ostree: provide LayerInfosForCopy

it enables the copy of compressed images.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

ostree/ostree_src.go

@@ -7,6 +7,7 @@ import (
 	"compress/gzip"
 	"context"
 	"encoding/base64"
+	"encoding/json"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -18,6 +19,7 @@ import (
 	"github.com/containers/image/types"
 	"github.com/containers/storage/pkg/ioutils"
 	"github.com/opencontainers/go-digest"
+	imgspecv1 "github.com/opencontainers/image-spec/specs-go/v1"
 	glib "github.com/ostreedev/ostree-go/pkg/glibobject"
 	"github.com/pkg/errors"
 	"github.com/vbatts/tar-split/tar/asm"
@@ -34,14 +36,15 @@ import (
 import "C"
 
 type ostreeImageSource struct {
-	ref    ostreeReference
-	tmpDir string
-	repo   *C.struct_OstreeRepo
+	ref        ostreeReference
+	tmpDir     string
+	repo       *C.struct_OstreeRepo
+	compressed map[digest.Digest]digest.Digest
 }
 
 // newImageSource returns an ImageSource for reading from an existing directory.
 func newImageSource(ctx *types.SystemContext, tmpDir string, ref ostreeReference) (types.ImageSource, error) {
-	return &ostreeImageSource{ref: ref, tmpDir: tmpDir}, nil
+	return &ostreeImageSource{ref: ref, tmpDir: tmpDir, compressed: make(map[digest.Digest]digest.Digest)}, nil
 }
 
 // Reference returns the reference used to set up this source.
@@ -255,7 +258,12 @@ func (s *ostreeImageSource) readSingleFile(commit, path string) (io.ReadCloser,
 
 // GetBlob returns a stream for the specified blob, and the blob's size.
 func (s *ostreeImageSource) GetBlob(info types.BlobInfo) (io.ReadCloser, int64, error) {
+
 	blob := info.Digest.Hex()
+	compressedBlob, found := s.compressed[info.Digest]
+	if found {
+		blob = compressedBlob.Hex()
+	}
 	branch := fmt.Sprintf("ociimage/%s", blob)
 
 	if s.repo == nil {
@@ -348,7 +356,62 @@ func (s *ostreeImageSource) GetSignatures(ctx context.Context, instanceDigest *d
 	return signatures, nil
 }
 
-// LayerInfosForCopy() returns updated layer info that should be used when reading, in preference to values in the manifest, if specified.
+// LayerInfosForCopy() returns the list of layer blobs that make up the root filesystem of
+// the image, after they've been decompressed.
 func (s *ostreeImageSource) LayerInfosForCopy() []types.BlobInfo {
-	return nil
+	updatedBlobInfos := []types.BlobInfo{}
+	manifestBlob, manifestType, err := s.GetManifest(nil)
+	if err != nil {
+		return nil
+	}
+
+	var schema manifestSchema
+	if err := json.Unmarshal(manifestBlob, &schema); err != nil {
+		return nil
+	}
+
+	uncompressedLayerType := ""
+	switch manifestType {
+	case imgspecv1.MediaTypeImageManifest:
+		uncompressedLayerType = imgspecv1.MediaTypeImageLayer
+	case manifest.DockerV2Schema1MediaType, manifest.DockerV2Schema1SignedMediaType, manifest.DockerV2Schema2MediaType:
+		// This is actually a compressed type, but there's no uncompressed type defined
+		uncompressedLayerType = manifest.DockerV2Schema2LayerMediaType
+	}
+
+	layers := []digest.Digest{}
+
+	for _, layer := range schema.LayersDescriptors {
+		layers = append(layers, layer.Digest)
+	}
+	for _, layer := range schema.FSLayers {
+		layers = append(layers, layer.BlobSum)
+	}
+
+	for _, layer := range layers {
+		branch := fmt.Sprintf("ociimage/%s", layer.Hex())
+		found, uncompressedDigestStr, err := readMetadata(s.repo, branch, "docker.uncompressed_digest")
+		if err != nil || !found {
+			return nil
+		}
+
+		found, uncompressedSizeStr, err := readMetadata(s.repo, branch, "docker.uncompressed_size")
+		if err != nil || !found {
+			return nil
+		}
+
+		uncompressedSize, err := strconv.ParseInt(uncompressedSizeStr, 10, 64)
+		if err != nil {
+			return nil
+		}
+		uncompressedDigest := digest.Digest(uncompressedDigestStr)
+		blobInfo := types.BlobInfo{
+			Digest:    uncompressedDigest,
+			Size:      uncompressedSize,
+			MediaType: uncompressedLayerType,
+		}
+		s.compressed[uncompressedDigest] = layer
+		updatedBlobInfos = append([]types.BlobInfo{blobInfo}, updatedBlobInfos...)
+	}
+	return updatedBlobInfos
 }