/*
Send a UDP datagram to the daytime server on another host.
Display the UDP datagram that comes back.
*/

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <signal.h>

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

void handle_sigalrm(int s);

int main(int argc, char **argv)
{
	const struct servent *const service = getservbyname("daytime", "udp");

	const char name[] = "aixmita1.urz.uni-heidelberg.de";
	const sa_family_t family = AF_INET;   /* IP version 4 */
	const struct hostent *host;

	int s;        /* file descriptor for socket */
	struct sockaddr_in address;
	socklen_t length = sizeof address;

	char buffer[100];
	char dotted[100];
	ssize_t n;    /* number of bytes received from socket */

	if (service == NULL) {
		fprintf(stderr, "%s: couldn't find udp service daytime\n",
			argv[0]);
		return 1;
	}

	host = gethostbyname(name);
	if (host == NULL) {
		fprintf(stderr,
			"%s: couldn't get IP address for %s, h_errno == %d\n", 
			argv[0], name, h_errno);
		return 2;
	}
		
	s = socket(family, SOCK_DGRAM, 0);
	if (s < 0) {
		perror(argv[0]);
		return 3;
	}

	bzero(&address, sizeof address);
	address.sin_family = family;
	address.sin_port = service->s_port;
	address.sin_addr.s_addr = *(in_addr_t *)host->h_addr_list[0];

	if (sendto(s, "", 0, 0, (const struct sockaddr *)&address,
		sizeof address) != 0) {
		perror(argv[0]);
		return 4;
	}

	if (getsockname(s, (struct sockaddr *)&address, &length) != 0) {
		perror(argv[0]);
		return 5;
	}

	if (inet_ntop(family, &address.sin_addr, buffer, sizeof buffer)
		== NULL) {
		perror(argv[0]);
		return 6;
	}

	printf("I sent an empty datagram from my port %d.\n",
		ntohs(address.sin_port));

	/* Remain in recvfrom for no more than 15 seconds. */
	if (signal(SIGALRM, handle_sigalrm) == SIG_ERR) {
		perror(argv[0]);
		return 7;
	}
	alarm(15);

	length = sizeof address;
	n = recvfrom(s, buffer, sizeof buffer, 0, (struct sockaddr *)&address,
		&length);

	if (n < 0) {
		perror(argv[0]);
		return 8;
	}

	if (inet_ntop(family, &address.sin_addr, dotted, sizeof dotted)
		== NULL) {
		perror(argv[0]);
		return 9;
	}

	printf("I then received a datagram containing the following %d bytes\n"
		"from port %d of %s", n, ntohs(address.sin_port), dotted);

	host = gethostbyaddr((const char *)&address.sin_addr,
		sizeof address.sin_addr, family);

	if (host != NULL) {
		printf(" (%s)", host->h_name);
	}
	printf("\n%*s\n", n, buffer);
	return EXIT_SUCCESS;
}

void handle_sigalrm(int s)
{
	printf("The datagram I was waiting for didn't arrive in 15 seconds.\n");
	exit(10);
}