channeldb: add local and remote balance to revocation log

This commit re-adds the LocalBalance and RemoteBalance fields to the
RevocationLog. The channeldb/migration30 is also adjusted so that anyone
who has not yet run the optional migration will not lose these fields if
they run the migration after this commit.

The reason for re-adding these fields is that they are needed if we want
to reconstruct all the info of the lnwallet.BreachRetribution without
having access to the breach spend transaction. In most cases we would
have access to the spend tx since we would see it on-chain at which time
we would want to reconstruct the retribution info. However, for the
watchtower subsystem, we sometimes want to construct the retribution
info withouth having access to the spend transaction.

A user can use the `--no-rev-log-amt-data` flag to opt-out of storing
these amount fields.

channeldb/revocation_log.go

@@ -9,6 +9,7 @@ import (
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/lightningnetwork/lnd/kvdb"
 	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/tlv"
 )
 
@@ -23,6 +24,8 @@ const (
 	revLogOurOutputIndexType   tlv.Type = 0
 	revLogTheirOutputIndexType tlv.Type = 1
 	revLogCommitTxHashType     tlv.Type = 2
+	revLogOurBalanceType       tlv.Type = 3
+	revLogTheirBalanceType     tlv.Type = 4
 )
 
 var (
@@ -185,9 +188,6 @@ func (h *HTLCEntry) toTlvStream() (*tlv.Stream, error) {
 // fields can be viewed as a subset of a ChannelCommitment's. In the database,
 // all historical versions of the RevocationLog are saved using the
 // CommitHeight as the key.
-//
-// NOTE: all the fields use the primitive go types so they can be made into tlv
-// records without further conversion.
 type RevocationLog struct {
 	// OurOutputIndex specifies our output index in this commitment. In a
 	// remote commitment transaction, this is the to remote output index.
@@ -204,6 +204,26 @@ type RevocationLog struct {
 	// HTLCEntries is the set of HTLCEntry's that are pending at this
 	// particular commitment height.
 	HTLCEntries []*HTLCEntry
+
+	// OurBalance is the current available balance within the channel
+	// directly spendable by us. In other words, it is the value of the
+	// to_remote output on the remote parties' commitment transaction.
+	//
+	// NOTE: this is a pointer so that it is clear if the value is zero or
+	// nil. Since migration 30 of the channeldb initially did not include
+	// this field, it could be the case that the field is not present for
+	// all revocation logs.
+	OurBalance *lnwire.MilliSatoshi
+
+	// TheirBalance is the current available balance within the channel
+	// directly spendable by the remote node. In other words, it is the
+	// value of the to_local output on the remote parties' commitment.
+	//
+	// NOTE: this is a pointer so that it is clear if the value is zero or
+	// nil. Since migration 30 of the channeldb initially did not include
+	// this field, it could be the case that the field is not present for
+	// all revocation logs.
+	TheirBalance *lnwire.MilliSatoshi
 }
 
 // putRevocationLog uses the fields `CommitTx` and `Htlcs` from a
@@ -228,6 +248,11 @@ func putRevocationLog(bucket kvdb.RwBucket, commit *ChannelCommitment,
 		HTLCEntries:      make([]*HTLCEntry, 0, len(commit.Htlcs)),
 	}
 
+	if !noAmtData {
+		rl.OurBalance = &commit.LocalBalance
+		rl.TheirBalance = &commit.RemoteBalance
+	}
+
 	for _, htlc := range commit.Htlcs {
 		// Skip dust HTLCs.
 		if htlc.OutputIndex < 0 {
@@ -292,6 +317,21 @@ func serializeRevocationLog(w io.Writer, rl *RevocationLog) error {
 		),
 	}
 
+	// Now we add any optional fields that are non-nil.
+	if rl.OurBalance != nil {
+		lb := uint64(*rl.OurBalance)
+		records = append(records, tlv.MakeBigSizeRecord(
+			revLogOurBalanceType, &lb,
+		))
+	}
+
+	if rl.TheirBalance != nil {
+		rb := uint64(*rl.TheirBalance)
+		records = append(records, tlv.MakeBigSizeRecord(
+			revLogTheirBalanceType, &rb,
+		))
+	}
+
 	// Create the tlv stream.
 	tlvStream, err := tlv.NewStream(records...)
 	if err != nil {
@@ -336,7 +376,11 @@ func serializeHTLCEntries(w io.Writer, htlcs []*HTLCEntry) error {
 
 // deserializeRevocationLog deserializes a RevocationLog based on tlv format.
 func deserializeRevocationLog(r io.Reader) (RevocationLog, error) {
-	var rl RevocationLog
+	var (
+		rl           RevocationLog
+		ourBalance   uint64
+		theirBalance uint64
+	)
 
 	// Create the tlv stream.
 	tlvStream, err := tlv.NewStream(
@@ -349,13 +393,31 @@ func deserializeRevocationLog(r io.Reader) (RevocationLog, error) {
 		tlv.MakePrimitiveRecord(
 			revLogCommitTxHashType, &rl.CommitTxHash,
 		),
+		tlv.MakeBigSizeRecord(revLogOurBalanceType, &ourBalance),
+		tlv.MakeBigSizeRecord(
+			revLogTheirBalanceType, &theirBalance,
+		),
 	)
+	if err != nil {
+		return rl, err
+	}
 
 	// Read the tlv stream.
-	if _, err := readTlvStream(r, tlvStream); err != nil {
+	parsedTypes, err := readTlvStream(r, tlvStream)
+	if err != nil {
 		return rl, err
 	}
 
+	if t, ok := parsedTypes[revLogOurBalanceType]; ok && t == nil {
+		lb := lnwire.MilliSatoshi(ourBalance)
+		rl.OurBalance = &lb
+	}
+
+	if t, ok := parsedTypes[revLogTheirBalanceType]; ok && t == nil {
+		rb := lnwire.MilliSatoshi(theirBalance)
+		rl.TheirBalance = &rb
+	}
+
 	// Read the HTLC entries.
 	rl.HTLCEntries, err = deserializeHTLCEntries(r)