[ENet-discuss] Broadcast Messages through the LAN - Trying an implementation

[Lee Salzman]

The following line is wrong:

mySocket = socket(AF_INET, SOCK_RAW, VT_UDP_SOCK);

This should be:

mySocket = socket(PF_INET, SOCK_DGRAM, 0);

Also, the host ip field of the IPv4 address "sin_addr.s_addr" is already 
in network byte order, so you shouldn't be using htonl() for that. Only 
for the port "sin_port" do you need to use htons(), since the port 
number you are providing is in host byte-order.

Note that you can really just reuse the enet_socket_*() and 
enet_address_*() functions for this, which should make things go much 
easier. They are not terribly documented yet, but what they do should be 
self-explanatory reading through unix.c. You would have to get the CVS 
source code of ENet (which is stable, not to worry), however, as the 
actual release package doesn't have some of the various functionality - 
like REUSEADDR - which I had recently added for this purpose.

If you use the CVS version of ENet, you can just do something like the 
following:

To setup client sending socket:
ENetSocket  pingsock = enet_socket_create(ENET_SOCKET_TYPE_DATAGRAM); // 
create UDP socket
enet_socket_set_option(pingsock, ENET_SOCKOPT_NONBLOCK, 1); // prevent 
send from blocking (through must be careful to check enet_socket_send() 
and enet_socket_receive() for return value of 0, meaning socket is busy
enet_socket_set_option(pingsock, ENET_SOCKOPT_BROADCAST, 1); // allow 
the socket to send to the broadcast address


To setup the server receiving socket:

ENetAddress address = /* something with fixed port value */;
ENetSocket pongock = enet_socket_create(ENET_SOCKET_TYPE_DATAGRAM);
enet_socket_set_option(pongsock, ENET_SOCKOPT_REUSEADDR, 1); // allow 
multiple servers on the same computer to listen to same port
enet_socket_bind(pongsock, &address); // bind to the address to listen 
on after REUSEADDR has been set
enet_socket_set_option(pongsock, ENET_SOCKOPT_NONBLOCK, 1); // no 
blocking again

To send data on either socket:

ENetAddress destinationAddress = /* something */;
ENetBuffer buf;
buf.data = /* pointer to data */;
buf.dataLength = /* size of data, in bytes */;
int err = enet_socket_send(socket, destinationAddress, &buf, 1);
if(err==0) { /* would have blocked, need to resend later */ }
else if(err < 0) { /* something went wrong, error! */ }

 To receive data on either socket:

ENetAddress senderAddress;
ENetBuffer buf;
buf.data = /* pointer to receive buffer */;
buf.dataLength = /* size of receive buffer, in bytes */;
int received = enet_socket_receive(socket, destinationAddress, &buf, 1);
if(receive==0) { /* would have blocked, need to resend later */ }
else if(receive < 0) { /* something went wrong, error! */ }
else { /* receive says the number of bytes written into buf.data */ }

Lee

David Orejuela wrote:
>
> I have tried to implement the solution you provided me, but there are 
> some problems sending data and I have some questions about it:
>
> --------
>
> SERVER:
>
> --------
>
> Server socket creation doesn't return errors, but I'm not sure if I'm 
> doing things right
>
> --- Socket creation---
>
> mySocket = socket(AF_INET, SOCK_RAW, VT_UDP_SOCK);
>
> //SOCK_RAW for raw UDP traffic?
>
> ---SetSockOpt---
>
> int reuseAddrOp = 1;
>
> setsockopt(mySocket,SOL_SOCKET/*IPPROTO_UDP*/,SO_REUSEADDR,&reuseAddrOp,sizeof(reuseAddrOp))
>
> //must I change option for IPPROTO_UDP or SOL_SOCKET?
>
> ---Bind---
>
> sockaddr_in inAddress;
>
> inAddress.sin_family = AF_INET;
>
> inAddress.sin_port = htons(DEFAULT_PORT); //#define DEFAULT_PORT 1001
>
> inAddress.sin_addr.s_addr = htonl(INADDR_ANY);
>
> //is INADDR_ANY address right?
>
> bind(mySocket,&inAddress,sizeof(inAddress));
>
> ---Listening thread---
>
> ...
>
> do
>
> {
>
> FindServerRequestMessage fsr_msg;
>
> //the sockaddr_in parameter is right? I want to listen any address...
>
> int result = recvfrom(mySocket,&fsr_msg, sizeof(fsr_msg), 0, 
> &inAddress, sizeof(inAddress));
>
> if(result > 0)
>
> {
>
> //Get fsr_msg data and answer
>
> }
>
> }
>
> while(1);
>
> --------
>
> CLIENT
>
> --------
>
> The client sends a FindServersRequest message through the socket.
>
> When I try to send data with the "sendto" function returns me a -1, 
> but I don't know why...
>
> ---Socket creation---
>
> Like the server
>
> ---SetSockOpt---
>
> Like the server
>
> ---Bind---
>
> Like the server
>
> ---Delivery---
>
> sockaddr_in outAddress;
>
> outAddress.sin_family = AF_INET;
>
> outAddress.sin_port = htons(1001);
>
> outAddress.sin_addr.s_addr = htonl(ENET_HOST_BROADCAST); // BROADCAST 
> sending, is it ok?
>
> sendto(mySocket,&fsr_msg, 
> sizeof(fsr_msg),0,&outAddress,sizeof(outAddress));
>
> ------------------------------------------------------------------------
>
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>