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Migrating to a new way of identifying devices
#include <sys/socket.h>
#include <sys/sysctl.h>
#include <net/if.h>
#include <net/if_dl.h>

- (NSString *)getMacAddress
{
  int                 mgmtInfoBase[6];
  char                *msgBuffer = NULL;
  size_t              length;
  unsigned char       macAddress[6];
  struct if_msghdr    *interfaceMsgStruct;
  struct sockaddr_dl  *socketStruct;
  NSString            *errorFlag = NULL;

  // Setup the management Information Base (mib)
  mgmtInfoBase[0] = CTL_NET;        // Request network subsystem
  mgmtInfoBase[1] = AF_ROUTE;       // Routing table info
  mgmtInfoBase[2] = 0;
  mgmtInfoBase[3] = AF_LINK;        // Request link layer information
  mgmtInfoBase[4] = NET_RT_IFLIST;  // Request all configured interfaces

  // With all configured interfaces requested, get handle index
  if ((mgmtInfoBase[5] = if_nametoindex("en0")) == 0)
    errorFlag = @"if_nametoindex failure";
  else
  {
    // Get the size of the data available (store in len)
    if (sysctl(mgmtInfoBase, 6, NULL, &length, NULL, 0) < 0)
      errorFlag = @"sysctl mgmtInfoBase failure";
    else
    {
      // Alloc memory based on above call
      if ((msgBuffer = malloc(length)) == NULL)
        errorFlag = @"buffer allocation failure";
      else
      {
        // Get system information, store in buffer
        if (sysctl(mgmtInfoBase, 6, msgBuffer, &length, NULL, 0) < 0)
          errorFlag = @"sysctl msgBuffer failure";
      }
    }
  }

  // Befor going any further...
  if (errorFlag != NULL)
  {
    NSLog(@"Error: %@", errorFlag);
    return errorFlag;
  }

  // Map msgbuffer to interface message structure
  interfaceMsgStruct = (struct if_msghdr *) msgBuffer;

  // Map to link-level socket structure
  socketStruct = (struct sockaddr_dl *) (interfaceMsgStruct + 1);

  // Copy link layer address data in socket structure to an array
  memcpy(&macAddress, socketStruct->sdl_data + socketStruct->sdl_nlen, 6);

  // Read from char array into a string object, into traditional Mac address format
  NSString *macAddressString = [NSString stringWithFormat:@"%02X:%02X:%02X:%02X:%02X:%02X",
                                macAddress[0], macAddress[1], macAddress[2],
                                macAddress[3], macAddress[4], macAddress[5]];
  NSLog(@"Mac Address: %@", macAddressString);

  // Release the buffer memory
  free(msgBuffer);

  return macAddressString;
}