loopd: add SOCKS proxy config option to dial swap server over Tor

client.go

@@ -78,7 +78,7 @@ type Client struct {
 }
 
 // NewClient returns a new instance to initiate swaps with.
-func NewClient(dbDir string, serverAddress string, insecure bool,
+func NewClient(dbDir string, serverAddress, proxyAddress string, insecure bool,
 	tlsPathServer string, lnd *lndclient.LndServices, maxLSATCost,
 	maxLSATFee btcutil.Amount) (*Client, func(), error) {
 
@@ -92,8 +92,8 @@ func NewClient(dbDir string, serverAddress string, insecure bool,
 	}
 
 	swapServerClient, err := newSwapServerClient(
-		serverAddress, insecure, tlsPathServer, lsatStore, lnd,
-		maxLSATCost, maxLSATFee,
+		serverAddress, proxyAddress, insecure, tlsPathServer, lsatStore,
+		lnd, maxLSATCost, maxLSATFee,
 	)
 	if err != nil {
 		return nil, nil, err

loopd/config.go

@@ -45,7 +45,8 @@ type config struct {
 	MaxLSATCost uint32 `long:"maxlsatcost" description:"Maximum cost in satoshis that loopd is going to pay for an LSAT token automatically. Does not include routing fees."`
 	MaxLSATFee  uint32 `long:"maxlsatfee" description:"Maximum routing fee in satoshis that we are willing to pay while paying for an LSAT token."`
 
-	Lnd *lndConfig `group:"lnd" namespace:"lnd"`
+	Lnd   *lndConfig `group:"lnd" namespace:"lnd"`
+	Proxy string     `long:"proxy" description:"The host:port of a SOCKS proxy through which all connections to the swap server will be established over."`
 
 	View viewParameters `command:"view" alias:"v" description:"View all swaps in the database. This command can only be executed when loopd is not running."`
 }

loopd/daemon.go

@@ -50,6 +50,8 @@ func daemon(config *config, lisCfg *listenerCfg) error {
 	// If no swap server is specified, use the default addresses for mainnet
 	// and testnet.
 	if config.SwapServer == "" {
+		// TODO(wilmer): Use onion service addresses when proxy is
+		// active.
 		switch config.Network {
 		case "mainnet":
 			config.SwapServer = mainnetServer

loopd/utils.go

@@ -19,7 +19,7 @@ func getClient(config *config, lnd *lndclient.LndServices) (*loop.Client,
 	}
 
 	swapClient, cleanUp, err := loop.NewClient(
-		storeDir, config.SwapServer, config.Insecure,
+		storeDir, config.SwapServer, config.Proxy, config.Insecure,
 		config.TLSPathSwapSrv, lnd, btcutil.Amount(config.MaxLSATCost),
 		btcutil.Amount(config.MaxLSATFee),
 	)

swap_server_client.go

@@ -6,6 +6,7 @@ import (
 	"encoding/hex"
 	"errors"
 	"fmt"
+	"net"
 	"time"
 
 	"github.com/btcsuite/btcd/btcec"
@@ -15,6 +16,7 @@ import (
 	"github.com/lightninglabs/loop/lsat"
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/routing/route"
+	"github.com/lightningnetwork/lnd/tor"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/credentials"
 )
@@ -52,8 +54,8 @@ type grpcSwapServerClient struct {
 
 var _ swapServerClient = (*grpcSwapServerClient)(nil)
 
-func newSwapServerClient(address string, insecure bool, tlsPath string,
-	lsatStore lsat.Store, lnd *lndclient.LndServices,
+func newSwapServerClient(address, proxyAddress string, insecure bool,
+	tlsPath string, lsatStore lsat.Store, lnd *lndclient.LndServices,
 	maxLSATCost, maxLSATFee btcutil.Amount) (*grpcSwapServerClient, error) {
 
 	// Create the server connection with the interceptor that will handle
@@ -62,7 +64,7 @@ func newSwapServerClient(address string, insecure bool, tlsPath string,
 		lnd, lsatStore, serverRPCTimeout, maxLSATCost, maxLSATFee,
 	)
 	serverConn, err := getSwapServerConn(
-		address, insecure, tlsPath, clientInterceptor,
+		address, proxyAddress, insecure, tlsPath, clientInterceptor,
 	)
 	if err != nil {
 		return nil, err
@@ -243,9 +245,11 @@ func (s *grpcSwapServerClient) Close() {
 	s.conn.Close()
 }
 
-// getSwapServerConn returns a connection to the swap server.
-func getSwapServerConn(address string, insecure bool, tlsPath string,
-	interceptor *lsat.Interceptor) (*grpc.ClientConn, error) {
+// getSwapServerConn returns a connection to the swap server. A non-empty
+// proxyAddr indicates that a SOCKS proxy found at the address should be used to
+// establish the connection.
+func getSwapServerConn(address, proxyAddress string, insecure bool,
+	tlsPath string, interceptor *lsat.Interceptor) (*grpc.ClientConn, error) {
 
 	// Create a dial options array.
 	opts := []grpc.DialOption{grpc.WithUnaryInterceptor(
@@ -273,6 +277,17 @@ func getSwapServerConn(address string, insecure bool, tlsPath string,
 		opts = append(opts, grpc.WithTransportCredentials(creds))
 	}
 
+	// If a SOCKS proxy address was specified, then we should dial through
+	// it.
+	if proxyAddress != "" {
+		log.Infof("Proxying connection to %v over Tor SOCKS proxy %v",
+			address, proxyAddress)
+		torDialer := func(_ context.Context, addr string) (net.Conn, error) {
+			return tor.Dial(addr, proxyAddress, false)
+		}
+		opts = append(opts, grpc.WithContextDialer(torDialer))
+	}
+
 	conn, err := grpc.Dial(address, opts...)
 	if err != nil {
 		return nil, fmt.Errorf("unable to connect to RPC server: %v",