Merge pull request #2668 from cfromknecht/dry-run-migration

Dry run migration

channeldb/db.go

@@ -25,6 +25,12 @@ const (
 	dbFilePermission = 0600
 )
 
+var (
+	// ErrDryRunMigrationOK signals that a migration executed successful,
+	// but we intentionally did not commit the result.
+	ErrDryRunMigrationOK = errors.New("Dry run migration successful")
+)
+
 // migration is a function which takes a prior outdated version of the database
 // instances and mutates the key/bucket structure to arrive at a more
 // up-to-date version of the database.
@@ -145,6 +151,7 @@ type DB struct {
 	dbPath string
 	graph  *ChannelGraph
 	clock  clock.Clock
+	dryRun bool
 }
 
 // Open opens an existing channeldb. Any necessary schemas migrations due to
@@ -174,6 +181,7 @@ func Open(dbPath string, modifiers ...OptionModifier) (*DB, error) {
 		Backend: bdb,
 		dbPath:  dbPath,
 		clock:   opts.clock,
+		dryRun:  opts.dryRun,
 	}
 	chanDB.graph = newChannelGraph(
 		chanDB, opts.RejectCacheSize, opts.ChannelCacheSize,
@@ -1227,7 +1235,18 @@ func (d *DB) syncVersions(versions []version) error {
 		}
 
 		meta.DbVersionNumber = latestVersion
-		return putMeta(meta, tx)
+		err := putMeta(meta, tx)
+		if err != nil {
+			return err
+		}
+
+		// In dry-run mode, return an error to prevent the transaction
+		// from committing.
+		if d.dryRun {
+			return ErrDryRunMigrationOK
+		}
+
+		return nil
 	})
 }
 

channeldb/db_test.go

@@ -45,6 +45,16 @@ func TestOpenWithCreate(t *testing.T) {
 	if !fileExists(dbPath) {
 		t.Fatalf("channeldb failed to create data directory")
 	}
+
+	// Now, reopen the same db in dry run migration mode. Since we have not
+	// applied any migrations, this should ignore the flag and not fail.
+	cdb, err = Open(dbPath, OptionDryRunMigration(true))
+	if err != nil {
+		t.Fatalf("unable to create channeldb: %v", err)
+	}
+	if err := cdb.Close(); err != nil {
+		t.Fatalf("unable to close channeldb: %v", err)
+	}
 }
 
 // TestWipe tests that the database wipe operation completes successfully

channeldb/meta_test.go

@@ -12,13 +12,14 @@ import (
 // applyMigration is a helper test function that encapsulates the general steps
 // which are needed to properly check the result of applying migration function.
 func applyMigration(t *testing.T, beforeMigration, afterMigration func(d *DB),
-	migrationFunc migration, shouldFail bool) {
+	migrationFunc migration, shouldFail bool, dryRun bool) {
 
 	cdb, cleanUp, err := makeTestDB()
 	defer cleanUp()
 	if err != nil {
 		t.Fatal(err)
 	}
+	cdb.dryRun = dryRun
 
 	// Create a test node that will be our source node.
 	testNode, err := createTestVertex(cdb)
@@ -54,6 +55,9 @@ func applyMigration(t *testing.T, beforeMigration, afterMigration func(d *DB),
 
 	defer func() {
 		if r := recover(); r != nil {
+			if dryRun && r != ErrDryRunMigrationOK {
+				t.Fatalf("expected dry run migration OK")
+			}
 			err = errors.New(r)
 		}
 
@@ -256,7 +260,8 @@ func TestMigrationWithPanic(t *testing.T) {
 		beforeMigrationFunc,
 		afterMigrationFunc,
 		migrationWithPanic,
-		true)
+		true,
+		false)
 }
 
 // TestMigrationWithFatal asserts that migrations which fail do not modify the
@@ -330,7 +335,8 @@ func TestMigrationWithFatal(t *testing.T) {
 		beforeMigrationFunc,
 		afterMigrationFunc,
 		migrationWithFatal,
-		true)
+		true,
+		false)
 }
 
