chanbackup: archive old channel backups

chanbackup/backupfile.go

@@ -2,8 +2,10 @@ package chanbackup
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"path/filepath"
+	"time"
 
 	"github.com/lightningnetwork/lnd/keychain"
 )
@@ -17,6 +19,10 @@ const (
 	// file that we'll use to atomically update the primary back up file
 	// when new channel are detected.
 	DefaultTempBackupFileName = "temp-dont-use.backup"
+
+	// DefaultChanBackupDirName is the default name of the directory that
+	// we'll use to store old channel backups.
+	DefaultChanBackupArchiveDirName = "channelarchives"
 )
 
 var (
@@ -44,22 +50,33 @@ type MultiFile struct {
 
 	// tempFile is an open handle to the temp back up file.
 	tempFile *os.File
+
+	// archiveDir is the directory where we'll store old channel backups.
+	archiveDir string
+
+	// deleteOldBackup indicates whether old backups should be deleted
+	// rather than archived.
+	deleteOldBackup bool
 }
 
 // NewMultiFile create a new multi-file instance at the target location on the
 // file system.
-func NewMultiFile(fileName string) *MultiFile {
-
+func NewMultiFile(fileName string, deleteOldBackup bool) *MultiFile {
 	// We'll our temporary backup file in the very same directory as the
 	// main backup file.
 	backupFileDir := filepath.Dir(fileName)
 	tempFileName := filepath.Join(
 		backupFileDir, DefaultTempBackupFileName,
 	)
+	archiveDir := filepath.Join(
+		backupFileDir, DefaultChanBackupArchiveDirName,
+	)
 
 	return &MultiFile{
-		fileName:     fileName,
-		tempFileName: tempFileName,
+		fileName:        fileName,
+		tempFileName:    tempFileName,
+		archiveDir:      archiveDir,
+		deleteOldBackup: deleteOldBackup,
 	}
 }
 
@@ -117,6 +134,21 @@ func (b *MultiFile) UpdateAndSwap(newBackup PackedMulti) error {
 		return fmt.Errorf("unable to close file: %w", err)
 	}
 
+	if !b.deleteOldBackup {
+		// We check if the main backup file exists, if it does we
+		// archive it before replacing it with the new backup.
+		if _, err := os.Stat(b.fileName); err == nil {
+			log.Infof("Archiving old backup file at %v", b.fileName)
+
+			if err := createArchiveFile(
+				b.archiveDir, b.fileName,
+			); err != nil {
+				return fmt.Errorf("unable to archive old "+
+					"backup file: %w", err)
+			}
+		}
+	}
+
 	// Finally, we'll attempt to atomically rename the temporary file to
 	// the main back up file. If this succeeds, then we'll only have a
 	// single file on disk once this method exits.
@@ -147,3 +179,48 @@ func (b *MultiFile) ExtractMulti(keyChain keychain.KeyRing) (*Multi, error) {
 	packedMulti := PackedMulti(multiBytes)
 	return packedMulti.Unpack(keyChain)
 }
+
+func createArchiveFile(archiveDir string, fileName string) error {
+	// Generate archive file path with timestamped name.
+	baseFileName := filepath.Base(fileName)
+	timestamp := time.Now().Format("2006-01-02-15-04-05")
+
+	archiveFileName := fmt.Sprintf("%s-%s", baseFileName, timestamp)
+	archiveFilePath := filepath.Join(archiveDir, archiveFileName)
+
+	oldBackupFile, err := os.Open(fileName)
+	if err != nil {
+		return fmt.Errorf("unable to open old backup file: %w", err)
+	}
+	defer func() {
+		if cerr := oldBackupFile.Close(); cerr != nil && err == nil {
+			err = fmt.Errorf("error closing old backup file: %w",
+				cerr)
+		}
+	}()
+
+	// Ensure the archive directory exists. If it doesn't we create it.
+	const archiveDirPermissions = 0o755
+	err = os.MkdirAll(archiveDir, archiveDirPermissions)
+	if err != nil {
+		return fmt.Errorf("unable to create archive directory: %w", err)
+	}
+
+	// Create new archive file.
+	archiveFile, err := os.Create(archiveFilePath)
+	if err != nil {
+		return fmt.Errorf("unable to create archive file: %w", err)
+	}
+	defer func() {
+		if cerr := archiveFile.Close(); cerr != nil && err == nil {
+			err = fmt.Errorf("error closing archive file: %w", cerr)
+		}
+	}()
+
+	// Copy contents of old backup to the newly created archive file.
+	if _, err := io.Copy(archiveFile, oldBackupFile); err != nil {
+		return fmt.Errorf("error copying to archive file: %w", err)
+	}
+
+	return nil
+}

