Add docker/archive.Reader.ManifestTagsForReference

to allow Podman default to localhost/$tag for unqualified $tag
values in docker-archive tarnballs.

(Note that only projectatomic/docker creates such tarballs;
almost no-one else should use this.)

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

docker/archive/reader.go

@@ -96,3 +96,25 @@ func (r *Reader) List() ([][]types.ImageReference, error) {
 	}
 	return res, nil
 }
+
+// ManifestTagsForReference returns the set of tags “matching” ref in reader, as strings
+// (i.e. exposing the short names before normalization).
+// The function reports an error if ref does not identify a single image.
+// If ref contains a NamedTagged reference, only a single tag “matching” ref is returned;
+// If ref contains a source index, or neither a NamedTagged nor a source index, all tags
+// matching the image are returned.
+// Almost all users should use List() or ImageReference.DockerReference() instead.
+func (r *Reader) ManifestTagsForReference(ref types.ImageReference) ([]string, error) {
+	archiveRef, ok := ref.(archiveReference)
+	if !ok {
+		return nil, errors.Errorf("Internal error: ManifestTagsForReference called for a non-docker/archive ImageReference %s", transports.ImageName(ref))
+	}
+	manifestItem, tagIndex, err := r.archive.ChooseManifestItem(archiveRef.ref, archiveRef.sourceIndex)
+	if err != nil {
+		return nil, err
+	}
+	if tagIndex != -1 {
+		return []string{manifestItem.RepoTags[tagIndex]}, nil
+	}
+	return manifestItem.RepoTags, nil
+}

docker/internal/tarfile/reader.go

@@ -130,41 +130,43 @@ func (r *Reader) Close() error {
 	return nil
 }
 
-// chooseManifestItem selects a manifest item from r.Manifest matching (ref, sourceIndex), one or
+// ChooseManifestItem selects a manifest item from r.Manifest matching (ref, sourceIndex), one or
 // both of which should be (nil, -1).
-func (r *Reader) chooseManifestItem(ref reference.NamedTagged, sourceIndex int) (*ManifestItem, error) {
+// On success, it returns the manifest item and an index of the matching tag, if a tag was used
+// for matching; the index is -1 if a tag was not used.
+func (r *Reader) ChooseManifestItem(ref reference.NamedTagged, sourceIndex int) (*ManifestItem, int, error) {
 	switch {
 	case ref != nil && sourceIndex != -1:
-		return nil, errors.Errorf("Internal error: Cannot have both ref %s and source index @%d",
+		return nil, -1, errors.Errorf("Internal error: Cannot have both ref %s and source index @%d",
 			ref.String(), sourceIndex)
 
 	case ref != nil:
 		refString := ref.String()
 		for i := range r.Manifest {
-			for _, tag := range r.Manifest[i].RepoTags {
+			for tagIndex, tag := range r.Manifest[i].RepoTags {
 				parsedTag, err := reference.ParseNormalizedNamed(tag)
 				if err != nil {
-					return nil, errors.Wrapf(err, "Invalid tag %#v in manifest.json item @%d", tag, i)
+					return nil, -1, errors.Wrapf(err, "Invalid tag %#v in manifest.json item @%d", tag, i)
 				}
 				if parsedTag.String() == refString {
-					return &r.Manifest[i], nil
+					return &r.Manifest[i], tagIndex, nil
 				}
 			}
 		}
-		return nil, errors.Errorf("Tag %#v not found", refString)
+		return nil, -1, errors.Errorf("Tag %#v not found", refString)
 
 	case sourceIndex != -1:
 		if sourceIndex >= len(r.Manifest) {
-			return nil, errors.Errorf("Invalid source index @%d, only %d manifest items available",
+			return nil, -1, errors.Errorf("Invalid source index @%d, only %d manifest items available",
 				sourceIndex, len(r.Manifest))
 		}
-		return &r.Manifest[sourceIndex], nil
+		return &r.Manifest[sourceIndex], -1, nil
 
 	default:
 		if len(r.Manifest) != 1 {
-			return nil, errors.Errorf("Unexpected tar manifest.json: expected 1 item, got %d", len(r.Manifest))
+			return nil, -1, errors.Errorf("Unexpected tar manifest.json: expected 1 item, got %d", len(r.Manifest))
 		}
-		return &r.Manifest[0], nil
+		return &r.Manifest[0], -1, nil
 	}
 }
 

docker/internal/tarfile/src.go

@@ -68,7 +68,7 @@ func (s *Source) ensureCachedDataIsPresent() error {
 // ensureCachedDataIsPresentPrivate is a private implementation detail of ensureCachedDataIsPresent.
 // Call ensureCachedDataIsPresent instead.
 func (s *Source) ensureCachedDataIsPresentPrivate() error {
-	tarManifest, err := s.archive.chooseManifestItem(s.ref, s.sourceIndex)
+	tarManifest, _, err := s.archive.ChooseManifestItem(s.ref, s.sourceIndex)
 	if err != nil {
 		return err
 	}