If you are using Arduino core for ESP32, than use digitalRead(pin); which will return value 0 or 1.
You need to pass one parameter which is GPIO pin number. For example,
#include <Arduino.h>

#define MyPin 15
#define LED_BUILTIN 2

//-----------------------------------------------------
void setup ...

I am also doing development similar to @fermienrico.
I have developed code for ESP32 in Arduino IDE. ESP32 working in access point mode.
I have developed Java code on windows machine which scan nearby WiFi device and connect to it. I am able to connect to ESP32 from windows machine and both side ...