Merge pull request #3224 from cfromknecht/wtserver-key-family

watchtower: use separate key family for wtserver public key, add watchtower subserver

cmd/lncli/main.go

@@ -300,11 +300,12 @@ func main() {
 		restoreChanBackupCommand,
 	}
 
-	// Add any extra autopilot commands determined by build flags.
+	// Add any extra commands determined by build flags.
 	app.Commands = append(app.Commands, autopilotCommands()...)
 	app.Commands = append(app.Commands, invoicesCommands()...)
 	app.Commands = append(app.Commands, routerCommands()...)
 	app.Commands = append(app.Commands, walletCommands()...)
+	app.Commands = append(app.Commands, watchtowerCommands()...)
 
 	if err := app.Run(os.Args); err != nil {
 		fatal(err)

cmd/lncli/watchtower_active.go

@@ -0,0 +1,65 @@
+// +build watchtowerrpc
+
+package main
+
+import (
+	"context"
+	"encoding/hex"
+
+	"github.com/lightningnetwork/lnd/lnrpc/watchtowerrpc"
+	"github.com/urfave/cli"
+)
+
+func watchtowerCommands() []cli.Command {
+	return []cli.Command{
+		{
+			Name:     "tower",
+			Usage:    "Interact with the watchtower.",
+			Category: "Watchtower",
+			Subcommands: []cli.Command{
+				towerInfoCommand,
+			},
+		},
+	}
+}
+
+func getWatchtowerClient(ctx *cli.Context) (watchtowerrpc.WatchtowerClient, func()) {
+	conn := getClientConn(ctx, false)
+	cleanup := func() {
+		conn.Close()
+	}
+	return watchtowerrpc.NewWatchtowerClient(conn), cleanup
+}
+
+var towerInfoCommand = cli.Command{
+	Name:   "info",
+	Usage:  "Returns basic information related to the active watchtower.",
+	Action: actionDecorator(towerInfo),
+}
+
+func towerInfo(ctx *cli.Context) error {
+	if ctx.NArg() != 0 || ctx.NumFlags() > 0 {
+		return cli.ShowCommandHelp(ctx, "info")
+	}
+
+	client, cleanup := getWatchtowerClient(ctx)
+	defer cleanup()
+
+	req := &watchtowerrpc.GetInfoRequest{}
+	resp, err := client.GetInfo(context.Background(), req)
+	if err != nil {
+		return err
+	}
+
+	printJSON(struct {
+		Pubkey    string   `json:"pubkey"`
+		Listeners []string `json:"listeners"`
+		URIs      []string `json:"uris"`
+	}{
+		Pubkey:    hex.EncodeToString(resp.Pubkey),
+		Listeners: resp.Listeners,
+		URIs:      resp.Uris,
+	})
+
+	return nil
+}

cmd/lncli/watchtower_default.go

@@ -0,0 +1,10 @@
+// +build !watchtowerrpc
+
+package main
+
+import "github.com/urfave/cli"
+
+// watchtowerCommands will return nil for non-watchtowerrpc builds.
+func watchtowerCommands() []cli.Command {
+	return nil
+}

keychain/derivation.go

@@ -96,6 +96,13 @@ const (
 	// session keys are limited to the lifetime of the session and are used
 	// to increase privacy in the watchtower protocol.
 	KeyFamilyTowerSession KeyFamily = 8
+
+	// KeyFamilyTowerID is the family of keys used to derive the public key
+	// of a watchtower. This made distinct from the node key to offer a form
+	// of rudimentary whitelisting, i.e. via knowledge of the pubkey,
+	// preventing others from having full access to the tower just as a
+	// result of knowing the node key.
+	KeyFamilyTowerID KeyFamily = 9
 )
 
 // KeyLocator is a two-tuple that can be used to derive *any* key that has ever

lnd.go

@@ -344,6 +344,18 @@ func Main() error {
 		}
 		defer towerDB.Close()
 
+		towerPrivKey, err := activeChainControl.wallet.DerivePrivKey(
+			keychain.KeyDescriptor{
+				KeyLocator: keychain.KeyLocator{
+					Family: keychain.KeyFamilyTowerID,
+					Index:  0,
+				},
+			},
+		)
+		if err != nil {
+			return err
+		}
+
 		wtConfig, err := cfg.Watchtower.Apply(&watchtower.Config{
 			BlockFetcher:   activeChainControl.chainIO,
 			DB:             towerDB,
@@ -354,7 +366,7 @@ func Main() error {
 					lnwallet.WitnessPubKey, false,
 				)
 			},
-			NodePrivKey: idPrivKey,
+			NodePrivKey: towerPrivKey,
 			PublishTx:   activeChainControl.wallet.PublishTransaction,
 			ChainHash:   *activeNetParams.GenesisHash,
 		}, lncfg.NormalizeAddresses)
@@ -406,7 +418,7 @@ func Main() error {
 	rpcServer, err := newRPCServer(
 		server, macaroonService, cfg.SubRPCServers, serverOpts,
 		restDialOpts, restProxyDest, atplManager, server.invoices,
-		tlsCfg,
+		tower, tlsCfg,
 	)
 	if err != nil {
 		srvrLog.Errorf("unable to start RPC server: %v", err)

