UPDATE 2019-04：

Install and ENABLE spice-webdavd SERVICE in WINDOWS guest from https://www.spice-space.org/download/windows/spice-webdavd/
Download virt-viewer in client from http://virt-manager.org, "Run as Administrator" remote-viewer
Select folder to be shared.

Guest libvirt xml

Add the following section in <devices>...</devices>:

<channel type='spiceport'>
        <source channel='org.spice-space.webdav.0'/>
        <target type='virtio' name='org.spice-space.webdav.0'/>
</channel>

a) in Windows guest OS:

Disable Windows Firewall
As Administrator, Install spice-webdavd in Windows guest from https://www.spice-space.org/download/windows/spice-webdavd/, and enable spice-webdavd service from task manager.
If not as a service, please manually run map-drive.bat from Program Files/Spice webdav/
You MAY need re-compile the https://gitlab.gnome.org/GNOME/phodav via mingw or just change another version of spice-webdav.msi.

b) in Linux guest OS:

It's similar to Windows guest, but you should build and run webdav-agent by yourself:

git clone phodav from upstream
yum -y install gnome-common  gcc gcc-c++ automake autoconf libtool
intltool gtk-doc glib2-devel libsoup-devel libxml-devel
./autogen.sh
make
make install
spice-webdavd -p 8000

In your virt-viewer client

The Spice client can share a folder with the remote guest. By default folder sharing is disabled. Use the remote-viewer "File" → "Preferences" menu to enable it. The default shared directory is the XDG Public Share directory (ie ~/Public if you use a regular system). You may specify a different folder with --spice-share-dir client option.

Reference:

http://www.spice-space.org/page/PlannedFeatures

http://www.spinics.net/lists/spice-devel/msg07812.html

http://lists.freedesktop.org/archives/spice-devel/2014-April/016582.html

https://elmarco.fedorapeople.org/