Image returns a new Image which wraps the given Image, whose layers will be pulled from the Cache if they are found, and written to the Cache as they are read from the underlying Image.

ImageIndex returns a new ImageIndex which wraps the given ImageIndex's children with either Image(child, c) or ImageIndex(child, c) depending on type.

NewFilesystemCache returns a Cache implementation backed by files.

ReadOnly returns a read-only implementation of the given Cache.

ErrNotFound is returned by Get when no layer with the given Hash is found.

Cache encapsulates methods to interact with cached layers.