Wrap lazyblob Reader call into a function (#305)

This would make it called only when needed by consumer but exactly
always when Reader is obtained so will make possible to reduce amount of
object downloads performed just to get its MIME type or calculate a
checksum.

Signed-off-by: Igor Shishkin <me@teran.ru>

cli/service/service.go

@@ -371,7 +371,12 @@ func (s *service) createObject(ctx context.Context, namespaceName, containerName
 			"url":    url,
 		}).Info("uploading BLOB ...")
 
-		if err := uploadBlob(ctx, url, object.Contents, object.Size); err != nil {
+		rd, err := object.Contents(ctx)
+		if err != nil {
+			return err
+		}
+
+		if err := uploadBlob(ctx, url, rd, object.Size); err != nil {
 			return err
 		}
 	}

cli/service/source/local/local.go

@@ -114,8 +114,10 @@ func (l *local) Process(ctx context.Context, handler func(ctx context.Context, o
 		defer fp.Close()
 
 		if err := handler(ctx, source.Object{
-			Path:     shortPath,
-			Contents: fp,
+			Path: shortPath,
+			Contents: func(ctx context.Context) (io.Reader, error) {
+				return fp, nil
+			},
 			SHA256:   checksum,
 			Size:     uint64(size),
 			MimeType: mimeType,

cli/service/source/source.go

@@ -7,7 +7,7 @@ import (
 
 type Object struct {
 	Path     string
-	Contents io.Reader
+	Contents func(ctx context.Context) (io.Reader, error)
 	SHA256   string
 	Size     uint64
 	MimeType string

cli/service/source/yum/yum.go

@@ -92,8 +92,10 @@ func (r *repository) Process(ctx context.Context, handler func(ctx context.Conte
 
 		log.Tracef("handler(%s, %s, %d)", k, checksum, size)
 		if err := handler(ctx, source.Object{
-			Path:     k,
-			Contents: bytes.NewReader(v),
+			Path: k,
+			Contents: func(ctx context.Context) (io.Reader, error) {
+				return bytes.NewReader(v), nil
+			},
 			SHA256:   checksum,
 			Size:     uint64(size),
 			MimeType: mimeType,
@@ -160,14 +162,9 @@ func (r *repository) Process(ctx context.Context, handler func(ctx context.Conte
 			}
 			mimeType := mimetype.Detect(data)
 
-			fp, err = lb.Reader(ctx)
-			if err != nil {
-				return errors.Wrap(err, "error getting object reader")
-			}
-
 			if err := handler(ctx, source.Object{
 				Path:     name,
-				Contents: fp,
+				Contents: lb.Reader,
 				SHA256:   checksum,
 				Size:     size,
 				MimeType: mimeType.String(),