/code>
                  if all buffers representing the body have been returned in previous
                  calls or if it sets <code class="computeroutput"><span class="identifier">ec</span></code>
                  to indicate an error. Otherwise, if there are buffers remaining
                  the function should return a pair with the first element containing
                  a non-zero length buffer sequence representing the next set of
                  octets in the body, while the second elemen