imagetools: add platforms filter to imagetools create

Allows specifying platforms that should be included
in the new image, making it possible to reduce platforms
of existing multi-arch image. Previously the individual
image manifests needed to be used as sources, but that
dropped their related attestation manifests.

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

util/imagetools/create.go

@@ -28,7 +28,7 @@ type Source struct {
 	Ref  reference.Named
 }
 
-func (r *Resolver) Combine(ctx context.Context, srcs []*Source, ann map[exptypes.AnnotationKey]string, preferIndex bool) ([]byte, ocispecs.Descriptor, error) {
+func (r *Resolver) Combine(ctx context.Context, srcs []*Source, ann map[exptypes.AnnotationKey]string, preferIndex bool) ([]byte, ocispecs.Descriptor, map[digest.Digest]*Source, error) {
 	eg, ctx := errgroup.WithContext(ctx)
 
 	dts := make([][]byte, len(srcs))
@@ -73,7 +73,7 @@ func (r *Resolver) Combine(ctx context.Context, srcs []*Source, ann map[exptypes
 	}
 
 	if err := eg.Wait(); err != nil {
-		return nil, ocispecs.Descriptor{}, err
+		return nil, ocispecs.Descriptor{}, nil, err
 	}
 
 	// on single source, return original bytes
@@ -83,18 +83,22 @@ func (r *Resolver) Combine(ctx context.Context, srcs []*Source, ann map[exptypes
 		// of preferIndex since if set to true then the source is already in the preferred format, and if false
 		// it doesn't matter since we're not going to split it into separate manifests
 		case images.MediaTypeDockerSchema2ManifestList, ocispecs.MediaTypeImageIndex:
-			return dts[0], srcs[0].Desc, nil
+			srcMap := map[digest.Digest]*Source{
+				srcs[0].Desc.Digest: srcs[0],
+			}
+			return dts[0], srcs[0].Desc, srcMap, nil
 		default:
 			if !preferIndex {
-				return dts[0], srcs[0].Desc, nil
+				return dts[0], srcs[0].Desc, nil, nil
 			}
 		}
 	}
 
 	indexes := map[digest.Digest]int{}
+	sources := map[digest.Digest]*Source{}
 	descs := make([]ocispecs.Descriptor, 0, len(srcs))
 
-	addDesc := func(d ocispecs.Descriptor) {
+	addDesc := func(d ocispecs.Descriptor, src *Source) {
 		idx, ok := indexes[d.Digest]
 		if ok {
 			old := descs[idx]
@@ -113,6 +117,7 @@ func (r *Resolver) Combine(ctx context.Context, srcs []*Source, ann map[exptypes
 			indexes[d.Digest] = len(descs)
 			descs = append(descs, d)
 		}
+		sources[d.Digest] = src
 	}
 
 	for i, src := range srcs {
@@ -120,13 +125,13 @@ func (r *Resolver) Combine(ctx context.Context, srcs []*Source, ann map[exptypes
 		case images.MediaTypeDockerSchema2ManifestList, ocispecs.MediaTypeImageIndex:
 			var mfst ocispecs.Index
 			if err := json.Unmarshal(dts[i], &mfst); err != nil {
-				return nil, ocispecs.Descriptor{}, errors.WithStack(err)
+				return nil, ocispecs.Descriptor{}, nil, errors.WithStack(err)
 			}
 			for _, d := range mfst.Manifests {
-				addDesc(d)
+				addDesc(d, src)
 			}
 		default:
-			addDesc(src.Desc)
+			addDesc(src.Desc, src)
 		}
 	}
 
@@ -163,9 +168,9 @@ func (r *Resolver) Combine(ctx context.Context, srcs []*Source, ann map[exptypes
 					}
 				}
 			case exptypes.AnnotationManifest, "":
-				return nil, ocispecs.Descriptor{}, errors.Errorf("%q annotations are not supported yet", k.Type)
+				return nil, ocispecs.Descriptor{}, nil, errors.Errorf("%q annotations are not supported yet", k.Type)
 			case exptypes.AnnotationIndexDescriptor:
-				return nil, ocispecs.Descriptor{}, errors.Errorf("%q annotations are invalid while creating an image", k.Type)
+				return nil, ocispecs.Descriptor{}, nil, errors.Errorf("%q annotations are invalid while creating an image", k.Type)
 			}
 		}
 	}
@@ -179,14 +184,14 @@ func (r *Resolver) Combine(ctx context.Context, srcs []*Source, ann map[exptypes
 		Annotations: indexAnnotation,
 	}, "", "  ")
 	if err != nil {
-		return nil, ocispecs.Descriptor{}, errors.Wrap(err, "failed to marshal index")
+		return nil, ocispecs.Descriptor{}, nil, errors.Wrap(err, "failed to marshal index")
 	}
 
 	return idxBytes, ocispecs.Descriptor{
 		MediaType: mt,
 		Size:      int64(len(idxBytes)),
 		Digest:    digest.FromBytes(idxBytes),
-	}, nil
+	}, sources, nil
 }
 
 func (r *Resolver) Push(ctx context.Context, ref reference.Named, desc ocispecs.Descriptor, dt []byte) error {