device: remove listen port race in tests

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

device/device_test.go

@@ -22,15 +22,6 @@ import (
 	"golang.zx2c4.com/wireguard/tun/tuntest"
 )
 
-func getFreePort(tb testing.TB) string {
-	l, err := net.ListenPacket("udp", "localhost:0")
-	if err != nil {
-		tb.Fatal(err)
-	}
-	defer l.Close()
-	return fmt.Sprintf("%d", l.LocalAddr().(*net.UDPAddr).Port)
-}
-
 // uapiCfg returns a string that contains cfg formatted use with IpcSet.
 // cfg is a series of alternating key/value strings.
 // uapiCfg exists because editors and humans like to insert
@@ -55,12 +46,7 @@ func uapiCfg(cfg ...string) string {
 
 // genConfigs generates a pair of configs that connect to each other.
 // The configs use distinct, probably-usable ports.
-func genConfigs(tb testing.TB) (cfgs [2]string) {
+func genConfigs(tb testing.TB) (cfgs [2]string, endpointCfgs [2]string) {
-	var port1, port2 string
-	for port1 == port2 {
-		port1 = getFreePort(tb)
-		port2 = getFreePort(tb)
-	}
 	var key1, key2 NoisePrivateKey
 	_, err := rand.Read(key1[:])
 	if err != nil {
@@ -74,23 +60,29 @@ func genConfigs(tb testing.TB) (cfgs [2]string) {
 
 	cfgs[0] = uapiCfg(
 		"private_key", hex.EncodeToString(key1[:]),
-		"listen_port", port1,
+		"listen_port", "0",
 		"replace_peers", "true",
 		"public_key", hex.EncodeToString(pub2[:]),
 		"protocol_version", "1",
 		"replace_allowed_ips", "true",
 		"allowed_ip", "1.0.0.2/32",
-		"endpoint", "127.0.0.1:"+port2,
+	)
+	endpointCfgs[0] = uapiCfg(
+		"public_key", hex.EncodeToString(pub2[:]),
+		"endpoint", "127.0.0.1:%d",
 	)
 	cfgs[1] = uapiCfg(
 		"private_key", hex.EncodeToString(key2[:]),
-		"listen_port", port2,
+		"listen_port", "0",
 		"replace_peers", "true",
 		"public_key", hex.EncodeToString(pub1[:]),
 		"protocol_version", "1",
 		"replace_allowed_ips", "true",
 		"allowed_ip", "1.0.0.1/32",
-		"endpoint", "127.0.0.1:"+port1,
+	)
+	endpointCfgs[1] = uapiCfg(
+		"public_key", hex.EncodeToString(pub1[:]),
+		"endpoint", "127.0.0.1:%d",
 	)
 	return
 }
@@ -154,19 +146,12 @@ func (pair *testPair) Send(tb testing.TB, ping SendDirection, done chan struct{}
 
 // genTestPair creates a testPair.
 func genTestPair(tb testing.TB) (pair testPair) {
-	const maxAttempts = 10
+	cfg, endpointCfg := genConfigs(tb)
-NextAttempt:
-	for i := 0; i < maxAttempts; i++ {
-		cfg := genConfigs(tb)
 	// Bring up a ChannelTun for each config.
 	for i := range pair {
 		p := &pair[i]
 		p.tun = tuntest.NewChannelTUN()
-			if i == 0 {
+		p.ip = net.IPv4(1, 0, 0, byte(i+1))
-				p.ip = net.ParseIP("1.0.0.1")
-			} else {
-				p.ip = net.ParseIP("1.0.0.2")
-			}
 		level := LogLevelVerbose
 		if _, ok := tb.(*testing.B); ok && !testing.Verbose() {
 			level = LogLevelError
@@ -174,32 +159,27 @@ NextAttempt:
 		p.dev = NewDevice(p.tun.TUN(), NewLogger(level, fmt.Sprintf("dev%d: ", i)))
 		p.dev.Up()
 		if err := p.dev.IpcSet(cfg[i]); err != nil {
-				// genConfigs attempted to pick ports that were free.
+			tb.Errorf("failed to configure device %d: %v", i, err)
-				// There's a tiny window between genConfigs closing the port
-				// and us opening it, during which another process could
-				// start using it. We probably just lost that race.
-				// Try again from the beginning.
-				// If there's something permanent wrong,
-				// we'll see that when we run out of attempts.
-				tb.Logf("failed to configure device %d: %v", i, err)
 			p.dev.Close()
-				continue NextAttempt
+			continue
 		}
-			// The device might still not be up, e.g. due to an error
-			// in RoutineTUNEventReader's call to dev.Up that got swallowed.
-			// Assume it's due to a transient error (port in use), and retry.
 		if !p.dev.isUp() {
-				tb.Logf("device %d did not come up, trying again", i)
+			tb.Errorf("device %d did not come up", i)
 			p.dev.Close()
-				continue NextAttempt
+			continue
 		}
-			// The device is up. Close it when the test completes.
+		endpointCfg[i^1] = fmt.Sprintf(endpointCfg[i^1], p.dev.net.port)
+	}
+	for i := range pair {
+		p := &pair[i]
+		if err := p.dev.IpcSet(endpointCfg[i]); err != nil {
+			tb.Errorf("failed to configure device endpoint %d: %v", i, err)
+			p.dev.Close()
+			continue
+		}
+		// The device is ready. Close it when the test completes.
 		tb.Cleanup(p.dev.Close)
 	}
-		return // success
-	}
-
-	tb.Fatalf("genChannelTUNs: failed %d times", maxAttempts)
 	return
 }