Bind member function of class to AsyncWebServer::on fails with version 3.9.0

[petricf]

I bind a member function of my class to AsyncWebServer::on (). Sample code:

class MyClass
{
...
void handlePage (AsyncWebServerRequest * request);
void handleOtherPage (AsyncWebServerRequest * request);
...
void bindCallbacks ();
};
`MyClass instance;` `AsyncWebServer webServer (80);`
void MyClass::bindCallbacks ()
{
webServer.on ("/page", HTTP_GET, std::bind (&MyClass::handlePage, this, std::placeholders::_1));
webServer.on ("/page2", HTTP_GET, std::bind (&MyClass::handleOtherPage, this, std::placeholders::_1));
}

This worked well until version 3.8.1.

With the change from 3.8.1 to 3.9.0 i get following compilation error:

/home/petric/Arduino/Waveshare-ESP32C6/MyClass.cpp:51:16: error: call of overloaded 'on(char [8], WebRequestMethod, std::_Bind_helper<false, void (MyClass::*)(AsyncWebServerRequest*), MyClass*, const std::_Placeholder<1>&>::type)' is ambiguous
51 | webServer.on ("/page", HTTP_GET, std::bind (&ActivityHandler::handleManagePage, this, std::placeholders::_1));
| ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/petric/Arduino/libraries/ESP_Async_WebServer/src/ESPAsyncWebServer.h:1526:28: note: candidate: 'AsyncCallbackWebHandler& AsyncWebServer::on(AsyncURIMatcher, WebRequestMethodComposite, ArRequestHandlerFunction, ArUploadHandlerFunction, ArBodyHandlerFunction)'
1526 | AsyncCallbackWebHandler &on(
| ^~
/home/petric/Arduino/libraries/ESP_Async_WebServer/src/ESPAsyncWebServer.h:1532:32: note: candidate: 'AsyncCallbackJsonWebHandler& AsyncWebServer::on(AsyncURIMatcher, WebRequestMethodComposite, ArJsonRequestHandlerFunction)'
1532 | AsyncCallbackJsonWebHandler &on(AsyncURIMatcher uri, WebRequestMethodComposite method, ArJsonRequestHandlerFunction onBody);
| ^~

Same error on binding handlerOtherPage.

I am not sure whether this is a bug or a coding error on my side.

Any ideas ?

[mathieucarbou]

This might be a side effect when we introduced the URIMatcher… I need to have a look deeper.

@willmmiles fyi

[mathieucarbou]

@petricf : ok so you have this issue in 3.9.0 because we added an overload for on(...) to handle json requests:

all the flavors: now available:

  AsyncCallbackWebHandler &on(AsyncURIMatcher uri, ArRequestHandlerFunction onRequest) { return on(std::move(uri), HTTP_ANY, onRequest); }
  AsyncCallbackWebHandler &on(AsyncURIMatcher uri, WebRequestMethodComposite method, ArRequestHandlerFunction onRequest, ArUploadHandlerFunction onUpload = nullptr, ArBodyHandlerFunction onBody = nullptr);
#if ASYNC_JSON_SUPPORT == 1
  AsyncCallbackJsonWebHandler &on(AsyncURIMatcher uri, WebRequestMethodComposite method, ArJsonRequestHandlerFunction onBody);
#endif

I suppose you have ArduinoJson in your compile path.

So the compiler is not able to make the difference between the last 2 functions.

One approach is to cast:

    server.on("/json1", HTTP_GET, static_cast<ArRequestHandlerFunction>(std::bind(&MyClass::handlePage, this, std::placeholders::_1)));
    server.on("/json2", HTTP_GET, static_cast<ArRequestHandlerFunction>(std::bind(&MyClass::handleOtherPage, this, std::placeholders::_1)));

another approach is to just use normal anonymous functions. Handlers should anyway only be setup once and only once.

class MyClass {
  void bindCallbacks() {
    server.on("/json1", HTTP_GET, [this](AsyncWebServerRequest *request) {
      ...
    });
    server.on("/json2", HTTP_GET, [this](AsyncWebServerRequest *request) {
      ...
    });
  }
};

Or have anonymous functions call the other ones and force inline ?

class MyClass {
  __attribute__((always_inline)) inline void handlePage(AsyncWebServerRequest *request) {}
  __attribute__((always_inline)) inline void handleOtherPage(AsyncWebServerRequest *request) {}
  void bindCallbacks() {
    server.on("/json1", HTTP_GET, [this](AsyncWebServerRequest *request) {
      handlePage(request);
    });
    server.on("/json2", HTTP_GET, [this](AsyncWebServerRequest *request) {
      handleOtherPage(request);
    });
  }
};

[petricf]

You are right - i use ArduinoJson in my project.

Using the static_cast solution solves most of the callback definitions.

But i have some HTTP_POST callbacks where i support uploading files. These take a fourth parameter. I pass
std::bind (&FirmwareHandler::uploadFirmware, this, std::placeholders::_1, std::placeholders::_2, std::placeholders::_3, std::placeholders::_4, std::placeholders::_5, std::placeholders::_6)

defined as
void uploadFirmware (AsyncWebServerRequest * request, String fileName, size_t index, uint8_t * data, size_t len, bool final);

Casting this to ArRequestHandlerFunction does not work here. I had to cast to ArUploadHandlerFunction. Now it compiles without errors.

Maybe some project docs would be helpful on how to use ESPAsyncWebServer with class function callbacks.

Thank you for your assistance.