lnrpc/watchtowerrpc/config_active.go

@@ -0,0 +1,13 @@
+// +build watchtowerrpc
+
+package watchtowerrpc
+
+// Config is the primary configuration struct for the watchtower RPC server. It
+// contains all items required for the RPC server to carry out its duties. The
+// fields with struct tags are meant to parsed as normal configuration options,
+// while if able to be populated, the latter fields MUST also be specified.
+type Config struct {
+	// Tower is the active watchtower which serves as the primary source for
+	// information presented via RPC.
+	Tower WatchtowerBackend
+}

lnrpc/watchtowerrpc/config_default.go

@@ -0,0 +1,6 @@
+// +build !watchtowerrpc
+
+package watchtowerrpc
+
+// Config is empty for non-watchtowerrpc builds.
+type Config struct{}

lnrpc/watchtowerrpc/driver.go

@@ -0,0 +1,55 @@
+// +build watchtowerrpc
+
+package watchtowerrpc
+
+import (
+	"fmt"
+
+	"github.com/lightningnetwork/lnd/lnrpc"
+)
+
+// createNewSubServer is a helper method that will create the new sub server
+// given the main config dispatcher method. If we're unable to find the config
+// that is meant for us in the config dispatcher, then we'll exit with an
+// error.
+func createNewSubServer(configRegistry lnrpc.SubServerConfigDispatcher) (
+	lnrpc.SubServer, lnrpc.MacaroonPerms, error) {
+
+	// We'll attempt to look up the config that we expect, according to our
+	// subServerName name. If we can't find this, then we'll exit with an
+	// error, as we're unable to properly initialize ourselves without this
+	// config.
+	subServerConf, ok := configRegistry.FetchConfig(subServerName)
+	if !ok {
+		return nil, nil, fmt.Errorf("unable to find config for "+
+			"subserver type %s", subServerName)
+	}
+
+	// Now that we've found an object mapping to our service name, we'll
+	// ensure that it's the type we need.
+	config, ok := subServerConf.(*Config)
+	if !ok {
+		return nil, nil, fmt.Errorf("wrong type of config for "+
+			"subserver %s, expected %T got %T", subServerName,
+			&Config{}, subServerConf)
+	}
+
+	return New(config)
+}
+
+func init() {
+	subServer := &lnrpc.SubServerDriver{
+		SubServerName: subServerName,
+		New: func(c lnrpc.SubServerConfigDispatcher) (lnrpc.SubServer,
+			lnrpc.MacaroonPerms, error) {
+			return createNewSubServer(c)
+		},
+	}
+
+	// If the build tag is active, then we'll register ourselves as a
+	// sub-RPC server within the global lnrpc package namespace.
+	if err := lnrpc.RegisterSubServer(subServer); err != nil {
+		panic(fmt.Sprintf("failed to register sub server driver "+
+			"'%s': %v", subServerName, err))
+	}
+}

