magicsock, wgengine, ipn, controlclient: plumb regular netchecks to map poll

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

control/controlclient/auto.go

@@ -498,6 +498,15 @@ func (c *Client) SetHostinfo(hi *tailcfg.Hostinfo) {
 	c.cancelMapSafely()
 }
 
+func (c *Client) SetNetInfo(ni *tailcfg.NetInfo) {
+	if ni == nil {
+		panic("nil NetInfo")
+	}
+	c.direct.SetNetInfo(ni)
+	// Send new Hostinfo (which includes NetInfo) to server
+	c.cancelMapSafely()
+}
+
 func (c *Client) sendStatus(who string, err error, url string, nm *NetworkMap) {
 	c.mu.Lock()
 	state := c.state

control/controlclient/direct.go

@@ -176,6 +176,23 @@ func (c *Direct) SetHostinfo(hi *tailcfg.Hostinfo) {
 	c.hostinfo = hi.Clone()
 }
 
+// SetNetInfo clones the provided NetInfo and remembers it for the
+// next update.
+func (c *Direct) SetNetInfo(ni *tailcfg.NetInfo) {
+	if ni == nil {
+		panic("nil NetInfo")
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if c.hostinfo == nil {
+		c.logf("[unexpected] SetNetInfo called with no HostInfo; ignoring NetInfo update: %+v", ni)
+		return
+	}
+	c.logf("NetInfo: %v\n", ni)
+	c.hostinfo.NetInfo = ni.Clone()
+}
+
 func (c *Direct) GetPersist() Persist {
 	c.mu.Lock()
 	defer c.mu.Unlock()
@@ -650,6 +667,12 @@ func encode(v interface{}, serverKey *wgcfg.Key, mkey *wgcfg.PrivateKey) ([]byte
 	if err != nil {
 		return nil, err
 	}
+	const debugMapRequests = false
+	if debugMapRequests {
+		if _, ok := v.(tailcfg.MapRequest); ok {
+			log.Printf("MapRequest: %s", b)
+		}
+	}
 	var nonce [24]byte
 	if _, err := io.ReadFull(rand.Reader, nonce[:]); err != nil {
 		panic(err)

ipn/local.go

@@ -5,7 +5,6 @@
 package ipn
 
 import (
-	"context"
 	"errors"
 	"fmt"
 	"log"
@@ -15,7 +14,6 @@ import (
 
 	"github.com/tailscale/wireguard-go/wgcfg"
 	"tailscale.com/control/controlclient"
-	"tailscale.com/netcheck"
 	"tailscale.com/portlist"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/empty"
@@ -84,6 +82,8 @@ func NewLocalBackend(logf logger.Logf, logid string, store StateStore, e wgengin
 	}
 	b.statusChanged = sync.NewCond(&b.statusLock)
 
+	e.SetNetInfoCallback(b.SetNetInfo)
+
 	if b.portpoll != nil {
 		go b.portpoll.Run()
 		go b.runPoller()
@@ -136,7 +136,6 @@ func (b *LocalBackend) Start(opts Options) error {
 	hi := controlclient.NewHostinfo()
 	hi.BackendLogID = b.backendLogID
 	hi.FrontendLogID = opts.FrontendLogID
-	b.populateNetworkConditions(hi)
 
 	b.mu.Lock()
 
@@ -783,33 +782,16 @@ func (b *LocalBackend) assertClientLocked() {
 	}
 }
 
-// populateNetworkConditions spends up to 2 seconds populating hi's
-// network condition fields.
-//
-// TODO: this is currently just done once at start-up, not regularly on
-// link changes. This will probably need to be moved & rethought. For now
-// we're just gathering some data.
-func (b *LocalBackend) populateNetworkConditions(hi *tailcfg.Hostinfo) {
-	logf := logger.WithPrefix(b.logf, "populateNetworkConditions: ")
-	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
-	defer cancel()
-
-	report, err := netcheck.GetReport(ctx, logf)
-	if err != nil {
-		logf("GetReport: %v", err)
-		return
+func (b *LocalBackend) SetNetInfo(ni *tailcfg.NetInfo) {
+	b.mu.Lock()
+	c := b.c
+	if b.hiCache != nil {
+		b.hiCache.NetInfo = ni.Clone()
 	}
+	b.mu.Unlock()
 
