OpenSSL::SSL::SSLSocket#stop

static VALUE
ossl_ssl_stop(VALUE self)
{
    SSL *ssl;
    int ret;

    GetSSL(self, ssl);
    if (!ssl_started(ssl))
        return Qnil;
    ret = SSL_shutdown(ssl);
    if (ret == 1) /* Have already received close_notify */
        return Qnil;
    if (ret == 0) /* Sent close_notify, but we don't wait for reply */
        return Qnil;

    /*
     * XXX: Something happened. Possibly it failed because the underlying socket
     * is not writable/readable, since it is in non-blocking mode. We should do
     * some proper error handling using SSL_get_error() and maybe retry, but we
     * can't block here. Give up for now.
     */
    ossl_clear_error();
    return Qnil;
}