Add diff service implementation

Add snapshot subcommand to ctr for creating diffs of RW layers.

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

services/diff/client.go

@@ -11,19 +11,24 @@ import (
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 )
 
+type DiffService interface {
+	rootfs.Applier
+	rootfs.MountDiffer
+}
+
 // NewApplierFromClient returns a new Applier which communicates
 // over a GRPC connection.
-func NewApplierFromClient(client diffapi.DiffClient) rootfs.Applier {
-	return &remoteApplier{
+func NewDiffServiceFromClient(client diffapi.DiffClient) DiffService {
+	return &remote{
 		client: client,
 	}
 }
 
-type remoteApplier struct {
+type remote struct {
 	client diffapi.DiffClient
 }
 
-func (r *remoteApplier) Apply(ctx context.Context, diff ocispec.Descriptor, mounts []containerd.Mount) (ocispec.Descriptor, error) {
+func (r *remote) Apply(ctx context.Context, diff ocispec.Descriptor, mounts []containerd.Mount) (ocispec.Descriptor, error) {
 	req := &diffapi.ApplyRequest{
 		Diff:   fromDescriptor(diff),
 		Mounts: fromMounts(mounts),
@@ -35,6 +40,20 @@ func (r *remoteApplier) Apply(ctx context.Context, diff ocispec.Descriptor, moun
 	return toDescriptor(resp.Applied), nil
 }
 
+func (r *remote) DiffMounts(ctx context.Context, a, b []containerd.Mount, media, ref string) (ocispec.Descriptor, error) {
+	req := &diffapi.DiffRequest{
+		Left:      fromMounts(a),
+		Right:     fromMounts(b),
+		MediaType: media,
+		Ref:       ref,
+	}
+	resp, err := r.client.Diff(ctx, req)
+	if err != nil {
+		return ocispec.Descriptor{}, err
+	}
+	return toDescriptor(resp.Diff), nil
+}
+
 func fromDescriptor(d ocispec.Descriptor) *descriptor.Descriptor {
 	return &descriptor.Descriptor{
 		MediaType: d.MediaType,

services/diff/service.go

@@ -102,8 +102,73 @@ func (s *service) Apply(ctx context.Context, er *diffapi.ApplyRequest) (*diffapi
 	return resp, nil
 }
 
-func (s *service) Diff(context.Context, *diffapi.DiffRequest) (*diffapi.DiffResponse, error) {
-	return nil, errors.New("not implemented")
+func (s *service) Diff(ctx context.Context, dr *diffapi.DiffRequest) (*diffapi.DiffResponse, error) {
+	aMounts := toMounts(dr.Left)
+	bMounts := toMounts(dr.Right)
+
+	aDir, err := ioutil.TempDir("", "left-")
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to create temporary directory")
+	}
+	defer os.RemoveAll(aDir)
+
+	bDir, err := ioutil.TempDir("", "right-")
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to create temporary directory")
+	}
+	defer os.RemoveAll(bDir)
+
+	if err := containerd.MountAll(aMounts, aDir); err != nil {
+		return nil, errors.Wrap(err, "failed to mount")
+	}
+	defer containerd.Unmount(aDir, 0)
+
+	if err := containerd.MountAll(bMounts, bDir); err != nil {
+		return nil, errors.Wrap(err, "failed to mount")
+	}
+	defer containerd.Unmount(bDir, 0)
+
+	cw, err := s.store.Writer(ctx, dr.Ref, 0, "")
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to open writer")
+	}
+
+	// TODO: Validate media type
+
+	// TODO: Support compressed media types (link compressed to uncompressed)
+	//dgstr := digest.SHA256.Digester()
+	//wc := &writeCounter{}
+	//compressed, err := compression.CompressStream(cw, compression.Gzip)
+	//if err != nil {
+	//	return nil, errors.Wrap(err, "failed to get compressed stream")
+	//}
+	//err = archive.WriteDiff(ctx, io.MultiWriter(compressed, dgstr.Hash(), wc), lowerDir, upperDir)
+	//compressed.Close()
+
+	err = archive.WriteDiff(ctx, cw, aDir, bDir)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to write diff")
+	}
+
+	dgst := cw.Digest()
+	if err := cw.Commit(0, dgst); err != nil {
+		return nil, errors.Wrap(err, "failed to commit")
+	}
+
+	info, err := s.store.Info(ctx, dgst)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to get info from content store")
+	}
+
+	desc := ocispec.Descriptor{
+		MediaType: dr.MediaType,
+		Digest:    info.Digest,
+		Size:      info.Size,
+	}
+
+	return &diffapi.DiffResponse{
+		Diff: fromDescriptor(desc),
+	}, nil
 }
 
 type readCounter struct {