add supprt for go1.20 http.rwUnwrapper to gin.responseWriter (#3489)

Author: davidmdm

response_writer.go

@@ -51,6 +51,10 @@ type responseWriter struct {
 
 var _ ResponseWriter = (*responseWriter)(nil)
 
+func (w *responseWriter) Unwrap() http.ResponseWriter {
+	return w.ResponseWriter
+}
+
 func (w *responseWriter) reset(writer http.ResponseWriter) {
 	w.ResponseWriter = writer
 	w.size = noWritten

response_writer_test.go

@@ -30,6 +30,12 @@ func init() {
 	SetMode(TestMode)
 }
 
+func TestResponseWriterUnwrap(t *testing.T) {
+	testWriter := httptest.NewRecorder()
+	writer := &responseWriter{ResponseWriter: testWriter}
+	assert.Same(t, testWriter, writer.Unwrap())
+}
+
 func TestResponseWriterReset(t *testing.T) {
 	testWriter := httptest.NewRecorder()
 	writer := &responseWriter{}