added metadata helper tool

pkg/fs/metadata.go

@@ -11,12 +11,14 @@ import (
 	"math"
 	"os"
 	"path/filepath"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
 
 	"github.com/go-logr/logr"
 	"golang.org/x/exp/maps"
+	"golang.org/x/sys/unix"
 )
 
 func now() int64 {
@@ -33,6 +35,58 @@ type MetadataHandler struct {
 	enc *json.Encoder
 }
 
+func MetadataGenerator(file, dst string) error {
+	if !filepath.IsAbs(file) {
+		return errors.New("metadata path is not absolute")
+	}
+	if !filepath.IsAbs(dst) {
+		return errors.New("dst path is not absolute")
+	}
+	f, err := os.OpenFile(file, os.O_RDWR|os.O_CREATE, 0o640)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	err = f.Truncate(0)
+	if err != nil {
+		return err
+	}
+	enc := json.NewEncoder(f)
+	md := make(map[string]*Metadata)
+	filepath.WalkDir(dst, func(path string, d stdfs.DirEntry, err error) error {
+		if err != nil {
+			return nil
+		}
+		if d.IsDir() {
+			return nil
+		}
+		var stat unix.Stat_t
+
+		f, err := os.Open(path)
+		if err != nil {
+			return nil
+		}
+		defer f.Close()
+		fi, err := f.Stat()
+		if err != nil {
+			return nil
+		}
+		size := fi.Size()
+		err = unix.Fstat(int(f.Fd()), &stat)
+		if err != nil {
+			return nil
+		}
+		if size <= stat.Blocks*512 {
+			md[strings.TrimPrefix(path, dst)] = &Metadata{
+				Size:   size,
+				Chunks: Chunks{{0, size}},
+			}
+		}
+		return nil
+	})
+	return enc.Encode(md)
+}
+
 func NewMetadataHandler(ctx context.Context, fs *FS, file, dst string, log logr.Logger) (mh *MetadataHandler, err error) {
 	if !filepath.IsAbs(file) {
 		return nil, errors.New("metadata path is not absolute")
@@ -216,6 +270,7 @@ func (mh *MetadataHandler) close() {
 	mh.mu.Unlock()
 	mh.flush()
 	mh.f.Close()
+	close(mh.fs.done)
 }
 
 type Metadata struct {