Re: UDP Broadcast

[Sean Conner <sean@...>]

It was thus said that the Great Sean Conner once stated:
> It was thus said that the Great Clark Snowdall once stated:
> > Everyone,
> > 
> > Thanks for the suggestions ... some of them were helpful.
> > 
> > I've done some more exploration, and I think the issue is I can't send  
> > a UDP broadcast packet.  I can see non-broadcast packets, but when I  
> > select the ip address for broadcast, it doesn't show up.  Could it be  
> > something with my router?  Or lua UDP doesn't really like broadcast?   
> > Any suggestions?
> 
>   If you want to send a broadcast packet, you need to set an option on the
> socket to do so.  In C (under Unix) this would be:
> 
>     rc = setsockopt(sock,SOL_SOCKET,SO_BROADCAST,&dummy,sizeof(dummy));
>     if (rc < 0)
>     {
>       perror("setsockopt(SO_BROADCAST)");
>       return(EXIT_FAILURE);
>     }
> 
>   You'll need to find the equivilent under the Lua library you are using.

  I checked back and I see you are setting the broadcast flag.  I checked an
old project of mine (testing broadcast UDP packets) and I see that in the
server side I have:

	local = "10.0.0.3:2020";	/* well, these are actually struct sockaddr */
	remote = "10.0.0.255:2020";	/* but you get the idea ... */

	sock = socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP);
	setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,&dummy,sizeof(dummy));
	setsockopt(sock,SOL_SOCKET,SO_BROADCAST,&dummy,sizeof(dummy));
	bind(sock,&local,sizeof(local));

	while(1)
	{
	  sendto(sock,data,sizeof(data),0,&remote,sizeof(remote));
	}

  And oddly enough, in the client side:

	local = "10.0.0.2:2020";

	sock = socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP);
	setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,&dummy,sizeof(dummy));
	setsockopt(sock,SOL_SOCKET,SO_BROADCAST,&dummy,sizeof(dummy));
	bind(sock,&local,sizeof(local));

	while(1)
	{
	  recvfrom(sock,&data,sizeof(data),0,&remote,&dum);
	}

  It looks like you need to set the recieving socket with the broadcast
option as well.

  -spc