err_t tcp_echoclient_recv(void *arg, struct tcp_pcb *tpcb, struct pbuf *p, err_t err)
{
struct echoclient *es;
err_t ret_err;

LWIP_ASSERT("arg != NULL", arg != NULL);

es = (struct echoclient *)arg;

/* if we receive an empty tcp frame from server => close connection */
if (p == NULL)
{
/* remote host closed connection */
es->state = ES_CLOSING;
if (es->p_tx == NULL)
{
/* we're done sending, close connection */
tcp_echoclient_connection_close(tpcb, es);
}
else
{
/* send remaining data*/
tcp_echoclient_send(tpcb, es);
}
ret_err = ERR_OK;
}
/* else : a non empty frame was received from echo server but for some reason err != ERR_OK */
else if (err != ERR_OK)
{
/* free received pbuf*/
if (p != NULL)
{
pbuf_free(p);
}
ret_err = err;
}
else if (es->state == ES_CONNECTED)
{
/* increment message count */
message_count++;

/* Acknowledge data reception */
tcp_recved(tpcb, p->tot_len);

es->p_tx = p;
char strmr[20] = "";
strncpy(strmr, es->p_tx->payload, es->p_tx->len); // здесь считали сообщение
printf("%d %s\n", message_count, strmr);

pbuf_free(p);
tcp_echoclient_connection_close(tpcb, es); // соединение закрывается
ret_err = ERR_OK;
}

/* data received when connection already closed */
else
{
/* Acknowledge data reception */
tcp_recved(tpcb, p->tot_len);
/* free pbuf and do nothing */
pbuf_free(p);
ret_err = ERR_OK;
}
return ret_err;
}

else if(es->state == ES_CONNECTED)
{
/* increment message count */
message_count++;

/* Acknowledge data reception */
tcp_recved(tpcb, p->tot_len);

es->p_tx = p;
char strmr[20] = "";
strncpy (strmr,es->p_tx->payload,es->p_tx->len);
//strmr[es->p_tx->len] = '\r';
printf ("%d %s\n", message_count, strmr);

if (strncmp(strmr, "OK", 2) == 0)
{
pbuf_free(p);
}
else
{
pbuf_free(p);
tcp_echoclient_connection_close(tpcb, es);
}
ret_err = ERR_OK;
}