Wt

I was trying to display some large text files in a Wt::WTextArea in a Wt::WMenu. After the size of the files exceeds the --max-memory-request-size size (128 KiB), I start to get errors in the log and the site doesn't always function correctly:

[2022-Dec-27 21:10:08.732] 25657 - [error] "wthttp: Rejecting WebSocket message because it exceeds --max-memory-request-size (= 131072 bytes)"

This log message doesn't occur when clicking on the menu item for a large file, but rather, when clicking off of it to a different menu item. The large file loads up and displays fine. I don't feel like adjusting the --max-memory-request-size command line argument is right approach because the documentation says that, "Bigger POSTs are handled using a spool file." In addition, I don't even know what the large websocket message is. It seems odd that hiding a large Wt::WTextArea in a Wt::WStackedWidget would require a large websocket message. I haven't looked into the Wt code to figure out what is going on yet though.

I'm hoping this is an easily fixable bug, or that there is a workaround that I can use. Maybe I am supposed to use a very large --max-memory-request-size?

For reference, here is a sample program that demonstrations the issue:

#include "Wt/WApplication.h"
#include "Wt/WContainerWidget.h"
#include "Wt/WMenu.h"
#include "Wt/WServer.h"
#include "Wt/WStackedWidget.h"
#include "Wt/WTextArea.h"

#include <memory>
#include <string>

////////////////////////////////////////////////////////////////////////////////
class Application final : public Wt::WApplication {
public:
  explicit Application(Wt::WEnvironment const& env) : Wt::WApplication{env}
  {
    auto contents = std::make_unique<Wt::WStackedWidget>();
    auto* menu = root()->addWidget(std::make_unique<Wt::WMenu>(contents.get()));

    menu->addItem("As",
                  std::make_unique<Wt::WTextArea>(std::string(65536, 'a')));

    menu->addItem("Bs",
                  std::make_unique<Wt::WTextArea>(std::string(131072, 'b')));

    menu->addItem("Cs",
                  std::make_unique<Wt::WTextArea>(std::string(262144, 'c')));

    root()->addWidget(std::move(contents));
  }
};

////////////////////////////////////////////////////////////////////////////////
int main(int argc, char** argv)
{
  try {
    Wt::WServer server{argc, argv};

    server.addEntryPoint(
      Wt::EntryPointType::Application,
      [](auto const& env) { return std::make_unique<Application>(env); },
      "/");

    server.run();
  } catch (std::exception& ex) {
    std::cerr << ex.what() << std::endl;
    return EXIT_FAILURE;
  } catch (...) {
    std::cerr << "unknown exception" << std::endl;
    return EXIT_FAILURE;
  }

  return EXIT_SUCCESS;
}

To reproduce the issue, click on "Bs", and then click on "As". The error message will then be logged.

127.0.0.1 - - [2022-Dec-27 21:24:50.380] "GET /?wtd=IlWXiLSwhtKlyit5&sid=1486711372&scrW=1920&scrH=1200&tz=-480&tzS=America%2FLos_Angeles&htmlHistory=true&deployPath=%2F&request=script&rand=3111065106 HTTP/1.1" 200 18785
[2022-Dec-27 21:24:50.380] 30037 - [info] "WebRequest: took 4.835 ms"
127.0.0.1 - - [2022-Dec-27 21:24:50.386] "GET /resources/webkit-transitions.css HTTP/1.1" 200 6814
127.0.0.1 - - [2022-Dec-27 21:24:50.387] "GET /resources/themes/default/wt.css HTTP/1.1" 200 20265
127.0.0.1 - - [2022-Dec-27 21:24:50.597] "POST /?wtd=IlWXiLSwhtKlyit5 HTTP/1.1" 200 48
[2022-Dec-27 21:24:50.597] 30037 - [info] "WebRequest: took 1.148 ms"
127.0.0.1 - - [2022-Dec-27 21:24:50.599] "GET /favicon.ico HTTP/1.1" 404 85
[2022-Dec-27 21:24:51.020] 30037 - [info] "wthttp: ws: connect with protocol version 13"
[2022-Dec-27 21:24:51.026] 30037 [/ IlWXiLSwhtKlyit5] [info] "WebRequest: took 0.093 ms"
[2022-Dec-27 21:24:58.329] 30037 [/ IlWXiLSwhtKlyit5] [info] "WebRequest: took 2.815 ms"
[2022-Dec-27 21:24:58.329] 30037 [/ IlWXiLSwhtKlyit5] [info] "WebRequest: took 3.551 ms"
[2022-Dec-27 21:25:01.817] 30037 - [error] "wthttp: Rejecting WebSocket message because it exceeds --max-memory-request-size (= 131072 bytes)"
[2022-Dec-27 21:25:01.817] 30037 - [info] "WebRequest: took 10796.8 ms"
[2022-Dec-27 21:25:03.811] 30037 - [info] "wthttp: ws: connect with protocol version 13"
127.0.0.1 - - [2022-Dec-27 21:25:03.874] "POST /?wtd=IlWXiLSwhtKlyit5 HTTP/1.1" 200 48
[2022-Dec-27 21:25:03.874] 30037 - [info] "WebRequest: took 0.253 ms"

I'm currently using version 4.6.1, but I also reproduced the issue on master (4.9.0-ish).