var ErrNotImplemented = errors.New("not implemented")

// ReadFrom implements support for calling internal io.ReaderFrom implementations
// returns an error if the underlying ResponseWriter does not implement io.ReaderFrom
func (lrw *ResponseRecorder) ReadFrom(r io.Reader) (int64, error) {
	if lrw.ReaderFrom != nil {
		n, err := lrw.ReaderFrom.ReadFrom(r)
		lrw.bytesWritten += int(n)
		return n, err
	}

		sr, ok := rc.(*sendFileReader)
		if ok {
			// Sendfile sends in 4MiB chunks per sendfile syscall which is more than enough
			// for most setups.
			_, err = rf.ReadFrom(sr.Reader)
			if !xnet.IsNetworkOrHostDown(err, true) { // do not need to log disconnected clients
				storageLogIf(r.Context(), err)
			}
			if err == nil || !errors.Is(err, xhttp.ErrNotImplemented) {
				return