Set content labels based on content type

Give control of the content labeling process for children to
the client. This allows the client to control the names
associated with the labels and filter out labels.

Signed-off-by: Derek McGowan <derek@mcg.dev>

images/mediatypes.go

@@ -124,3 +124,31 @@ func IsKnownConfig(mt string) bool {
 	}
 	return false
 }
+
+// ChildGCLabels returns the label for a given descriptor to reference it
+func ChildGCLabels(desc ocispec.Descriptor) []string {
+	mt := desc.MediaType
+	if IsKnownConfig(mt) {
+		return []string{"containerd.io/gc.ref.content.config"}
+	}
+
+	switch mt {
+	case MediaTypeDockerSchema2Manifest, ocispec.MediaTypeImageManifest:
+		return []string{"containerd.io/gc.ref.content.m."}
+	}
+
+	if IsLayerType(mt) {
+		return []string{"containerd.io/gc.ref.content.l."}
+	}
+
+	return []string{"containerd.io/gc.ref.content."}
+}
+
+// ChildGCLabelsFilterLayers returns the labels for a given descriptor to
+// reference it, skipping layer media types
+func ChildGCLabelsFilterLayers(desc ocispec.Descriptor) []string {
+	if IsLayerType(desc.MediaType) {
+		return nil
+	}
+	return ChildGCLabels(desc)
+}