tain another row of data from the server during a
       <code class="command">COPY</code>.  Data is always returned one data row at
       a time; if only a partial row is available, it is not returned.
       Successful return of a data row involves allocating a chunk of
       memory to hold the data.  The <em class="parameter"><code>buffer</code></em> parameter must
       be non-<code class="symbol">NULL</code>.  <em class="parameter"><code>*buffer</code></em> is set to
       point to the allocated me