// Compress only if the compression is enabled during initial multipart.
	var idxCb func() []byte
	if isCompressed {
		wantEncryption := crypto.Requested(r.Header) || isEncrypted
		s2c, cb := newS2CompressReader(reader, actualPartSize, wantEncryption)
		idxCb = cb
		defer s2c.Close()
		reader = etag.Wrap(s2c, reader)
		length = -1
	}

	srcInfo.Reader, err = hash.NewReader(ctx, reader, length, "", "", actualPartSize)
	if err != nil {

		reader = etag.NewReader(ctx, reader, nil, nil)
		wantEncryption := crypto.Requested(r.Header)
		s2c, cb := newS2CompressReader(reader, actualSize, wantEncryption)
		dstOpts.IndexCB = cb
		defer s2c.Close()
		reader = etag.Wrap(s2c, reader)
		length = -1
	} else {
		delete(srcInfo.UserDefined, ReservedMetadataPrefix+"compression")

// If the remote is restarted will return ErrRemoteRestart.
// If nil will be returned remote call sent EOF or ErrDone is returned by the callback.
// If ErrDone is returned on cb nil will be returned.
func (c *Connection) Stateless(ctx context.Context, h HandlerID, req []byte, cb func([]byte) error) error {
	client, err := c.newMuxClient(ctx)
	if err != nil {
		return err
	}
	defer c.outgoing.Delete(client.MuxID)