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

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

TargetSizeLabel is a label which contains layer size.

TargetSociIndexDigestLabel is a label which contains the digest of the soci index.

Source is a typed blob source information.

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

RegistryHosts is copied from [github.com/awslabs/soci-snapshotter/service/resolver.RegistryHosts] to reduce package dependency.