add uncompressed media type

Add a new mime type [1] to represent uncompressed DockerV2 layers, and
propagate it to the destination's manifest.

[1] application/vnd.docker.image.rootfs.diff.tar

Fixes: github.com/containers/podman/issues/2013
Signed-off-by: Valentin Rothberg <[email protected]>

copy/copy.go

@@ -14,6 +14,7 @@ import (
 	"time"
 
 	"github.com/containers/image/image"
+	"github.com/containers/image/manifest"
 	"github.com/containers/image/pkg/blobinfocache"
 	"github.com/containers/image/pkg/compression"
 	"github.com/containers/image/signature"
@@ -813,6 +814,17 @@ func (c *copier) copyBlobFromStream(ctx context.Context, srcStream io.Reader, sr
 		return types.BlobInfo{}, errors.Wrap(err, "Error writing blob")
 	}
 
+	switch compressionOperation {
+	case types.Compress:
+		uploadedInfo.MediaType = manifest.DockerV2Schema2LayerMediaType
+	case types.Decompress:
+		uploadedInfo.MediaType = manifest.DockerV2SchemeLayerMediaTypeUncompressed
+	case types.PreserveOriginal:
+		// preserve whatever the destination sets by default
+	default:
+		panic("unexpected compression operation")
+	}
+
 	// This is fairly horrible: the writer from getOriginalLayerCopyWriter wants to consumer
 	// all of the input (to compute DiffIDs), even if dest.PutBlob does not need it.
 	// So, read everything from originalLayerReader, which will cause the rest to be

directory/directory_dest.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"path/filepath"
 
+	"github.com/containers/image/manifest"
 	"github.com/containers/image/types"
 	"github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
@@ -172,7 +173,7 @@ func (d *dirImageDestination) PutBlob(ctx context.Context, stream io.Reader, inp
 		return types.BlobInfo{}, err
 	}
 	succeeded = true
-	return types.BlobInfo{Digest: computedDigest, Size: size}, nil
+	return types.BlobInfo{Digest: computedDigest, Size: size, MediaType: manifest.DockerV2SchemeLayerMediaTypeUncompressed}, nil
 }
 
 // TryReusingBlob checks whether the transport already contains, or can efficiently reuse, a blob, and if so, applies it to the current destination
@@ -194,7 +195,7 @@ func (d *dirImageDestination) TryReusingBlob(ctx context.Context, info types.Blo
 	if err != nil {
 		return false, types.BlobInfo{}, err
 	}
-	return true, types.BlobInfo{Digest: info.Digest, Size: finfo.Size()}, nil
+	return true, types.BlobInfo{Digest: info.Digest, Size: finfo.Size(), MediaType: manifest.DockerV2SchemeLayerMediaTypeUncompressed}, nil
 
 }
 

manifest/docker_schema2.go

@@ -207,7 +207,10 @@ func (m *Schema2) UpdateLayerInfos(layerInfos []types.BlobInfo) error {
 	original := m.LayersDescriptors
 	m.LayersDescriptors = make([]Schema2Descriptor, len(layerInfos))
 	for i, info := range layerInfos {
-		m.LayersDescriptors[i].MediaType = original[i].MediaType
+		m.LayersDescriptors[i].MediaType = info.MediaType
+		if m.LayersDescriptors[i].MediaType == "" {
+			m.LayersDescriptors[i].MediaType = original[i].MediaType
+		}
 		m.LayersDescriptors[i].Digest = info.Digest
 		m.LayersDescriptors[i].Size = info.Size
 		m.LayersDescriptors[i].URLs = info.URLs

manifest/manifest.go

@@ -24,6 +24,8 @@ const (
 	DockerV2Schema2ConfigMediaType = "application/vnd.docker.container.image.v1+json"
 	// DockerV2Schema2LayerMediaType is the MIME type used for schema 2 layers.
 	DockerV2Schema2LayerMediaType = "application/vnd.docker.image.rootfs.diff.tar.gzip"
+	// DockerV2SchemeLayerMediaTypeUncompressed is the mediaType used for layers which are not compressed.
+	DockerV2SchemeLayerMediaTypeUncompressed = "application/vnd.docker.image.rootfs.diff.tar"
 	// DockerV2ListMediaType MIME type represents Docker manifest schema 2 list
 	DockerV2ListMediaType = "application/vnd.docker.distribution.manifest.list.v2+json"
 	// DockerV2Schema2ForeignLayerMediaType is the MIME type used for schema 2 foreign layers.