netann: add new HostAnnouncer to support dynamic IPs via domains

In this commit, we add a new sub-system, then `HostAnnouncer` which
allows a users without a static IP address to ensure that lnd always
announces the most up to date address based on a domain name. A new
command line flag `--external-hosts` has been added which allows a user
to specify one or most hosts that should be periodically resolved to
update any advertised IPs the node has.

Fixes #1624.

config.go

@@ -80,6 +80,11 @@ const (
 
 	defaultAlias = ""
 	defaultColor = "#3399FF"
+
+	// defaultHostSampleInterval is the default amount of time that the
+	// HostAnnouncer will wait between DNS resolutions to check if the
+	// backing IP of a host has changed.
+	defaultHostSampleInterval = time.Minute * 5
 )
 
 var (
@@ -157,6 +162,7 @@ type Config struct {
 	RawRESTListeners []string `long:"restlisten" description:"Add an interface/port/socket to listen for REST connections"`
 	RawListeners     []string `long:"listen" description:"Add an interface/port to listen for peer connections"`
 	RawExternalIPs   []string `long:"externalip" description:"Add an ip:port to the list of local addresses we claim to listen on to peers. If a port is not specified, the default (9735) will be used regardless of other parameters"`
+	ExternalHosts    []string `long:"externalhosts" description:"A set of hosts that should be periodically resolved to announce IPs for"`
 	RPCListeners     []net.Addr
 	RESTListeners    []net.Addr
 	RestCORS         []string `long:"restcors" description:"Add an ip:port/hostname to allow cross origin access from. To allow all origins, set as \"*\"."`
@@ -659,6 +665,10 @@ func ValidateConfig(cfg Config, usageMessage string) (*Config, error) {
 		return nil, errors.New("NAT traversal cannot be used when " +
 			"listening is disabled")
 	}
+	if cfg.NAT && len(cfg.ExternalHosts) != 0 {
+		return nil, errors.New("NAT support and externalhosts are " +
+			"mutually exclusive, only one should be selected")
+	}
 