lnrpc/watchtowerrpc/handler.go

@@ -0,0 +1,131 @@
+// +build watchtowerrpc
+
+package watchtowerrpc
+
+import (
+	"context"
+	"errors"
+	fmt "fmt"
+
+	"github.com/lightningnetwork/lnd/lnrpc"
+	"google.golang.org/grpc"
+	"gopkg.in/macaroon-bakery.v2/bakery"
+)
+
+const (
+	// subServerName is the name of the sub rpc server. We'll use this name
+	// to register ourselves, and we also require that the main
+	// SubServerConfigDispatcher instance recognizes it as the name of our
+	// RPC service.
+	subServerName = "WatchtowerRPC"
+)
+
+var (
+	// macPermissions maps RPC calls to the permissions they require.
+	macPermissions = map[string][]bakery.Op{
+		"/watchtowerrpc.Watchtower/GetInfo": {{
+			Entity: "info",
+			Action: "read",
+		}},
+	}
+
+	// ErrTowerNotActive signals that RPC calls cannot be processed because
+	// the watchtower is not active.
+	ErrTowerNotActive = errors.New("watchtower not active")
+)
+
+// Handler is the RPC server we'll use to interact with the backing active
+// watchtower.
+type Handler struct {
+	cfg Config
+}
+
+// A compile time check to ensure that Handler fully implements the Handler gRPC
+// service.
+var _ WatchtowerServer = (*Handler)(nil)
+
+// New returns a new instance of the Watchtower sub-server. We also return the
+// set of permissions for the macaroons that we may create within this method.
+// If the macaroons we need aren't found in the filepath, then we'll create them
+// on start up. If we're unable to locate, or create the macaroons we need, then
+// we'll return with an error.
+func New(cfg *Config) (*Handler, lnrpc.MacaroonPerms, error) {
+	return &Handler{*cfg}, macPermissions, nil
+}
+
+// Start launches any helper goroutines required for the Handler to function.
+//
+// NOTE: This is part of the lnrpc.SubServer interface.
+func (c *Handler) Start() error {
+	return nil
+}
+
+// Stop signals any active goroutines for a graceful closure.
+//
+// NOTE: This is part of the lnrpc.SubServer interface.
+func (c *Handler) Stop() error {
+	return nil
+}
+
+// Name returns a unique string representation of the sub-server. This can be
+// used to identify the sub-server and also de-duplicate them.
+//
+// NOTE: This is part of the lnrpc.SubServer interface.
+func (c *Handler) Name() string {
+	return subServerName
+}
+
+// RegisterWithRootServer will be called by the root gRPC server to direct a sub
+// RPC server to register itself with the main gRPC root server. Until this is
+// called, each sub-server won't be able to have requests routed towards it.
+//
+// NOTE: This is part of the lnrpc.SubServer interface.
+func (c *Handler) RegisterWithRootServer(grpcServer *grpc.Server) error {
+	// We make sure that we register it with the main gRPC server to ensure
+	// all our methods are routed properly.
+	RegisterWatchtowerServer(grpcServer, c)
+
+	log.Debugf("Watchtower RPC server successfully register with root " +
+		"gRPC server")
+
+	return nil
+}
+
+// AddTower adds a new watchtower reachable at the given address and considers
+// it for new sessions. If the watchtower already exists, then any new addresses
+// included will be considered when dialing it for session negotiations and
+// backups.
+func (c *Handler) GetInfo(ctx context.Context,
+	req *GetInfoRequest) (*GetInfoResponse, error) {
+
+	if err := c.isActive(); err != nil {
+		return nil, err
+	}
+
+	pubkey := c.cfg.Tower.PubKey().SerializeCompressed()
+
+	var listeners []string
+	for _, addr := range c.cfg.Tower.ListeningAddrs() {
+		listeners = append(listeners, addr.String())
+	}
+
+	var uris []string
+	for _, addr := range c.cfg.Tower.ExternalIPs() {
+		uris = append(uris, fmt.Sprintf("%x@%v", pubkey, addr))
+	}
+
+	return &GetInfoResponse{
+		Pubkey:    pubkey,
+		Listeners: listeners,
+		Uris:      uris,
+	}, nil
+}
+
+// isActive returns nil if the tower backend is initialized, and the Handler can
+// proccess RPC requests.
+func (c *Handler) isActive() error {
+	if c.cfg.Tower != nil {
+		return nil
+	}
+	return ErrTowerNotActive
+}

lnrpc/watchtowerrpc/interface.go

@@ -0,0 +1,23 @@
+package watchtowerrpc
+
+import (
+	"net"
+
+	"github.com/btcsuite/btcd/btcec"
+)
+
+// WatchtowerBackend abstracts access to the watchtower information that is
+// served via RPC connections.
+type WatchtowerBackend interface {
+	// PubKey returns the public key for the watchtower used to
+	// authentication and encrypt traffic with clients.
+	PubKey() *btcec.PublicKey
+
+	// ListeningAddrs returns the listening addresses where the watchtower
+	// server can accept client connections.
+	ListeningAddrs() []net.Addr
+
+	// ExternalIPs returns the addresses where the watchtower can be reached
+	// by clients externally.
+	ExternalIPs() []net.Addr
+}

lnrpc/watchtowerrpc/log.go

@@ -0,0 +1,47 @@
+package watchtowerrpc
+
+import (
+	"github.com/btcsuite/btclog"
+	"github.com/lightningnetwork/lnd/build"
+)
+
+// Subsystem defines the logging code for this subsystem.
+const Subsystem = "WRPC"
+
+// log is a logger that is initialized with no output filters. This means the
+// package will not perform any logging by default until the caller requests it.
+var log btclog.Logger
+
+// The default amount of logging is none.
+func init() {
+	UseLogger(build.NewSubLogger(Subsystem, nil))
+}
+
+// DisableLog disables all library log output. Logging output is disabled by by
+// default until UseLogger is called.
+func DisableLog() {
+	UseLogger(btclog.Disabled)
+}
+
+// UseLogger uses a specified Logger to output package logging info. This
+// should be used in preference to SetLogWriter if the caller is also using
+// btclog.
+func UseLogger(logger btclog.Logger) {
+	log = logger
+}
+
+// logClosure is used to provide a closure over expensive logging operations so
+// don't have to be performed when the logging level doesn't warrant it.
+type logClosure func() string
+
+// String invokes the underlying function and returns the result.
+func (c logClosure) String() string {
+	return c()
+}
+
+// newLogClosure returns a new closure over a function that returns a string
+// which itself provides a Stringer interface so that it can be used with the
+// logging system.
+func newLogClosure(c func() string) logClosure {
+	return logClosure(c)
+}

