Writing Advanced Functions in C - PostgreSQL Server Programming - page 244

heap_form_tuple(funcctx->tuple_desc, retvals,
retnulls);
SRF_RETURN_NEXT(funcctx,
HeapTupleGetDatum( rettuple ));
}
else /* do when there is no more left */
{
SRF_RETURN_DONE(funcctx);
}
}