Simple program that detects nearby Bluetooth devices.

simplescan.c

// Simple program that detects nearby Bluetooth devices.
// Based on https://people.csail.mit.edu/albert/bluez-intro/c404.html#simplescan.c
// Enhanced with comments and personal notes.

// To compile:
// `gcc -o simplescan simplescan.c -lbluetooth`
// Install libbluetooth-dev:
// `sudo apt-get install libbluetooth-dev`

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h> // for close()
#include <sys/socket.h>
#include <string.h> // for memset()
#include <bluetooth/bluetooth.h>
#include <bluetooth/hci.h> // for inquiry_info, IREQ_CACHE_FLUSH
#include <bluetooth/hci_lib.h> // for hci_get_route, hci_open_dev, hci_read_remote_name

int main(void){
  // inquiry_info is a structure defined in hci.h
  // it contains a field bdaddr which is the Bluetooth Device address.
  inquiry_info *ii = NULL;
  
  int max_rsp; // Maximum responses
  int num_rsp; // Number of actual responses
  int dev_id;  // ID of Bluetooth adapter
  int sock, len, flags;
  int i;
  char addr[19] = {0};
  char name[248] = {0};

  // Get Device ID
  dev_id = hci_get_route(NULL); // NULL will be the first adapter, usually there is only one
                                // If we know adapter adress (`hciconfig -a`) we can also do
                                // bdaddr_t bdaddr = {0xDC, 0xA6, 0x32, 0xE4, 0x9C, 0x05};
                                // dev_id = hci_get_route(&bdaddr);
                                // or
                                // dev_id = hci_devid("DC:A6:32:E4:9C:12");
  printf("dev_id = %d\n", dev_id);

  // Get Socket ?
  sock = hci_open_dev(dev_id);
  printf("sock = %d\n", sock);

  // Check Errors
  if(dev_id < 0 || sock < 0) {
    perror("opening socket");
    exit(1);
  }

  len = 8;
  max_rsp = 255;
  flags = IREQ_CACHE_FLUSH; // = 1, hci_inquiry flush previously detected devices
 
  ii = (inquiry_info*)malloc(max_rsp*sizeof(inquiry_info));

  // hci_inquiry will fill ii with all the found responses
  num_rsp = hci_inquiry(dev_id, len, max_rsp, NULL, &ii, flags);
  if(num_rsp < 0)
    perror("hci_inquiry");
  printf("num_rsp = %d\n", num_rsp);

  // Loop through Responses
  for(i = 0; i < num_rsp; i++){

    // Get Response Address
    ba2str(&(ii+i)->bdaddr, addr);
    memset(name, 0, sizeof(name));

    // Get Response Name
    if(hci_read_remote_name(sock, &(ii+i)->bdaddr, sizeof(name), name, 0) < 0)
      strcpy(name, "[unknown]");

    // Print name and address of scanned BT Devices
    printf("%s  %s\n", addr, name);
  }

  free(ii);
  close(sock);
  
  printf("OK!\n");
  return 0;
}