multi: Added Tor support

This commit adds Tor support. Users can set the --TorSocks flag
to specify which port Tor's SOCKS5 proxy is listening on so that
lnd can connect to it. When this flag is set, ALL traffic gets
routed over Tor including DNS traffic. Special functions for
DNS lookups were added, and since Tor doesn't natively support
SRV requests, the proxySRV function routes connects us to
a DNS server via Tor and SRV requests can be issued directly
to the DNS server.

Co-authored-by: MeshCollider <dobsonsa68@gmail.com>

server.go

@@ -13,6 +13,7 @@ import (
 	"time"
 
 	"github.com/boltdb/bolt"
+	"github.com/btcsuite/go-socks/socks"
 	"github.com/lightningnetwork/lightning-onion"
 	"github.com/lightningnetwork/lnd/autopilot"
 	"github.com/lightningnetwork/lnd/brontide"
@@ -213,7 +214,9 @@ func newServer(listenAddrs []string, chanDB *channeldb.DB, cc *chainControl,
 	})
 
 	// If external IP addresses have been specified, add those to the list
-	// of this server's addresses.
+	// of this server's addresses. We need to use the general lndResolveTCP
+	// function in case we wish to resolve hosts over Tor since domains
+	// CAN be passed into the ExternalIPs configuration option.
 	selfAddrs := make([]net.Addr, 0, len(cfg.ExternalIPs))
 	for _, ip := range cfg.ExternalIPs {
 		var addr string
@@ -224,7 +227,7 @@ func newServer(listenAddrs []string, chanDB *channeldb.DB, cc *chainControl,
 			addr = ip
 		}
 
-		lnAddr, err := net.ResolveTCPAddr("tcp", addr)
+		lnAddr, err := lndResolveTCP("tcp", addr)
 		if err != nil {
 			return nil, err
 		}
@@ -602,6 +605,7 @@ func initNetworkBootstrappers(s *server) ([]discovery.NetworkPeerBootstrapper, e
 
 			dnsBootStrapper, err := discovery.NewDNSSeedBootstrapper(
 				dnsSeeds,
+				[]interface{}{lndLookup, lndLookupSRV},
 			)
 			if err != nil {
 				return nil, err
@@ -641,10 +645,18 @@ func (s *server) peerBootstrapper(numTargetPeers uint32,
 
 	// With our initial set of peers obtained, we'll launch a goroutine to
 	// attempt to connect out to each of them. We'll be waking up shortly
-	// below to sample how many of these connections succeeded.
+	// below to sample how many of these connections succeeded. We check
+	// cfg.dial for nil in case Tor's proxy dialer option was set in the
+	// configuration.
 	for _, addr := range bootStrapAddrs {
 		go func(a *lnwire.NetAddress) {
-			conn, err := brontide.Dial(s.identityPriv, a)
+			var conn *brontide.Conn
+			var err error
+			if cfg.dial == nil {
+				conn, err = brontide.Dial(s.identityPriv, a)
+			} else {
+				conn, err = brontide.Dial(s.identityPriv, a, cfg.dial)
+			}
 			if err != nil {
 				srvrLog.Errorf("unable to connect to %v: %v",
 					a, err)
@@ -754,7 +766,16 @@ func (s *server) peerBootstrapper(numTargetPeers uint32,
 				go func(a *lnwire.NetAddress) {
 					// TODO(roasbeef): can do AS, subnet,
 					// country diversity, etc
-					conn, err := brontide.Dial(s.identityPriv, a)
+					// We check cfg.dial for nil in case
+					// a Tor's proxy dialer configuration was
+					// set.
+					var conn *brontide.Conn
+					var err error
+					if cfg.dial == nil {
+						conn, err = brontide.Dial(s.identityPriv, a)
+					} else {
+						conn, err = brontide.Dial(s.identityPriv, a, cfg.dial)
+					}
 					if err != nil {
 						srvrLog.Errorf("unable to connect "+
 							"to %v: %v", a, err)
@@ -1271,10 +1292,25 @@ func (s *server) peerConnected(conn net.Conn, connReq *connmgr.ConnReq,
 	inbound bool) {
 
 	brontideConn := conn.(*brontide.Conn)
-	peerAddr := &lnwire.NetAddress{
-		IdentityKey: brontideConn.RemotePub(),
-		Address:     conn.RemoteAddr().(*net.TCPAddr),
-		ChainNet:    activeNetParams.Net,
+	var peerAddr *lnwire.NetAddress
+	if cfg.dial == nil {
+		peerAddr = &lnwire.NetAddress{
+			IdentityKey: brontideConn.RemotePub(),
+			Address:     conn.RemoteAddr().(*net.TCPAddr),
+			ChainNet:    activeNetParams.Net,
+		}
+	} else {
+		// We are connected to a Tor SOCKS5 proxy, extract our
+		// connection information.
+		proxiedAddr := conn.RemoteAddr().(*socks.ProxiedAddr)
+		peerAddr = &lnwire.NetAddress{
+			IdentityKey: brontideConn.RemotePub(),
+			Address: &net.TCPAddr{
+				IP:   net.ParseIP(proxiedAddr.Host),
+				Port: proxiedAddr.Port,
+			},
+			ChainNet: activeNetParams.Net,
+		}
 	}
 
 	// With the brontide connection established, we'll now craft the local
@@ -1659,8 +1695,14 @@ func (s *server) ConnectToPeer(addr *lnwire.NetAddress, perm bool) error {
 	// If we're not making a persistent connection, then we'll attempt to
 	// connect to the target peer. If the we can't make the connection, or
 	// the crypto negotiation breaks down, then return an error to the
-	// caller.
-	conn, err := brontide.Dial(s.identityPriv, addr)
+	// caller. We check cfg.dial for nil in case Tor's proxy dialer function
+	// was set in the configuration options.
+	var conn *brontide.Conn
+	if cfg.dial == nil {
+		conn, err = brontide.Dial(s.identityPriv, addr)
+	} else {
+		conn, err = brontide.Dial(s.identityPriv, addr, cfg.dial)
+	}
 	if err != nil {
 		return err
 	}