lnrpc/watchtowerrpc/watchtower.pb.go

@@ -0,0 +1,217 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// source: watchtowerrpc/watchtower.proto
+
+package watchtowerrpc
+
+import (
+	context "context"
+	fmt "fmt"
+	proto "github.com/golang/protobuf/proto"
+	grpc "google.golang.org/grpc"
+	math "math"
+)
+
+// Reference imports to suppress errors if they are not otherwise used.
+var _ = proto.Marshal
+var _ = fmt.Errorf
+var _ = math.Inf
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the proto package it is being compiled against.
+// A compilation error at this line likely means your copy of the
+// proto package needs to be updated.
+const _ = proto.ProtoPackageIsVersion3 // please upgrade the proto package
+
+type GetInfoRequest struct {
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *GetInfoRequest) Reset()         { *m = GetInfoRequest{} }
+func (m *GetInfoRequest) String() string { return proto.CompactTextString(m) }
+func (*GetInfoRequest) ProtoMessage()    {}
+func (*GetInfoRequest) Descriptor() ([]byte, []int) {
+	return fileDescriptor_9f019c0e859ad3d6, []int{0}
+}
+
+func (m *GetInfoRequest) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_GetInfoRequest.Unmarshal(m, b)
+}
+func (m *GetInfoRequest) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_GetInfoRequest.Marshal(b, m, deterministic)
+}
+func (m *GetInfoRequest) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_GetInfoRequest.Merge(m, src)
+}
+func (m *GetInfoRequest) XXX_Size() int {
+	return xxx_messageInfo_GetInfoRequest.Size(m)
+}
+func (m *GetInfoRequest) XXX_DiscardUnknown() {
+	xxx_messageInfo_GetInfoRequest.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_GetInfoRequest proto.InternalMessageInfo
+
+type GetInfoResponse struct {
+	/// The public key of the watchtower.
+	Pubkey []byte `protobuf:"bytes,1,opt,name=pubkey,proto3" json:"pubkey,omitempty"`
+	/// The listening addresses of the watchtower.
+	Listeners []string `protobuf:"bytes,2,rep,name=listeners,proto3" json:"listeners,omitempty"`
+	/// The URIs of the watchtower.
+	Uris                 []string `protobuf:"bytes,3,rep,name=uris,proto3" json:"uris,omitempty"`
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *GetInfoResponse) Reset()         { *m = GetInfoResponse{} }
+func (m *GetInfoResponse) String() string { return proto.CompactTextString(m) }
+func (*GetInfoResponse) ProtoMessage()    {}
+func (*GetInfoResponse) Descriptor() ([]byte, []int) {
+	return fileDescriptor_9f019c0e859ad3d6, []int{1}
+}
+
+func (m *GetInfoResponse) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_GetInfoResponse.Unmarshal(m, b)
+}
+func (m *GetInfoResponse) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_GetInfoResponse.Marshal(b, m, deterministic)
+}
+func (m *GetInfoResponse) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_GetInfoResponse.Merge(m, src)
+}
+func (m *GetInfoResponse) XXX_Size() int {
+	return xxx_messageInfo_GetInfoResponse.Size(m)
+}
+func (m *GetInfoResponse) XXX_DiscardUnknown() {
+	xxx_messageInfo_GetInfoResponse.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_GetInfoResponse proto.InternalMessageInfo
+
+func (m *GetInfoResponse) GetPubkey() []byte {
+	if m != nil {
+		return m.Pubkey
+	}
+	return nil
+}
+
+func (m *GetInfoResponse) GetListeners() []string {
+	if m != nil {
+		return m.Listeners
+	}
+	return nil
+}
+
+func (m *GetInfoResponse) GetUris() []string {
+	if m != nil {
+		return m.Uris
+	}
+	return nil
+}
+
+func init() {
+	proto.RegisterType((*GetInfoRequest)(nil), "watchtowerrpc.GetInfoRequest")
+	proto.RegisterType((*GetInfoResponse)(nil), "watchtowerrpc.GetInfoResponse")
+}
+
+func init() { proto.RegisterFile("watchtowerrpc/watchtower.proto", fileDescriptor_9f019c0e859ad3d6) }
+
+var fileDescriptor_9f019c0e859ad3d6 = []byte{
+	// 213 bytes of a gzipped FileDescriptorProto
+	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0xe2, 0x92, 0x2b, 0x4f, 0x2c, 0x49,
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+	0x0a, 0x8c, 0x1a, 0x3c, 0x41, 0x50, 0x9e, 0x90, 0x0c, 0x17, 0x67, 0x4e, 0x66, 0x71, 0x49, 0x6a,
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+	0x49, 0xc9, 0xe1, 0x92, 0x86, 0xb8, 0xd0, 0xc9, 0x34, 0xca, 0x38, 0x3d, 0xb3, 0x24, 0xa3, 0x34,
+	0x49, 0x2f, 0x39, 0x3f, 0x57, 0x3f, 0x27, 0x33, 0x3d, 0xa3, 0x24, 0x2f, 0x33, 0x2f, 0x3d, 0x2f,
+	0xb5, 0xa4, 0x3c, 0xbf, 0x28, 0x5b, 0x3f, 0x27, 0x2f, 0x45, 0x3f, 0x27, 0x0f, 0x35, 0x3c, 0x8a,
+	0x0a, 0x92, 0x93, 0xd8, 0xc0, 0x61, 0x62, 0x0c, 0x08, 0x00, 0x00, 0xff, 0xff, 0xa1, 0x23, 0x0b,
+	0x68, 0x35, 0x01, 0x00, 0x00,
+}
+
+// Reference imports to suppress errors if they are not otherwise used.
+var _ context.Context
+var _ grpc.ClientConn
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the grpc package it is being compiled against.
+const _ = grpc.SupportPackageIsVersion4
+
+// WatchtowerClient is the client API for Watchtower service.
+//
+// For semantics around ctx use and closing/ending streaming RPCs, please refer to https://godoc.org/google.golang.org/grpc#ClientConn.NewStream.
+type WatchtowerClient interface {
+	//* lncli: tower info
+	//GetInfo returns general information concerning the companion watchtower
+	//including it's public key and URIs where the server is currently
+	//listening for clients.
+	GetInfo(ctx context.Context, in *GetInfoRequest, opts ...grpc.CallOption) (*GetInfoResponse, error)
+}
+
+type watchtowerClient struct {
+	cc *grpc.ClientConn
+}
+
+func NewWatchtowerClient(cc *grpc.ClientConn) WatchtowerClient {
+	return &watchtowerClient{cc}
+}
+
+func (c *watchtowerClient) GetInfo(ctx context.Context, in *GetInfoRequest, opts ...grpc.CallOption) (*GetInfoResponse, error) {
+	out := new(GetInfoResponse)
+	err := c.cc.Invoke(ctx, "/watchtowerrpc.Watchtower/GetInfo", in, out, opts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+// WatchtowerServer is the server API for Watchtower service.
+type WatchtowerServer interface {
+	//* lncli: tower info
+	//GetInfo returns general information concerning the companion watchtower
+	//including it's public key and URIs where the server is currently
+	//listening for clients.
+	GetInfo(context.Context, *GetInfoRequest) (*GetInfoResponse, error)
+}
+
+func RegisterWatchtowerServer(s *grpc.Server, srv WatchtowerServer) {
+	s.RegisterService(&_Watchtower_serviceDesc, srv)
+}
+
+func _Watchtower_GetInfo_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(GetInfoRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(WatchtowerServer).GetInfo(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: "/watchtowerrpc.Watchtower/GetInfo",
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(WatchtowerServer).GetInfo(ctx, req.(*GetInfoRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
+var _Watchtower_serviceDesc = grpc.ServiceDesc{
+	ServiceName: "watchtowerrpc.Watchtower",
+	HandlerType: (*WatchtowerServer)(nil),
+	Methods: []grpc.MethodDesc{
+		{
+			MethodName: "GetInfo",
+			Handler:    _Watchtower_GetInfo_Handler,
+		},
+	},
+	Streams:  []grpc.StreamDesc{},
+	Metadata: "watchtowerrpc/watchtower.proto",
+}

