ipn: don't listen on the unspecified address in test

To avoid the Mac firewall dialog of (test) death.

See 4521a59f30
which I added to help debug this.

ipn/e2e_test.go

@@ -13,6 +13,7 @@ import (
 	"net/http/cookiejar"
 	"net/http/httptest"
 	"net/url"
+	"os"
 	"strings"
 	"testing"
 	"time"
@@ -26,6 +27,13 @@ import (
 	"tailscale.io/control" // not yet released
 )
 
+func init() {
+	// Hacky way to signal to magicsock for now not to bind on the
+	// unspecified address. TODO(bradfitz): clean up wgengine's
+	// constructors.
+	os.Setenv("IN_TS_TEST", "1")
+}
+
 func TestIPN(t *testing.T) {
 	testy.FixLogs(t)
 	defer testy.UnfixLogs(t)

wgengine/magicsock/magicsock.go

@@ -1487,16 +1487,20 @@ func (c *Conn) initialBind() error {
 }
 
 func (c *Conn) bind1(ruc **RebindingUDPConn, which string) error {
+	host := ""
+	if v, _ := strconv.ParseBool(os.Getenv("IN_TS_TEST")); v {
+		host = "127.0.0.1"
+	}
 	var pc net.PacketConn
 	var err error
 	if c.pconnPort == 0 && DefaultPort != 0 {
-		pc, err = net.ListenPacket(which, fmt.Sprintf(":%d", DefaultPort))
+		pc, err = net.ListenPacket(which, fmt.Sprintf("%s:%d", host, DefaultPort))
 		if err != nil {
 			c.logf("magicsock: bind: default port %s/%v unavailable; picking random", which, DefaultPort)
 		}
 	}
 	if pc == nil {
-		pc, err = net.ListenPacket(which, fmt.Sprintf(":%d", c.pconnPort))
+		pc, err = net.ListenPacket(which, fmt.Sprintf("%s:%d", host, c.pconnPort))
 	}
 	if err != nil {
 		c.logf("magicsock: bind(%s/%v): %v", which, c.pconnPort, err)
@@ -1512,12 +1516,16 @@ func (c *Conn) bind1(ruc **RebindingUDPConn, which string) error {
 // Rebind closes and re-binds the UDP sockets.
 // It should be followed by a call to ReSTUN.
 func (c *Conn) Rebind() {
+	host := ""
+	if v, _ := strconv.ParseBool(os.Getenv("IN_TS_TEST")); v {
+		host = "127.0.0.1"
+	}
 	if c.pconnPort != 0 {
 		c.pconn4.mu.Lock()
 		if err := c.pconn4.pconn.Close(); err != nil {
 			c.logf("magicsock: link change close failed: %v", err)
 		}
-		packetConn, err := net.ListenPacket("udp4", fmt.Sprintf(":%d", c.pconnPort))
+		packetConn, err := net.ListenPacket("udp4", fmt.Sprintf("%s:%d", host, c.pconnPort))
 		if err == nil {
 			c.logf("magicsock: link change rebound port: %d", c.pconnPort)
 			c.pconn4.pconn = packetConn.(*net.UDPConn)
@@ -1528,7 +1536,7 @@ func (c *Conn) Rebind() {
 		c.pconn4.mu.Unlock()
 	}
 	c.logf("magicsock: link change, binding new port")
-	packetConn, err := net.ListenPacket("udp4", ":0")
+	packetConn, err := net.ListenPacket("udp4", host+":0")
 	if err != nil {
 		c.logf("magicsock: link change failed to bind new port: %v", err)
 		return