htlcswith/link: resend fundingLocked from channelLink when numUpdates == 0.

In the case where the channelLink get started and the number of
updates on this channel is zero, this means no paymenys has been
done using this channel. This might mean that the fundingLocked
never was sent successfully, so we resend to make sure this
channel gets opened correctly.

htlcswitch/link.go

@@ -322,7 +322,26 @@ func (l *channelLink) htlcManager() {
 
 	// TODO(roasbeef): fail chan in case of protocol violation
 
-	// TODO(roasbeef): resend funding locked if state zero
+	// If the number of updates on this channel has been zero, we should
+	// resend the fundingLocked message. This is because in this case we
+	// cannot be sure if the peer really received the last fundingLocked we
+	// sent, so resend now.
+	if l.channel.StateSnapshot().NumUpdates == 0 {
+		log.Debugf("Resending fundingLocked message to peer.")
+
+		nextRevocation, err := l.channel.NextRevocationKey()
+		if err != nil {
+			log.Errorf("unable to create next revocation: %v", err)
+		}
+
+		fundingLockedMsg := lnwire.NewFundingLocked(l.ChanID(),
+			nextRevocation)
+		err = l.cfg.Peer.SendMessage(fundingLockedMsg)
+		if err != nil {
+			log.Errorf("failed resending fundingLocked to peer: %v",
+				err)
+		}
+	}
 
 out:
 	for {

htlcswitch/mock.go

@@ -280,6 +280,9 @@ func (s *mockServer) readHandler(message lnwire.Message) error {
 		targetChan = msg.ChanID
 	case *lnwire.CommitSig:
 		targetChan = msg.ChanID
+	case *lnwire.FundingLocked:
+		// Ignore
+		return nil
 	default:
 		return errors.New("unknown message type")
 	}