AM2732: LwIP UDP data corruption

Hi Andrea Coradi,
LwIP socket APIs are not well supported by LwIP, instead LwIP netconn APIs are suggested. 
Can you modify the application and use netconn APIs to send UDP packets.

Ref: https://lwip.fandom.com/wiki/Application_API_layers

With regards,
Pradeep

Hi PRADEEP HN 
While trying to modify the example to use netconn API I also noticed that the socket API is built on top of netconn + netbuf.
As you can see from the implementation of lwip_sendto:

ssize_t
lwip_sendto(int s, const void *data, size_t size, int flags,
            const struct sockaddr *to, socklen_t tolen)
{
  struct lwip_sock *sock;
  err_t err;
  u16_t short_size;
  u16_t remote_port;
  struct netbuf buf;

  sock = get_socket(s);
  if (!sock) {
    return -1;
  }

  if (NETCONNTYPE_GROUP(netconn_type(sock->conn)) == NETCONN_TCP) {
#if LWIP_TCP
    done_socket(sock);
    return lwip_send(s, data, size, flags);
#else /* LWIP_TCP */
    LWIP_UNUSED_ARG(flags);
    set_errno(err_to_errno(ERR_ARG));
    done_socket(sock);
    return -1;
#endif /* LWIP_TCP */
  }

  if (size > LWIP_MIN(0xFFFF, SSIZE_MAX)) {
    /* cannot fit into one datagram (at least for us) */
    set_errno(EMSGSIZE);
    done_socket(sock);
    return -1;
  }
  short_size = (u16_t)size;
  LWIP_ERROR("lwip_sendto: invalid address", (((to == NULL) && (tolen == 0)) ||
             (IS_SOCK_ADDR_LEN_VALID(tolen) &&
              ((to != NULL) && (IS_SOCK_ADDR_TYPE_VALID(to) && IS_SOCK_ADDR_ALIGNED(to))))),
             set_errno(err_to_errno(ERR_ARG)); done_socket(sock); return -1;);
  LWIP_UNUSED_ARG(tolen);

  /* initialize a buffer */
  buf.p = buf.ptr = NULL;
#if LWIP_CHECKSUM_ON_COPY
  buf.flags = 0;
#endif /* LWIP_CHECKSUM_ON_COPY */
  if (to) {
    SOCKADDR_TO_IPADDR_PORT(to, &buf.addr, remote_port);
  } else {
    remote_port = 0;
    ip_addr_set_any(NETCONNTYPE_ISIPV6(netconn_type(sock->conn)), &buf.addr);
  }
  netbuf_fromport(&buf) = remote_port;


  LWIP_DEBUGF(SOCKETS_DEBUG, ("lwip_sendto(%d, data=%p, short_size=%"U16_F", flags=0x%x to=",
                              s, data, short_size, flags));
  ip_addr_debug_print_val(SOCKETS_DEBUG, buf.addr);
  LWIP_DEBUGF(SOCKETS_DEBUG, (" port=%"U16_F"\n", remote_port));

  /* make the buffer point to the data that should be sent */
#if LWIP_NETIF_TX_SINGLE_PBUF
  /* Allocate a new netbuf and copy the data into it. */
  if (netbuf_alloc(&buf, short_size) == NULL) {
    err = ERR_MEM;
  } else {
#if LWIP_CHECKSUM_ON_COPY
    if (NETCONNTYPE_GROUP(netconn_type(sock->conn)) != NETCONN_RAW) {
      u16_t chksum = LWIP_CHKSUM_COPY(buf.p->payload, data, short_size);
      netbuf_set_chksum(&buf, chksum);
    } else
#endif /* LWIP_CHECKSUM_ON_COPY */
    {
      MEMCPY(buf.p->payload, data, short_size);
    }
    err = ERR_OK;
  }
#else /* LWIP_NETIF_TX_SINGLE_PBUF */
  err = netbuf_ref(&buf, data, short_size);
#endif /* LWIP_NETIF_TX_SINGLE_PBUF */
  if (err == ERR_OK) {
#if LWIP_IPV4 && LWIP_IPV6
    /* Dual-stack: Unmap IPv4 mapped IPv6 addresses */
    if (IP_IS_V6_VAL(buf.addr) && ip6_addr_isipv4mappedipv6(ip_2_ip6(&buf.addr))) {
      unmap_ipv4_mapped_ipv6(ip_2_ip4(&buf.addr), ip_2_ip6(&buf.addr));
      IP_SET_TYPE_VAL(buf.addr, IPADDR_TYPE_V4);
    }
#endif /* LWIP_IPV4 && LWIP_IPV6 */

    /* send the data */
    err = netconn_send(sock->conn, &buf);
  }

  /* deallocated the buffer */
  netbuf_free(&buf);

  set_errno(err_to_errno(err));
  done_socket(sock);
  return (err == ERR_OK ? short_size : -1);
}