lnrpc/watchtowerrpc/watchtower.proto

@@ -0,0 +1,28 @@
+syntax = "proto3";
+
+package watchtowerrpc;
+
+option go_package = "github.com/lightningnetwork/lnd/lnrpc/watchtowerrpc";
+
+service Watchtower {
+        /** lncli: tower info
+        GetInfo returns general information concerning the companion watchtower
+        including it's public key and URIs where the server is currently
+        listening for clients.
+        */
+        rpc GetInfo(GetInfoRequest) returns (GetInfoResponse);
+}
+
+message GetInfoRequest{
+}
+
+message GetInfoResponse {
+        /// The public key of the watchtower.
+        bytes pubkey = 1 [json_name = "pubkey"];
+
+        /// The listening addresses of the watchtower.
+        repeated string listeners = 2 [json_name = "listeners"];
+
+        /// The URIs of the watchtower.
+        repeated string uris = 3 [json_name = "uris" ];
+}

lntest/itest/lnd_test.go

@@ -42,6 +42,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/invoicesrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/routerrpc"
+	"github.com/lightningnetwork/lnd/lnrpc/watchtowerrpc"
 	"github.com/lightningnetwork/lnd/lntest"
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/lnwire"
@@ -7620,6 +7621,7 @@ func testRevokedCloseRetributionAltruistWatchtower(net *lntest.NetworkHarness,
 		chanAmt     = lnd.MaxBtcFundingAmount
 		paymentAmt  = 10000
 		numInvoices = 6
+		externalIP  = "1.2.3.4"
 	)
 
