ICMP协议写的ping函数

ICMP是&＃xff08;Internet Control Message Protocol&＃xff09;Internet控制报文协议。它是TCP/IP协议族的一个子协议&＃xff0c;用于在IP主机、路由器之间传递控制消息。控制消息是指网络通不通、主机是否可达、路由是否可用等网络本身的消息。这些控制消息虽然并不传输用户数据&＃xff0c;但是对于用户数据的传递起着重要的作用。

unsigned short cal_chksum(unsigned short *addr, int len)
{
    int nleft&＃61;len;
    int sum&＃61;0;
    unsigned short *w&＃61;addr;
    unsigned short answer&＃61;0;

    while(nleft > 1)
    {
        sum &＃43;&＃61; *w&＃43;&＃43;;
        nleft -&＃61; 2;
    }

    if( nleft &＃61;&＃61; 1)
    {      
        *(unsigned char *)(&answer) &＃61; *(unsigned char *)w;
        sum &＃43;&＃61; answer;
    }

    sum &＃61; (sum >> 16) &＃43; (sum & 0xffff);
    sum &＃43;&＃61; (sum >> 16);
    answer &＃61; ~sum;

    return answer;
}

int ping( char *ips, int timeout)
{
    struct timeval timeo;
    int sockfd;
    struct sockaddr_in addr;
    struct sockaddr_in from;

    struct timeval *tval;
    struct ip *iph;
    struct icmp *icmp;

    char sendpacket[PACKET_SIZE];
    char recvpacket[PACKET_SIZE];

    int n, ret &＃61; SUCCESS;
    pid_t pid;
    int maxfds &＃61; 0, CountNum &＃61; 0;
    fd_set readfds;

    bzero(&addr,sizeof(addr));
    addr.sin_family &＃61; AF_INET;
    addr.sin_addr.s_addr &＃61; inet_addr(ips);  

    sockfd &＃61; socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
    if (sockfd <0)
    {
        syslog(LOG_INFO,"ip:%s,socket error",ips);
        return ERROR;
    }

    timeo.tv_sec &＃61; timeout / 1000;
    timeo.tv_usec &＃61; timeout % 1000;

    if (setsockopt(sockfd, SOL_SOCKET, SO_SNDTIMEO, &timeo, sizeof(timeo)) &＃61;&＃61; -1)
    {
        syslog(LOG_INFO,"ip:%s,setsockopt error",ips);
        close(sockfd);
        return ERROR;
    }

    memset(sendpacket, 0, sizeof(sendpacket));

    // PID ping Sequence ID
    pid&＃61;getpid();
    int i,packsize;
    icmp&＃61;(struct icmp*)sendpacket;
    icmp->icmp_type&＃61;ICMP_ECHO;
    icmp->icmp_code&＃61;0;
    icmp->icmp_cksum&＃61;0;
    icmp->icmp_seq&＃61;0;
    icmp->icmp_id&＃61;pid;
    packsize&＃61;8&＃43;56;
    tval&＃61; (struct timeval *)icmp->icmp_data;
    gettimeofday(tval,NULL);
    icmp->icmp_cksum&＃61;cal_chksum((unsigned short *)icmp,packsize);

    n &＃61; sendto(sockfd, (char *)&sendpacket, packsize, 0, (struct sockaddr *)&addr, sizeof(addr));
    if (n <1)
    {
        printf("ip:%s,sendto error.\n",ips);
        close(sockfd);
        return ERROR;
    }

    CountNum &＃61; 0;
    while(CountNum&＃43;&＃43;    {
        FD_ZERO(&readfds);
        FD_SET(sockfd, &readfds);
        maxfds &＃61; sockfd &＃43; 1;
        n &＃61; select(maxfds, &readfds, NULL, NULL, &timeo);
        if (n <&＃61; 0)
        {
            printf("ip:%s,Time out error.\n",ips);
            ret&＃61; ERROR;
            break;
        }

        //accept
        memset(recvpacket, 0, sizeof(recvpacket));
        int fromlen &＃61; sizeof(from);
        n &＃61; recvfrom(sockfd, recvpacket, sizeof(recvpacket), 0, (struct sockaddr *)&from, &fromlen);
        if (n <1)
        {
            printf("ip:%s, recvfrom error.\n",ips);
            ret&＃61; ERROR;
            break;
        }

        // Check this echo reply if belong to myself
        char *from_ip &＃61; (char *)inet_ntoa(from.sin_addr);
        printf("fomr ip:%s.\n",from_ip);
        if (strcmp(from_ip,ips) !&＃61; 0)
        {
            printf("ip:%s,Ip wrong.\n",ips);
            ret &＃61; ERROR;
            break;
        }

        iph &＃61; (struct ip *)recvpacket;

        icmp&＃61;(struct icmp *)(recvpacket &＃43; (iph->ip_hl<<2));

        printf("ip:%s,icmp->icmp_type:%d,icmp->icmp_id:%d.\n",ips,icmp->icmp_type,icmp->icmp_id);
        //check reply contents
        if (icmp->icmp_type &＃61;&＃61; ICMP_ECHOREPLY && icmp->icmp_id &＃61;&＃61; pid)
        {
            //ping success
            ret &＃61; SUCCESS;
            break;
        }
        else
        {
            //continue wait
            continue;
        }
    }

    close(sockfd);

    if(ret &＃61;&＃61; SUCCESS)
    {
        printf("Connect:%s success!\n",ips);
    }
    else
    {
        printf("Connect:%s FAIL!!!\n",ips);
    }
    return ret;
}