【二十五】 Linux网络编程——模仿Ping命令的实现

【二十五】 Linux网络编程——模仿Ping命令的实现

/*Myping.c*/

#include  
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#define PACKET_SIZE 4096 
#define MAX_WAIT_TIME 3 
#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"); 
   if (nsend == 0)
   {
	   printf("%d packets transmitted\n", nsend);
   }
   else 
   {
	   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; 

    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"); 
		statistics(0);
    }

	return;
} 

/*接收所有ICMP报文*/ 
void recv_packet() 
{ 
     int n,fromlen; 
     extern int errno; 
     signal(SIGALRM,statistics); 
     fromlen=sizeof(from); 
     alarm(MAX_WAIT_TIME); 
     while( 1 ) 
     { 
       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++; 
	   break;
     } 
	 alarm(0);
} 
/*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/1000.0; /*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); 
		return 0;
    } 
    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,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); 
		dest_addr.sin_addr.s_addr = inaddr;
    /*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); 
	while ( 1 )
	{
    	send_packet(); /*发送所有ICMP报文*/ 
    	recv_packet(); /*接收所有ICMP报文*/ 
		sleep(1);
	}
    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 -----------*/