Merge pull request #4015 from bhandras/kv-etcd

kvdb wrapper for etcd

channeldb/channel_test.go

@@ -98,13 +98,22 @@ func makeTestDB() (*DB, func(), error) {
 	}
 
 	// Next, create channeldb for the first time.
-	cdb, err := Open(tempDirName, OptionClock(testClock))
+	backend, backendCleanup, err := kvdb.GetTestBackend(tempDirName, "cdb")
 	if err != nil {
+		backendCleanup()
+		return nil, nil, err
+	}
+
+	cdb, err := CreateWithBackend(backend, OptionClock(testClock))
+	if err != nil {
+		backendCleanup()
+		os.RemoveAll(tempDirName)
 		return nil, nil, err
 	}
 
 	cleanUp := func() {
 		cdb.Close()
+		backendCleanup()
 		os.RemoveAll(tempDirName)
 	}
 

channeldb/db.go

@@ -6,11 +6,11 @@ import (
 	"fmt"
 	"net"
 	"os"
-	"path/filepath"
 	"time"
 
 	"github.com/btcsuite/btcd/btcec"
 	"github.com/btcsuite/btcd/wire"
+	"github.com/btcsuite/btcwallet/walletdb"
 	"github.com/go-errors/errors"
 	"github.com/lightningnetwork/lnd/channeldb/kvdb"
 	"github.com/lightningnetwork/lnd/channeldb/migration12"
@@ -148,21 +148,70 @@ var (
 // schedules, and reputation data.
 type DB struct {
 	kvdb.Backend
+
 	dbPath string
 	graph  *ChannelGraph
 	clock  clock.Clock
 	dryRun bool
 }
 
-// Open opens an existing channeldb. Any necessary schemas migrations due to
-// updates will take place as necessary.
-func Open(dbPath string, modifiers ...OptionModifier) (*DB, error) {
-	path := filepath.Join(dbPath, dbName)
+// Update is a wrapper around walletdb.Update which calls into the extended
+// backend when available. This call is needed to be able to cast DB to
+// ExtendedBackend.
+func (db *DB) Update(f func(tx walletdb.ReadWriteTx) error) error {
+	if v, ok := db.Backend.(kvdb.ExtendedBackend); ok {
+		return v.Update(f)
+	}
+	return walletdb.Update(db, f)
+}
 
-	if !fileExists(path) {
-		if err := createChannelDB(dbPath); err != nil {
-			return nil, err
-		}
+// View is a wrapper around walletdb.View which calls into the extended
+// backend when available. This call is needed to be able to cast DB to
+// ExtendedBackend.
+func (db *DB) View(f func(tx walletdb.ReadTx) error) error {
+	if v, ok := db.Backend.(kvdb.ExtendedBackend); ok {
+		return v.View(f)
+	}
+
+	return walletdb.View(db, f)
+}
+
+// PrintStats calls into the extended backend if available. This call is needed
+// to be able to cast DB to ExtendedBackend.
+func (db *DB) PrintStats() string {
+	if v, ok := db.Backend.(kvdb.ExtendedBackend); ok {
+		return v.PrintStats()
+	}
+
+	return "unimplemented"
+}
+
+// Open opens or creates channeldb. Any necessary schemas migrations due
+// to updates will take place as necessary.
+// TODO(bhandras): deprecate this function.
+func Open(dbPath string, modifiers ...OptionModifier) (*DB, error) {
+	opts := DefaultOptions()
+	for _, modifier := range modifiers {
+		modifier(&opts)
+	}
+
+	backend, err := kvdb.GetBoltBackend(dbPath, dbName, opts.NoFreelistSync)
+	if err != nil {
+		return nil, err
+	}
+
+	db, err := CreateWithBackend(backend, modifiers...)
+	if err == nil {
+		db.dbPath = dbPath
+	}
+	return db, err
+}
+
+// CreateWithBackend creates channeldb instance using the passed kvdb.Backend.
+// Any necessary schemas migrations due to updates will take place as necessary.
+func CreateWithBackend(backend kvdb.Backend, modifiers ...OptionModifier) (*DB, error) {
+	if err := initChannelDB(backend); err != nil {
+		return nil, err
 	}
 
 	opts := DefaultOptions()
@@ -170,16 +219,8 @@ func Open(dbPath string, modifiers ...OptionModifier) (*DB, error) {
 		modifier(&opts)
 	}
 
-	// Specify bbolt freelist options to reduce heap pressure in case the
-	// freelist grows to be very large.
-	bdb, err := kvdb.Open(kvdb.BoltBackendName, path, opts.NoFreelistSync)
-	if err != nil {
-		return nil, err
-	}
-
 	chanDB := &DB{
-		Backend: bdb,
-		dbPath:  dbPath,
+		Backend: backend,
 		clock:   opts.clock,
 		dryRun:  opts.dryRun,
 	}
@@ -189,7 +230,7 @@ func Open(dbPath string, modifiers ...OptionModifier) (*DB, error) {
 
 	// Synchronize the version of database and apply migrations if needed.
 	if err := chanDB.syncVersions(dbVersions); err != nil {
-		bdb.Close()
+		backend.Close()
 		return nil, err
 	}
 
@@ -251,20 +292,15 @@ func (d *DB) Wipe() error {
 // the case that the target path has not yet been created or doesn't yet exist,
 // then the path is created. Additionally, all required top-level buckets used
 // within the database are created.
-func createChannelDB(dbPath string) error {
-	if !fileExists(dbPath) {
-		if err := os.MkdirAll(dbPath, 0700); err != nil {
-			return err
+func initChannelDB(db kvdb.Backend) error {
+	err := kvdb.Update(db, func(tx kvdb.RwTx) error {
+		meta := &Meta{}
+		// Check if DB is already initialized.
+		err := fetchMeta(meta, tx)
+		if err == nil {
+			return nil
 		}
-	}
 
-	path := filepath.Join(dbPath, dbName)
-	bdb, err := kvdb.Create(kvdb.BoltBackendName, path, true)
-	if err != nil {
-		return err
-	}
-
-	err = kvdb.Update(bdb, func(tx kvdb.RwTx) error {
 		if _, err := tx.CreateTopLevelBucket(openChannelBucket); err != nil {
 			return err
 		}
@@ -331,16 +367,14 @@ func createChannelDB(dbPath string) error {
 			return err
 		}
 
-		meta := &Meta{
-			DbVersionNumber: getLatestDBVersion(dbVersions),
-		}
+		meta.DbVersionNumber = getLatestDBVersion(dbVersions)
 		return putMeta(meta, tx)
 	})
 	if err != nil {
-		return fmt.Errorf("unable to create new channeldb")
+		return fmt.Errorf("unable to create new channeldb: %v", err)
 	}
 
-	return bdb.Close()
+	return nil
 }
 
 // fileExists returns true if the file exists, and false otherwise.
@@ -373,7 +407,7 @@ func (d *DB) FetchOpenChannels(nodeID *btcec.PublicKey) ([]*OpenChannel, error)
 // stored currently active/open channels associated with the target nodeID. In
 // the case that no active channels are known to have been created with this
 // node, then a zero-length slice is returned.
-func (d *DB) fetchOpenChannels(tx kvdb.ReadTx,
+func (db *DB) fetchOpenChannels(tx kvdb.ReadTx,
 	nodeID *btcec.PublicKey) ([]*OpenChannel, error) {
 
 	// Get the bucket dedicated to storing the metadata for open channels.
@@ -409,7 +443,7 @@ func (d *DB) fetchOpenChannels(tx kvdb.ReadTx,
 
 		// Finally, we both of the necessary buckets retrieved, fetch
 		// all the active channels related to this node.
-		nodeChannels, err := d.fetchNodeChannels(chainBucket)
+		nodeChannels, err := db.fetchNodeChannels(chainBucket)
 		if err != nil {
 			return fmt.Errorf("unable to read channel for "+
 				"chain_hash=%x, node_key=%x: %v",
@@ -426,7 +460,7 @@ func (d *DB) fetchOpenChannels(tx kvdb.ReadTx,
 // fetchNodeChannels retrieves all active channels from the target chainBucket
 // which is under a node's dedicated channel bucket. This function is typically
 // used to fetch all the active channels related to a particular node.
-func (d *DB) fetchNodeChannels(chainBucket kvdb.ReadBucket) ([]*OpenChannel, error) {
+func (db *DB) fetchNodeChannels(chainBucket kvdb.ReadBucket) ([]*OpenChannel, error) {
 
 	var channels []*OpenChannel
 
@@ -452,7 +486,7 @@ func (d *DB) fetchNodeChannels(chainBucket kvdb.ReadBucket) ([]*OpenChannel, err
 			return fmt.Errorf("unable to read channel data for "+
 				"chan_point=%v: %v", outPoint, err)
 		}
-		oChannel.Db = d
+		oChannel.Db = db
 
 		channels = append(channels, oChannel)
 
@@ -906,8 +940,8 @@ func (d *DB) MarkChanFullyClosed(chanPoint *wire.OutPoint) error {
 // pruneLinkNode determines whether we should garbage collect a link node from
 // the database due to no longer having any open channels with it. If there are
 // any left, then this acts as a no-op.
-func (d *DB) pruneLinkNode(tx kvdb.RwTx, remotePub *btcec.PublicKey) error {
-	openChannels, err := d.fetchOpenChannels(tx, remotePub)
+func (db *DB) pruneLinkNode(tx kvdb.RwTx, remotePub *btcec.PublicKey) error {
+	openChannels, err := db.fetchOpenChannels(tx, remotePub)
 	if err != nil {
 		return fmt.Errorf("unable to fetch open channels for peer %x: "+
 			"%v", remotePub.SerializeCompressed(), err)
@@ -920,7 +954,7 @@ func (d *DB) pruneLinkNode(tx kvdb.RwTx, remotePub *btcec.PublicKey) error {
 	log.Infof("Pruning link node %x with zero open channels from database",
 		remotePub.SerializeCompressed())
 
-	return d.deleteLinkNode(tx, remotePub)
+	return db.deleteLinkNode(tx, remotePub)
 }
 
 // PruneLinkNodes attempts to prune all link nodes found within the databse with
@@ -1132,16 +1166,16 @@ func (d *DB) AddrsForNode(nodePub *btcec.PublicKey) ([]net.Addr, error) {
 // database. If the channel was already removed (has a closed channel entry),
 // then we'll return a nil error. Otherwise, we'll insert a new close summary
 // into the database.
-func (d *DB) AbandonChannel(chanPoint *wire.OutPoint, bestHeight uint32) error {
+func (db *DB) AbandonChannel(chanPoint *wire.OutPoint, bestHeight uint32) error {
 	// With the chanPoint constructed, we'll attempt to find the target
 	// channel in the database. If we can't find the channel, then we'll
 	// return the error back to the caller.
-	dbChan, err := d.FetchChannel(*chanPoint)
+	dbChan, err := db.FetchChannel(*chanPoint)
 	switch {
 	// If the channel wasn't found, then it's possible that it was already
 	// abandoned from the database.
 	case err == ErrChannelNotFound:
-		_, closedErr := d.FetchClosedChannel(chanPoint)
+		_, closedErr := db.FetchClosedChannel(chanPoint)
 		if closedErr != nil {
 			return closedErr
 		}
@@ -1304,9 +1338,9 @@ func fetchHistoricalChanBucket(tx kvdb.ReadTx,
 
 // FetchHistoricalChannel fetches open channel data from the historical channel
 // bucket.
-func (d *DB) FetchHistoricalChannel(outPoint *wire.OutPoint) (*OpenChannel, error) {
+func (db *DB) FetchHistoricalChannel(outPoint *wire.OutPoint) (*OpenChannel, error) {
 	var channel *OpenChannel
-	err := kvdb.View(d, func(tx kvdb.ReadTx) error {
+	err := kvdb.View(db, func(tx kvdb.ReadTx) error {
 		chanBucket, err := fetchHistoricalChanBucket(tx, outPoint)
 		if err != nil {
 			return err

channeldb/db_test.go

@@ -15,6 +15,7 @@ import (
 	"github.com/btcsuite/btcd/wire"
 	"github.com/btcsuite/btcutil"
 	"github.com/davecgh/go-spew/spew"
+	"github.com/lightningnetwork/lnd/channeldb/kvdb"
 	"github.com/lightningnetwork/lnd/keychain"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/shachain"
@@ -33,7 +34,13 @@ func TestOpenWithCreate(t *testing.T) {
 
 	// Next, open thereby creating channeldb for the first time.
 	dbPath := filepath.Join(tempDirName, "cdb")
-	cdb, err := Open(dbPath)
+	backend, cleanup, err := kvdb.GetTestBackend(dbPath, "cdb")
+	if err != nil {
+		t.Fatalf("unable to get test db backend: %v", err)
+	}
+	defer cleanup()
+
+	cdb, err := CreateWithBackend(backend)
 	if err != nil {
 		t.Fatalf("unable to create channeldb: %v", err)
 	}
@@ -73,7 +80,13 @@ func TestWipe(t *testing.T) {
 
 	// Next, open thereby creating channeldb for the first time.
 	dbPath := filepath.Join(tempDirName, "cdb")
-	cdb, err := Open(dbPath)
+	backend, cleanup, err := kvdb.GetTestBackend(dbPath, "cdb")
+	if err != nil {
+		t.Fatalf("unable to get test db backend: %v", err)
+	}
+	defer cleanup()
+
+	cdb, err := CreateWithBackend(backend)
 	if err != nil {
 		t.Fatalf("unable to create channeldb: %v", err)
 	}

channeldb/kvdb/backend.go

@@ -0,0 +1,70 @@
+package kvdb
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	_ "github.com/btcsuite/btcwallet/walletdb/bdb" // Import to register backend.
+)
+
+// fileExists returns true if the file exists, and false otherwise.
+func fileExists(path string) bool {
+	if _, err := os.Stat(path); err != nil {
+		if os.IsNotExist(err) {
+			return false
+		}
+	}
+
+	return true
+}
+
+// GetBoltBackend opens (or creates if doesn't exits) a bbolt
+// backed database and returns a kvdb.Backend wrapping it.
+func GetBoltBackend(path, name string, noFreeListSync bool) (Backend, error) {
+	dbFilePath := filepath.Join(path, name)
+	var (
+		db  Backend
+		err error
+	)
+
+	if !fileExists(dbFilePath) {
+		if !fileExists(path) {
+			if err := os.MkdirAll(path, 0700); err != nil {
+				return nil, err
+			}
+		}
+
+		db, err = Create(BoltBackendName, dbFilePath, noFreeListSync)
+	} else {
+		db, err = Open(BoltBackendName, dbFilePath, noFreeListSync)
+	}
+
+	if err != nil {
+		return nil, err
+	}
+
+	return db, nil
+}
+
+// GetTestBackend opens (or creates if doesn't exist) a bbolt or etcd
+// backed database (for testing), and returns a kvdb.Backend and a cleanup
+// func. Whether to create/open bbolt or embedded etcd database is based
+// on the TestBackend constant which is conditionally compiled with build tag.
+// The passed path is used to hold all db files, while the name is only used
+// for bbolt.
+func GetTestBackend(path, name string) (Backend, func(), error) {
+	empty := func() {}
+
+	if TestBackend == BoltBackendName {
+		db, err := GetBoltBackend(path, name, true)
+		if err != nil {
+			return nil, nil, err
+		}
+		return db, empty, nil
+	} else if TestBackend == EtcdBackendName {
+		return GetEtcdTestBackend(path, name)
+	}
+
+	return nil, nil, fmt.Errorf("unknown backend")
+}

channeldb/kvdb/bbolt.go

@@ -1,10 +0,0 @@
-package kvdb
-
-import (
-	_ "github.com/btcsuite/btcwallet/walletdb/bdb" // Import to register backend.
-)
-
-// BoltBackendName is the name of the backend that should be passed into
-// kvdb.Create to initialize a new instance of kvdb.Backend backed by a live
-// instance of bbolt.
-const BoltBackendName = "bdb"

channeldb/kvdb/config.go

@@ -0,0 +1,33 @@
+package kvdb
+
+// BoltBackendName is the name of the backend that should be passed into
+// kvdb.Create to initialize a new instance of kvdb.Backend backed by a live
+// instance of bbolt.
+const BoltBackendName = "bdb"
+
+// EtcdBackendName is the name of the backend that should be passed into
+// kvdb.Create to initialize a new instance of kvdb.Backend backed by a live
+// instance of etcd.
+const EtcdBackendName = "etcd"
+
+// BoltConfig holds bolt configuration.
+type BoltConfig struct {
+	NoFreeListSync bool `long:"nofreelistsync" description:"If true, prevents the database from syncing its freelist to disk"`
+}
+
+// EtcdConfig holds etcd configuration.
+type EtcdConfig struct {
+	Host string `long:"host" description:"Etcd database host."`
+
+	User string `long:"user" description:"Etcd database user."`
+
+	Pass string `long:"pass" description:"Password for the database user."`
+
+	CertFile string `long:"cert_file" description:"Path to the TLS certificate for etcd RPC."`
+
+	KeyFile string `long:"key_file" description:"Path to the TLS private key for etcd RPC."`
+
+	InsecureSkipVerify bool `long:"insecure_skip_verify" description:"Whether we intend to skip TLS verification"`
+
+	CollectStats bool `long:"collect_stats" description:"Whether to collect etcd commit stats."`
+}

channeldb/kvdb/etcd/bucket.go

@@ -0,0 +1,79 @@
+// +build kvdb_etcd
+
+package etcd
+
+import (
+	"crypto/sha256"
+)
+
+const (
+	bucketIDLength = 32
+)
+
+var (
+	bucketPrefix   = []byte("b")
+	valuePrefix    = []byte("v")
+	sequencePrefix = []byte("$")
+)
+
+// makeBucketID returns a deterministic key for the passed byte slice.
+// Currently it returns the sha256 hash of the slice.
+func makeBucketID(key []byte) [bucketIDLength]byte {
+	return sha256.Sum256(key)
+}
+
+// isValidBucketID checks if the passed slice is the required length to be a
+// valid bucket id.
+func isValidBucketID(s []byte) bool {
+	return len(s) == bucketIDLength
+}
+
+// makeKey concatenates prefix, parent and key into one byte slice.
+// The prefix indicates the use of this key (whether bucket, value or sequence),
+// while parentID refers to the parent bucket.
+func makeKey(prefix, parent, key []byte) []byte {
+	keyBuf := make([]byte, len(prefix)+len(parent)+len(key))
+	copy(keyBuf, prefix)
+	copy(keyBuf[len(prefix):], parent)
+	copy(keyBuf[len(prefix)+len(parent):], key)
+
+	return keyBuf
+}
+
+// makePrefix concatenates prefix with parent into one byte slice.
+func makePrefix(prefix []byte, parent []byte) []byte {
+	prefixBuf := make([]byte, len(prefix)+len(parent))
+	copy(prefixBuf, prefix)
+	copy(prefixBuf[len(prefix):], parent)
+
+	return prefixBuf
+}
+
+// makeBucketKey returns a bucket key from the passed parent bucket id and
+// the key.
+func makeBucketKey(parent []byte, key []byte) []byte {
+	return makeKey(bucketPrefix, parent, key)
+}
+
+// makeValueKey returns a value key from the passed parent bucket id and
+// the key.
+func makeValueKey(parent []byte, key []byte) []byte {
+	return makeKey(valuePrefix, parent, key)
+}
+
+// makeSequenceKey returns a sequence key of the passed parent bucket id.
+func makeSequenceKey(parent []byte) []byte {
+	return makeKey(sequencePrefix, parent, nil)
+}
+
+// makeBucketPrefix returns the bucket prefix of the passed parent bucket id.
+// This prefix is used for all sub buckets.
+func makeBucketPrefix(parent []byte) []byte {
+	return makePrefix(bucketPrefix, parent)
+}
+
+// makeValuePrefix returns the value prefix of the passed parent bucket id.
+// This prefix is used for all key/values in the bucket.
+func makeValuePrefix(parent []byte) []byte {
+	return makePrefix(valuePrefix, parent)
+}

