linux 下ping命令的实现

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <signal.h>

#include <arpa/inet.h>

#include <sys/types.h>

#include <sys/socket.h>

#include <unistd.h>

#include <netinet/in.h>

#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,ntotal = 3;

struct sockaddr_in dest_addr;

pid_t pid;

struct sockaddr_in from;

struct timeval tvrecv;

void tv_sub(struct timeval *out,struct timeval *in);

void handler(int signo){;}

void statistics(int signo)

{

printf("\n--------------------PING statistics-------------------\n");

printf("%d packets transmitted, %d received , %%%d

lost\n",nsend,nreceived,(nsend-nreceived)*100/nsend);

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)

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 */

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 n = ntotal;

//printf("send package %d\n", nsend);

//printf("destaddr:%s\n", inet_ntoa(dest_addr.sin_addr));

if(sendto(sockfd,sendpacket,packetsize,0,(struct sockaddr *)&dest_addr,sizeof(dest_addr))<0 )

{