watchtower: add channelID index

In this commit, a new channel-ID index is added to the tower client db
with the help of a migration. This index holds a mapping from a
db-assigned-ID (a uint64 encoded using BigSize encoding) to real channel
ID (32 bytes). This mapping will help us save space in future when
persisting references to channels.

watchtower/wtdb/client_db.go

@@ -10,6 +10,7 @@ import (
 	"github.com/btcsuite/btcd/btcec/v2"
 	"github.com/lightningnetwork/lnd/kvdb"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/tlv"
 	"github.com/lightningnetwork/lnd/watchtower/blob"
 )
 
@@ -20,6 +21,7 @@ var (
 
 	// cChanDetailsBkt is a top-level bucket storing:
 	//   channel-id => cChannelSummary -> encoded ClientChanSummary.
+	//  		=> cChanDBID -> db-assigned-id
 	cChanDetailsBkt = []byte("client-channel-detail-bucket")
 
 	// cChanDBID is a key used in the cChanDetailsBkt to store the
@@ -48,6 +50,10 @@ var (
 	//    seqnum -> encoded BackupID.
 	cSessionAcks = []byte("client-session-acks")
 
+	// cChanIDIndexBkt is a top-level bucket storing:
+	//    db-assigned-id -> channel-ID
+	cChanIDIndexBkt = []byte("client-channel-id-index")
+
 	// cTowerBkt is a top-level bucket storing:
 	//    tower-id -> encoded Tower.
 	cTowerBkt = []byte("client-tower-bucket")
@@ -215,6 +221,7 @@ func initClientDBBuckets(tx kvdb.RwTx) error {
 		cTowerBkt,
 		cTowerIndexBkt,
 		cTowerToSessionIndexBkt,
+		cChanIDIndexBkt,
 	}
 
 	for _, bucket := range buckets {
@@ -955,6 +962,37 @@ func (c *ClientDB) RegisterChannel(chanID lnwire.ChannelID,
 			return err
 		}
 
+		// Get the channel-id-index bucket.
+		indexBkt := tx.ReadWriteBucket(cChanIDIndexBkt)
+		if indexBkt == nil {
+			return ErrUninitializedDB
+		}
+
+		// Request the next unique id from the bucket.
+		nextSeq, err := indexBkt.NextSequence()
+		if err != nil {
+			return err
+		}
+
+		// Use BigSize encoding to encode the db-assigned index.
+		newIndex, err := writeBigSize(nextSeq)
+		if err != nil {
+			return err
+		}
+
+		// Add the new db-assigned ID to channel-ID pair.
+		err = indexBkt.Put(newIndex, chanID[:])
+		if err != nil {
+			return err
+		}
+
+		// Add the db-assigned ID to the channel's channel details
+		// bucket under the cChanDBID key.
+		err = chanDetails.Put(cChanDBID, newIndex)
+		if err != nil {
+			return err
+		}
+
 		summary := ClientChanSummary{
 			SweepPkScript: sweepPkScript,
 		}
@@ -1484,3 +1522,50 @@ func putTower(towers kvdb.RwBucket, tower *Tower) error {
 
 	return towers.Put(tower.ID.Bytes(), b.Bytes())
 }
+
+// getDBChanID returns the db-assigned channel ID for the given real channel ID.
+// It returns both the uint64 and byte representation.
+func getDBChanID(chanDetailsBkt kvdb.RBucket, chanID lnwire.ChannelID) (uint64,
+	[]byte, error) {
+
+	chanDetails := chanDetailsBkt.NestedReadBucket(chanID[:])
+	if chanDetails == nil {
+		return 0, nil, ErrChannelNotRegistered
+	}
+
+	idBytes := chanDetails.Get(cChanDBID)
+	if len(idBytes) == 0 {
+		return 0, nil, fmt.Errorf("no db-assigned ID found for "+
+			"channel ID %s", chanID)
+	}
+
+	id, err := readBigSize(idBytes)
+	if err != nil {
+		return 0, nil, err
+	}
+
+	return id, idBytes, nil
+}
+
+// writeBigSize will encode the given uint64 as a BigSize byte slice.
+func writeBigSize(i uint64) ([]byte, error) {
+	var b bytes.Buffer
+	err := tlv.WriteVarInt(&b, i, &[8]byte{})
+	if err != nil {
+		return nil, err
+	}
+
+	return b.Bytes(), nil
+}
+
+// readBigSize converts the given byte slice into a uint64 and assumes that the
+// bytes slice is using BigSize encoding.
+func readBigSize(b []byte) (uint64, error) {
+	r := bytes.NewReader(b)
+	i, err := tlv.ReadVarInt(r, &[8]byte{})
+	if err != nil {
+		return 0, err
+	}
+
+	return i, nil
+}

