linux:c++实现ping算法

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h> /* for bzero */
#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>

#define MAX_WAIT_TIME 5
#define PACKET_SIZE 4096    /* 数据包的大小 */
#define MAX_NO_PACKETS 3    /* 发送3个ICMP报文 */

char    sendpacket[PACKET_SIZE];    /* 发送的数据包 */
char    recvpacket[PACKET_SIZE];    /* 接收的数据包 */

pid_t    pid;
int    sockfd;
int    datalen = 56;    /* icmp数据包中数据的长度 */
int    nsend = 0;       /* 发送的次数 */
int    nreceived = 0;   /* 接收的次数 */

struct sockaddr_in    dest_addr;  /* icmp包目的地址 */
struct sockaddr_in    from;       /* icmp包源地址 */
struct timeval    tvrecv;

void statistics(int signo);
unsigned short cal_chksum(unsigned short *addr,int len);
int pack(int pack_no);
void send_packet(void);
void recv_packet(void);
int unpack(char *buf,int len);
void tv_sub(struct timeval *out,struct timeval *in);

void statistics(int signo)
{
        printf("\n--------------------PING statistics-------------------\n");
        /*
         * 总共发送nsend个icmp包,总共接收到返回的nreceived个包,
         * icmp包的丢失率(nsend-nreceived)/nsend
         */
        printf("%d packets transmitted, %d received , %%%d lost\n",
                nsend, nreceived, (nsend-nreceived)/nsend*100);
        close(sockfd);
        exit(1);
}

/* 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;
}

/* 设置ICMP报头,以及将发送的时间设置为ICMP的末尾的数据部分和校验和 */
int pack(int pack_no)
{
        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 = pack_no;       /* 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*/

        return packsize;
}

/* 发送三个ICMP报文 */
void send_packet()
{
        int packetsize;

        /* 每一次发送3个icmp包 */
        while(nsend < MAX_NO_PACKETS){    // #define MAX_NO_PACKETS 3
                nsend++;
                packetsize = pack(nsend); /* 设置ICMP报头 */
                if(sendto(sockfd, sendpacket, packetsize, 0,
                          (struct sockaddr *)&dest_addr, sizeof(dest_addr)) < 0){
                        perror("sendto error");
                        continue;
                }
                sleep(1); /* 每隔一秒发送一个ICMP报文 */
        }
}

/* 接收所有ICMP报文 */
void recv_packet()
{
        int n, fromlen;
        extern int errno;

        signal(SIGALRM,statistics);
        fromlen = sizeof(from);        /* icmp包源地址的大小*/

        while(nreceived < nsend){
                alarm(MAX_WAIT_TIME);
                if((n = recvfrom(sockfd, recvpacket, sizeof(recvpacket), 0,
                                (struct sockaddr *)&from, (socklen_t *)&fromlen)) < 0)
                {
                        if(errno == EINTR)
                            continue;
                        perror("recvfrom error");
                        continue;
                }
                gettimeofday(&tvrecv, NULL); /* 记录接收到icmp包时的时间 */
                if(unpack(recvpacket, n) == -1)
                    continue;
                nreceived++;
        }
}

/* 对ICMP报头解包 */
int unpack(char *buf, int len)
{
        int iphdrlen;
        struct ip *ip;
        struct icmp *icmp;
        struct timeval *tvsend;
        double rtt;

        ip = (struct ip *)buf;
        iphdrlen = ip->ip_hl << 2;    /* 求ip报头长度,即ip报头的长度标志乘4 */

        icmp = (struct icmp *)(buf + iphdrlen); /* 越过ip报头,指向ICMP报头 */
        len -= iphdrlen;        /* ICMP报头及ICMP数据报的总长度 */
        if(len < 8){                /* 小于ICMP报头长度则不合理 */
                printf("ICMP packets\'s length is less than 8\n");
                return -1;
        }
        /* 确保所接收的是我所发的的ICMP的回应 */
        if((icmp->icmp_type == ICMP_ECHOREPLY) && (icmp->icmp_id == pid)){
                tvsend = (struct timeval *)icmp->icmp_data;
                tv_sub(&tvrecv, tvsend);   /* 接收和发送的时间差 */
                /* 以毫秒为单位计算发送和接收的时间差rtt */
                rtt = tvrecv.tv_sec * 1000 + tvrecv.tv_usec / 1000;
                /* 显示相关信息 */
                printf("%d byte from %s: icmp_seq=%u ttl=%d time=%.3f ms\n",
                        len,        /* ICMP报头及ICMP数据报的总长度 */
                        inet_ntoa(from.sin_addr),    /* ICMP的源地址 */
                        icmp->icmp_seq,        /* icmp包发送的顺序 */
                        ip->ip_ttl,            /* icmp存活的时间 */
                        rtt);        /* 以毫秒为单位计算发送和接收的时间差rtt */
                return 0;
        }
        else
            return -1;
}

int main(int argc,char *argv[])
{
    struct hostent    *host;
    struct protoent *protocol;
    unsigned long    inaddr = 0l;
    int    size = 50*1024;        //50k

    if(argc < 2){
            printf("usage:%s hostname/IP address\n",argv[0]);
            exit(1);
    }
    if((protocol = getprotobyname("icmp")) == NULL){
            perror("getprotobyname");
            exit(1);
    }
    /* 生成使用ICMP的原始套接字,这种套接字只有root才能生成 */
    if((sockfd = socket(AF_INET, SOCK_RAW, protocol->p_proto)) < 0){
            perror("socket error");
            exit(1);
    }

    setuid(getuid());    /* 回收root权限,设置当前用户权限 */

    /*
     * 扩大套接字接收缓冲区到50K这样做主要为了减小接收缓冲区溢出的
     * 的可能性,若无意中ping一个广播地址或多播地址,将会引来大量应答
     */
    setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &size, sizeof(size) );
    bzero(&dest_addr, sizeof(dest_addr));
    dest_addr.sin_family = AF_INET;

    /* 判断argv[1]是主机名还是ip地址 */
    if((inaddr=inet_addr(argv[1])) == INADDR_NONE){
        if((host = gethostbyname(argv[1])) == NULL){    /* 是主机名 */
                perror("gethostbyname error");
                exit(1);
        }
        memcpy((char*)&dest_addr.sin_addr, host->h_addr, host->h_length);
    }else {/* 是ip地址 */
        memcpy((char*)&dest_addr.sin_addr, (char*)&inaddr, sizeof(inaddr));
    }
    pid = getpid();        /*获取main的进程id,用于设置ICMP的标志符*/
    printf("PING %s(%s): %d bytes data in ICMP packets.\n",
            argv[1], inet_ntoa(dest_addr.sin_addr), datalen);

    send_packet();     /* 发送所有ICMP报文 */
    recv_packet();     /* 接收所有ICMP报文 */
    statistics(SIGALRM);     /* 进行统计 */

    return 0;
}

/* 两个timeval结构相减 */
void tv_sub(struct timeval *recv, struct timeval *send){
        if((recv->tv_usec -= send->tv_usec) < 0){
                --recv->tv_sec;
                recv->tv_usec += 1000000;
        }
        recv->tv_sec -= send->tv_sec;
}

文章转载自:http://blog.chinaunix.net/uid-25909722-id-2762079.html