channeldb/kvdb/etcd/bucket_test.go

@@ -0,0 +1,42 @@
+// +build kvdb_etcd
+
+package etcd
+
+// bkey is a helper functon used in tests to create a bucket key from passed
+// bucket list.
+func bkey(buckets ...string) string {
+	var bucketKey []byte
+
+	rootID := makeBucketID([]byte(""))
+	parent := rootID[:]
+
+	for _, bucketName := range buckets {
+		bucketKey = makeBucketKey(parent, []byte(bucketName))
+		id := makeBucketID(bucketKey)
+		parent = id[:]
+	}
+
+	return string(bucketKey)
+}
+
+// bval is a helper function used in tests to create a bucket value (the value
+// for a bucket key) from the passed bucket list.
+func bval(buckets ...string) string {
+	id := makeBucketID([]byte(bkey(buckets...)))
+	return string(id[:])
+}
+
+// vkey is a helper function used in tests to create a value key from the
+// passed key and bucket list.
+func vkey(key string, buckets ...string) string {
+	rootID := makeBucketID([]byte(""))
+	bucket := rootID[:]
+
+	for _, bucketName := range buckets {
+		bucketKey := makeBucketKey(bucket, []byte(bucketName))
+		id := makeBucketID(bucketKey)
+		bucket = id[:]
+	}
+
+	return string(makeValueKey(bucket, []byte(key)))
+}

channeldb/kvdb/etcd/db.go

@@ -0,0 +1,291 @@
+// +build kvdb_etcd
+
+package etcd
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"runtime"
+	"sync"
+	"time"
+
+	"github.com/btcsuite/btcwallet/walletdb"
+	"github.com/coreos/etcd/clientv3"
+	"github.com/coreos/etcd/pkg/transport"
+)
+
+const (
+	// etcdConnectionTimeout is the timeout until successful connection to the
+	// etcd instance.
+	etcdConnectionTimeout = 10 * time.Second
+
+	// etcdLongTimeout is a timeout for longer taking etcd operatons.
+	etcdLongTimeout = 30 * time.Second
+)
+
+// callerStats holds commit stats for a specific caller. Currently it only
+// holds the max stat, meaning that for a particular caller the largest
+// commit set is recorded.
+type callerStats struct {
+	count       int
+	commitStats CommitStats
+}
+
+func (s callerStats) String() string {
+	return fmt.Sprintf("count: %d, retries: %d, rset: %d, wset: %d",
+		s.count, s.commitStats.Retries, s.commitStats.Rset, s.commitStats.Wset)
+}
+
+// commitStatsCollector collects commit stats for commits succeeding
+// and also for commits failing.
+type commitStatsCollector struct {
+	sync.RWMutex
+	succ map[string]*callerStats
+	fail map[string]*callerStats
+}
+
+// newCommitStatsColletor creates a new commitStatsCollector instance.
+func newCommitStatsColletor() *commitStatsCollector {
+	return &commitStatsCollector{
+		succ: make(map[string]*callerStats),
+		fail: make(map[string]*callerStats),
+	}
+}
+
+// PrintStats returns collected stats pretty printed into a string.
+func (c *commitStatsCollector) PrintStats() string {
+	c.RLock()
+	defer c.RUnlock()
+
+	s := "\nFailure:\n"
+	for k, v := range c.fail {
+		s += fmt.Sprintf("%s\t%s\n", k, v)
+	}
+
+	s += "\nSuccess:\n"
+	for k, v := range c.succ {
+		s += fmt.Sprintf("%s\t%s\n", k, v)
+	}
+
+	return s
+}
+
+// updateStatsMap updatess commit stats map for a caller.
+func updateStatMap(
+	caller string, stats CommitStats, m map[string]*callerStats) {
+
+	if _, ok := m[caller]; !ok {
+		m[caller] = &callerStats{}
+	}
+
+	curr := m[caller]
+	curr.count++
+
+	// Update only if the total commit set is greater or equal.
+	currTotal := curr.commitStats.Rset + curr.commitStats.Wset
+	if currTotal <= (stats.Rset + stats.Wset) {
+		curr.commitStats = stats
+	}
+}
+
+// callback is an STM commit stats callback passed which can be passed
+// using a WithCommitStatsCallback to the STM upon construction.
+func (c *commitStatsCollector) callback(succ bool, stats CommitStats) {
+	caller := "unknown"
+
+	// Get the caller. As this callback is called from
+	// the backend interface that means we need to ascend
+	// 4 frames in the callstack.
+	_, file, no, ok := runtime.Caller(4)
+	if ok {
+		caller = fmt.Sprintf("%s#%d", file, no)
+	}
+
+	c.Lock()
+	defer c.Unlock()
+
+	if succ {
+		updateStatMap(caller, stats, c.succ)
+	} else {
+		updateStatMap(caller, stats, c.fail)
+	}
+}
+
+// db holds a reference to the etcd client connection.
+type db struct {
+	config               BackendConfig
+	cli                  *clientv3.Client
+	commitStatsCollector *commitStatsCollector
+}
+
+// Enforce db implements the walletdb.DB interface.
+var _ walletdb.DB = (*db)(nil)
+
+// BackendConfig holds and etcd backend config and connection parameters.
+type BackendConfig struct {
+	// Host holds the peer url of the etcd instance.
+	Host string
+
+	// User is the username for the etcd peer.
+	User string
+
+	// Pass is the password for the etcd peer.
+	Pass string
+
+	// CertFile holds the path to the TLS certificate for etcd RPC.
+	CertFile string
+
+	// KeyFile holds the path to the TLS private key for etcd RPC.
+	KeyFile string
+
+	// InsecureSkipVerify should be set to true if we intend to
+	// skip TLS verification.
+	InsecureSkipVerify bool
+
+	// Prefix the hash of the prefix will be used as the root
+	// bucket id. This enables key space separation similar to
+	// name spaces.
+	Prefix string
+
+	// CollectCommitStats indicates wheter to commit commit stats.
+	CollectCommitStats bool
+}
+
+// newEtcdBackend returns a db object initialized with the passed backend
+// config. If etcd connection cannot be estabished, then returns error.
+func newEtcdBackend(config BackendConfig) (*db, error) {
+	tlsInfo := transport.TLSInfo{
+		CertFile:           config.CertFile,
+		KeyFile:            config.KeyFile,
+		InsecureSkipVerify: config.InsecureSkipVerify,
+	}
+
+	tlsConfig, err := tlsInfo.ClientConfig()
+	if err != nil {
+		return nil, err
+	}
+
+	cli, err := clientv3.New(clientv3.Config{
+		Endpoints:   []string{config.Host},
+		DialTimeout: etcdConnectionTimeout,
+		Username:    config.User,
+		Password:    config.Pass,
+		TLS:         tlsConfig,
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	backend := &db{
+		cli:    cli,
+		config: config,
+	}
+
+	if config.CollectCommitStats {
+		backend.commitStatsCollector = newCommitStatsColletor()
+	}
+
+	return backend, nil
+}
+
+// getSTMOptions creats all STM options based on the backend config.
+func (db *db) getSTMOptions() []STMOptionFunc {
+	opts := []STMOptionFunc{}
+	if db.config.CollectCommitStats {
+		opts = append(opts,
+			WithCommitStatsCallback(db.commitStatsCollector.callback),
+		)
+	}
+
+	return opts
+}
+
+// View opens a database read transaction and executes the function f with the
+// transaction passed as a parameter.  After f exits, the transaction is rolled
+// back.  If f errors, its error is returned, not a rollback error (if any
+// occur).
+func (db *db) View(f func(tx walletdb.ReadTx) error) error {
+	apply := func(stm STM) error {
+		return f(newReadWriteTx(stm, db.config.Prefix))
+	}
+
+	return RunSTM(db.cli, apply, db.getSTMOptions()...)
+}
+
+// Update opens a database read/write transaction and executes the function f
+// with the transaction passed as a parameter.  After f exits, if f did not
+// error, the transaction is committed.  Otherwise, if f did error, the
+// transaction is rolled back.  If the rollback fails, the original error
+// returned by f is still returned.  If the commit fails, the commit error is
+// returned.
+func (db *db) Update(f func(tx walletdb.ReadWriteTx) error) error {
+	apply := func(stm STM) error {
+		return f(newReadWriteTx(stm, db.config.Prefix))
+	}
+
+	return RunSTM(db.cli, apply, db.getSTMOptions()...)
+}
+
+// PrintStats returns all collected stats pretty printed into a string.
+func (db *db) PrintStats() string {
+	if db.commitStatsCollector != nil {
+		return db.commitStatsCollector.PrintStats()
+	}
+
+	return ""
+}
+
+// BeginReadTx opens a database read transaction.
+func (db *db) BeginReadWriteTx() (walletdb.ReadWriteTx, error) {
+	return newReadWriteTx(
+		NewSTM(db.cli, db.getSTMOptions()...),
+		db.config.Prefix,
+	), nil
+}
+
+// BeginReadWriteTx opens a database read+write transaction.
+func (db *db) BeginReadTx() (walletdb.ReadTx, error) {
+	return newReadWriteTx(
+		NewSTM(db.cli, db.getSTMOptions()...),
+		db.config.Prefix,
+	), nil
+}
+
+// Copy writes a copy of the database to the provided writer.  This call will
+// start a read-only transaction to perform all operations.
+// This function is part of the walletdb.Db interface implementation.
+func (db *db) Copy(w io.Writer) error {
+	ctx := context.Background()
+
+	ctx, cancel := context.WithTimeout(ctx, etcdLongTimeout)
+	defer cancel()
+
+	readCloser, err := db.cli.Snapshot(ctx)
+	if err != nil {
+		return err
+	}
+
+	_, err = io.Copy(w, readCloser)
+
+	return err
+}
+
+// Close cleanly shuts down the database and syncs all data.
+// This function is part of the walletdb.Db interface implementation.
+func (db *db) Close() error {
+	return db.cli.Close()
+}
+
+// Batch opens a database read/write transaction and executes the function f
+// with the transaction passed as a parameter.  After f exits, if f did not
+// error, the transaction is committed.  Otherwise, if f did error, the
+// transaction is rolled back.  If the rollback fails, the original error
+// returned by f is still returned.  If the commit fails, the commit error is
+// returned.
+//
+// Batch is only useful when there are multiple goroutines calling it.
+func (db *db) Batch(apply func(tx walletdb.ReadWriteTx) error) error {
+	return db.Update(apply)
+}

channeldb/kvdb/etcd/db_test.go

@@ -0,0 +1,44 @@
+// +build kvdb_etcd
+
+package etcd
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/btcsuite/btcwallet/walletdb"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCopy(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	err = db.Update(func(tx walletdb.ReadWriteTx) error {
+		// "apple"
+		apple, err := tx.CreateTopLevelBucket([]byte("apple"))
+		assert.NoError(t, err)
+		assert.NotNil(t, apple)
+
+		assert.NoError(t, apple.Put([]byte("key"), []byte("val")))
+		return nil
+	})
+
+	// Expect non-zero copy.
+	var buf bytes.Buffer
+
+	assert.NoError(t, db.Copy(&buf))
+	assert.Greater(t, buf.Len(), 0)
+	assert.Nil(t, err)
+
+	expected := map[string]string{
+		bkey("apple"):        bval("apple"),
+		vkey("key", "apple"): "val",
+	}
+	assert.Equal(t, expected, f.Dump())
+}

channeldb/kvdb/etcd/driver.go

@@ -0,0 +1,68 @@
+// +build kvdb_etcd
+
+package etcd
+
+import (
+	"fmt"
+
+	"github.com/btcsuite/btcwallet/walletdb"
+)
+
+const (
+	dbType = "etcd"
+)
+
+// parseArgs parses the arguments from the walletdb Open/Create methods.
+func parseArgs(funcName string, args ...interface{}) (*BackendConfig, error) {
+	if len(args) != 1 {
+		return nil, fmt.Errorf("invalid number of arguments to %s.%s -- "+
+			"expected: etcd.BackendConfig",
+			dbType, funcName,
+		)
+	}
+
+	config, ok := args[0].(BackendConfig)
+	if !ok {
+		return nil, fmt.Errorf("argument to %s.%s is invalid -- "+
+			"expected: etcd.BackendConfig",
+			dbType, funcName,
+		)
+	}
+
+	return &config, nil
+}
+
+// createDBDriver is the callback provided during driver registration that
+// creates, initializes, and opens a database for use.
+func createDBDriver(args ...interface{}) (walletdb.DB, error) {
+	config, err := parseArgs("Create", args...)
+	if err != nil {
+		return nil, err
+	}
+
+	return newEtcdBackend(*config)
+}
+
+// openDBDriver is the callback provided during driver registration that opens
+// an existing database for use.
+func openDBDriver(args ...interface{}) (walletdb.DB, error) {
+	config, err := parseArgs("Open", args...)
+	if err != nil {
+		return nil, err
+	}
+
+	return newEtcdBackend(*config)
+}
+
+func init() {
+	// Register the driver.
+	driver := walletdb.Driver{
+		DbType: dbType,
+		Create: createDBDriver,
+		Open:   openDBDriver,
+	}
+	if err := walletdb.RegisterDriver(driver); err != nil {
+		panic(fmt.Sprintf("Failed to regiser database driver '%s': %v",
+			dbType, err))
+	}
+}

channeldb/kvdb/etcd/driver_test.go

@@ -0,0 +1,30 @@
+// +build kvdb_etcd
+
+package etcd
+
+import (
+	"testing"
+
+	"github.com/btcsuite/btcwallet/walletdb"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestOpenCreateFailure(t *testing.T) {
+	t.Parallel()
+
+	db, err := walletdb.Open(dbType)
+	assert.Error(t, err)
+	assert.Nil(t, db)
+
+	db, err = walletdb.Open(dbType, "wrong")
+	assert.Error(t, err)
+	assert.Nil(t, db)
+
+	db, err = walletdb.Create(dbType)
+	assert.Error(t, err)
+	assert.Nil(t, db)
+
+	db, err = walletdb.Create(dbType, "wrong")
+	assert.Error(t, err)
+	assert.Nil(t, db)
+}

channeldb/kvdb/etcd/embed.go

@@ -0,0 +1,75 @@
+// +build kvdb_etcd
+
+package etcd
+
+import (
+	"fmt"
+	"net"
+	"net/url"
+	"time"
+
+	"github.com/coreos/etcd/embed"
+)
+
+const (
+	// readyTimeout is the time until the embedded etcd instance should start.
+	readyTimeout = 10 * time.Second
+)
+
+// getFreePort returns a random open TCP port.
+func getFreePort() int {
+	ln, err := net.Listen("tcp", "[::]:0")
+	if err != nil {
+		panic(err)
+	}
+
+	port := ln.Addr().(*net.TCPAddr).Port
+
+	err = ln.Close()
+	if err != nil {
+		panic(err)
+	}
+
+	return port
+}
+
+// NewEmbeddedEtcdInstance creates an embedded etcd instance for testing,
+// listening on random open ports. Returns the backend config and a cleanup
+// func that will stop the etcd instance.
+func NewEmbeddedEtcdInstance(path string) (*BackendConfig, func(), error) {
+	cfg := embed.NewConfig()
+	cfg.Dir = path
+
+	// To ensure that we can submit large transactions.
+	cfg.MaxTxnOps = 1000
+
+	// Listen on random free ports.
+	clientURL := fmt.Sprintf("127.0.0.1:%d", getFreePort())
+	peerURL := fmt.Sprintf("127.0.0.1:%d", getFreePort())
+	cfg.LCUrls = []url.URL{{Host: clientURL}}
+	cfg.LPUrls = []url.URL{{Host: peerURL}}
+
+	etcd, err := embed.StartEtcd(cfg)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	select {
+	case <-etcd.Server.ReadyNotify():
+	case <-time.After(readyTimeout):
+		etcd.Close()
+		return nil, nil,
+			fmt.Errorf("etcd failed to start after: %v", readyTimeout)
+	}
+
+	connConfig := &BackendConfig{
+		Host:               "http://" + peerURL,
+		User:               "user",
+		Pass:               "pass",
+		InsecureSkipVerify: true,
+	}
+
+	return connConfig, func() {
+		etcd.Close()
+	}, nil
+}

channeldb/kvdb/etcd/fixture_test.go

@@ -0,0 +1,129 @@
+// +build kvdb_etcd
+
+package etcd
+
+import (
+	"context"
+	"io/ioutil"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/coreos/etcd/clientv3"
+)
+
+const (
+	// testEtcdTimeout is used for all RPC calls initiated by the test fixture.
+	testEtcdTimeout = 5 * time.Second
+)
+
+// EtcdTestFixture holds internal state of the etcd test fixture.
+type EtcdTestFixture struct {
+	t       *testing.T
+	cli     *clientv3.Client
+	config  *BackendConfig
+	cleanup func()
+}
+
+// NewTestEtcdInstance creates an embedded etcd instance for testing, listening
+// on random open ports. Returns the connection config and a cleanup func that
+// will stop the etcd instance.
+func NewTestEtcdInstance(t *testing.T, path string) (*BackendConfig, func()) {
+	t.Helper()
+
+	config, cleanup, err := NewEmbeddedEtcdInstance(path)
+	if err != nil {
+		t.Fatalf("error while staring embedded etcd instance: %v", err)
+	}
+
+	return config, cleanup
+}
+
+// NewTestEtcdTestFixture creates a new etcd-test fixture. This is helper
+// object to facilitate etcd tests and ensure pre and post conditions.
+func NewEtcdTestFixture(t *testing.T) *EtcdTestFixture {
+	tmpDir, err := ioutil.TempDir("", "etcd")
+	if err != nil {
+		t.Fatalf("unable to create temp dir: %v", err)
+	}
+
+	config, etcdCleanup := NewTestEtcdInstance(t, tmpDir)
+
+	cli, err := clientv3.New(clientv3.Config{
+		Endpoints: []string{config.Host},
+		Username:  config.User,
+		Password:  config.Pass,
+	})
+	if err != nil {
+		os.RemoveAll(tmpDir)
+		t.Fatalf("unable to create etcd test fixture: %v", err)
+	}
+
+	return &EtcdTestFixture{
+		t:      t,
+		cli:    cli,
+		config: config,
+		cleanup: func() {
+			etcdCleanup()
+			os.RemoveAll(tmpDir)
+		},
+	}
+}
+
+// Put puts a string key/value into the test etcd database.
+func (f *EtcdTestFixture) Put(key, value string) {
+	ctx, cancel := context.WithTimeout(context.TODO(), testEtcdTimeout)
+	defer cancel()
+
+	_, err := f.cli.Put(ctx, key, value)
+	if err != nil {
+		f.t.Fatalf("etcd test fixture failed to put: %v", err)
+	}
+}
+
+// Get queries a key and returns the stored value from the test etcd database.
+func (f *EtcdTestFixture) Get(key string) string {
+	ctx, cancel := context.WithTimeout(context.TODO(), testEtcdTimeout)
+	defer cancel()
+
+	resp, err := f.cli.Get(ctx, key)
+	if err != nil {
+		f.t.Fatalf("etcd test fixture failed to put: %v", err)
+	}
+
+	if len(resp.Kvs) > 0 {
+		return string(resp.Kvs[0].Value)
+	}
+
+	return ""
+}
+
+// Dump scans and returns all key/values from the test etcd database.
+func (f *EtcdTestFixture) Dump() map[string]string {
+	ctx, cancel := context.WithTimeout(context.TODO(), testEtcdTimeout)
+	defer cancel()
+
+	resp, err := f.cli.Get(ctx, "", clientv3.WithPrefix())
+	if err != nil {
+		f.t.Fatalf("etcd test fixture failed to put: %v", err)
+	}
+
+	result := make(map[string]string)
+	for _, kv := range resp.Kvs {
+		result[string(kv.Key)] = string(kv.Value)
+	}
+
+	return result
+}
+
+// BackendConfig returns the backend config for connecting to theembedded
+// etcd instance.
+func (f *EtcdTestFixture) BackendConfig() BackendConfig {
+	return *f.config
+}
+
+// Cleanup should be called at test fixture teardown to stop the embedded
+// etcd instance and remove all temp db files form the filesystem.
+func (f *EtcdTestFixture) Cleanup() {
+	f.cleanup()
+}

