利用c实现简易的ping

#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_ICMP_PACKETS  4

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;
}

/*发送四个ICMP报文*/
void send_packet()
{
int packetsize;
while( nsend < MAX_ICMP_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;
}
}
}

/*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;
}

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*/
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 -----------*/