to_der

static VALUE
ossl_dsa_to_der(VALUE self)
{
    EVP_PKEY *pkey;
    int (*i2d_func)_((DSA*, unsigned char**));
    unsigned char *p;
    long len;
    VALUE str;

    GetPKeyDSA(self, pkey);
    if(DSA_HAS_PRIVATE(pkey->pkey.dsa))
        i2d_func = (int(*)_((DSA*,unsigned char**)))i2d_DSAPrivateKey;
    else
        i2d_func = i2d_DSA_PUBKEY;
    if((len = i2d_func(pkey->pkey.dsa, NULL)) <= 0)
        ossl_raise(eDSAError, NULL);
    str = rb_str_new(0, len);
    p = (unsigned char *)RSTRING_PTR(str);
    if(i2d_func(pkey->pkey.dsa, &p) < 0)
        ossl_raise(eDSAError, NULL);
    ossl_str_adjust(str, p);

    return str;
}