Add --tarball to crane digest (#896)

If specified, tag can be omitted for single-image tarballs.

cmd/crane/cmd/digest.go

@@ -24,16 +24,51 @@ 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...)
+		Args:  cobra.MaximumNArgs(1),
+		Run: func(cmd *cobra.Command, args []string) {
+			if tarball == "" && len(args) == 0 {
+				cmd.Help()
+				log.Fatalf("image reference required without --tarball")
+			}
+
+			digest, err := getDigest(tarball, args, options)
 			if err != nil {
-				log.Fatalf("computing digest: %v", err)
+				log.Fatal(err)
 			}
 			fmt.Println(digest)
 		},
 	}
+
+	cmd.Flags().StringVar(&tarball, "tarball", "", "(Optional) path to tarball containing the image")
+
+	return cmd
+}
+
+func getDigest(tarball string, args []string, options *[]crane.Option) (string, error) {
+	if tarball != "" {
+		return getTarballDigest(tarball, args, options)
+	}
+
+	return crane.Digest(args[0], *options...)
+}
+
+func getTarballDigest(tarball string, args []string, options *[]crane.Option) (string, error) {
+	tag := ""
+	if len(args) > 0 {
+		tag = args[0]
+	}
+
+	img, err := crane.LoadTag(tarball, tag, *options...)
+	if err != nil {
+		return "", fmt.Errorf("loading image from %q: %v", tarball, err)
+	}
+	digest, err := img.Digest()
+	if err != nil {
+		return "", fmt.Errorf("computing digest: %v", err)
+	}
+	return digest.String(), nil
 }

pkg/crane/crane_test.go

@@ -558,6 +558,8 @@ func TestBadInputs(t *testing.T) {
 		{"Catalog(invalid)", e(crane.Catalog(invalid))},
 		{"Catalog(404)", e(crane.Catalog(u.Host))},
 		{"PullLayer(invalid)", e(crane.PullLayer(invalid))},
+		{"LoadTag(_, invalid)", e(crane.LoadTag("", invalid))},
+		{"LoadTag(invalid, 404)", e(crane.LoadTag(invalid, valid404))},
 	} {
 		if tc.err == nil {
 			t.Errorf("%s: expected err, got nil", tc.desc)

pkg/crane/push.go

@@ -24,9 +24,23 @@ import (
 )
 
 // Load reads the tarball at path as a v1.Image.
-func Load(path string) (v1.Image, error) {
-	// TODO: Allow tag?
-	return tarball.ImageFromPath(path, nil)
+func Load(path string, opt ...Option) (v1.Image, error) {
+	return LoadTag(path, "")
+}
+
+// LoadTag reads a tag from the tarball at path as a v1.Image.
+// If tag is "", will attempt to read the tarball as a single image.
+func LoadTag(path, tag string, opt ...Option) (v1.Image, error) {
+	if tag == "" {
+		return tarball.ImageFromPath(path, nil)
+	}
+
+	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.