linux c ping 实现

用c语言实现的linux中的ping命令

 #include <stdio.h>
 #include <signal.h>
 #include <arpa/inet.h>
 #include <pthread.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   5
 #define MAX_NO_PACKETS  3
 char sendpacket[PACKET_SIZE];
 char recvpacket[PACKET_SIZE];
 int sockfd,datalen=;
 int nsend=,nreceived=;
 struct sockaddr_in dest_addr;
 pid_t pid;
 struct sockaddr_in from;
 struct timeval tvrecv;
 pthread_t tid;
 void statistics();
 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()
 {       printf("\n--------------------PING statistics-------------------\n");
         printf("%d packets transmitted, %d received , %%%d lost\n",nsend,nreceived,
                         (nsend-nreceived)/nsend*);
         close(sockfd);
         exit();
 }
 /*校验和算法*/
 unsigned short cal_chksum(unsigned short *addr,int len)
 {       int nleft=len;
         int sum=;
         unsigned short *w=addr;
         unsigned short answer=;

 /*把ICMP报头二进制数据以2字节为单位累加起来*/
         while(nleft>)
         {       sum+=*w++;
                 nleft-=;
         }
         /*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==)
         {       *(unsigned char *)(&answer)=*(unsigned char *)w;
                 sum+=answer;
         }
         sum=(sum>>)+(sum&0xffff);
         sum+=(sum>>);
         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=;
         icmp->icmp_cksum=;
         icmp->icmp_seq=pack_no;
         icmp->icmp_id=pid;
         packsize=+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,,(struct sockaddr *)&dest_addr,sizeof(dest_addr) )<  )
         {
         perror("sendto error");
                 return;
         }
     alarm();

 }
 /*接收所有ICMP报文*/
 void recv_packet(void )
 {
     //int send = *(int *) arg;
     int n,fromlen;
         extern int errno;
         fromlen=sizeof(from);
     while()
         {    if( (n=recvfrom(sockfd,recvpacket,sizeof(recvpacket),, (struct sockaddr *)&from,&fromlen)) <)
             {
             if(errno==EINTR)
                     {
                 perror("recvfrom error");
             }
             continue;

             }
             gettimeofday(&tvrecv,NULL);  /*记录接收时间*/
         unpack(recvpacket,n);
             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<<;    /*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<)                /*小于ICMP报头长度则不合理*/
         {       printf("ICMP packets\'s length is less than 8\n");
                 return -;
         }
         /*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*+tvrecv.tv_usec/;  /*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);
         }
         else    return -;
 }
 main(int argc,char *argv[])
 {       struct hostent *host;
         struct protoent *protocol;
         unsigned long inaddr=0l;
         int waittime=MAX_WAIT_TIME;
         int size=*;
         if(argc<)
         {       printf("usage:%s hostname/IP address\n",argv[]);
                 exit();
         }
         if( (protocol=getprotobyname("icmp") )==NULL)
         {       perror("getprotobyname");
                 exit();
         }
         /*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) )<)
         {       perror("socket error");
                 exit();
         }
         /* 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[])==INADDR_NONE)
         {       if((host=gethostbyname(argv[]) )==NULL) /*是主机名*/
                 {       perror("gethostbyname error");
                         exit();
                 }
                 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);
         /*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[],
                         inet_ntoa(dest_addr.sin_addr),datalen);

         signal(SIGALRM,send_packet);
     signal(SIGINT,statistics);
         send_packet();  /*发送所有ICMP报文*/
         //recv_packet();  /*接收所有ICMP报文*/
     int ret = pthread_create(&tid, NULL, (void*)recv_packet, NULL);
     if(ret != )
     {
         printf("Thread Create Error\n");
         exit();
     }
         //statistics(SIGALRM); /*进行统计*/
     pthread_join(tid, NULL);
         return ;
 }
 /*两个timeval结构相减*/
 void tv_sub(struct timeval *out,struct timeval *in)
 {       if( (out->tv_usec-=in->tv_usec)<)
         {       --out->tv_sec;
                 out->tv_usec+=;
         }
         out->tv_sec-=in->tv_sec;
 }

涉及到的技术线程，信号量。

在使用线程的时候注意pthread_join的使用，该函数类似于waitpid 。由于不知道哪个进程先结束，如果主线程先结束了，那么有些变量多个线程都在使用，有可能由于主线程的结束使一些资源（该例子中的socket），致使其他线程无法使用。

su root

gcc ping.c -o ping -lpthread

./ping www.baidu.com