bin/free-port: Try random ports over sequential ones

To diminish race-conditions where two separate processes call
free-port(1) and get the same port that is free at that time, but only
one is able to bind to it.

1 files changed, 7 insertions, 2 deletions

diff --git a/bin/free-port b/bin/free-port
index 2476b4b..1c2af61 100755
--- a/bin/free-port
+++ b/bin/free-port
@@ -61,13 +61,18 @@ done
 shift $((OPTIND - 1))
 
 
-PORT=1024
+MIN_PORT=1024
+MAX_PORT=65536
+
+gen_port() {
+	shuf -n1 -i "${MIN_PORT}-${MAX_PORT}"
+}
 
 while true; do
+	PORT="$(gen_port)"
 	if ! lsof -s TCP:LISTEN -i ":$PORT" >/dev/null; then
 		break
 	fi
-	PORT=$((PORT + 1))
 done
 
 echo "$PORT"