 	// Since we'd like to test some multi-hop failure scenarios, we'll
@@ -7635,28 +7637,57 @@ func testRevokedCloseRetributionAltruistWatchtower(net *lntest.NetworkHarness,
 	// Willy the watchtower will protect Dave from Carol's breach. He will
 	// remain online in order to punish Carol on Dave's behalf, since the
 	// breach will happen while Dave is offline.
-	willy, err := net.NewNode("Willy", []string{"--watchtower.active"})
+	willy, err := net.NewNode("Willy", []string{
+		"--watchtower.active",
+		"--watchtower.externalip=" + externalIP,
+	})
 	if err != nil {
 		t.Fatalf("unable to create new nodes: %v", err)
 	}
 	defer shutdownAndAssert(net, t, willy)
 
 	ctxt, _ := context.WithTimeout(ctxb, defaultTimeout)
-	willyInfo, err := willy.GetInfo(ctxt, &lnrpc.GetInfoRequest{})
+	willyInfo, err := willy.WatchtowerClient.GetInfo(
+		ctxt, &watchtowerrpc.GetInfoRequest{},
+	)
 	if err != nil {
 		t.Fatalf("unable to getinfo from willy: %v", err)
 	}
 
-	willyAddr := willyInfo.Uris[0]
+	// Assert that Willy has one listener and it is 0.0.0.0:9911 or
-	parts := strings.Split(willyAddr, ":")
+	// [::]:9911. Since no listener is explicitly specified, one of these
-	willyTowerAddr := parts[0]
+	// should be the default depending on whether the host supports IPv6 or
+	// not.
+	if len(willyInfo.Listeners) != 1 {
+		t.Fatalf("Willy should have 1 listener, has %d",
+			len(willyInfo.Listeners))
+	}
+	listener := willyInfo.Listeners[0]
+	if listener != "0.0.0.0:9911" && listener != "[::]:9911" {
+		t.Fatalf("expected listener on 0.0.0.0:9911 or [::]:9911, "+
+			"got %v", listener)
+	}
+
+	// Assert the Willy's URIs properly display the chosen external IP.
+	if len(willyInfo.Uris) != 1 {
+		t.Fatalf("Willy should have 1 uri, has %d",
+			len(willyInfo.Uris))
+	}
+	if !strings.Contains(willyInfo.Uris[0], externalIP) {
+		t.Fatalf("expected uri with %v, got %v",
+			externalIP, willyInfo.Uris[0])
+	}
+
+	// Construct a URI from listening port and public key, since aren't
+	// actually connecting remotely.
+	willyTowerURI := fmt.Sprintf("%x@%s", willyInfo.Pubkey, listener)
 
 	// Dave will be the breached party. We set --nolisten to ensure Carol
 	// won't be able to connect to him and trigger the channel data
 	// protection logic automatically.
 	dave, err := net.NewNode("Dave", []string{
 		"--nolisten",
-		"--wtclient.private-tower-uris=" + willyTowerAddr,
+		"--wtclient.private-tower-uris=" + willyTowerURI,
 	})
 	if err != nil {
 		t.Fatalf("unable to create new node: %v", err)

lntest/node.go

@@ -25,6 +25,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnrpc/invoicesrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/routerrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/walletrpc"
+	"github.com/lightningnetwork/lnd/lnrpc/watchtowerrpc"
 	"github.com/lightningnetwork/lnd/macaroons"
 	"golang.org/x/net/context"
 	"google.golang.org/grpc"
@@ -250,10 +251,11 @@ type HarnessNode struct {
 
 	invoicesrpc.InvoicesClient
 
-	// RouterClient and WalletKitClient cannot be embedded, because a name
+	// RouterClient, WalletKitClient, WatchtowerClient cannot be embedded,
-	// collision would occur with LightningClient.
+	// because a name collision would occur with LightningClient.
-	RouterClient    routerrpc.RouterClient
+	RouterClient     routerrpc.RouterClient
-	WalletKitClient walletrpc.WalletKitClient
+	WalletKitClient  walletrpc.WalletKitClient
+	WatchtowerClient watchtowerrpc.WatchtowerClient
 }
 
 // Assert *HarnessNode implements the lnrpc.LightningClient interface.
@@ -515,6 +517,7 @@ func (hn *HarnessNode) initLightningClient(conn *grpc.ClientConn) error {
 	hn.InvoicesClient = invoicesrpc.NewInvoicesClient(conn)
 	hn.RouterClient = routerrpc.NewRouterClient(conn)
 	hn.WalletKitClient = walletrpc.NewWalletKitClient(conn)
+	hn.WatchtowerClient = watchtowerrpc.NewWatchtowerClient(conn)
 
