Get digest of multi-arch images

Fixes #4156

Signed-off-by: David Gageot <[email protected]>

Author: dgageot

pkg/skaffold/docker/remote.go

@@ -50,17 +50,17 @@ func AddRemoteTag(src, target string, insecureRegistries map[string]bool) error
 }
 
 func getRemoteDigest(identifier string, insecureRegistries map[string]bool) (string, error) {
-	img, err := remoteImage(identifier, insecureRegistries)
-	if err != nil {
-		return "", fmt.Errorf("getting image: %w", err)
+	idx, err := remoteIndex(identifier, insecureRegistries)
+	if err == nil {
+		return digest(idx)
 	}
 
-	h, err := img.Digest()
+	img, err := remoteImage(identifier, insecureRegistries)
 	if err != nil {
-		return "", fmt.Errorf("getting digest: %w", err)
+		return "", fmt.Errorf("getting image: %w", err)
 	}
 
-	return h.String(), nil
+	return digest(img)
 }
 
 // RetrieveRemoteConfig retrieves the remote config file for an image
@@ -101,6 +101,15 @@ func remoteImage(identifier string, insecureRegistries map[string]bool) (v1.Imag
 	return getRemoteImageImpl(ref)
 }
 
+func remoteIndex(identifier string, insecureRegistries map[string]bool) (v1.ImageIndex, error) {
+	ref, err := parseReference(identifier, insecureRegistries)
+	if err != nil {
+		return nil, err
+	}
+
+	return remote.Index(ref, remote.WithAuthFromKeychain(masterKeychain))
+}
+
 // IsInsecure tests if an image is pulled from an insecure registry; default is false
 func IsInsecure(ref name.Reference, insecureRegistries map[string]bool) bool {
 	return insecureRegistries[ref.Context().Registry.Name()]
@@ -125,3 +134,16 @@ func parseReference(s string, insecureRegistries map[string]bool, opts ...name.O
 
 	return ref, nil
 }
+
+type digester interface {
+	Digest() (v1.Hash, error)
+}
+
+func digest(d digester) (string, error) {
+	h, err := d.Digest()
+	if err != nil {
+		return "", fmt.Errorf("getting digest: %w", err)
+	}
+
+	return h.String(), nil
+}