Updated.

service/predictor.go

@@ -55,9 +55,10 @@ func (p Predictor) Next(handler interface{}) restlet.RequestHandler {
 				panic("unsupported handler: " + reflect.TypeOf(handler).Name())
 			}
 		} else {
-			w.Header().Set("Content-Type", "plain/text")
-			w.WriteHeader(http.StatusForbidden)
-			_, _ = w.Write([]byte(s))
+			return restlet.FailureResponse(w, http.StatusForbidden, s)
+			//w.Header().Set("Content-Type", "plain/text")
+			//w.WriteHeader(http.StatusForbidden)
+			//_, _ = w.Write([]byte(s))
 		}
 		return nil
 	}