 	// Set the harness node's pubkey to what the node claims in GetInfo.
 	err := hn.FetchNodeInfo()
@@ -717,6 +720,7 @@ func (hn *HarnessNode) stop() error {
 	hn.processExit = nil
 	hn.LightningClient = nil
 	hn.WalletUnlockerClient = nil
+	hn.WatchtowerClient = nil
 	return nil
 }
 

make/testing_flags.mk

@@ -56,7 +56,7 @@ endif
 
 
 # Construct the integration test command with the added build flags.
-ITEST_TAGS := $(DEV_TAGS) rpctest chainrpc walletrpc signrpc invoicesrpc autopilotrpc routerrpc
+ITEST_TAGS := $(DEV_TAGS) rpctest chainrpc walletrpc signrpc invoicesrpc autopilotrpc routerrpc watchtowerrpc
 
 # Default to btcd backend if not set.
 ifneq ($(backend),)

rpcserver.go

@@ -17,6 +17,7 @@ import (
 
 	"github.com/lightningnetwork/lnd/lnrpc/routerrpc"
 	"github.com/lightningnetwork/lnd/routing/route"
+	"github.com/lightningnetwork/lnd/watchtower"
 
 	"github.com/btcsuite/btcd/blockchain"
 	"github.com/btcsuite/btcd/btcec"
@@ -440,7 +441,7 @@ func newRPCServer(s *server, macService *macaroons.Service,
 	subServerCgs *subRPCServerConfigs, serverOpts []grpc.ServerOption,
 	restDialOpts []grpc.DialOption, restProxyDest string,
 	atpl *autopilot.Manager, invoiceRegistry *invoices.InvoiceRegistry,
-	tlsCfg *tls.Config) (*rpcServer, error) {
+	tower *watchtower.Standalone, tlsCfg *tls.Config) (*rpcServer, error) {
 
 	// Set up router rpc backend.
 	channelGraph := s.chanDB.ChannelGraph()
@@ -494,6 +495,7 @@ func newRPCServer(s *server, macService *macaroons.Service,
 		s.cc, networkDir, macService, atpl, invoiceRegistry,
 		s.htlcSwitch, activeNetParams.Params, s.chanRouter,
 		routerBackend, s.nodeSigner, s.chanDB, s.sweeper,
+		tower,
 	)
 	if err != nil {
 		return nil, err

subrpcserver_config.go

@@ -15,10 +15,12 @@ import (
 	"github.com/lightningnetwork/lnd/lnrpc/routerrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/signrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/walletrpc"
+	"github.com/lightningnetwork/lnd/lnrpc/watchtowerrpc"
 	"github.com/lightningnetwork/lnd/macaroons"
 	"github.com/lightningnetwork/lnd/netann"
 	"github.com/lightningnetwork/lnd/routing"
 	"github.com/lightningnetwork/lnd/sweep"
+	"github.com/lightningnetwork/lnd/watchtower"
 )
 
 // subRPCServerConfigs is special sub-config in the main configuration that
@@ -56,6 +58,10 @@ type subRPCServerConfigs struct {
 	// payment related queries such as requests for estimates of off-chain
 	// fees.
 	RouterRPC *routerrpc.Config `group:"routerrpc" namespace:"routerrpc"`
+
+	// WatchtowerRPC is a sub-RPC server that exposes functionality allowing
+	// clients to monitor and control their embedded watchtower.
+	WatchtowerRPC *watchtowerrpc.Config `group:"watchtowerrpc" namespace:"watchtowerrpc"`
 }
 
 // PopulateDependencies attempts to iterate through all the sub-server configs
@@ -74,7 +80,8 @@ func (s *subRPCServerConfigs) PopulateDependencies(cc *chainControl,
 	routerBackend *routerrpc.RouterBackend,
 	nodeSigner *netann.NodeSigner,
 	chanDB *channeldb.DB,
-	sweeper *sweep.UtxoSweeper) error {
+	sweeper *sweep.UtxoSweeper,
+	tower *watchtower.Standalone) error {
 
 	// First, we'll use reflect to obtain a version of the config struct
 	// that allows us to programmatically inspect its fields.
@@ -206,6 +213,13 @@ func (s *subRPCServerConfigs) PopulateDependencies(cc *chainControl,
 				reflect.ValueOf(routerBackend),
 			)
 
+		case *watchtowerrpc.Config:
+			subCfgValue := extractReflectValue(subCfg)
+
+			subCfgValue.FieldByName("Tower").Set(
+				reflect.ValueOf(tower),
+			)
+
 		default:
 			return fmt.Errorf("unknown field: %v, %T", fieldName,
 				cfg)

watchtower/conf.go

@@ -1,6 +1,7 @@
 package watchtower
 
 import (
+	"strconv"
 	"time"
 )
 
@@ -10,6 +11,9 @@ type Conf struct {
 	// RawListeners configures the watchtower's listening ports/interfaces.
 	RawListeners []string `long:"listen" description:"Add interfaces/ports to listen for peer connections"`
 
