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.

Note that consumers of the containers/image library need to update
opencontainers/image-spec to commit 775207bd45b6cb8153ce218cc59351799217451f.

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

Signed-off-by: Valentin Rothberg <[email protected]>

copy/copy.go

@@ -911,6 +911,12 @@ func (c *copier) copyBlobFromStream(ctx context.Context, srcStream io.Reader, sr
 		return types.BlobInfo{}, errors.Wrap(err, "Error writing blob")
 	}
 
+	uploadedInfo.CompressionOperation = compressionOperation
+	// If we can modify the layer's blob, set the desired algorithm for it to be set in the manifest.
+	if canModifyBlob && !isConfig {
+		uploadedInfo.CompressionAlgorithm = &desiredCompressionFormat
+	}
+
 	// 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/docker_schema2.go

@@ -6,6 +6,7 @@ import (
 	"crypto/sha256"
 	"encoding/hex"
 	"encoding/json"
+	"fmt"
 	"io/ioutil"
 	"strings"
 
@@ -207,12 +208,21 @@ func (m *manifestSchema2) convertToManifestOCI1(ctx context.Context) (types.Imag
 	layers := make([]imgspecv1.Descriptor, len(m.m.LayersDescriptors))
 	for idx := range layers {
 		layers[idx] = oci1DescriptorFromSchema2Descriptor(m.m.LayersDescriptors[idx])
-		if m.m.LayersDescriptors[idx].MediaType == manifest.DockerV2Schema2ForeignLayerMediaType {
+		switch m.m.LayersDescriptors[idx].MediaType {
+		case manifest.DockerV2Schema2ForeignLayerMediaType:
 			layers[idx].MediaType = imgspecv1.MediaTypeImageLayerNonDistributable
-		} else {
-			// we assume layers are gzip'ed because docker v2s2 only deals with
-			// gzip'ed layers. However, OCI has non-gzip'ed layers as well.
+		case manifest.DockerV2Schema2ForeignLayerMediaTypeGzip:
+			layers[idx].MediaType = imgspecv1.MediaTypeImageLayerNonDistributableGzip
+		case manifest.DockerV2Schema2ForeignLayerMediaTypeZstd:
+			layers[idx].MediaType = imgspecv1.MediaTypeImageLayerNonDistributableZstd
+		case manifest.DockerV2SchemaLayerMediaTypeUncompressed:
+			layers[idx].MediaType = imgspecv1.MediaTypeImageLayer
+		case manifest.DockerV2Schema2LayerMediaType:
 			layers[idx].MediaType = imgspecv1.MediaTypeImageLayerGzip
+		case manifest.DockerV2Schema2LayerMediaTypeZstd:
+			layers[idx].MediaType = imgspecv1.MediaTypeImageLayerZstd
+		default:
+			return nil, fmt.Errorf("Unknown media type during manifest conversion: %q", m.m.LayersDescriptors[idx].MediaType)
 		}
 	}
 

image/oci.go

@@ -3,6 +3,7 @@ package image
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"io/ioutil"
 
 	"github.com/containers/image/docker/reference"
@@ -187,7 +188,22 @@ func (m *manifestOCI1) convertToManifestSchema2() (types.Image, error) {
 	layers := make([]manifest.Schema2Descriptor, len(m.m.Layers))
 	for idx := range layers {
 		layers[idx] = schema2DescriptorFromOCI1Descriptor(m.m.Layers[idx])
-		layers[idx].MediaType = manifest.DockerV2Schema2LayerMediaType
+		switch layers[idx].MediaType {
+		case imgspecv1.MediaTypeImageLayerNonDistributable:
+			layers[idx].MediaType = manifest.DockerV2Schema2ForeignLayerMediaType
+		case imgspecv1.MediaTypeImageLayerNonDistributableGzip:
+			layers[idx].MediaType = manifest.DockerV2Schema2ForeignLayerMediaTypeGzip
+		case imgspecv1.MediaTypeImageLayerNonDistributableZstd:
+			layers[idx].MediaType = manifest.DockerV2Schema2ForeignLayerMediaTypeZstd
+		case imgspecv1.MediaTypeImageLayer:
+			layers[idx].MediaType = manifest.DockerV2SchemaLayerMediaTypeUncompressed
+		case imgspecv1.MediaTypeImageLayerGzip:
+			layers[idx].MediaType = manifest.DockerV2Schema2LayerMediaType
+		case imgspecv1.MediaTypeImageLayerZstd:
+			layers[idx].MediaType = manifest.DockerV2Schema2LayerMediaTypeZstd
+		default:
+			return nil, fmt.Errorf("Unknown media type during manifest conversion: %q", layers[idx].MediaType)
+		}
 	}
 