watchtower/wtdb/codec_test.go

@@ -125,9 +125,9 @@ type dbObject interface {
 	Decode(io.Reader) error
 }
 
-// TestCodec serializes and deserializes wtdb objects in order to test that that
-// the codec understands all of the required field types. The test also asserts
-// that decoding an object into another results in an equivalent object.
+// TestCodec serializes and deserializes wtdb objects in order to test that the
+// codec understands all of the required field types. The test also asserts that
+// decoding an object into another results in an equivalent object.
 func TestCodec(tt *testing.T) {
 
 	var t *testing.T

watchtower/wtdb/log.go

@@ -5,6 +5,7 @@ import (
 	"github.com/lightningnetwork/lnd/build"
 	"github.com/lightningnetwork/lnd/watchtower/wtdb/migration1"
 	"github.com/lightningnetwork/lnd/watchtower/wtdb/migration2"
+	"github.com/lightningnetwork/lnd/watchtower/wtdb/migration3"
 )
 
 // log is a logger that is initialized with no output filters.  This
@@ -30,6 +31,7 @@ func UseLogger(logger btclog.Logger) {
 	log = logger
 	migration1.UseLogger(logger)
 	migration2.UseLogger(logger)
+	migration3.UseLogger(logger)
 }
 
 // logClosure is used to provide a closure over expensive logging operations so

watchtower/wtdb/migration3/client_db.go

@@ -0,0 +1,104 @@
+package migration3
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+
+	"github.com/lightningnetwork/lnd/kvdb"
+	"github.com/lightningnetwork/lnd/tlv"
+)
+
+var (
+	// cChanDetailsBkt is a top-level bucket storing:
+	//   channel-id => cChannelSummary -> encoded ClientChanSummary.
+	// 		=> cChanDBID -> db-assigned-id
+	cChanDetailsBkt = []byte("client-channel-detail-bucket")
+
+	// cChanDBID is a key used in the cChanDetailsBkt to store the
+	// db-assigned-id of a channel.
+	cChanDBID = []byte("client-channel-db-id")
+
+	// cChanIDIndexBkt is a top-level bucket storing:
+	//    db-assigned-id -> channel-ID
+	cChanIDIndexBkt = []byte("client-channel-id-index")
+
+	// cChannelSummary is a key used in cChanDetailsBkt to store the encoded
+	// body of ClientChanSummary.
+	cChannelSummary = []byte("client-channel-summary")
+
+	// ErrUninitializedDB signals that top-level buckets for the database
+	// have not been initialized.
+	ErrUninitializedDB = errors.New("db not initialized")
+
+	// ErrCorruptChanDetails signals that the clients channel detail's
+	// on-disk structure deviates from what is expected.
+	ErrCorruptChanDetails = errors.New("channel details corrupted")
+
+	byteOrder = binary.BigEndian
+)
+
+// MigrateChannelIDIndex adds a new channel ID index to the tower client db.
+// This index is a mapping from db-assigned ID (a uint64 encoded using BigSize
+// encoding) to real channel ID (32 bytes). This mapping will allow us to
+// persist channel pointers with fewer bytes in the future.
+func MigrateChannelIDIndex(tx kvdb.RwTx) error {
+	log.Infof("Migrating the tower client db to add a new channel ID " +
+		"index which stores a mapping from db-assigned ID to real " +
+		"channel ID")
+
+	// Create a new top-level bucket for the new index.
+	indexBkt, err := tx.CreateTopLevelBucket(cChanIDIndexBkt)
+	if err != nil {
+		return err
+	}
+
+	// Get the top-level channel-details bucket. The keys of this bucket
+	// are the real channel IDs.
+	chanDetailsBkt := tx.ReadWriteBucket(cChanDetailsBkt)
+	if chanDetailsBkt == nil {
+		return ErrUninitializedDB
+	}
+
+	// Iterate over the keys of the channel-details bucket.
+	return chanDetailsBkt.ForEach(func(chanID, _ []byte) error {
+		// Ask the db for a new, unique, ID for the index bucket.
+		nextSeq, err := indexBkt.NextSequence()
+		if err != nil {
+			return err
+		}
+
+		// Encode the sequence number using BigSize encoding.
+		var newIndex bytes.Buffer
+		err = tlv.WriteVarInt(&newIndex, nextSeq, &[8]byte{})
+		if err != nil {
+			return err
+		}
+
+		// Add the mapping from the db-assigned ID to the channel ID
+		// to the new index.
+		newIndexBytes := newIndex.Bytes()
+		err = indexBkt.Put(newIndexBytes, chanID)
+		if err != nil {
+			return err
+		}
+
+		chanDetails := chanDetailsBkt.NestedReadWriteBucket(chanID)
+		if chanDetails == nil {
+			return ErrCorruptChanDetails
+		}
+
+		// Here we ensure that the channel-details bucket includes a
+		// channel summary. The only reason we do this is so that we can
+		// simulate a migration fail in a test to ensure that a
+		// migration fail results in an untouched db.
+		chanSummaryBytes := chanDetails.Get(cChannelSummary)
+		if chanSummaryBytes == nil {
+			return ErrCorruptChanDetails
+		}
+
+		// In the channel-details sub-bucket for this channel, add the
+		// new DB-assigned ID for this channel under the cChanDBID key.
+		return chanDetails.Put(cChanDBID, newIndexBytes)
+	})
+}

