ipn/ipnlocal: pass down interface state to peerapi ListenConfig hook

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

ipn/ipnlocal/local.go

@@ -143,6 +143,7 @@ func NewLocalBackend(logf logger.Logf, logid string, store ipn.StateStore, e wge
 	b.statusChanged = sync.NewCond(&b.statusLock)
 
 	linkMon := e.GetLinkMonitor()
+	b.prevIfState = linkMon.InterfaceState()
 	// Call our linkChange code once with the current state, and
 	// then also whenever it changes:
 	b.linkChange(false, linkMon.InterfaceState())
@@ -1446,7 +1447,7 @@ func (b *LocalBackend) initPeerAPIListener() {
 	b.peerAPIListeners = nil
 
 	for _, a := range b.netMap.Addresses {
-		ln, err := peerAPIListen(a.IP)
+		ln, err := peerAPIListen(a.IP, b.prevIfState)
 		if err != nil {
 			b.logf("[unexpected] peerAPI listen(%q) error: %v", a.IP, err)
 			continue

ipn/ipnlocal/peerapi.go

@@ -16,18 +16,19 @@ import (
 	"strconv"
 
 	"inet.af/netaddr"
+	"tailscale.com/net/interfaces"
 	"tailscale.com/tailcfg"
 )
 
-var initListenConfig func(*net.ListenConfig, netaddr.IP) error
+var initListenConfig func(*net.ListenConfig, netaddr.IP, *interfaces.State) error
 
-func peerAPIListen(ip netaddr.IP) (ln net.Listener, err error) {
+func peerAPIListen(ip netaddr.IP, ifState *interfaces.State) (ln net.Listener, err error) {
 	var lc net.ListenConfig
 	if initListenConfig != nil {
 		// On iOS/macOS, this sets the lc.Control hook to
 		// setsockopt the interface index to bind to, to get
 		// out of the network sandbox.
-		if err := initListenConfig(&lc, ip); err != nil {
+		if err := initListenConfig(&lc, ip, ifState); err != nil {
 			return nil, err
 		}
 	}