tx_helper_append_iovec
tx_helper_append_iovec(h, iov[i].buf, iov[i].buf_len);
tx_helper_append_iovec(h, chunks[i % 2].iov[j].buf,
if (!tx_helper_append_iovec(h, encoded, encoded_len))
if (!tx_helper_append_iovec(h, h->txn.data, l)) {