libvirt users - Aug 2015 - who is the end user of libvirt-iohelper?

Hello everybody!
I'm trying to make some experiments with writing/reading stream to/from
volume. I've realized that libvirt-iohelper are ran to make this
operations:
1) reading stream from stdin and writng to a file
2) reading stream from a file and writing to stdout
I've also realized that virsh uses libvirt-iohelper via
virStorageVolUpload/virStorageVolDownload. But i can't find the place where
virsh works with stdin/stdout (reading/writing full data to this I/O).