Listen() succeeding is not the same as being reachable. OpsLog binds 0.0.0.0,
and Windows lets a second program bind the SAME port on the specific address
127.0.0.1. Connections to localhost then go to the more specific listener, so
every client reaches the other program while ours sits there having logged
"sharing CAT on port 4532" and never seeing a single connection.
Found with Nexus, which starts its own rigctld on 127.0.0.1:4532 and talks to
it. Neither side reports anything wrong: the operator gets a CAT timeout from a
daemon with no radio behind it, and OpsLog's log is silent because nothing ever
arrived. Three exchanges went into establishing that the connection simply never
reached us — the port table was what settled it, not the code.
So the server now dials its own port at startup and checks the connection lands
on its own accept loop. If it does not, it says which program will be receiving
the CAT connections and what to do. The counter it compares can only be raised
by our own accept loop, so a real client arriving during the probe makes the
check pass, never fail wrongly.
rouggy
0c8d79e2fa