channeldb/kvdb/etcd/readwrite_bucket.go

@@ -0,0 +1,364 @@
+// +build kvdb_etcd
+
+package etcd
+
+import (
+	"bytes"
+	"strconv"
+
+	"github.com/btcsuite/btcwallet/walletdb"
+)
+
+// readWriteBucket stores the bucket id and the buckets transaction.
+type readWriteBucket struct {
+	// id is used to identify the bucket and is created by
+	// hashing the parent id with the bucket key. For each key/value,
+	// sub-bucket or the bucket sequence the bucket id is used with the
+	// appropriate prefix to prefix the key.
+	id []byte
+
+	// tx holds the parent transaction.
+	tx *readWriteTx
+}
+
+// newReadWriteBucket creates a new rw bucket with the passed transaction
+// and bucket id.
+func newReadWriteBucket(tx *readWriteTx, key, id []byte) *readWriteBucket {
+	if !bytes.Equal(id, tx.rootBucketID[:]) {
+		// Add the bucket key/value to the lock set.
+		tx.lock(string(key), string(id))
+	}
+
+	return &readWriteBucket{
+		id: id,
+		tx: tx,
+	}
+}
+
+// NestedReadBucket retrieves a nested read bucket with the given key.
+// Returns nil if the bucket does not exist.
+func (b *readWriteBucket) NestedReadBucket(key []byte) walletdb.ReadBucket {
+	return b.NestedReadWriteBucket(key)
+}
+
+// ForEach invokes the passed function with every key/value pair in
+// the bucket. This includes nested buckets, in which case the value
+// is nil, but it does not include the key/value pairs within those
+// nested buckets.
+func (b *readWriteBucket) ForEach(cb func(k, v []byte) error) error {
+	prefix := makeValuePrefix(b.id)
+	prefixLen := len(prefix)
+
+	// Get the first matching key that is in the bucket.
+	kv, err := b.tx.stm.First(string(prefix))
+	if err != nil {
+		return err
+	}
+
+	for kv != nil {
+		if err := cb([]byte(kv.key[prefixLen:]), []byte(kv.val)); err != nil {
+			return err
+		}
+
+		// Step to the next key.
+		kv, err = b.tx.stm.Next(string(prefix), kv.key)
+		if err != nil {
+			return err
+		}
+	}
+
+	// Make a bucket prefix. This prefixes all sub buckets.
+	prefix = makeBucketPrefix(b.id)
+	prefixLen = len(prefix)
+
+	// Get the first bucket.
+	kv, err = b.tx.stm.First(string(prefix))
+	if err != nil {
+		return err
+	}
+
+	for kv != nil {
+		if err := cb([]byte(kv.key[prefixLen:]), nil); err != nil {
+			return err
+		}
+
+		// Step to the next bucket.
+		kv, err = b.tx.stm.Next(string(prefix), kv.key)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// Get returns the value for the given key. Returns nil if the key does
+// not exist in this bucket.
+func (b *readWriteBucket) Get(key []byte) []byte {
+	// Return nil if the key is empty.
+	if len(key) == 0 {
+		return nil
+	}
+
+	// Fetch the associated value.
+	val, err := b.tx.stm.Get(string(makeValueKey(b.id, key)))
+	if err != nil {
+		// TODO: we should return the error once the
+		// kvdb inteface is extended.
+		return nil
+	}
+
+	if val == nil {
+		return nil
+	}
+
+	return val
+}
+
+func (b *readWriteBucket) ReadCursor() walletdb.ReadCursor {
+	return newReadWriteCursor(b)
+}
+
+// NestedReadWriteBucket retrieves a nested bucket with the given key.
+// Returns nil if the bucket does not exist.
+func (b *readWriteBucket) NestedReadWriteBucket(key []byte) walletdb.ReadWriteBucket {
+	if len(key) == 0 {
+		return nil
+	}
+
+	// Get the bucket id (and return nil if bucket doesn't exist).
+	bucketKey := makeBucketKey(b.id, key)
+	bucketVal, err := b.tx.stm.Get(string(bucketKey))
+	if err != nil {
+		// TODO: we should return the error once the
+		// kvdb inteface is extended.
+		return nil
+	}
+
+	if !isValidBucketID(bucketVal) {
+		return nil
+	}
+
+	// Return the bucket with the fetched bucket id.
+	return newReadWriteBucket(b.tx, bucketKey, bucketVal)
+}
+
+// CreateBucket creates and returns a new nested bucket with the given
+// key. Returns ErrBucketExists if the bucket already exists,
+// ErrBucketNameRequired if the key is empty, or ErrIncompatibleValue
+// if the key value is otherwise invalid for the particular database
+// implementation.  Other errors are possible depending on the
+// implementation.
+func (b *readWriteBucket) CreateBucket(key []byte) (
+	walletdb.ReadWriteBucket, error) {
+
+	if len(key) == 0 {
+		return nil, walletdb.ErrBucketNameRequired
+	}
+
+	// Check if the bucket already exists.
+	bucketKey := makeBucketKey(b.id, key)
+
+	bucketVal, err := b.tx.stm.Get(string(bucketKey))
+	if err != nil {
+		return nil, err
+	}
+
+	if isValidBucketID(bucketVal) {
+		return nil, walletdb.ErrBucketExists
+	}
+
+	// Create a deterministic bucket id from the bucket key.
+	newID := makeBucketID(bucketKey)
+
+	// Create the bucket.
+	b.tx.put(string(bucketKey), string(newID[:]))
+
+	return newReadWriteBucket(b.tx, bucketKey, newID[:]), nil
+}
+
+// CreateBucketIfNotExists creates and returns a new nested bucket with
+// the given key if it does not already exist.  Returns
+// ErrBucketNameRequired if the key is empty or ErrIncompatibleValue
+// if the key value is otherwise invalid for the particular database
+// backend.  Other errors are possible depending on the implementation.
+func (b *readWriteBucket) CreateBucketIfNotExists(key []byte) (
+	walletdb.ReadWriteBucket, error) {
+
+	if len(key) == 0 {
+		return nil, walletdb.ErrBucketNameRequired
+	}
+
+	// Check for the bucket and create if it doesn't exist.
+	bucketKey := makeBucketKey(b.id, key)
+
+	bucketVal, err := b.tx.stm.Get(string(bucketKey))
+	if err != nil {
+		return nil, err
+	}
+
+	if !isValidBucketID(bucketVal) {
+		newID := makeBucketID(bucketKey)
+		b.tx.put(string(bucketKey), string(newID[:]))
+
+		return newReadWriteBucket(b.tx, bucketKey, newID[:]), nil
+	}
+
+	// Otherwise return the bucket with the fetched bucket id.
+	return newReadWriteBucket(b.tx, bucketKey, bucketVal), nil
+}
+
+// DeleteNestedBucket deletes the nested bucket and its sub-buckets
+// pointed to by the passed key. All values in the bucket and sub-buckets
+// will be deleted as well.
+func (b *readWriteBucket) DeleteNestedBucket(key []byte) error {
+	// TODO shouldn't empty key return ErrBucketNameRequired ?
+	if len(key) == 0 {
+		return walletdb.ErrIncompatibleValue
+	}
+
+	// Get the bucket first.
+	bucketKey := string(makeBucketKey(b.id, key))
+
+	bucketVal, err := b.tx.stm.Get(bucketKey)
+	if err != nil {
+		return err
+	}
+
+	if !isValidBucketID(bucketVal) {
+		return walletdb.ErrBucketNotFound
+	}
+
+	// Enqueue the top level bucket id.
+	queue := [][]byte{bucketVal}
+
+	// Traverse the buckets breadth first.
+	for len(queue) != 0 {
+		if !isValidBucketID(queue[0]) {
+			return walletdb.ErrBucketNotFound
+		}
+
+		id := queue[0]
+		queue = queue[1:]
+
+		// Delete values in the current bucket
+		valuePrefix := string(makeValuePrefix(id))
+
+		kv, err := b.tx.stm.First(valuePrefix)
+		if err != nil {
+			return err
+		}
+
+		for kv != nil {
+			b.tx.del(kv.key)
+
+			kv, err = b.tx.stm.Next(valuePrefix, kv.key)
+			if err != nil {
+				return err
+			}
+		}
+
+		// Iterate sub buckets
+		bucketPrefix := string(makeBucketPrefix(id))
+
+		kv, err = b.tx.stm.First(bucketPrefix)
+		if err != nil {
+			return err
+		}
+
+		for kv != nil {
+			// Delete sub bucket key.
+			b.tx.del(kv.key)
+			// Queue it for traversal.
+			queue = append(queue, []byte(kv.val))
+
+			kv, err = b.tx.stm.Next(bucketPrefix, kv.key)
+			if err != nil {
+				return err
+			}
+		}
+	}
+
+	// Delete the top level bucket.
+	b.tx.del(bucketKey)
+
+	return nil
+}
+
+// Put updates the value for the passed key.
+// Returns ErrKeyRequred if te passed key is empty.
+func (b *readWriteBucket) Put(key, value []byte) error {
+	if len(key) == 0 {
+		return walletdb.ErrKeyRequired
+	}
+
+	// Update the transaction with the new value.
+	b.tx.put(string(makeValueKey(b.id, key)), string(value))
+
+	return nil
+}
+
+// Delete deletes the key/value pointed to by the passed key.
+// Returns ErrKeyRequred if the passed key is empty.
+func (b *readWriteBucket) Delete(key []byte) error {
+	if len(key) == 0 {
+		return walletdb.ErrKeyRequired
+	}
+
+	// Update the transaction to delete the key/value.
+	b.tx.del(string(makeValueKey(b.id, key)))
+
+	return nil
+}
+
+// ReadWriteCursor returns a new read-write cursor for this bucket.
+func (b *readWriteBucket) ReadWriteCursor() walletdb.ReadWriteCursor {
+	return newReadWriteCursor(b)
+}
+
+// Tx returns the buckets transaction.
+func (b *readWriteBucket) Tx() walletdb.ReadWriteTx {
+	return b.tx
+}
+
+// NextSequence returns an autoincrementing sequence number for this bucket.
+// Note that this is not a thread safe function and as such it must not be used
+// for synchronization.
+func (b *readWriteBucket) NextSequence() (uint64, error) {
+	seq := b.Sequence() + 1
+
+	return seq, b.SetSequence(seq)
+}
+
+// SetSequence updates the sequence number for the bucket.
+func (b *readWriteBucket) SetSequence(v uint64) error {
+	// Convert the number to string.
+	val := strconv.FormatUint(v, 10)
+
+	// Update the transaction with the new value for the sequence key.
+	b.tx.put(string(makeSequenceKey(b.id)), val)
+
+	return nil
+}
+
+// Sequence returns the current sequence number for this bucket without
+// incrementing it.
+func (b *readWriteBucket) Sequence() uint64 {
+	val, err := b.tx.stm.Get(string(makeSequenceKey(b.id)))
+	if err != nil {
+		// TODO: This update kvdb interface such that error
+		// may be returned here.
+		return 0
+	}
+
+	if val == nil {
+		// If the sequence number is not yet
+		// stored, then take the default value.
+		return 0
+	}
+
+	// Otherwise try to parse a 64 bit unsigned integer from the value.
+	num, _ := strconv.ParseUint(string(val), 10, 64)
+
+	return num
+}

channeldb/kvdb/etcd/readwrite_bucket_test.go

@@ -0,0 +1,404 @@
+// +build kvdb_etcd
+
+package etcd
+
+import (
+	"fmt"
+	"math"
+	"testing"
+
+	"github.com/btcsuite/btcwallet/walletdb"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestBucketCreation(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	err = db.Update(func(tx walletdb.ReadWriteTx) error {
+		// empty bucket name
+		b, err := tx.CreateTopLevelBucket(nil)
+		assert.Error(t, walletdb.ErrBucketNameRequired, err)
+		assert.Nil(t, b)
+
+		// empty bucket name
+		b, err = tx.CreateTopLevelBucket([]byte(""))
+		assert.Error(t, walletdb.ErrBucketNameRequired, err)
+		assert.Nil(t, b)
+
+		// "apple"
+		apple, err := tx.CreateTopLevelBucket([]byte("apple"))
+		assert.NoError(t, err)
+		assert.NotNil(t, apple)
+
+		// Check bucket tx.
+		assert.Equal(t, tx, apple.Tx())
+
+		// "apple" already created
+		b, err = tx.CreateTopLevelBucket([]byte("apple"))
+		assert.NoError(t, err)
+		assert.NotNil(t, b)
+
+		// "apple/banana"
+		banana, err := apple.CreateBucket([]byte("banana"))
+		assert.NoError(t, err)
+		assert.NotNil(t, banana)
+
+		banana, err = apple.CreateBucketIfNotExists([]byte("banana"))
+		assert.NoError(t, err)
+		assert.NotNil(t, banana)
+
+		// Try creating "apple/banana" again
+		b, err = apple.CreateBucket([]byte("banana"))
+		assert.Error(t, walletdb.ErrBucketExists, err)
+		assert.Nil(t, b)
+
+		// "apple/mango"
+		mango, err := apple.CreateBucket([]byte("mango"))
+		assert.Nil(t, err)
+		assert.NotNil(t, mango)
+
+		// "apple/banana/pear"
+		pear, err := banana.CreateBucket([]byte("pear"))
+		assert.Nil(t, err)
+		assert.NotNil(t, pear)
+
+		// empty bucket
+		assert.Nil(t, apple.NestedReadWriteBucket(nil))
+		assert.Nil(t, apple.NestedReadWriteBucket([]byte("")))
+
+		// "apple/pear" doesn't exist
+		assert.Nil(t, apple.NestedReadWriteBucket([]byte("pear")))
+
+		// "apple/banana" exits
+		assert.NotNil(t, apple.NestedReadWriteBucket([]byte("banana")))
+		assert.NotNil(t, apple.NestedReadBucket([]byte("banana")))
+		return nil
+	})
+
+	assert.Nil(t, err)
+
+	expected := map[string]string{
+		bkey("apple"):                   bval("apple"),
+		bkey("apple", "banana"):         bval("apple", "banana"),
+		bkey("apple", "mango"):          bval("apple", "mango"),
+		bkey("apple", "banana", "pear"): bval("apple", "banana", "pear"),
+	}
+	assert.Equal(t, expected, f.Dump())
+}
+
+func TestBucketDeletion(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	err = db.Update(func(tx walletdb.ReadWriteTx) error {
+		// "apple"
+		apple, err := tx.CreateTopLevelBucket([]byte("apple"))
+		assert.Nil(t, err)
+		assert.NotNil(t, apple)
+
+		// "apple/banana"
+		banana, err := apple.CreateBucket([]byte("banana"))
+		assert.Nil(t, err)
+		assert.NotNil(t, banana)
+
+		kvs := []KV{{"key1", "val1"}, {"key2", "val2"}, {"key3", "val3"}}
+
+		for _, kv := range kvs {
+			assert.NoError(t, banana.Put([]byte(kv.key), []byte(kv.val)))
+			assert.Equal(t, []byte(kv.val), banana.Get([]byte(kv.key)))
+		}
+
+		// Delete a k/v from "apple/banana"
+		assert.NoError(t, banana.Delete([]byte("key2")))
+		// Try getting/putting/deleting invalid k/v's.
+		assert.Nil(t, banana.Get(nil))
+		assert.Error(t, walletdb.ErrKeyRequired, banana.Put(nil, []byte("val")))
+		assert.Error(t, walletdb.ErrKeyRequired, banana.Delete(nil))
+
+		// Try deleting a k/v that doesn't exist.
+		assert.NoError(t, banana.Delete([]byte("nokey")))
+
+		// "apple/pear"
+		pear, err := apple.CreateBucket([]byte("pear"))
+		assert.Nil(t, err)
+		assert.NotNil(t, pear)
+
+		// Put some values into "apple/pear"
+		for _, kv := range kvs {
+			assert.Nil(t, pear.Put([]byte(kv.key), []byte(kv.val)))
+			assert.Equal(t, []byte(kv.val), pear.Get([]byte(kv.key)))
+		}
+
+		// Create nested bucket "apple/pear/cherry"
+		cherry, err := pear.CreateBucket([]byte("cherry"))
+		assert.Nil(t, err)
+		assert.NotNil(t, cherry)
+
+		// Put some values into "apple/pear/cherry"
+		for _, kv := range kvs {
+			assert.NoError(t, cherry.Put([]byte(kv.key), []byte(kv.val)))
+		}
+
+		// Read back values in "apple/pear/cherry" trough a read bucket.
+		cherryReadBucket := pear.NestedReadBucket([]byte("cherry"))
+		for _, kv := range kvs {
+			assert.Equal(
+				t, []byte(kv.val),
+				cherryReadBucket.Get([]byte(kv.key)),
+			)
+		}
+
+		// Try deleting some invalid buckets.
+		assert.Error(t,
+			walletdb.ErrBucketNameRequired, apple.DeleteNestedBucket(nil),
+		)
+
+		// Try deleting a non existing bucket.
+		assert.Error(
+			t,
+			walletdb.ErrBucketNotFound,
+			apple.DeleteNestedBucket([]byte("missing")),
+		)
+
+		// Delete "apple/pear"
+		assert.Nil(t, apple.DeleteNestedBucket([]byte("pear")))
+
+		// "apple/pear" deleted
+		assert.Nil(t, apple.NestedReadWriteBucket([]byte("pear")))
+
+		// "apple/pear/cherry" deleted
+		assert.Nil(t, pear.NestedReadWriteBucket([]byte("cherry")))
+
+		// Values deleted too.
+		for _, kv := range kvs {
+			assert.Nil(t, pear.Get([]byte(kv.key)))
+			assert.Nil(t, cherry.Get([]byte(kv.key)))
+		}
+
+		// "aple/banana" exists
+		assert.NotNil(t, apple.NestedReadWriteBucket([]byte("banana")))
+		return nil
+	})
+
+	assert.Nil(t, err)
+
+	expected := map[string]string{
+		bkey("apple"):                   bval("apple"),
+		bkey("apple", "banana"):         bval("apple", "banana"),
+		vkey("key1", "apple", "banana"): "val1",
+		vkey("key3", "apple", "banana"): "val3",
+	}
+	assert.Equal(t, expected, f.Dump())
+}
+
+func TestBucketForEach(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	err = db.Update(func(tx walletdb.ReadWriteTx) error {
+		// "apple"
+		apple, err := tx.CreateTopLevelBucket([]byte("apple"))
+		assert.Nil(t, err)
+		assert.NotNil(t, apple)
+
+		// "apple/banana"
+		banana, err := apple.CreateBucket([]byte("banana"))
+		assert.Nil(t, err)
+		assert.NotNil(t, banana)
+
+		kvs := []KV{{"key1", "val1"}, {"key2", "val2"}, {"key3", "val3"}}
+
+		// put some values into "apple" and "apple/banana" too
+		for _, kv := range kvs {
+			assert.Nil(t, apple.Put([]byte(kv.key), []byte(kv.val)))
+			assert.Equal(t, []byte(kv.val), apple.Get([]byte(kv.key)))
+
+			assert.Nil(t, banana.Put([]byte(kv.key), []byte(kv.val)))
+			assert.Equal(t, []byte(kv.val), banana.Get([]byte(kv.key)))
+		}
+
+		got := make(map[string]string)
+		err = apple.ForEach(func(key, val []byte) error {
+			got[string(key)] = string(val)
+			return nil
+		})
+
+		expected := map[string]string{
+			"key1":   "val1",
+			"key2":   "val2",
+			"key3":   "val3",
+			"banana": "",
+		}
+
+		assert.NoError(t, err)
+		assert.Equal(t, expected, got)
+
+		got = make(map[string]string)
+		err = banana.ForEach(func(key, val []byte) error {
+			got[string(key)] = string(val)
+			return nil
+		})
+
+		assert.NoError(t, err)
+		// remove the sub-bucket key
+		delete(expected, "banana")
+		assert.Equal(t, expected, got)
+
+		return nil
+	})
+
+	assert.Nil(t, err)
+
+	expected := map[string]string{
+		bkey("apple"):                   bval("apple"),
+		bkey("apple", "banana"):         bval("apple", "banana"),
+		vkey("key1", "apple"):           "val1",
+		vkey("key2", "apple"):           "val2",
+		vkey("key3", "apple"):           "val3",
+		vkey("key1", "apple", "banana"): "val1",
+		vkey("key2", "apple", "banana"): "val2",
+		vkey("key3", "apple", "banana"): "val3",
+	}
+	assert.Equal(t, expected, f.Dump())
+}
+
+func TestBucketForEachWithError(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	err = db.Update(func(tx walletdb.ReadWriteTx) error {
+		// "apple"
+		apple, err := tx.CreateTopLevelBucket([]byte("apple"))
+		assert.Nil(t, err)
+		assert.NotNil(t, apple)
+
+		// "apple/banana"
+		banana, err := apple.CreateBucket([]byte("banana"))
+		assert.Nil(t, err)
+		assert.NotNil(t, banana)
+
+		// "apple/pear"
+		pear, err := apple.CreateBucket([]byte("pear"))
+		assert.Nil(t, err)
+		assert.NotNil(t, pear)
+
+		kvs := []KV{{"key1", "val1"}, {"key2", "val2"}}
+
+		// Put some values into "apple" and "apple/banana" too.
+		for _, kv := range kvs {
+			assert.Nil(t, apple.Put([]byte(kv.key), []byte(kv.val)))
+			assert.Equal(t, []byte(kv.val), apple.Get([]byte(kv.key)))
+		}
+
+		got := make(map[string]string)
+		i := 0
+		// Error while iterating value keys.
+		err = apple.ForEach(func(key, val []byte) error {
+			if i == 1 {
+				return fmt.Errorf("error")
+			}
+
+			got[string(key)] = string(val)
+			i++
+			return nil
+		})
+
+		expected := map[string]string{
+			"key1": "val1",
+		}
+
+		assert.Equal(t, expected, got)
+		assert.Error(t, err)
+
+		got = make(map[string]string)
+		i = 0
+		// Erro while iterating buckets.
+		err = apple.ForEach(func(key, val []byte) error {
+			if i == 3 {
+				return fmt.Errorf("error")
+			}
+
+			got[string(key)] = string(val)
+			i++
+			return nil
+		})
+
+		expected = map[string]string{
+			"key1":   "val1",
+			"key2":   "val2",
+			"banana": "",
+		}
+
+		assert.Equal(t, expected, got)
+		assert.Error(t, err)
+		return nil
+	})
+
+	assert.Nil(t, err)
+
+	expected := map[string]string{
+		bkey("apple"):           bval("apple"),
+		bkey("apple", "banana"): bval("apple", "banana"),
+		bkey("apple", "pear"):   bval("apple", "pear"),
+		vkey("key1", "apple"):   "val1",
+		vkey("key2", "apple"):   "val2",
+	}
+	assert.Equal(t, expected, f.Dump())
+}
+
+func TestBucketSequence(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	err = db.Update(func(tx walletdb.ReadWriteTx) error {
+		apple, err := tx.CreateTopLevelBucket([]byte("apple"))
+		assert.Nil(t, err)
+		assert.NotNil(t, apple)
+
+		banana, err := apple.CreateBucket([]byte("banana"))
+		assert.Nil(t, err)
+		assert.NotNil(t, banana)
+
+		assert.Equal(t, uint64(0), apple.Sequence())
+		assert.Equal(t, uint64(0), banana.Sequence())
+
+		assert.Nil(t, apple.SetSequence(math.MaxUint64))
+		assert.Equal(t, uint64(math.MaxUint64), apple.Sequence())
+
+		for i := uint64(0); i < uint64(5); i++ {
+			s, err := apple.NextSequence()
+			assert.Nil(t, err)
+			assert.Equal(t, i, s)
+		}
+
+		return nil
+	})
+
+	assert.Nil(t, err)
+}

