#include <BLEDevice.h>
        #include <BLEUtils.h>
        #include <BLEServer.h>

        // See the following for generating UUIDs:
        // https://www.uuidgenerator.net/

        #define SERVICE_UUID        "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
        #define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"


        class MyCallbacks: public BLECharacteristicCallbacks {
            void onWrite(BLECharacteristic *pCharacteristic) {
                std::string value = pCharacteristic->getValue();

                if (value.length() > 0) {
                Serial.println("*********");
                Serial.print("New value: ");
                for (int i = 0; i < value.length(); i++)
                Serial.print(value[i]);

                Serial.println();
                Serial.println("*********");
                }
            }
        };

        void setup() {
            Serial.begin(115200);

            BLEDevice::init("MyESP32");
            BLEServer *pServer = BLEDevice::createServer();

            BLEService *pService = pServer->createService(SERVICE_UUID);

            BLECharacteristic *pCharacteristic = pService->createCharacteristic(
                                         CHARACTERISTIC_UUID,
                                         BLECharacteristic::PROPERTY_READ |
                                         BLECharacteristic::PROPERTY_WRITE
                                       );

            pCharacteristic->setCallbacks(new MyCallbacks());

            pCharacteristic->setValue("Hello World");
            pService->start();

            BLEAdvertising *pAdvertising = pServer->getAdvertising();
            pAdvertising->start();
        }

        void loop() {
            // put your main code here, to run repeatedly:
            delay(2000);
        }