Linux下Ping的实现代码

Linux下Ping的实现代码：

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netdb.h>

#define PACKET_SIZE     4096
#define ERROR           0
#define SUCCESS         1

// 效验算法
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;
}

// Ping函数
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;
    pid_t pid;
    int maxfds = 0;
    fd_set readfds;
   
    // 设定Ip信息
    bzero(&addr,sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = inet_addr(ips);  

    // 取得socket
    sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
    if (sockfd < 0)
    {
        syslog(LOG_INFO,"ip:%s,socket error",ips);
        return ERROR;
    }
   
    // 设定TimeOut时间
    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);
        return ERROR;
    }
   
    // 设定Ping包
    memset(sendpacket, 0, sizeof(sendpacket));
   
    // 取得PID，作为Ping的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);

    // 发包
    n = sendto(sockfd, (char *)&sendpacket, packsize, 0, (struct sockaddr *)&addr, sizeof(addr));
    if (n < 1)
    {
        syslog(LOG_INFO,"ip:%s,sendto error",ips);
        return ERROR;
    }

    // 接受
    // 由于可能接受到其他Ping的应答消息，所以这里要用循环
    while(1)
    {
        // 设定TimeOut时间，这次才是真正起作用的
        FD_ZERO(&readfds);
        FD_SET(sockfd, &readfds);
        maxfds = sockfd + 1;
        n = select(maxfds, &readfds, NULL, NULL, &timeo);
        if (n <= 0)
        {
            syslog(LOG_INFO,"ip:%s,Time out error",ips);
            close(sockfd);
            return ERROR;
        }

        // 接受
        memset(recvpacket, 0, sizeof(recvpacket));
        int fromlen = sizeof(from);
        n = recvfrom(sockfd, recvpacket, sizeof(recvpacket), 0, (struct sockaddr *)&from, &fromlen);
        if (n < 1) {
            break;
        }
       
        // 判断是否是自己Ping的回复
        char *from_ip = (char *)inet_ntoa(from.sin_addr);
        syslog(LOG_INFO,"fomr ip:%s",from_ip);
         if (strcmp(from_ip,ips) != 0)
         {
            syslog(LOG_INFO,"ip:%s,Ip wang",ips);
            break;
         }
       
        iph = (struct ip *)recvpacket;
   
        icmp=(struct icmp *)(recvpacket + (iph->ip_hl<<2));