ping在类unix下的实现

1. 参考链接：http://blog.csdn.net/firefoxbug/article/details/7773390
2. http://blog.csdn.net/petershina/article/details/8571562
3. http://www.cnblogs.com/noble/p/4144139.html
4. http://blog.csdn.net/zzucsliang/article/details/41407387
   

1. ping程序使用原始套接字，发送以太网首部＋ip首部＋icmp首部+56字节的数据
2. 在发送时将icmp标志设置为进程pid，同时icmp序列号由１递增，数据部分为发送时的时间，在icmp应答报文中将请求回显报文中的标志位和数据原封不动的返回，便于计算往返时延rtt。
3. icmp报头+数据　检验采用循环二进制反码求和
4. 流程：创建通信的套接字-->将地址、端口信息与套接字绑定-->构建IP包头与ICMP包头-->发送构建的数据包-->接收对方主机的回应-->给出程序反馈信息

5. 编译时要加上-lpthread
   包含头文件了，仅能说明有了线程函数的声明， 但是还没有实现， 加上-lpthread是在链接阶段，链接这个库

6. 写注释时注意别在注释外面写全角空格和英文，编译器不识别
   
7. protoent结构：

   struct protoent{char *p_name; //网络协议名char **p_aliases;//别名int p_proto;//网络协议编号} 

8. ip结构

   typedef struct _ip_hdr  {      #if LITTLE_ENDIAN      unsigned char ihl:4;     //首部长度      unsigned char version:4, //版本       #else      unsigned char version:4, //版本      unsigned char ihl:4;     //首部长度      #endif      unsigned char tos;       //服务类型      unsigned short tot_len;  //总长度      unsigned short id;       //标志      unsigned short frag_off; //分片偏移      unsigned char ttl;       //生存时间      unsigned char protocol;  //协议      unsigned short chk_sum;  //检验和      struct in_addr srcaddr;  //源IP地址      struct in_addr dstaddr;  //目的IP地址  }ip_hdr; 

9. icmp结构

   typedef struct _icmphdr{unsigned char i_type; //8位类型, 本实验用 8: ECHO 0:ECHO REPLYunsigned char i_code; //8位代码, 本实验置零unsigned short i_cksum; //16位校验和, 从TYPE开始,直到最后一位用户数据,如果为字节数为奇数则补充一位unsigned short i_id ; //识别号（一般用进程号作为识别号）, 用于匹配ECHO和ECHO REPLY包unsigned short i_seq ; //报文序列号, 用于标记ECHO报文顺序unsigned int timestamp; //时间戳}ICMP_HEADER;

