Forward host UNIX socket to guest TCP port

This bug has been copied automatically from: https://bugs.launchpad.net/qemu/+bug/1887604
Reported by 'Ralph G' on 2020-07-15 :

Hello. I've been racking my brain trying to work out if this is possible.

I would like to be able to forward to a guest TCP port, via a host UNIX
socket to avoid opening a TCP port on the host. For example:

qemu-system-i386 [...] -nic user,hostfwd=unix:/path/to/socket-:22

and then connect to the VM like:

ssh -o "ProxyCommand socat - unix-connect:/path/to/socket" user@0.0.0.0

QEMU, as versatile as it is, doesn't appreciate my intuited syntax
"hostfwd=unix:...". It is also unhappy with:

qemu-system-i386 [...] \
    -chardev socket,id=foo,path=/path/to/socket,server,nowait \
    -nic user,hostfwd=chardev:foo-:22

And:

qemu-system-i386 [...] \
    -nic user \
    -chardev socket,id=foo,path=/path/to/socket,server,nowait \
    -chardev socket,id=foo,host=10.0.2.15,port=22

I already found out how to connect in the opposite direction, **from**
guest TCP to host UNIX, via guestfwd -> cmd -> socat. So I feel like there
ought to be a way.

If this is not yet a feature I would like to request it, and if it is,
please tell me how!