allow annotations for OCI image index

Signed-off-by: Qasim Sarfraz <qasimsarfraz@microsoft.com>

util/imagetools/create.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"encoding/json"
 	"net/url"
+	"regexp"
 	"strings"
 
 	"github.com/containerd/containerd/content"
@@ -13,6 +14,7 @@ import (
 	"github.com/containerd/containerd/platforms"
 	"github.com/containerd/containerd/remotes"
 	"github.com/docker/distribution/reference"
+	"github.com/moby/buildkit/exporter/containerimage/exptypes"
 	"github.com/moby/buildkit/util/contentutil"
 	"github.com/opencontainers/go-digest"
 	"github.com/opencontainers/image-spec/specs-go"
@@ -26,7 +28,7 @@ type Source struct {
 	Ref  reference.Named
 }
 
-func (r *Resolver) Combine(ctx context.Context, srcs []*Source) ([]byte, ocispec.Descriptor, error) {
+func (r *Resolver) Combine(ctx context.Context, srcs []*Source, ann map[string]string) ([]byte, ocispec.Descriptor, error) {
 	eg, ctx := errgroup.WithContext(ctx)
 
 	dts := make([][]byte, len(srcs))
@@ -75,7 +77,7 @@ func (r *Resolver) Combine(ctx context.Context, srcs []*Source) ([]byte, ocispec
 	}
 
 	// on single source, return original bytes
-	if len(srcs) == 1 {
+	if len(srcs) == 1 && len(ann) == 0 {
 		if mt := srcs[0].Desc.MediaType; mt == images.MediaTypeDockerSchema2ManifestList || mt == ocispec.MediaTypeImageIndex {
 			return dts[0], srcs[0].Desc, nil
 		}
@@ -138,12 +140,39 @@ func (r *Resolver) Combine(ctx context.Context, srcs []*Source) ([]byte, ocispec
 		mt = ocispec.MediaTypeImageIndex
 	}
 
+	// annotations are only allowed on OCI indexes
+	indexAnnotation := make(map[string]string)
+	if mt == ocispec.MediaTypeImageIndex {
+		annotations, err := parseAnnotations(ann)
+		if err != nil {
+			return nil, ocispec.Descriptor{}, err
+		}
+		if len(annotations[exptypes.AnnotationIndex]) > 0 {
+			for k, v := range annotations[exptypes.AnnotationIndex] {
+				indexAnnotation[k.Key] = v
+			}
+		}
+		if len(annotations[exptypes.AnnotationManifestDescriptor]) > 0 {
+			for i := 0; i < len(newDescs); i++ {
+				if newDescs[i].Annotations == nil {
+					newDescs[i].Annotations = map[string]string{}
+				}
+				for k, v := range annotations[exptypes.AnnotationManifestDescriptor] {
+					if k.Platform == nil || k.PlatformString() == platforms.Format(*newDescs[i].Platform) {
+						newDescs[i].Annotations[k.Key] = v
+					}
+				}
+			}
+		}
+	}
+
 	idxBytes, err := json.MarshalIndent(ocispec.Index{
 		MediaType: mt,
 		Versioned: specs.Versioned{
 			SchemaVersion: 2,
 		},
-		Manifests: newDescs,
+		Manifests:   newDescs,
+		Annotations: indexAnnotation,
 	}, "", "  ")
 	if err != nil {
 		return nil, ocispec.Descriptor{}, errors.Wrap(err, "failed to marshal index")
@@ -266,3 +295,52 @@ func detectMediaType(dt []byte) (string, error) {
 
 	return images.MediaTypeDockerSchema2ManifestList, nil
 }
+
+func parseAnnotations(ann map[string]string) (map[string]map[exptypes.AnnotationKey]string, error) {
+	// TODO: use buildkit's annotation parser once it supports setting custom prefix and ":" separator
+	annotationRegexp := regexp.MustCompile(`^([a-z-]+)(?:\[([A-Za-z0-9_/-]+)\])?:(\S+)$`)
+	indexAnnotations := make(map[exptypes.AnnotationKey]string)
+	manifestDescriptorAnnotations := make(map[exptypes.AnnotationKey]string)
+	for k, v := range ann {
+		groups := annotationRegexp.FindStringSubmatch(k)
+		if groups == nil {
+			return nil, errors.Errorf("invalid annotation format, expected <type>:<key>=<value>, got %q", k)
+		}
+
+		typ, platform, key := groups[1], groups[2], groups[3]
+		var ociPlatform *ocispec.Platform
+		if platform != "" {
+			p, err := platforms.Parse(platform)
+			if err != nil {
+				return nil, errors.Wrapf(err, "invalid platform %q", platform)
+			}
+			ociPlatform = &p
+		}
+		switch typ {
+		case exptypes.AnnotationIndex:
+			ak := exptypes.AnnotationKey{
+				Type:     typ,
+				Platform: ociPlatform,
+				Key:      key,
+			}
+			indexAnnotations[ak] = v
+		case exptypes.AnnotationManifestDescriptor:
+			ak := exptypes.AnnotationKey{
+				Type:     typ,
+				Platform: ociPlatform,
+				Key:      key,
+			}
+			manifestDescriptorAnnotations[ak] = v
+		case exptypes.AnnotationManifest:
+			return nil, errors.Errorf("%q annotations are not supported yet", typ)
+		case exptypes.AnnotationIndexDescriptor:
+			return nil, errors.Errorf("%q annotations are invalid while creating an image", typ)
+		default:
+			return nil, errors.Errorf("unknown annotation type %q", typ)
+		}
+	}
+	return map[string]map[exptypes.AnnotationKey]string{
+		exptypes.AnnotationIndex:              indexAnnotations,
+		exptypes.AnnotationManifestDescriptor: manifestDescriptorAnnotations,
+	}, nil
+}