lnwallet+htlcswitch: add NewCommitState struct, modify send/recv sig to accept

In this commit, we add a new NewCommitState struct. This preps us for
the future change wherein a partial signature is also added to the mix.
All related tests and type signatures have also been updated
accordingly.

lnwallet/channel.go

@@ -3716,6 +3716,30 @@ func (lc *LightningChannel) validateCommitmentSanity(theirLogCounter,
 	return nil
 }
 
+// CommitSig holds the set of related signatures for a new commitment
+// transaction state.
+type CommitSigs struct {
+	// CommitSig is the normal commitment signature. This will only be a
+	// non-zero commitment signature for taproot channels.
+	CommitSig lnwire.Sig
+
+	// HtlcSigs is the set of signatures for all HTLCs in the commitment
+	// transaction. Depending on the channel type, these will either be
+	// ECDSA or Schnorr signatures.
+	HtlcSigs []lnwire.Sig
+}
+
+// NewCommitState wraps the various signatures needed to properly
+// propose/accept a new commitment state. This includes the signer's nonce for
+// musig2 channels.
+type NewCommitState struct {
+	*CommitSigs
+
+	// PendingHTLCs is the set of new/pending HTLCs produced by this
+	// commitment state.
+	PendingHTLCs []channeldb.HTLC
+}
+
 // SignNextCommitment signs a new commitment which includes any previous
 // unsettled HTLCs, any new HTLCs, and any modifications to prior HTLCs
 // committed in previous commitment updates. Signing a new commitment
@@ -3727,8 +3751,7 @@ func (lc *LightningChannel) validateCommitmentSanity(theirLogCounter,
 // any). The HTLC signatures are sorted according to the BIP 69 order of the
 // HTLC's on the commitment transaction. Finally, the new set of pending HTLCs
 // for the remote party's commitment are also returned.
-func (lc *LightningChannel) SignNextCommitment() (lnwire.Sig, []lnwire.Sig,
-	[]channeldb.HTLC, error) {
+func (lc *LightningChannel) SignNextCommitment() (*NewCommitState, error) {
 
 	lc.Lock()
 	defer lc.Unlock()
@@ -3755,7 +3778,7 @@ func (lc *LightningChannel) SignNextCommitment() (lnwire.Sig, []lnwire.Sig,
 	if unacked || commitPoint == nil {
 		lc.log.Tracef("waiting for remote ack=%v, nil "+
 			"RemoteNextRevocation: %v", unacked, commitPoint == nil)
-		return sig, htlcSigs, nil, ErrNoWindow
+		return nil, ErrNoWindow
 	}
 
 	// Determine the last update on the remote log that has been locked in.
@@ -3770,7 +3793,7 @@ func (lc *LightningChannel) SignNextCommitment() (lnwire.Sig, []lnwire.Sig,
 		remoteACKedIndex, lc.localUpdateLog.logIndex, true, nil, nil,
 	)
 	if err != nil {
-		return sig, htlcSigs, nil, err
+		return nil, err
 	}
 
 	// Grab the next commitment point for the remote party. This will be
@@ -3793,7 +3816,7 @@ func (lc *LightningChannel) SignNextCommitment() (lnwire.Sig, []lnwire.Sig,
 		remoteACKedIndex, remoteHtlcIndex, keyRing,
 	)
 	if err != nil {
-		return sig, htlcSigs, nil, err
+		return nil, err
 	}
 
 	lc.log.Tracef("extending remote chain to height %v, "+
@@ -3824,7 +3847,7 @@ func (lc *LightningChannel) SignNextCommitment() (lnwire.Sig, []lnwire.Sig,
 		&lc.channelState.RemoteChanCfg, newCommitView,
 	)
 	if err != nil {
-		return sig, htlcSigs, nil, err
+		return nil, err
 	}
 	lc.sigPool.SubmitSignBatch(sigBatch)
 
@@ -3835,12 +3858,12 @@ func (lc *LightningChannel) SignNextCommitment() (lnwire.Sig, []lnwire.Sig,
 	rawSig, err := lc.Signer.SignOutputRaw(newCommitView.txn, lc.signDesc)
 	if err != nil {
 		close(cancelChan)
-		return sig, htlcSigs, nil, err
+		return nil, err
 	}
 	sig, err = lnwire.NewSigFromSignature(rawSig)
 	if err != nil {
 		close(cancelChan)
-		return sig, htlcSigs, nil, err
+		return nil, err
 	}
 
 	// We'll need to send over the signatures to the remote party in the
@@ -3860,7 +3883,7 @@ func (lc *LightningChannel) SignNextCommitment() (lnwire.Sig, []lnwire.Sig,
 		// jobs.
 		if jobResp.Err != nil {
 			close(cancelChan)
-			return sig, htlcSigs, nil, jobResp.Err
+			return nil, jobResp.Err
 		}
 
 		htlcSigs = append(htlcSigs, jobResp.Sig)
@@ -3871,11 +3894,11 @@ func (lc *LightningChannel) SignNextCommitment() (lnwire.Sig, []lnwire.Sig,
 	// can retransmit it if necessary.
 	commitDiff, err := lc.createCommitDiff(newCommitView, sig, htlcSigs)
 	if err != nil {
-		return sig, htlcSigs, nil, err
+		return nil, err
 	}
 	err = lc.channelState.AppendRemoteCommitChain(commitDiff)
 	if err != nil {
-		return sig, htlcSigs, nil, err
+		return nil, err
 	}
 