watchtower/wtdb/migration3/client_db_test.go

@@ -0,0 +1,149 @@
+package migration3
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/lightningnetwork/lnd/channeldb/migtest"
+	"github.com/lightningnetwork/lnd/kvdb"
+	"github.com/lightningnetwork/lnd/tlv"
+)
+
+var (
+
+	// pre is the expected data in the cChanDetailsBkt bucket before the
+	// migration.
+	pre = map[string]interface{}{
+		channelIDString(100): map[string]interface{}{
+			string(cChannelSummary): string([]byte{1, 2, 3}),
+		},
+		channelIDString(222): map[string]interface{}{
+			string(cChannelSummary): string([]byte{4, 5, 6}),
+		},
+	}
+
+	// preFailCorruptDB should fail the migration due to no channel summary
+	// being found for a given channel ID.
+	preFailCorruptDB = map[string]interface{}{
+		channelIDString(100): map[string]interface{}{},
+	}
+
+	// post is the expected data in the new index after migration.
+	postIndex = map[string]interface{}{
+		indexToString(1): channelIDString(100),
+		indexToString(2): channelIDString(222),
+	}
+
+	// postDetails is the expected data in the cChanDetailsBkt bucket after
+	// the migration.
+	postDetails = map[string]interface{}{
+		channelIDString(100): map[string]interface{}{
+			string(cChannelSummary): string([]byte{1, 2, 3}),
+			string(cChanDBID):       indexToString(1),
+		},
+		channelIDString(222): map[string]interface{}{
+			string(cChannelSummary): string([]byte{4, 5, 6}),
+			string(cChanDBID):       indexToString(2),
+		},
+	}
+)
+
+// TestMigrateChannelIDIndex tests that the MigrateChannelIDIndex function
+// correctly adds a new channel-id index to the DB and also correctly updates
+// the existing channel-details bucket.
+func TestMigrateChannelIDIndex(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name        string
+		shouldFail  bool
+		pre         map[string]interface{}
+		postDetails map[string]interface{}
+		postIndex   map[string]interface{}
+	}{
+		{
+			name:        "migration ok",
+			shouldFail:  false,
+			pre:         pre,
+			postDetails: postDetails,
+			postIndex:   postIndex,
+		},
+		{
+			name:       "fail due to corrupt db",
+			shouldFail: true,
+			pre:        preFailCorruptDB,
+		},
+		{
+			name:        "no channel details",
+			shouldFail:  false,
+			pre:         nil,
+			postDetails: nil,
+			postIndex:   nil,
+		},
+	}
+
+	for _, test := range tests {
+		test := test
+
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+
+			// Before the migration we have a details bucket.
+			before := func(tx kvdb.RwTx) error {
+				return migtest.RestoreDB(
+					tx, cChanDetailsBkt, test.pre,
+				)
+			}
+
+			// After the migration, we should have an untouched
+			// summary bucket and a new index bucket.
+			after := func(tx kvdb.RwTx) error {
