all: avoid repeated default interface lookups

On some platforms (notably macOS and iOS) we look up the default
interface to bind outgoing connections to. This is both duplicated
work and results in logspam when the default interface is not available
(i.e. when a phone has no connectivity, we log an error and thus cause
more things that we will try to upload and fail).

Fixed by passing around a netmon.Monitor to more places, so that we can
use its cached interface state.

Fixes #7850
Updates #7621

Signed-off-by: Mihai Parparita <mihai@tailscale.com>

cmd/derper/depaware.txt

@@ -86,7 +86,7 @@ tailscale.com/cmd/derper dependencies: (generated by github.com/tailscale/depawa
      💣 tailscale.com/net/interfaces                                 from tailscale.com/net/netns+
         tailscale.com/net/netaddr                                    from tailscale.com/ipn+
         tailscale.com/net/netknob                                    from tailscale.com/net/netns
-        tailscale.com/net/netmon                                     from tailscale.com/net/sockstats
+        tailscale.com/net/netmon                                     from tailscale.com/net/sockstats+
         tailscale.com/net/netns                                      from tailscale.com/derp/derphttp
         tailscale.com/net/netutil                                    from tailscale.com/client/tailscale
         tailscale.com/net/packet                                     from tailscale.com/wgengine/filter

cmd/tailscale/cli/netcheck.go

@@ -19,6 +19,7 @@ import (
 	"tailscale.com/envknob"
 	"tailscale.com/ipn"
 	"tailscale.com/net/netcheck"
+	"tailscale.com/net/netmon"
 	"tailscale.com/net/portmapper"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/logger"
@@ -45,9 +46,14 @@ var netcheckArgs struct {
 }
 
 func runNetcheck(ctx context.Context, args []string) error {
+	logf := logger.WithPrefix(log.Printf, "portmap: ")
+	netMon, err := netmon.New(logf)
+	if err != nil {
+		return err
+	}
 	c := &netcheck.Client{
 		UDPBindAddr: envknob.String("TS_DEBUG_NETCHECK_UDP_BIND"),
-		PortMapper:  portmapper.NewClient(logger.WithPrefix(log.Printf, "portmap: "), nil, nil),
+		PortMapper:  portmapper.NewClient(logf, netMon, nil, nil),
 		UseDNSCache: false, // always resolve, don't cache
 	}
 	if netcheckArgs.verbose {

cmd/tailscale/depaware.txt

@@ -74,7 +74,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         tailscale.com/net/netcheck                                   from tailscale.com/cmd/tailscale/cli
         tailscale.com/net/neterror                                   from tailscale.com/net/netcheck+
         tailscale.com/net/netknob                                    from tailscale.com/net/netns
-        tailscale.com/net/netmon                                     from tailscale.com/net/sockstats
+        tailscale.com/net/netmon                                     from tailscale.com/net/sockstats+
         tailscale.com/net/netns                                      from tailscale.com/derp/derphttp+
         tailscale.com/net/netutil                                    from tailscale.com/client/tailscale+
         tailscale.com/net/packet                                     from tailscale.com/wgengine/filter+

cmd/tailscaled/debug.go

@@ -193,8 +193,8 @@ func checkDerp(ctx context.Context, derpRegion string) (err error) {
 	priv1 := key.NewNode()
 	priv2 := key.NewNode()
 
-	c1 := derphttp.NewRegionClient(priv1, log.Printf, getRegion)
-	c2 := derphttp.NewRegionClient(priv2, log.Printf, getRegion)
+	c1 := derphttp.NewRegionClient(priv1, log.Printf, nil, getRegion)
+	c2 := derphttp.NewRegionClient(priv2, log.Printf, nil, getRegion)
 	defer func() {
 		if err != nil {
 			c1.Close()

cmd/tailscaled/tailscaled.go

@@ -329,7 +329,15 @@ var logPol *logpolicy.Policy
 var debugMux *http.ServeMux
 
 func run() error {
-	pol := logpolicy.New(logtail.CollectionNode)
+	var logf logger.Logf = log.Printf
+	netMon, err := netmon.New(func(format string, args ...any) {
+		logf(format, args...)
+	})
+	if err != nil {
+		return fmt.Errorf("netmon.New: %w", err)
+	}
+
+	pol := logpolicy.New(logtail.CollectionNode, netMon)
 	pol.SetVerbosityLevel(args.verbose)
 	logPol = pol
 	defer func() {
@@ -353,7 +361,6 @@ func run() error {
 		return nil
 	}
 