+	// RawExternalIPs configures the watchtower's external ports/interfaces.
+	RawExternalIPs []string `long:"externalip" description:"Add interfaces/ports where the watchtower can accept peer connections"`
+
 	// ReadTimeout specifies the duration the tower will wait when trying to
 	// read a message from a client before hanging up.
 	ReadTimeout time.Duration `long:"readtimeout" description:"Duration the watchtower server will wait for messages to be received before hanging up on clients"`
@@ -36,7 +40,7 @@ func (c *Conf) Apply(cfg *Config,
 		// If no addresses are specified by the Config, we will resort
 		// to the default peer port.
 		if len(c.RawListeners) == 0 {
-			addr := DefaultPeerPortStr
+			addr := DefaultListenAddr
 			c.RawListeners = append(c.RawListeners, addr)
 		}
 
@@ -44,7 +48,25 @@ func (c *Conf) Apply(cfg *Config,
 		// used by the brontide listener.
 		var err error
 		cfg.ListenAddrs, err = normalizer(
-			c.RawListeners, DefaultPeerPortStr,
+			c.RawListeners, strconv.Itoa(DefaultPeerPort),
+			cfg.Net.ResolveTCPAddr,
+		)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	// Set the Config's external ips if they are empty.
+	if cfg.ExternalIPs == nil {
+		// Without a network, we will be unable to resolve the external
+		// IP addresses.
+		if cfg.Net == nil {
+			return nil, ErrNoNetwork
+		}
+
+		var err error
+		cfg.ExternalIPs, err = normalizer(
+			c.RawExternalIPs, strconv.Itoa(DefaultPeerPort),
 			cfg.Net.ResolveTCPAddr,
 		)
 		if err != nil {

watchtower/config.go

@@ -28,8 +28,9 @@ const (
 )
 
 var (
-	// DefaultPeerPortStr is the default server port as a string.
+	// DefaultListenAddr is the default watchtower address listening on all
-	DefaultPeerPortStr = fmt.Sprintf(":%d", DefaultPeerPort)
+	// interfaces.
+	DefaultListenAddr = fmt.Sprintf(":%d", DefaultPeerPort)
 )
 
 // Config defines the resources and parameters used to configure a Watchtower.
@@ -73,9 +74,13 @@ type Config struct {
 	// have stronger guarantees wrt. returned error types.
 	PublishTx func(*wire.MsgTx) error
 
-	// ListenAddrs specifies which address to which clients may connect.
+	// ListenAddrs specifies the listening addresses of the tower.
 	ListenAddrs []net.Addr
 
+	// ExternalIPs specifies the addresses to which clients may connect to
+	// the tower.
+	ExternalIPs []net.Addr
+
 	// ReadTimeout specifies how long a client may go without sending a
 	// message.
 	ReadTimeout time.Duration

watchtower/standalone.go

@@ -4,6 +4,7 @@ import (
 	"net"
 	"sync/atomic"
 
+	"github.com/btcsuite/btcd/btcec"
 	"github.com/lightningnetwork/lnd/brontide"
 	"github.com/lightningnetwork/lnd/watchtower/lookout"
 	"github.com/lightningnetwork/lnd/watchtower/wtserver"
@@ -20,6 +21,9 @@ type Standalone struct {
 
 	cfg *Config
 
+	// listeners is a reference to the wtserver's listeners.
+	listeners []net.Listener
+
 	// server is the client endpoint, used for negotiating sessions and
 	// uploading state updates.
 	server wtserver.Interface
@@ -92,9 +96,10 @@ func New(cfg *Config) (*Standalone, error) {
 	}
 
 	return &Standalone{
-		cfg:     cfg,
+		cfg:       cfg,
-		server:  server,
+		listeners: listeners,
-		lookout: lookout,
+		server:    server,
+		lookout:   lookout,
 	}, nil
 }
 
@@ -136,3 +141,37 @@ func (w *Standalone) Stop() error {
 
 	return nil
 }
+
+// PubKey returns the public key for the watchtower used to authentication and
+// encrypt traffic with clients.
+//
+// NOTE: Part of the watchtowerrpc.WatchtowerBackend interface.
+func (w *Standalone) PubKey() *btcec.PublicKey {
+	return w.cfg.NodePrivKey.PubKey()
+}
+
+// ListeningAddrs returns the listening addresses where the watchtower server
+// can accept client connections.
+//
+// NOTE: Part of the watchtowerrpc.WatchtowerBackend interface.
+func (w *Standalone) ListeningAddrs() []net.Addr {
+	addrs := make([]net.Addr, 0, len(w.listeners))
+	for _, listener := range w.listeners {
+		addrs = append(addrs, listener.Addr())
+	}
+
+	return addrs
+}
+
+// ExternalIPs returns the addresses where the watchtower can be reached by
+// clients externally.
+//
+// NOTE: Part of the watchtowerrpc.WatchtowerBackend interface.
+func (w *Standalone) ExternalIPs() []net.Addr {
+	addrs := make([]net.Addr, 0, len(w.cfg.ExternalIPs))
+	for _, addr := range w.cfg.ExternalIPs {
+		addrs = append(addrs, addr)
+	}
+
+	return addrs
+}