自己写ping的实现

#include
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#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);

void statistics(int signo)
{
   printf("\n--------------------PING statistics-------------------\n");
   printf("%d packets transmitted, %d received , %%%d lost\n",nsend,nreceived,(nsend-nreceived)/nsend*100);
   close(sockfd);
   exit(1);
}
/*校验和算法*/
unsigned short cal_chksum(unsigned short *addr,int len)
{
   int nleft=len;
   int sum=0;
   unsigned short *w=addr;
   unsigned short answer=0;

   /*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，
   这个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;
   }
   sum=(sum>>16)+(sum&0xffff);
   sum+=(sum>>16);
   answer=~sum;
   return answer;
}
/*设置ICMP报头*/
int pack(int pack_no)
{
    int i,packsize;
    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); /*记录发送时间*/
    icmp->icmp_cksum=cal_chksum( (unsigned short *)icmp,packsize); /*校验算法*/
    return packsize;
}

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

      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");
 exit(-1);
      }
}

/*接收所有ICMP报文*/
void recv_packet()
{
     int n,fromlen;
     extern int errno;
     signal(SIGALRM,statistics);
     fromlen=sizeof(from);
      
     alarm(MAX_WAIT_TIME);
       if( (n=recvfrom(sockfd,recvpacket,sizeof(recvpacket),0,(struct sockaddr *)&from,&fromlen)) <0)
       {
           if(errno==EINTR)
    {
              perror("recvfrom error");
              return;
    }
       }
       gettimeofday(&tvrecv,NULL); /*记录接收时间*/
       if(unpack(recvpacket,n)==-1) return;
       nreceived++;
}
/*剥去ICMP报头*/
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; /*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*/
        rtt=tvrecv.tv_sec*1000+(float)tvrecv.tv_usec/1000; /*以毫秒为单位计算rtt*/
        /*显示相关信息*/
        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;
}

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;

    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);
    }
    /* 回收root权限,设置当前用户权限*/
    setuid(getuid());
    /*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,(char *)&inaddr,host->h_length);
  dest_addr.sin_addr.s_addr = inaddr;
    /*获取main的进程id,用于设置ICMP的标志符*/
    pid=getpid();
    printf("PING %s(%s): %d bytes data in ICMP packets.\n",argv[1],
    inet_ntoa(dest_addr.sin_addr),datalen);
    while (nsend < 3)
    { 
     send_packet(); /*发送所有ICMP报文*/
     recv_packet(); /*接收所有ICMP报文*/
        sleep(1);
    }
  statistics(SIGALRM); /*进行统计*/

    return 0;

}
/*两个timeval结构相减*/
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;
}

/*------------- The End -----------*/