to_der

static VALUE
ossl_spki_to_der(VALUE self)
{
    NETSCAPE_SPKI *spki;
    VALUE str;
    long len;
    unsigned char *p;

    GetSPKI(self, spki);
    if ((len = i2d_NETSCAPE_SPKI(spki, NULL)) <= 0)
        ossl_raise(eX509CertError, NULL);
    str = rb_str_new(0, len);
    p = (unsigned char *)RSTRING_PTR(str);
    if (i2d_NETSCAPE_SPKI(spki, &p) <= 0)
        ossl_raise(eX509CertError, NULL);
    ossl_str_adjust(str, p);
    
    return str;
}