Add --tarball to crane digest

cmd/crane/cmd/digest.go

@@ -24,16 +24,33 @@ import (
 
 // NewCmdDigest creates a new cobra.Command for the digest subcommand.
 func NewCmdDigest(options *[]crane.Option) *cobra.Command {
-	return &cobra.Command{
+	var tarball string
+	cmd := &cobra.Command{
 		Use:   "digest IMAGE",
 		Short: "Get the digest of an image",
 		Args:  cobra.ExactArgs(1),
 		Run: func(_ *cobra.Command, args []string) {
-			digest, err := crane.Digest(args[0], *options...)
-			if err != nil {
-				log.Fatalf("computing digest: %v", err)
+			if tarball != "" {
+				img, err := crane.LoadTag(tarball, args[0], *options...)
+				if err != nil {
+					log.Fatalf("loading image %q from %q: %v", tarball, args[0], err)
+				}
+				digest, err := img.Digest()
+				if err != nil {
+					log.Fatalf("computing digest: %v", err)
+				}
+				fmt.Println(digest.String())
+			} else {
+				digest, err := crane.Digest(args[0], *options...)
+				if err != nil {
+					log.Fatalf("computing digest: %v", err)
+				}
+				fmt.Println(digest)
 			}
-			fmt.Println(digest)
 		},
 	}
+
+	cmd.Flags().StringVar(&tarball, "tarball", "", "(Optional) path to tarball containing the image")
+
+	return cmd
 }

pkg/crane/push.go

@@ -29,6 +29,16 @@ func Load(path string) (v1.Image, error) {
 	return tarball.ImageFromPath(path, nil)
 }
 
+// LoadTag reads a tag from the tarball at path as a v1.Image.
+func LoadTag(path, tag string, opt ...Option) (v1.Image, error) {
+	o := makeOptions(opt...)
+	t, err := name.NewTag(tag, o.name...)
+	if err != nil {
+		return nil, fmt.Errorf("parsing tag %q: %v", tag, err)
+	}
+	return tarball.ImageFromPath(path, &t)
+}
+
 // Push pushes the v1.Image img to a registry as dst.
 func Push(img v1.Image, dst string, opt ...Option) error {
 	o := makeOptions(opt...)