import: Add option to skip creating digest image

Signed-off-by: Kohei Tokunaga <ktokunaga.mail@gmail.com>

import.go

@@ -34,6 +34,7 @@ type importOpts struct {
 	indexName    string
 	imageRefT    func(string) string
 	dgstRefT     func(digest.Digest) string
+	skipDgstRef  func(string) bool
 	allPlatforms bool
 	compress     bool
 }
@@ -59,6 +60,17 @@ func WithDigestRef(f func(digest.Digest) string) ImportOpt {
 	}
 }
 
+// WithSkipDigestRef is used to specify when to skip applying
+// WithDigestRef. The callback receives an image reference (or an empty
+// string if not specified in the image). When the callback returns true,
+// the skip occurs.
+func WithSkipDigestRef(f func(string) bool) ImportOpt {
+	return func(c *importOpts) error {
+		c.skipDgstRef = f
+		return nil
+	}
+}
+
 // WithIndexName creates a tag pointing to the imported index
 func WithIndexName(name string) ImportOpt {
 	return func(c *importOpts) error {
@@ -152,6 +164,11 @@ func (c *Client) Import(ctx context.Context, reader io.Reader, opts ...ImportOpt
 					Target: m,
 				})
 			}
+			if iopts.skipDgstRef != nil {
+				if iopts.skipDgstRef(name) {
+					continue
+				}
+			}
 			if iopts.dgstRefT != nil {
 				ref := iopts.dgstRefT(m.Digest)
 				if ref != "" {