lnrpc/walletrpc: implement the WalletKitServer gRPC service

In this commit, we implement the newly defiend WalletKitServer gRPC
service. We use the same template w.r.t build tags as the existing
signrpc service.

lnrpc/walletrpc/config_active.go

@@ -0,0 +1,41 @@
+// +build walletrpc
+
+package walletrpc
+
+import (
+	"github.com/lightningnetwork/lnd/keychain"
+	"github.com/lightningnetwork/lnd/lnwallet"
+	"github.com/lightningnetwork/lnd/macaroons"
+)
+
+// Config is the primary configuration struct for the WalletKit RPC server. It
+// contains all the items required for the signer rpc server to carry out its
+// duties. The fields with struct tags are meant to be parsed as normal
+// configuration options, while if able to be populated, the latter fields MUST
+// also be specified.
+type Config struct {
+	// WalletKitMacPath is the path for the signer macaroon. If unspecified
+	// then we assume that the macaroon will be found under the network
+	// directory, named DefaultWalletKitMacFilename.
+	WalletKitMacPath string `long:"walletkitmacaroonpath" description:"Path to the wallet kit macaroon"`
+
+	// NetworkDir is the main network directory wherein the signer rpc
+	// server will find the macaroon named DefaultWalletKitMacFilename.
+	NetworkDir string
+
+	// MacService is the main macaroon service that we'll use to handle
+	// authentication for the signer rpc server.
+	MacService *macaroons.Service
+
+	// FeeEstimator is an instance of the primary fee estimator instance
+	// the WalletKit will use to respond to fee estimation requests.
+	FeeEstimator lnwallet.FeeEstimator
+
+	// Wallet is the primary wallet that the WalletKit will use to proxy
+	// any relevant requests to.
+	Wallet lnwallet.WalletController
+
+	// KeyRing is an interface that the WalletKit will use to derive any
+	// keys due to incoming client requests.
+	KeyRing keychain.KeyRing
+}

lnrpc/walletrpc/config_default.go

@@ -0,0 +1,8 @@
+// +build !walletrpc
+
+package walletrpc
+
+// Config is the primary configuration struct for the WalletKit RPC server.
+// When the server isn't active (via the build flag), callers outside this
+// package will see this shell of a config file.
+type Config struct{}

lnrpc/walletrpc/driver.go

@@ -0,0 +1,73 @@
+// +build walletrpc
+
+package walletrpc
+
+import (
+	"fmt"
+
+	"github.com/lightningnetwork/lnd/lnrpc"
+)
+
+// createNewSubServer is a helper method that will create the new WalletKit RPC
+// 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.
+	walletKitServerConf, 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 := walletKitServerConf.(*Config)
+	if !ok {
+		return nil, nil, fmt.Errorf("wrong type of config for "+
+			"subserver %s, expected %T got %T", subServerName,
+			&Config{}, walletKitServerConf)
+	}
+
+	// Before we try to make the new WalletKit service instance, we'll
+	// perform some sanity checks on the arguments to ensure that they're
+	// useable.
+	switch {
+	case config.MacService != nil && config.NetworkDir == "":
+		return nil, nil, fmt.Errorf("NetworkDir must be set to " +
+			"create WalletKit RPC server")
+
+	case config.FeeEstimator == nil:
+		return nil, nil, fmt.Errorf("FeeEstimator must be set to " +
+			"create WalletKit RPC server")
+
+	case config.Wallet == nil:
+		return nil, nil, fmt.Errorf("Wallet must be set to create " +
+			"WalletKit RPC server")
+
+	case config.KeyRing == nil:
+		return nil, nil, fmt.Errorf("KeyRing must be set to create " +
+			"WalletKit RPC server")
+	}
+
+	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/walletrpc/log.go

@@ -0,0 +1,45 @@
+package walletrpc
+
+import (
+	"github.com/btcsuite/btclog"
+	"github.com/lightningnetwork/lnd/build"
+)
+
+// 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("WLKT", 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/walletrpc/walletkit_server.go

