用C语言实现Ping程序功能

PING localhost.localdomain (127.0.0.1) from 127.0.0.1 : 56(84) bytes of data.
64 bytes from localhost.localdomain (127.0.0.1): icmp_seq=0 ttl=255 time=112 usec
64 bytes from localhost.localdomain (127.0.0.1): icmp_seq=1 ttl=255 time=79 usec
64 bytes from localhost.localdomain (127.0.0.1): icmp_seq=2 ttl=255 time=78 usec
64 bytes from localhost.localdomain (127.0.0.1): icmp_seq=3 ttl=255 time=82 usec
--- localhost.localdomain ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max/mdev = 0.078/0.087/0.112/0.018 ms

struct ip
{
#if __BYTE_ORDER == __LITTLE_ENDIAN
unsigned int ip_hl:4;       /* header length */
unsigned int ip_v:4;        /* version */
#endif
#if __BYTE_ORDER == __BIG_ENDIAN
unsigned int ip_v:4;        /* version */
unsigned int ip_hl:4;       /* header length */
#endif
u_int8_t ip_tos;            /* type of service */
u_short ip_len;         /* total length */
u_short ip_id;          /* identification */
u_short ip_off;         /* fragment offset field */
#define IP_RF 0x8000            /* reserved fragment flag */
#define IP_DF 0x4000            /* dont fragment flag */
#define IP_MF 0x2000            /* more fragments flag */
#define IP_OFFMASK 0x1fff       /* mask for fragmenting bits */
u_int8_t ip_ttl;            /* time to live */
u_int8_t ip_p;          /* protocol */
u_short ip_sum;         /* checksum */
struct in_addr ip_src, ip_dst;  /* source and dest address */
};

#define ICMP_ECHO   0
#define ICMP_ECHOREPLY  8

struct icmp
{
u_int8_t  icmp_type;  /* type of message, see below */
u_int8_t  icmp_code;  /* type sub code */
u_int16_t icmp_cksum; /* ones complement checksum of struct */
union
{
u_char ih_pptr;     /* ICMP_PARAMPROB */
struct in_addr ih_gwaddr;   /* gateway address */
struct ih_idseq     /* echo datagram */
{
u_int16_t icd_id;
u_int16_t icd_seq;
} ih_idseq;
u_int32_t ih_void;
/* ICMP_UNREACH_NEEDFRAG -- Path MTU Discovery (RFC1191) */
struct ih_pmtu
{
u_int16_t ipm_void;
u_int16_t ipm_nextmtu;
} ih_pmtu;
struct ih_rtradv
{
u_int8_t irt_num_addrs;
u_int8_t irt_wpa;
u_int16_t irt_lifetime;
} ih_rtradv;
} icmp_hun;
#define icmp_pptr   icmp_hun.ih_pptr
#define icmp_gwaddr icmp_hun.ih_gwaddr
#define icmp_id     icmp_hun.ih_idseq.icd_id
#define icmp_seq        icmp_hun.ih_idseq.icd_seq
#define icmp_void   icmp_hun.ih_void
#define icmp_pmvoid icmp_hun.ih_pmtu.ipm_void
#define icmp_nextmtu    icmp_hun.ih_pmtu.ipm_nextmtu
#define icmp_num_addrs  icmp_hun.ih_rtradv.irt_num_addrs
#define icmp_wpa    icmp_hun.ih_rtradv.irt_wpa
#define icmp_lifetime   icmp_hun.ih_rtradv.irt_lifetime
union
{
struct
{
u_int32_t its_otime;
u_int32_t its_rtime;
u_int32_t its_ttime;
} id_ts;
struct
{
struct ip idi_ip;
/* options and then 64 bits of data */
} id_ip;
struct icmp_ra_addr id_radv;
u_int32_t   id_mask;
u_int8_t    id_data[1];
} icmp_dun;
#define icmp_otime  icmp_dun.id_ts.its_otime
#define icmp_rtime  icmp_dun.id_ts.its_rtime
#define icmp_ttime  icmp_dun.id_ts.its_ttime
#define icmp_ip     icmp_dun.id_ip.idi_ip
#define icmp_radv   icmp_dun.id_radv
#define icmp_mask   icmp_dun.id_mask
#define icmp_data   icmp_dun.id_data
};

#include
int gettimeofday(struct timeval *tp,void *tzp)
其中timeval结构如下：
struct timeval{
long tv_sec;
long tv_usec;
}

/***********************************************************
* 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     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;
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,(char *)&inaddr,host->h_length);
/*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 -----------*/

PING www.cn.ibm.com(202.95.2.148): 56 bytes data in ICMP packets.
64 byte from 202.95.2.148: icmp_seq=1 ttl=242 rtt=3029.000 ms
64 byte from 202.95.2.148: icmp_seq=2 ttl=242 rtt=2020.000 ms
64 byte from 202.95.2.148: icmp_seq=3 ttl=242 rtt=1010.000 ms
--------------------PING statistics-------------------
3 packets transmitted, 3 received , %0 lost