importer: refactor

- Use lease API (previoisly, GC was not supported)
- Refactored interfaces for ease of future Docker v1 importer support

For usage, please refer to `ctr images import --help`.

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

export.go

@@ -1,189 +0,0 @@
-package containerd
-
-import (
-	"archive/tar"
-	"context"
-	"encoding/json"
-	"io"
-	"sort"
-
-	"github.com/containerd/containerd/content"
-	"github.com/containerd/containerd/images"
-	"github.com/containerd/containerd/platforms"
-	ocispecs "github.com/opencontainers/image-spec/specs-go"
-	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
-	"github.com/pkg/errors"
-)
-
-func (c *Client) exportToOCITar(ctx context.Context, desc ocispec.Descriptor, writer io.Writer, eopts exportOpts) error {
-	tw := tar.NewWriter(writer)
-	defer tw.Close()
-
-	records := []tarRecord{
-		ociLayoutFile(""),
-		ociIndexRecord(desc),
-	}
-
-	cs := c.ContentStore()
-	algorithms := map[string]struct{}{}
-	exportHandler := func(ctx context.Context, desc ocispec.Descriptor) ([]ocispec.Descriptor, error) {
-		records = append(records, blobRecord(cs, desc))
-		algorithms[desc.Digest.Algorithm().String()] = struct{}{}
-		return nil, nil
-	}
-
-	handlers := images.Handlers(
-		images.ChildrenHandler(cs, platforms.Default()),
-		images.HandlerFunc(exportHandler),
-	)
-
-	// Walk sequentially since the number of fetchs is likely one and doing in
-	// parallel requires locking the export handler
-	if err := images.Walk(ctx, handlers, desc); err != nil {
-		return err
-	}
-
-	if len(algorithms) > 0 {
-		records = append(records, directoryRecord("blobs/", 0755))
-		for alg := range algorithms {
-			records = append(records, directoryRecord("blobs/"+alg+"/", 0755))
-		}
-	}
-
-	return writeTar(ctx, tw, records)
-}
-
-type tarRecord struct {
-	Header *tar.Header
-	CopyTo func(context.Context, io.Writer) (int64, error)
-}
-
-func blobRecord(cs content.Store, desc ocispec.Descriptor) tarRecord {
-	path := "blobs/" + desc.Digest.Algorithm().String() + "/" + desc.Digest.Hex()
-	return tarRecord{
-		Header: &tar.Header{
-			Name:     path,
-			Mode:     0444,
-			Size:     desc.Size,
-			Typeflag: tar.TypeReg,
-		},
-		CopyTo: func(ctx context.Context, w io.Writer) (int64, error) {
-			r, err := cs.ReaderAt(ctx, desc.Digest)
-			if err != nil {
-				return 0, err
-			}
-			defer r.Close()
-
-			// Verify digest
-			dgstr := desc.Digest.Algorithm().Digester()
-
-			n, err := io.Copy(io.MultiWriter(w, dgstr.Hash()), content.NewReader(r))
-			if err != nil {
-				return 0, err
-			}
-			if dgstr.Digest() != desc.Digest {
-				return 0, errors.Errorf("unexpected digest %s copied", dgstr.Digest())
-			}
-			return n, nil
-		},
-	}
-}
-
-func directoryRecord(name string, mode int64) tarRecord {
-	return tarRecord{
-		Header: &tar.Header{
-			Name:     name,
-			Mode:     mode,
-			Typeflag: tar.TypeDir,
-		},
-	}
-}
-
-func ociLayoutFile(version string) tarRecord {
-	if version == "" {
-		version = ocispec.ImageLayoutVersion
-	}
-	layout := ocispec.ImageLayout{
-		Version: version,
-	}
-
-	b, err := json.Marshal(layout)
-	if err != nil {
-		panic(err)
-	}
-
-	return tarRecord{
-		Header: &tar.Header{
-			Name:     ocispec.ImageLayoutFile,
-			Mode:     0444,
-			Size:     int64(len(b)),
-			Typeflag: tar.TypeReg,
-		},
-		CopyTo: func(ctx context.Context, w io.Writer) (int64, error) {
-			n, err := w.Write(b)
-			return int64(n), err
-		},
-	}
-
-}
-
-func ociIndexRecord(manifests ...ocispec.Descriptor) tarRecord {
-	index := ocispec.Index{
-		Versioned: ocispecs.Versioned{
-			SchemaVersion: 2,
-		},
-		Manifests: manifests,
-	}
-
-	b, err := json.Marshal(index)
-	if err != nil {
-		panic(err)
-	}
-
-	return tarRecord{
-		Header: &tar.Header{
-			Name:     "index.json",
-			Mode:     0644,
-			Size:     int64(len(b)),
-			Typeflag: tar.TypeReg,
-		},
-		CopyTo: func(ctx context.Context, w io.Writer) (int64, error) {
-			n, err := w.Write(b)
-			return int64(n), err
-		},
-	}
-}
-
-func writeTar(ctx context.Context, tw *tar.Writer, records []tarRecord) error {
-	sort.Sort(tarRecordsByName(records))
-
-	for _, record := range records {
-		if err := tw.WriteHeader(record.Header); err != nil {
-			return err
-		}
-		if record.CopyTo != nil {
-			n, err := record.CopyTo(ctx, tw)
-			if err != nil {
-				return err
-			}
-			if n != record.Header.Size {
-				return errors.Errorf("unexpected copy size for %s", record.Header.Name)
-			}
-		} else if record.Header.Size > 0 {
-			return errors.Errorf("no content to write to record with non-zero size for %s", record.Header.Name)
-		}
-	}
-	return nil
-}
-
-type tarRecordsByName []tarRecord
-
-func (t tarRecordsByName) Len() int {
-	return len(t)
-}
-func (t tarRecordsByName) Swap(i, j int) {
-	t[i], t[j] = t[j], t[i]
-}
-func (t tarRecordsByName) Less(i, j int) bool {
-	return t[i].Header.Name < t[j].Header.Name
-}