net/tsdial: move more weirdo dialing into new tsdial package, plumb

Not done yet, but this move more of the outbound dial special casing
from random packages into tsdial, which aspires to be the one unified
place for all outbound dialing shenanigans.

Then this plumbs it all around, so everybody is ultimately
holding on to the same dialer.

As of this commit, macOS/iOS using an exit node should be able to
reach to the exit node's DoH DNS proxy over peerapi, doing the sockopt
to stay within the Network Extension.

A number of steps remain, including but limited to:

* move a bunch more random dialing stuff

* make netstack-mode tailscaled be able to use exit node's DNS proxy,
  teaching tsdial's resolver to use it when an exit node is in use.

Updates #1713

Change-Id: I1e8ee378f125421c2b816f47bc2c6d913ddcd2f5
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/local.go

@@ -36,6 +36,7 @@ import (
 	"tailscale.com/net/dns"
 	"tailscale.com/net/interfaces"
 	"tailscale.com/net/tsaddr"
+	"tailscale.com/net/tsdial"
 	"tailscale.com/paths"
 	"tailscale.com/portlist"
 	"tailscale.com/tailcfg"
@@ -88,6 +89,7 @@ type LocalBackend struct {
 	statsLogf             logger.Logf        // for printing peers stats on change
 	e                     wgengine.Engine
 	store                 ipn.StateStore
+	dialer                *tsdial.Dialer // non-nil
 	backendLogID          string
 	unregisterLinkMon     func()
 	unregisterHealthWatch func()
@@ -155,10 +157,18 @@ type clientGen func(controlclient.Options) (controlclient.Client, error)
 
 // NewLocalBackend returns a new LocalBackend that is ready to run,
 // but is not actually running.
-func NewLocalBackend(logf logger.Logf, logid string, store ipn.StateStore, e wgengine.Engine) (*LocalBackend, error) {
+//
+// If dialer is nil, a new one is made.
+func NewLocalBackend(logf logger.Logf, logid string, store ipn.StateStore, dialer *tsdial.Dialer, e wgengine.Engine) (*LocalBackend, error) {
 	if e == nil {
-		panic("ipn.NewLocalBackend: wgengine must not be nil")
+		panic("ipn.NewLocalBackend: engine must not be nil")
 	}
+	if dialer == nil {
+		dialer = new(tsdial.Dialer)
+	}
+	e.AddNetworkMapCallback(func(nm *netmap.NetworkMap) {
+		dialer.SetDNSMap(tsdial.DNSMapFromNetworkMap(nm))
+	})
 
 	osshare.SetFileSharingEnabled(false, logf)
 
@@ -176,11 +186,14 @@ func NewLocalBackend(logf logger.Logf, logid string, store ipn.StateStore, e wge
 		statsLogf:      logger.LogOnChange(logf, 5*time.Minute, time.Now),
 		e:              e,
 		store:          store,
+		dialer:         dialer,
 		backendLogID:   logid,
 		state:          ipn.NoState,
 		portpoll:       portpoll,
 		gotPortPollRes: make(chan struct{}),
 	}
+	dialer.SetPeerDialControlFuncGetter(b.peerDialControlFunc)
+
 	// Default filter blocks everything and logs nothing, until Start() is called.
 	b.setFilter(filter.NewAllowNone(logf, &netaddr.IPSet{}))
 
@@ -210,6 +223,11 @@ func NewLocalBackend(logf logger.Logf, logid string, store ipn.StateStore, e wge
 	return b, nil
 }
 
+// Dialer returns the backend's dialer.
+func (b *LocalBackend) Dialer() *tsdial.Dialer {
+	return b.dialer
+}
+
 // SetDirectFileRoot sets the directory to download files to directly,
 // without buffering them through an intermediate daemon-owned
 // tailcfg.UserID-specific directory.
@@ -3035,9 +3053,9 @@ func disabledSysctls(sysctls ...string) (disabled []string, err error) {
 // bind to dial out to other peers.
 var peerDialControlFunc func(*LocalBackend) func(network, address string, c syscall.RawConn) error
 
-// PeerDialControlFunc returns a net.Dialer.Control func (possibly nil) to use to
+// peerDialControlFunc returns a net.Dialer.Control func (possibly nil) to use to
 // dial other Tailscale peers from the current environment.
-func (b *LocalBackend) PeerDialControlFunc() func(network, address string, c syscall.RawConn) error {
+func (b *LocalBackend) peerDialControlFunc() func(network, address string, c syscall.RawConn) error {
 	if peerDialControlFunc != nil {
 		return peerDialControlFunc(b)
 	}

ipn/ipnlocal/local_test.go

@@ -445,7 +445,7 @@ func TestLazyMachineKeyGeneration(t *testing.T) {
 		t.Fatalf("NewFakeUserspaceEngine: %v", err)
 	}
 	t.Cleanup(eng.Close)
-	lb, err := NewLocalBackend(logf, "logid", store, eng)
+	lb, err := NewLocalBackend(logf, "logid", store, nil, eng)
 	if err != nil {
 		t.Fatalf("NewLocalBackend: %v", err)
 	}

ipn/ipnlocal/loglines_test.go

@@ -54,7 +54,7 @@ func TestLocalLogLines(t *testing.T) {
 	}
 	t.Cleanup(e.Close)
 
-	lb, err := NewLocalBackend(logf, idA.String(), store, e)
+	lb, err := NewLocalBackend(logf, idA.String(), store, nil, e)
 	if err != nil {
 		t.Fatal(err)
 	}

ipn/ipnlocal/state_test.go

@@ -284,7 +284,7 @@ func TestStateMachine(t *testing.T) {
 	t.Cleanup(e.Close)
 
 	cc := newMockControl(t)
-	b, err := NewLocalBackend(logf, "logid", store, e)
+	b, err := NewLocalBackend(logf, "logid", store, nil, e)
 	if err != nil {
 		t.Fatalf("NewLocalBackend: %v", err)
 	}
@@ -941,7 +941,7 @@ func TestWGEngineStatusRace(t *testing.T) {
 	eng, err := wgengine.NewFakeUserspaceEngine(logf, 0)
 	c.Assert(err, qt.IsNil)
 	t.Cleanup(eng.Close)
-	b, err := NewLocalBackend(logf, "logid", new(ipn.MemoryStore), eng)
+	b, err := NewLocalBackend(logf, "logid", new(ipn.MemoryStore), nil, eng)
 	c.Assert(err, qt.IsNil)
 
 	cc := newMockControl(t)