linux ping源码

以下是Linux系统中ping命令的源代码：

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

#define PACKET_SIZE     4096
#define MAX_WAIT_TIME   5
#define MAX_NO_PACKETS  3

char sendpacket[PACKET_SIZE];
char recvpacket[PACKET_SIZE];
int sockfd,datalen=56;
int nsend=0,nreceived=0;
struct sockaddr_in dest_addr;
pid_t pid;
struct sockaddr_in from;
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)
{
    if ((out->tv_usec -= in->tv_usec) < 0)
    {
        --out->tv_sec;
        out->tv_usec += 1000000;
    }
    out->tv_sec -= in->tv_sec;
}

int main(int argc,char *argv[])
{
    struct hostent *host;
    struct protoent *protocol;
    unsigned long inaddr=0l;
    int waittime=MAX_WAIT_TIME;
    int size=50*1024;
    int ttl=255;
    int i=0;
    bzero(&dest_addr,sizeof(dest_addr));

    if(argc<2)
    {
        printf("usage:%s hostname/IP address\n",argv[0]);
        exit(1);
    }

    if((protocol=getprotobyname("icmp"))==NULL)
    {
        perror("getprotobyname");
        exit(1);
    }

    if((sockfd=socket(AF_INET,SOCK_RAW,protocol->p_proto))<0)
    {
        perror("socket error");
        exit(1);
    }

    setuid(getuid());
    setsockopt(sockfd,SOL_SOCKET,SO_RCVBUF,&size,sizeof(size));
    setsockopt(sockfd,IPPROTO_IP,IP_TTL,&ttl,sizeof(ttl));

    bzero(&dest_addr,sizeof(dest_addr));
    dest_addr.sin_family=AF_INET;

    if(inaddr=inet_addr(argv[1])==INADDR_NONE)
    {
        if((host=gethostbyname(argv[1]))==NULL)
        {
            perror("gethostbyname error");
            exit(1);
        }
        memcpy((char *)&dest_addr.sin_addr,host->h_addr,host->h_length);
    }
    else
        dest_addr.sin_addr.s_addr=inaddr;

    pid=getpid();

    printf("PING %s(%s):%d bytes of data.\n",argv[1],inet_ntoa(dest_addr.sin_addr),datalen);

    for(i=0;i<MAX_NO_PACKETS;i++)
    {
        if(pack(i)<0)
            continue;
        send_packet();
        recv_packet();
        sleep(1);
    }

    statistics(SIGALRM);
    return 0;
}

void statistics(int signo)
{
    printf("\n--------------------PING statistics-------------------\n");
    printf("%d packets transmitted,%d received,%.0f%% packet loss\n",
            nsend,nreceived,(float)(nsend-nreceived)/nsend*100);
    close(sockfd);
    exit(0);
}

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 pack(int pack_no)
{
    int i=0;
    int packsize=0;
    struct icmp *icmp;
    struct timeval *tval;

    icmp=(struct icmp*)sendpacket;
    icmp->icmp_type=ICMP_ECHO;
    icmp->icmp_code=0;
    icmp->icmp_cksum=0;
    icmp->icmp_seq=pack_no;
    icmp->icmp_id=pid;
    packsize=8+datalen;
    tval= (struct timeval *)icmp->icmp_data;
    gettimeofday(tval,NULL);
    icmp->icmp_cksum=cal_chksum((unsigned short *)icmp,packsize);
    return packsize;
}

void send_packet()
{
    int packetsize=0;

    nsend++;
    packetsize=pack(nsend);
    if(sendto(sockfd,sendpacket,packetsize,0,(struct sockaddr *)&dest_addr,sizeof(dest_addr))<0)
        perror("sendto error");
}

void recv_packet()
{
    int n,fromlen;
    extern int errno;
    signal(SIGALRM,statistics);
    fromlen=sizeof(from);
    alarm(MAX_WAIT_TIME);
    while(1)
    {
        if((n=recvfrom(sockfd,recvpacket,sizeof(recvpacket),0,(struct sockaddr *)&from,&fromlen))<0)
        {
            if(errno==EINTR)
                continue;
            perror("recvfrom error");
            continue;
        }
        gettimeofday(&tvrecv,NULL);
        if(unpack(recvpacket,n)==-1)
            continue;
        nreceived++;
        break;
    }
}

int unpack(char *buf,int len)
{
    int i,iphdrlen;
    struct ip *ip;
    struct icmp *icmp;
    struct timeval *tvsend;
    double rtt;

    ip=(struct ip *)buf;
    iphdrlen=ip->ip_hl<<2;

    icmp=(struct icmp *)(buf+iphdrlen);
    len-=iphdrlen;
    if(len<8)
    {
        printf("ICMP packets\'s length is less than 8\n");
        return -1;
    }

    if((icmp->icmp_type==ICMP_ECHOREPLY)&&(icmp->icmp_id==pid))
    {
        tvsend=(struct timeval *)icmp->icmp_data;
        tv_sub(&tvrecv,tvsend);
        rtt=tvrecv.tv_sec*1000+tvrecv.tv_usec/1000;
        printf("%d byte from %s: icmp_seq=%u ttl=%d rtt=%.3f ms\n",
                len,inet_ntoa(from.sin_addr),icmp->icmp_seq,ip->ip_ttl,rtt);
    }
    else
        return -1;
}

上述代码实现了ping命令的基本功能，包括构造ICMP报文、发送ICMP报文、接收ICMP报文、计算RTT等。