/* alternating bit sender for internet datagram demo */

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

#define DATA 1
#define ACK  2

struct Msg {
	struct 	sockaddr_in dst;
	struct 	sockaddr_in src;
	char 	msgtype;
	char    buf[80];
	char	alternating_bit; } ;

help_msg()
{
	printf("format: absender -[dn] rcvhost rcvportno c1host c1portno\n");
	printf("          option: n set the number of messages to be sent\n");
	printf("          option: d set debug mode\n");
}

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));
}


main(argc, argv)
int argc;
char *argv[];
{
	int sock; 
	struct sockaddr_in from;
	struct sockaddr_in to;
	struct hostent *hp, *gethostbyname();

	struct Msg mto, mfrom;
	extern char *optarg;
	extern int   optind;
	int option_exist = 0;
	int c;
	int length;
	int flag = 1;
	int debug = 0;
	int n = 5;
	int i;
	char *rcvHost;  /* receiver's host name */
	int rcvPortNo;
	char *C1Host;  /* channel C1's host name */
	int C1PortNo;
	char hostname[80];

	/* process command line args */
	while ((c=getopt(argc,argv,"dn:")) != EOF)
	{
		option_exist = 1;
		switch(c)
		{
		case 'n':
			if ((n = atoi(optarg)) < 1) n = 1;
			printf("The number of messages to be sent is %d\n", n);
			break;
		case 'd':
			debug = 1;
			printf("set debug mode on\n");
			exit (1);
		default:
			fprintf (stderr, "unrecognized arg >%s<\n", optarg);
			help_msg();
			exit (1);
		}
	}

	rcvHost = argv[optind++];
	rcvPortNo = atoi(argv[optind++]);
	C1Host = argv[optind++];
	C1PortNo = atoi(argv[optind++]);
	/* 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));

	mto.src.sin_family = from.sin_family;
	mto.src.sin_port = from.sin_port;

	/* from.sin_addr.s_addr does not have the 4 byte internet address 
	mto.src.sin_addr.s_addr = from.sin_addr.s_addr;
	replaced by the following code using gethostbyname()  
	*/
	if (debug) printf("from.sin_addr.s_addr=%4x\n", from.sin_addr.s_addr);

	gethostname(hostname, sizeof(hostname));
    hp = gethostbyname(hostname);
    if (hp == 0) {
        fprintf(stderr, "%s: unknown host",rcvHost);
        exit(2);
    }
    bcopy(hp->h_addr, &mto.src.sin_addr, hp->h_length); 
    /* in system V unix use memcpy */
    /* memcpy(&mto.dst.sin_addr, hp->h_addr, hp->h_length); */
	if (debug) {
		printf("mto.src:");
		printsockaddr(&mto.src);
	}

    /* construct name of the socket to send to
     * gethostbyname() returns a structure including the network address
     * of the specified host from /etc/hosts. The port number is taken from
     * the cmd line
     * create name structure for the UNIX domain socket
     * use the name from cmd argument
     */
    hp = gethostbyname(rcvHost);
    if (hp == 0) {
        fprintf(stderr, "%s: unknown host",rcvHost);
        exit(2);
    }
    bcopy(hp->h_addr, &mto.dst.sin_addr, hp->h_length); 
	printf("hp->h_length=%d\n", hp->h_length);
    /* in system V unix use memcpy */
    /* memcpy(&mto.dst.sin_addr, hp->h_addr, hp->h_length); */
    mto.dst.sin_family = AF_INET;
    mto.dst.sin_port = htons(rcvPortNo);
	if (debug) {
		printf("mto.dst:");
		printsockaddr(&mto.dst);
		printf("mto.src:");
		printsockaddr(&mto.src);
	}
    hp = gethostbyname(C1Host);
    if (hp == 0) {
        fprintf(stderr, "%s: unknown host", C1Host);
        exit(2);
    }
    bcopy(hp->h_addr, &to.sin_addr, hp->h_length); 
    /* in system V unix use memcpy */
    /* memcpy(&to.sin_addr, hp->h_addr, hp->h_length); */
    to.sin_family = AF_INET;
    to.sin_port = htons(C1PortNo);
	bzero(mto.buf, sizeof(mto.buf));
	/* in SysV UNIX, memset(mto.buf, 0, sizeof(mto.buf)); */

	for (i=0; i<n; i++) {
		mto.msgtype = DATA;
		sprintf(mto.buf, "packet %d\0", i);
		mto.alternating_bit = i%2;
		if (sendto(sock, &mto, sizeof(mto), 0, &to, sizeof(to))<0)
			perror("send datagram message");
	}
	n = recv(sock, &mfrom, sizeof(mfrom), 0);
	if (n < 0) perror("receiving datagram message");
	printf("number of bytes received=%d\n", n);
	if (mfrom.msgtype == ACK) {
		printf("\treceived ack msg\n");
		printf("\talternating bit is %d\n", mfrom.alternating_bit);
		}
	close(sock);
}