type TreeCache interface {
	// GetEntry with the given key for the given path.
	GetEntry(key string, path ...string) (interface{}, bool)

	// Get a list of values including wildcards labels (e.g. "*").
	GetValuesForPathWithWildcards(path ...string) []*skymsg.Service

	// SetEntry creates the entire path if it doesn't already exist in
	// the cache, then sets the given service record under the given
	// key. The path this entry would have occupied in an etcd datastore
	// is computed from the given fqdn and stored as the "Key" of the
	// skydns service; this is only required because skydns expects the
	// service record to contain a key in a specific format (presumably
	// for legacy compatibility). Note that the fqnd string typically
	// contains both the key and all elements in the path.
	SetEntry(key string, val *skymsg.Service, fqdn string, path ...string)

	// SetSubCache inserts the given subtree under the given
	// path:key. Usually the key is the name of a Kubernetes Service,
	// and the path maps to the cluster subdomains matching the Service.
	SetSubCache(key string, subCache TreeCache, path ...string)

	// DeletePath removes all entries associated with a given path.
	DeletePath(path ...string) bool

	// Serialize dumps a JSON representation of the cache.
	Serialize() (string, error)
}