Jakub Janků authored May 29, 2020 and Frediano Ziglio committed Sep 09, 2020

When an app advertises the "text/uri-list" target, the user
probably wants to copy/move files. Spice-gtk then sends
a grab message to the vdagent advertising the
VD_AGENT_CLIPBOARD_FILE_LIST type.

Vdagent can then request clipboard data in this type.

Spice-gtk tries to talk to the app that owns the clipboard
in its native format in order to determine the preferred
file operation (copy X move).

For GNOME Nautilus, that's simply "UTF8_TEXT",
for KDE Dolphin, "application/x-kde-cutselection".

Otherwise the generic "text/uri-list" is used that does not
provide any additional information.

Once the uri list is obtained from the app, spice-gtk
creates a unique virtual dir in the ".spice-clipboard"
directory that is designated for this purpose.

Each file is attached inside this virtual dir using
phodav_virtual_dir_attach_real_child(), see phodav API
for details.

A list of paths in the phodav server is then sent to vdagent,
as specified in the spice-protocol.
Such path can for example look like this:
    /.spice-clipboard/b8f0249c-082a-4da9-9a38-2de3237a66f0/file

It is up to the vdagent to ensure that the spice shared folder
is accessible and to set the clipboard data in a format that
other apps understand.

This requires new phodav with PhodavVirtualDir API.

Signed-off-by: Jakub Janků <jjanku@redhat.com>
Acked-by: Frediano Ziglio <fziglio@redhat.com>