-	var logf logger.Logf = log.Printf
 	if envknob.Bool("TS_DEBUG_MEMORY") {
 		logf = logger.RusagePrefixLog(logf)
 	}
@@ -379,10 +386,10 @@ func run() error {
 		debugMux = newDebugMux()
 	}
 
-	return startIPNServer(context.Background(), logf, pol.PublicID)
+	return startIPNServer(context.Background(), logf, pol.PublicID, netMon)
 }
 
-func startIPNServer(ctx context.Context, logf logger.Logf, logID logid.PublicID) error {
+func startIPNServer(ctx context.Context, logf logger.Logf, logID logid.PublicID, netMon *netmon.Monitor) error {
 	ln, err := safesocket.Listen(args.socketpath)
 	if err != nil {
 		return fmt.Errorf("safesocket.Listen: %v", err)
@@ -408,7 +415,7 @@ func startIPNServer(ctx context.Context, logf logger.Logf, logID logid.PublicID)
 		}
 	}()
 
-	srv := ipnserver.New(logf, logID)
+	srv := ipnserver.New(logf, logID, netMon)
 	if debugMux != nil {
 		debugMux.HandleFunc("/debug/ipn", srv.ServeHTMLStatus)
 	}
@@ -426,7 +433,7 @@ func startIPNServer(ctx context.Context, logf logger.Logf, logID logid.PublicID)
 				return
 			}
 		}
-		lb, err := getLocalBackend(ctx, logf, logID)
+		lb, err := getLocalBackend(ctx, logf, logID, netMon)
 		if err == nil {
 			logf("got LocalBackend in %v", time.Since(t0).Round(time.Millisecond))
 			srv.SetLocalBackend(lb)
@@ -450,11 +457,7 @@ func startIPNServer(ctx context.Context, logf logger.Logf, logID logid.PublicID)
 	return nil
 }
 
-func getLocalBackend(ctx context.Context, logf logger.Logf, logID logid.PublicID) (_ *ipnlocal.LocalBackend, retErr error) {
-	netMon, err := netmon.New(logf)
-	if err != nil {
-		return nil, fmt.Errorf("netmon.New: %w", err)
-	}
+func getLocalBackend(ctx context.Context, logf logger.Logf, logID logid.PublicID, netMon *netmon.Monitor) (_ *ipnlocal.LocalBackend, retErr error) {
 	if logPol != nil {
 		logPol.Logtail.SetNetMon(netMon)
 	}

cmd/tailscaled/tailscaled_windows.go

@@ -45,6 +45,7 @@ import (
 	"tailscale.com/logpolicy"
 	"tailscale.com/logtail/backoff"
 	"tailscale.com/net/dns"
+	"tailscale.com/net/netmon"
 	"tailscale.com/net/tstun"
 	"tailscale.com/types/logger"
 	"tailscale.com/types/logid"
@@ -291,8 +292,13 @@ func beWindowsSubprocess() bool {
 		}
 	}()
 
+	netMon, err := netmon.New(log.Printf)
+	if err != nil {
+		log.Printf("Could not create netMon: %v", err)
+		netMon = nil
+	}
 	publicLogID, _ := logid.ParsePublicID(logID)
-	err := startIPNServer(ctx, log.Printf, publicLogID)
+	err = startIPNServer(ctx, log.Printf, publicLogID, netMon)
 	if err != nil {
 		log.Fatalf("ipnserver: %v", err)
 	}

cmd/tsconnect/wasm/wasm_js.go

@@ -123,7 +123,7 @@ func newIPN(jsConfig js.Value) map[string]any {
 	}
 
 	logid := lpc.PublicID
-	srv := ipnserver.New(logf, logid)
+	srv := ipnserver.New(logf, logid, nil /* no netMon */)
 	lb, err := ipnlocal.NewLocalBackend(logf, logid, store, dialer, eng, controlclient.LoginEphemeral)
 	if err != nil {
 		log.Fatalf("ipnlocal.NewLocalBackend: %v", err)