update local targets and root metadata before adding delegation

Signed-off-by: Marina Moore <mnm678@gmail.com>

tuf-notary/cmd/delegate.go

@@ -45,10 +45,17 @@ func cmdDelegate(args []string, opts docopt.Opts) error {
 	registry := args[0]
 	delegatee := args[1]
 
-	//TODO: pull current targets metadata from the registry
+	err := tufnotary.DownloadTUFMetadata(registry, repository, "root")
+	if err != nil {
+		return err
+	}
+	err = tufnotary.DownloadTUFMetadata(registry, repository, "targets")
+	if err != nil {
+		return err
+	}
 
 	//add delegation
-	err := tufnotary.Delegate(repository, delegatee, keyfiles, threshold)
+	err = tufnotary.Delegate(repository, delegatee, keyfiles, threshold)
 
 	if err != nil {
 		return err

tuf-notary/registry-access.go

@@ -53,3 +53,21 @@ func UploadTUFMetadata(registry string, repository string, name string, referenc
 
 	return desc, nil
 }
+
+func DownloadTUFMetadata(registry string, repository string, name string) error {
+	ref := registry + "/" + repository + ":" + name
+
+	mediaType := "application/vnd.cncf.notary.tuf+json"
+	ctx := context.Background()
+
+	reg, err := content.NewRegistry(content.RegistryOptions{PlainHTTP: true})
+	if err != nil {
+		return err
+	}
+
+	fileStore := content.NewFile("")
+	defer fileStore.Close()
+	allowedMediaTypes := []string{mediaType}
+	desc, err := oras.Copy(ctx, reg, ref, fileStore, "", oras.WithAllowedMediaTypes(allowedMediaTypes))
+	return err
+}