/* jednoduchy chat s multicastem *
 * Radek Brich, 7.11.2004        */

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define TRUE	1
#define FALSE	0
#define BUF_SIZE	1024

#define MCAST_ADDR	"231.23.45.67"
#define CHAT_PORT	3500
#define TTL_VALUE	1
#define LOOPBACK	TRUE

int main(int argc, char *argv[])
{
	int sock;	/* socket pro zapis i cteni */
	int i;		/* pomocna promenna */
	struct sockaddr_in sa_local,	/* adresa lokalniho rozhrani */
			   sa_dest,	/* adresa prijemce pro zapis */
			   sa_src;	/* adresa odesilatele při cteni */
	int sa_size = sizeof(struct sockaddr_in);
	struct ip_mreq mreq;
	pid_t pid;

	/* novy UDP socket */
	sock = socket(AF_INET, SOCK_DGRAM, 0);

	/* povolit vice procesum pouzit stejnou adresu */ 
	i = TRUE;
	setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &i, sizeof(i));

	/* socket pripojime k sitovemu rozhrani */
	sa_local.sin_family = AF_INET;
	sa_local.sin_addr.s_addr = htonl(INADDR_ANY);
	sa_local.sin_port = htons(CHAT_PORT);
	bind(sock, (struct sockaddr*) &sa_local, sizeof(sa_local));

	/* pripojeni k multicastove skupine  */
	mreq.imr_multiaddr.s_addr = inet_addr(MCAST_ADDR);
	mreq.imr_interface.s_addr = INADDR_ANY;
	setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));

	/* nastavime hodnotu TTL - urcuje, jak daleko bude packet smerovan */
	i = TTL_VALUE;
	setsockopt(sock, IPPROTO_IP, IP_MULTICAST_TTL, &i, sizeof(i));
     
	/* loopback */
	i = LOOPBACK;
	setsockopt(sock, IPPROTO_IP, IP_MULTICAST_LOOP, &i, sizeof(i));

	/* adresa pro vysilani (= adresa multicastove skupiny) */
	sa_dest.sin_family = AF_INET;
	sa_dest.sin_addr.s_addr = inet_addr(MCAST_ADDR);
	sa_dest.sin_port = htons(CHAT_PORT);

	if ((pid = fork()) > 0) { /* RODIC */
		char msg[BUF_SIZE];
		for(;;) {
			/* prijima data z multicastove skupiny
			   a tiskne je na stdout  */
			i = recvfrom(sock, msg, BUF_SIZE, 0,
			    (struct sockaddr* )&sa_src, &sa_size);
			if (i < 0) {
				perror("* recvfrom() failed\n");
				exit(1);
			}
			printf("[%s] %s", inet_ntoa(sa_src.sin_addr), msg);
		}
	} else if (pid == 0) { /* POTOMEK */
		char msg[BUF_SIZE];
		for(;;) {
			/* vysila text z stdin multicastem */
			fgets(msg, BUF_SIZE, stdin);
			i = sendto(sock, msg, strlen(msg)+1, 0,
			    (struct sockaddr*) &sa_dest, sa_size);
			if (i < 0) {
				perror("* sendto() failed\n");
				exit(1);
			}
		}
	} else
		err(1, "fork()");

	close(sock);
	return(0);
}