Wait for NFC tag and verify against a stored UID using libnfc

NFC UID Test

#include <stdlib.h>
#include <nfc/nfc.h>

const uint8_t UID[] = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};

void
checkForTag(nfc_device *pnd, nfc_modulation nm)
{
  nfc_target nt;

  if(nfc_initiator_select_passive_target(pnd, nm, NULL, 0, &nt) > 0) {
    int i;
    uint8_t scannedUid[nt.nti.nai.szUidLen];
    for(i = 0; i < (int) nt.nti.nai.szUidLen; i++) {
      scannedUid[i] = nt.nti.nai.abtUid[i];
    }

    if(memcmp(scannedUid, UID, sizeof(UID)) == 0) {
      printf("Valid tag found!\n");
    } else {
      printf("Invalid tag...\n");
    }
  }

  checkForTag(pnd, nm);
}

int
main(int argc, const char *argv[])
{
  nfc_device *pnd;
  nfc_context *context;

  // Initialize libnfc and set the nfc_context
  nfc_init(&context);
  if (context == NULL) {
    printf("Unable to init libnfc (malloc)\n");
    exit(EXIT_FAILURE);
  }

  // Open NFC device
  pnd = nfc_open(context, NULL);
  if (pnd == NULL) {
    printf("ERROR: %s\n", "Unable to open NFC device.");
    exit(EXIT_FAILURE);
  }

  // Set opened NFC device to initiator mode
  if (nfc_initiator_init(pnd) < 0) {
    nfc_perror(pnd, "nfc_initiator_init");
    exit(EXIT_FAILURE);
  }

  // Poll for a ISO14443A (MIFARE) tag
  const nfc_modulation nm = {
    .nmt = NMT_ISO14443A,
    .nbr = NBR_106,
  };
  checkForTag(pnd, nm);

  // Close and release NFC device
  nfc_close(pnd);
  nfc_exit(context);
  exit(EXIT_SUCCESS);
}