channeldb/kvdb/etcd/readwrite_cursor.go

@@ -0,0 +1,145 @@
+// +build kvdb_etcd
+
+package etcd
+
+// readWriteCursor holds a reference to the cursors bucket, the value
+// prefix and the current key used while iterating.
+type readWriteCursor struct {
+	// bucket holds the reference to the parent bucket.
+	bucket *readWriteBucket
+
+	// prefix holds the value prefix which is in front of each
+	// value key in the bucket.
+	prefix string
+
+	// currKey holds the current key of the cursor.
+	currKey string
+}
+
+func newReadWriteCursor(bucket *readWriteBucket) *readWriteCursor {
+	return &readWriteCursor{
+		bucket: bucket,
+		prefix: string(makeValuePrefix(bucket.id)),
+	}
+}
+
+// First positions the cursor at the first key/value pair and returns
+// the pair.
+func (c *readWriteCursor) First() (key, value []byte) {
+	// Get the first key with the value prefix.
+	kv, err := c.bucket.tx.stm.First(c.prefix)
+	if err != nil {
+		// TODO: revise this once kvdb interface supports errors
+		return nil, nil
+	}
+
+	if kv != nil {
+		c.currKey = kv.key
+		// Chop the prefix and return the key/value.
+		return []byte(kv.key[len(c.prefix):]), []byte(kv.val)
+	}
+
+	return nil, nil
+}
+
+// Last positions the cursor at the last key/value pair and returns the
+// pair.
+func (c *readWriteCursor) Last() (key, value []byte) {
+	kv, err := c.bucket.tx.stm.Last(c.prefix)
+	if err != nil {
+		// TODO: revise this once kvdb interface supports errors
+		return nil, nil
+	}
+
+	if kv != nil {
+		c.currKey = kv.key
+		// Chop the prefix and return the key/value.
+		return []byte(kv.key[len(c.prefix):]), []byte(kv.val)
+	}
+
+	return nil, nil
+}
+
+// Next moves the cursor one key/value pair forward and returns the new
+// pair.
+func (c *readWriteCursor) Next() (key, value []byte) {
+	kv, err := c.bucket.tx.stm.Next(c.prefix, c.currKey)
+	if err != nil {
+		// TODO: revise this once kvdb interface supports errors
+		return nil, nil
+	}
+
+	if kv != nil {
+		c.currKey = kv.key
+		// Chop the prefix and return the key/value.
+		return []byte(kv.key[len(c.prefix):]), []byte(kv.val)
+	}
+
+	return nil, nil
+}
+
+// Prev moves the cursor one key/value pair backward and returns the new
+// pair.
+func (c *readWriteCursor) Prev() (key, value []byte) {
+	kv, err := c.bucket.tx.stm.Prev(c.prefix, c.currKey)
+	if err != nil {
+		// TODO: revise this once kvdb interface supports errors
+		return nil, nil
+	}
+
+	if kv != nil {
+		c.currKey = kv.key
+		// Chop the prefix and return the key/value.
+		return []byte(kv.key[len(c.prefix):]), []byte(kv.val)
+	}
+
+	return nil, nil
+}
+
+// Seek positions the cursor at the passed seek key.  If the key does
+// not exist, the cursor is moved to the next key after seek.  Returns
+// the new pair.
+func (c *readWriteCursor) Seek(seek []byte) (key, value []byte) {
+	// Return nil if trying to seek to an empty key.
+	if seek == nil {
+		return nil, nil
+	}
+
+	// Seek to the first key with prefix + seek. If that key is not present
+	// STM will seek to the next matching key with prefix.
+	kv, err := c.bucket.tx.stm.Seek(c.prefix, c.prefix+string(seek))
+	if err != nil {
+		// TODO: revise this once kvdb interface supports errors
+		return nil, nil
+	}
+
+	if kv != nil {
+		c.currKey = kv.key
+		// Chop the prefix and return the key/value.
+		return []byte(kv.key[len(c.prefix):]), []byte(kv.val)
+	}
+
+	return nil, nil
+}
+
+// Delete removes the current key/value pair the cursor is at without
+// invalidating the cursor.  Returns ErrIncompatibleValue if attempted
+// when the cursor points to a nested bucket.
+func (c *readWriteCursor) Delete() error {
+	// Get the next key after the current one. We could do this
+	// after deletion too but it's one step more efficient here.
+	nextKey, err := c.bucket.tx.stm.Next(c.prefix, c.currKey)
+	if err != nil {
+		return err
+	}
+
+	// Delete the current key.
+	c.bucket.tx.stm.Del(c.currKey)
+
+	// Set current key to the next one if possible.
+	if nextKey != nil {
+		c.currKey = nextKey.key
+	}
+
+	return nil
+}

channeldb/kvdb/etcd/readwrite_cursor_test.go

@@ -0,0 +1,293 @@
+// +build kvdb_etcd
+
+package etcd
+
+import (
+	"testing"
+
+	"github.com/btcsuite/btcwallet/walletdb"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestReadCursorEmptyInterval(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	err = db.Update(func(tx walletdb.ReadWriteTx) error {
+		b, err := tx.CreateTopLevelBucket([]byte("alma"))
+		assert.NoError(t, err)
+		assert.NotNil(t, b)
+
+		return nil
+	})
+	assert.NoError(t, err)
+
+	err = db.View(func(tx walletdb.ReadTx) error {
+		b := tx.ReadBucket([]byte("alma"))
+		assert.NotNil(t, b)
+
+		cursor := b.ReadCursor()
+		k, v := cursor.First()
+		assert.Nil(t, k)
+		assert.Nil(t, v)
+
+		k, v = cursor.Next()
+		assert.Nil(t, k)
+		assert.Nil(t, v)
+
+		k, v = cursor.Last()
+		assert.Nil(t, k)
+		assert.Nil(t, v)
+
+		k, v = cursor.Prev()
+		assert.Nil(t, k)
+		assert.Nil(t, v)
+
+		return nil
+	})
+	assert.NoError(t, err)
+}
+
+func TestReadCursorNonEmptyInterval(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	testKeyValues := []KV{
+		{"b", "1"},
+		{"c", "2"},
+		{"da", "3"},
+		{"e", "4"},
+	}
+
+	err = db.Update(func(tx walletdb.ReadWriteTx) error {
+		b, err := tx.CreateTopLevelBucket([]byte("alma"))
+		assert.NoError(t, err)
+		assert.NotNil(t, b)
+
+		for _, kv := range testKeyValues {
+			assert.NoError(t, b.Put([]byte(kv.key), []byte(kv.val)))
+		}
+		return nil
+	})
+
+	assert.NoError(t, err)
+
+	err = db.View(func(tx walletdb.ReadTx) error {
+		b := tx.ReadBucket([]byte("alma"))
+		assert.NotNil(t, b)
+
+		// Iterate from the front.
+		var kvs []KV
+		cursor := b.ReadCursor()
+		k, v := cursor.First()
+
+		for k != nil && v != nil {
+			kvs = append(kvs, KV{string(k), string(v)})
+			k, v = cursor.Next()
+		}
+		assert.Equal(t, testKeyValues, kvs)
+
+		// Iterate from the back.
+		kvs = []KV{}
+		k, v = cursor.Last()
+
+		for k != nil && v != nil {
+			kvs = append(kvs, KV{string(k), string(v)})
+			k, v = cursor.Prev()
+		}
+		assert.Equal(t, reverseKVs(testKeyValues), kvs)
+
+		// Random access
+		perm := []int{3, 0, 2, 1}
+		for _, i := range perm {
+			k, v := cursor.Seek([]byte(testKeyValues[i].key))
+			assert.Equal(t, []byte(testKeyValues[i].key), k)
+			assert.Equal(t, []byte(testKeyValues[i].val), v)
+		}
+
+		// Seek to nonexisting key.
+		k, v = cursor.Seek(nil)
+		assert.Nil(t, k)
+		assert.Nil(t, v)
+
+		k, v = cursor.Seek([]byte("x"))
+		assert.Nil(t, k)
+		assert.Nil(t, v)
+
+		return nil
+	})
+
+	assert.NoError(t, err)
+}
+
+func TestReadWriteCursor(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	testKeyValues := []KV{
+		{"b", "1"},
+		{"c", "2"},
+		{"da", "3"},
+		{"e", "4"},
+	}
+
+	count := len(testKeyValues)
+
+	// Pre-store the first half of the interval.
+	assert.NoError(t, db.Update(func(tx walletdb.ReadWriteTx) error {
+		b, err := tx.CreateTopLevelBucket([]byte("apple"))
+		assert.NoError(t, err)
+		assert.NotNil(t, b)
+
+		for i := 0; i < count/2; i++ {
+			err = b.Put(
+				[]byte(testKeyValues[i].key),
+				[]byte(testKeyValues[i].val),
+			)
+			assert.NoError(t, err)
+		}
+		return nil
+	}))
+
+	err = db.Update(func(tx walletdb.ReadWriteTx) error {
+		b := tx.ReadWriteBucket([]byte("apple"))
+		assert.NotNil(t, b)
+
+		// Store the second half of the interval.
+		for i := count / 2; i < count; i++ {
+			err = b.Put(
+				[]byte(testKeyValues[i].key),
+				[]byte(testKeyValues[i].val),
+			)
+			assert.NoError(t, err)
+		}
+
+		cursor := b.ReadWriteCursor()
+
+		// First on valid interval.
+		fk, fv := cursor.First()
+		assert.Equal(t, []byte("b"), fk)
+		assert.Equal(t, []byte("1"), fv)
+
+		// Prev(First()) = nil
+		k, v := cursor.Prev()
+		assert.Nil(t, k)
+		assert.Nil(t, v)
+
+		// Last on valid interval.
+		lk, lv := cursor.Last()
+		assert.Equal(t, []byte("e"), lk)
+		assert.Equal(t, []byte("4"), lv)
+
+		// Next(Last()) = nil
+		k, v = cursor.Next()
+		assert.Nil(t, k)
+		assert.Nil(t, v)
+
+		// Delete first item, then add an item before the
+		// deleted one. Check that First/Next will "jump"
+		// over the deleted item and return the new first.
+		_, _ = cursor.First()
+		assert.NoError(t, cursor.Delete())
+		assert.NoError(t, b.Put([]byte("a"), []byte("0")))
+		fk, fv = cursor.First()
+
+		assert.Equal(t, []byte("a"), fk)
+		assert.Equal(t, []byte("0"), fv)
+
+		k, v = cursor.Next()
+		assert.Equal(t, []byte("c"), k)
+		assert.Equal(t, []byte("2"), v)
+
+		// Similarly test that a new end is returned if
+		// the old end is deleted first.
+		_, _ = cursor.Last()
+		assert.NoError(t, cursor.Delete())
+		assert.NoError(t, b.Put([]byte("f"), []byte("5")))
+
+		lk, lv = cursor.Last()
+		assert.Equal(t, []byte("f"), lk)
+		assert.Equal(t, []byte("5"), lv)
+
+		k, v = cursor.Prev()
+		assert.Equal(t, []byte("da"), k)
+		assert.Equal(t, []byte("3"), v)
+
+		// Overwrite k/v in the middle of the interval.
+		assert.NoError(t, b.Put([]byte("c"), []byte("3")))
+		k, v = cursor.Prev()
+		assert.Equal(t, []byte("c"), k)
+		assert.Equal(t, []byte("3"), v)
+
+		// Insert new key/values.
+		assert.NoError(t, b.Put([]byte("cx"), []byte("x")))
+		assert.NoError(t, b.Put([]byte("cy"), []byte("y")))
+
+		k, v = cursor.Next()
+		assert.Equal(t, []byte("cx"), k)
+		assert.Equal(t, []byte("x"), v)
+
+		k, v = cursor.Next()
+		assert.Equal(t, []byte("cy"), k)
+		assert.Equal(t, []byte("y"), v)
+
+		expected := []KV{
+			{"a", "0"},
+			{"c", "3"},
+			{"cx", "x"},
+			{"cy", "y"},
+			{"da", "3"},
+			{"f", "5"},
+		}
+
+		// Iterate from the front.
+		var kvs []KV
+		k, v = cursor.First()
+
+		for k != nil && v != nil {
+			kvs = append(kvs, KV{string(k), string(v)})
+			k, v = cursor.Next()
+		}
+		assert.Equal(t, expected, kvs)
+
+		// Iterate from the back.
+		kvs = []KV{}
+		k, v = cursor.Last()
+
+		for k != nil && v != nil {
+			kvs = append(kvs, KV{string(k), string(v)})
+			k, v = cursor.Prev()
+		}
+		assert.Equal(t, reverseKVs(expected), kvs)
+
+		return nil
+	})
+
+	assert.NoError(t, err)
+
+	expected := map[string]string{
+		bkey("apple"):       bval("apple"),
+		vkey("a", "apple"):  "0",
+		vkey("c", "apple"):  "3",
+		vkey("cx", "apple"): "x",
+		vkey("cy", "apple"): "y",
+		vkey("da", "apple"): "3",
+		vkey("f", "apple"):  "5",
+	}
+	assert.Equal(t, expected, f.Dump())
+}

channeldb/kvdb/etcd/readwrite_tx.go

@@ -0,0 +1,152 @@
+// +build kvdb_etcd
+
+package etcd
+
+import (
+	"github.com/btcsuite/btcwallet/walletdb"
+)
+
+// readWriteTx holds a reference to the STM transaction.
+type readWriteTx struct {
+	// stm is the reference to the parent STM.
+	stm STM
+
+	// rootBucketID holds the sha256 hash of the root bucket id, which is used
+	// for key space spearation.
+	rootBucketID [bucketIDLength]byte
+
+	// active is true if the transaction hasn't been committed yet.
+	active bool
+
+	// dirty is true if we intent to update a value in this transaction.
+	dirty bool
+
+	// lset holds key/value set that we want to lock on. If upon commit the
+	// transaction is dirty and the lset is not empty, we'll bump the mod
+	// version of these key/values.
+	lset map[string]string
+}
+
+// newReadWriteTx creates an rw transaction with the passed STM.
+func newReadWriteTx(stm STM, prefix string) *readWriteTx {
+	return &readWriteTx{
+		stm:          stm,
+		active:       true,
+		rootBucketID: makeBucketID([]byte(prefix)),
+		lset:         make(map[string]string),
+	}
+}
+
+// rooBucket is a helper function to return the always present
+// pseudo root bucket.
+func rootBucket(tx *readWriteTx) *readWriteBucket {
+	return newReadWriteBucket(tx, tx.rootBucketID[:], tx.rootBucketID[:])
+}
+
+// lock adds a key value to the lock set.
+func (tx *readWriteTx) lock(key, val string) {
+	tx.stm.Lock(key)
+	if !tx.dirty {
+		tx.lset[key] = val
+	} else {
+		// Bump the mod version of the key,
+		// leaving the value intact.
+		tx.stm.Put(key, val)
+	}
+}
+
+// put updates the passed key/value.
+func (tx *readWriteTx) put(key, val string) {
+	tx.stm.Put(key, val)
+	tx.setDirty()
+}
+
+// del marks the passed key deleted.
+func (tx *readWriteTx) del(key string) {
+	tx.stm.Del(key)
+	tx.setDirty()
+}
+
+// setDirty marks the transaction dirty and bumps
+// mod version for the existing lock set if it is
+// not empty.
+func (tx *readWriteTx) setDirty() {
+	// Bump the lock set.
+	if !tx.dirty && len(tx.lset) > 0 {
+		for key, val := range tx.lset {
+			// Bump the mod version of the key,
+			// leaving the value intact.
+			tx.stm.Put(key, val)
+		}
+
+		// Clear the lock set.
+		tx.lset = make(map[string]string)
+	}
+
+	// Set dirty.
+	tx.dirty = true
+}
+
+// ReadBucket opens the root bucket for read only access.  If the bucket
+// described by the key does not exist, nil is returned.
+func (tx *readWriteTx) ReadBucket(key []byte) walletdb.ReadBucket {
+	return rootBucket(tx).NestedReadWriteBucket(key)
+}
+
+// Rollback closes the transaction, discarding changes (if any) if the
+// database was modified by a write transaction.
+func (tx *readWriteTx) Rollback() error {
+	// If the transaction has been closed roolback will fail.
+	if !tx.active {
+		return walletdb.ErrTxClosed
+	}
+
+	// Rollback the STM and set the tx to inactive.
+	tx.stm.Rollback()
+	tx.active = false
+
+	return nil
+}
+
+// ReadWriteBucket opens the root bucket for read/write access.  If the
+// bucket described by the key does not exist, nil is returned.
+func (tx *readWriteTx) ReadWriteBucket(key []byte) walletdb.ReadWriteBucket {
+	return rootBucket(tx).NestedReadWriteBucket(key)
+}
+
+// CreateTopLevelBucket creates the top level bucket for a key if it
+// does not exist.  The newly-created bucket it returned.
+func (tx *readWriteTx) CreateTopLevelBucket(key []byte) (walletdb.ReadWriteBucket, error) {
+	return rootBucket(tx).CreateBucketIfNotExists(key)
+}
+
+// DeleteTopLevelBucket deletes the top level bucket for a key.  This
+// errors if the bucket can not be found or the key keys a single value
+// instead of a bucket.
+func (tx *readWriteTx) DeleteTopLevelBucket(key []byte) error {
+	return rootBucket(tx).DeleteNestedBucket(key)
+}
+
+// Commit commits the transaction if not already committed. Will return
+// error if the underlying STM fails.
+func (tx *readWriteTx) Commit() error {
+	// Commit will fail if the transaction is already committed.
+	if !tx.active {
+		return walletdb.ErrTxClosed
+	}
+
+	// Try committing the transaction.
+	if err := tx.stm.Commit(); err != nil {
+		return err
+	}
+
+	// Mark the transaction as not active after commit.
+	tx.active = false
+
+	return nil
+}
+
+// OnCommit sets the commit callback (overriding if already set).
+func (tx *readWriteTx) OnCommit(cb func()) {
+	tx.stm.OnCommit(cb)
+}

