Make Diff/Apply plugable

Signed-off-by: Volodymyr Burenin <vburenin@gmail.com>

differ/differ.go

@@ -0,0 +1,164 @@
+package differ
+
+import (
+	"io"
+	"io/ioutil"
+	"os"
+
+	"github.com/containerd/containerd/archive"
+	"github.com/containerd/containerd/archive/compression"
+	"github.com/containerd/containerd/content"
+	"github.com/containerd/containerd/mount"
+	"github.com/containerd/containerd/plugin"
+	"github.com/containerd/containerd/snapshot"
+	digest "github.com/opencontainers/go-digest"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"github.com/pkg/errors"
+	"golang.org/x/net/context"
+)
+
+func init() {
+	plugin.Register("diff-base", &plugin.Registration{
+		Type: plugin.DiffPlugin,
+		Init: func(ic *plugin.InitContext) (interface{}, error) {
+			return newBaseDiff(ic.Content, ic.Snapshotter)
+		},
+	})
+}
+
+type BaseDiff struct {
+	store       content.Store
+	snapshotter snapshot.Snapshotter
+}
+
+var _ plugin.Differ = &BaseDiff{}
+
+var emptyDesc = ocispec.Descriptor{}
+
+func newBaseDiff(store content.Store, snapshotter snapshot.Snapshotter) (*BaseDiff, error) {
+	return &BaseDiff{
+		store:       store,
+		snapshotter: snapshotter,
+	}, nil
+}
+
+func (s *BaseDiff) Apply(ctx context.Context, desc ocispec.Descriptor, mounts []mount.Mount) (ocispec.Descriptor, error) {
+	// TODO: Check for supported media types
+	dir, err := ioutil.TempDir("", "extract-")
+	if err != nil {
+		return emptyDesc, errors.Wrap(err, "failed to create temporary directory")
+	}
+	defer os.RemoveAll(dir)
+
+	if err := mount.MountAll(mounts, dir); err != nil {
+		return emptyDesc, errors.Wrap(err, "failed to mount")
+	}
+	defer mount.Unmount(dir, 0)
+
+	r, err := s.store.Reader(ctx, desc.Digest)
+	if err != nil {
+		return emptyDesc, errors.Wrap(err, "failed to get reader from content store")
+	}
+	defer r.Close()
+
+	// TODO: only decompress stream if media type is compressed
+	ds, err := compression.DecompressStream(r)
+	if err != nil {
+		return emptyDesc, err
+	}
+	defer ds.Close()
+
+	digester := digest.Canonical.Digester()
+	rc := &readCounter{
+		r: io.TeeReader(ds, digester.Hash()),
+	}
+
+	if _, err := archive.Apply(ctx, dir, rc); err != nil {
+		return emptyDesc, err
+	}
+
+	// Read any trailing data
+	if _, err := io.Copy(ioutil.Discard, rc); err != nil {
+		return emptyDesc, err
+	}
+
+	return ocispec.Descriptor{
+		MediaType: ocispec.MediaTypeImageLayer,
+		Size:      rc.c,
+		Digest:    digester.Digest(),
+	}, nil
+}
+
+func (s *BaseDiff) DiffMounts(ctx context.Context, lower, upper []mount.Mount, media, ref string) (ocispec.Descriptor, error) {
+
+	aDir, err := ioutil.TempDir("", "left-")
+	if err != nil {
+		return emptyDesc, errors.Wrap(err, "failed to create temporary directory")
+	}
+	defer os.RemoveAll(aDir)
+
+	bDir, err := ioutil.TempDir("", "right-")
+	if err != nil {
+		return emptyDesc, errors.Wrap(err, "failed to create temporary directory")
+	}
+	defer os.RemoveAll(bDir)
+
+	if err := mount.MountAll(lower, aDir); err != nil {
+		return emptyDesc, errors.Wrap(err, "failed to mount")
+	}
+	defer mount.Unmount(aDir, 0)
+
+	if err := mount.MountAll(upper, bDir); err != nil {
+		return emptyDesc, errors.Wrap(err, "failed to mount")
+	}
+	defer mount.Unmount(bDir, 0)
+
+	cw, err := s.store.Writer(ctx, ref, 0, "")
+	if err != nil {
+		return emptyDesc, 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 emptyDesc, errors.Wrap(err, "failed to write diff")
+	}
+
+	dgst := cw.Digest()
+	if err := cw.Commit(0, dgst); err != nil {
+		return emptyDesc, errors.Wrap(err, "failed to commit")
+	}
+
+	info, err := s.store.Info(ctx, dgst)
+	if err != nil {
+		return emptyDesc, errors.Wrap(err, "failed to get info from content store")
+	}
+
+	return ocispec.Descriptor{
+		MediaType: media,
+		Size:      info.Size,
+		Digest:    info.Digest,
+	}, nil
+}
+
+type readCounter struct {
+	r io.Reader
+	c int64
+}
+
+func (rc *readCounter) Read(p []byte) (n int, err error) {
+	n, err = rc.r.Read(p)
+	rc.c += int64(n)
+	return
+}