scanner.c

// To compile this program, you need to install:
//   sudo apt-get install libbluetooth-dev
// Then you can compile it with:
//   cc scanner.c -lbluetooth -o scanner
// You can then run it with:
//   ./scanner

// Copyright (c) 2021 David G. Young
// Copyright (c) 2015 Damian Kołakowski. All rights reserved.
// License: BSD 3.  See: https://github.com/davidgyoung/ble-scanner

#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <bluetooth/bluetooth.h>
#include <bluetooth/hci.h>
#include <bluetooth/hci_lib.h>
#include <time.h>

struct hci_request ble_hci_request(uint16_t ocf, int clen, void * status, void * cparam)
{
	struct hci_request rq;
	memset(&rq, 0, sizeof(rq));
	rq.ogf = OGF_LE_CTL;
	rq.ocf = ocf;
	rq.cparam = cparam;
	rq.clen = clen;
	rq.rparam = status;
	rq.rlen = 1;
	return rq;
}

int main()
{
	int ret, status;

	// Get HCI device.

	int device = hci_open_dev(1);
	if ( device < 0 ) {
		device = hci_open_dev(0);
		if (device >= 0) {
   		printf("Using hci0\n");
		}
	}
	else {
   		printf("Using hci1\n");
	}

	if ( device < 0 ) {
		perror("Failed to open HCI device.");
		return 0;
	}

	// Set BLE scan parameters.

	le_set_scan_parameters_cp scan_params_cp;
	memset(&scan_params_cp, 0, sizeof(scan_params_cp));
	scan_params_cp.type 			= 0x00;
	scan_params_cp.interval 		= htobs(0x0010);
	scan_params_cp.window 			= htobs(0x0010);
	scan_params_cp.own_bdaddr_type 	= 0x00; // Public Device Address (default).
	scan_params_cp.filter 			= 0x00; // Accept all.

	struct hci_request scan_params_rq = ble_hci_request(OCF_LE_SET_SCAN_PARAMETERS, LE_SET_SCAN_PARAMETERS_CP_SIZE, &status, &scan_params_cp);

	ret = hci_send_req(device, &scan_params_rq, 1000);
	if ( ret < 0 ) {
		hci_close_dev(device);
		perror("Failed to set scan parameters data.");
		return 0;
	}

	// Set BLE events report mask.

	le_set_event_mask_cp event_mask_cp;
	memset(&event_mask_cp, 0, sizeof(le_set_event_mask_cp));
	int i = 0;
	for ( i = 0 ; i < 8 ; i++ ) event_mask_cp.mask[i] = 0xFF;

	struct hci_request set_mask_rq = ble_hci_request(OCF_LE_SET_EVENT_MASK, LE_SET_EVENT_MASK_CP_SIZE, &status, &event_mask_cp);
	ret = hci_send_req(device, &set_mask_rq, 1000);
	if ( ret < 0 ) {
		hci_close_dev(device);
		perror("Failed to set event mask.");
		return 0;
	}

	// Enable scanning.

	le_set_scan_enable_cp scan_cp;
	memset(&scan_cp, 0, sizeof(scan_cp));
	scan_cp.enable 		= 0x01;	// Enable flag.
	scan_cp.filter_dup 	= 0x00; // Filtering disabled.

	struct hci_request enable_adv_rq = ble_hci_request(OCF_LE_SET_SCAN_ENABLE, LE_SET_SCAN_ENABLE_CP_SIZE, &status, &scan_cp);

	ret = hci_send_req(device, &enable_adv_rq, 1000);
	if ( ret < 0 ) {
		hci_close_dev(device);
		perror("Failed to enable scan.");
		return 0;
	}

	// Get Results.

	struct hci_filter nf;
	hci_filter_clear(&nf);
	hci_filter_set_ptype(HCI_EVENT_PKT, &nf);
	hci_filter_set_event(EVT_LE_META_EVENT, &nf);
	if ( setsockopt(device, SOL_HCI, HCI_FILTER, &nf, sizeof(nf)) < 0 ) {
		hci_close_dev(device);
		perror("Could not set socket options\n");
		return 0;
	}


	uint8_t buf[HCI_MAX_EVENT_SIZE];
	evt_le_meta_event * meta_event;
	le_advertising_info * info;
	int len;

    int count = 0;
    unsigned now = (unsigned)time(NULL);
    unsigned last_detection_time = now;
    // Keep scanning until we see nothing for 10 secs or we have seen lots of advertisements.  Then exit.
    // We exit in this case because the scan may have failed or stopped. Higher level code can restart
	while ( last_detection_time - now < 10 && count < 1000 ) {
		len = read(device, buf, sizeof(buf));
		if ( len >= HCI_EVENT_HDR_SIZE ) {
		    count++;
            last_detection_time = (unsigned)time(NULL);
			meta_event = (evt_le_meta_event*)(buf+HCI_EVENT_HDR_SIZE+1);
			if ( meta_event->subevent == EVT_LE_ADVERTISING_REPORT ) {
				uint8_t reports_count = meta_event->data[0];
				void * offset = meta_event->data + 1;
				while ( reports_count-- ) {
					info = (le_advertising_info *)offset;
					char addr[18];
					ba2str(&(info->bdaddr), addr);
                    printf("%s %d", addr, (int8_t)info->data[info->length]);
                    for (int i = 0; i < info->length; i++) {
                       printf(" %02X", (unsigned char)info->data[i]);
                    }
                    printf("\n");
					offset = info->data + info->length + 2;
				}
			}
		}
        now = (unsigned)time(NULL);
	}

	// Disable scanning.

	memset(&scan_cp, 0, sizeof(scan_cp));
	scan_cp.enable = 0x00;	// Disable flag.

	struct hci_request disable_adv_rq = ble_hci_request(OCF_LE_SET_SCAN_ENABLE, LE_SET_SCAN_ENABLE_CP_SIZE, &status, &scan_cp);
	ret = hci_send_req(device, &disable_adv_rq, 1000);
	if ( ret < 0 ) {
		hci_close_dev(device);
		perror("Failed to disable scan.");
		return 0;
	}

	hci_close_dev(device);

	return 0;
}

I gave it a try and it works well, but the output is a bit "bursty" for 1-2 seconds i get nothing then 3-4 things at once then nothing for 1-2 seconds and so on. Is there a way i can make it return results each 0.5 seconds constantly?

I decided to convert this GIST into a hosted project and created an answer to your question here: davidgyoung/ble-scanner#1. Please feel free to comment there.