channeldb/kvdb/etcd/readwrite_tx_test.go

@@ -0,0 +1,156 @@
+// +build kvdb_etcd
+
+package etcd
+
+import (
+	"testing"
+
+	"github.com/btcsuite/btcwallet/walletdb"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTxManualCommit(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	tx, err := db.BeginReadWriteTx()
+	assert.NoError(t, err)
+	assert.NotNil(t, tx)
+
+	committed := false
+
+	tx.OnCommit(func() {
+		committed = true
+	})
+
+	apple, err := tx.CreateTopLevelBucket([]byte("apple"))
+	assert.NoError(t, err)
+	assert.NotNil(t, apple)
+	assert.NoError(t, apple.Put([]byte("testKey"), []byte("testVal")))
+
+	banana, err := tx.CreateTopLevelBucket([]byte("banana"))
+	assert.NoError(t, err)
+	assert.NotNil(t, banana)
+	assert.NoError(t, banana.Put([]byte("testKey"), []byte("testVal")))
+	assert.NoError(t, tx.DeleteTopLevelBucket([]byte("banana")))
+
+	assert.NoError(t, tx.Commit())
+	assert.True(t, committed)
+
+	expected := map[string]string{
+		bkey("apple"):            bval("apple"),
+		vkey("testKey", "apple"): "testVal",
+	}
+	assert.Equal(t, expected, f.Dump())
+}
+
+func TestTxRollback(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	tx, err := db.BeginReadWriteTx()
+	assert.Nil(t, err)
+	assert.NotNil(t, tx)
+
+	apple, err := tx.CreateTopLevelBucket([]byte("apple"))
+	assert.Nil(t, err)
+	assert.NotNil(t, apple)
+
+	assert.NoError(t, apple.Put([]byte("testKey"), []byte("testVal")))
+
+	assert.NoError(t, tx.Rollback())
+	assert.Error(t, walletdb.ErrTxClosed, tx.Commit())
+	assert.Equal(t, map[string]string{}, f.Dump())
+}
+
+func TestChangeDuringManualTx(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	tx, err := db.BeginReadWriteTx()
+	assert.Nil(t, err)
+	assert.NotNil(t, tx)
+
+	apple, err := tx.CreateTopLevelBucket([]byte("apple"))
+	assert.Nil(t, err)
+	assert.NotNil(t, apple)
+
+	assert.NoError(t, apple.Put([]byte("testKey"), []byte("testVal")))
+
+	// Try overwriting the bucket key.
+	f.Put(bkey("apple"), "banana")
+
+	// TODO: translate error
+	assert.NotNil(t, tx.Commit())
+	assert.Equal(t, map[string]string{
+		bkey("apple"): "banana",
+	}, f.Dump())
+}
+
+func TestChangeDuringUpdate(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	count := 0
+
+	err = db.Update(func(tx walletdb.ReadWriteTx) error {
+		apple, err := tx.CreateTopLevelBucket([]byte("apple"))
+		assert.NoError(t, err)
+		assert.NotNil(t, apple)
+
+		assert.NoError(t, apple.Put([]byte("key"), []byte("value")))
+
+		if count == 0 {
+			f.Put(vkey("key", "apple"), "new_value")
+			f.Put(vkey("key2", "apple"), "value2")
+		}
+
+		cursor := apple.ReadCursor()
+		k, v := cursor.First()
+		assert.Equal(t, []byte("key"), k)
+		assert.Equal(t, []byte("value"), v)
+		assert.Equal(t, v, apple.Get([]byte("key")))
+
+		k, v = cursor.Next()
+		if count == 0 {
+			assert.Nil(t, k)
+			assert.Nil(t, v)
+		} else {
+			assert.Equal(t, []byte("key2"), k)
+			assert.Equal(t, []byte("value2"), v)
+		}
+
+		count++
+		return nil
+	})
+
+	assert.Nil(t, err)
+	assert.Equal(t, count, 2)
+
+	expected := map[string]string{
+		bkey("apple"):         bval("apple"),
+		vkey("key", "apple"):  "value",
+		vkey("key2", "apple"): "value2",
+	}
+	assert.Equal(t, expected, f.Dump())
+}

channeldb/kvdb/etcd/stm.go

@@ -0,0 +1,802 @@
+// +build kvdb_etcd
+
+package etcd
+
+import (
+	"context"
+	"fmt"
+	"math"
+	"strings"
+
+	v3 "github.com/coreos/etcd/clientv3"
+)
+
+type CommitStats struct {
+	Rset    int
+	Wset    int
+	Retries int
+}
+
+// KV stores a key/value pair.
+type KV struct {
+	key string
+	val string
+}
+
+// STM is an interface for software transactional memory.
+// All calls that return error will do so only if STM is manually handled and
+// abort the apply closure otherwise. In both case the returned error is a
+// DatabaseError.
+type STM interface {
+	// Get returns the value for a key and inserts the key in the txn's read
+	// set. Returns nil if there's no matching key, or the key is empty.
+	Get(key string) ([]byte, error)
+
+	// Lock adds a key to the lock set. If the lock set is not empty, we'll
+	// only check for conflicts in the lock set and the write set, instead
+	// of all read keys plus the write set.
+	Lock(key string)
+
+	// Put adds a value for a key to the txn's write set.
+	Put(key, val string)
+
+	// Del adds a delete operation for the key to the txn's write set.
+	Del(key string)
+
+	// First returns the first k/v that begins with prefix or nil if there's
+	// no such k/v pair. If the key is found it is inserted to the txn's
+	// read set. Returns nil if there's no match.
+	First(prefix string) (*KV, error)
+
+	// Last returns the last k/v that begins with prefix or nil if there's
+	// no such k/v pair. If the key is found it is inserted to the txn's
+	// read set. Returns nil if there's no match.
+	Last(prefix string) (*KV, error)
+
+	// Prev returns the previous k/v before key that begins with prefix or
+	// nil if there's no such k/v. If the key is found it is inserted to the
+	// read set. Returns nil if there's no match.
+	Prev(prefix, key string) (*KV, error)
+
+	// Next returns the next k/v after key that begins with prefix or nil
+	// if there's no such k/v. If the key is found it is inserted to the
+	// txn's read set. Returns nil if there's no match.
+	Next(prefix, key string) (*KV, error)
+
+	// Seek will return k/v at key beginning with prefix. If the key doesn't
+	// exists Seek will return the next k/v after key beginning with prefix.
+	// If a matching k/v is found it is inserted to the txn's read set. Returns
+	// nil if there's no match.
+	Seek(prefix, key string) (*KV, error)
+
+	// OnCommit calls the passed callback func upon commit.
+	OnCommit(func())
+
+	// Commit attempts to apply the txn's changes to the server.
+	// Commit may return CommitError if transaction is outdated and needs retry.
+	Commit() error
+
+	// Rollback emties the read and write sets such that a subsequent commit
+	// won't alter the database.
+	Rollback()
+}
+
+// CommitError is used to check if there was an error
+// due to stale data in the transaction.
+type CommitError struct{}
+
+// Error returns a static string for CommitError for
+// debugging/logging purposes.
+func (e CommitError) Error() string {
+	return "commit failed"
+}
+
+// DatabaseError is used to wrap errors that are not
+// related to stale data in the transaction.
+type DatabaseError struct {
+	msg string
+	err error
+}
+
+// Unwrap returns the wrapped error in a DatabaseError.
+func (e *DatabaseError) Unwrap() error {
+	return e.err
+}
+
+// Error simply converts DatabaseError to a string that
+// includes both the message and the wrapped error.
+func (e DatabaseError) Error() string {
+	return fmt.Sprintf("etcd error: %v - %v", e.msg, e.err)
+}
+
+// stmGet is the result of a read operation,
+// a value and the mod revision of the key/value.
+type stmGet struct {
+	val string
+	rev int64
+}
+
+// readSet stores all reads done in an STM.
+type readSet map[string]stmGet
+
+// stmPut stores a value and an operation (put/delete).
+type stmPut struct {
+	val string
+	op  v3.Op
+}
+
+// writeSet stroes all writes done in an STM.
+type writeSet map[string]stmPut
+
+// stm implements repeatable-read software transactional memory
+// over etcd.
+type stm struct {
+	// client is an etcd client handling all RPC communications
+	// to the etcd instance/cluster.
+	client *v3.Client
+
+	// manual is set to true for manual transactions which don't
+	// execute in the STM run loop.
+	manual bool
+
+	// options stores optional settings passed by the user.
+	options *STMOptions
+
+	// prefetch hold prefetched key values and revisions.
+	prefetch readSet
+
+	// rset holds read key values and revisions.
+	rset readSet
+
+	// wset holds overwritten keys and their values.
+	wset writeSet
+
+	// lset holds keys we intent to lock on.
+	lset map[string]interface{}
+
+	// getOpts are the opts used for gets.
+	getOpts []v3.OpOption
+
+	// revision stores the snapshot revision after first read.
+	revision int64
+
+	// onCommit gets called upon commit.
+	onCommit func()
+}
+
+// STMOptions can be used to pass optional settings
+// when an STM is created.
+type STMOptions struct {
+	// ctx holds an externally provided abort context.
+	ctx                 context.Context
+	commitStatsCallback func(bool, CommitStats)
+}
+
+// STMOptionFunc is a function that updates the passed STMOptions.
+type STMOptionFunc func(*STMOptions)
+
+// WithAbortContext specifies the context for permanently
+// aborting the transaction.
+func WithAbortContext(ctx context.Context) STMOptionFunc {
+	return func(so *STMOptions) {
+		so.ctx = ctx
+	}
+}
+
+func WithCommitStatsCallback(cb func(bool, CommitStats)) STMOptionFunc {
+	return func(so *STMOptions) {
+		so.commitStatsCallback = cb
+	}
+}
+
+// RunSTM runs the apply function by creating an STM using serializable snapshot
+// isolation, passing it to the apply and handling commit errors and retries.
+func RunSTM(cli *v3.Client, apply func(STM) error, so ...STMOptionFunc) error {
+	return runSTM(makeSTM(cli, false, so...), apply)
+}
+
+// NewSTM creates a new STM instance, using serializable snapshot isolation.
+func NewSTM(cli *v3.Client, so ...STMOptionFunc) STM {
+	return makeSTM(cli, true, so...)
+}
+
+// makeSTM is the actual constructor of the stm. It first apply all passed
+// options then creates the stm object and resets it before returning.
+func makeSTM(cli *v3.Client, manual bool, so ...STMOptionFunc) *stm {
+	opts := &STMOptions{
+		ctx: cli.Ctx(),
+	}
+
+	// Apply all functional options.
+	for _, fo := range so {
+		fo(opts)
+	}
+
+	s := &stm{
+		client:   cli,
+		manual:   manual,
+		options:  opts,
+		prefetch: make(map[string]stmGet),
+	}
+
+	// Reset read and write set.
+	s.Rollback()
+
+	return s
+}
+
+// runSTM implements the run loop of the STM, running the apply func, catching
+// errors and handling commit. The loop will quit on every error except
+// CommitError which is used to indicate a necessary retry.
+func runSTM(s *stm, apply func(STM) error) error {
+	out := make(chan error, 1)
+
+	go func() {
+		var (
+			retries int
+			stats   CommitStats
+		)
+
+		defer func() {
+			// Recover DatabaseError panics so
+			// we can return them.
+			if r := recover(); r != nil {
+				e, ok := r.(DatabaseError)
+				if !ok {
+					// Unknown panic.
+					panic(r)
+				}
+
+				// Return the error.
+				out <- e.Unwrap()
+			}
+		}()
+
+		var err error
+
+		// In a loop try to apply and commit and roll back
+		// if the database has changed (CommitError).
+		for {
+			// Abort STM if there was an application error.
+			if err = apply(s); err != nil {
+				break
+			}
+
+			stats, err = s.commit()
+
+			// Re-apply only upon commit error
+			// (meaning the database was changed).
+			if _, ok := err.(CommitError); !ok {
+				// Anything that's not a CommitError
+				// aborts the STM run loop.
+				break
+			}
+
+			// Rollback before trying to re-apply.
+			s.Rollback()
+			retries++
+		}
+
+		if s.options.commitStatsCallback != nil {
+			stats.Retries = retries
+			s.options.commitStatsCallback(err == nil, stats)
+		}
+
+		// Return the error to the caller.
+		out <- err
+	}()
+
+	return <-out
+}
+
+// add inserts a txn response to the read set. This is useful when the txn
+// fails due to conflict where the txn response can be used to prefetch
+// key/values.
+func (rs readSet) add(txnResp *v3.TxnResponse) {
+	for _, resp := range txnResp.Responses {
+		getResp := (*v3.GetResponse)(resp.GetResponseRange())
+		for _, kv := range getResp.Kvs {
+			rs[string(kv.Key)] = stmGet{
+				val: string(kv.Value),
+				rev: kv.ModRevision,
+			}
+		}
+	}
+}
+
+// gets is a helper to create an op slice for transaction
+// construction.
+func (rs readSet) gets() []v3.Op {
+	ops := make([]v3.Op, 0, len(rs))
+
+	for k := range rs {
+		ops = append(ops, v3.OpGet(k))
+	}
+
+	return ops
+}
+
+// cmps returns a cmp list testing values in read set didn't change.
+func (rs readSet) cmps(lset map[string]interface{}) []v3.Cmp {
+	if len(lset) > 0 {
+		cmps := make([]v3.Cmp, 0, len(lset))
+		for key, _ := range lset {
+			if getValue, ok := rs[key]; ok {
+				cmps = append(
+					cmps,
+					v3.Compare(v3.ModRevision(key), "=", getValue.rev),
+				)
+			}
+		}
+		return cmps
+	}
+
+	cmps := make([]v3.Cmp, 0, len(rs))
+	for key, getValue := range rs {
+		cmps = append(cmps, v3.Compare(v3.ModRevision(key), "=", getValue.rev))
+	}
+
+	return cmps
+}
+
+// cmps returns a cmp list testing no writes have happened past rev.
+func (ws writeSet) cmps(rev int64) []v3.Cmp {
+	cmps := make([]v3.Cmp, 0, len(ws))
+	for key := range ws {
+		cmps = append(cmps, v3.Compare(v3.ModRevision(key), "<", rev))
+	}
+
+	return cmps
+}
+
+// puts is the list of ops for all pending writes.
+func (ws writeSet) puts() []v3.Op {
+	puts := make([]v3.Op, 0, len(ws))
+	for _, v := range ws {
+		puts = append(puts, v.op)
+	}
+
+	return puts
+}
+
+// fetch is a helper to fetch key/value given options. If a value is returned
+// then fetch will try to fix the STM's snapshot revision (if not already set).
+// We'll also cache the returned key/value in the read set.
+func (s *stm) fetch(key string, opts ...v3.OpOption) ([]KV, error) {
+	resp, err := s.client.Get(
+		s.options.ctx, key, append(opts, s.getOpts...)...,
+	)
+	if err != nil {
+		dbErr := DatabaseError{
+			msg: "stm.fetch() failed",
+			err: err,
+		}
+
+		// Do not panic when executing a manual transaction.
+		if s.manual {
+			return nil, dbErr
+		}
+
+		// Panic when executing inside the STM runloop.
+		panic(dbErr)
+	}
+
+	// Set revison and serializable options upon first fetch
+	// for any subsequent fetches.
+	if s.getOpts == nil {
+		s.revision = resp.Header.Revision
+		s.getOpts = []v3.OpOption{
+			v3.WithRev(s.revision),
+			v3.WithSerializable(),
+		}
+	}
+
+	var result []KV
+
+	// Fill the read set with key/values returned.
+	for _, kv := range resp.Kvs {
+		// Remove from prefetch.
+		key := string(kv.Key)
+		val := string(kv.Value)
+
+		delete(s.prefetch, key)
+
+		// Add to read set.
+		s.rset[key] = stmGet{
+			val: val,
+			rev: kv.ModRevision,
+		}
+
+		result = append(result, KV{key, val})
+	}
+
+	return result, nil
+}
+
+// Get returns the value for key. If there's no such
+// key/value in the database or the passed key is empty
+// Get will return nil.
+func (s *stm) Get(key string) ([]byte, error) {
+	if key == "" {
+		return nil, nil
+	}
+
+	// Return freshly written value if present.
+	if put, ok := s.wset[key]; ok {
+		if put.op.IsDelete() {
+			return nil, nil
+		}
+
+		return []byte(put.val), nil
+	}
+
+	// Populate read set if key is present in
+	// the prefetch set.
+	if getValue, ok := s.prefetch[key]; ok {
+		delete(s.prefetch, key)
+		s.rset[key] = getValue
+	}
+
+	// Return value if alread in read set.
+	if getVal, ok := s.rset[key]; ok {
+		return []byte(getVal.val), nil
+	}
+
+	// Fetch and return value.
+	kvs, err := s.fetch(key)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(kvs) > 0 {
+		return []byte(kvs[0].val), nil
+	}
+
+	// Return empty result if key not in DB.
+	return nil, nil
+}
+
+// Lock adds a key to the lock set. If the lock set is
+// not empty, we'll only check conflicts for the keys
+// in the lock set.
+func (s *stm) Lock(key string) {
+	s.lset[key] = nil
+}
+
+// First returns the first key/value matching prefix. If there's no key starting
+// with prefix, Last will return nil.
+func (s *stm) First(prefix string) (*KV, error) {
+	return s.next(prefix, prefix, true)
+}
+
+// Last returns the last key/value with prefix. If there's no key starting with
+// prefix, Last will return nil.
+func (s *stm) Last(prefix string) (*KV, error) {
+	// As we don't know the full range, fetch the last
+	// key/value with this prefix first.
+	resp, err := s.fetch(prefix, v3.WithLastKey()...)
+	if err != nil {
+		return nil, err
+	}
+
+	var (
+		kv    KV
+		found bool
+	)
+
+	if len(resp) > 0 {
+		kv = resp[0]
+		found = true
+	}
+
+	// Now make sure there's nothing in the write set
+	// that is a better match, meaning it has the same
+	// prefix but is greater or equal than the current
+	// best candidate. Note that this is not efficient
+	// when the write set is large!
+	for k, put := range s.wset {
+		if put.op.IsDelete() {
+			continue
+		}
+
+		if strings.HasPrefix(k, prefix) && k >= kv.key {
+			kv.key = k
+			kv.val = put.val
+			found = true
+		}
+	}
+
+	if found {
+		return &kv, nil
+	}
+
+	return nil, nil
+}
+
+// Prev returns the prior key/value before key (with prefix). If there's no such
+// key Next will return nil.
+func (s *stm) Prev(prefix, startKey string) (*KV, error) {
+	var result KV
+
+	fetchKey := startKey
+	matchFound := false
+
+	for {
+		// Ask etcd to retrieve one key that is a
+		// match in descending order from the passed key.
+		opts := []v3.OpOption{
+			v3.WithRange(fetchKey),
+			v3.WithSort(v3.SortByKey, v3.SortDescend),
+			v3.WithLimit(1),
+		}
+
+		kvs, err := s.fetch(prefix, opts...)
+		if err != nil {
+			return nil, err
+		}
+
+		if len(kvs) == 0 {
+			break
+		}
+
+		kv := &kvs[0]
+
+		// WithRange and WithPrefix can't be used
+		// together, so check prefix here. If the
+		// returned key no longer has the prefix,
+		// then break out.
+		if !strings.HasPrefix(kv.key, prefix) {
+			break
+		}
+
+		// Fetch the prior key if this is deleted.
+		if put, ok := s.wset[kv.key]; ok && put.op.IsDelete() {
+			fetchKey = kv.key
+			continue
+		}
+
+		result = *kv
+		matchFound = true
+
+		break
+	}
+
+	// Closre holding all checks to find a possibly
+	// better match.
+	matches := func(key string) bool {
+		if !strings.HasPrefix(key, prefix) {
+			return false
+		}
+
+		if !matchFound {
+			return key < startKey
+		}
+
+		// matchFound == true
+		return result.key <= key && key < startKey
+	}
+
+	// Now go trough the write set and check
+	// if there's an even better match.
+	for k, put := range s.wset {
+		if !put.op.IsDelete() && matches(k) {
+			result.key = k
+			result.val = put.val
+			matchFound = true
+		}
+	}
+
+	if !matchFound {
+		return nil, nil
+	}
+
+	return &result, nil
+}
+
+// Next returns the next key/value after key (with prefix). If there's no such
+// key Next will return nil.
+func (s *stm) Next(prefix string, key string) (*KV, error) {
+	return s.next(prefix, key, false)
+}
+
+// Seek "seeks" to the key (with prefix). If the key doesn't exists it'll get
+// the next key with the same prefix. If no key fills this criteria, Seek will
+// return nil.
+func (s *stm) Seek(prefix, key string) (*KV, error) {
+	return s.next(prefix, key, true)
+}
+
+// next will try to retrieve the next match that has prefix and starts with the
+// passed startKey. If includeStartKey is set to true, it'll return the value
+// of startKey (essentially implementing seek).
+func (s *stm) next(prefix, startKey string, includeStartKey bool) (*KV, error) {
+	var result KV
+
+	fetchKey := startKey
+	firstFetch := true
+	matchFound := false
+
+	for {
+		// Ask etcd to retrieve one key that is a
+		// match in ascending order from the passed key.
+		opts := []v3.OpOption{
+			v3.WithFromKey(),
+			v3.WithSort(v3.SortByKey, v3.SortAscend),
+			v3.WithLimit(1),
+		}
+
+		// By default we include the start key too
+		// if it is a full match.
+		if includeStartKey && firstFetch {
+			firstFetch = false
+		} else {
+			// If we'd like to retrieve the first key
+			// after the start key.
+			fetchKey += "\x00"
+		}
+
+		kvs, err := s.fetch(fetchKey, opts...)
+		if err != nil {
+			return nil, err
+		}
+
+		if len(kvs) == 0 {
+			break
+		}
+
+		kv := &kvs[0]
+		// WithRange and WithPrefix can't be used
+		// together, so check prefix here. If the
+		// returned key no longer has the prefix,
+		// then break the fetch loop.
+		if !strings.HasPrefix(kv.key, prefix) {
+			break
+		}
+
+		// Move on to fetch starting with the next
+		// key if this one is marked deleted.
+		if put, ok := s.wset[kv.key]; ok && put.op.IsDelete() {
+			fetchKey = kv.key
+			continue
+		}
+
+		result = *kv
+		matchFound = true
+
+		break
+	}
+
+	// Closure holding all checks to find a possibly
+	// better match.
+	matches := func(k string) bool {
+		if !strings.HasPrefix(k, prefix) {
+			return false
+		}
+
+		if includeStartKey && !matchFound {
+			return startKey <= k
+		}
+
+		if !includeStartKey && !matchFound {
+			return startKey < k
+		}
+
+		if includeStartKey && matchFound {
+			return startKey <= k && k <= result.key
+		}
+
+		// !includeStartKey && matchFound.
+		return startKey < k && k <= result.key
+	}
+
+	// Now go trough the write set and check
+	// if there's an even better match.
+	for k, put := range s.wset {
+		if !put.op.IsDelete() && matches(k) {
+			result.key = k
+			result.val = put.val
+			matchFound = true
+		}
+	}
+
+	if !matchFound {
+		return nil, nil
+	}
+
+	return &result, nil
+}
+
+// Put sets the value of the passed key. The actual put will happen upon commit.
+func (s *stm) Put(key, val string) {
+	s.wset[key] = stmPut{
+		val: val,
+		op:  v3.OpPut(key, val),
+	}
+}
+
+// Del marks a key as deleted. The actual delete will happen upon commit.
+func (s *stm) Del(key string) {
+	s.wset[key] = stmPut{
+		val: "",
+		op:  v3.OpDelete(key),
+	}
+}
+
+// OnCommit sets the callback that is called upon committing the STM
+// transaction.
+func (s *stm) OnCommit(cb func()) {
+	s.onCommit = cb
+}
+
+// commit builds the final transaction and tries to execute it. If commit fails
+// because the keys have changed return a CommitError, otherwise return a
+// DatabaseError.
+func (s *stm) commit() (CommitStats, error) {
+	rset := s.rset.cmps(s.lset)
+	wset := s.wset.cmps(s.revision + 1)
+
+	stats := CommitStats{
+		Rset: len(rset),
+		Wset: len(wset),
+	}
+
+	// Create the compare set.
+	cmps := append(rset, wset...)
+	// Create a transaction with the optional abort context.
+	txn := s.client.Txn(s.options.ctx)
+
+	// If the compare set holds, try executing the puts.
+	txn = txn.If(cmps...)
+	txn = txn.Then(s.wset.puts()...)
+
+	// Prefetch keys in case of conflict to save
+	// a round trip to etcd.
+	txn = txn.Else(s.rset.gets()...)
+
+	txnresp, err := txn.Commit()
+	if err != nil {
+		return stats, DatabaseError{
+			msg: "stm.Commit() failed",
+			err: err,
+		}
+	}
+
+	// Call the commit callback if the transaction
+	// was successful.
+	if txnresp.Succeeded {
+		if s.onCommit != nil {
+			s.onCommit()
+		}
+
+		return stats, nil
+	}
+
+	// Load prefetch before if commit failed.
+	s.rset.add(txnresp)
+	s.prefetch = s.rset
+
+	// Return CommitError indicating that the transaction
+	// can be retried.
+	return stats, CommitError{}
+}
+
+// Commit simply calls commit and the commit stats callback if set.
+func (s *stm) Commit() error {
+	stats, err := s.commit()
+
+	if s.options.commitStatsCallback != nil {
+		s.options.commitStatsCallback(err == nil, stats)
+	}
+
+	return err
+}
+
+// Rollback resets the STM. This is useful for uncommitted transaction rollback
+// and also used in the STM main loop to reset state if commit fails.
+func (s *stm) Rollback() {
+	s.rset = make(map[string]stmGet)
+	s.wset = make(map[string]stmPut)
+	s.lset = make(map[string]interface{})
+	s.getOpts = nil
+	s.revision = math.MaxInt64 - 1
+}