-	ni := &tailcfg.NetInfo{
-		DERPLatency:           map[string]float64{},
-		MappingVariesByDestIP: report.MappingVariesByDestIP,
-		HairPinning:           report.HairPinning,
-	}
-	for server, d := range report.DERPLatency {
-		ni.DERPLatency[server] = d.Seconds()
+	if c == nil {
+		return
 	}
-	ni.WorkingIPv6.Set(report.IPv6)
-	ni.WorkingUDP.Set(report.UDP)
-
-	hi.NetInfo = ni
+	c.SetNetInfo(ni)
 }

ipn/local_test.go

@@ -1,25 +0,0 @@
-// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package ipn
-
-import (
-	"flag"
-	"testing"
-
-	"tailscale.com/tailcfg"
-)
-
-var external = flag.Bool("external", false, "run external network tests")
-
-func TestPopulateNetworkConditions(t *testing.T) {
-	if !*external {
-		t.Skip("skipping network test without -external flag")
-	}
-	b := &LocalBackend{logf: t.Logf}
-	hi := new(tailcfg.Hostinfo)
-	b.populateNetworkConditions(hi)
-	t.Logf("Got: %+v", hi)
-
-}

netcheck/netcheck.go

@@ -27,6 +27,7 @@ type Report struct {
 	IPv6                  bool                     // IPv6 works
 	MappingVariesByDestIP opt.Bool                 // for IPv4
 	HairPinning           opt.Bool                 // for IPv4
+	PreferredDERP         int                      // or 0 for unknown
 	DERPLatency           map[string]time.Duration // keyed by STUN host:port
 
 	// TODO: update Clone when adding new fields
@@ -81,6 +82,10 @@ func GetReport(ctx context.Context, logf logger.Logf) (*Report, error) {
 			ret.IPv6 = true
 		}
 		gotIP[server] = ip
+
+		if ret.PreferredDERP == 0 {
+			ret.PreferredDERP = derpIndexOfSTUNHostPort(server)
+		}
 	}
 	addHair := func(server, ip string, d time.Duration) {
 		mu.Lock()
@@ -204,3 +209,14 @@ func GetReport(ctx context.Context, logf logger.Logf) (*Report, error) {
 
 	return ret.Clone(), nil
 }
+
+// derpIndexOfSTUNHostPort extracts the derp indes from a STUN host:port like
+// "derp1-v6.tailscale.com:3478" or "derp2.tailscale.com:3478".
+// It returns 0 on unexpected input.
+func derpIndexOfSTUNHostPort(hp string) int {
+	hp = strings.TrimSuffix(hp, ".tailscale.com:3478")
+	hp = strings.TrimSuffix(hp, "-v6")
+	hp = strings.TrimPrefix(hp, "derp")
+	n, _ := strconv.Atoi(hp)
+	return n // 0 on error is okay
+}

tailcfg/tailcfg.go

@@ -260,6 +260,17 @@ type NetInfo struct {
 	// WorkingUDP is whether UDP works.
 	WorkingUDP opt.Bool
 
+	// PreferredDERP is this node's preferred DERP server
+	// for incoming traffic. The node might be be temporarily
+	// connected to multiple DERP servers (to send to other nodes)
+	// but PreferredDERP is the instance number that the node
+	// subscribes to traffic at.
+	// Zero means disconnected or unknown.
+	PreferredDERP int
+
+	// LinkType is the current link type, if known.
+	LinkType string // "wired", "wifi", "mobile" (LTE, 4G, 3G, etc)
+
 	// DERPLatency is the fastest recent time to reach various
 	// DERP STUN servers, in seconds. The map key is the DERP
 	// server's STUN host:port.
@@ -268,6 +279,25 @@ type NetInfo struct {
 	// material change, as any change here also gets uploaded to
 	// the control plane.
 	DERPLatency map[string]float64 `json:",omitempty"`
+
+	// Update Clone and BasicallyEqual when adding fields.
+}
+
+// BasicallyEqual reports whether ni and ni2 are basically equal, ignoring
+// changes in DERPLatency.
+func (ni *NetInfo) BasicallyEqual(ni2 *NetInfo) bool {
+	if (ni == nil) != (ni2 == nil) {
+		return false
+	}
+	if ni == nil {
+		return true
+	}
+	return ni.MappingVariesByDestIP == ni2.MappingVariesByDestIP &&
+		ni.HairPinning == ni2.HairPinning &&
+		ni.WorkingIPv6 == ni2.WorkingIPv6 &&
+		ni.WorkingUDP == ni2.WorkingUDP &&
+		ni.PreferredDERP == ni2.PreferredDERP &&
+		ni.LinkType == ni2.LinkType
 }
 