10. 实现代码：

    #include<stdio.h>#include<stdlib.h>#include<signal.h>#include<unistd.h>#include<netinet/ip_icmp.h>#include<netdb.h>/*名字与地址转换*/#include<string.h>#include<sys/types.h>#include<sys/socket.h>#include<sys/time.h>#include<netinet/in.h>/*字节排序*/#include<arpa/inet.h>/*字符串与网络字节序转化*/#include<pthread.h>struct sockaddr_in dst_addr;struct sockaddr_in recv_addr;struct timeval tvrecv;char icmp_pkt[1024]={0};char recv_pkt[1024]={0};int sockfd=0,bytes=56,nsend_pkt = 0 , nrecv_pkt = 0;pid_t pid;void statistics();int in_chksum(unsigned short * buf, int size);/*检验和算法*/int pack(int send_pkt);/*设置icmp报头*/void *send_ping();/*发送三个icmp报文*/int unpack(char *recv_pkt,int size);/*剥去icmp报头*/void *recv_ping();/*接受所有icmp报文*/void tv_sub(struct timeval *out,struct timeval *in);/*两个time_val结构相减*//*struct protoent{char *p_name; //网络协议名char **p_aliases;//别名int p_proto;//网络协议编号} */int main(int argc, char *argv[]){int size = 50 * 1024;int errno=-1;int ttl=64;void *tret;pthread_t send_id,recv_id;struct in_addr ipv4_addr;struct hostent *ipv4_host;struct protoent *protocol = NULL;if(argc < 2 ){printf("Usage : ./ping <host>\n");exit(1);}if((protocol = getprotobyname("icmp")) == NULL)/*不可重入，线程不安全*/{printf("unkown protocol\n");exit(1);} /*使用原始套接字，只有root权限才可以创建，以太网首部＋ip首部＋icmp首部＋56字节的数据，直接使用底层协议*/if((sockfd=socket(AF_INET,SOCK_RAW,protocol->p_proto)) < 0){printf("socket fail\n");exit(1);}/*回收root权限，设置当前实际用户权限。*/setuid(getuid());/*扩大套件字接受缓冲区到50k，避免缓冲区溢出的可能性，若无意中ping一个广播或多播地址，可能会收到大量应答*/setsockopt(sockfd,SOL_SOCKET,SO_RCVBUF,&size,sizeof(size));/*指定为IPPROTO_IP级别，制定外出TTL。*/setsockopt(sockfd, IPPROTO_IP,IP_MULTICAST_TTL,&ttl,sizeof(ttl));   /*指定存活时间*/setsockopt(sockfd,IPPROTO_IP,IP_TTL,&ttl,sizeof(ttl));/*memset(&dst_addr,0,sizeof(dst_addr));*/     bzero(&dst_addr,sizeof(dst_addr)); dst_addr.sin_family=AF_INET; errno=inet_aton(argv[1],&ipv4_addr); if(errno == 0) { ipv4_host = gethostbyname(argv[1]); if(ipv4_host == NULL) { printf("connect: Invalid argument\n"); return -1; } dst_addr.sin_addr=*((struct in_addr  *)ipv4_host->h_addr); } else { dst_addr.sin_addr= ipv4_addr; } pid=getpid(); printf("PING %s (%s) %d bytes of data.\n",argv[1],inet_ntoa(dst_addr.sin_addr),bytes);     signal(SIGINT,statistics); if((errno=pthread_create(&send_id,NULL,send_ping,NULL)) !=0) { printf("send_ping thread fail\n"); exit(1); }    if((errno=pthread_create(&recv_id,NULL,recv_ping,NULL)) !=0) { printf("recv_ping thread fail\n"); exit(1); } if((errno =pthread_join(send_id,&tret)) !=0) { printf("can't join with thread send"); exit(1); } if((errno =pthread_join(recv_id,&tret)) != 0) { printf("can't join with thread recv"); exit(1); } return 0;}/*在收到终端信号时，输出ping　的检测状态 */   void statistics(){printf("\n--- %s ping statistics ---\n",inet_ntoa(dst_addr.sin_addr));printf("%d packets transmitted, %d recvived,%.3f%c packet loss\n",nsend_pkt,nrecv_pkt,(float)100*(nsend_pkt-nrecv_pkt)/nsend_pkt,'%');close(sockfd);exit(0);}/*校验和算法 icmp首部＋数据*/int in_chksum(unsigned short *buf,int size){     int nleft=size; int sum=0; unsigned short *w=buf; unsigned short ans=0; /*将ICMP二进制数据以两个字节相加*/ while(nleft > 1) { sum+=*w; /*相加16bits*/ w++;  /* 移动sizeof(short)2个大小的字节*/ nleft-=2; } /*若只剩下一个字节的数据，则将最后一个字节视为两个字节的高字节，低字节视为0，继续相加*/ if(nleft == 1) { *(unsigned char *)(&ans)= *(unsigned char *)w; sum+=ans; } /*将高16位与低16位相加，可能产生进位，故第二次移位相加*/ sum=(sum>>16)+(sum & 0xFFFF); sum+=(sum>>16); ans=~sum; return ans;}int pack(int send_pkt){   struct icmp *pkt= (struct icmp  *)icmp_pkt;   struct timeval *time=NULL;   pkt->icmp_type = ICMP_ECHO;   pkt->icmp_code = 0;   pkt->icmp_cksum= 0;   pkt->icmp_seq= htons(send_pkt);   pkt->icmp_id = pid;   time = (struct timeval *)pkt->icmp_data;   gettimeofday(time,NULL);/*记录发送时间*/   pkt->icmp_cksum=in_chksum((unsigned short *)pkt,bytes + 8);/*进行校验*/     return bytes + 8;}void *send_ping(){int send_bytes=0;int ret=-1;while(1){       nsend_pkt++;   send_bytes= pack(nsend_pkt);       ret=sendto(sockfd,icmp_pkt,send_bytes,0,(struct sockaddr *)&dst_addr,sizeof(dst_addr));   if(ret == -1)   printf("send fail \n");   sleep(1);}}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;}int unpack(char *recv_pkt ,int size){struct iphdr *ip= NULL;int iphdrlen;struct icmp *icmp;struct timeval *tvsend;double rtt;ip = (struct iphdr *)recv_pkt;iphdrlen = ip->ihl<<2;/*求ip报头的长度，单位为4个字节*/icmp = (struct icmp *)(recv_pkt + iphdrlen);size-=iphdrlen;if(size <8)/*小于icmp报头长度则不合理*/{printf("ICMP size is less than 8\n");exit(1);}if((icmp->icmp_type == ICMP_ECHOREPLY) && (icmp->icmp_id == pid)){tvsend = (struct timeval *)icmp->icmp_data;tv_sub(&tvrecv,tvsend);rtt = tvrecv.tv_sec * 1000 + (double)tvrecv.tv_usec /(double)1000;printf("%d byte from %s: icmp_seq = %d ttl=%d rtt=%.3fms\n",size,inet_ntoa(recv_addr.sin_addr),ntohs(icmp->icmp_seq),ip->ttl,rtt);}else{return -1;}return 0;}void *recv_ping(){fd_set rd_set;struct timeval time;time.tv_sec = 5;time.tv_usec =0;    int ret = 0, nread =0, recv_len =0;    recv_len= sizeof(recv_addr);while(1){FD_ZERO(&rd_set);FD_SET(sockfd,&rd_set);ret=select(sockfd+1,&rd_set,NULL,NULL,&time);if(ret <= 0)continue;else if(FD_ISSET(sockfd,&rd_set)){nread=recvfrom(sockfd,recv_pkt,sizeof(recv_pkt),0,(struct sockaddr *)&recv_addr,(socklen_t *)&recv_len);if(nread < 0)continue;gettimeofday(&tvrecv,NULL);if(unpack(recv_pkt,nread) == -1)  continue;  nrecv_pkt++;}}}

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