add Pusher function for http2 server push

response_writer.go

@@ -37,6 +37,9 @@ type ResponseWriter interface {
 
 	// Forces to write the http header (status code + headers).
 	WriteHeaderNow()
+
+	// get the http.Pusher for server push
+	Pusher()
 }
 
 type responseWriter struct {
@@ -112,3 +115,10 @@ func (w *responseWriter) CloseNotify() <-chan bool {
 func (w *responseWriter) Flush() {
 	w.ResponseWriter.(http.Flusher).Flush()
 }
+
+func (w *responseWriter) Pusher() (pusher http.Pusher) {
+	if pusher, ok := w.ResponseWriter.(http.ResponseWriter).(http.Pusher); ok {
+		return pusher
+	}
+	return nil
+}