 func (ni *NetInfo) Clone() (res *NetInfo) {

tailcfg/tailcfg_test.go

@@ -304,3 +304,19 @@ func TestNodeEqual(t *testing.T) {
 		}
 	}
 }
+
+func TestNetInfoFields(t *testing.T) {
+	handled := []string{
+		"MappingVariesByDestIP",
+		"HairPinning",
+		"WorkingIPv6",
+		"WorkingUDP",
+		"PreferredDERP",
+		"LinkType",
+		"DERPLatency",
+	}
+	if have := fieldsOf(reflect.TypeOf(NetInfo{})); !reflect.DeepEqual(have, handled) {
+		t.Errorf("NetInfo.Clone/BasicallyEqually check might be out of sync\nfields: %q\nhandled: %q\n",
+			have, handled)
+	}
+}

wgengine/magicsock/derpmap.go

@@ -19,8 +19,9 @@ const DerpMagicIP = "127.3.3.40"
 var derpMagicIP = net.ParseIP(DerpMagicIP).To4()
 
 var (
-	derpHostOfIndex = map[int]string{} // index (fake port number) -> hostname
+	derpHostOfIndex = map[int]string{} // node ID index (fake port number) -> hostname
 	derpIndexOfHost = map[string]int{} // derpHostOfIndex reversed
+	derpNodeID      []int
 )
 
 const (
@@ -42,6 +43,7 @@ func addDerper(i int, host string) {
 	}
 	derpHostOfIndex[i] = host
 	derpIndexOfHost[host] = i
+	derpNodeID = append(derpNodeID, i)
 }
 
 // derpHost returns the hostname of a DERP server index (a fake port

wgengine/magicsock/magicsock.go

@@ -11,7 +11,9 @@ import (
 	"encoding/binary"
 	"errors"
 	"fmt"
+	"hash/fnv"
 	"log"
+	"math/rand"
 	"net"
 	"os"
 	"strconv"
@@ -28,9 +30,12 @@ import (
 	"tailscale.com/derp"
 	"tailscale.com/derp/derphttp"
 	"tailscale.com/interfaces"
+	"tailscale.com/netcheck"
 	"tailscale.com/stun"
 	"tailscale.com/stunner"
+	"tailscale.com/tailcfg"
 	"tailscale.com/types/key"
+	"tailscale.com/types/logger"
 	"tailscale.com/version"
 )
 
@@ -66,6 +71,10 @@ type Conn struct {
 	// Its Loaded value is always non-nil.
 	stunReceiveFunc atomic.Value // of func(p []byte, fromAddr *net.UDPAddr)
 
+	netInfoMu   sync.Mutex
+	netInfoFunc func(*tailcfg.NetInfo) // nil until set
+	netInfoLast *tailcfg.NetInfo
+
 	udpRecvCh  chan udpReadResult
 	derpRecvCh chan derpReadResult
 
@@ -204,15 +213,17 @@ func (c *Conn) epUpdate(ctx context.Context) {
 
 		go func() {
 			defer close(lastDone)
-			nearestDerp, endpoints, err := c.determineEndpoints(epCtx)
+
+			c.updateNetInfo() // best effort
+
+			endpoints, err := c.determineEndpoints(epCtx)
 			if err != nil {
 				c.logf("magicsock.Conn: endpoint update failed: %v", err)
 				// TODO(crawshaw): are there any conditions under which
 				// we should trigger a retry based on the error here?
 				return
 			}
-			derpChanged := c.setNearestDerp(nearestDerp)
-			if stringsEqual(endpoints, lastEndpoints) && !derpChanged {
+			if stringsEqual(endpoints, lastEndpoints) {
 				return
 			}
 			lastEndpoints = endpoints
@@ -222,6 +233,98 @@ func (c *Conn) epUpdate(ctx context.Context) {
 	}
 }
 
