static char *mk_file_path(const char *dir, const char *file)
{
    char *full_file = NULL;
    size_t full_file_l = 0;
    const char *sep = "";
#ifndef OPENSSL_SYS_VMS
    sep = "/";
#endif

    full_file_l = strlen(dir) + strlen(sep) + strlen(file) + 1;
    full_file = OPENSSL_zalloc(full_file_l);
    if (full_file != NULL) {
        OPENSSL_strlcpy(full_file, dir, full_file_l);
        OPENSSL_strlcat(full_file, sep, full_file_l);
        OPENSSL_strlcat(full_file, file, full_file_l);
    }

    return full_file;
}