 	// Determine the active chain configuration and its parameters.
 	switch {

netann/host_ann.go

@@ -0,0 +1,198 @@
+package netann
+
+import (
+	"net"
+	"sync"
+
+	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/ticker"
+)
+
+// HostAnnouncerConfig is the main config for the HostAnnouncer.
+type HostAnnouncerConfig struct {
+	// Hosts is the set of hosts we should watch for IP changes.
+	Hosts []string
+
+	// RefreshTicker ticks each time we should check for any address
+	// changes.
+	RefreshTicker ticker.Ticker
+
+	// LookupHost performs DNS resolution on a given host and returns its
+	// addresses.
+	LookupHost func(string) (net.Addr, error)
+
+	// AdvertisedIPs is the set of IPs that we've already announced with
+	// our current NodeAnnouncement. This set will be constructed to avoid
+	// unnecessary node NodeAnnouncement updates.
+	AdvertisedIPs map[string]struct{}
+
+	// AnnounceNewIPs announces a new set of IP addresses for the backing
+	// Lightning node. The first set of addresses is the new set of
+	// addresses that we should advertise, while the other set are the
+	// stale addresses that we should no longer advertise.
+	AnnounceNewIPs func([]net.Addr, map[string]struct{}) error
+}
+
+// HostAnnouncer is a sub-system that allows a user to specify a set of hosts
+// for lnd that will be continually resolved to notice any IP address changes.
+// If the target IP address for a host changes, then we'll generate a new
+// NodeAnnouncement that includes these new IPs.
+type HostAnnouncer struct {
+	cfg HostAnnouncerConfig
+
+	quit chan struct{}
+	wg   sync.WaitGroup
+
+	startOnce sync.Once
+	stopOnce  sync.Once
+}
+
+// NewHostAnnouncer returns a new instance of the HostAnnouncer.
+func NewHostAnnouncer(cfg HostAnnouncerConfig) *HostAnnouncer {
+	return &HostAnnouncer{
+		cfg:  cfg,
+		quit: make(chan struct{}),
+	}
+}
+
+// Start starts the HostAnnouncer.
+func (h *HostAnnouncer) Start() error {
+	h.startOnce.Do(func() {
+		h.wg.Add(1)
+		go h.hostWatcher()
+	})
+
+	return nil
+}
+
+// Stop signals the HostAnnouncer for a graceful stop.
+func (h *HostAnnouncer) Stop() error {
+	h.stopOnce.Do(func() {
+		close(h.quit)
+		h.wg.Wait()
+	})
+
+	return nil
+}
+
+// hostWatcher periodically attempts to resolve the IP for each host, updating
+// them if they change within the interval.
+func (h *HostAnnouncer) hostWatcher() {
+	defer h.wg.Done()
+
+	ipMapping := make(map[string]net.Addr)
+	refreshHosts := func() {
+
+		// We'll now run through each of our hosts to check if they had
+		// their backing IPs changed. If so, we'll want to re-announce
+		// them.
+		var addrsToUpdate []net.Addr
+		addrsToRemove := make(map[string]struct{})
+		for _, host := range h.cfg.Hosts {
+			newAddr, err := h.cfg.LookupHost(host)
+			if err != nil {
+				log.Warnf("unable to resolve IP for "+
+					"host %v: %v", host, err)
+				continue
+			}
+
+			// If nothing has changed since the last time we
+			// checked, then we don't need to do any updates.
+			oldAddr, oldAddrFound := ipMapping[host]
+			if oldAddrFound && oldAddr.String() == newAddr.String() {
+				continue
+			}
+
+			// Update the IP mapping now, as if this is the first
+			// time then we don't need to send a new announcement.
+			ipMapping[host] = newAddr
+
+			// If this IP has already been announced, then we'll
+			// skip it to avoid triggering an unnecessary node
+			// announcement update.
+			_, ipAnnounced := h.cfg.AdvertisedIPs[newAddr.String()]
+			if ipAnnounced {
+				continue
+			}
+
+			// If we've reached this point, then the old address
+			// was found, and the new address we just looked up
+			// differs from the old one.
+			log.Debugf("IP change detected! %v: %v -> %v", host,
+				oldAddr, newAddr)
+
+			// If we had already advertised an addr for this host,
+			// then we'll need to remove that old stale address.
+			if oldAddr != nil {
+				addrsToRemove[oldAddr.String()] = struct{}{}
+			}
+
+			addrsToUpdate = append(addrsToUpdate, newAddr)
+		}
+
+		// If we don't have any addresses to update, then we can skip
+		// things around until the next round.
+		if len(addrsToUpdate) == 0 {
+			log.Debugf("No IP changes detected for hosts: %v",
+				h.cfg.Hosts)
+			return
+		}
+
+		// Now that we know the set of IPs we need to update, we'll do
+		// them all in a single batch.
+		err := h.cfg.AnnounceNewIPs(addrsToUpdate, addrsToRemove)
+		if err != nil {
+			log.Warnf("unable to announce new IPs: %v", err)
+		}
+	}
+
+	refreshHosts()
+
+	h.cfg.RefreshTicker.Resume()
+
+	for {
+		select {
+		case <-h.cfg.RefreshTicker.Ticks():
+			log.Debugf("HostAnnouncer checking for any IP " +
+				"changes...")
+
+			refreshHosts()
+
+		case <-h.quit:
+			return
+		}
+	}
+}
+
+// NodeAnnUpdater describes a function that's able to update our current node
+// announcement on disk. It returns the updated node announcement given a set
+// of updates to be applied to the current node announcement.
+type NodeAnnUpdater func(refresh bool, modifier ...NodeAnnModifier,
+) (lnwire.NodeAnnouncement, error)
+
+// IPAnnouncer is a factory function that generates a new function that uses
+// the passed annUpdater function to to announce new IP changes for a given
+// host.
+func IPAnnouncer(annUpdater NodeAnnUpdater) func([]net.Addr, map[string]struct{}) error {
+	return func(newAddrs []net.Addr, oldAddrs map[string]struct{}) error {
+		_, err := annUpdater(true, func(currentNodeAnn *lnwire.NodeAnnouncement) {
+			// To ensure we don't duplicate any addresses, we'll
+			// filter out the same of addresses we should no longer
+			// advertise.
+			filteredAddrs := make(
+				[]net.Addr, 0, len(currentNodeAnn.Addresses),
+			)
+			for _, addr := range currentNodeAnn.Addresses {
+				if _, ok := oldAddrs[addr.String()]; ok {
+					continue
+				}
+
+				filteredAddrs = append(filteredAddrs, addr)
+			}
+
+			filteredAddrs = append(filteredAddrs, newAddrs...)
+			currentNodeAnn.Addresses = filteredAddrs
+		})
+		return err
+	}
+}