 	// Rather than copying the ConfigBlob now, we just pass m.src to the

image/sourced.go

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

manifest/docker_schema2.go

@@ -2,12 +2,15 @@ package manifest
 
 import (
 	"encoding/json"
+	"fmt"
 	"time"
 
+	"github.com/containers/image/pkg/compression"
 	"github.com/containers/image/pkg/strslice"
 	"github.com/containers/image/types"
 	"github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
 )
 
 // Schema2Descriptor is a “descriptor” in docker/distribution schema 2.
@@ -207,7 +210,58 @@ 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
+		// Set the correct media types based on the specified compression
+		// operation, the desired compression algorithm AND the original media
+		// type.
+		switch info.CompressionOperation {
+		case types.PreserveOriginal:
+			// Keep the original media type.
+			m.LayersDescriptors[i].MediaType = original[i].MediaType
+
+		case types.Decompress:
+			// Decompress the original media type and check if it was
+			// non-distributable one or not.
+			switch original[i].MediaType {
+			case DockerV2Schema2ForeignLayerMediaTypeGzip, DockerV2Schema2ForeignLayerMediaTypeZstd:
+				m.LayersDescriptors[i].MediaType = DockerV2Schema2ForeignLayerMediaType
+			default:
+				m.LayersDescriptors[i].MediaType = DockerV2SchemaLayerMediaTypeUncompressed
+			}
+
+		// TODO: should this only work on "known" media types?
+		// For background, please refer to:
+		// https://github.com/containers/image/pull/563#discussion_r316772562
+		case types.Compress:
+			if info.CompressionAlgorithm == nil {
+				logrus.Debugf("Preparing updated manifest: blob %q was compressed but does not specify by which algorithm: falling back to use the original blob", info.Digest)
+				m.LayersDescriptors[i].MediaType = original[i].MediaType
+				break
+			}
+			// Compress the original media type and set the new one based on
+			// that type (distributable or not) and the specified compression
+			// algorithm. Throw an error if the algorithm is not supported.
+			switch info.CompressionAlgorithm.Name() {
+			case compression.Gzip.Name():
+				switch original[i].MediaType {
+				case DockerV2Schema2ForeignLayerMediaType, DockerV2Schema2ForeignLayerMediaTypeZstd:
+					m.LayersDescriptors[i].MediaType = DockerV2Schema2ForeignLayerMediaTypeGzip
+				default:
+					m.LayersDescriptors[i].MediaType = DockerV2Schema2LayerMediaType
+				}
+			case compression.Zstd.Name():
+				switch original[i].MediaType {
+				case DockerV2Schema2ForeignLayerMediaType, DockerV2Schema2ForeignLayerMediaTypeGzip:
+					m.LayersDescriptors[i].MediaType = DockerV2Schema2ForeignLayerMediaTypeZstd
+				default:
+					m.LayersDescriptors[i].MediaType = DockerV2Schema2LayerMediaTypeZstd
+				}
+			default:
+				return fmt.Errorf("Error preparing updated manifest: unknown compression algorithm %q fo layer %q", info.CompressionAlgorithm.Name(), info.Digest)
+			}
+
+		default:
+			return fmt.Errorf("Error preparing updated manifest: unknown compression operation (%d) for layer %q", info.CompressionOperation, info.Digest)
+		}
 		m.LayersDescriptors[i].Digest = info.Digest
 		m.LayersDescriptors[i].Size = info.Size
 		m.LayersDescriptors[i].URLs = info.URLs