network scanning does not find any networks on ESP32

[pljakobs]

on arch Esp32, network scan does not return any networks.
Tested with Basic_WiFi, the result is ok for Esp8266 but 0 for Esp32 devices.
I have added some debug code

void StationImpl::staticScanCompleted(wifi_event_sta_scan_done_t* event, uint8_t status)
{
    BssList list;
    if(status == OK) {
        debug_i("Scan completed successfully");
        if(station.scanCompletedCallback) {
            uint16_t number = event->number;
            debug_i("Number of networks found: %u", number);
            wifi_ap_record_t ap_info[number];
            uint16_t ap_count{0};
            memset(ap_info, 0, sizeof(ap_info));
            esp_err_t err;

            err = esp_wifi_scan_get_ap_records(&number, ap_info);
            if (err != ESP_OK) {
                debug_e("Failed to get AP records: %s", esp_err_to_name(err));
            }

            err = esp_wifi_scan_get_ap_num(&ap_count);
            if (err != ESP_OK) {
                debug_e("Failed to get AP count: %s", esp_err_to_name(err));
            }

            debug_i("AP count: %u", ap_count);

            // TODO: Handle hidden APs
            for(unsigned i = 0; (i < event->number) && (i < ap_count); i++) {
                debug_i("AP %u: SSID: %s, RSSI: %d", i, ap_info[i].ssid, ap_info[i].rssi);
                list.addElement(new BssInfoImpl(&ap_info[i]));
            }
            station.scanCompletedCallback(true, list);
        } else {
            debug_w("No scanCompletedCallback set");
        }

        debug_i("scan completed: %u found", list.count());
    } else {
        debug_e("scan failed %u", status);
        if(station.scanCompletedCallback) {
            station.scanCompletedCallback(false, list);
        } else {
            debug_w("No scanCompletedCallback set");
        }
    }
}

the resulting output is

5903497 Scan completed successfully
5903530 Number of networks found: 4
5904023 AP count: 0
5904108 scan completed: 0 found

also, on the Esp32, the scan seems to run only once while on the 8266, it runs continuously.

[pljakobs]

it seems that esp_wifi_scan_get_ap_num() returns 0 even though there are valid networks (and I suppose APs for them)

outputing the elements of ap_info[] show the expected five networks, but since ap_count is the number used to return valid networks, zero are being returned.

removing the loop condition ap_count results in the correct number of networks being returned

    for(unsigned i = 0; (i < event->number) && (i < ap_count); i++) {

    for(unsigned i = 0; (i < event->number); i++) {

I can't see, why esp_wifi_scan_get_ap_num() returns 0, though.

5900183 Scan completed successfully
5900212 Number of networks found: 5
5900707 AP count: 0
5900743 AP 0: SSID: UranusHertz, RSSI: -70
5900863 AP 1: SSID: IoT, RSSI: -70
5900899 AP 2: SSID: IoT1, RSSI: -72
5901293 AP 3: SSID: SDongleA-HV2280314807, RSSI: -77
5901876 AP 4: SSID: SUN2000-HV2280486954, RSSI: -91
	WiFi: UranusHertz, WPA2_PSK
	WiFi: IoT, WPA2_PSK
	WiFi: IoT1, WPA2_PSK
	WiFi: SDongleA-HV2280314807, WPA2_PSK
	WiFi: SUN2000-HV2280486954, WPA2_PSK
5904077 scan completed: 5 found

[pljakobs]

the issue was that esp_wifi_scan_get_ap_records() clears the ap data and therefore, if esp_wifi_scan_ap_num() is called afterwards, it doesn't find any APs. Switching the order around, fixes the problem.

			ESP_ERROR_CHECK(esp_wifi_scan_get_ap_num(&ap_count));
			ESP_ERROR_CHECK(esp_wifi_scan_get_ap_records(&number, ap_info));