docker/archive/transport.go
func (ref archiveReference) NewImageSource(ctx context.Context, sys *types.SystemContext) (types.ImageSource, error) {
	return newImageSource(ctx, ref)
}
func (ref archiveReference) NewImageSource(ctx context.Context, sys *types.SystemContext) (types.ImageSource, error) {
	return newImageSource(ctx, ref)
}
// NewImageSource returns a types.ImageSource for this reference.
// The caller must call .Close() on the returned ImageSource.