fig16.18

W.Richard Stevens经典教程 UNIX环境高级编程第二版 配套学习代码

#include "apue.h"
#include <netdb.h>
#include <errno.h>
#include <sys/socket.h>

#define BUFLEN		128
#define TIMEOUT		20

void
sigalrm(int signo)
{
}

void
print_uptime(int sockfd, struct addrinfo *aip)
{
	int		n;
	char	buf[BUFLEN];

	buf[0] = 0;
	if (sendto(sockfd, buf, 1, 0, aip->ai_addr, aip->ai_addrlen) < 0)
		err_sys("sendto error");
	alarm(TIMEOUT);
	if ((n = recvfrom(sockfd, buf, BUFLEN, 0, NULL, NULL)) < 0) {
		if (errno != EINTR)
			alarm(0);
		err_sys("recv error");
	}
	alarm(0);
	write(STDOUT_FILENO, buf, n);
}

int
main(int argc, char *argv[])
{
	struct addrinfo		*ailist, *aip;
	struct addrinfo		hint;
	int					sockfd, err;
	struct sigaction	sa;

	if (argc != 2)
		err_quit("usage: ruptime hostname");
	sa.sa_handler = sigalrm;
	sa.sa_flags = 0;
	sigemptyset(&sa.sa_mask);
	if (sigaction(SIGALRM, &sa, NULL) < 0)
		err_sys("sigaction error");
	hint.ai_flags = 0;
	hint.ai_family = 0;
	hint.ai_socktype = SOCK_DGRAM;
	hint.ai_protocol = 0;
	hint.ai_addrlen = 0;
	hint.ai_canonname = NULL;
	hint.ai_addr = NULL;
	hint.ai_next = NULL;
	if ((err = getaddrinfo(argv[1], "ruptime", &hint, &ailist)) != 0)
		err_quit("getaddrinfo error: %s", gai_strerror(err));

	for (aip = ailist; aip != NULL; aip = aip->ai_next) {
		if ((sockfd = socket(aip->ai_family, SOCK_DGRAM, 0)) < 0) {
			err = errno;
		} else {
			print_uptime(sockfd, aip);
			exit(0);
		}
	}

	fprintf(stderr, "can't contact %s: %s\n", argv[1], strerror(err));
	exit(1);
}