to_der

static VALUE
ossl_asn1prim_to_der(VALUE self)
{
    ASN1_TYPE *asn1;
    long alllen, bodylen;
    unsigned char *p0, *p1;
    int j, tag, tc, state;
    VALUE str;

    if (ossl_asn1_default_tag(self) == -1) {
        str = ossl_asn1_get_value(self);
        return to_der_internal(self, 0, 0, StringValue(str));
    }

    asn1 = ossl_asn1_get_asn1type(self);
    alllen = i2d_ASN1_TYPE(asn1, NULL);
    if (alllen < 0) {
        ASN1_TYPE_free(asn1);
        ossl_raise(eASN1Error, "i2d_ASN1_TYPE");
    }
    str = ossl_str_new(NULL, alllen, &state);
    if (state) {
        ASN1_TYPE_free(asn1);
        rb_jump_tag(state);
    }
    p0 = p1 = (unsigned char *)RSTRING_PTR(str);
    i2d_ASN1_TYPE(asn1, &p0);
    ASN1_TYPE_free(asn1);
    assert(p0 - p1 == alllen);

    /* Strip header since to_der_internal() wants only the payload */
    j = ASN1_get_object((const unsigned char **)&p1, &bodylen, &tag, &tc, alllen);
    if (j & 0x80)
        ossl_raise(eASN1Error, "ASN1_get_object"); /* should not happen */

    return to_der_internal(self, 0, 0, rb_str_drop_bytes(str, alllen - bodylen));
}