This is probably the most simple D-Bus program you could conceive
To test, run `DBUSXX_VERBOSE=1 ./echo-server` and try the following commands:
dbus-send --dest=org.freedesktop.DBus.Examples.Echo --type=method_call --print-reply /org/freedesktop/DBus/Examples/Echo org.freedesktop.DBus.EchoDemo.Random
dbus-send --dest=org.freedesktop.DBus.Examples.Echo --type=method_call --print-reply /org/freedesktop/DBus/Examples/Echo org.freedesktop.DBus.EchoDemo.Hello string:"world"
dbus-send --dest=org.freedesktop.DBus.Examples.Echo --type=method_call --print-reply /org/freedesktop/DBus/Examples/Echo org.freedesktop.DBus.EchoDemo.Sum array:int32:10,100,250