Bug: crash when handling ESP_GATTS_MTU_EVT event without m_pServerCallbacks set

[Marcus10110]

I'm attempting to connect to the BLE Server demo using the iOS application LightBlue.

Hardware: Adafruit ESP32 Feather & iPhone
arduino-esp32 version 2.0.0-rc1, Arduino IDE 1.8.15

The sample code from here can reproduce the issue:
https://www.electronicshub.org/esp32-ble-tutorial/

To reproduce:

1. Program ESP32 with sample code above.
2. Open LightBlue app on iPhone. locate the device in the list, and select it.

Expected: the app should interregate the BLE device for information and display it.
Actual: the ESP32 crashes with this call stack:

PC: 0x400d6d15: BLEServer::handleGATTServerEvent(esp_gatts_cb_event_t, unsigned char, esp_ble_gatts_cb_param_t*) at C:\Users\markg\AppData\Local\Arduino15\packages\esp32\hardware\esp32\2.0.0-rc1\libraries\BLE\src\BLEServer.cpp line 160
EXCVADDR: 0x00000000

Decoding stack results
0x400d6d12: BLEServer::handleGATTServerEvent(esp_gatts_cb_event_t, unsigned char, esp_ble_gatts_cb_param_t*) at C:\Users\markg\AppData\Local\Arduino15\packages\esp32\hardware\esp32\2.0.0-rc1\libraries\BLE\src\BLEServer.cpp line 160
0x400d525d: BLEDevice::gattServerEventHandler(esp_gatts_cb_event_t, unsigned char, esp_ble_gatts_cb_param_t*) at C:\Users\markg\AppData\Local\Arduino15\packages\esp32\hardware\esp32\2.0.0-rc1\libraries\BLE\src\BLEDevice.cpp line 123
0x400ea835: btc_gatts_cb_handler at /Users/ficeto/Desktop/ESP32/ESP32S2/esp-idf-public/components/bt/host/bluedroid/btc/profile/std/gatt/btc_gatts.c line 46
0x4011409f: btc_thread_handler at /Users/ficeto/Desktop/ESP32/ESP32S2/esp-idf-public/components/bt/common/btc/core/btc_task.c line 184
0x40115f23: osi_thread_run at /Users/ficeto/Desktop/ESP32/ESP32S2/esp-idf-public/components/bt/common/osi/thread.c line 67

Specifically, when BLEServer::handleGATTServerEvent tries to handle a ESP_GATTS_MTU_EVT, it tries to call a method on m_pServerCallbacks without checking if it's null first.

All other calls to m_pServerCallbacks are wrapped with a null check.

Simply adding a server callback object gets around the crash:

BLEServer *pServer = BLEDevice::createServer();
pServer->setCallbacks(new BLEServerCallbacks());

arduino-esp32/libraries/BLE/src/BLEServer.cpp

Line 160 in 90c01da

m_pServerCallbacks->onMtuChanged(this, param);

If I have time later I'll open a PR. I'm pretty sure this will fix it:

		case ESP_GATTS_MTU_EVT:
			updatePeerMTU(param->mtu.conn_id, param->mtu.mtu);
			if (m_pServerCallbacks != nullptr) {
				m_pServerCallbacks->onMtuChanged(this, param);
			}
			break;

[Marcus10110]

Pull request opened here:
#5603