tests: fix race in csync2_u test harness helper function

Author: lge

tests/include.sh

@@ -283,19 +283,35 @@ require()
 
 csync2_u()
 {
+local tmp kid now client_exit nc_exit server_exit
 if csync2 -N $1 -M > /dev/null; then
 csync2 -N $2 -iii -vvv &
 kid=$!
 
+# try to avoid the connect-before-listen race,
+# wait for the expected listening socket to show up,
+# with timeout using bash magic $SECONDS.
+now=$SECONDS
+while ! ss -tnl src $2:csync2 | grep -q ^LISTEN; do
+kill -0 $kid
+(( SECONDS - now < 2 ))
+sleep 0.1
+done
+
 csync2 -N $1 -uvvv
 client_exit=$?
 
-# server still alive?
-# then no connection was made...
-# attempt do one now.
-tmp=$(nc $2 $CSYNC2_PORT <<<"BYE" )
-nc_exit=$?
-
+if ss -tnl src $2:csync2 | grep -q ^LISTEN; then
+# server still alive?
+# then no connection was made...
+# attempt to do one now.
+tmp=$(nc $2 $CSYNC2_PORT <<<"BYE" )
+nc_exit=$?
+
+[[ $nc_exit = 0 ]] || kill $kid
+else
+nc_exit=1
+fi
 wait $kid
 server_exit=$?
 [[ $client_exit = 0 && $server_exit = 0 && $nc_exit != 0 ]]