Linux C++ 实现一个简易版的ping （也就是imcp协议）

背景：

想实现一个在没外网的时候就自动重启路由器的功能。

又不想用ping命令，因为在代码里调用system("ping"); 可能会比较耗时，得单开线程。于是找了个实现ICMP协议的代码。

参考：https://blog.csdn.net/qivan/article/details/7237051

代码：

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/time.h>
#include <unistd.h>
#include <netdb.h>
#include <string.h> 

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

//效验算法（百度下有注释，但是还是看不太明白）
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 *tval;
    int maxfds = 0;
    fd_set readfds;  

    struct sockaddr_in addr;
    struct sockaddr_in from;
    // 设定Ip信息
    bzero(&addr,sizeof(addr));
    addr.sin_family = AF_INET;  

    addr.sin_addr.s_addr = inet_addr(ips);  

#if 1
    int sockfd;
    // 取得socket  。  如果没加sudo 这里会报错
    sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
    if (sockfd < 0)
    {
        printf("ip:%s,socket error\n",ips);
        return ERROR;
    }  

    struct timeval timeo;
    // 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)
    {
        printf("ip:%s,setsockopt error\n",ips);
        return ERROR;
    }  

    char sendpacket[PACKET_SIZE];
    char recvpacket[PACKET_SIZE];
    // 设定Ping包
    memset(sendpacket, 0, sizeof(sendpacket));  

    pid_t pid;
    // 取得PID，作为Ping的Sequence ID
    pid=getpid();  

    struct ip *iph;
    struct icmp *icmp;  

    icmp=(struct icmp*)sendpacket;
    icmp->icmp_type=ICMP_ECHO;  //回显请求
    icmp->icmp_code=0;
    icmp->icmp_cksum=0;
    icmp->icmp_seq=0;
    icmp->icmp_id=pid;
    tval= (struct timeval *)icmp->icmp_data;
    gettimeofday(tval,NULL);
    icmp->icmp_cksum=cal_chksum((unsigned short *)icmp,sizeof(struct icmp));  //校验

    int n;
    // 发包 。可以把这个发包挪到循环里面去。
    n = sendto(sockfd, (char *)&sendpacket, sizeof(struct icmp), 0, (struct sockaddr *)&addr, sizeof(addr));
    if (n < 1)
    {
        printf("ip:%s,sendto error\n",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)
        {
        printf("ip:%s,Time out error\n",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, (socklen_t *)&fromlen);
    printf("recvfrom Len:%d\n",n);
        if (n < 1)
    {
        return ERROR;
        }          

        char *from_ip = (char *)inet_ntoa(from.sin_addr);
        // 判断是否是自己Ping的回复
        if (strcmp(from_ip,ips) != 0)
        {
            printf("NowPingip:%s Fromip:%s NowPingip is not same to Fromip,so ping wrong!\n",ips,from_ip);
           return ERROR;
        }  

        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);
        // 判断Ping回复包的状态
        if (icmp->icmp_type == ICMP_ECHOREPLY && icmp->icmp_id == pid)   //ICMP_ECHOREPLY回显应答
        {
            // 正常就退出循环
        printf("icmp succecss .............  \n");
            break;
        }
        else
        {
            // 否则继续等
            continue;
        }
    }
#endif
    return SUCCESS;
}

int main()
{
#if 1
    char cPing[16];
    printf("Please input ping IP:");
    scanf("%s",cPing);
#else
    char *cPing = "192.168.1.200";
#endif
    if(ping(cPing,10000))
    {
        printf("Ping succeed!\n");
    }
    else
    {
        printf("Ping wrong!\n");
    }

    return 0;
}

实际效果：

补充说明：

0）直接用参考链接上的代码时编译不过，不知道是不是因为我用的是cpp，没太深究。

1）实际使用的时候需要加上sudo，不然在创建套接字那个地方会报错。我还没想好怎么在代码里用sudo，（因为实际项目运行起来是不需要加sudo的）。