#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>   /* for inet_ntop */
#include <arpa/inet.h>
#include <netdb.h>        /* for getservbyname */
#include <signal.h>

const char *progname;
void handle_sigalrm(int sig);

int main(int argc, char **argv)
{
	const int s = socket(AF_INET, SOCK_DGRAM, 0);
	int ttl = 10;   /* time to live */
	int length = sizeof ttl;
	const struct servent *service;
	char name[1000] = "aixmita1.urz.uni-heidelberg.de";
	const struct hostent *host;
	struct sockaddr_in address;
	socklen_t socklen = sizeof address;
	ssize_t n;
	char buffer[100];
	int len;

	progname = argv[0];
	if (s < 0) {
		perror(progname);
		return 1;
	}

	if (setsockopt(s, IPPROTO_IP, IP_TTL, &ttl, sizeof ttl) != 0) {
		perror(progname);
		return 2;
	}

	if (getsockopt(s, IPPROTO_IP, IP_TTL, &ttl, &length) != 0) {
		perror(progname);
		return 3;
	}

	printf("The time to live was set to %d.\n", ttl);
	
	service = getservbyname("daytime", "udp");
	if (service == NULL) {
		fprintf(stderr, "%s: couldn't find udp service daytime\n",
			progname);
		return 4;
	}

	host = gethostbyname(name);
	if (host == NULL) {
		fprintf(stderr, "%s: couldn't find \"%s\", h_errno == %d\n",
			progname, name, h_errno);
		return 5;
	}

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

	/* Send a datagram. */
	if (sendto(s, NULL, 0, 0,
		(const struct sockaddr *)&address, sizeof address) != 0) {
		perror(progname);
		return 6;
	}

	if (getsockname(s,  (struct sockaddr *)&address, &socklen) != 0) {
		perror(progname);
		return 7;
	}

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

	if (signal(SIGALRM, handle_sigalrm) == SIG_ERR) {
		perror(progname);
		return 8;
	}

	alarm(15);

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

	if (n < 0) {
		perror(progname);
		return 9;
	}

	if (inet_ntop(AF_INET, &address.sin_addr, name, sizeof name) == NULL) {
		perror(progname);
		return 10;
	}

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

	host = gethostbyaddr((const char *)&address.sin_addr,
		sizeof address.sin_addr, AF_INET);
	if (host != NULL) {
		printf(" (%s)", host->h_name);
	}

	printf("\n%s\n", buffer);
	return EXIT_SUCCESS;
}

void handle_sigalrm(int sig)
{
	if (sig != SIGALRM) {
		fprintf(stderr, "%s: signal handler called with signal %d "
			"instead of %d\n", progname, sig, SIGALRM);
		exit(11);
	}

	fprintf(stderr, "%s: The datagram I was waiting for "
		"didn't arrive in 15 seconds.\n", progname);
	exit(12);
}