client: move diff client to containerd package

Signed-off-by: Jess Valarezo <valarezo.jessica@gmail.com>

diff.go

@@ -0,0 +1,83 @@
+package containerd
+
+import (
+	diffapi "github.com/containerd/containerd/api/services/diff/v1"
+	"github.com/containerd/containerd/api/types"
+	"github.com/containerd/containerd/diff"
+	"github.com/containerd/containerd/mount"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"golang.org/x/net/context"
+)
+
+// NewDiffServiceFromClient returns a new diff service which communicates
+// over a GRPC connection.
+func NewDiffServiceFromClient(client diffapi.DiffClient) diff.Differ {
+	return &diffRemote{
+		client: client,
+	}
+}
+
+type diffRemote struct {
+	client diffapi.DiffClient
+}
+
+func (r *diffRemote) Apply(ctx context.Context, diff ocispec.Descriptor, mounts []mount.Mount) (ocispec.Descriptor, error) {
+	req := &diffapi.ApplyRequest{
+		Diff:   fromDescriptor(diff),
+		Mounts: fromMounts(mounts),
+	}
+	resp, err := r.client.Apply(ctx, req)
+	if err != nil {
+		return ocispec.Descriptor{}, err
+	}
+	return toDescriptor(resp.Applied), nil
+}
+
+func (r *diffRemote) DiffMounts(ctx context.Context, a, b []mount.Mount, opts ...diff.Opt) (ocispec.Descriptor, error) {
+	var config diff.Config
+	for _, opt := range opts {
+		if err := opt(&config); err != nil {
+			return ocispec.Descriptor{}, err
+		}
+	}
+	req := &diffapi.DiffRequest{
+		Left:      fromMounts(a),
+		Right:     fromMounts(b),
+		MediaType: config.MediaType,
+		Ref:       config.Reference,
+		Labels:    config.Labels,
+	}
+	resp, err := r.client.Diff(ctx, req)
+	if err != nil {
+		return ocispec.Descriptor{}, err
+	}
+	return toDescriptor(resp.Diff), nil
+}
+
+func toDescriptor(d *types.Descriptor) ocispec.Descriptor {
+	return ocispec.Descriptor{
+		MediaType: d.MediaType,
+		Digest:    d.Digest,
+		Size:      d.Size_,
+	}
+}
+
+func fromDescriptor(d ocispec.Descriptor) *types.Descriptor {
+	return &types.Descriptor{
+		MediaType: d.MediaType,
+		Digest:    d.Digest,
+		Size_:     d.Size,
+	}
+}
+
+func fromMounts(mounts []mount.Mount) []*types.Mount {
+	apiMounts := make([]*types.Mount, len(mounts))
+	for i, m := range mounts {
+		apiMounts[i] = &types.Mount{
+			Type:    m.Type,
+			Source:  m.Source,
+			Options: m.Options,
+		}
+	}
+	return apiMounts
+}