int update_pic(User *user, const char *filename) {

    if (strlen(filename) > MAX_NAME) {
        return 2;
    }
    FILE *output_file = fopen(filename, "r");
    if (output_file == NULL) {
        fclose(output_file);
        return 1;
    } else {
        strncpy(user->profile_pic, filename, MAX_NAME);
        return 0;
    }
    fclose(output_file);
}
/*
 * Change the filename for the profile pic of the given user.
 *
 * Return:
 *   - 0 on success.
 *   - 1 if the file does not exist or cannot be opened.
 *   - 2 if the filename is too long.
 */