[lwip-users] to free or not to free (pbuf_free in tcp_recv)

[cbergs]

Hi, 

I'm working with the lwIP 1.4.1 on a TI M4 platform with rawapi and I'm
having trouble to understand the documentation correctly.
In particular the callback for tcp_recv(). In the rawapi.txt is said 

"If there are no errors and the callback function is to return ERR_OK, then
it must free the pbuf. 
Otherwise, it must not  free the pbuf so that lwIP core code can store it."

But in the echo example there is this part: 
echo_recv() { 
...
else if(err != ERR_OK)
  {
    /* cleanup, for unkown reason */
    if (p != NULL)
    {
      es->p = NULL;
      pbuf_free(p);
    }
    ret_err = err;
  }

The pbuf is freed AND the callback function returns an error. What would
happen with the pbuf if it is not freed? 

Kind regards,
Chris