code: @Override
      public void handleRequest(final HttpServerExchange exchange) throws Exception
      {
          if (this.defaultResponseListener != null) {
              exchange.addDefaultResponseListener(defaultResponseListener);
          }
  
          long fiGlobal = this.headers.fastIterateNonEmpty();
  
          while (fiGlobal != -1) {
              final HeaderValues headerValues = headers.fiCurrent(fiGlobal);
  
              exchange.getResponseHeaders().addAll(headerValues.getHeaderName(), headerValues);
  
              fiGlobal = headers.fiNextNonEmpty(fiGlobal);
          }
  
          next.handleRequest(exchange);
      }
docs: /*
  (non-Javadoc)
  @see io.undertow.server.HttpHandler#handleRequest(io.undertow.server.HttpServerExchange)