backup: implement --skip-if-unchanged

cmd/restic/cmd_backup.go

@@ -87,6 +87,7 @@ type BackupOptions struct {
 	DryRun            bool
 	ReadConcurrency   uint
 	NoScan            bool
+	SkipIfUnchanged   bool
 }
 
 var backupOptions BackupOptions
@@ -133,6 +134,7 @@ func init() {
 	if runtime.GOOS == "windows" {
 		f.BoolVar(&backupOptions.UseFsSnapshot, "use-fs-snapshot", false, "use filesystem snapshot where possible (currently only Windows VSS)")
 	}
+	f.BoolVar(&backupOptions.SkipIfUnchanged, "skip-if-unchanged", false, "skip snapshot creation if identical to parent snapshot")
 
 	// parse read concurrency from env, on error the default value will be used
 	readConcurrency, _ := strconv.ParseUint(os.Getenv("RESTIC_READ_CONCURRENCY"), 10, 32)
@@ -638,13 +640,14 @@ func runBackup(ctx context.Context, opts BackupOptions, gopts GlobalOptions, ter
 	}
 
 	snapshotOpts := archiver.SnapshotOptions{
-		Excludes:       opts.Excludes,
-		Tags:           opts.Tags.Flatten(),
-		BackupStart:    backupStart,
-		Time:           timeStamp,
-		Hostname:       opts.Host,
-		ParentSnapshot: parentSnapshot,
-		ProgramVersion: "restic " + version,
+		Excludes:        opts.Excludes,
+		Tags:            opts.Tags.Flatten(),
+		BackupStart:     backupStart,
+		Time:            timeStamp,
+		Hostname:        opts.Host,
+		ParentSnapshot:  parentSnapshot,
+		ProgramVersion:  "restic " + version,
+		SkipIfUnchanged: opts.SkipIfUnchanged,
 	}
 
 	if !gopts.JSON {
@@ -665,9 +668,6 @@ func runBackup(ctx context.Context, opts BackupOptions, gopts GlobalOptions, ter
 
 	// Report finished execution
 	progressReporter.Finish(id, summary, opts.DryRun)
-	if !gopts.JSON && !opts.DryRun {
-		progressPrinter.P("snapshot %s saved\n", id.Str())
-	}
 	if !success {
 		return ErrInvalidSourceData
 	}

cmd/restic/cmd_backup_integration_test.go

@@ -641,3 +641,18 @@ func TestBackupEmptyPassword(t *testing.T) {
 	testListSnapshots(t, env.gopts, 1)
 	testRunCheck(t, env.gopts)
 }
+
+func TestBackupSkipIfUnchanged(t *testing.T) {
+	env, cleanup := withTestEnvironment(t)
+	defer cleanup()
+
+	testSetupBackupData(t, env)
+	opts := BackupOptions{SkipIfUnchanged: true}
+
+	for i := 0; i < 3; i++ {
+		testRunBackup(t, filepath.Dir(env.testdata), []string{"testdata"}, opts, env.gopts)
+		testListSnapshots(t, env.gopts, 1)
+	}
+
+	testRunCheck(t, env.gopts)
+}

doc/075_scripting.rst

@@ -173,7 +173,8 @@ Summary is the last output line in a successful backup.
 +---------------------------+---------------------------------------------------------+
 | ``total_duration``        | Total time it took for the operation to complete        |
 +---------------------------+---------------------------------------------------------+
-| ``snapshot_id``           | ID of the new snapshot                                  |
+| ``snapshot_id``           | ID of the new snapshot. Field is omitted if snapshot    |
+|                           | creation was skipped                                    |
 +---------------------------+---------------------------------------------------------+
 
 

internal/archiver/archiver.go

@@ -767,6 +767,8 @@ type SnapshotOptions struct {
 	Time           time.Time
 	ParentSnapshot *restic.Snapshot
 	ProgramVersion string
+	// SkipIfUnchanged omits the snapshot creation if it is identical to the parent snapshot.
+	SkipIfUnchanged bool
 }
 
 // loadParentTree loads a tree referenced by snapshot id. If id is null, nil is returned.
@@ -880,6 +882,13 @@ func (arch *Archiver) Snapshot(ctx context.Context, targets []string, opts Snaps
 		return nil, restic.ID{}, nil, err
 	}
 
+	if opts.ParentSnapshot != nil && opts.SkipIfUnchanged {
+		ps := opts.ParentSnapshot
+		if ps.Tree != nil && rootTreeID.Equal(*ps.Tree) {
+			return nil, restic.ID{}, arch.summary, nil
+		}
+	}
+
 	sn, err := restic.NewSnapshot(targets, opts.Tags, opts.Hostname, opts.Time)
 	if err != nil {
 		return nil, restic.ID{}, nil, err

internal/ui/backup/json.go

@@ -164,6 +164,11 @@ func (b *JSONProgress) ReportTotal(start time.Time, s archiver.ScanStats) {
 
 // Finish prints the finishing messages.
 func (b *JSONProgress) Finish(snapshotID restic.ID, start time.Time, summary *archiver.Summary, dryRun bool) {
+	id := ""
+	// empty if snapshot creation was skipped
+	if !snapshotID.IsNull() {
+		id = snapshotID.String()
+	}
 	b.print(summaryOutput{
 		MessageType:         "summary",
 		FilesNew:            summary.Files.New,
@@ -179,7 +184,7 @@ func (b *JSONProgress) Finish(snapshotID restic.ID, start time.Time, summary *ar
 		TotalFilesProcessed: summary.Files.New + summary.Files.Changed + summary.Files.Unchanged,
 		TotalBytesProcessed: summary.ProcessedBytes,
 		TotalDuration:       time.Since(start).Seconds(),
-		SnapshotID:          snapshotID.String(),
+		SnapshotID:          id,
 		DryRun:              dryRun,
 	})
 }
@@ -235,6 +240,6 @@ type summaryOutput struct {
 	TotalFilesProcessed uint    `json:"total_files_processed"`
 	TotalBytesProcessed uint64  `json:"total_bytes_processed"`
 	TotalDuration       float64 `json:"total_duration"` // in seconds
-	SnapshotID          string  `json:"snapshot_id"`
+	SnapshotID          string  `json:"snapshot_id,omitempty"`
 	DryRun              bool    `json:"dry_run,omitempty"`
 }

internal/ui/backup/text.go

@@ -126,7 +126,7 @@ func (b *TextProgress) Reset() {
 }
 
 // Finish prints the finishing messages.
-func (b *TextProgress) Finish(_ restic.ID, start time.Time, summary *archiver.Summary, dryRun bool) {
+func (b *TextProgress) Finish(id restic.ID, start time.Time, summary *archiver.Summary, dryRun bool) {
 	b.P("\n")
 	b.P("Files:       %5d new, %5d changed, %5d unmodified\n", summary.Files.New, summary.Files.Changed, summary.Files.Unchanged)
 	b.P("Dirs:        %5d new, %5d changed, %5d unmodified\n", summary.Dirs.New, summary.Dirs.Changed, summary.Dirs.Unchanged)
@@ -145,4 +145,12 @@ func (b *TextProgress) Finish(_ restic.ID, start time.Time, summary *archiver.Su
 		ui.FormatBytes(summary.ProcessedBytes),
 		ui.FormatDuration(time.Since(start)),
 	)
+
+	if !dryRun {
+		if id.IsNull() {
+			b.P("skipped creating snapshot\n")
+		} else {
+			b.P("snapshot %s saved\n", id.Str())
+		}
+	}
 }