XActiveDataSink and XOutputStream give the caller read-only
access to the contents. XActiveDataStreamer offers both read and
write access to the contents.
If an XActiveDataSink is supplied, the implementation of the command
needs to provide an implementation of an object implementing the
interface ::com::sun::star::io::XInputStream. It is
highly recommended that this object also implements the interface
::com::sun::star::io::XSeekable, if this can be done
without wasting resources (i.e. allocating huge memory buffers).
The implementation object has to be supplied to the data sink.