client: create oci-layout file in StoreIndex

This code is used by both the local cache exporter backend and the oci
exporter when tar=false is set. Previously, these components would not
create the oci-layout file which is required by opencontainers/image-spec.

With this change, clients will now create this file next to index.json.

Signed-off-by: Justin Chadwell <[email protected]>

Author: jedevc

client/ociindex/ociindex.go

@@ -20,15 +20,18 @@ const (
 )
 
 type StoreIndex struct {
-	indexPath string
-	lockPath  string
+	indexPath  string
+	lockPath   string
+	layoutPath string
 }
 
 func NewStoreIndex(storePath string) StoreIndex {
 	indexPath := path.Join(storePath, indexFile)
+	layoutPath := path.Join(storePath, ocispecs.ImageLayoutFile)
 	return StoreIndex{
-		indexPath: indexPath,
-		lockPath:  indexPath + lockFileSuffix,
+		indexPath:  indexPath,
+		lockPath:   indexPath + lockFileSuffix,
+		layoutPath: layoutPath,
 	}
 }
 
@@ -58,6 +61,7 @@ func (s StoreIndex) Read() (*ocispecs.Index, error) {
 }
 
 func (s StoreIndex) Put(tag string, desc ocispecs.Descriptor) error {
+	// lock the store to prevent concurrent access
 	lock := flock.New(s.lockPath)
 	locked, err := lock.TryLock()
 	if err != nil {
@@ -71,36 +75,49 @@ func (s StoreIndex) Put(tag string, desc ocispecs.Descriptor) error {
 		os.RemoveAll(s.lockPath)
 	}()
 
-	f, err := os.OpenFile(s.indexPath, os.O_RDWR|os.O_CREATE, 0644)
+	// create the oci-layout file
+	layout := ocispecs.ImageLayout{
+		Version: ocispecs.ImageLayoutVersion,
+	}
+	layoutData, err := json.Marshal(layout)
+	if err != nil {
+		return err
+	}
+	if err := os.WriteFile(s.layoutPath, layoutData, 0644); err != nil {
+		return err
+	}
+
+	// modify the index file
+	idxFile, err := os.OpenFile(s.indexPath, os.O_RDWR|os.O_CREATE, 0644)
 	if err != nil {
 		return errors.Wrapf(err, "could not open %s", s.indexPath)
 	}
-	defer f.Close()
+	defer idxFile.Close()
 
 	var idx ocispecs.Index
-	b, err := io.ReadAll(f)
+	idxData, err := io.ReadAll(idxFile)
 	if err != nil {
 		return errors.Wrapf(err, "could not read %s", s.indexPath)
 	}
-	if len(b) > 0 {
-		if err := json.Unmarshal(b, &idx); err != nil {
-			return errors.Wrapf(err, "could not unmarshal %s (%q)", s.indexPath, string(b))
+	if len(idxData) > 0 {
+		if err := json.Unmarshal(idxData, &idx); err != nil {
+			return errors.Wrapf(err, "could not unmarshal %s (%q)", s.indexPath, string(idxData))
 		}
 	}
 
 	if err = insertDesc(&idx, desc, tag); err != nil {
 		return err
 	}
 
-	b, err = json.Marshal(idx)
+	idxData, err = json.Marshal(idx)
 	if err != nil {
 		return err
 	}
-	if _, err = f.WriteAt(b, 0); err != nil {
-		return err
+	if _, err = idxFile.WriteAt(idxData, 0); err != nil {
+		return errors.Wrapf(err, "could not write %s", s.indexPath)
 	}
-	if err = f.Truncate(int64(len(b))); err != nil {
-		return err
+	if err = idxFile.Truncate(int64(len(idxData))); err != nil {
+		return errors.Wrapf(err, "could not truncate %s", s.indexPath)
 	}
 	return nil
 }