C Tutorial: Socket Programming in C - Simple multicast server.

To compile :

      * linux : gcc -Wall -o foo foo.c
      * solaris : gcc -Wall -o foo foo.c -lsocket -lnsl


1. IP multicast

      * multicast server : simple multicast server that prints received
messages.
         source : mcastServer.c
         usage : ./mcastServer multicast_group
      * multicast client : simple multicast client that sends data on
multicast group.
         source : mcastClient.c
         usage : ./mcastClient multicast_group data1 ... dataN

/********************* mcastServer.c ***********************/

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>
#include <unistd.h> /* close */

#define SERVER_PORT 1500
#define MAX_MSG 100

int main(int argc, char *argv[]) {

   int sd, rc, n, cliLen;
   struct ip_mreq mreq;
   struct sockaddr_in cliAddr, servAddr;
   struct in_addr mcastAddr;
   struct hostent *h;
   char msg[MAX_MSG];

   if(argc!=2) {
      printf("usage : %s <mcast address>\n",argv[0]);
      exit(0);
   }

   /* get mcast address to listen to */
   h=gethostbyname(argv[1]);
   if(h==NULL) {
      printf("%s : unknown group '%s'\n",argv[0],argv[1]);
      exit(1);
   }
   
   memcpy(&mcastAddr, h->h_addr_list[0],h->h_length);
   
   /* check given address is multicast */
   if(!IN_MULTICAST(ntohl(mcastAddr.s_addr))) {
      printf("%s : given address '%s' is not multicast\n",argv[0],
       inet_ntoa(mcastAddr));
      exit(1);
   }

   /* create socket */
   sd = socket(AF_INET,SOCK_DGRAM,0);
   if(sd<0) {
      printf("%s : cannot create socket\n",argv[0]);
      exit(1);
   }

   /* bind port */
   servAddr.sin_family=AF_INET;
   servAddr.sin_addr.s_addr=htonl(INADDR_ANY);
   servAddr.sin_port=htons(SERVER_PORT);   
   if(bind(sd,(struct sockaddr *) &servAddr, sizeof(servAddr))<0) {
      printf("%s : cannot bind port %d \n",argv[0],SERVER_PORT);
      exit(1);
   }

   /* join multicast group */
   mreq.imr_multiaddr.s_addr=mcastAddr.s_addr;
   mreq.imr_interface.s_addr=htonl(INADDR_ANY);
   
   rc = setsockopt(sd,IPPROTO_IP,IP_ADD_MEMBERSHIP,
         (void *) &mreq, sizeof(mreq));
   if(rc<0) {
      printf("%s : cannot join multicast group '%s'",argv[0],
       inet_ntoa(mcastAddr));
      exit(1);
   }
   else {
      printf("%s : listening to mgroup %s:%d\n",
       argv[0],inet_ntoa(mcastAddr), SERVER_PORT);
   

      /* infinite server loop */
      while(1) {
         cliLen=sizeof(cliAddr);
         n = recvfrom(sd,msg,MAX_MSG,0,(struct sockaddr *) &cliAddr,&cliLen);
         if(n<n) {
   printf("%s : cannot receive data\n",argv[0]);
   continue;
         }

         printf("%s : from %s:%d on %s : %s\n",argv[0],
          inet_ntoa(cliAddr.sin_addr),ntohs(cliAddr.sin_port),
          argv[1],
          msg);
      }/* end of infinite server loop */

   }

return 0;

}

/********************* mcastClient.c ***********************/

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>
#include <unistd.h> /* close */

#define SERVER_PORT 1500
#define MAX_MSG 100

int main(int argc, char *argv[]) {

   int sd, rc, i;
   unsigned char ttl = 1;
   struct sockaddr_in cliAddr, servAddr;
   struct hostent *h;

   if(argc<3) {
      printf("usage %s <mgroup> <data1> <data2> ... <dataN>\n",argv[0]);
      exit(1);
   }

   h = gethostbyname(argv[1]);
   if(h==NULL) {
      printf("%s : unknown host '%s'\n",argv[0],argv[2]);
      exit(1);
   }

   servAddr.sin_family = h->h_addrtype;
   memcpy((char *) &servAddr.sin_addr.s_addr,
h->h_addr_list[0],h->h_length);
   servAddr.sin_port = htons(SERVER_PORT);
   
   /* check if dest address is multicast */
   if(!IN_MULTICAST(ntohl(servAddr.sin_addr.s_addr))) {
      printf("%s : given address '%s' is not multicast \n",argv[0],
       inet_ntoa(servAddr.sin_addr));
      exit(1);
   }

   /* create socket */
   sd = socket(AF_INET,SOCK_DGRAM,0);
   if (sd<0) {
      printf("%s : cannot open socket\n",argv[0]);
      exit(1);
   }
   
   /* bind any port number */
   cliAddr.sin_family = AF_INET;
   cliAddr.sin_addr.s_addr = htonl(INADDR_ANY);
   cliAddr.sin_port = htons(0);
   if(bind(sd,(struct sockaddr *) &cliAddr,sizeof(cliAddr))<0) {
      perror("bind");
      exit(1);
   }

   if(setsockopt(sd,IPPROTO_IP,IP_MULTICAST_TTL, &ttl,sizeof(ttl))<0) {
      printf("%s : cannot set ttl = %d \n",argv[0],ttl);
      exit(1);
   }

   printf("%s : sending data on multicast group '%s' (%s)\n",argv[0],
    h->h_name,inet_ntoa(*(struct in_addr *) h->h_addr_list[0]));
   

   /* send data */
   for(i=2;i<argc;i++) {
      rc = sendto(sd,argv[i],strlen(argv[i])+1,0,
      (struct sockaddr *) &servAddr, sizeof(servAddr));
      
      if (rc<0) {
         printf("%s : cannot send data %d\n",argv[0],i-1);
         close(sd);
         exit(1);
      }

   }/* end for */

   /* close socket and exit */
   close(sd);
   exit(0);
}