ping.c

ping程序

//==================================================================
#include <stdio.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.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 <errno.h>
#define ICMP_HEADSIZE 8 /* icmp packet header size */
#define PACKET_SIZE     4096
#define MAX_WAIT_TIME   1
#define MAX_NO_PACKETS  4
struct timeval tvsend,tvrecv;//
struct sockaddr_in dest_addr,from;
int sockfd;
pid_t pid;//use the process id as ICMP's id

//definition of fuctions
void timeout(int signo);
void statistics(int signo);
unsigned short cal_chksum(unsigned short *addr,int len);//
int pack(int pkt_no,char *sendpacket);//
int send_packet(int pkt_no,char *sendpacket);//
int recv_packet(int pkt_no,char *recvpacket);
int unpack(int cur_seq,char *buf,int len);//
void tv_sub(struct timeval *out,struct timeval *in);
void timeout(int signo)
{
	printf("Request Timed Out\n");
	exit(1);
}
/*checksum computing*/
unsigned short cal_chksum(unsigned short *addr,int len)
{       int nleft=len;
        int sum=0;
        unsigned short *w=addr;
        unsigned short answer=0;
        while(nleft>1)
        {       sum+=*w++;
                nleft-=2;
        }
        if( nleft==1)
        {       *(unsigned char *)(&answer)=*(unsigned char *)w;
                sum+=answer;
        }
        sum=(sum>>16)+(sum&0xffff);
        sum+=(sum>>16);
        answer=~sum;
        return answer;
}
int pack(int pkt_no,char*sendpacket)
{       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=pkt_no;
        icmp->icmp_id=pid;
        packsize=ICMP_HEADSIZE+sizeof(struct timeval);
        tval= (struct timeval *)icmp->icmp_data;
        gettimeofday(tval,NULL);
        icmp->icmp_cksum=cal_chksum( (unsigned short *)icmp,packsize); 
        return packsize;
}

int send_packet(int pkt_no,char *sendpacket)
{    
	int packetsize;       
       	packetsize=pack(pkt_no,sendpacket); /*set the ICMP header*/
	gettimeofday(&tvsend,NULL);    
      	if(sendto(sockfd,sendpacket,packetsize,0,(struct sockaddr *)&dest_addr,sizeof(dest_addr) )<0)
        {      
		perror("sendto error");
                return -1;
        }
	return 0;
}

int recv_packet(int pkt_no,char *recvpacket)
{       	
	int n,fromlen;
        extern int errno;
        signal(SIGALRM,timeout);
        fromlen=sizeof(from);
        alarm(MAX_WAIT_TIME);
	while(1){
     	  if( (n=recvfrom(sockfd,recvpacket,PACKET_SIZE,0,(struct sockaddr *)&from,&fromlen)) <0)
    	  {   
		if(errno==EINTR)return -1;
          	perror("recvfrom error");
                return -2;
      	  }	
	  gettimeofday(&tvrecv,NULL); 
      	  if(unpack(pkt_no,recvpacket,n)==-1)continue;
       	  return 0;
	}
}

int unpack(int cur_seq,char *buf,int len)
{    
	
	int iphdrlen;
        struct ip *ip;
        struct icmp *icmp;
        
        ip=(struct ip *)buf;
        iphdrlen=ip->ip_hl<<2;
        icmp=(struct icmp *)(buf+iphdrlen);
        len-=iphdrlen;
        if( len<8)
                return -1;       
        if( (icmp->icmp_type==ICMP_ECHOREPLY) && (icmp->icmp_id==pid) && (icmp->icmp_seq==cur_seq))
       		return 0;	
        else     return -1;
}
main(int argc,char *argv[])
{     
	char sendpacket[PACKET_SIZE];
	char recvpacket[PACKET_SIZE];	
	
	double rtt;
	char hostname[32];
	struct hostent *host;
	struct protoent *protocol;
     	int i,recv_status;

        if(argc!=2)
        {       printf("usage:%s hostname/IPaddress\n",argv[0]);
                exit(1);
        }
        if( (protocol=getprotobyname("icmp") )==NULL)
        {       perror("getprotobyname");
                exit(1);
        }
        /* set destination host information */
	strcpy(hostname,argv[1]);
	bzero(&dest_addr, sizeof(dest_addr));
	dest_addr.sin_family = AF_INET;	
	if((host=gethostbyname(hostname))==NULL){
		fprintf(stderr,"Cant get serverhost info!\n");
		exit(1);
	}
	bcopy((char*)host->h_addr,(char*)&dest_addr.sin_addr,host->h_length);

	/* creat the raw socket for icmp */
	if ((sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) < 0) {
		perror("socket");
		exit(2);
	}

        /*get process id and used as icmp id*/
        pid=getpid();
        printf("PING %s(%s):\n",hostname,inet_ntoa(dest_addr.sin_addr));	
	for(i=0;i<MAX_NO_PACKETS;i++){		
		if(fork()==0)
		{			
       			if(send_packet(i,sendpacket)<0)continue;	
			if(!recv_packet(i,recvpacket)){	
              			tv_sub(&tvrecv,&tvsend);
                		rtt=tvrecv.tv_sec*1000+tvrecv.tv_usec/1000;  
                		printf("reply from %s(%s): time=%.3f ms\n",hostname,inet_ntoa(dest_addr.sin_addr),rtt);
				exit(0);
			}
		}
		else wait(&recv_status);		
	}       
        return 0;
}

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;
}