channeldb/kvdb/etcd/stm_test.go

@@ -0,0 +1,344 @@
+// +build kvdb_etcd
+
+package etcd
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func reverseKVs(a []KV) []KV {
+	for i, j := 0, len(a)-1; i < j; i, j = i+1, j-1 {
+		a[i], a[j] = a[j], a[i]
+	}
+
+	return a
+}
+
+func TestPutToEmpty(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	apply := func(stm STM) error {
+		stm.Put("123", "abc")
+		return nil
+	}
+
+	err = RunSTM(db.cli, apply)
+	assert.NoError(t, err)
+
+	assert.Equal(t, "abc", f.Get("123"))
+}
+
+func TestGetPutDel(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.cleanup()
+
+	testKeyValues := []KV{
+		{"a", "1"},
+		{"b", "2"},
+		{"c", "3"},
+		{"d", "4"},
+		{"e", "5"},
+	}
+
+	for _, kv := range testKeyValues {
+		f.Put(kv.key, kv.val)
+	}
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	apply := func(stm STM) error {
+		// Get some non existing keys.
+		v, err := stm.Get("")
+		assert.NoError(t, err)
+		assert.Nil(t, v)
+
+		v, err = stm.Get("x")
+		assert.NoError(t, err)
+		assert.Nil(t, v)
+
+		// Get all existing keys.
+		for _, kv := range testKeyValues {
+			v, err = stm.Get(kv.key)
+			assert.NoError(t, err)
+			assert.Equal(t, []byte(kv.val), v)
+		}
+
+		// Overwrite, then delete an existing key.
+		stm.Put("c", "6")
+
+		v, err = stm.Get("c")
+		assert.NoError(t, err)
+		assert.Equal(t, []byte("6"), v)
+
+		stm.Del("c")
+
+		v, err = stm.Get("c")
+		assert.NoError(t, err)
+		assert.Nil(t, v)
+
+		// Re-add the deleted key.
+		stm.Put("c", "7")
+
+		v, err = stm.Get("c")
+		assert.NoError(t, err)
+		assert.Equal(t, []byte("7"), v)
+
+		// Add a new key.
+		stm.Put("x", "x")
+
+		v, err = stm.Get("x")
+		assert.NoError(t, err)
+		assert.Equal(t, []byte("x"), v)
+
+		return nil
+	}
+
+	err = RunSTM(db.cli, apply)
+	assert.NoError(t, err)
+
+	assert.Equal(t, "1", f.Get("a"))
+	assert.Equal(t, "2", f.Get("b"))
+	assert.Equal(t, "7", f.Get("c"))
+	assert.Equal(t, "4", f.Get("d"))
+	assert.Equal(t, "5", f.Get("e"))
+	assert.Equal(t, "x", f.Get("x"))
+}
+
+func TestFirstLastNextPrev(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	testKeyValues := []KV{
+		{"kb", "1"},
+		{"kc", "2"},
+		{"kda", "3"},
+		{"ke", "4"},
+		{"w", "w"},
+	}
+	for _, kv := range testKeyValues {
+		f.Put(kv.key, kv.val)
+	}
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	apply := func(stm STM) error {
+		// First/Last on valid multi item interval.
+		kv, err := stm.First("k")
+		assert.NoError(t, err)
+		assert.Equal(t, &KV{"kb", "1"}, kv)
+
+		kv, err = stm.Last("k")
+		assert.NoError(t, err)
+		assert.Equal(t, &KV{"ke", "4"}, kv)
+
+		// First/Last on single item interval.
+		kv, err = stm.First("w")
+		assert.NoError(t, err)
+		assert.Equal(t, &KV{"w", "w"}, kv)
+
+		kv, err = stm.Last("w")
+		assert.NoError(t, err)
+		assert.Equal(t, &KV{"w", "w"}, kv)
+
+		// Next/Prev on start/end.
+		kv, err = stm.Next("k", "ke")
+		assert.NoError(t, err)
+		assert.Nil(t, kv)
+
+		kv, err = stm.Prev("k", "kb")
+		assert.NoError(t, err)
+		assert.Nil(t, kv)
+
+		// Next/Prev in the middle.
+		kv, err = stm.Next("k", "kc")
+		assert.NoError(t, err)
+		assert.Equal(t, &KV{"kda", "3"}, kv)
+
+		kv, err = stm.Prev("k", "ke")
+		assert.NoError(t, err)
+		assert.Equal(t, &KV{"kda", "3"}, kv)
+
+		// Delete first item, then add an item before the
+		// deleted one. Check that First/Next will "jump"
+		// over the deleted item and return the new first.
+		stm.Del("kb")
+		stm.Put("ka", "0")
+
+		kv, err = stm.First("k")
+		assert.NoError(t, err)
+		assert.Equal(t, &KV{"ka", "0"}, kv)
+
+		kv, err = stm.Prev("k", "kc")
+		assert.NoError(t, err)
+		assert.Equal(t, &KV{"ka", "0"}, kv)
+
+		// Similarly test that a new end is returned if
+		// the old end is deleted first.
+		stm.Del("ke")
+		stm.Put("kf", "5")
+
+		kv, err = stm.Last("k")
+		assert.NoError(t, err)
+		assert.Equal(t, &KV{"kf", "5"}, kv)
+
+		kv, err = stm.Next("k", "kda")
+		assert.NoError(t, err)
+		assert.Equal(t, &KV{"kf", "5"}, kv)
+
+		// Overwrite one in the middle.
+		stm.Put("kda", "6")
+
+		kv, err = stm.Next("k", "kc")
+		assert.NoError(t, err)
+		assert.Equal(t, &KV{"kda", "6"}, kv)
+
+		// Add three in the middle, then delete one.
+		stm.Put("kdb", "7")
+		stm.Put("kdc", "8")
+		stm.Put("kdd", "9")
+		stm.Del("kdc")
+
+		// Check that stepping from first to last returns
+		// the expected sequence.
+		var kvs []KV
+
+		curr, err := stm.First("k")
+		assert.NoError(t, err)
+
+		for curr != nil {
+			kvs = append(kvs, *curr)
+			curr, err = stm.Next("k", curr.key)
+			assert.NoError(t, err)
+		}
+
+		expected := []KV{
+			{"ka", "0"},
+			{"kc", "2"},
+			{"kda", "6"},
+			{"kdb", "7"},
+			{"kdd", "9"},
+			{"kf", "5"},
+		}
+		assert.Equal(t, expected, kvs)
+
+		// Similarly check that stepping from last to first
+		// returns the expected sequence.
+		kvs = []KV{}
+
+		curr, err = stm.Last("k")
+		assert.NoError(t, err)
+
+		for curr != nil {
+			kvs = append(kvs, *curr)
+			curr, err = stm.Prev("k", curr.key)
+			assert.NoError(t, err)
+		}
+
+		expected = reverseKVs(expected)
+		assert.Equal(t, expected, kvs)
+
+		return nil
+	}
+
+	err = RunSTM(db.cli, apply)
+	assert.NoError(t, err)
+
+	assert.Equal(t, "0", f.Get("ka"))
+	assert.Equal(t, "2", f.Get("kc"))
+	assert.Equal(t, "6", f.Get("kda"))
+	assert.Equal(t, "7", f.Get("kdb"))
+	assert.Equal(t, "9", f.Get("kdd"))
+	assert.Equal(t, "5", f.Get("kf"))
+	assert.Equal(t, "w", f.Get("w"))
+}
+
+func TestCommitError(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	// Preset DB state.
+	f.Put("123", "xyz")
+
+	// Count the number of applies.
+	cnt := 0
+
+	apply := func(stm STM) error {
+		// STM must have the key/value.
+		val, err := stm.Get("123")
+		assert.NoError(t, err)
+
+		if cnt == 0 {
+			assert.Equal(t, []byte("xyz"), val)
+
+			// Put a conflicting key/value during the first apply.
+			f.Put("123", "def")
+		}
+
+		// We'd expect to
+		stm.Put("123", "abc")
+
+		cnt++
+		return nil
+	}
+
+	err = RunSTM(db.cli, apply)
+	assert.NoError(t, err)
+	assert.Equal(t, 2, cnt)
+
+	assert.Equal(t, "abc", f.Get("123"))
+}
+
+func TestManualTxError(t *testing.T) {
+	t.Parallel()
+
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+
+	db, err := newEtcdBackend(f.BackendConfig())
+	assert.NoError(t, err)
+
+	// Preset DB state.
+	f.Put("123", "xyz")
+
+	stm := NewSTM(db.cli)
+
+	val, err := stm.Get("123")
+	assert.NoError(t, err)
+	assert.Equal(t, []byte("xyz"), val)
+
+	// Put a conflicting key/value.
+	f.Put("123", "def")
+
+	// Should still get the original version.
+	val, err = stm.Get("123")
+	assert.NoError(t, err)
+	assert.Equal(t, []byte("xyz"), val)
+
+	// Commit will fail with CommitError.
+	err = stm.Commit()
+	var e CommitError
+	assert.True(t, errors.As(err, &e))
+
+	// We expect that the transacton indeed did not commit.
+	assert.Equal(t, "def", f.Get("123"))
+}

channeldb/kvdb/etcd/walletdb_interface_test.go

@@ -0,0 +1,17 @@
+// +build kvdb_etcd
+
+package etcd
+
+import (
+	"testing"
+
+	"github.com/btcsuite/btcwallet/walletdb/walletdbtest"
+)
+
+// TestWalletDBInterface performs the WalletDB interface test suite for the
+// etcd database driver.
+func TestWalletDBInterface(t *testing.T) {
+	f := NewEtcdTestFixture(t)
+	defer f.Cleanup()
+	walletdbtest.TestInterface(t, dbType, f.BackendConfig())
+}

channeldb/kvdb/interface.go

@@ -11,13 +11,24 @@ import (
 // transaction is rolled back. If the rollback fails, the original error
 // returned by f is still returned. If the commit fails, the commit error is
 // returned.
-var Update = walletdb.Update
+func Update(db Backend, f func(tx RwTx) error) error {
+	if extendedDB, ok := db.(ExtendedBackend); ok {
+		return extendedDB.Update(f)
+	}
+	return walletdb.Update(db, f)
+}
 
 // View opens a database read transaction and executes the function f with the
 // transaction passed as a parameter. After f exits, the transaction is rolled
 // back. If f errors, its error is returned, not a rollback error (if any
 // occur).
-var View = walletdb.View
+func View(db Backend, f func(tx ReadTx) error) error {
+	if extendedDB, ok := db.(ExtendedBackend); ok {
+		return extendedDB.View(f)
+	}
+
+	return walletdb.View(db, f)
+}
 
 // Batch is identical to the Update call, but it attempts to combine several
 // individual Update transactions into a single write database transaction on
@@ -36,6 +47,29 @@ var Create = walletdb.Create
 // through read or read+write transactions.
 type Backend = walletdb.DB
 
+// ExtendedBackend is and interface that supports View and Update and also able
+// to collect database access patterns.
+type ExtendedBackend interface {
+	Backend
+
+	// PrintStats returns all collected stats pretty printed into a string.
+	PrintStats() string
+
+	// View opens a database read transaction and executes the function f with
+	// the transaction passed as a parameter. After f exits, the transaction is
+	// rolled back. If f errors, its error is returned, not a rollback error
+	// (if any occur).
+	View(f func(tx walletdb.ReadTx) error) error
+
+	// Update opens a database read/write transaction and executes the function
+	// f with the transaction passed as a parameter. After f exits, if f did not
+	// error, the transaction is committed. Otherwise, if f did error, the
+	// transaction is rolled back. If the rollback fails, the original error
+	// returned by f is still returned. If the commit fails, the commit error is
+	// returned.
+	Update(f func(tx walletdb.ReadWriteTx) error) error
+}
+
 // Open opens an existing database for the specified type. The arguments are
 // specific to the database type driver. See the documentation for the database
 // driver for further details.

