func restoreCache(src string, s storage.Storage, a archive.Archive) error {
reader, writer := io.Pipe()
cw := make(chan error, 1)
defer close(cw)
go func() {
defer writer.Close()
cw <- s.Get(src, writer)
}()
err := a.Unpack("", reader)
werr := <-cw
if werr != nil {
return werr
}
return err
}
