实现ping的C程序

￡神魔★判官ぃ 2022-08-24 11:07 138阅读 0赞

#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>
    
    #include <pthread.h>
    
    #define PACKET_SIZE       4096
    
    struct sockaddr_in dest_addr;
    struct sockaddr_in recv_addr;
    
    struct timeval tvrecv;
    char sendpacket[PACKET_SIZE];
    char recvpacket[PACKET_SIZE];
    int sockfd,datalen=56;
    int nsend=0,nreceived=0;
    
    pid_t pid;
    
    void statistics(int signo);
    unsigned short cal_chksum(unsigned short *addr,int len);
    int pack(int pack_no);
    void *send_packet(void *arg);
    void *recv_packet(void *arg);
    int unpack(char *buf,int len);
    void tv_sub(struct timeval *out,struct timeval *in);
    
    int main(int argc,char *argv[])
    {         
        struct hostent *host;
        struct protoent *protocol;
        unsigned long inaddr=0l;
        int size=50*1024;
        pthread_t send_id,recv_id;
        if(argc<2)
        {  
    
             printf("usage:%s hostname/IP address\n",argv[0]);
            exit(1);
        }
        if(argc==4)
        {
              if(argv[2][0]=='-'&&argv[2][1]=='c')
             {
                  /*调用alarm 可以设定一个闹钟，也就是告诉内核在seconds 秒之后
                  给当前进程发SIGALRM信号，该信号的默认处理动作是终止当前进程。*/
                 alarm(atoi(argv[3]));
              }
        }
        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;
    
        inaddr=inet_addr(argv[1]);
        /*判断是主机名还是ip地址*/
        if( inaddr==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*/
        {
              inet_pton(AF_INET,argv[1],&dest_addr.sin_addr);
        }
        /*当程序收到SIGALRM 就会去执行statistics 指向的函数*/
        signal(SIGALRM,statistics);
         /*当程序收到SIGINT（ctrl+c） 就会去执行statistics 指向的函数*/
        signal(SIGINT, statistics);
        /*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);
         pthread_create(&send_id, NULL, send_packet, NULL);
         pthread_create(&recv_id, NULL, recv_packet, NULL);
         pthread_join(send_id, NULL);  
         pthread_join(recv_id, NULL);
         return 0;
    
    }
    /* 信号处理函数*/
    void statistics(int signo)
    {   
          printf("\n----------------%s ping statistics-----------------\n",inet_ntoa(dest_addr.sin_addr));
          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ICMP报文*/
    void *send_packet(void *arg)
    {         
        int send_bytes = 0;
        while(1)
        {         
              nsend++;
              send_bytes=pack(nsend); /*设置ICMP报头*/
              if( sendto(sockfd,sendpacket,send_bytes,0,\
               (struct sockaddr *)&dest_addr,sizeof(dest_addr) )<0    )
              {         
                  perror("sendto error");
                  continue;
              }
             sleep(1); /*每隔一秒发送一个ICMP报文*/
          }
    }
    
    /*接收所有ICMP报文*/
    void *recv_packet(void *arg)
    {         
          int n;
          int recv_addr_len;
          extern int errno;
          recv_addr_len=sizeof(recv_addr);
          while(1)
          {      
                if( (n=recvfrom(sockfd,recvpacket,sizeof(recvpacket),0,\
                    (struct sockaddr *)&recv_addr,&recv_addr_len)) <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(recv_addr.sin_addr),\
                     icmp->icmp_seq,\
                     ip->ip_ttl,\
                     rtt);
           }
          else      
              return -1;
    
          reutn 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;
    }