Why does `esp_bt_gap_register_callback` reject NULL callback?

[vyo2003]

I'm currently digging into Bluetooth stack of ESP32 and have stumped upon one weird thing: esp_bt_gap_register_callback specifically rejects NULL callback, in turn making it impossible to disable callback completely. Here's esp_bt_gap_register_callback:

Code: Untitled.c Select all

esp_err_t esp_bt_gap_register_callback(esp_bt_gap_cb_t callback)

{

    if (esp_bluedroid_get_status() != ESP_BLUEDROID_STATUS_ENABLED) {

        return ESP_ERR_INVALID_STATE;

    }



    if (callback == NULL) {

        return ESP_FAIL;

    }



    btc_profile_cb_set(BTC_PID_GAP_BT, callback);

    return ESP_OK;

}

The only place callback is retrieved is here:

Code: Untitled.c Select all

static inline void btc_gap_bt_cb_to_app(esp_bt_gap_cb_event_t event, esp_bt_gap_cb_param_t *param)

{

    esp_bt_gap_cb_t cb = (esp_bt_gap_cb_t)btc_profile_cb_get(BTC_PID_GAP_BT);

    if (cb) {

        cb(event, param);

    }

}

(Note: inline does not do a thing here) As you can see, there's an explicit check for presence of callback. Moreover, callback is NULL by default and it's possible to manually reset it using btc_profile_cb_set directly!

So what's the reason behind banning such reset using simply esp_bt_gap_register_callback?