I've only commented the parts that are different from the directed_client.
// page04.html,v 1.11 1999/09/22 03:13:43 jcej Exp
#include "ace/SOCK_Dgram_Bcast.h"
#include "ace/INET_Addr.h"
static const u_short PORT = ACE_DEFAULT_SERVER_PORT;
int
main (int argc,char *argv[])
{
ACE_INET_Addr local ((u_short) 0);
/* Instead of creating the ACE_SOCK_Dgram we created last time,
we'll create an ACE_SOCK_Dgram_Bcast. "Bcast" means, of course,
"Broadcast". This ACE object is clever enough to go out to the OS
and find all of the network interfaces. When you send() on a
Dgram_Bcast, it will send the datagram out on all of those
interfaces. This is quiet handy if you do it on a multi-homed
host that plays router... */
ACE_SOCK_Dgram_Bcast dgram;
if (dgram.open (local) == -1)
ACE_ERROR_RETURN ((LM_ERROR,
"%p\n",
"datagram open"),
-1);
char buf[BUFSIZ];
sprintf (buf, "Hello World!");
/* The only other difference between us and the directed client is
that we don't specify a host to receive the datagram. Instead, we
use the magic value "INADDR_BROADCAST". All hosts are obliged to
respond to datagrams directed to this address the same as they
would to datagrams sent to their hostname.
Remember, the Dgram_Bcast will send a datagram to all interfaces
on the host. That's true even if the address is for a specific
host (and the host address makes sense for the interface). The
real power is in using an INADDR_BROADCAST addressed datagram
against all interfaces. */
ACE_INET_Addr remote (PORT,
INADDR_BROADCAST);
ACE_DEBUG ((LM_DEBUG,
"(%P|%t) Sending (%s) to the server.\n",
buf));
if (dgram.send (buf,
ACE_OS::strlen (buf) + 1,
remote) == -1)
ACE_ERROR_RETURN ((LM_ERROR,
"%p\n",
"send"),
-1);
if (dgram.recv (buf,
sizeof (buf),
remote) == -1)
ACE_ERROR_RETURN ((LM_ERROR,
"%p\n",
"recv"),
-1);
ACE_DEBUG ((LM_DEBUG,
"(%P|%t) The server said: %s\n",
buf));
/* Using the "remote" object instance, find out where the server
lives. We could then save this address and use directed datagrams
to chat with the server for a while. */
ACE_DEBUG ((LM_DEBUG,
"(%P|%t) The server can be found at: (%s:%d)\n",
remote.get_host_name(),
PORT));
return 0;
}
About that subnet thing:
If you run this client on a host that has multiple network interfaces, the broadcast will go to all of those (sub)networks. What do you do, though, if you need to get past a router? My advice is to write a server that will run on hosts on both sides of your router. When a server on one side of the router receives a broadcast, it would send a directed datagram to it's counterpart on the other side of the router. The counterpart would then re-broadcast the original datagram on that sub-net. Cheap, simple and effective.One final word of warning:
When creating your broadcast datagrams you may see something like this: ACE_SOCK_Dgram_Bcast::mk_broadcast: Broadcast is not enable for this interface.: Unknown error. There are some interfaces (ppp, slip) that don't support broadcast datagrams. That's what you're seeing here.Ok, one more warning:
If you happen to have multiple servers running on your network when you invoke this client, the response could come from any one of them.