 	// TODO(roasbeef): check that one eclair bug
@@ -3886,7 +3909,13 @@ func (lc *LightningChannel) SignNextCommitment() (lnwire.Sig, []lnwire.Sig,
 	// latest commitment update.
 	lc.remoteCommitChain.addCommitment(newCommitView)
 
-	return sig, htlcSigs, commitDiff.Commitment.Htlcs, nil
+	return &NewCommitState{
+		CommitSigs: &CommitSigs{
+			CommitSig: sig,
+			HtlcSigs:  htlcSigs,
+		},
+		PendingHTLCs: commitDiff.Commitment.Htlcs,
+	}, nil
 }
 
 // ProcessChanSyncMsg processes a ChannelReestablish message sent by the remote
@@ -4044,19 +4073,21 @@ func (lc *LightningChannel) ProcessChanSyncMsg(
 		// revocation, but also initiate a state transition to re-sync
 		// them.
 		if lc.OweCommitment() {
-			commitSig, htlcSigs, _, err := lc.SignNextCommitment()
+			newCommit, err := lc.SignNextCommitment()
 			switch {
 
 			// If we signed this state, then we'll accumulate
 			// another update to send over.
 			case err == nil:
-				updates = append(updates, &lnwire.CommitSig{
+				commitSig := &lnwire.CommitSig{
 					ChanID: lnwire.NewChanIDFromOutPoint(
 						&lc.channelState.FundingOutpoint,
 					),
-					CommitSig: commitSig,
-					HtlcSigs:  htlcSigs,
-				})
+					CommitSig: newCommit.CommitSig,
+					HtlcSigs:  newCommit.HtlcSigs,
+				}
+
+				updates = append(updates, commitSig)
 
 			// If we get a failure due to not knowing their next
 			// point, then this is fine as they'll either send
@@ -4535,8 +4566,7 @@ var _ error = (*InvalidCommitSigError)(nil)
 // to our local commitment chain. Once we send a revocation for our prior
 // state, then this newly added commitment becomes our current accepted channel
 // state.
-func (lc *LightningChannel) ReceiveNewCommitment(commitSig lnwire.Sig,
-	htlcSigs []lnwire.Sig) error {
+func (lc *LightningChannel) ReceiveNewCommitment(commitSigs *CommitSigs) error {
 
 	lc.Lock()
 	defer lc.Unlock()
@@ -4631,7 +4661,7 @@ func (lc *LightningChannel) ReceiveNewCommitment(commitSig lnwire.Sig,
 		leaseExpiry = lc.channelState.ThawHeight
 	}
 	verifyJobs, err := genHtlcSigValidationJobs(
-		localCommitmentView, keyRing, htlcSigs,
+		localCommitmentView, keyRing, commitSigs.HtlcSigs,
 		lc.channelState.ChanType, lc.channelState.IsInitiator,
 		leaseExpiry, &lc.channelState.LocalChanCfg,
 		&lc.channelState.RemoteChanCfg,
@@ -4648,7 +4678,7 @@ func (lc *LightningChannel) ReceiveNewCommitment(commitSig lnwire.Sig,
 	// signature.
 	verifyKey := lc.channelState.RemoteChanCfg.MultiSigKey.PubKey
 
-	cSig, err := commitSig.ToSignature()
+	cSig, err := commitSigs.CommitSig.ToSignature()
 	if err != nil {
 		return err
 	}
@@ -4663,7 +4693,7 @@ func (lc *LightningChannel) ReceiveNewCommitment(commitSig lnwire.Sig,
 		localCommitTx.Serialize(&txBytes)
 		return &InvalidCommitSigError{
 			commitHeight: nextHeight,
-			commitSig:    commitSig.ToSignatureBytes(),
+			commitSig:    commitSigs.CommitSig.ToSignatureBytes(),
 			sigHash:      sigHash,
 			commitTx:     txBytes.Bytes(),
 		}
@@ -4703,7 +4733,7 @@ func (lc *LightningChannel) ReceiveNewCommitment(commitSig lnwire.Sig,
 
 	// The signature checks out, so we can now add the new commitment to
 	// our local commitment chain.
-	localCommitmentView.sig = commitSig.ToSignatureBytes()
+	localCommitmentView.sig = commitSigs.CommitSig.ToSignatureBytes()
 	lc.localCommitChain.addCommitment(localCommitmentView)
 
 	return nil
@@ -5721,7 +5751,7 @@ func (lc *LightningChannel) RemoteUpfrontShutdownScript() lnwire.DeliveryAddress
 // AbsoluteThawHeight determines a frozen channel's absolute thaw height. If
 // the channel is not frozen, then 0 is returned.
 //
-// An error is returned if the channel is penidng, or is an unconfirmed zero
+// An error is returned if the channel is pending, or is an unconfirmed zero
 // conf channel.
 func (lc *LightningChannel) AbsoluteThawHeight() (uint32, error) {
 	return lc.channelState.AbsoluteThawHeight()