+				// If the migration fails, the details bucket
+				// should be untouched.
+				if test.shouldFail {
+					if err := migtest.VerifyDB(
+						tx, cChanDetailsBkt, test.pre,
+					); err != nil {
+						return err
+					}
+
+					return nil
+				}
+
+				// Else, we expect an updated summary bucket
+				// and a new index bucket.
+				err := migtest.VerifyDB(
+					tx, cChanDetailsBkt, test.postDetails,
+				)
+				if err != nil {
+					return err
+				}
+
+				return migtest.VerifyDB(
+					tx, cChanIDIndexBkt, test.postIndex,
+				)
+			}
+
+			migtest.ApplyMigration(
+				t, before, after, MigrateChannelIDIndex,
+				test.shouldFail,
+			)
+		})
+	}
+}
+
+func indexToString(id uint64) string {
+	var newIndex bytes.Buffer
+	err := tlv.WriteVarInt(&newIndex, id, &[8]byte{})
+	if err != nil {
+		panic(err)
+	}
+
+	return newIndex.String()
+}
+
+func channelIDString(id uint64) string {
+	var chanID ChannelID
+	byteOrder.PutUint64(chanID[:], id)
+	return chanID.String()
+}

watchtower/wtdb/migration3/codec.go

@@ -0,0 +1,19 @@
+package migration3
+
+import (
+	"encoding/hex"
+)
+
+// ChannelID is a series of 32-bytes that uniquely identifies all channels
+// within the network. The ChannelID is computed using the outpoint of the
+// funding transaction (the txid, and output index). Given a funding output the
+// ChannelID can be calculated by XOR'ing the big-endian serialization of the
+// txid and the big-endian serialization of the output index, truncated to
+// 2 bytes.
+type ChannelID [32]byte
+
+// String returns the string representation of the ChannelID. This is just the
+// hex string encoding of the ChannelID itself.
+func (c ChannelID) String() string {
+	return hex.EncodeToString(c[:])
+}

watchtower/wtdb/migration3/log.go

@@ -0,0 +1,14 @@
+package migration3
+
+import (
+	"github.com/btcsuite/btclog"
+)
+
+// log is a logger that is initialized as disabled.  This means the package will
+// not perform any logging by default until a logger is set.
+var log = btclog.Disabled
+
+// UseLogger uses a specified Logger to output package logging info.
+func UseLogger(logger btclog.Logger) {
+	log = logger
+}

watchtower/wtdb/version.go

@@ -5,6 +5,7 @@ import (
 	"github.com/lightningnetwork/lnd/kvdb"
 	"github.com/lightningnetwork/lnd/watchtower/wtdb/migration1"
 	"github.com/lightningnetwork/lnd/watchtower/wtdb/migration2"
+	"github.com/lightningnetwork/lnd/watchtower/wtdb/migration3"
 )
 
 // migration is a function which takes a prior outdated version of the database
@@ -33,6 +34,9 @@ var clientDBVersions = []version{
 	{
 		migration: migration2.MigrateClientChannelDetails,
 	},
+	{
+		migration: migration3.MigrateChannelIDIndex,
+	},
 }
 
 // getLatestDBVersion returns the last known database version.