Add support for zstd layer upload

It is now possible to `crane append -f bla.tar.zstd` to upload Zstd layer, both from file and from pipe.

Before this commit, crane would erroneously upload such layer with gzip mime type.

While this PR does not _fully_ solve #1501, it is very close to that.

Signed-off-by: Marat Radchenko <[email protected]>

cmd/crane/cmd/flatten.go

@@ -228,7 +228,11 @@ func flattenImage(old v1.Image, repo name.Repository, use string, o crane.Option
 	}
 
 	// TODO: Make compression configurable?
-	layer := stream.NewLayer(mutate.Extract(old), stream.WithCompressionLevel(gzip.BestCompression))
+	layer, err := stream.NewLayer(mutate.Extract(old), stream.WithCompressionLevel(gzip.BestCompression))
+	if err != nil {
+		return nil, fmt.Errorf("new layer: %w", err)
+	}
+
 	if err := remote.WriteLayer(repo, layer, o.Remote...); err != nil {
 		return nil, fmt.Errorf("uploading layer: %w", err)
 	}

internal/zstd/zstd.go

@@ -102,6 +102,14 @@ func UnzipReadCloser(r io.ReadCloser) (io.ReadCloser, error) {
 	}, nil
 }
 
+func UnzipReader(r io.Reader) (io.Reader, error) {
+	return zstd.NewReader(r)
+}
+
+func NewWriterLevel(w io.Writer, level int) (*zstd.Encoder, error) {
+	return zstd.NewWriter(w, zstd.WithEncoderLevel(zstd.EncoderLevelFromZstd(level)))
+}
+
 // Is detects whether the input stream is compressed.
 func Is(r io.Reader) (bool, error) {
 	magicHeader := make([]byte, 4)

pkg/compression/compression.go

@@ -15,6 +15,12 @@
 // Package compression abstracts over gzip and zstd.
 package compression
 
+import (
+	"fmt"
+
+	"github.com/google/go-containerregistry/pkg/v1/types"
+)
+
 // Compression is an enumeration of the supported compression algorithms
 type Compression string
 
@@ -24,3 +30,29 @@ const (
 	GZip Compression = "gzip"
 	ZStd Compression = "zstd"
 )
+
+func (compression Compression) ToMediaType(oci bool) (types.MediaType, error) {
+	if oci {
+		switch compression {
+		case ZStd:
+			return types.OCILayerZStd, nil
+		case GZip:
+			return types.OCILayer, nil
+		case None:
+			return types.OCIUncompressedLayer, nil
+		default:
+			return types.OCILayer, fmt.Errorf("unsupported compression: %s", compression)
+		}
+	} else {
+		switch compression {
+		case ZStd:
+			return types.DockerLayerZstd, nil
+		case GZip:
+			return types.DockerLayer, nil
+		case None:
+			return types.DockerUncompressedLayer, nil
+		default:
+			return types.DockerLayer, fmt.Errorf("unsupported compression: %s", compression)
+		}
+	}
+}

pkg/crane/append.go

@@ -55,15 +55,11 @@ func Append(base v1.Image, paths ...string) (v1.Image, error) {
 		return nil, fmt.Errorf("getting base image media type: %w", err)
 	}
 
-	layerType := types.DockerLayer
-
-	if baseMediaType == types.OCIManifestSchema1 {
-		layerType = types.OCILayer
-	}
+	oci := baseMediaType == types.OCIManifestSchema1
 
 	layers := make([]v1.Layer, 0, len(paths))
 	for _, path := range paths {
-		layer, err := getLayer(path, layerType)
+		layer, err := getLayer(path, oci)
 		if err != nil {
 			return nil, fmt.Errorf("reading layer %q: %w", path, err)
 		}
@@ -81,16 +77,16 @@ func Append(base v1.Image, paths ...string) (v1.Image, error) {
 	return mutate.AppendLayers(base, layers...)
 }
 
-func getLayer(path string, layerType types.MediaType) (v1.Layer, error) {
+func getLayer(path string, oci bool) (v1.Layer, error) {
 	f, err := streamFile(path)
 	if err != nil {
 		return nil, err
 	}
 	if f != nil {
-		return stream.NewLayer(f, stream.WithMediaType(layerType)), nil
+		return stream.NewLayer(f, stream.WithOCIMediaType(oci))
 	}
 
-	return tarball.LayerFromFile(path, tarball.WithMediaType(layerType))
+	return tarball.LayerFromFile(path, tarball.WithOCIMediaType(oci))
 }
 
 // If we're dealing with a named pipe, trying to open it multiple times will

pkg/v1/stream/layer.go

@@ -26,6 +26,9 @@ import (
 	"os"
 	"sync"
 
+	internalcomp "github.com/google/go-containerregistry/internal/compression"
+	"github.com/google/go-containerregistry/internal/zstd"
+	"github.com/google/go-containerregistry/pkg/compression"
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/types"
 )
@@ -42,14 +45,19 @@ var (
 
