Re: [lwip-users] UDP socket receive

[Gisle Vanem]

"Fabian Cenedese" <address@hidden> wrote:

> I'm trying to use socket and UDP (DGRAM) to receive data
> from other devices.
>
> addr.sin_len=sizeof(addr);
> addr.sin_family=AF_INET;
> addr.sin_port=PP_HTONS(MyPort);
> addr.sin_addr.s_addr=PP_HTONL(INADDR_ANY);
> s=socket(AF_INET, SOCK_DGRAM, 0);
> ret=connect(s, (struct sockaddr*)&addr, sizeof(addr));
>
> ret=read(s, buffer, size);
>
> The calls are all successful, read is waiting. I can see the udp frame coming
> in with the right port. However the frame is discarded in udp_input:

You'll have to add a call to bind(). Something like:

if (bind(sockfd, (struct sockaddr*)&addr, sizeof(struct sockaddr)) == -1)
{
  perror ("bind");
  return (-1);
}

> From "man bind":
   The bind(2) function assigns an address addr to an unnamed socket s. When
   a socket is created with socket(2) it exists in a name space (address
   family) but has no name assigned. The bind(2) function requests that name
   be assigned to the socket.

When you don't call  bind(), the socket remains "unnamed" (in BSD-lingo).
Hence, in lwIP lingo, the socket has "no recv function registered". Makes sense?

BTW. It's smarter to clear 'addr' before settting up the rest of it:
 memset (&addr, 0, sizeof(addr));

--gv