Add oci/layout.List

Signed-off-by: Miloslav Trmač <[email protected]>

oci/layout/reader.go

@@ -0,0 +1,57 @@
+package layout
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/containers/image/v5/types"
+	digest "github.com/opencontainers/go-digest"
+	imgspecv1 "github.com/opencontainers/image-spec/specs-go/v1"
+)
+
+// This file is named reader.go for consistency with other transports
+// handling of “image containers”, but we don’t  actually need a stateful reader object.
+
+// ListResult wraps the image reference and the manifest for loading
+type ListResult struct {
+	Reference     types.ImageReference
+	MIMEType      string
+	Digest        digest.Digest
+	ReferenceName string // imgspecv1.AnnotationRefName or ""
+}
+
+// List returns a slice of manifests included in the archive
+func List(dir string) ([]ListResult, error) {
+	var res []ListResult
+
+	indexJSON, err := os.ReadFile(filepath.Join(dir, imgspecv1.ImageIndexFile))
+	if err != nil {
+		return nil, err
+	}
+	var index imgspecv1.Index
+	if err := json.Unmarshal(indexJSON, &index); err != nil {
+		return nil, err
+	}
+
+	for manifestIndex, md := range index.Manifests {
+		refName := md.Annotations[imgspecv1.AnnotationRefName]
+		index := -1
+		if refName == "" {
+			index = manifestIndex
+		}
+		ref, err := newReference(dir, refName, index)
+		if err != nil {
+			return nil, fmt.Errorf("error creating image reference: %w", err)
+		}
+		reference := ListResult{
+			Reference:     ref,
+			MIMEType:      md.MediaType,
+			Digest:        md.Digest,
+			ReferenceName: refName,
+		}
+		res = append(res, reference)
+	}
+	return res, nil
+}