buffer_reserve
buffer_reserve(buffer, written + 1);
void buffer_reserve(buffer_type *buffer, size_t amount);
buffer_reserve(b, 1);
buffer_reserve(b, 8);
buffer_reserve(b, 2);
buffer_reserve(b, 4);
buffer_reserve(b, len+1);
buffer_reserve(b, sizeof(*acl));
buffer_reserve(output, size * 2 + 1);
buffer_reserve(output, size * 2 + 1);
buffer_reserve(output, size * 2);
buffer_reserve(output, datalen * 2 + 1);