 // Layer is a streaming implementation of v1.Layer.
 type Layer struct {
-	blob        io.ReadCloser
-	consumed    bool
-	compression int
+	closer             io.Closer
+	uncompressedReader io.Reader
+
+	consumed bool
+
+	compression      compression.Compression
+	compressionLevel int
 
 	mu             sync.Mutex
 	digest, diffID *v1.Hash
 	size           int64
-	mediaType      types.MediaType
+
+	oci bool
 }
 
 var _ v1.Layer = (*Layer)(nil)
@@ -60,32 +68,53 @@ type LayerOption func(*Layer)
 // WithCompressionLevel sets the gzip compression. See `gzip.NewWriterLevel` for possible values.
 func WithCompressionLevel(level int) LayerOption {
 	return func(l *Layer) {
-		l.compression = level
+		l.compressionLevel = level
 	}
 }
 
-// WithMediaType is a functional option for overriding the layer's media type.
-func WithMediaType(mt types.MediaType) LayerOption {
+// WithOCIMediaType is a functional option for overriding the layer's media type.
+func WithOCIMediaType(oci bool) LayerOption {
 	return func(l *Layer) {
-		l.mediaType = mt
+		l.oci = oci
 	}
 }
 
 // NewLayer creates a Layer from an io.ReadCloser.
-func NewLayer(rc io.ReadCloser, opts ...LayerOption) *Layer {
+func NewLayer(rc io.ReadCloser, opts ...LayerOption) (*Layer, error) {
+	comp, peekReader, err := internalcomp.PeekCompression(rc)
+	if err != nil {
+		return nil, err
+	}
+
 	layer := &Layer{
-		blob:        rc,
-		compression: gzip.BestSpeed,
-		// We use DockerLayer for now as uncompressed layers
-		// are unimplemented
-		mediaType: types.DockerLayer,
+		closer:      rc,
+		compression: comp,
+	}
+
+	switch comp {
+	case compression.ZStd:
+		layer.compression = comp
+		layer.uncompressedReader, err = zstd.UnzipReader(peekReader)
+		if err != nil {
+			return nil, err
+		}
+	case compression.GZip:
+		layer.compression = comp
+		layer.uncompressedReader, err = gzip.NewReader(peekReader)
+		if err != nil {
+			return nil, err
+		}
+	default:
+		// No support for uncompressed layers for now
+		layer.compression = compression.GZip
+		layer.uncompressedReader = peekReader
 	}
 
 	for _, opt := range opts {
 		opt(layer)
 	}
 
-	return layer
+	return layer, nil
 }
 
 // Digest implements v1.Layer.
@@ -120,7 +149,7 @@ func (l *Layer) Size() (int64, error) {
 
 // MediaType implements v1.Layer
 func (l *Layer) MediaType() (types.MediaType, error) {
-	return l.mediaType, nil
+	return l.compression.ToMediaType(l.oci)
 }
 
 // Uncompressed implements v1.Layer.
@@ -183,9 +212,27 @@ func newCompressedReader(l *Layer) (*compressedReader, error) {
 	// Buffer the output of the gzip writer so we don't have to wait on pr to keep writing.
 	// 64K ought to be small enough for anybody.
 	bw := bufio.NewWriterSize(mw, 2<<16)
-	zw, err := gzip.NewWriterLevel(bw, l.compression)
-	if err != nil {
-		return nil, err
+
+	var compressedWriter io.Writer
+	var compressedCloser io.Closer
+
+	switch l.compression {
+	case compression.ZStd:
+		w, err := zstd.NewWriterLevel(bw, l.compressionLevel)
+		if err != nil {
+			return nil, err
+		}
+		compressedWriter = w
+		compressedCloser = w
+	case compression.GZip:
+		w, err := gzip.NewWriterLevel(bw, l.compressionLevel)
+		if err != nil {
+			return nil, err
+		}
+		compressedWriter = w
+		compressedCloser = w
+	case compression.None:
+		compressedWriter = bw
 	}
 
 	doneDigesting := make(chan struct{})
@@ -211,7 +258,7 @@ func newCompressedReader(l *Layer) (*compressedReader, error) {
 			//
 			// NOTE: net/http will call close on success, so if we've already
 			// closed the inner rc, it's not an error.
-			if err := l.blob.Close(); err != nil && !errors.Is(err, os.ErrClosed) {
+			if err := l.closer.Close(); err != nil && !errors.Is(err, os.ErrClosed) {
 				return err
 			}
 
@@ -223,13 +270,16 @@ func newCompressedReader(l *Layer) (*compressedReader, error) {
 	go func() {
 		// Copy blob into the gzip writer, which also hashes and counts the
 		// size of the compressed output, and hasher of the raw contents.
-		_, copyErr := io.Copy(io.MultiWriter(h, zw), l.blob)
+		_, copyErr := io.Copy(io.MultiWriter(h, compressedWriter), l.uncompressedReader)
 
 		// Close the gzip writer once copying is done. If this is done in the
 		// Close method of compressedReader instead, then it can cause a panic
 		// when the compressedReader is closed before the blob is fully
 		// consumed and io.Copy in this goroutine is still blocking.
-		closeErr := zw.Close()
+		var closeErr error
+		if compressedCloser != nil {
+			closeErr = compressedCloser.Close()
+		}
 
 		// Check errors from writing and closing streams.
 		if copyErr != nil {