Of course their `php_userstream_flush()` is inconsistent with `php_stream_flush()`.
```php
        if (call_result == SUCCESS && retval != NULL && zval_is_true(retval))
                call_result = 0;
        else
                call_result = -1;
```
To me, this is incorrect.  I agree with `php_stream_flush()`: if you don't have a `stream_flush()` method, you didn't mean "error".