fix merging indexes in pkg manifest command

Signed-off-by: Avi Deitcher <avi@deitcher.net>

src/cmd/linuxkit/registry/manifest.go

@@ -94,6 +94,11 @@ func PushManifest(img string, options ...remote.Option) (hash string, length int
 	if err != nil {
 		return hash, length, fmt.Errorf("getting index digest: %w", err)
 	}
+	// if it is unchanged, do nothing
+	if desc != nil && desc.Digest == dig {
+		log.Debugf("not pushing manifest list for %s, unchanged", img)
+		return dig.String(), size, nil
+	}
 	log.Debugf("pushing manifest list for %s -> %#v", img, index)
 	err = remote.WriteIndex(baseRef, index, options...)
 	if err != nil {

src/cmd/linuxkit/util/index.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 
 	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/mutate"
 )
 
 const (
@@ -14,12 +15,15 @@ const (
 	AnnotationSPDXDoc               = "https://spdx.dev/Document"
 )
 
-// AppendIndex appends the elements of secondary ImageIndex into primary ImageIndex,
+// AppendIndex creates a new ImageIndex composed of the merge of the elements of secondary ImageIndex
-// returning the updated primary ImageIndex.
+// and primary ImageIndex.
 // In the case of conflicts, the primary ImageIndex wins.
 // For example, if both have a manifest for a specific platform, then use the one from primary.
 // The append is aware of the buildkit-style attestations, and will keep any attestations that point to a valid
 // manifest in the list, discarding any that do not.
+// If either of the two ImageIndexes is nil, the other is returned.
+// If the secondary ImageIndex is a precise superset of primary,
+// then the returned new ImageIndex is an identical copy of the secondary ImageIndex.
 func AppendIndex(primary, secondary v1.ImageIndex) (v1.ImageIndex, error) {
 	primaryManifest, err := primary.IndexManifest()
 	if err != nil {
@@ -35,10 +39,14 @@ func AppendIndex(primary, secondary v1.ImageIndex) (v1.ImageIndex, error) {
 	// 2. attestation - after all platforms, does it point to something in the updated index?
 	//      If not, remove
 
+	if indexSuperset(primaryManifest, secondaryManifest) {
+		return secondary, nil
+	}
 	// make a map of all the digests already in the index, so we can know what is there
 	var (
 		manifestMap = map[v1.Hash]bool{}
 		platformMap = map[string]bool{}
+		adds        []mutate.IndexAddendum
 	)
 	for _, m := range primaryManifest.Manifests {
 		if m.Platform == nil || m.Platform.Architecture == "" {
@@ -63,7 +71,15 @@ func AppendIndex(primary, secondary v1.ImageIndex) (v1.ImageIndex, error) {
 			// we already have this one, so we can skip it
 			continue
 		}
-		primaryManifest.Manifests = append(primaryManifest.Manifests, m)
+		img, err := secondary.Image(m.Digest)
+		if err != nil {
+			return nil, fmt.Errorf("could not get image %s: %v", m.Digest, err)
+		}
+		adds = append(adds, mutate.IndexAddendum{
+			Add:        img,
+			Descriptor: m,
+		})
+		// want to add manifest "m"
 		manifestMap[m.Digest] = true
 	}
 
@@ -73,7 +89,7 @@ func AppendIndex(primary, secondary v1.ImageIndex) (v1.ImageIndex, error) {
 	// we either add them to the local index, or remove them if they are no longer valid
 	// we assume the ones in the local index are valid because they would have been generated now
 	for _, m := range secondaryManifest.Manifests {
-		if m.Platform == nil || m.Platform.Architecture != "unknown" || m.Platform.OS == "unknown" || m.Annotations == nil || m.Annotations[AnnotationDockerReferenceDigest] == "" {
+		if m.Platform == nil || m.Platform.Architecture != "unknown" || m.Platform.OS != "unknown" || m.Annotations == nil || m.Annotations[AnnotationDockerReferenceDigest] == "" {
 			continue
 		}
 		// if we already have this one, we are good
@@ -90,8 +106,34 @@ func AppendIndex(primary, secondary v1.ImageIndex) (v1.ImageIndex, error) {
 		if _, ok := manifestMap[dig]; !ok {
 			continue
 		}
-		primaryManifest.Manifests = append(primaryManifest.Manifests, m)
+		img, err := secondary.Image(m.Digest)
+		if err != nil {
+			return nil, fmt.Errorf("could not get image %s: %v", m.Digest, err)
+		}
+		adds = append(adds, mutate.IndexAddendum{
+			Add:        img,
+			Descriptor: m,
+		})
+		// want to add manifest "m"
 		manifestMap[m.Digest] = true
 	}
-	return primary, nil
+	ret := mutate.AppendManifests(primary, adds...)
+
+	return ret, nil
+}
+
+func indexSuperset(inner, outer *v1.IndexManifest) bool {
+	var manifestMap = map[v1.Hash]bool{}
+	if len(inner.Manifests) > len(outer.Manifests) {
+		return false
+	}
+	for _, m := range outer.Manifests {
+		manifestMap[m.Digest] = true
+	}
+	for _, m := range inner.Manifests {
+		if _, ok := manifestMap[m.Digest]; !ok {
+			return false
+		}
+	}
+	return true
 }