Linux and Bluetooth

There are 2 widespread Bluetooth stack implementations in Linux: BlueZ and Affix. Today we will use the BlueZ library for writing a simple "nearby device finder" program. Before you start, make sure you have installed the necessary Bluetooth packages. Ubuntu users can install them by running:
    sudo apt-get install bluez libbluetooth-dev
At first we need to include the following BlueZ header files
#include <bluetooth/bluetooth.h>
#include <bluetooth/hci.h>
#include <bluetooth/hci_lib.h>

To work with a Bluetooth device we need a device id, which can be retrieved by "hci_get_route"  function: if pass NULL argument to "hci_get_route", it will return the id of first available device, or -1 if there isn't any. Now we can use "hci_get_route" function, which search the nearby Bluetooth devices and return basic information about them in a "inquiry_info" structure:

typedef struct {
  bdaddr_t  bdaddr;
  uint8_t   pscan_rep_mode;
  uint8_t   pscan_period_mode;
  uint8_t   pscan_mode;
  uint8_t   dev_class[3];
  uint16_t  clock_offset;
} __attribute__ ((packed)) inquiry_info;

The "bdaddr" member contains the address of a device (it is like a MAC address of network devices, by the way they have the same syntax).
There are 2 functions to convert between strigns and "bdaddr_t" structures.

int str2ba( const char *str, bdaddr_t *ba );
int ba2str( const bdaddr_t *ba, char *str );

The address of remote Bluetooth device is enough to work with it, but the end users usually work with the device names. The "hci_read_remote_name" function retrieve the name of remote device using it's address. But "hci_open_dev" require an open socket. The "hci_open_dev" function opens an appropriate Bluetooth socket. And at last we can use "hci_open_dev" function to get the name and address of the local Bluetooth device.
See the source code for details:

	// Compile using "gcc -o scanner 1.c -lbluetooth" command
	// System
	#include <stdio.h>
	#include <stdlib.h>
	// Bluetooth
	#include <bluetooth/bluetooth.h>
	#include <bluetooth/hci.h>
	#include <bluetooth/hci_lib.h>
	int
	main() {
	// Get bluetooth device id
	int device_id = hci_get_route(NULL); // Passing NULL argument will retrieve the id of first avalaibe device
	if (device_id < 0) {
	printf("Error: Bluetooth device not found");
	exit(1);
	}
	// Get device Information
	struct hci_dev_info device_info;
	if (hci_devinfo(device_id, &device_info) == 0) {
	char device_address[18];
	ba2str(&device_info.bdaddr, device_address);
	printf("Local Device: %s %s\n", device_address, device_info.name);
	}
	// Find nearby devices
	int len = 8; // Search time = 1.28 * len seconds
	int max_rsp = 255; // Return maximum max_rsp devices
	int flags = IREQ_CACHE_FLUSH; // Flush out the cache of previously detected devices.
	inquiry_info* i_infs = (inquiry_info*) malloc(max_rsp * sizeof(inquiry_info));
	int num_rsp = hci_inquiry(device_id, len, max_rsp, NULL, &i_infs, flags); // search
	if (num_rsp < 0) {
	printf("Error: the hci_inquiry fails");
	exit(1);
	}
	printf("Found %d remote device\n", num_rsp);
	// Open socket
	int socket = hci_open_dev(device_id);
	if (socket < 0) {
	printf("Error: Cannot open socket");
	exit(1);
	}
	int i;
	for (i = 0; i < num_rsp; i++) {
	inquiry_info* remote_device = i_infs + i;
	char remote_device_address[18];
	char remote_device_name[300];
	// Get HEX address
	ba2str(&(remote_device->bdaddr), remote_device_address);
	// Get device name
	if (hci_read_remote_name(socket, &(remote_device->bdaddr), sizeof(remote_device_name), remote_device_name, 0) < 0) {
	strcpy(remote_device_name, "[unknown]"); // If cannot retrieve the name then set it "unknown"
	}
	// print address and name
	printf("Remote Device: %s %s\n", remote_device_address, remote_device_name);
	}
	// Close the socket
	close(socket);
	// Remove allocated memory
	free(i_infs);
	return 0;
	}

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