	}
+}