【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 <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> #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 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 -----------*/