/* receiver for internet datagram demo */

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

#define ENDPACKET "end"

help_msg()
{
	printf("format: idgr\n");
}

main(argc, argv)
int argc;
char *argv[];
{
	int sockTo;
	int sockFrom;
	struct sockaddr_in to;
	struct sockaddr_in from;
	struct hostent *hp, *gethostbyname();
	int n, i;
	char c;
	char toBuf[1024];
	char fromBuf[1024];
	char hostname[64];
	extern char *optarg;
	extern int   optind;
	int option_exist = 0;
	int c;
	int debug = 0;
	char rcv_name[64];  /* receiver's socket name */
	int toPort_no;
	int length;
	int fromlen;
	int quitFlag = 1;

	/* create socket from which to read */
	sockFrom = socket(AF_INET, SOCK_DGRAM, 0);
	if (sockFrom < 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(sockFrom, &from, sizeof(struct sockaddr_in))) {
		perror("binding name to datagram socket");
		exit(1);
	}
	length = sizeof(from);
	if (getsockname(sockFrom, &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));

	/* create socket on which to sent */
	sockTo = socket(AF_INET, SOCK_DGRAM, 0);
	if (sockTo < 0) {
		perror("opening datagram socket");
		exit(1);
	}
	to.sin_family = AF_INET;
	to.sin_addr.s_addr = INADDR_ANY;
	to.sin_port = 0;  /* without this line, SUN version was denied in bind() */
	if (bind(sockTo, &to, sizeof(struct sockaddr_in))) {
		perror("binding name to datagram socket to");
		exit(1);
	}
	/* receive message */
	while (quitFlag) {
		n = recv(sockFrom, fromBuf, 1024);
		if (n < 0) perror("receiving datagram message");
		fromBuf[n] = 0; /* null terminate */
		switch (fromBuf[0])  {
		case 'E' :
			sscanf(fromBuf, "%c%s %d ", c, rcv_name, &toPort_no);
			printf("n=%d\n", n);
			printf("received msg=%s\n", fromBuf);
			printf("from host=%s, port=%d\n", rcv_name, &toPort_no);

			/* 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(rcv_name);
			if (hp == 0) {
				fprintf(stderr, "%s: unknown host",rcv_name);
				exit(2);
			}
			bcopy(hp->h_addr, &to.sin_addr, hp->h_length);
			to.sin_family = AF_INET;
			to.sin_port = htons(toPort_no);
			/* replying with ack message */
			sprintf(toBuf, "A%s\n", fromBuf);
			if (sendto(sockTo, toBuf, strlen(toBuf), 0, &to, sizeof(to)) < 0)
				perror("sending datagram message");
			break;
		case 'q':
			quitFlag = 0;
		default:
			break;
		}
	}
	close(sockFrom);
	close(sockTo);
}