@@ -0,0 +1,345 @@
+// +build walletrpc
+
+package walletrpc
+
+import (
+	"bytes"
+	fmt "fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	"github.com/btcsuite/btcd/wire"
+	"github.com/lightningnetwork/lnd/keychain"
+	"github.com/lightningnetwork/lnd/lnrpc"
+	signrpc "github.com/lightningnetwork/lnd/lnrpc/signrpc"
+	"github.com/lightningnetwork/lnd/lnwallet"
+	context "golang.org/x/net/context"
+	grpc "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 recognize as the name of our
+	subServerName = "WalletKitRPC"
+)
+
+var (
+	// macaroonOps are the set of capabilities that our minted macaroon (if
+	// it doesn't already exist) will have.
+	macaroonOps = []bakery.Op{
+		{
+			Entity: "address",
+			Action: "write",
+		},
+		{
+			Entity: "address",
+			Action: "read",
+		},
+		{
+			Entity: "onchain",
+			Action: "write",
+		},
+		{
+			Entity: "onchain",
+			Action: "read",
+		},
+	}
+
+	// macPermissions maps RPC calls to the permissions they require.
+	macPermissions = map[string][]bakery.Op{
+		"/walletrpc.WalletKit/DeriveNextKey": {{
+			Entity: "address",
+			Action: "read",
+		}},
+		"/walletrpc.WalletKit/DeriveKey": {{
+			Entity: "address",
+			Action: "read",
+		}},
+		"/walletrpc.WalletKit/NextAddr": {{
+			Entity: "address",
+			Action: "read",
+		}},
+		"/walletrpc.WalletKit/PublishTransaction": {{
+			Entity: "onchain",
+			Action: "write",
+		}},
+		"/walletrpc.WalletKit/SendOutputs": {{
+			Entity: "onchain",
+			Action: "write",
+		}},
+		"/walletrpc.WalletKit/EstimateFee": {{
+			Entity: "onchain",
+			Action: "read",
+		}},
+	}
+
+	// DefaultWalletKitMacFilename is the default name of the wallet kit
+	// macaroon that we expect to find via a file handle within the main
+	// configuration file in this package.
+	DefaultWalletKitMacFilename = "walletkit.macaroon"
+)
+
+// WalletKit is a sub-RPC server that exposes a tool kit which allows clients
+// to execute common wallet operations. This includes requesting new addresses,
+// keys (for contracts!), and publishing transactions.
+type WalletKit struct {
+	cfg *Config
+}
+
+// A compile time check to ensure that WalletKit fully implements the
+// WalletKitServer gRPC service.
+var _ WalletKitServer = (*WalletKit)(nil)
+
+// fileExists reports whether the named file or directory exists.
+func fileExists(name string) bool {
+	if _, err := os.Stat(name); err != nil {
+		if os.IsNotExist(err) {
+			return false
+		}
+	}
+	return true
+}
+
+// New creates a new instance of the WalletKit sub-RPC server.
+func New(cfg *Config) (*WalletKit, lnrpc.MacaroonPerms, error) {
+	// If the path of the wallet kit macaroon wasn't specified, then we'll
+	// assume that it's found at the default network directory.
+	if cfg.WalletKitMacPath == "" {
+		cfg.WalletKitMacPath = filepath.Join(
+			cfg.NetworkDir, DefaultWalletKitMacFilename,
+		)
+	}
+
+	// Now that we know the full path of the wallet kit macaroon, we can
+	// check to see if we need to create it or not.
+	macFilePath := cfg.WalletKitMacPath
+	if !fileExists(macFilePath) && cfg.MacService != nil {
+		log.Infof("Baking macaroons for WaleltKit RPC Server at: %v",
+			macFilePath)
+
+		// At this point, we know that the wallet kit macaroon doesn't
+		// yet, exist, so we need to create it with the help of the
+		// main macaroon service.
+		walletKitMac, err := cfg.MacService.Oven.NewMacaroon(
+			context.Background(), bakery.LatestVersion, nil,
+			macaroonOps...,
+		)
+		if err != nil {
+			return nil, nil, err
+		}
+		walletKitMacBytes, err := walletKitMac.M().MarshalBinary()
+		if err != nil {
+			return nil, nil, err
+		}
+		err = ioutil.WriteFile(macFilePath, walletKitMacBytes, 0644)
+		if err != nil {
+			os.Remove(macFilePath)
+			return nil, nil, err
+		}
+	}
+
+	walletKit := &WalletKit{
+		cfg: cfg,
+	}
+
+	return walletKit, macPermissions, nil
+}
+
+// Start launches any helper goroutines required for the sub-server to function.
+//
+// NOTE: This is part of the lnrpc.SubServer interface.
+func (w *WalletKit) Start() error {
+	return nil
+}
+
+// Stop signals any active goroutines for a graceful closure.
+//
+// NOTE: This is part of the lnrpc.SubServer interface.
+func (w *WalletKit) 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 (w *WalletKit) 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 (w *WalletKit) 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.
+	RegisterWalletKitServer(grpcServer, w)
+
+	log.Debugf("WalletKit RPC server successfully registered with " +
+		"root gRPC server")
+
+	return nil
+}
+
