From 54414c2bfb0a176d9c855365d4f987dfeb508e13 Mon Sep 17 00:00:00 2001
From: Evgeniy Kulikov <kim@nspcc.ru>
Date: Thu, 19 Nov 2020 16:01:52 +0300
Subject: [PATCH] Fix NPE when response isn't http.Flusher

Signed-off-by: Evgeniy Kulikov <kim@nspcc.ru>
---
 api/response.go | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/api/response.go b/api/response.go
index cf9e1c608..6640d4cb2 100644
--- a/api/response.go
+++ b/api/response.go
@@ -175,9 +175,13 @@ func WriteResponse(w http.ResponseWriter, statusCode int, response []byte, mType
 	}
 	w.Header().Set(hdrContentLength, strconv.Itoa(len(response)))
 	w.WriteHeader(statusCode)
-	if response != nil {
-		_, _ = w.Write(response)
-		w.(http.Flusher).Flush()
+	if response == nil {
+		return
+	}
+
+	_, _ = w.Write(response)
+	if flusher, ok := w.(http.Flusher); ok {
+		flusher.Flush()
 	}
 }