+func (c *Conn) updateNetInfo() {
+	logf := logger.WithPrefix(c.logf, "updateNetInfo: ")
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	report, err := netcheck.GetReport(ctx, logf)
+	if err != nil {
+		logf("GetReport: %v", err)
+		return
+	}
+
+	ni := &tailcfg.NetInfo{
+		DERPLatency:           map[string]float64{},
+		MappingVariesByDestIP: report.MappingVariesByDestIP,
+		HairPinning:           report.HairPinning,
+	}
+	for server, d := range report.DERPLatency {
+		ni.DERPLatency[server] = d.Seconds()
+	}
+	ni.WorkingIPv6.Set(report.IPv6)
+	ni.WorkingUDP.Set(report.UDP)
+	ni.PreferredDERP = report.PreferredDERP
+
+	if ni.PreferredDERP == 0 {
+		// Perhaps UDP is blocked. Pick a deterministic but arbitrary
+		// one.
+		ni.PreferredDERP = c.pickDERPFallback()
+	}
+	c.setNearestDerp(ni.PreferredDERP)
+
+	// TODO: set link type
+
+	c.callNetInfoCallback(ni)
+}
+
+var processStartUnixNano = time.Now().UnixNano()
+
+// pickDERPFallback returns a non-zero but deterministic DERP node to
+// connect to.  This is only used if netcheck couldn't find the
+// nearest one (for instance, if UDP is blocked and thus STUN latency
+// checks aren't working).
+func (c *Conn) pickDERPFallback() int {
+	c.derpMu.Lock()
+	defer c.derpMu.Unlock()
+
+	if c.myDerp != 0 {
+		// If we already had one in the past, stay on it.
+		return c.myDerp
+	}
+
+	if len(derpNodeID) == 0 {
+		// No DERP nodes registered.
+		return 0
+	}
+
+	h := fnv.New64()
+	h.Write([]byte(fmt.Sprintf("%p/%d", c, processStartUnixNano))) // arbitrary
+	return derpNodeID[rand.New(rand.NewSource(int64(h.Sum64()))).Intn(len(derpNodeID))]
+}
+
+// callNetInfoCallback calls the NetInfo callback (if previously
+// registered with SetNetInfoCallback) if ni has substantially changed
+// since the last state.
+//
+// callNetInfoCallback takes ownership of ni.
+func (c *Conn) callNetInfoCallback(ni *tailcfg.NetInfo) {
+	c.netInfoMu.Lock()
+	defer c.netInfoMu.Unlock()
+	if ni.BasicallyEqual(c.netInfoLast) {
+		return
+	}
+	c.netInfoLast = ni
+	if c.netInfoFunc != nil {
+		c.logf("netInfo update: %+v", ni)
+		go c.netInfoFunc(ni)
+	}
+}
+
+func (c *Conn) SetNetInfoCallback(fn func(*tailcfg.NetInfo)) {
+	if fn == nil {
+		panic("nil NetInfoCallback")
+	}
+	c.netInfoMu.Lock()
+	last := c.netInfoLast
+	c.netInfoFunc = fn
+	c.netInfoMu.Unlock()
+
+	if last != nil {
+		fn(last)
+	}
+}
+
 func (c *Conn) setNearestDerp(derpNum int) (changed bool) {
 	c.derpMu.Lock()
 	defer c.derpMu.Unlock()
@@ -236,8 +339,7 @@ func (c *Conn) setNearestDerp(derpNum int) (changed bool) {
 
 // determineEndpoints returns the machine's endpoint addresses. It
 // does a STUN lookup to determine its public address.
-func (c *Conn) determineEndpoints(ctx context.Context) (nearestDerp int, ipPorts []string, err error) {
-	nearestDerp = derpNYC // for now
+func (c *Conn) determineEndpoints(ctx context.Context) (ipPorts []string, err error) {
 	var (
 		alreadyMu sync.Mutex
 		already   = make(map[string]bool) // endpoint -> true
@@ -265,7 +367,7 @@ func (c *Conn) determineEndpoints(ctx context.Context) (nearestDerp int, ipPorts
 	c.stunReceiveFunc.Store(s.Receive)
 
