Client: Validate product only on successful responses (#371)

Author: Anaethelion

elasticsearch.go

@@ -304,7 +304,7 @@ func (c *Client) Perform(req *http.Request) (*http.Response, error) {
 	res, err := c.Transport.Perform(req)
 
 	// ResponseCheck path continues, we run the header check on the first answer from ES.
-	if err == nil {
+	if err == nil && (res.StatusCode >= 200 && res.StatusCode < 300){
 		checkHeader := func(context.Context) error {
 			return genuineCheckHeader(res.Header)
 		}

elasticsearch_internal_test.go

@@ -630,6 +630,7 @@ func TestResponseCheckOnly(t *testing.T) {
 			name:                 "Valid answer without header and response check",
 			useResponseCheckOnly: true,
 			response: &http.Response{
+				StatusCode: http.StatusOK,
 				Body: ioutil.NopCloser(strings.NewReader("{}")),
 			},
 			wantErr: true,