OpenSSL::X509::Extension#oid

static VALUE
ossl_x509ext_get_oid(VALUE obj)
{
    X509_EXTENSION *ext;
    ASN1_OBJECT *extobj;
    BIO *out;
    VALUE ret;
    int nid;

    GetX509Ext(obj, ext);
    extobj = X509_EXTENSION_get_object(ext);
    if ((nid = OBJ_obj2nid(extobj)) != NID_undef)
        ret = rb_str_new2(OBJ_nid2sn(nid));
    else{
        if (!(out = BIO_new(BIO_s_mem())))
            ossl_raise(eX509ExtError, NULL);
        i2a_ASN1_OBJECT(out, extobj);
        ret = ossl_membio2str(out);
    }

    return ret;
}