diff --git a/weed/operation/chunked_file.go b/weed/operation/chunked_file.go
index 4983245cc..b20c2551e 100644
--- a/weed/operation/chunked_file.go
+++ b/weed/operation/chunked_file.go
@@ -8,11 +8,10 @@ import (
 	"io/ioutil"
 	"net/http"
 	"sort"
+	"sync"
 
 	"google.golang.org/grpc"
 
-	"sync"
-
 	"github.com/chrislusf/seaweedfs/weed/glog"
 	"github.com/chrislusf/seaweedfs/weed/util"
 )
@@ -126,6 +125,13 @@ func readChunkNeedle(fileUrl string, w io.Writer, offset int64) (written int64,
 	return io.Copy(w, resp.Body)
 }
 
+func NewChunkedFileReader(chunkManifest *ChunkManifest, master string) *ChunkedFileReader {
+	return &ChunkedFileReader{
+		Manifest: chunkManifest,
+		Master:   master,
+	}
+}
+
 func (cf *ChunkedFileReader) Seek(offset int64, whence int) (int64, error) {
 	var err error
 	switch whence {
diff --git a/weed/server/volume_server_handlers_read.go b/weed/server/volume_server_handlers_read.go
index 6e603d158..c412062a6 100644
--- a/weed/server/volume_server_handlers_read.go
+++ b/weed/server/volume_server_handlers_read.go
@@ -187,10 +187,7 @@ func (vs *VolumeServer) tryHandleChunkedFile(n *needle.Needle, fileName string,
 
 	w.Header().Set("X-File-Store", "chunked")
 
-	chunkedFileReader := &operation.ChunkedFileReader{
-		Manifest: chunkManifest,
-		Master:   vs.GetMaster(),
-	}
+	chunkedFileReader := operation.NewChunkedFileReader(chunkManifest, vs.GetMaster())
 	defer chunkedFileReader.Close()
 
 	rs := conditionallyResizeImages(chunkedFileReader, ext, r)