channeldb/kvdb/kvdb_etcd.go

@@ -0,0 +1,49 @@
+// +build kvdb_etcd
+
+package kvdb
+
+import (
+	"github.com/lightningnetwork/lnd/channeldb/kvdb/etcd"
+)
+
+// TestBackend is conditionally set to etcd when the kvdb_etcd build tag is
+// defined, allowing testing our database code with etcd backend.
+const TestBackend = EtcdBackendName
+
+// GetEtcdBackend returns an etcd backend configured according to the
+// passed etcdConfig.
+func GetEtcdBackend(prefix string, etcdConfig *EtcdConfig) (Backend, error) {
+	// Config translation is needed here in order to keep the
+	// etcd package fully independent from the rest of the source tree.
+	backendConfig := etcd.BackendConfig{
+		Host:               etcdConfig.Host,
+		User:               etcdConfig.User,
+		Pass:               etcdConfig.Pass,
+		CertFile:           etcdConfig.CertFile,
+		KeyFile:            etcdConfig.KeyFile,
+		InsecureSkipVerify: etcdConfig.InsecureSkipVerify,
+		Prefix:             prefix,
+		CollectCommitStats: etcdConfig.CollectStats,
+	}
+
+	return Open(EtcdBackendName, backendConfig)
+}
+
+// GetEtcdTestBackend creates an embedded etcd backend for testing
+// storig the database at the passed path.
+func GetEtcdTestBackend(path, name string) (Backend, func(), error) {
+	empty := func() {}
+
+	config, cleanup, err := etcd.NewEmbeddedEtcdInstance(path)
+	if err != nil {
+		return nil, empty, err
+	}
+
+	backend, err := Open(EtcdBackendName, *config)
+	if err != nil {
+		cleanup()
+		return nil, empty, err
+	}
+
+	return backend, cleanup, nil
+}

channeldb/kvdb/kvdb_no_etcd.go

@@ -0,0 +1,24 @@
+// +build !kvdb_etcd
+
+package kvdb
+
+import (
+	"fmt"
+)
+
+// TestBackend is conditionally set to bdb when the kvdb_etcd build tag is
+// not defined, allowing testing our database code with bolt backend.
+const TestBackend = BoltBackendName
+
+var errEtcdNotAvailable = fmt.Errorf("etcd backend not available")
+
+// GetEtcdBackend is a stub returning nil and errEtcdNotAvailable error.
+func GetEtcdBackend(prefix string, etcdConfig *EtcdConfig) (Backend, error) {
+	return nil, errEtcdNotAvailable
+}
+
+// GetTestEtcdBackend  is a stub returning nil, an empty closure and an
+// errEtcdNotAvailable error.
+func GetEtcdTestBackend(path, name string) (Backend, func(), error) {
+	return nil, func() {}, errEtcdNotAvailable
+}

channeldb/meta_test.go

@@ -3,6 +3,7 @@ package channeldb
 import (
 	"bytes"
 	"io/ioutil"
+	"os"
 	"testing"
 
 	"github.com/go-errors/errors"
@@ -421,12 +422,21 @@ func TestMigrationReversion(t *testing.T) {
 	t.Parallel()
 
 	tempDirName, err := ioutil.TempDir("", "channeldb")
+	defer func() {
+		os.RemoveAll(tempDirName)
+	}()
 	if err != nil {
 		t.Fatalf("unable to create temp dir: %v", err)
 	}
 
-	cdb, err := Open(tempDirName)
+	backend, cleanup, err := kvdb.GetTestBackend(tempDirName, "cdb")
 	if err != nil {
+		t.Fatalf("unable to get test db backend: %v", err)
+	}
+
+	cdb, err := CreateWithBackend(backend)
+	if err != nil {
+		cleanup()
 		t.Fatalf("unable to open channeldb: %v", err)
 	}
 
@@ -442,12 +452,19 @@ func TestMigrationReversion(t *testing.T) {
 
 	// Close the database. Even if we succeeded, our next step is to reopen.
 	cdb.Close()
+	cleanup()
 
 	if err != nil {
 		t.Fatalf("unable to increase db version: %v", err)
 	}
 
-	_, err = Open(tempDirName)
+	backend, cleanup, err = kvdb.GetTestBackend(tempDirName, "cdb")
+	if err != nil {
+		t.Fatalf("unable to get test db backend: %v", err)
+	}
+	defer cleanup()
+
+	_, err = CreateWithBackend(backend)
 	if err != ErrDBReversion {
 		t.Fatalf("unexpected error when opening channeldb, "+
 			"want: %v, got: %v", ErrDBReversion, err)

channeldb/payment_control_test.go

@@ -5,7 +5,6 @@ import (
 	"crypto/sha256"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"reflect"
 	"testing"
 	"time"
@@ -15,20 +14,6 @@ import (
 	"github.com/lightningnetwork/lnd/record"
 )
 
-func initDB() (*DB, error) {
-	tempPath, err := ioutil.TempDir("", "switchdb")
-	if err != nil {
-		return nil, err
-	}
-
-	db, err := Open(tempPath)
-	if err != nil {
-		return nil, err
-	}
-
-	return db, err
-}
-
 func genPreimage() ([32]byte, error) {
 	var preimage [32]byte
 	if _, err := io.ReadFull(rand.Reader, preimage[:]); err != nil {
@@ -66,7 +51,8 @@ func genInfo() (*PaymentCreationInfo, *HTLCAttemptInfo,
 func TestPaymentControlSwitchFail(t *testing.T) {
 	t.Parallel()
 
-	db, err := initDB()
+	db, cleanup, err := makeTestDB()
+	defer cleanup()
 	if err != nil {
 		t.Fatalf("unable to init db: %v", err)
 	}
@@ -202,7 +188,9 @@ func TestPaymentControlSwitchFail(t *testing.T) {
 func TestPaymentControlSwitchDoubleSend(t *testing.T) {
 	t.Parallel()
 
-	db, err := initDB()
+	db, cleanup, err := makeTestDB()
+	defer cleanup()
+
 	if err != nil {
 		t.Fatalf("unable to init db: %v", err)
 	}
@@ -282,7 +270,9 @@ func TestPaymentControlSwitchDoubleSend(t *testing.T) {
 func TestPaymentControlSuccessesWithoutInFlight(t *testing.T) {
 	t.Parallel()
 
-	db, err := initDB()
+	db, cleanup, err := makeTestDB()
+	defer cleanup()
+
 	if err != nil {
 		t.Fatalf("unable to init db: %v", err)
 	}
@@ -313,7 +303,9 @@ func TestPaymentControlSuccessesWithoutInFlight(t *testing.T) {
 func TestPaymentControlFailsWithoutInFlight(t *testing.T) {
 	t.Parallel()
 
-	db, err := initDB()
+	db, cleanup, err := makeTestDB()
+	defer cleanup()
+
 	if err != nil {
 		t.Fatalf("unable to init db: %v", err)
 	}
@@ -339,7 +331,9 @@ func TestPaymentControlFailsWithoutInFlight(t *testing.T) {
 func TestPaymentControlDeleteNonInFligt(t *testing.T) {
 	t.Parallel()
 
-	db, err := initDB()
+	db, cleanup, err := makeTestDB()
+	defer cleanup()
+
 	if err != nil {
 		t.Fatalf("unable to init db: %v", err)
 	}
@@ -481,7 +475,9 @@ func TestPaymentControlMultiShard(t *testing.T) {
 	}
 
 	runSubTest := func(t *testing.T, test testCase) {
-		db, err := initDB()
+		db, cleanup, err := makeTestDB()
+		defer cleanup()
+
 		if err != nil {
 			t.Fatalf("unable to init db: %v", err)
 		}
@@ -728,7 +724,9 @@ func TestPaymentControlMultiShard(t *testing.T) {
 func TestPaymentControlMPPRecordValidation(t *testing.T) {
 	t.Parallel()
 
-	db, err := initDB()
+	db, cleanup, err := makeTestDB()
+	defer cleanup()
+
 	if err != nil {
 		t.Fatalf("unable to init db: %v", err)
 	}

channeldb/payments_test.go

@@ -351,7 +351,9 @@ func TestQueryPayments(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			t.Parallel()
 
-			db, err := initDB()
+			db, cleanup, err := makeTestDB()
+			defer cleanup()
+
 			if err != nil {
 				t.Fatalf("unable to init db: %v", err)
 			}

config.go

@@ -248,6 +248,8 @@ type Config struct {
 
 	AllowCircularRoute bool `long:"allow-circular-route" description:"If true, our node will allow htlc forwards that arrive and depart on the same channel."`
 
+	DB *lncfg.DB `group:"db" namespace:"db"`
+
 	// registeredChains keeps track of all chains that have been registered
 	// with the daemon.
 	registeredChains *chainRegistry
@@ -358,6 +360,7 @@ func DefaultConfig() Config {
 		},
 		MaxOutgoingCltvExpiry:   htlcswitch.DefaultMaxOutgoingCltvExpiry,
 		MaxChannelFeeAllocation: htlcswitch.DefaultMaxLinkFeeAllocation,
+		DB:                      lncfg.DefaultDB(),
 		registeredChains:        newChainRegistry(),
 	}
 }
@@ -1073,6 +1076,7 @@ func ValidateConfig(cfg Config, usageMessage string) (*Config, error) {
 		cfg.Workers,
 		cfg.Caches,
 		cfg.WtClient,
+		cfg.DB,
 	)
 	if err != nil {
 		return nil, err
@@ -1090,6 +1094,18 @@ func ValidateConfig(cfg Config, usageMessage string) (*Config, error) {
 	return &cfg, err
 }
 
+// localDatabaseDir returns the default directory where the
+// local bolt db files are stored.
+func (c *Config) localDatabaseDir() string {
+	return filepath.Join(c.DataDir,
+		defaultGraphSubDirname,
+		normalizeNetwork(activeNetParams.Name))
+}
+
+func (c *Config) networkName() string {
+	return normalizeNetwork(activeNetParams.Name)
+}
+
 // CleanAndExpandPath expands environment variables and leading ~ in the
 // passed path, cleans the result, and returns it.
 // This function is taken from https://github.com/btcsuite/btcd

go.mod

@@ -14,10 +14,18 @@ require (
 	github.com/btcsuite/btcwallet/wallet/txrules v1.0.0
 	github.com/btcsuite/btcwallet/walletdb v1.3.1
 	github.com/btcsuite/btcwallet/wtxmgr v1.1.1-0.20200515224913-e0e62245ecbe
+	github.com/coreos/etcd v3.3.18+incompatible
+	github.com/coreos/go-semver v0.3.0 // indirect
+	github.com/coreos/go-systemd v0.0.0-00010101000000-000000000000 // indirect
+	github.com/coreos/pkg v0.0.0-20180928190104-399ea9e2e55f // indirect
 	github.com/davecgh/go-spew v1.1.1
+	github.com/dgrijalva/jwt-go v3.2.0+incompatible // indirect
 	github.com/go-errors/errors v1.0.1
 	github.com/go-openapi/strfmt v0.19.5 // indirect
+	github.com/golang/groupcache v0.0.0-20200121045136-8c9f03a8e57e // indirect
 	github.com/golang/protobuf v1.3.1
+	github.com/google/btree v1.0.0 // indirect
+	github.com/gorilla/websocket v1.4.1 // indirect
 	github.com/grpc-ecosystem/go-grpc-middleware v1.0.0
 	github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0
 	github.com/grpc-ecosystem/grpc-gateway v1.8.6
@@ -25,7 +33,9 @@ require (
 	github.com/jackpal/go-nat-pmp v0.0.0-20170405195558-28a68d0c24ad
 	github.com/jedib0t/go-pretty v4.3.0+incompatible
 	github.com/jessevdk/go-flags v1.4.0
+	github.com/jonboulle/clockwork v0.1.0 // indirect
 	github.com/jrick/logrotate v1.0.0
+	github.com/json-iterator/go v1.1.9 // indirect
 	github.com/juju/clock v0.0.0-20190205081909-9c5c9712527c // indirect
 	github.com/juju/errors v0.0.0-20190806202954-0232dcc7464d // indirect
 	github.com/juju/loggo v0.0.0-20190526231331-6e530bcce5d8 // indirect
@@ -43,12 +53,19 @@ require (
 	github.com/ltcsuite/ltcd v0.0.0-20190101042124-f37f8bf35796
 	github.com/mattn/go-runewidth v0.0.9 // indirect
 	github.com/miekg/dns v0.0.0-20171125082028-79bfde677fa8
+	github.com/modern-go/reflect2 v1.0.1 // indirect
 	github.com/prometheus/client_golang v0.9.3
 	github.com/rogpeppe/fastuuid v1.2.0 // indirect
+	github.com/soheilhy/cmux v0.1.4 // indirect
+	github.com/stretchr/testify v1.4.0
+	github.com/tmc/grpc-websocket-proxy v0.0.0-20190109142713-0ad062ec5ee5 // indirect
 	github.com/tv42/zbase32 v0.0.0-20160707012821-501572607d02
 	github.com/urfave/cli v1.18.0
+	github.com/xiang90/probing v0.0.0-20190116061207-43a291ad63a2 // indirect
+	go.etcd.io/bbolt v1.3.3
+	go.uber.org/zap v1.14.1 // indirect
 	golang.org/x/crypto v0.0.0-20200510223506-06a226fb4e37
-	golang.org/x/net v0.0.0-20190206173232-65e2d4e15006
+	golang.org/x/net v0.0.0-20190620200207-3b0461eec859
 	golang.org/x/sys v0.0.0-20200116001909-b77594299b42 // indirect
 	golang.org/x/time v0.0.0-20180412165947-fbb02b2291d2
 	google.golang.org/genproto v0.0.0-20190201180003-4b09977fb922
@@ -57,6 +74,7 @@ require (
 	gopkg.in/macaroon-bakery.v2 v2.0.1
 	gopkg.in/macaroon.v2 v2.0.0
 	gopkg.in/mgo.v2 v2.0.0-20190816093944-a6b53ec6cb22 // indirect
+	sigs.k8s.io/yaml v1.1.0 // indirect
 )
 
 replace github.com/lightningnetwork/lnd/ticker => ./ticker
@@ -71,4 +89,6 @@ replace git.schwanenlied.me/yawning/bsaes.git => github.com/Yawning/bsaes v0.0.0
 // btcsuite/btcutil package requests a newer version.
 replace golang.org/x/crypto => golang.org/x/crypto v0.0.0-20190211182817-74369b46fc67
 
+replace github.com/coreos/go-systemd => github.com/coreos/go-systemd/v22 v22.0.0
+
 go 1.12

