etcd: decouple embedded etcd instance startup

This refactor changes how we instantiate the etcd based Backend to allow
separate initialization and startup for the embedded instance.

channeldb/kvdb/backend.go

@@ -1,6 +1,7 @@
 package kvdb
 
 import (
+	"context"
 	"encoding/binary"
 	"fmt"
 	"io/ioutil"
@@ -253,7 +254,14 @@ func GetTestBackend(path, name string) (Backend, func(), error) {
 		}
 		return db, empty, nil
 	} else if TestBackend == EtcdBackendName {
-		return GetEtcdTestBackend(path, 0, 0)
+		etcdConfig, cancel, err := StartEtcdTestBackend(path, 0, 0)
+		if err != nil {
+			return nil, empty, err
+		}
+		backend, err := Open(
+			EtcdBackendName, context.TODO(), etcdConfig,
+		)
+		return backend, cancel, err
 	}
 
 	return nil, nil, fmt.Errorf("unknown backend")

channeldb/kvdb/kvdb_etcd.go

@@ -3,8 +3,6 @@
 package kvdb
 
 import (
-	"context"
-
 	"github.com/lightningnetwork/lnd/channeldb/kvdb/etcd"
 )
 
@@ -12,33 +10,12 @@ import (
 // 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(ctx context.Context, etcdConfig *etcd.Config) (
-	Backend, error) {
-
-	return Open(EtcdBackendName, etcdConfig)
-}
-
 // GetEtcdTestBackend creates an embedded etcd backend for testing
 // storig the database at the passed path.
-func GetEtcdTestBackend(path string, clientPort, peerPort uint16) (
-	Backend, func(), error) {
+func StartEtcdTestBackend(path string, clientPort, peerPort uint16) (
+	*etcd.Config, func(), error) {
 
-	empty := func() {}
-
-	config, cleanup, err := etcd.NewEmbeddedEtcdInstance(
+	return etcd.NewEmbeddedEtcdInstance(
 		path, clientPort, peerPort,
 	)
-	if err != nil {
-		return nil, empty, err
-	}
-
-	backend, err := Open(EtcdBackendName, context.Background(), config)
-	if err != nil {
-		cleanup()
-		return nil, empty, err
-	}
-
-	return backend, cleanup, nil
 }

channeldb/kvdb/kvdb_no_etcd.go

@@ -3,7 +3,6 @@
 package kvdb
 
 import (
-	"context"
 	"fmt"
 
 	"github.com/lightningnetwork/lnd/channeldb/kvdb/etcd"
@@ -15,17 +14,9 @@ const TestBackend = BoltBackendName
 
 var errEtcdNotAvailable = fmt.Errorf("etcd backend not available")
 
-// GetEtcdBackend is a stub returning nil and errEtcdNotAvailable error.
-func GetEtcdBackend(ctx context.Context, etcdConfig *etcd.Config) (
-	Backend, error) {
-
-	return nil, errEtcdNotAvailable
-}
-
-// GetTestEtcdBackend  is a stub returning nil, an empty closure and an
-// errEtcdNotAvailable error.
-func GetEtcdTestBackend(path string, clientPort, peerPort uint16) (
-	Backend, func(), error) {
+// StartEtcdTestBackend  is a stub returning nil, and errEtcdNotAvailable error.
+func StartEtcdTestBackend(path string, clientPort, peerPort uint16) (
+	*etcd.Config, func(), error) {
 
 	return nil, func() {}, errEtcdNotAvailable
 }

lncfg/db.go

@@ -57,6 +57,27 @@ func (db *DB) Validate() error {
 	return nil
 }
 
+// Init should be called upon start to pre-initialize database access dependent
+// on configuration.
+func (db *DB) Init(ctx context.Context, dbPath string) error {
+	// Start embedded etcd server if requested.
+	if db.Backend == EtcdBackend && db.Etcd.Embedded {
+		cfg, _, err := kvdb.StartEtcdTestBackend(
+			dbPath, db.Etcd.EmbeddedClientPort,
+			db.Etcd.EmbeddedPeerPort,
+		)
+		if err != nil {
+			return err
+		}
+
+		// Override the original config with the config for
+		// the embedded instance.
+		db.Etcd = cfg
+	}
+
+	return nil
+}
+
 // DatabaseBackends is a two-tuple that holds the set of active database
 // backends for the daemon. The two backends we expose are the local database
 // backend, and the remote backend. The LocalDB attribute will always be
@@ -83,14 +104,9 @@ func (db *DB) GetBackends(ctx context.Context, dbPath string) (
 	)
 
 	if db.Backend == EtcdBackend {
-		if db.Etcd.Embedded {
-			remoteDB, _, err = kvdb.GetEtcdTestBackend(
-				dbPath, db.Etcd.EmbeddedClientPort,
-				db.Etcd.EmbeddedPeerPort,
-			)
-		} else {
-			remoteDB, err = kvdb.GetEtcdBackend(ctx, db.Etcd)
-		}
+		remoteDB, err = kvdb.Open(
+			kvdb.EtcdBackendName, ctx, db.Etcd,
+		)
 		if err != nil {
 			return nil, err
 		}

lnd.go

@@ -234,6 +234,13 @@ func Main(cfg *Config, lisCfg ListenerCfg, interceptor signal.Interceptor) error
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
 
+	// Run configuration dependent DB pre-initialization. Note that this
+	// needs to be done early and once during the startup process, before
+	// any DB access.
+	if err := cfg.DB.Init(ctx, cfg.localDatabaseDir()); err != nil {
+		return err
+	}
+
 	localChanDB, remoteChanDB, cleanUp, err := initializeDatabases(ctx, cfg)
 	switch {
 	case err == channeldb.ErrDryRunMigrationOK: