假如意图主机在工 输出在工状况 假如5妙内无相应 用SIGALRM信号中止进程
#include unp.h
void send_echo_req(int sockfd, struct sockaddr_in *dstaddr);
uint16_t in_cksum(uint16_t *addr, int len);
void recv_echo_reply(int sockfd);
int main(int argc, char **argv)
{
int sockfd;
struct sockaddr_in dstaddr;
if ((sockfd = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP)) == -1)
err_sys(socket);
bzero(dstaddr, sizeof(dstaddr));
dstaddr.sin_family = AF_INET;
dstaddr.sin_port = htons(0);
if (inet_pton(AF_INET, argv[1], dstaddr.sin_addr) = 0)
err_sys(inet_pton);
send_echo_req(sockfd, dstaddr);
recv_echo_reply(sockfd);
exit(0);
}
void send_echo_req(int sockfd, struct sockaddr_in *dstaddr)
{
char buf[100];
size_t len = sizeof(struct icmp);
struct icmp *icmp;
socklen_t dstlen = sizeof(struct sockaddr_in);
bzero(buf, sizeof(buf));
icmp = (struct icmp *)buf;
icmp->icmp_type = ICMP_ECHO;
icmp->icmp_code = 0;
icmp->icmp_id = getpid();
icmp->icmp_seq = 1;
icmp->icmp_cksum = in_cksum((uint16_t *) icmp, sizeof(struct icmp));
if (sendto(sockfd, buf, len, 0, (SA *)dstaddr, dstlen) == -1)
err_sys(sendto);
}
void recv_echo_reply(int sockfd)
{
char buf[100];
ssize_t n;
struct ip *ip;
struct icmp *icmp;
while (1) {
alarm(5); /* set timeout */
if ((n = read(sockfd, buf, sizeof(buf))) == -1)
err_sys(read);
ip = (struct ip *)buf;
if (ip->ip_p != IPPROTO_ICMP) {
fprintf(stderr, protocol error.\r\n);
exit(1);
}
icmp = (struct icmp *)(buf + sizeof(struct ip));
if (icmp->icmp_type == ICMP_ECHOREPLY) {
if (icmp->icmp_id != getpid()) {
fprintf(stderr, not this process.\r\n);
exit(1);
} else {
printf(destination host is alive.\r\n);
break;
}
}
}
}
uint16_t in_cksum(uint16_t *addr, int len)
{
int nleft = len;
uint32_t sum = 0;
uint16_t *w = addr;
uint16_t answer = 0;
while (nleft > 1) {
sum += *w++;
nleft -= 2;
}
if (nleft == 1) {
*(unsigned char *)(answer) = *(unsigned char *)w ;
sum += answer;
}
sum = (sum >> 16) + (sum 0xffff);
sum += (sum >> 16);
answer = ~sum;
return(answer);
}
void err_sys(const char *errmsg)
{
perror(errmsg);
exit(1);
}
