Add layer offset (WIP)

Author: errordeveloper

api/v1beta2/ocirepository_types.go

@@ -166,7 +166,8 @@ type OCIRepositoryRef struct {
 type OCILayerSelector struct {
 	// MediaType specifies the OCI media type of the layer
 	// which should be extracted from the OCI Artifact. The
-	// first layer matching this type is selected.
+	// first layer matching this type is selected by default,
+	// otherwise 'offest' needs to be specified.
 	// +optional
 	MediaType string `json:"mediaType,omitempty"`
 
@@ -177,6 +178,11 @@ type OCILayerSelector struct {
 	// +kubebuilder:validation:Enum=extract;copy
 	// +optional
 	Operation string `json:"operation,omitempty"`
+
+	// Offset specifies the index of the layer which should be extracted.
+	// +kubebuilder:validation:Minimum=0
+	// +optional
+	Offset *int `json:"offset,omitempty"`
 }
 
 // OCIRepositoryVerification verifies the authenticity of an OCI Artifact
@@ -307,6 +313,14 @@ func (in *OCIRepository) GetLayerOperation() string {
 	return in.Spec.LayerSelector.Operation
 }
 
+func (in *OCIRepository) GetLayerOffset() int {
+	if in.Spec.LayerSelector == nil || in.Spec.LayerSelector.Offset == nil {
+		return 0
+	}
+
+	return *in.Spec.LayerSelector.Offset
+}
+
 // +genclient
 // +genclient:Namespaced
 // +kubebuilder:storageversion

internal/controller/ocirepository_controller.go

@@ -539,30 +539,40 @@ func (r *OCIRepositoryReconciler) selectLayer(obj *ociv1.OCIRepository, image gc
 		return nil, fmt.Errorf("failed to parse artifact layers: %w", err)
 	}
 
-	if len(layers) < 1 {
+	offset := obj.GetLayerOffset()
+	mediaType := obj.GetLayerMediaType()
+
+	if len(layers) == 0 {
 		return nil, fmt.Errorf("no layers found in artifact")
 	}
 
+	if len(layers) <= offset {
+		return nil, fmt.Errorf("layer offset %d is out of bounds", offset)
+	}
+
 	var layer gcrv1.Layer
 	switch {
-	case obj.GetLayerMediaType() != "":
+	case mediaType != "":
 		var found bool
 		for i, l := range layers {
+			if i < offset {
+				continue
+			}
 			md, err := l.MediaType()
 			if err != nil {
 				return nil, fmt.Errorf("failed to determine the media type of layer[%v] from artifact: %w", i, err)
 			}
-			if string(md) == obj.GetLayerMediaType() {
+			if string(md) == mediaType {
 				layer = layers[i]
 				found = true
 				break
 			}
 		}
 		if !found {
-			return nil, fmt.Errorf("failed to find layer with media type '%s' in artifact", obj.GetLayerMediaType())
+			return nil, fmt.Errorf("failed to find layer with media type '%s' in artifact at offset %d", obj.GetLayerMediaType(), offset)
 		}
 	default:
-		layer = layers[0]
+		layer = layers[offset]
 	}
 
 	blob, err := layer.Compressed()