esp32 BLE client application - connect to device name

You can't connect to a device using the advertised name, not directly at least.

If you want to use the advertised name you have to scan for all BLE devices around you and select the one matching your name. The BLE scan example shows you how this is done. The code scans for a scanTime of 5 seconds, waits 2 seconds and starts scanning again:

void loop() {
  // put your main code here, to run repeatedly:
  BLEScanResults foundDevices = pBLEScan->start(scanTime, false);
  Serial.print("Devices found: ");
  Serial.println(foundDevices.getCount());
  Serial.println("Scan done!");
  pBLEScan->clearResults();   // delete results fromBLEScan buffer to release memory
  delay(2000);
}

The example just prints the amount of found devices, you want to search through them and look for the correct name. The BLEScan returns an object of type BLEScanResults. You can access the found devices using getDevice with an index. Something like this might work to print the names of all found devices:

BLEAdvertisedDevice device;
for (int i = 0; i < foundDevices.getCount(); ++i) {
  device = foundDevices.getDevice(i);
  Serial.println(device.getName().c_str());
}

Now you can compare the names and work with the correct device.

To my understanding,

1. You want the client to connect to the server with given advertised name.
2. After connection is success, server turns on led.

You do have notification service running on server, but your client isn't interested. Below is the client code which only connects to server with name "BOX_A1".

1. First Set our callback function that checks if device name matches when scanner discovers the devices:

class MyAdvertisedDeviceCallbacks: public BLEAdvertisedDeviceCallbacks 
{
  void onResult(BLEAdvertisedDevice advertisedDevice) 
  {
    if (advertisedDevice.getName() == "BOX_A1") 
    { 
      advertisedDevice.getScan()->stop(); //Scan can be stopped, we found what we are looking for
      foundDevice = new BLEAdvertisedDevice(advertisedDevice);
      deviceFound = true;
      
      Serial.print("Device found:  ");
      Serial.println(advertisedDevice.toString().c_str());
    }
  }
};

2. Use the BLEAdvertisedDevice object i.e. foundDevice object to connect to this server.

BLEClient* connectToServer(BLEAdvertisedDevice* device) {
  BLEClient* pClient = BLEDevice::createClient();

  if (pClient->connect(device)){ // Connect to the remote BLE Server.
      Serial.println(" - Connected to server");
      return pClient;
  }
  else{
    Serial.println("Failed to Connect to device");
    return NULL;
  }
}

3. Use following line to call this connect function, it return the client object which can be used to disconnect from server.

if(deviceFound==true){
    BLEClient* myDevice = connectToServer(device);
    if(myDevice!=NULL){
      Serial.print("Connected to the BLE Server: ");
      Serial.println(device->getName().c_str());//print name of server
      
      //DO SOME STUFF
      
      //disconnect the device
      myDevice->disconnect();
      Serial.println("Device disconnected.");
    }
  }

This was the client side.

At server side to set the connection status flag use the following:

//Setup callbacks onConnect and onDisconnect
class MyServerCallbacks: public BLEServerCallbacks {
  void onConnect(BLEServer* pServer) {
    Serial.println("Client Connected");
    deviceConnected = true;
  };
  void onDisconnect(BLEServer* pServer) {
    Serial.println("Client Disconnected");
    deviceConnected = false;
  }
};