tier storage: support downloading the remote dat files

weed/storage/backend/s3_backend/s3_backend.go

@@ -9,10 +9,11 @@ import (
 
 	"github.com/aws/aws-sdk-go/service/s3"
 	"github.com/aws/aws-sdk-go/service/s3/s3iface"
+	"github.com/google/uuid"
+
 	"github.com/chrislusf/seaweedfs/weed/glog"
 	"github.com/chrislusf/seaweedfs/weed/pb/volume_server_pb"
 	"github.com/chrislusf/seaweedfs/weed/storage/backend"
-	"github.com/google/uuid"
 )
 
 func init() {
@@ -85,6 +86,24 @@ func (s *S3BackendStorage) CopyFile(f *os.File, fn func(progressed int64, percen
 	return
 }
 
+func (s *S3BackendStorage) DownloadFile(fileName string, key string, fn func(progressed int64, percentage float32) error) (size int64, err error) {
+
+	glog.V(1).Infof("download dat file of %s from remote s3.%s as %s", fileName, s.id, key)
+
+	size, err = downloadFromS3(s.conn, fileName, s.bucket, key, fn)
+
+	return
+}
+
+func (s *S3BackendStorage) DeleteFile(key string) (err error) {
+
+	glog.V(1).Infof("delete dat file %s from remote", key)
+
+	err = deleteFromS3(s.conn, s.bucket, key)
+
+	return
+}
+
 type S3BackendStorageFile struct {
 	backendStorage *S3BackendStorage
 	key            string