/* receiver for internet datagram demo */
/* modification 9/20/93 with Louis Sanchez's bug fix */

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

#define ENDPACKET "end"

/************************************************************
printsockaddr prints the contents of a sockaddr_in structure when
called with a pointer to such a structure.
************************************************************/


void printsockaddr(struct sockaddr_in *arg)
{
	struct hostent *hp;
	printf("  sockaddr_in: ");
	printf("Domain=%d, ", arg->sin_family);
	hp=gethostbyaddr((const char *) &(arg->sin_addr), sizeof(arg->sin_addr), AF_INET);
	printf("Hostname=%s, ", hp->h_name);
	printf("Port=%d, ", ntohs(arg->sin_port));
	printf("Address=%s,\n", inet_ntoa(arg->sin_addr));
}



help_msg()
{
	printf("format: ex2r -[oeta]\n");
	printf("       option d set debug mode\n");
	printf("       option o set lose odd msg mode\n");
	printf("       option k set lose msg out of 3 msgs mode\n");
	printf("       option a set lose all msg mode\n");

}

main(argc, argv)
int argc;
char *argv[];
{
	int sock; 
	struct sockaddr_in from;
	int n, i;
	char toBuf[2048];
	char fromBuf[2048];
	extern char *optarg;
	extern int   optind;
   int option_exist = 0;
   int c;
   int debug = 0;
	int odd = 0;
   int all = 0;
   int three = 0;

	int length;
	int flag = 1;

	/* process command line args */
   while ((c=getopt(argc,argv,"dota")) != EOF)
   {
      option_exist = 1;
      switch(c)
      {
      case 'd':
         debug = 1;
         if (debug)
            printf("turn on debug mode.\n");
         break;
      case 'o':
         odd = 1;
			printf("lose every odd number msg\n");
         break;
      case 't':
         three = 1;
			printf("lose two out of every three msgs\n");
         break;
      case 'a':
         all = 1;
			printf("lose all msgs\n");
         break;
      case '?':
         help_msg();
         exit (1);
      default:
         fprintf (stderr, "unrecognized arg >%s<\n", optarg);
         help_msg();
         exit (1);
      }
   }

	/* create socket */
	sock = socket(AF_INET, SOCK_DGRAM, 0);
	if (sock < 0) {
		perror("opening datagram socket");
		exit(1);
	}
	/* create name structure with wildcard using INADDR_ANY */
	from.sin_family = AF_INET;
	from.sin_addr.s_addr = INADDR_ANY;
	from.sin_port = 0;  
	/* port no. < 1024 IPPORT_RESERVED is for privillege process */
	/* here just initialized it, it will be assigned value after call */
	/* getsockname() */
	if (bind(sock, &from, sizeof(struct sockaddr_in))) {
		perror("binding name to datagram socket");
		exit(1);
	}
	length = sizeof(from);
	if (getsockname(sock, &from, &length)) {
		perror("getting socket name");
		exit(1);
	}
	/* Find assigned port value and print out. */
	printf("socket has port #%d\n", ntohs(from.sin_port));

	/* receive message */
	while (1) {
		n = recvfrom(sock, fromBuf, sizeof(fromBuf), 0, &from, &length);
		if (n < 0) perror("receiving datagram message");
		fromBuf[n] = 0; /* null terminate */
		printf("The no. of bytes received=%d\n", n);
		printf("received msg=");
		for (i=0; i<n; i++) {
			if ((i+1)%80 == 0) printf("\n");
			else printf("%c", fromBuf[i]);
		}
		printf("rcvd ");
		printsockaddr(&from);

		/* use the returned sender's socket address in the from structure to
		        send the reply message */
		sprintf(toBuf, "received message: %s\n", fromBuf);
		if (odd && flag%2 != 0) {
			printf("throw away odd message!\n");
		} else if (all) {
			printf("throw away all message!\n");
		} else if (three && flag%3 != 0) {
			printf("throw away two out of every 3 messages!\n");
		} else {
			printf("send reply msg=%s\n", toBuf);
			if (sendto(sock, toBuf, strlen(toBuf), 0, &from, sizeof(from)) < 0)  {
				perror("sending datagram message");
				exit(1);
		   }
		}
		flag++;
	}
	close(sock);
}