chanbackup/backupfile_test.go

@@ -94,7 +94,7 @@ func TestUpdateAndSwap(t *testing.T) {
 		},
 	}
 	for i, testCase := range testCases {
-		backupFile := NewMultiFile(testCase.fileName)
+		backupFile := NewMultiFile(testCase.fileName, false)
 
 		// To start with, we'll make a random byte slice that'll pose
 		// as our packed multi backup.
@@ -238,7 +238,7 @@ func TestExtractMulti(t *testing.T) {
 	}
 	for i, testCase := range testCases {
 		// First, we'll make our backup file with the specified name.
-		backupFile := NewMultiFile(testCase.fileName)
+		backupFile := NewMultiFile(testCase.fileName, false)
 
 		// With our file made, we'll now attempt to read out the
 		// multi-file.

config.go

@@ -247,6 +247,12 @@ const (
 	bitcoindBackendName = "bitcoind"
 	btcdBackendName     = "btcd"
 	neutrinoBackendName = "neutrino"
+
+	// defaultDisableBackupArchive indicates whether to disable archiving of
+	// channel backups. When false (default), old backups are archived to a
+	// designated location. When true, old backups are simply deleted or
+	// replaced.
+	defaultDisableBackupArchive = false
 )
 
 var (
@@ -364,6 +370,8 @@ type Config struct {
 	MaxPendingChannels int    `long:"maxpendingchannels" description:"The maximum number of incoming pending channels permitted per peer."`
 	BackupFilePath     string `long:"backupfilepath" description:"The target location of the channel backup file"`
 
+	DisableBackupArchive bool `long:"disable-backup-archive" description:"If set to true, channel backups will be deleted or replaced rather than being archived to a separate location."`
+
 	FeeURL string `long:"feeurl" description:"DEPRECATED: Use 'fee.url' option. Optional URL for external fee estimation. If no URL is specified, the method for fee estimation will depend on the chosen backend and network. Must be set for neutrino on mainnet." hidden:"true"`
 
 	Bitcoin      *lncfg.Chain    `group:"Bitcoin" namespace:"bitcoin"`
@@ -738,9 +746,10 @@ func DefaultConfig() Config {
 			ServerPingTimeout: defaultGrpcServerPingTimeout,
 			ClientPingMinWait: defaultGrpcClientPingMinWait,
 		},
-		LogConfig:         build.DefaultLogConfig(),
-		WtClient:          lncfg.DefaultWtClientCfg(),
-		HTTPHeaderTimeout: DefaultHTTPHeaderTimeout,
+		LogConfig:            build.DefaultLogConfig(),
+		WtClient:             lncfg.DefaultWtClientCfg(),
+		HTTPHeaderTimeout:    DefaultHTTPHeaderTimeout,
+		DisableBackupArchive: defaultDisableBackupArchive,
 	}
 }
 

sample-lnd.conf

@@ -309,6 +309,10 @@
 ; Example:
 ;   backupfilepath=~/.lnd/data/chain/bitcoin/mainnet/channel.backup
 
+; When false (default), old channel backups are archived to a designated location.
+; When true, old backups are simply deleted or replaced.
+; disable-backup-archive=true
+
 ; The maximum capacity of the block cache in bytes. Increasing this will result
 ; in more blocks being kept in memory but will increase performance when the
 ; same block is required multiple times.

server.go

@@ -1595,7 +1595,9 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		chanNotifier: s.channelNotifier,
 		addrs:        dbs.ChanStateDB,
 	}
-	backupFile := chanbackup.NewMultiFile(cfg.BackupFilePath)
+	backupFile := chanbackup.NewMultiFile(
+		cfg.BackupFilePath, cfg.DisableBackupArchive,
+	)
 	startingChans, err := chanbackup.FetchStaticChanBackups(
 		s.chanStateDB, s.addrSource,
 	)