AppendDefaultLabelsHandlerWrapper makes a handler which appends image's basic information to each layer descriptor as annotations during unpack.

AppendExtraLabelsHandler adds optional labels that aren't provided by "github.com/containerd/containerd/pkg/snapshotters" but can be used for stargz snapshotter's extra functionalities.

FromDefaultLabels returns a function for converting snapshot labels to source information based on labels.

Source is a typed blob source information.

GetSources is a function for converting snapshot labels into typed blob sources information.

RegistryHosts returns a list of registries that provides the specified image.