OpenSSL::PKCS7#to_der

static VALUE
ossl_pkcs7_to_der(VALUE self)
{
    PKCS7 *pkcs7;
    VALUE str;
    long len;
    unsigned char *p;

    GetPKCS7(self, pkcs7);
    if((len = i2d_PKCS7(pkcs7, NULL)) <= 0)
        ossl_raise(ePKCS7Error, NULL);
    str = rb_str_new(0, len);
    p = (unsigned char *)RSTRING_PTR(str);
    if(i2d_PKCS7(pkcs7, &p) <= 0)
        ossl_raise(ePKCS7Error, NULL);
    ossl_str_adjust(str, p);

    return str;
}