//-------------------------------------------------------------------
//	multirecv.cpp
//
//	This application joins a IP-multicast group and displays all
//	the group messages it receives on the standard output device
//	until the user terminates the program by typing <CONTROL>-C.
//
//	     to compile:  $ g++ multirecv.cpp -o multirecv
//	     to execute:  $ ./multirecv  
//
//	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: 19 MAR 2009
//-------------------------------------------------------------------

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

#define HELLO_PORT 54321
#define HELLO_GROUP "224.3.3.6"
#define MSGBUFSIZE 256

int main( int argc, char **argv )
{
	//------------------------------------------------
	// setup our 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 	= htonl( INADDR_ANY );

	//------------------------------------------------
	// 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 allow multiple sockets to use the same port 
	//------------------------------------------------ 
	unsigned int	yes = 1;
	int		ysiz = sizeof( yes );
	if ( setsockopt( sock, SOL_SOCKET, SO_REUSEADDR, &yes, ysiz ) < 0 )
		{ perror( "setsockopt REUSEADDR" ); exit(1); }

	//-----------------------------------------
	// bind our socket to this receive address
	//-----------------------------------------
	if ( bind( sock, (sockaddr*)&saddr, sizeof( saddr ) ) < 0 )
		{ perror( "bind" ); exit(1); }

	//----------------------------------------------------
	// we use the 'setsockopt()' function to request that 
	// the kernel 'join' our specified IP-multicast group	
	//----------------------------------------------------
	struct ip_mreq	mreq = { 0 };
	int		msiz = sizeof( mreq );
	mreq.imr_multiaddr.s_addr = inet_addr( HELLO_GROUP );
	mreq.imr_interface.s_addr = htonl( INADDR_ANY );
	if ( setsockopt( sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, msiz ) )
		{ perror( "setsockopt ADD_MEMBERSHIP" ); exit(1); }

	//-----------------------------------------
	// now we just enter a read-and-print loop
	//----------------------------------------- 
	while ( 1 )
		{
		char	buf[ MSGBUFSIZE ] = { 0 };
		int	len = sizeof( buf );

		int	nbytes = recv( sock, buf, len, 0 );
		if ( nbytes < 0 ) { perror( "recvfrom" ); exit(1); }

		puts( buf );
		}
}