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>

control/controlclient/noise.go

@@ -19,9 +19,11 @@ import (
 	"golang.org/x/net/http2"
 	"tailscale.com/control/controlbase"
 	"tailscale.com/control/controlhttp"
+	"tailscale.com/net/netmon"
 	"tailscale.com/net/tsdial"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/key"
+	"tailscale.com/types/logger"
 	"tailscale.com/util/mak"
 	"tailscale.com/util/multierr"
 	"tailscale.com/util/singleflight"
@@ -167,6 +169,9 @@ type NoiseClient struct {
 	// be nil.
 	dialPlan func() *tailcfg.ControlDialPlan
 
+	logf   logger.Logf
+	netMon *netmon.Monitor
+
 	// mu only protects the following variables.
 	mu       sync.Mutex
 	last     *noiseConn // or nil
@@ -177,8 +182,9 @@ type NoiseClient struct {
 // NewNoiseClient returns a new noiseClient for the provided server and machine key.
 // serverURL is of the form https://<host>:<port> (no trailing slash).
 //
+// netMon may be nil, if non-nil it's used to do faster interface lookups.
 // dialPlan may be nil
-func NewNoiseClient(privKey key.MachinePrivate, serverPubKey key.MachinePublic, serverURL string, dialer *tsdial.Dialer, dialPlan func() *tailcfg.ControlDialPlan) (*NoiseClient, error) {
+func NewNoiseClient(privKey key.MachinePrivate, serverPubKey key.MachinePublic, serverURL string, dialer *tsdial.Dialer, logf logger.Logf, netMon *netmon.Monitor, dialPlan func() *tailcfg.ControlDialPlan) (*NoiseClient, error) {
 	u, err := url.Parse(serverURL)
 	if err != nil {
 		return nil, err
@@ -207,6 +213,8 @@ func NewNoiseClient(privKey key.MachinePrivate, serverPubKey key.MachinePublic,
 		httpsPort:    httpsPort,
 		dialer:       dialer,
 		dialPlan:     dialPlan,
+		logf:         logf,
+		netMon:       netMon,
 	}
 
 	// Create the HTTP/2 Transport using a net/http.Transport
@@ -366,6 +374,8 @@ func (nc *NoiseClient) dial() (*noiseConn, error) {
 		ProtocolVersion: uint16(tailcfg.CurrentCapabilityVersion),
 		Dialer:          nc.dialer.SystemDial,
 		DialPlan:        dialPlan,
+		Logf:            nc.logf,
+		NetMon:          nc.netMon,
 	}).Dial(ctx)
 	if err != nil {
 		return nil, err