chore: consolidate various randomPort() implementations (#12362)

Consolidates our existing randomPort() implementations to package testutil

testutil/port.go

@@ -0,0 +1,45 @@
+package testutil
+
+import (
+	"math/rand"
+	"net"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+var (
+	// nolint:gosec // not used for cryptography
+	rnd   = rand.New(rand.NewSource(time.Now().Unix()))
+	rndMu sync.Mutex
+)
+
+// RandomPort is a helper function to find a free random port.
+// Note that the OS may reallocate the port very quickly, so
+// this is not _guaranteed_.
+func RandomPort(t *testing.T) int {
+	random, err := net.Listen("tcp", "127.0.0.1:0")
+	require.NoError(t, err, "failed to listen on localhost")
+	_ = random.Close()
+	tcpAddr, valid := random.Addr().(*net.TCPAddr)
+	require.True(t, valid, "random port address is not a *net.TCPAddr?!")
+	return tcpAddr.Port
+}
+
+// RandomPortNoListen returns a random port in the ephemeral port range.
+// Does not attempt to listen and close to find a port as the OS may
+// reallocate the port very quickly.
+func RandomPortNoListen(*testing.T) uint16 {
+	const (
+		// Overlap of windows, linux in https://en.wikipedia.org/wiki/Ephemeral_port
+		min = 49152
+		max = 60999
+	)
+	n := max - min
+	rndMu.Lock()
+	x := rnd.Intn(n)
+	rndMu.Unlock()
+	return uint16(min + x)
+}