ICMP协议写的ping函数

ICMP是（Internet Control Message Protocol）Internet控制报文协议。它是TCP/IP协议族的一个子协议，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，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=len;
    int sum=0;
    unsigned short *w=addr;
    unsigned short 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;
}

 

 

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 = SUCCESS;
    pid_t pid;
    int maxfds = 0, CountNum = 0;
    fd_set readfds;

 

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

 

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

 

    timeo.tv_sec = timeout / 1000;
    timeo.tv_usec = timeout % 1000;

 

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

 

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

 

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

 

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

 

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

 

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

 

        iph = (struct ip *)recvpacket;

 

        icmp=(struct icmp *)(recvpacket + (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 == ICMP_ECHOREPLY && icmp->icmp_id == pid)
        {
            //ping success
            ret = SUCCESS;
            break;
        }
        else
        {
            //continue wait
            continue;
        }
    }

 

    close(sockfd);

 

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