watchtower: add externalip CLI configuration

watchtower/conf.go

@@ -11,6 +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"`
@@ -53,6 +56,24 @@ func (c *Conf) Apply(cfg *Config,
 		}
 	}
 
+	// 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 {
+			return nil, err
+		}
+	}
+
 	// If the Config has no read timeout, we will use the parsed Conf
 	// value.
 	if cfg.ReadTimeout == 0 && c.ReadTimeout != 0 {

watchtower/config.go

@@ -74,9 +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