Support for multi-arch image unpacking

Resolves the platform on multi-arch manifests during unpack and config resolving.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

images/image.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"github.com/containerd/containerd/content"
+	"github.com/containerd/containerd/errdefs"
 	"github.com/containerd/containerd/platforms"
 	digest "github.com/opencontainers/go-digest"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
@@ -40,16 +41,16 @@ type Store interface {
 //
 // The caller can then use the descriptor to resolve and process the
 // configuration of the image.
-func (image *Image) Config(ctx context.Context, provider content.Provider) (ocispec.Descriptor, error) {
-	return Config(ctx, provider, image.Target)
+func (image *Image) Config(ctx context.Context, provider content.Provider, platform string) (ocispec.Descriptor, error) {
+	return Config(ctx, provider, image.Target, platform)
 }
 
 // RootFS returns the unpacked diffids that make up and images rootfs.
 //
 // These are used to verify that a set of layers unpacked to the expected
 // values.
-func (image *Image) RootFS(ctx context.Context, provider content.Provider) ([]digest.Digest, error) {
-	desc, err := image.Config(ctx, provider)
+func (image *Image) RootFS(ctx context.Context, provider content.Provider, platform string) ([]digest.Digest, error) {
+	desc, err := image.Config(ctx, provider, platform)
 	if err != nil {
 		return nil, err
 	}
@@ -68,17 +69,23 @@ func (image *Image) Size(ctx context.Context, provider content.Provider) (int64,
 	}), ChildrenHandler(provider)), image.Target)
 }
 
-// Config resolves the image configuration descriptor using a content provided
-// to resolve child resources on the image.
-//
-// The caller can then use the descriptor to resolve and process the
-// configuration of the image.
-func Config(ctx context.Context, provider content.Provider, image ocispec.Descriptor) (ocispec.Descriptor, error) {
-	var configDesc ocispec.Descriptor
-	return configDesc, Walk(ctx, HandlerFunc(func(ctx context.Context, desc ocispec.Descriptor) ([]ocispec.Descriptor, error) {
+func Manifest(ctx context.Context, provider content.Provider, image ocispec.Descriptor, platform string) (ocispec.Manifest, error) {
+	var (
+		matcher platforms.Matcher
+		m       *ocispec.Manifest
+		err     error
+	)
+	if platform != "" {
+		matcher, err = platforms.Parse(platform)
+		if err != nil {
+			return ocispec.Manifest{}, err
+		}
+	}
+
+	if err := Walk(ctx, HandlerFunc(func(ctx context.Context, desc ocispec.Descriptor) ([]ocispec.Descriptor, error) {
 		switch desc.MediaType {
 		case MediaTypeDockerSchema2Manifest, ocispec.MediaTypeImageManifest:
-			p, err := content.ReadBlob(ctx, provider, image.Digest)
+			p, err := content.ReadBlob(ctx, provider, desc.Digest)
 			if err != nil {
 				return nil, err
 			}
@@ -88,14 +95,80 @@ func Config(ctx context.Context, provider content.Provider, image ocispec.Descri
 				return nil, err
 			}
 
-			configDesc = manifest.Config
+			if platform != "" {
+				if desc.Platform != nil && !matcher.Match(*desc.Platform) {
+					return nil, nil
+				}
+
+				if desc.Platform == nil {
+					p, err := content.ReadBlob(ctx, provider, manifest.Config.Digest)
+					if err != nil {
+						return nil, err
+					}
+
+					var image ocispec.Image
+					if err := json.Unmarshal(p, &image); err != nil {
+						return nil, err
+					}
+
+					if !matcher.Match(platforms.Normalize(ocispec.Platform{OS: image.OS, Architecture: image.Architecture})) {
+						return nil, nil
+					}
+
+				}
+			}
+
+			m = &manifest
 
 			return nil, nil
-		default:
-			return nil, errors.New("could not resolve config")
-		}
+		case MediaTypeDockerSchema2ManifestList, ocispec.MediaTypeImageIndex:
+			p, err := content.ReadBlob(ctx, provider, desc.Digest)
+			if err != nil {
+				return nil, err
+			}
 
-	}), image)
+			var idx ocispec.Index
+			if err := json.Unmarshal(p, &idx); err != nil {
+				return nil, err
+			}
+
+			if platform == "" {
+				return idx.Manifests, nil
+			}
+
+			var descs []ocispec.Descriptor
+			for _, d := range idx.Manifests {
+				if d.Platform == nil || matcher.Match(*d.Platform) {
+					descs = append(descs, d)
+				}
+			}
+
+			return descs, nil
+
+		}
+		return nil, errors.New("could not resolve manifest")
+	}), image); err != nil {
+		return ocispec.Manifest{}, err
+	}
+
+	if m == nil {
+		return ocispec.Manifest{}, errors.Wrap(errdefs.ErrNotFound, "manifest not found")
+	}
+
+	return *m, nil
+}
+
+// Config resolves the image configuration descriptor using a content provided
+// to resolve child resources on the image.
+//
+// The caller can then use the descriptor to resolve and process the
+// configuration of the image.
+func Config(ctx context.Context, provider content.Provider, image ocispec.Descriptor, platform string) (ocispec.Descriptor, error) {
+	manifest, err := Manifest(ctx, provider, image, platform)
+	if err != nil {
+		return ocispec.Descriptor{}, err
+	}
+	return manifest.Config, err
 }
 
 // Platforms returns one or more platforms supported by the image.