lnwallet: handle nonce init in ProcessChanSyncMsg

In this commit, we update the logic to handle nonce init in
ProcessChanSyncMsg. Once a channel is already open, this is where we'll
get the new nonce data from the remote party we'll use to gain the nonce
we need to sign for their next state.

htlcswitch/link.go

@@ -698,7 +698,6 @@ func (l *channelLink) syncChanStates() error {
 		return fmt.Errorf("unable to generate chan sync message for "+
 			"ChannelPoint(%v)", l.channel.ChannelPoint())
 	}
-
 	if err := l.cfg.Peer.SendMessage(true, localChanSyncMsg); err != nil {
 		return fmt.Errorf("unable to send chan sync message for "+
 			"ChannelPoint(%v): %v", l.channel.ChannelPoint(), err)
@@ -738,6 +737,13 @@ func (l *channelLink) syncChanStates() error {
 				l.ChanID(), nextRevocation,
 			)
 
+			// If this is a taproot channel, then we'll send the
+			// very same nonce that we sent above, as they should
+			// take the latest verification nonce we send.
+			if chanState.ChanType.IsTaproot() {
+				fundingLockedMsg.NextLocalNonce = localChanSyncMsg.LocalNonce
+			}
+
 			// For channels that negotiated the option-scid-alias
 			// feature bit, ensure that we send over the alias in
 			// the funding_locked message. We'll send the first
@@ -1930,8 +1936,8 @@ func (l *channelLink) handleUpstreamMsg(msg lnwire.Message) {
 		// chain, validate this new commitment, closing the link if
 		// invalid.
 		err = l.channel.ReceiveNewCommitment(&lnwallet.CommitSigs{
-			CommitSig:  msg.CommitSig,
-			HtlcSigs:   msg.HtlcSigs,
+			CommitSig: msg.CommitSig,
+			HtlcSigs:  msg.HtlcSigs,
 		})
 		if err != nil {
 			// If we were unable to reconstruct their proposed
@@ -2309,9 +2315,9 @@ func (l *channelLink) updateCommitTx() error {
 	}
 
 	commitSig := &lnwire.CommitSig{
-		ChanID:     l.ChanID(),
-		CommitSig:  newCommit.CommitSig,
-		HtlcSigs:   newCommit.HtlcSigs,
+		ChanID:    l.ChanID(),
+		CommitSig: newCommit.CommitSig,
+		HtlcSigs:  newCommit.HtlcSigs,
 	}
 	l.cfg.Peer.SendMessage(false, commitSig)
 

lnwallet/channel.go

@@ -4094,8 +4094,6 @@ func (lc *LightningChannel) ProcessChanSyncMsg(
 	msg *lnwire.ChannelReestablish) ([]lnwire.Message, []models.CircuitKey,
 	[]models.CircuitKey, error) {
 
-	// TODO(roasbeef): need to replace w/ received nonces
-
 	// Now we'll examine the state we have, vs what was contained in the
 	// chain sync message. If we're de-synchronized, then we'll send a
 	// batch of messages which when applied will kick start the chain
@@ -4135,6 +4133,25 @@ func (lc *LightningChannel) ProcessChanSyncMsg(
 		}
 	}
 
+	// If this is a taproot channel, then we expect that the remote party
+	// has sent the next verification nonce. If they haven't, then we'll
+	// bail out, otherwise we'll init our local session then continue as
+	// normal.
+	switch {
+	case lc.channelState.ChanType.IsTaproot() && msg.LocalNonce == nil:
+		return nil, nil, nil, fmt.Errorf("remote verification nonce " +
+			"not sent")
+
+	case lc.channelState.ChanType.IsTaproot() && msg.LocalNonce != nil:
+		err := lc.InitRemoteMusigNonces(&musig2.Nonces{
+			PubNonce: *msg.LocalNonce,
+		})
+		if err != nil {
+			return nil, nil, nil, fmt.Errorf("unable to init "+
+				"remote nonce: %w", err)
+		}
+	}
+
 	// If we detect that this is is a restored channel, then we can skip a
 	// portion of the verification, as we already know that we're unable to
 	// proceed with any updates.
@@ -4212,12 +4229,12 @@ func (lc *LightningChannel) ProcessChanSyncMsg(
 			"while we have %v, we owe them a revocation",
 			msg.RemoteCommitTailHeight, localTailHeight)
 
-		revocationMsg, err := lc.generateRevocation(
-			localTailHeight - 1,
-		)
+		heightToRetransmit := localTailHeight - 1
+		revocationMsg, err := lc.generateRevocation(heightToRetransmit)
 		if err != nil {
 			return nil, nil, nil, err
 		}
+
 		updates = append(updates, revocationMsg)
 
 		// Next, as a precaution, we'll check a special edge case. If