 	if err := s.Run(ctx); err != nil {
-		return 0, nil, err
+		return nil, err
 	}
 
 	c.ignoreSTUNPackets()
@@ -273,7 +375,7 @@ func (c *Conn) determineEndpoints(ctx context.Context) (nearestDerp int, ipPorts
 	if localAddr := c.pconn.LocalAddr(); localAddr.IP.IsUnspecified() {
 		ips, loopback, err := interfaces.LocalAddresses()
 		if err != nil {
-			return 0, nil, err
+			return nil, err
 		}
 		reason := "localAddresses"
 		if len(ips) == 0 {
@@ -303,7 +405,7 @@ func (c *Conn) determineEndpoints(ctx context.Context) (nearestDerp int, ipPorts
 	// The STUN address(es) are always first so that legacy wireguard
 	// can use eps[0] as its only known endpoint address (although that's
 	// obviously non-ideal).
-	return nearestDerp, eps, nil
+	return eps, nil
 }
 
 func stringsEqual(x, y []string) bool {

wgengine/magicsock/magicsock_test.go

@@ -80,3 +80,42 @@ func TestDerpIPConstant(t *testing.T) {
 		t.Errorf("derpMagicIP is len %d; want 4", len(derpMagicIP))
 	}
 }
+
+func TestPickDERPFallback(t *testing.T) {
+	if len(derpNodeID) == 0 {
+		t.Fatal("no DERP nodes registered; this test needs an update after DERP node runtime discovery")
+	}
+
+	c := new(Conn)
+	a := c.pickDERPFallback()
+	if a == 0 {
+		t.Fatalf("pickDERPFallback returned 0")
+	}
+
+	// Test that it's consistent.
+	for i := 0; i < 50; i++ {
+		b := c.pickDERPFallback()
+		if a != b {
+			t.Fatalf("got inconsistent %d vs %d values", a, b)
+		}
+	}
+
+	// Test that that the pointer value of c is blended in and
+	// distribution over nodes works.
+	got := map[int]int{}
+	for i := 0; i < 50; i++ {
+		c = new(Conn)
+		got[c.pickDERPFallback()]++
+	}
+	t.Logf("distribution: %v", got)
+	if len(got) < 2 {
+		t.Errorf("expected more than 1 node; got %v", got)
+	}
+
+	// Test that stickiness works.
+	const someNode = 123456
+	c.myDerp = someNode
+	if got := c.pickDERPFallback(); got != someNode {
+		t.Errorf("not sticky: got %v; want %v", got, someNode)
+	}
+}

wgengine/userspace.go

@@ -603,3 +603,7 @@ func (e *userspaceEngine) LinkChange(isExpensive bool) {
 		e.logf("IpcSetOperation: %v\n", err)
 	}
 }
+
+func (e *userspaceEngine) SetNetInfoCallback(cb NetInfoCallback) {
+	e.magicConn.SetNetInfoCallback(cb)
+}

wgengine/watchdog.go

@@ -69,6 +69,9 @@ func (e *watchdogEngine) SetFilter(filt *filter.Filter) {
 func (e *watchdogEngine) SetStatusCallback(cb StatusCallback) {
 	e.watchdog("SetStatusCallback", func() { e.wrap.SetStatusCallback(cb) })
 }
+func (e *watchdogEngine) SetNetInfoCallback(cb NetInfoCallback) {
+	e.watchdog("SetNetInfoCallback", func() { e.wrap.SetNetInfoCallback(cb) })
+}
 func (e *watchdogEngine) RequestStatus() {
 	e.watchdog("RequestStatus", func() { e.wrap.RequestStatus() })
 }

wgengine/wgengine.go

@@ -40,6 +40,9 @@ type Status struct {
 // Exactly one of Status or error is non-nil.
 type StatusCallback func(*Status, error)
 
+// NetInfoCallback is the type used by Engine.SetNetInfoCallback.
+type NetInfoCallback func(*tailcfg.NetInfo)
+
 // RouteSettings is the full WireGuard config data (set of peers keys,
 // IP, etc in wgcfg.Config) plus the things that WireGuard doesn't do
 // itself, like DNS stuff.
@@ -123,4 +126,8 @@ type Engine interface {
 	// where sending packets uses substantial power or money,
 	// such as mobile data on a phone.
 	LinkChange(isExpensive bool)
+
+	// SetNetInfoCallback sets the function to call when a
+	// new NetInfo summary is available.
+	SetNetInfoCallback(NetInfoCallback)
 }