/* 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>

/************************************************************
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(&(arg->sin_addr), sizeof(arg->sin_addr), AF_INET);
  printf("Hostname=%s, ", hp->h_name);
  printf("Address=%s,\n", inet_ntoa(arg->sin_addr));
  printf("Port=%d, ", ntohs(arg->sin_port));
}

help_msg()
{
	printf("format: idgr3 [-dv]\n");
	printf("          option: v set verbose mode print rcvd msg\n");
	printf("                  d set debug mode\n");
}

main(argc, argv)
int argc;
char *argv[];
{
	int sock; 
	struct sockaddr_in to;
	struct sockaddr_in from;
	struct hostent *hp, *gethostbyname();
	int msgNo;
	int n, i;
	char toBuf[2048];
	char fromBuf[2048];
	char hostname[64];
	extern char *optarg;
	extern int   optind;
	int option_exist = 0;
	int c;
	int debug = 0;
	int verbose = 0;
	char rcv_name[64];  /* receiver's socket name */
	int toPort_no;
	int length;
	int fromlen;

	/* process command line args */
	while ((c=getopt(argc,argv,"dn:")) != EOF)
	{
		option_exist = 1;
		switch(c)
		{
		case 'd':
			debug = 1;
			printf("turn on debug mode.\n");
			break;

		case 'v':
			verbose = 1;
			printf("turn on verbose mode print each rcvd msg.\n");
			break;
		case '?':
			help_msg();
			exit (1);
		default:
			fprintf (stderr, "unrecognized arg >%s<\n", optarg);
			help_msg();
			exit (1);
		}
	}

	/* create socket from which to read */
	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) {
		length = sizeof(to);
		n = recvfrom(sock, fromBuf, 2048, 0, &to, &length);
		if (n < 0) perror("receiving datagram message");
		if (debug) printsockaddr(&to);
		fromBuf[n] = 0; /* null terminate */
		sscanf(fromBuf, "packet %d", &msgNo);
		if (verbose) printf("received %s\n", fromBuf);

		/* replying with ack message */
		sprintf(toBuf, "ACK %d\n", msgNo);
		if (sendto(sock, toBuf, strlen(toBuf), 0, &to, sizeof(to)) < 0) 
			perror("sending datagram message");
	}
	close(sock);
}