copy: set media types

When copying an image, record the compression in the BlobInfo and use
the information when updating the manifest's layer infos to set the
layers' media types correctly.

Fixes: github.com/containers/podman/issues/2013
Fixes: github.com/containers/buildah/issues/1589

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

copy/copy.go

@@ -869,6 +869,11 @@ func (c *copier) copyBlobFromStream(ctx context.Context, srcStream io.Reader, sr
 		return types.BlobInfo{}, errors.Wrap(err, "Error writing blob")
 	}
 
+	// If we can modify the layer's blob, set the desired compression for it to be set in the manifest.
+	if canModifyBlob && !isConfig {
+		uploadedInfo.Compression = c.dest.DesiredLayerCompression()
+	}
+
 	// 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

image/sourced.go

@@ -5,6 +5,7 @@ package image
 
 import (
 	"context"
+
 	"github.com/containers/image/types"
 )
 

manifest/docker_schema1.go

@@ -142,6 +142,12 @@ func (m *Schema1) UpdateLayerInfos(layerInfos []types.BlobInfo) error {
 	}
 	m.FSLayers = make([]Schema1FSLayers, len(layerInfos))
 	for i, info := range layerInfos {
+		switch info.Compression {
+		case types.Decompress:
+			m.FSLayers[(len(layerInfos)-1)-i].MediaType = DockerV2SchemaLayerMediaTypeUncompressed
+		case types.Compress:
+			m.FSLayers[(len(layerInfos)-1)-i].MediaType = DockerV2SchemaLayerMediaType
+		}
 		// (docker push) sets up m.ExtractedV1Compatibility[].{Id,Parent} based on values of info.Digest,
 		// but (docker pull) ignores them in favor of computing DiffIDs from uncompressed data, except verifying the child->parent links and uniqueness.
 		// So, we don't bother recomputing the IDs in m.History.V1Compatibility.

manifest/docker_schema2.go

@@ -207,7 +207,14 @@ 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
+		switch info.Compression {
+		case types.PreserveOriginal:
+			m.LayersDescriptors[i].MediaType = original[i].MediaType
+		case types.Decompress:
+			m.LayersDescriptors[i].MediaType = DockerV2SchemaLayerMediaTypeUncompressed
+		case types.Compress:
+			m.LayersDescriptors[i].MediaType = DockerV2SchemaLayerMediaType
+		}
 		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"
+	// DockerV2SchemaLayerMediaTypeUncompressed is the mediaType used for uncompressed layers.
+	DockerV2SchemaLayerMediaTypeUncompressed = "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.

manifest/oci.go

@@ -81,7 +81,14 @@ func (m *OCI1) UpdateLayerInfos(layerInfos []types.BlobInfo) error {
 	original := m.Layers
 	m.Layers = make([]imgspecv1.Descriptor, len(layerInfos))
 	for i, info := range layerInfos {
-		m.Layers[i].MediaType = original[i].MediaType
+		switch info.Compression {
+		case types.PreserveOriginal:
+			m.Layers[i].MediaType = original[i].MediaType
+		case types.Decompress:
+			m.Layers[i].MediaType = imgspecv1.MediaTypeImageLayer
+		case types.Compress:
+			m.Layers[i].MediaType = imgspecv1.MediaTypeImageLayerGzip
+		}
 		m.Layers[i].Digest = info.Digest
 		m.Layers[i].Size = info.Size
 		m.Layers[i].Annotations = info.Annotations

types/types.go

@@ -7,7 +7,7 @@ import (
 
 	"github.com/containers/image/docker/reference"
 	"github.com/opencontainers/go-digest"
-	"github.com/opencontainers/image-spec/specs-go/v1"
+	v1 "github.com/opencontainers/image-spec/specs-go/v1"
 )
 
 // ImageTransport is a top-level namespace for ways to to store/load an image.
@@ -90,6 +90,19 @@ type ImageReference interface {
 	DeleteImage(ctx context.Context, sys *SystemContext) error
 }
 
+// LayerCompression indicates if layers must be compressed, decompressed or preserved
+type LayerCompression int
+
+const (
+	// PreserveOriginal indicates the layer must be preserved, ie
+	// no compression or decompression.
+	PreserveOriginal LayerCompression = iota
+	// Decompress indicates the layer must be decompressed
+	Decompress
+	// Compress indicates the layer must be compressed
+	Compress
+)
+
 // BlobInfo collects known information about a blob (layer/config).
 // In some situations, some fields may be unknown, in others they may be mandatory; documenting an “unknown” value here does not override that.
 type BlobInfo struct {
@@ -98,6 +111,7 @@ type BlobInfo struct {
 	URLs        []string
 	Annotations map[string]string
 	MediaType   string
+	Compression LayerCompression
 }
 
 // BICTransportScope encapsulates transport-dependent representation of a “scope” where blobs are or are not present.
@@ -211,19 +225,6 @@ type ImageSource interface {
 	LayerInfosForCopy(ctx context.Context) ([]BlobInfo, error)
 }
 
-// LayerCompression indicates if layers must be compressed, decompressed or preserved
-type LayerCompression int
-
-const (
-	// PreserveOriginal indicates the layer must be preserved, ie
-	// no compression or decompression.
-	PreserveOriginal LayerCompression = iota
-	// Decompress indicates the layer must be decompressed
-	Decompress
-	// Compress indicates the layer must be compressed
-	Compress
-)
-
 // ImageDestination is a service, possibly remote (= slow), to store components of a single image.
 //
 // There is a specific required order for some of the calls: