for detecting end-of-data.
      </p><p>
       On each call, <a class="xref" href="libpq-copy.html#LIBPQ-PQGETLINEASYNC"><code class="function">PQgetlineAsync</code></a> will return data if a
       complete data row is available in <span class="application">libpq</span>'s input buffer.
       Otherwise, no data is returned until the rest of the row arrives.
       The function returns -1 if the end-of-copy-data marker has been recognized,
       or 0 if no data is available, or a positive number giving th