netann/host_ann_test.go

@@ -0,0 +1,276 @@
+package netann
+
+import (
+	"net"
+	"testing"
+	"time"
+
+	"github.com/lightningnetwork/lnd/ticker"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestHostAnnouncerUpdates tests that the HostAnnouncer will properly announce
+// a new set of addresses each time a target host changes and will noop if not
+// change happens during an interval.
+func TestHostAnnouncerUpdates(t *testing.T) {
+	t.Parallel()
+
+	hosts := []string{"test.com", "example.com"}
+	startingAddrs := []net.Addr{
+		&net.TCPAddr{
+			IP: net.ParseIP("1.1.1.1"),
+		},
+		&net.TCPAddr{
+			IP: net.ParseIP("8.8.8.8"),
+		},
+	}
+
+	ticker := ticker.NewForce(time.Hour * 24)
+
+	testTimeout := time.Millisecond * 200
+
+	type annReq struct {
+		newAddrs     []net.Addr
+		removedAddrs map[string]struct{}
+	}
+
+	testCases := []struct {
+		preAdvertisedIPs map[string]struct{}
+		startingAddrs    []net.Addr
+
+		preTickHosts  map[string]net.Addr
+		postTickHosts map[string]net.Addr
+
+		updateTriggered bool
+
+		newAddrs     []net.Addr
+		removedAddrs map[string]struct{}
+	}{
+		// The set of addresses are the same before and after a tick we
+		// expect no change.
+		{
+			preTickHosts: map[string]net.Addr{
+				"test.com": &net.TCPAddr{
+					IP: net.ParseIP("1.1.1.1"),
+				},
+				"example.com": &net.TCPAddr{
+					IP: net.ParseIP("8.8.8.8"),
+				},
+			},
+			startingAddrs: startingAddrs,
+
+			postTickHosts: map[string]net.Addr{
+				"test.com": &net.TCPAddr{
+					IP: net.ParseIP("1.1.1.1"),
+				},
+				"example.com": &net.TCPAddr{
+					IP: net.ParseIP("8.8.8.8"),
+				},
+			},
+
+			updateTriggered: false,
+		},
+
+		// Half of the addresses are changed out, the new one should be
+		// added with the old one forgotten.
+		{
+			preTickHosts: map[string]net.Addr{
+				"test.com": &net.TCPAddr{
+					IP: net.ParseIP("1.1.1.1"),
+				},
+				"example.com": &net.TCPAddr{
+					IP: net.ParseIP("8.8.8.8"),
+				},
+			},
+			startingAddrs: startingAddrs,
+
+			postTickHosts: map[string]net.Addr{
+				"test.com": &net.TCPAddr{
+					IP: net.ParseIP("1.1.1.1"),
+				},
+				"example.com": &net.TCPAddr{
+					IP: net.ParseIP("9.9.9.9"),
+				},
+			},
+
+			updateTriggered: true,
+			newAddrs: []net.Addr{
+				&net.TCPAddr{
+					IP: net.ParseIP("9.9.9.9"),
+				},
+			},
+			removedAddrs: map[string]struct{}{
+				"8.8.8.8:0": {},
+			},
+		},
+
+		// All addresses change, they should all be refreshed.
+		{
+			preTickHosts: map[string]net.Addr{
+				"test.com": &net.TCPAddr{
+					IP: net.ParseIP("1.1.1.1"),
+				},
+				"example.com": &net.TCPAddr{
+					IP: net.ParseIP("8.8.8.8"),
+				},
+			},
+			startingAddrs: startingAddrs,
+
+			postTickHosts: map[string]net.Addr{
+				"test.com": &net.TCPAddr{
+					IP: net.ParseIP("2.2.2.2"),
+				},
+				"example.com": &net.TCPAddr{
+					IP: net.ParseIP("9.9.9.9"),
+				},
+			},
+
+			updateTriggered: true,
+			newAddrs: []net.Addr{
+				&net.TCPAddr{
+					IP: net.ParseIP("2.2.2.2"),
+				},
+				&net.TCPAddr{
+					IP: net.ParseIP("9.9.9.9"),
+				},
+			},
+			removedAddrs: map[string]struct{}{
+				"8.8.8.8:0": {},
+				"1.1.1.1:0": {},
+			},
+		},
+
+		// Two addresses, one has already been advertised on start up,
+		// so we only expect one of them to be announced again. After
+		// the tick we don't expect an update trigger since nothing.
