code: private void sendError(ChannelHandlerContext ctx, HttpResponseStatus status) {
      HttpResponse response = new DefaultHttpResponse(HttpVersion.HTTP_1_1, status);
      response.headers().set(HttpHeaderNames.CONTENT_TYPE, "text/plain; charset=UTF-8");
      ByteBuf content = Unpooled.copiedBuffer("Failure: " + status.toString() + "\r\n", CharsetUtil.UTF_8);
  
      ctx.write(response);
      // Close the connection as soon as the error message is sent.
      ctx.writeAndFlush(content).addListener(ChannelFutureListener.CLOSE);
    }
docs: Sends an Error response with status message
  
  @param ctx channel context
  @param status status