 // TestMigrationWithoutErrors asserts that a successful migration has its
@@ -404,6 +410,7 @@ func TestMigrationWithoutErrors(t *testing.T) {
 		beforeMigrationFunc,
 		afterMigrationFunc,
 		migrationWithoutErrors,
+		false,
 		false)
 }
 
@@ -446,3 +453,38 @@ func TestMigrationReversion(t *testing.T) {
 			"want: %v, got: %v", ErrDBReversion, err)
 	}
 }
+
+// TestMigrationDryRun ensures that opening the database in dry run migration
+// mode will fail and not commit the migration.
+func TestMigrationDryRun(t *testing.T) {
+	t.Parallel()
+
+	// Nothing to do, will inspect version number.
+	beforeMigrationFunc := func(d *DB) {}
+
+	// Check that version of database version is not modified.
+	afterMigrationFunc := func(d *DB) {
+		err := kvdb.View(d, func(tx kvdb.ReadTx) error {
+			meta, err := d.FetchMeta(nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if meta.DbVersionNumber != 0 {
+				t.Fatal("dry run migration was not aborted")
+			}
+
+			return nil
+		})
+		if err != nil {
+			t.Fatalf("unable to apply after func: %v", err)
+		}
+	}
+
+	applyMigration(t,
+		beforeMigrationFunc,
+		afterMigrationFunc,
+		func(kvdb.RwTx) error { return nil },
+		true,
+		true)
+}

channeldb/options.go

@@ -31,6 +31,10 @@ type Options struct {
 
 	// clock is the time source used by the database.
 	clock clock.Clock
+
+	// dryRun will fail to commit a successful migration when opening the
+	// database if set to true.
+	dryRun bool
 }
 
 // DefaultOptions returns an Options populated with default values.
@@ -73,3 +77,11 @@ func OptionClock(clock clock.Clock) OptionModifier {
 		o.clock = clock
 	}
 }
+
+// OptionDryRunMigration controls whether or not to intentially fail to commit a
+// successful migration that occurs when opening the database.
+func OptionDryRunMigration(dryRun bool) OptionModifier {
+	return func(o *Options) {
+		o.dryRun = dryRun
+	}
+}

config.go

@@ -340,6 +340,8 @@ type config struct {
 
 	MaxChannelFeeAllocation float64 `long:"max-channel-fee-allocation" description:"The maximum percentage of total funds that can be allocated to a channel's commitment fee. This only applies for the initiator of the channel. Valid values are within [0.1, 1]."`
 
+	DryRunMigration bool `long:"dry-run-migration" description:"If true, lnd will abort committing a migration if it would otherwise have been successful. This leaves the database unmodified, and still compatible with the previously active version of lnd."`
+
 	net tor.Net
 
 	EnableUpfrontShutdown bool `long:"enable-upfront-shutdown" description:"If true, option upfront shutdown script will be enabled. If peers that we open channels with support this feature, we will automatically set the script to which cooperative closes should be paid out to on channel open. This offers the partial protection of a channel peer disconnecting from us if cooperative close is attempted with a different script."`

lnd.go

@@ -235,10 +235,15 @@ func Main(lisCfg ListenerCfg) error {
 		channeldb.OptionSetRejectCacheSize(cfg.Caches.RejectCacheSize),
 		channeldb.OptionSetChannelCacheSize(cfg.Caches.ChannelCacheSize),
 		channeldb.OptionSetSyncFreelist(cfg.SyncFreelist),
+		channeldb.OptionDryRunMigration(cfg.DryRunMigration),
 	)
-	if err != nil {
-		err := fmt.Errorf("unable to open channeldb: %v", err)
-		ltndLog.Error(err)
+	switch {
+	case err == channeldb.ErrDryRunMigrationOK:
+		ltndLog.Info("%v, exiting", err)
+		return nil
+
+	case err != nil:
+		ltndLog.Errorf("Unable to open channeldb: %v", err)
 		return err
 	}
 	defer chanDB.Close()