+		// changed.
+		{
+			preAdvertisedIPs: map[string]struct{}{
+				"1.1.1.1:0": {},
+			},
+			startingAddrs: []net.Addr{
+				&net.TCPAddr{
+					IP: net.ParseIP("8.8.8.8"),
+				},
+			},
+			preTickHosts: map[string]net.Addr{
+				"test.com": &net.TCPAddr{
+					IP: net.ParseIP("1.1.1.1"),
+				},
+				"example.com": &net.TCPAddr{
+					IP: net.ParseIP("8.8.8.8"),
+				},
+			},
+			postTickHosts: map[string]net.Addr{
+				"test.com": &net.TCPAddr{
+					IP: net.ParseIP("1.1.1.1"),
+				},
+				"example.com": &net.TCPAddr{
+					IP: net.ParseIP("8.8.8.8"),
+				},
+			},
+
+			updateTriggered: false,
+		},
+	}
+	for idx, testCase := range testCases {
+		hostResps := make(chan net.Addr)
+		annReqs := make(chan annReq)
+		hostAnncer := NewHostAnnouncer(HostAnnouncerConfig{
+			Hosts:         hosts,
+			AdvertisedIPs: testCase.preAdvertisedIPs,
+			RefreshTicker: ticker,
+			LookupHost: func(str string) (net.Addr, error) {
+				return <-hostResps, nil
+			},
+			AnnounceNewIPs: func(newAddrs []net.Addr,
+				removeAddrs map[string]struct{}) error {
+
+				annReqs <- annReq{
+					newAddrs:     newAddrs,
+					removedAddrs: removeAddrs,
+				}
+
+				return nil
+			},
+		})
+		if err := hostAnncer.Start(); err != nil {
+			t.Fatalf("unable to start announcer: %v", err)
+		}
+
+		// As soon as the announcer starts, it'll try to query for the
+		// state of the hosts. We'll return the preTick state for all
+		// hosts.
+		for i := 0; i < len(hosts); i++ {
+			hostResps <- testCase.preTickHosts[hosts[i]]
+		}
+
+		// Since this is the first time the announcer is starting up,
+		// we expect it to advertise the hosts as they exist before any
+		// updates.
+		select {
+		case addrUpdate := <-annReqs:
+			assert.Equal(
+				t, testCase.startingAddrs, addrUpdate.newAddrs,
+				"addresses should match",
+			)
+			assert.Empty(
+				t, addrUpdate.removedAddrs,
+				"removed addrs should match",
+			)
+
+		case <-time.After(testTimeout):
+			t.Fatalf("#%v: no addr update sent", idx)
+		}
+
+		// We'll now force a tick which'll force another query. This
+		// time we'll respond with the set of the hosts as they should
+		// be post-tick.
+		ticker.Force <- time.Time{}
+
+		for i := 0; i < len(hosts); i++ {
+			hostResps <- testCase.postTickHosts[hosts[i]]
+		}
+
+		// If we expect an update, then we'll assert that we received
+		// the proper set of modified addresses.
+		if testCase.updateTriggered {
+
+			select {
+			// The receive update should match exactly what the
+			// test case dictates.
+			case addrUpdate := <-annReqs:
+				require.Equal(
+					t, testCase.newAddrs, addrUpdate.newAddrs,
+					"addresses should match",
+				)
+
+				require.Equal(
+					t, testCase.removedAddrs, addrUpdate.removedAddrs,
+					"removed addrs should match",
+				)
+
+			case <-time.After(testTimeout):
+				t.Fatalf("#%v: no addr update set", idx)
+			}
+
+			if err := hostAnncer.Stop(); err != nil {
+				t.Fatalf("unable to stop announcer: %v", err)
+			}
+			continue
+		}
+
+		// Otherwise, no updates should be sent since nothing changed.
+		select {
+		case <-annReqs:
+			t.Fatalf("#%v: expected no call to AnnounceNewIPs", idx)
+
+		case <-time.After(testTimeout):
+		}
+
+		if err := hostAnncer.Stop(); err != nil {
+			t.Fatalf("unable to stop announcer: %v", err)
+		}
+	}
+}