+// DeriveNextKey attempts to derive the *next* key within the key family
+// (account in BIP43) specified. This method should return the next external
+// child within this branch.
+func (w *WalletKit) DeriveNextKey(ctx context.Context,
+	req *KeyReq) (*signrpc.KeyDescriptor, error) {
+
+	nextKeyDesc, err := w.cfg.KeyRing.DeriveNextKey(
+		keychain.KeyFamily(req.KeyFamily),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return &signrpc.KeyDescriptor{
+		Key: &signrpc.KeyDescriptor_KeyLoc{
+			KeyLoc: &signrpc.KeyLocator{
+				KeyFamily: int32(nextKeyDesc.Family),
+				KeyIndex:  int32(nextKeyDesc.Index),
+			},
+		},
+	}, nil
+}
+
+// DeriveKey attempts to derive an arbitrary key specified by the passed
+// KeyLocator.
+func (w *WalletKit) DeriveKey(ctx context.Context,
+	req *signrpc.KeyLocator) (*signrpc.KeyDescriptor, error) {
+
+	keyDesc, err := w.cfg.KeyRing.DeriveKey(keychain.KeyLocator{
+		Family: keychain.KeyFamily(req.KeyFamily),
+		Index:  uint32(req.KeyIndex),
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	return &signrpc.KeyDescriptor{
+		Key: &signrpc.KeyDescriptor_KeyLoc{
+			KeyLoc: &signrpc.KeyLocator{
+				KeyFamily: int32(keyDesc.Family),
+				KeyIndex:  int32(keyDesc.Index),
+			},
+		},
+	}, nil
+}
+
+// NextAddr returns the next unused address within the wallet.
+func (w *WalletKit) NextAddr(ctx context.Context,
+	req *AddrRequest) (*AddrResponse, error) {
+
+	addr, err := w.cfg.Wallet.NewAddress(lnwallet.WitnessPubKey, false)
+	if err != nil {
+		return nil, err
+	}
+
+	return &AddrResponse{
+		Addr: addr.String(),
+	}, nil
+}
+
+// Attempts to publish the passed transaction to the network. Once this returns
+// without an error, the wallet will continually attempt to re-broadcast the
+// transaction on start up, until it enters the chain.
+func (w *WalletKit) PublishTransaction(ctx context.Context,
+	req *Transaction) (*PublishResponse, error) {
+
+	switch {
+	// If the client doesn't specify a transaction, then there's nothing to
+	// publish.
+	case len(req.TxHex) == 0:
+		return nil, fmt.Errorf("must provide a transaction to " +
+			"publish")
+	}
+
+	tx := &wire.MsgTx{}
+	txReader := bytes.NewReader(req.TxHex)
+	if err := tx.Deserialize(txReader); err != nil {
+		return nil, err
+	}
+
+	err := w.cfg.Wallet.PublishTransaction(tx)
+	if err != nil {
+		return nil, err
+	}
+
+	return &PublishResponse{}, nil
+}
+
+// SendOutputs is similar to the existing sendmany call in Bitcoind, and allows
+// the caller to create a transaction that sends to several outputs at once.
+// This is ideal when wanting to batch create a set of transactions.
+func (w *WalletKit) SendOutputs(ctx context.Context,
+	req *SendOutputsRequest) (*SendOutputsResponse, error) {
+
+	switch {
+	// If the client didn't specify any outputs to create, then  we can't
+	// proceed .
+	case len(req.Outputs) == 0:
+		return nil, fmt.Errorf("must specify at least one output " +
+			"to create")
+	}
+
+	// Before we can request this transaction to be created, we'll need to
+	// amp the protos back into the format that the internal wallet will
+	// recognize.
+	outputsToCreate := make([]*wire.TxOut, 0, len(req.Outputs))
+	for _, output := range req.Outputs {
+		outputsToCreate = append(outputsToCreate, &wire.TxOut{
+			Value:    output.Value,
+			PkScript: output.PkScript,
+		})
+	}
+
+	// Now that we have the outputs mapped, we can request that the wallet
+	// attempt to create this transaction.
+	tx, err := w.cfg.Wallet.SendOutputs(
+		outputsToCreate, lnwallet.SatPerKWeight(req.SatPerKw),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	var b bytes.Buffer
+	if err := tx.Serialize(&b); err != nil {
+		return nil, err
+	}
+
+	return &SendOutputsResponse{
+		RawTx: b.Bytes(),
+	}, nil
+}
+
+// EstimateFee attempts to query the internal fee estimator of the wallet to
+// determine the fee (in sat/kw) to attach to a transaction in order to achieve
+// the confirmation target.
+func (w *WalletKit) EstimateFee(ctx context.Context,
+	req *EstimateFeeRequest) (*EstimateFeeResponse, error) {
+
+	switch {
+	// A confirmation target of zero doesn't make any sense. Similarly, we
+	// reject confirmation targets of 1 as they're unreasonable.
+	case req.ConfTarget == 0 || req.ConfTarget == 1:
+		return nil, fmt.Errorf("confirmation target must be greater " +
+			"than 1")
+	}
+
+	satPerKw, err := w.cfg.FeeEstimator.EstimateFeePerKW(
+		uint32(req.ConfTarget),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return &EstimateFeeResponse{
+		SatPerKw: int64(satPerKw),
+	}, nil
+}