netutil: improve port allocation (#5485)

pkg/netutil/netutil_test.go

@@ -0,0 +1,24 @@
+package netutil_test
+
+import (
+	"testing"
+
+	"github.com/minio/minio-go/v7/pkg/set"
+	"github.com/stretchr/testify/assert"
+
+	"github.com/pomerium/pomerium/pkg/netutil"
+)
+
+func TestAllocatePorts(t *testing.T) {
+	t.Parallel()
+
+	seen := set.NewStringSet()
+	for i := 0; i < 100; i++ {
+		ports, err := netutil.AllocatePorts(3)
+		assert.NoError(t, err)
+		for _, p := range ports {
+			assert.False(t, seen.Contains(p), "should not re-use ports")
+			seen.Add(p)
+		}
+	}
+}