server.go

@@ -271,6 +271,8 @@ type server struct {
 	// provide insights into their health and performance.
 	chanEventStore *chanfitness.ChannelEventStore
 
+	hostAnn *netann.HostAnnouncer
+
 	quit chan struct{}
 
 	wg sync.WaitGroup
@@ -1231,6 +1233,26 @@ func newServer(cfg *Config, listenAddrs []net.Addr, chanDB *channeldb.DB,
 		}
 	}
 
+	if len(cfg.ExternalHosts) != 0 {
+		advertisedIPs := make(map[string]struct{})
+		for _, addr := range s.currentNodeAnn.Addresses {
+			advertisedIPs[addr.String()] = struct{}{}
+		}
+
+		s.hostAnn = netann.NewHostAnnouncer(netann.HostAnnouncerConfig{
+			Hosts:         cfg.ExternalHosts,
+			RefreshTicker: ticker.New(defaultHostSampleInterval),
+			LookupHost: func(host string) (net.Addr, error) {
+				return lncfg.ParseAddressString(
+					host, strconv.Itoa(defaultPeerPort),
+					cfg.net.ResolveTCPAddr,
+				)
+			},
+			AdvertisedIPs:  advertisedIPs,
+			AnnounceNewIPs: netann.IPAnnouncer(s.genNodeAnnouncement),
+		})
+	}
+
 	// Create the connection manager which will be responsible for
 	// maintaining persistent outbound connections and also accepting new
 	// incoming connections
@@ -1274,6 +1296,13 @@ func (s *server) Start() error {
 			go s.watchExternalIP()
 		}
 
+		if s.hostAnn != nil {
+			if err := s.hostAnn.Start(); err != nil {
+				startErr = err
+				return
+			}
+		}
+
 		// Start the notification server. This is used so channel
 		// management goroutines can be notified when a funding
 		// transaction reaches a sufficient number of confirmations, or
@@ -1492,6 +1521,13 @@ func (s *server) Stop() error {
 			s.towerClient.Stop()
 		}
 
+		if s.hostAnn != nil {
+			if err := s.hostAnn.Stop(); err != nil {
+				srvrLog.Warnf("unable to shut down host "+
+					"annoucner: %v", err)
+			}
+		}
+
 		// Wait for all lingering goroutines to quit.
 		s.wg.Wait()