OpenSSL::PKCS7#to_s

static VALUE
ossl_pkcs7_to_pem(VALUE self)
{
    PKCS7 *pkcs7;
    BIO *out;
    VALUE str;

    GetPKCS7(self, pkcs7);
    if (!(out = BIO_new(BIO_s_mem()))) {
        ossl_raise(ePKCS7Error, NULL);
    }
    if (!PEM_write_bio_PKCS7(out, pkcs7)) {
        BIO_free(out);
        ossl_raise(ePKCS7Error, NULL);
    }
    str = ossl_membio2str(out);

    return str;
}