Hang up or error on watch on MacOS P2P

[Roland Roßgotterer]

Dear DBus maintainers,

first of all thanks a lot for the great explanation in
https://gitlab.freedesktop.org/dbus/dbus/issues/248. I was indeed not aware
of this limitation. However, I was trying already some of the suggestions
before and they didn't work. Hence I raised a bug instead of asking here
first.

So here I am and first things first. I'm contributing to an application
that acts as an add on to Flight Simulators. Since Flight Simulator X-Plane
does not offer any interface via TCP/Pipes/Sockets, we thought we introduce
our own one via DBus. This is done by adding a small plugin to X-Plane
which offers all the required functionality of X-Plane SDK via DBus P2P.
Communication will mostly be local on the same machine for latency reasons,
so using DBus should be fine.
I tried TCP sockets first since the application runs on Windows, MacOS and
Linux - TCP sockets were the common denominator - and that works perfectly
on all other OSes.
For the sake of testing, I changed to unix sockets and also tried anonymous
authentication but I still run into the same symptom: The connection seems
to be dropped randomly. Sometimes right during EXTERNAL auth not even
trying anything other mechanism. Sometimes authentication succeeds and the
first messages are passing. I initially thought this had something to do
with getpeereid() failing but instead its just a random connection drop.
The only related message I could find was:

[dbus-transport-socket.c(964):socket_handle_watch] Hang up or error on watch

Worth to note that everything works perfectly when running via session bus.
Only P2P shows this behavior and only on MacOS.

Do you have any hint or suggestions how I could proceed with the
investigation?

Thanks for your help.
Cheers Roland
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