libfreefare/examples/ntag-write.c

#include <err.h>
#include <stdlib.h>

#include <nfc/nfc.h>

#include <freefare.h>


int
main(int argc, char *argv[])
{
    int error = EXIT_SUCCESS;
    nfc_device *device = NULL;
    FreefareTag *tags = NULL;

    if (argc > 1)
	errx(EXIT_FAILURE, "usage: %s", argv[0]);

    nfc_connstring devices[8];
    size_t device_count;

    nfc_context *context;
    nfc_init(&context);
    if (context == NULL)
	errx(EXIT_FAILURE, "Unable to init libnfc (malloc)");

    device_count = nfc_list_devices(context, devices, sizeof(devices) / sizeof(*devices));
    if (device_count <= 0)
	errx(EXIT_FAILURE, "No NFC device found");

    for (size_t d = 0; d < device_count; d++) {
	if (!(device = nfc_open(context, devices[d]))) {
	    warnx("nfc_open() failed.");
	    error = EXIT_FAILURE;
	    continue;
	}

	if (!(tags = freefare_get_tags(device))) {
	    nfc_close(device);
	    errx(EXIT_FAILURE, "Error listing tags.");
	}

	for (int i = 0; (!error) && tags[i]; i++) {
	    switch (freefare_get_tag_type(tags[i])) {
	    case NTAG_21x:
		break;
	    default:
		continue;
	    }

	    char *tag_uid = freefare_get_tag_uid(tags[i]);
	    printf("Tag with UID %s is a %s\n", tag_uid, freefare_get_tag_friendly_name(tags[i]));
	    FreefareTag tag = tags[i];
	    int res;
	    if (ntag21x_connect(tag) < 0)
		errx(EXIT_FAILURE, "Error connecting to tag.");

	    uint8_t data [4] = {0xfa, 0xca, 0xac, 0xad}; // Data to write on tag
	    uint8_t read[4]; // Buffer for reading data from tag

	    bool flag_match = true;
	    switch (true) {
	    case true:
		/*
		   Get information about tag
		   MUST do, because here we are recognizing tag subtype (NTAG213,NTAG215,NTAG216), and gathering all parameters
		   */
		res = ntag21x_get_info(tag);
		if (res < 0) {
		    printf("Error getting info from tag\n");
		    break;
		}

		// writing to tag 4 bytes on page 0x27 (check specs for NTAG21x before changing page number !!!)
		res = ntag21x_write(tag, 0x27, data);
		if (res < 0) {
		    printf("Error writing to tag\n");
		    break;
		}
		res = ntag21x_fast_read4(tag, 0x27, read); // Reading page from tag (4 bytes), you can also use ntag21x_read4 or ntag21x_read (16 bytes) or ntag21x_fast_read (start_page to end_page)
		if (res < 0) {
		    printf("Error reading tag\n");
		    break;
		}
		for (int i = 0; i < 4; i++) // Checking if we can read what we have written earlyer
		    if (data[i] != read[i]) {
			flag_match = false;
			break;
		    }
		if (!flag_match)
		    printf("Data don't match\n");
		else
		    printf("Data match\n");
	    }
	    ntag21x_disconnect(tag);
	    free(tag_uid);
	}
	freefare_free_tags(tags);
	nfc_close(device);
    }
    nfc_exit(context);
    exit(error);
}