shell: add ec.decode command

weed/storage/super_block/super_block_read.go.go

@@ -0,0 +1,44 @@
+package super_block
+
+import (
+	"fmt"
+
+	"github.com/golang/protobuf/proto"
+
+	"github.com/chrislusf/seaweedfs/weed/pb/master_pb"
+	"github.com/chrislusf/seaweedfs/weed/storage/backend"
+	"github.com/chrislusf/seaweedfs/weed/storage/needle"
+	"github.com/chrislusf/seaweedfs/weed/util"
+)
+
+// ReadSuperBlock reads from data file and load it into volume's super block
+func ReadSuperBlock(datBackend backend.BackendStorageFile) (superBlock SuperBlock, err error) {
+
+	header := make([]byte, SuperBlockSize)
+	if _, e := datBackend.ReadAt(header, 0); e != nil {
+		err = fmt.Errorf("cannot read volume %s super block: %v", datBackend.Name(), e)
+		return
+	}
+
+	superBlock.Version = needle.Version(header[0])
+	if superBlock.ReplicaPlacement, err = NewReplicaPlacementFromByte(header[1]); err != nil {
+		err = fmt.Errorf("cannot read replica type: %s", err.Error())
+		return
+	}
+	superBlock.Ttl = needle.LoadTTLFromBytes(header[2:4])
+	superBlock.CompactionRevision = util.BytesToUint16(header[4:6])
+	superBlock.ExtraSize = util.BytesToUint16(header[6:8])
+
+	if superBlock.ExtraSize > 0 {
+		// read more
+		extraData := make([]byte, int(superBlock.ExtraSize))
+		superBlock.Extra = &master_pb.SuperBlockExtra{}
+		err = proto.Unmarshal(extraData, superBlock.Extra)
+		if err != nil {
+			err = fmt.Errorf("cannot read volume %s super block extra: %v", datBackend.Name(), err)
+			return
+		}
+	}
+
+	return
+}