//-------------------------------------------------------------------
//	multihop.cpp	  (Addendum to of our 'multisend.cpp' demo)
//
//	This application will transmit a "Hello, World!" message to 
//	its designated IP-multicast group once every second until a
//	user decides to conclude the program by typing <CONTROL>-C. 
//
//	ADDENDUM: modified default multicast TTL via socket-option. 
//
//	     to compile:  $ g++ multihop.cpp -o multihop
//	     to execute:  $ ./multihop <ttl>
//
//      NOTE: Adapted from the online example by Antony Courtney and
//      Frederic Bastien, posted at Trinity College, Dublin, Ireland 
//      <http://ntrg.cs.tcd.ie/undergrad/4ba2/multicast/antony/>.
//
//	programmer: ALLAN CRUSE
//	written on: 26 MAR 2009
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), perror() 
#include <stdlib.h>	// for exit() 
#include <unistd.h>	// for sleep() 
#include <string.h>	// for strlen()
#include <arpa/inet.h>	// for htons(), socket()

#define HELLO_PORT 54321
#define HELLO_GROUP "224.3.3.6"

int main( int argc, char **argv )
{
	//-------------------------------------------------------
	// we let the user specify a value for the multicast TTL
	//------------------------------------------------------- 
	int	tval = ( argc > 1 ) ? atoi( argv[1] ) : 2; 

	//------------------------------------------------
     	// we open what looks like an ordinary UDP socket 
	//------------------------------------------------
     	int	sock = socket( AF_INET, SOCK_DGRAM, IPPROTO_UDP );
	if ( sock < 0 ) { perror("socket"); exit(1); }

	//---------------------------------------------------------
	// we modify the default value of TTL in multicast packets
	//---------------------------------------------------------- 
	int	tlen = sizeof( tval );
	if ( setsockopt( sock, SOL_IP, IP_MULTICAST_TTL, &tval, tlen ) < 0 )
		{ perror( "setsockopt" ); exit(1); }

	//----------------------------------------------------
     	// we set up the destination socket-address structure
	//----------------------------------------------------
	struct sockaddr_in 	saddr = { 0 };
     	saddr.sin_family 	= AF_INET;
     	saddr.sin_port		= htons( HELLO_PORT );
     	saddr.sin_addr.s_addr 	= inet_addr( HELLO_GROUP );
     
	//---------------------------------------------------------
     	// now we just 'sendto()' our destination once each second
	//---------------------------------------------------------
     	char	message[] = "Hello, World!";
	for(;;)	{
	  	sleep( 1 );
	  	if ( sendto( sock, message, sizeof( message ), 0,
			(sockaddr *)&saddr, sizeof( saddr ) ) < 0 ) 
				{ perror("sendto"); exit(1); }
     		}
}