OpenSSL::X509::Certificate#to_der

static VALUE
ossl_x509_to_der(VALUE self)
{
    X509 *x509;
    VALUE str;
    long len;
    unsigned char *p;

    GetX509(self, x509);
    if ((len = i2d_X509(x509, NULL)) <= 0)
        ossl_raise(eX509CertError, NULL);
    str = rb_str_new(0, len);
    p = (unsigned char *)RSTRING_PTR(str);
    if (i2d_X509(x509, &p) <= 0)
        ossl_raise(eX509CertError, NULL);
    ossl_str_adjust(str, p);

    return str;
}