/*
Send one UDP datagram to port 7 of the host labinfu.unipv.it
*/

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <netdb.h>    /* for gethostbyname */

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

void handle_sigalrm(int s);

int main(int argc, char **argv)
{
	const int s = socket(AF_INET, SOCK_DGRAM, 0);
	struct hostent *entry;

	struct sockaddr_in address;
	size_t length = sizeof address;

	struct sockaddr_in client_address;
	socklen_t client_length = sizeof client_address;
	u_short client_port; /* ephemeral port number, assigned by operating system */

	char buffer[100];
	ssize_t n;   /* socket size */

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

	entry = gethostbyname("labinfu.unipv.it");
	if (entry == NULL) {
		fprintf(stderr, "%s: h_errno == %d\n", argv[0], h_errno);
		return 2;
	}

	bzero(&address, length);
	address.sin_family = AF_INET;
	address.sin_port = htons(7);
	address.sin_addr.s_addr = *(in_addr_t *)entry->h_addr_list[0];

	/* Send a datagram. */
	if (sendto(s, "Hello", 5, 0,
		(const struct sockaddr *)&address, sizeof address) < 0) {
		perror(argv[0]);
		return 3;
	}

	/* getsockname must come after sendto. */
	if (getsockname(s, (struct sockaddr *)&client_address, &client_length) != 0) {
		perror(argv[0]);
		return 4;
	}

	client_port = ntohs(client_address.sin_port);
	printf("My port number is %u.  (I am the client.)\n", client_port);

	sprintf(buffer, "/bin/netstat -a -f inet -P udp |"
		" awk '2 <= NR && NR <= 4 || $1 ~ /\\.%d/'\n", client_port);
	system(buffer);

	/* Remain in recvfrom for no more than 30 seconds. */
	if (signal(SIGALRM, handle_sigalrm) == SIG_ERR) {
		perror(argv[0]);
		return 5;
	}
	alarm(30);

	n = recvfrom(s, buffer, sizeof buffer, 0, (struct sockaddr *)&address, &length);
	if (n < 0) {
		perror(argv[0]);
		return 6;
	}

	printf ("I received a datagram containing the %d bytes \"%.*s\"\n"
		"from port number %u of ",
		n, n, buffer, ntohs(address.sin_port));

	if (inet_ntop(AF_INET, &address.sin_addr, buffer, sizeof buffer) == NULL) {
		perror(argv[0]);
		return 7;
	}

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

void handle_sigalrm(int s)
{
	printf("The datagram I was waiting for never arrived.\n");
	exit(8);
}