[X2Go-User] Opening URLs on remote application

[Bill Merriam]

When I run applications (such as email and web browser) on two different
remote machines using SSH X-Windows forwarding they can correctly open
URLs in the other application.  So clicking on a HTTP link in an email
launches that URL in the browser.  Clicking on a mailto link on a web
page launches that in the email program.  If there is a name for this
process I don't know what it is.  Firefox talks about it here.
https://www-archive.mozilla.org/unix/remote.html

X2go provides me with much better performance than standard X forwarding
but the URL magic doesn't seem to work.  The email program launches a
browser on the machine it is running on rather than the existing
browser.  The browser does the same thing with mailto links.

The firefox link seems to suggest this magic is done with the X toolkit,
intrinsic properties, and actions.  There is also the MIME database to
look at, and I think D-Bus might be involved.  If I can figure out how
it works with X forwarding perhaps I could write a patch for X2go or
write a wrapper script around it that makes that possible.

Can you steer me in the right direction to understand this process and
what x2go code I should look at?

For reference I am running openSuSE 42.3 on an X86_64 machine with the
KVM hypervisor.  I am using an XFCE desktop.  The "remote" machines are
running on virtual machines under KVM on the same hardware.  My email
client is Evolution 3.12.11 running on one VM and my browser is Firefox
57 running on another.

I have tried both the X2goclient 4.1.0 (which I guess is C) and
pyhoca-gui 0.5.0 which should be python.  Maybe there is a configuration
option I need to use that I missed.  I can't find anything in the
documentation about this feature, although it would help if I had a name
for this bit of magic.

If this feature isn't already there I would be pleased to write, test
and submit a patch.

Thanks.
Bill