#include <stdio.h>#include <stdlib.h>#include <string.h>#include <strings.h>#include <signal.h>#include <sys/time.h>#include <arpa/inet.h>#include <sys/types.h>#include <sys/socket.h>#include <unistd.h>#include <netinet/in.h>#include <netinet/ip.h>#include <netinet/ip_icmp.h>#include <netdb.h>#include <setjmp.h>#include <errno.h>#include <sys/select.h>#include <fcntl.h>#define PACKET_SIZE 4096/* 计算校验和的算法 */unsigned short cal_chksum(unsigned short *addr,int len){    int sum=0;    int nleft = len;    unsigned short *w = addr;    unsigned short answer = 0;    /* 把ICMP报头二进制数据以2字节为单位累加起来 */    while(nleft > 1){        sum += *w++;        nleft -= 2;    }    /*     * 若ICMP报头为奇数个字节，会剩下最后一字节。     * 把最后一个字节视为一个2字节数据的高字节，     * 这2字节数据的低字节为0，继续累加     */    if(nleft == 1){        *(unsigned char *)(&answer) = *(unsigned char *)w;        sum += answer;    /* 这里将 answer 转换成 int 整数 */    }    sum = (sum >> 16) + (sum & 0xffff);        /* 高位低位相加 */    sum += (sum >> 16);        /* 上一步溢出时，将溢出位也加到sum中 */    answer = ~sum;             /* 注意类型转换，现在的校验和为16位 */    return answer;}int livetest(char* ip) {    char    sendpacket[PACKET_SIZE];    /* 发送的数据包 */    char    recvpacket[PACKET_SIZE];    /* 接收的数据包 */    pid_t    pid;    int    datalen = 56;    /* icmp数据包中数据的长度 */    struct protoent *protocol;    protocol = getprotobyname("icmp");    int sockfd;    int size = 50*1024;    if((sockfd = socket(AF_INET, SOCK_RAW, protocol->p_proto)) < 0) {        perror("socket error");    }    setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &size, sizeof(size) );        struct sockaddr_in dest_addr;    bzero(&dest_addr, sizeof(dest_addr));    dest_addr.sin_family = AF_INET;    dest_addr.sin_addr.s_addr = inet_addr(ip);    //send packet;    int packsize;    struct icmp *icmp;    struct timeval *tval;    icmp = (struct icmp*)sendpacket;    icmp->icmp_type = ICMP_ECHO;    /* icmp的类型 */    icmp->icmp_code = 0;            /* icmp的编码 */    icmp->icmp_cksum = 0;           /* icmp的校验和 */    icmp->icmp_seq = 1;       /* icmp的顺序号 */    icmp->icmp_id = pid;            /* icmp的标志符 */    packsize = 8 + datalen;   /* icmp8字节的头 加上数据的长度(datalen=56), packsize = 64 */    tval = (struct timeval *)icmp->icmp_data;    /* 获得icmp结构中最后的数据部分的指针 */    gettimeofday(tval, NULL); /* 将发送的时间填入icmp结构中最后的数据部分 */    icmp->icmp_cksum = cal_chksum((unsigned short *)icmp, packsize);/*填充发送方的校验和*/    if(sendto(sockfd, sendpacket, packsize, 0, (struct sockaddr *)&dest_addr, sizeof(dest_addr)) < 0){        perror("sendto error");    }    printf("send %d, send done\n",1 );    int n;    struct sockaddr_in from;    int fromlen = sizeof(from);    fcntl(sockfd, F_SETFL, O_NONBLOCK);    struct timeval timeo = {1,0};    fd_set set;    FD_ZERO(&set);    FD_SET(sockfd, &set);    //read , write;    int retval = select(sockfd+1, &set, NULL, NULL, &timeo);    if(retval == -1) {        printf("select error\n");        return 0;    }else if(retval == 0 ) {        printf("timeout\n");        return 0;    }else{        if( FD_ISSET(sockfd, &set) ){            printf("host is live\n");            return 1;        }    }    // n = recvfrom(sockfd, recvpacket,sizeof(recvpacket), 0, (struct sockaddr *)&from, (socklen_t *)&fromlen);    // if(n<0) {    //     perror("recvfrom error");    // }else{    //     printf("%d\n",n);    // }    //return 0;}int main(int argc, char* argv[]) {    printf("%d\n" , livetest(argv[1]));    return 0;}