a bit refactoring to prepare for volume format change and backward

compatibility.

3 files changed, 68 insertions, 57 deletions

diff --git a/go/storage/volume.go b/go/storage/volume.go
index 7bd8e7467..dec560545 100644
--- a/go/storage/volume.go
+++ b/go/storage/volume.go
@@ -12,22 +12,6 @@ import (
 	"time"
 )
 
-const (
-	SuperBlockSize = 8
-)
-
-type SuperBlock struct {
-	Version          Version
-	ReplicaPlacement *ReplicaPlacement
-}
-
-func (s *SuperBlock) Bytes() []byte {
-	header := make([]byte, SuperBlockSize)
-	header[0] = byte(s.Version)
-	header[1] = s.ReplicaPlacement.Byte()
-	return header
-}
-
 type Volume struct {
 	Id         VolumeId
 	dir        string
@@ -122,7 +106,7 @@ func (v *Volume) load(alsoLoadIndex bool, createDatIfMissing bool) error {
 	return e
 }
 func (v *Volume) Version() Version {
-	return v.SuperBlock.Version
+	return v.SuperBlock.Version()
 }
 func (v *Volume) Size() int64 {
 	stat, e := v.dataFile.Stat()
@@ -138,44 +122,6 @@ func (v *Volume) Close() {
 	v.nm.Close()
 	_ = v.dataFile.Close()
 }
-func (v *Volume) maybeWriteSuperBlock() error {
-	stat, e := v.dataFile.Stat()
-	if e != nil {
-		glog.V(0).Infof("failed to stat datafile %s: %s", v.dataFile, e.Error())
-		return e
-	}
-	if stat.Size() == 0 {
-		v.SuperBlock.Version = CurrentVersion
-		_, e = v.dataFile.Write(v.SuperBlock.Bytes())
-		if e != nil && os.IsPermission(e) {
-			//read-only, but zero length - recreate it!
-			if v.dataFile, e = os.Create(v.dataFile.Name()); e == nil {
-				if _, e = v.dataFile.Write(v.SuperBlock.Bytes()); e == nil {
-					v.readOnly = false
-				}
-			}
-		}
-	}
-	return e
-}
-func (v *Volume) readSuperBlock() (err error) {
-	if _, err = v.dataFile.Seek(0, 0); err != nil {
-		return fmt.Errorf("cannot seek to the beginning of %s: %s", v.dataFile.Name(), err.Error())
-	}
-	header := make([]byte, SuperBlockSize)
-	if _, e := v.dataFile.Read(header); e != nil {
-		return fmt.Errorf("cannot read superblock: %s", e.Error())
-	}
-	v.SuperBlock, err = ParseSuperBlock(header)
-	return err
-}
-func ParseSuperBlock(header []byte) (superBlock SuperBlock, err error) {
-	superBlock.Version = Version(header[0])
-	if superBlock.ReplicaPlacement, err = NewReplicaPlacementFromByte(header[1]); err != nil {
-		err = fmt.Errorf("cannot read replica type: %s", err.Error())
-	}
-	return
-}
 func (v *Volume) NeedToReplicate() bool {
 	return v.ReplicaPlacement.GetCopyCount() > 1
 }
diff --git a/go/storage/volume_super_block.go b/go/storage/volume_super_block.go
new file mode 100644
index 000000000..95f7c30bb
--- /dev/null
+++ b/go/storage/volume_super_block.go
@@ -0,0 +1,65 @@
+package storage
+
+import (
+	"code.google.com/p/weed-fs/go/glog"
+	"fmt"
+	"os"
+)
+
+const (
+	SuperBlockSize = 8
+)
+
+type SuperBlock struct {
+	version          Version
+	ReplicaPlacement *ReplicaPlacement
+}
+
+func (s *SuperBlock) Version() Version {
+	return s.version
+}
+func (s *SuperBlock) Bytes() []byte {
+	header := make([]byte, SuperBlockSize)
+	header[0] = byte(s.version)
+	header[1] = s.ReplicaPlacement.Byte()
+	return header
+}
+
+func (v *Volume) maybeWriteSuperBlock() error {
+	stat, e := v.dataFile.Stat()
+	if e != nil {
+		glog.V(0).Infof("failed to stat datafile %s: %s", v.dataFile, e.Error())
+		return e
+	}
+	if stat.Size() == 0 {
+		v.SuperBlock.version = CurrentVersion
+		_, e = v.dataFile.Write(v.SuperBlock.Bytes())
+		if e != nil && os.IsPermission(e) {
+			//read-only, but zero length - recreate it!
+			if v.dataFile, e = os.Create(v.dataFile.Name()); e == nil {
+				if _, e = v.dataFile.Write(v.SuperBlock.Bytes()); e == nil {
+					v.readOnly = false
+				}
+			}
+		}
+	}
+	return e
+}
+func (v *Volume) readSuperBlock() (err error) {
+	if _, err = v.dataFile.Seek(0, 0); err != nil {
+		return fmt.Errorf("cannot seek to the beginning of %s: %s", v.dataFile.Name(), err.Error())
+	}
+	header := make([]byte, SuperBlockSize)
+	if _, e := v.dataFile.Read(header); e != nil {
+		return fmt.Errorf("cannot read superblock: %s", e.Error())
+	}
+	v.SuperBlock, err = ParseSuperBlock(header)
+	return err
+}
+func ParseSuperBlock(header []byte) (superBlock SuperBlock, err error) {
+	superBlock.version = Version(header[0])
+	if superBlock.ReplicaPlacement, err = NewReplicaPlacementFromByte(header[1]); err != nil {
+		err = fmt.Errorf("cannot read replica type: %s", err.Error())
+	}
+	return
+}
diff --git a/go/weed/export.go b/go/weed/export.go
index 3f8ff85bb..f79ab1a5f 100644
--- a/go/weed/export.go
+++ b/go/weed/export.go
@@ -27,7 +27,7 @@ var cmdExport = &Command{
 	UsageLine: "export -dir=/tmp -volumeId=234 -o=/dir/name.tar -fileNameFormat={{.Name}}",
 	Short:     "list or export files from one volume data file",
 	Long: `List all files in a volume, or Export all files in a volume to a tar file if the output is specified.
-	
+
 	The format of file name in the tar file can be customized. Default is {{.Mime}}/{{.Id}}:{{.Name}}. Also available is {{.Key}}.
 
   `,
@@ -100,7 +100,7 @@ func runExport(cmd *Command, args []string) bool {
 	var version storage.Version
 
 	err = storage.ScanVolumeFile(*exportVolumePath, *exportCollection, vid, func(superBlock storage.SuperBlock) error {
-		version = superBlock.Version
+		version = superBlock.Version()
 		return nil
 	}, true, func(n *storage.Needle, offset int64) error {
 		nv, ok := nm.Get(n.Id)