Hi folks,
I'm looking for a good way to implement cut+paste support for vnc.
The vnc core protocol has support for text/plain cut+paste, and there
is an extension adding support for other formats. That'll cover one
part of the problem, exchanging cut+paste data between vnc client and
qemu vnc server.
The tricky part is the second: the guest <=> qemu communication.
I see basically two possible approaches here:
(1) Have some guest agent (spice does it that way).
Advantage: more flexible, allows more features.
Disadvantage: requires agent in the guest.
(2) Send text as key events.
Advantage: no guest agent needed.
Disadvantage: is translated by guests keyboard map, so qemu
needs to know the map for proper char -> key event translation.
Only works for text/plain and only for chars you can easily
type, anything needing input methods (emoji 😊 for example)
isn't going to fly.
I think that (1) is clearly the better way. Given that the agent
would need to run in user wayland/xorg session context the existing
qemu-guest-agent will not work. Also linking against some UI library
like gtk3 for clipboard handling is not something we want for the
qemu-guest-agent. So we need another one, I'll name it
qemu-clipboard-agent for the rest of this mail. And we need a
communication channel.
I'd tend to model the qemu-clipboard-agent simliar to the
qemu-guest-agent, i.e. have some stream as communication path and run
some stream protocol over it.
Stream options I see are (in order of personal preference):
(1) New virtio-serial port. virtio-serial likely is there anyway
for the qemu-guest-agent ...
(2) Have qemu-clipboard-agent and qemu-guest-agent share the agent
channel, i.e. qemu-clipboard-agent will proxy everything through
qemu-guest-agent (spice does it that way).
Protocol options I see are (not sure yet which to prefer, need to have
a closer look at the candidates):
(1) Add clipboard commands to QMP and use these.
(2) Reuse the clipboard bits of the vnc protocol (forward
VNC_MSG_CLIENT_CUT_TEXT messages to the guest agent)
(3) Reuse the clipboard bits of the spice-agent protocol.
(4) Reuse the clipboard bits of the wayland protocol.
Once we have sorted the qemu <-> guest communication path it should be
possible to also hook up other UIs (specifically gtk) without too much
effort. Which probably makes (2) a rather poor choice.
Comments?
Suggestions?
Other ideas?
take care,
Gerd
