Update dist pull to use client

Replaced pull unpacker with boolean to call unpack.
Added unpack and target to image type.
Updated progress logic for pull.
Added list images to client.
Updated rootfs unpacker to use client.

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

image.go

@@ -1,9 +1,22 @@
 package containerd
 
-import "github.com/containerd/containerd/images"
+import (
+	"context"
+	"encoding/json"
+
+	"github.com/containerd/containerd/content"
+	"github.com/containerd/containerd/images"
+	"github.com/containerd/containerd/rootfs"
+	"github.com/opencontainers/image-spec/specs-go/v1"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"github.com/pkg/errors"
+)
 
 type Image interface {
 	Name() string
+	Target() ocispec.Descriptor
+
+	Unpack(context.Context) error
 }
 
 var _ = (Image)(&image{})
@@ -17,3 +30,47 @@ type image struct {
 func (i *image) Name() string {
 	return i.i.Name
 }
+
+func (i *image) Target() ocispec.Descriptor {
+	return i.i.Target
+}
+
+func (i *image) Unpack(ctx context.Context) error {
+	layers, err := i.getLayers(ctx)
+	if err != nil {
+		return err
+	}
+	if _, err := rootfs.ApplyLayers(ctx, layers, i.client.SnapshotService(), i.client.DiffService()); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (i *image) getLayers(ctx context.Context) ([]rootfs.Layer, error) {
+	cs := i.client.ContentStore()
+	p, err := content.ReadBlob(ctx, cs, i.i.Target.Digest)
+	if err != nil {
+		return nil, errors.Wrapf(err, "failed to read manifest blob")
+	}
+	var manifest v1.Manifest
+	if err := json.Unmarshal(p, &manifest); err != nil {
+		return nil, errors.Wrap(err, "failed to unmarshal manifest")
+	}
+	diffIDs, err := i.i.RootFS(ctx, cs)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to resolve rootfs")
+	}
+	if len(diffIDs) != len(manifest.Layers) {
+		return nil, errors.Errorf("mismatched image rootfs and manifest layers")
+	}
+	layers := make([]rootfs.Layer, len(diffIDs))
+	for i := range diffIDs {
+		layers[i].Diff = v1.Descriptor{
+			// TODO: derive media type from compressed type
+			MediaType: v1.MediaTypeImageLayer,
+			Digest:    diffIDs[i],
+		}
+		layers[i].Blob = manifest.Layers[i]
+	}
+	return layers, nil
+}