go.sum

@@ -44,7 +44,6 @@ github.com/btcsuite/btcwallet/wallet/txrules v1.0.0/go.mod h1:UwQE78yCerZ313EXZw
 github.com/btcsuite/btcwallet/wallet/txsizes v1.0.0 h1:6DxkcoMnCPY4E9cUDPB5tbuuf40SmmMkSQkoE8vCT+s=
 github.com/btcsuite/btcwallet/wallet/txsizes v1.0.0/go.mod h1:pauEU8UuMFiThe5PB3EO+gO5kx87Me5NvdQDsTuq6cs=
 github.com/btcsuite/btcwallet/walletdb v1.0.0/go.mod h1:bZTy9RyYZh9fLnSua+/CD48TJtYJSHjjYcSaszuxCCk=
-github.com/btcsuite/btcwallet/walletdb v1.2.0 h1:E0+M4jHOToAvGWZ27ew5AaDAHDi6fUiXkjUJUnoEOD0=
 github.com/btcsuite/btcwallet/walletdb v1.2.0/go.mod h1:9cwc1Yyg4uvd4ZdfdoMnALji+V9gfWSMfxEdLdR5Vwc=
 github.com/btcsuite/btcwallet/walletdb v1.3.1 h1:lW1Ac3F1jJY4K11P+YQtRNcP5jFk27ASfrV7C6mvRU0=
 github.com/btcsuite/btcwallet/walletdb v1.3.1/go.mod h1:9cwc1Yyg4uvd4ZdfdoMnALji+V9gfWSMfxEdLdR5Vwc=
@@ -70,10 +69,20 @@ github.com/cespare/xxhash v1.1.0/go.mod h1:XrSqR1VqqWfGrhpAt58auRo0WTKS1nRRg3ghf
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
 github.com/coreos/bbolt v1.3.3 h1:n6AiVyVRKQFNb6mJlwESEvvLoDyiTzXX7ORAUlkeBdY=
 github.com/coreos/bbolt v1.3.3/go.mod h1:iRUV2dpdMOn7Bo10OQBFzIJO9kkE559Wcmn+qkEiiKk=
+github.com/coreos/etcd v3.3.18+incompatible h1:Zz1aXgDrFFi1nadh58tA9ktt06cmPTwNNP3dXwIq1lE=
+github.com/coreos/etcd v3.3.18+incompatible/go.mod h1:uF7uidLiAD3TWHmW31ZFd/JWoc32PjwdhPthX9715RE=
+github.com/coreos/go-semver v0.3.0 h1:wkHLiw0WNATZnSG7epLsujiMCgPAc9xhjJ4tgnAxmfM=
+github.com/coreos/go-semver v0.3.0/go.mod h1:nnelYz7RCh+5ahJtPPxZlU+153eP4D4r3EedlOD2RNk=
+github.com/coreos/go-systemd/v22 v22.0.0 h1:XJIw/+VlJ+87J+doOxznsAWIdmWuViOVhkQamW5YV28=
+github.com/coreos/go-systemd/v22 v22.0.0/go.mod h1:xO0FLkIi5MaZafQlIrOotqXZ90ih+1atmu1JpKERPPk=
+github.com/coreos/pkg v0.0.0-20180928190104-399ea9e2e55f h1:lBNOc5arjvs8E5mO2tbpBpLoyyu8B6e44T7hJy6potg=
+github.com/coreos/pkg v0.0.0-20180928190104-399ea9e2e55f/go.mod h1:E3G3o1h8I7cfcXa63jLwjI0eiQQMgzzUDFVpN/nH/eA=
 github.com/davecgh/go-spew v0.0.0-20171005155431-ecdeabc65495/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/dgrijalva/jwt-go v3.2.0+incompatible h1:7qlOGliEKZXTDg6OTjfoBKDXWrumCAMpl/TFQ4/5kLM=
+github.com/dgrijalva/jwt-go v3.2.0+incompatible/go.mod h1:E3ru+11k8xSBh+hMPgOLZmtrrCbhqsmaPHjLKYnJCaQ=
 github.com/dgryski/go-sip13 v0.0.0-20181026042036-e10d5fee7954/go.mod h1:vAd38F8PWV+bWy6jNmig1y/TA+kYO4g3RSRF0IAv0no=
 github.com/frankban/quicktest v1.2.2 h1:xfmOhhoH5fGPgbEAlhLpJH9p0z/0Qizio9osmvn9IUY=
 github.com/frankban/quicktest v1.2.2/go.mod h1:Qh/WofXFeiAFII1aEBu529AtJo6Zg2VHscnEsbBnJ20=
@@ -91,20 +100,31 @@ github.com/go-openapi/strfmt v0.19.5 h1:0utjKrw+BAh8s57XE9Xz8DUBsVvPmRUB6styvl9w
 github.com/go-openapi/strfmt v0.19.5/go.mod h1:eftuHTlB/dI8Uq8JJOyRlieZf+WkkxUuk0dgdHXr2Qk=
 github.com/go-stack/stack v1.8.0 h1:5SgMzNM5HxrEjV0ww2lTmX6E2Izsfxas4+YHWRs3Lsk=
 github.com/go-stack/stack v1.8.0/go.mod h1:v0f6uXyyMGvRgIKkXu+yp6POWl0qKG85gN/melR3HDY=
+github.com/godbus/dbus/v5 v5.0.3/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
+github.com/gogo/protobuf v1.1.1 h1:72R+M5VuhED/KujmZVcIquuo8mBgX4oVda//DQb3PXo=
 github.com/gogo/protobuf v1.1.1/go.mod h1:r8qH/GZQm5c6nD/R0oafs1akxWv10x8SbQlK7atdtwQ=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b h1:VKtxabqXZkF25pY9ekfRL6a582T4P37/31XEstQ5p58=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
+github.com/golang/groupcache v0.0.0-20200121045136-8c9f03a8e57e/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
 github.com/golang/lint v0.0.0-20180702182130-06c8688daad7/go.mod h1:tluoj9z5200jBnyusfRPU2LqT6J+DAorxEvtC7LHB+E=
 github.com/golang/mock v1.1.1/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
 github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
 github.com/golang/protobuf v1.3.1 h1:YF8+flBXS5eO826T4nzqPrxfhQThhXl0YzfuUPu4SBg=
 github.com/golang/protobuf v1.3.1/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
+github.com/google/btree v1.0.0 h1:0udJVsspx3VBr5FwtLhQQtuAsVc79tTq0ocGIPAU6qo=
+github.com/google/btree v1.0.0/go.mod h1:lNA+9X1NB3Zf8V7Ke586lFgjr2dZNuvo3lPJSGZ5JPQ=
 github.com/google/go-cmp v0.2.1-0.20190312032427-6f77996f0c42 h1:q3pnF5JFBNRz8sRD+IRj7Y6DMyYGTNqnZ9axTbSfoNI=
 github.com/google/go-cmp v0.2.1-0.20190312032427-6f77996f0c42/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/google/go-cmp v0.3.0 h1:crn/baboCvb5fXaQ0IJ1SGTsTVrWpDsCWC8EGETZijY=
 github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
+github.com/google/gofuzz v1.0.0/go.mod h1:dBl0BpW6vV/+mYPU4Po3pmUjxk6FQPldtuIdl/M65Eg=
+github.com/google/renameio v0.1.0/go.mod h1:KWCgfxg9yswjAJkECMjeO8J8rahYeXnNhOm40UhjYkI=
+github.com/google/uuid v1.1.1 h1:Gkbcsh/GbpXz7lPftLA3P6TYMwjCLYm83jiFQZF/3gY=
 github.com/google/uuid v1.1.1 h1:Gkbcsh/GbpXz7lPftLA3P6TYMwjCLYm83jiFQZF/3gY=
 github.com/google/uuid v1.1.1/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/google/uuid v1.1.1/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/gorilla/websocket v1.4.1 h1:q7AeDBpnBk8AogcD4DSag/Ukw/KV+YhzLj2bP5HvKCM=
+github.com/gorilla/websocket v1.4.1/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
 github.com/grpc-ecosystem/go-grpc-middleware v1.0.0 h1:Iju5GlWwrvL6UBg4zJJt3btmonfrMlCDdsejg4CZE7c=
 github.com/grpc-ecosystem/go-grpc-middleware v1.0.0/go.mod h1:FiyG127CGDf3tlThmgyCl78X/SZQqEOJBCDaAfeWzPs=
 github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0 h1:Ovs26xHkKqVztRpIrF/92BcuyuQ/YW4NSIpoGtfXNho=
@@ -122,8 +142,12 @@ github.com/jedib0t/go-pretty v4.3.0+incompatible/go.mod h1:XemHduiw8R651AF9Pt4Fw
 github.com/jessevdk/go-flags v0.0.0-20141203071132-1679536dcc89/go.mod h1:4FA24M0QyGHXBuZZK/XkWh8h0e1EYbRYJSGM75WSRxI=
 github.com/jessevdk/go-flags v1.4.0 h1:4IU2WS7AumrZ/40jfhf4QVDMsQwqA7VEHozFRrGARJA=
 github.com/jessevdk/go-flags v1.4.0/go.mod h1:4FA24M0QyGHXBuZZK/XkWh8h0e1EYbRYJSGM75WSRxI=
+github.com/jonboulle/clockwork v0.1.0 h1:VKV+ZcuP6l3yW9doeqz6ziZGgcynBVQO+obU0+0hcPo=
+github.com/jonboulle/clockwork v0.1.0/go.mod h1:Ii8DK3G1RaLaWxj9trq07+26W01tbo22gdxWY5EU2bo=
 github.com/jrick/logrotate v1.0.0 h1:lQ1bL/n9mBNeIXoTUoYRlK4dHuNJVofX9oWqBtPnSzI=
 github.com/jrick/logrotate v1.0.0/go.mod h1:LNinyqDIJnpAur+b8yyulnQw/wDuN1+BYKlTRt3OuAQ=
+github.com/json-iterator/go v1.1.9 h1:9yzud/Ht36ygwatGx56VwCZtlI/2AD15T1X2sjSuGns=
+github.com/json-iterator/go v1.1.9/go.mod h1:KdQUCv79m/52Kvf8AW2vK1V8akMuk1QjK/uOdHXbAo4=
 github.com/juju/clock v0.0.0-20190205081909-9c5c9712527c h1:3UvYABOQRhJAApj9MdCN+Ydv841ETSoy6xLzdmmr/9A=
 github.com/juju/clock v0.0.0-20190205081909-9c5c9712527c/go.mod h1:nD0vlnrUjcjJhqN5WuCWZyzfd5AHZAC9/ajvbSx69xA=
 github.com/juju/errors v0.0.0-20190806202954-0232dcc7464d h1:hJXjZMxj0SWlMoQkzeZDLi2cmeiWKa7y1B8Rg+qaoEc=
@@ -170,6 +194,11 @@ github.com/miekg/dns v0.0.0-20171125082028-79bfde677fa8 h1:PRMAcldsl4mXKJeRNB/KV
 github.com/miekg/dns v0.0.0-20171125082028-79bfde677fa8/go.mod h1:W1PPwlIAgtquWBMBEV9nkV9Cazfe8ScdGz/Lj7v3Nrg=
 github.com/mitchellh/mapstructure v1.1.2 h1:fmNYVwqnSfB9mZU6OS2O6GsXM+wcskZDuKQzvN1EDeE=
 github.com/mitchellh/mapstructure v1.1.2/go.mod h1:FVVH3fgwuzCH5S8UJGiWEs2h04kUh9fWfEaFds41c1Y=
+github.com/modern-go/concurrent v0.0.0-20180228061459-e0a39a4cb421 h1:ZqeYNhU3OHLH3mGKHDcjJRFFRrJa6eAM5H+CtDdOsPc=
+github.com/modern-go/concurrent v0.0.0-20180228061459-e0a39a4cb421/go.mod h1:6dJC0mAP4ikYIbvyc7fijjWJddQyLn8Ig3JB5CqoB9Q=
+github.com/modern-go/reflect2 v0.0.0-20180701023420-4b7aa43c6742/go.mod h1:bx2lNnkwVCuqBIxFjflWJWanXIb3RllmbCylyMrvgv0=
+github.com/modern-go/reflect2 v1.0.1 h1:9f412s+6RmYXLWZSEzVVgPGK7C2PphHj5RJrvfx9AWI=
+github.com/modern-go/reflect2 v1.0.1/go.mod h1:bx2lNnkwVCuqBIxFjflWJWanXIb3RllmbCylyMrvgv0=
 github.com/mwitkow/go-conntrack v0.0.0-20161129095857-cc309e4a2223/go.mod h1:qRWi+5nqEBWmkhHvq77mSJWrCKwh8bxhgT7d/eI7P4U=
 github.com/oklog/ulid v1.3.1/go.mod h1:CirwcVhetQ6Lv90oh/F+FBtV6XMibvdAFo93nm5qn4U=
 github.com/onsi/ginkgo v1.6.0/go.mod h1:lLunBs/Ym6LB5Z9jYTR76FiuTmxDTDusOGeTQH+WWjE=
@@ -179,6 +208,7 @@ github.com/onsi/gomega v1.4.1/go.mod h1:C1qb7wdrVGGVU+Z6iS04AVkA3Q65CEZX59MT0QO5
 github.com/onsi/gomega v1.4.3 h1:RE1xgDvH7imwFD45h+u2SgIfERHlS2yNG4DObb5BSKU=
 github.com/onsi/gomega v1.4.3/go.mod h1:ex+gbHU/CVuBBDIJjb2X0qEXbFg53c61hWP/1CpauHY=
 github.com/pkg/errors v0.8.0/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
+github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/prometheus/client_golang v0.9.1/go.mod h1:7SWBe2y4D6OKWSNQJUaRYU/AaXPKyh/dDVn+NZz0KFw=
@@ -197,30 +227,50 @@ github.com/prometheus/tsdb v0.7.1/go.mod h1:qhTCs0VvXwvX/y3TZrWD7rabWM+ijKTux40T
 github.com/rogpeppe/fastuuid v0.0.0-20150106093220-6724a57986af/go.mod h1:XWv6SoW27p1b0cqNHllgS5HIMJraePCO15w5zCzIWYg=
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+go.uber.org/atomic v1.6.0 h1:Ezj3JGmsOnG1MoRWQkPBsKLe9DwWD9QeXzTRzzldNVk=
+go.uber.org/atomic v1.6.0/go.mod h1:sABNBOSYdrvTF6hTgEIbc7YasKWGhgEQZyfxyTvoXHQ=
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+go.uber.org/multierr v1.5.0/go.mod h1:FeouvMocqHpRaaGuG9EjoKcStLC43Zu/fmqdUMPcKYU=
+go.uber.org/tools v0.0.0-20190618225709-2cfd321de3ee/go.mod h1:vJERXedbb3MVM5f9Ejo0C68/HhF8uaILCdgjnY+goOA=
+go.uber.org/zap v1.14.1 h1:nYDKopTbvAPq/NrUVZwT15y2lpROBiLLyoRTbXOYWOo=
+go.uber.org/zap v1.14.1/go.mod h1:Mb2vm2krFEG5DV0W9qcHBYFtp/Wku1cvYaqPsS/WYfc=
 golang.org/x/crypto v0.0.0-20190211182817-74369b46fc67 h1:ng3VDlRp5/DHpSWl02R4rM9I+8M2rhmsuLwAMmkLQWE=
 golang.org/x/crypto v0.0.0-20190211182817-74369b46fc67/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20190510104115-cbcb75029529 h1:iMGN4xG0cnqj3t+zOM8wUB0BiPKHEwSxEZCvzcbZuvk=
+golang.org/x/crypto v0.0.0-20190510104115-cbcb75029529/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/lint v0.0.0-20180702182130-06c8688daad7/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
 golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
+golang.org/x/lint v0.0.0-20190930215403-16217165b5de/go.mod h1:6SW0HCj/g11FgYtHlgUYUwCkIfeOF89ocIRzGO/8vkc=
+golang.org/x/mod v0.0.0-20190513183733-4bf6d317e70e/go.mod h1:mXi4GBBbnImb6dmsKGUJ2LatrhH/nqhxcFungHvyanc=
 golang.org/x/net v0.0.0-20180719180050-a680a1efc54d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180826012351-8a410e7b638d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180906233101-161cd47e91fd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
@@ -229,10 +279,15 @@ golang.org/x/net v0.0.0-20181114220301-adae6a3d119a/go.mod h1:mL1N/T3taQHkDXs73r
 golang.org/x/net v0.0.0-20181220203305-927f97764cc3/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20190206173232-65e2d4e15006 h1:bfLnR+k0tq5Lqt6dflRLcZiz6UaXCMt3vhYJ1l4FQ80=
 golang.org/x/net v0.0.0-20190206173232-65e2d4e15006/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
+golang.org/x/net v0.0.0-20190311183353-d8887717615a/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859 h1:R/3boaszxrf1GEUWTVDzSKVwLmSJpwZ1yqXm8j0v2QI=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20181108010431-42b317875d0f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
@@ -241,6 +296,8 @@ golang.org/x/sys v0.0.0-20181107165924-66b7b1311ac8/go.mod h1:STP8DvDyc/dI5b8T5h
 golang.org/x/sys v0.0.0-20181116152217-5ac8a444bdc5/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190209173611-3b5209105503 h1:5SvYFrOM3W8Mexn9/oA44Ji7vhXAZQ9hiP+1Q/DMrWg=
 golang.org/x/sys v0.0.0-20190209173611-3b5209105503/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190904154756-749cb33beabd h1:DBH9mDw0zluJT/R+nGuV3jWFWLFaHyYZWD4tOT+cjn0=
 golang.org/x/sys v0.0.0-20190904154756-749cb33beabd/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200116001909-b77594299b42 h1:vEOn+mP2zCOVzKckCZy6YsCtDblrpj/w7B9nxGNELpg=
@@ -252,6 +309,11 @@ golang.org/x/time v0.0.0-20180412165947-fbb02b2291d2 h1:+DCIGbF/swA92ohVg0//6X2I
 golang.org/x/time v0.0.0-20180412165947-fbb02b2291d2/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
 golang.org/x/tools v0.0.0-20180828015842-6cd1fcedba52/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20190114222345-bf090417da8b/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+golang.org/x/tools v0.0.0-20190311212946-11955173bddd/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
+golang.org/x/tools v0.0.0-20190621195816-6e04913cbbac/go.mod h1:/rFqwRUd4F7ZHNgwSSTFct+R/Kf4OFW1sUzUTQQTgfc=
+golang.org/x/tools v0.0.0-20191029041327-9cc4af7d6b2c/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/tools v0.0.0-20191029190741-b9c20aec41a5/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 google.golang.org/appengine v1.1.0/go.mod h1:EbEs0AVv82hx2wNQdGPgUI5lhzA/G0D9YwlJXL52JkM=
 google.golang.org/genproto v0.0.0-20180817151627-c66870c02cf8/go.mod h1:JiN7NxoALGmiZfu7CAH4rXhgtRTLTxftemlI0sWmxmc=
 google.golang.org/genproto v0.0.0-20190201180003-4b09977fb922 h1:mBVYJnbrXLA/ZCBTCe7PtEgAUP+1bg92qTaFoPHdz+8=
@@ -267,6 +329,7 @@ gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 h1:qIbj1fsPNlZgppZ+VLlY7N33
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/errgo.v1 v1.0.1 h1:oQFRXzZ7CkBGdm1XZm/EbQYaYNNEElNBOd09M6cqNso=
 gopkg.in/errgo.v1 v1.0.1/go.mod h1:3NjfXwocQRYAPTq4/fzX+CwUhPRcR/azYRhj8G+LqMo=
+gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=
 gopkg.in/fsnotify.v1 v1.4.7 h1:xOHLXZwVvI9hhs+cLKq5+I5onOuwQLhQwiu63xxlHs4=
 gopkg.in/fsnotify.v1 v1.4.7/go.mod h1:Tz8NjZHkW78fSQdbUxIjBTcgA1z1m8ZHf0WmKUhAMys=
 gopkg.in/macaroon-bakery.v2 v2.0.1 h1:0N1TlEdfLP4HXNCg7MQUMp5XwvOoxk+oe9Owr2cpvsc=
@@ -284,3 +347,6 @@ gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 honnef.co/go/tools v0.0.0-20180728063816-88497007e858/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
 honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
+honnef.co/go/tools v0.0.1-2019.2.3/go.mod h1:a3bituU0lyd329TUQxRnasdCoJDkEUEAqEt0JzvZhAg=
+sigs.k8s.io/yaml v1.1.0 h1:4A07+ZFc2wgJwo8YNlQpr1rVlgUDlxXHhPJciaPY5gs=
+sigs.k8s.io/yaml v1.1.0/go.mod h1:UJmg0vDUVViEyp3mgSv9WPwZCDxu4rQW1olrI1uml+o=

lncfg/db.go

@@ -0,0 +1,65 @@
+package lncfg
+
+import (
+	"fmt"
+
+	"github.com/lightningnetwork/lnd/channeldb/kvdb"
+)
+
+const (
+	dbName      = "channel.db"
+	boltBackend = "bolt"
+	etcdBackend = "etcd"
+)
+
+// DB holds database configuration for LND.
+type DB struct {
+	Backend string `long:"backend" description:"The selected database backend."`
+
+	Etcd *kvdb.EtcdConfig `group:"etcd" namespace:"etcd" description:"Etcd settings."`
+
+	Bolt *kvdb.BoltConfig `group:"bolt" namespace:"bolt" description:"Bolt settings."`
+}
+
+// NewDB creates and returns a new default DB config.
+func DefaultDB() *DB {
+	return &DB{
+		Backend: boltBackend,
+		Bolt: &kvdb.BoltConfig{
+			NoFreeListSync: true,
+		},
+	}
+}
+
+// Validate validates the DB config.
+func (db *DB) Validate() error {
+	switch db.Backend {
+	case boltBackend:
+
+	case etcdBackend:
+		if db.Etcd.Host == "" {
+			return fmt.Errorf("etcd host must be set")
+		}
+
+	default:
+		return fmt.Errorf("unknown backend, must be either \"%v\" or \"%v\"",
+			boltBackend, etcdBackend)
+	}
+
+	return nil
+}
+
+// GetBackend returns a kvdb.Backend as set in the DB config.
+func (db *DB) GetBackend(dbPath string, networkName string) (
+	kvdb.Backend, error) {
+
+	if db.Backend == etcdBackend {
+		// Prefix will separate key/values in the db.
+		return kvdb.GetEtcdBackend(networkName, db.Etcd)
+	}
+
+	return kvdb.GetBoltBackend(dbPath, dbName, db.Bolt.NoFreeListSync)
+}
+
+// Compile-time constraint to ensure Workers implements the Validator interface.
+var _ Validator = (*DB)(nil)

lnd.go

@@ -247,18 +247,22 @@ func Main(cfg *Config, lisCfg ListenerCfg, shutdownChan <-chan struct{}) error {
 	}
 
 	// Create the network-segmented directory for the channel database.
-	graphDir := filepath.Join(cfg.DataDir,
-		defaultGraphSubDirname,
-		normalizeNetwork(activeNetParams.Name))
-
 	ltndLog.Infof("Opening the main database, this might take a few " +
 		"minutes...")
 
+	chanDbBackend, err := cfg.DB.GetBackend(
+		cfg.localDatabaseDir(), cfg.networkName(),
+	)
+	if err != nil {
+		ltndLog.Error(err)
+		return err
+	}
+
 	// Open the channeldb, which is dedicated to storing channel, and
 	// network related metadata.
 	startOpenTime := time.Now()
-	chanDB, err := channeldb.Open(
-		graphDir,
+	chanDB, err := channeldb.CreateWithBackend(
+		chanDbBackend,
 		channeldb.OptionSetRejectCacheSize(cfg.Caches.RejectCacheSize),
 		channeldb.OptionSetChannelCacheSize(cfg.Caches.ChannelCacheSize),
 		channeldb.OptionSetSyncFreelist(cfg.SyncFreelist),
@@ -493,7 +497,7 @@ func Main(cfg *Config, lisCfg ListenerCfg, shutdownChan <-chan struct{}) error {
 	var towerClientDB *wtdb.ClientDB
 	if cfg.WtClient.Active {
 		var err error
-		towerClientDB, err = wtdb.OpenClientDB(graphDir)
+		towerClientDB, err = wtdb.OpenClientDB(cfg.localDatabaseDir())
 		if err != nil {
 			err := fmt.Errorf("unable to open watchtower client "+
 				"database: %v", err)

server.go

@@ -377,8 +377,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr, chanDB *channeldb.DB,
 
 	// Initialize the sphinx router, placing it's persistent replay log in
 	// the same directory as the channel graph database.
-	graphDir := chanDB.Path()
-	sharedSecretPath := filepath.Join(graphDir, "sphinxreplay.db")
+	sharedSecretPath := filepath.Join(cfg.localDatabaseDir(), "sphinxreplay.db")
 	replayLog := htlcswitch.NewDecayedLog(sharedSecretPath, cc.chainNotifier)
 	sphinxRouter := sphinx.NewRouter(
 		nodeKeyECDH, activeNetParams.Params, replayLog,