Produces empty file

        val content = StreamConverters.asOutputStream().mapMaterializedValue { os =>
          writeXlsDataToStream(os)
          os.close()
        }
        Ok.chunked(content).as("application/xls").withHeaders(
          "Mime-Type" -> "application/xls",
          "Content-disposition" -> s"attachment; filename=Report${DateTimeFormat.forPattern("_ddMMMYYYY_HHmmss").print(new DateTime)}.xls"
        )

Works

        val content = Source.fromPublisher(Streams.enumeratorToPublisher(Enumerator.outputStream { os =>
          writeXlsDataToStream(os)
          os.close()
        } >>> Enumerator.eof))
        Ok.chunked(content).as("application/xls").withHeaders(
          "Mime-Type" -> "application/xls",
          "Content-disposition" -> s"attachment; filename=Report${DateTimeFormat.forPattern("_ddMMMYYYY_HHmmss").print(new DateTime)}.xls"
        )