ipn/ipnlocal: get peerapi ~working in macOS/iOS NetworkExtension sandbox

IPv4 and IPv6 both work remotely, but IPv6 doesn't yet work from the
machine itself due to routing mysteries.

Untested yet on iOS, but previous prototype worked on iOS, so should
work the same.

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/local.go

@@ -9,8 +9,10 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"net"
 	"os"
 	"runtime"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -248,7 +250,7 @@ func (b *LocalBackend) updateStatus(sb *ipnstate.StatusBuilder, extraLocked func
 	})
 	sb.MutateSelfStatus(func(ss *ipnstate.PeerStatus) {
 		for _, pln := range b.peerAPIListeners {
-			ss.PeerAPIURL = append(ss.PeerAPIURL, "http://"+pln.ln.Addr().String())
+			ss.PeerAPIURL = append(ss.PeerAPIURL, pln.urlStr)
 		}
 	})
 	// TODO: hostinfo, and its networkinfo
@@ -1446,8 +1448,14 @@ func (b *LocalBackend) initPeerAPIListener() {
 	}
 	b.peerAPIListeners = nil
 
+	var tunName string
+	if ge, ok := b.e.(wgengine.InternalsGetter); ok {
+		tunDev, _ := ge.GetInternals()
+		tunName, _ = tunDev.Name()
+	}
+
 	for _, a := range b.netMap.Addresses {
-		ln, err := peerAPIListen(a.IP, b.prevIfState)
+		ln, err := peerAPIListen(a.IP, b.prevIfState, tunName)
 		if err != nil {
 			b.logf("[unexpected] peerAPI listen(%q) error: %v", a.IP, err)
 			continue
@@ -1456,6 +1464,8 @@ func (b *LocalBackend) initPeerAPIListener() {
 			ln: ln,
 			lb: b,
 		}
+		pln.urlStr = "http://" + net.JoinHostPort(a.IP.String(), strconv.Itoa(pln.Port()))
+
 		go pln.serve()
 		b.peerAPIListeners = append(b.peerAPIListeners, pln)
 	}