ping4.c

实现ping功能,返回ping的结果.可以直接调用此函数,通则返回true,不通则返回false.

/***********************************************************
* 作者:梁俊辉                               *
* 时间:2001年10月                           *
* 名称：myping.c                             *
* 说明:本程序用于演示ping命令的实现原理             *
***********************************************************/
#include <stdio.h>
#include <signal.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 PACKET_SIZE   32
#define MAX_WAIT_TIME   1
#define MAX_NO_PACKETS 1

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

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.sin_addr,(char *)&inaddr,sizeof(dest_addr.sin_addr));
    /*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);
    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 *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 -----------*/