Fixes reading BLE Remote Descriptor (espressif#6903)

Author: SuGlider

libraries/BLE/src/BLERemoteDescriptor.cpp

@@ -51,9 +51,26 @@ BLEUUID BLERemoteDescriptor::getUUID() {
 
 void BLERemoteDescriptor::gattClientEventHandler(esp_gattc_cb_event_t event, esp_gatt_if_t gattc_if, esp_ble_gattc_cb_param_t* evtParam) {
 switch(event) {
+// ESP_GATTC_READ_DESCR_EVT
+// This event indicates that the server has responded to the read request.
+//
+// read:
+// - esp_gatt_status_t status
+// - uint16_t conn_id
+// - uint16_t handle
+// - uint8_t* value
+// - uint16_t value_len
 case ESP_GATTC_READ_DESCR_EVT:
-if (evtParam->read.handle != getHandle())
-break;
+// If this event is not for us, then nothing further to do.
+if (evtParam->read.handle != getHandle()) break;
+// At this point, we have determined that the event is for us, so now we save the value
+if (evtParam->read.status == ESP_GATT_OK) {
+// it will read the cached value of the descriptor
+m_value = std::string((char*) evtParam->read.value, evtParam->read.value_len);
+} else {
+m_value = "";
+}
+// Unlock the semaphore to ensure that the requestor of the data can continue.
 m_semaphoreReadDescrEvt.give();
 break;