UNIX网络编程:网络数据包检测
返回值: 成功返回0, 失败返回-1, 被中断返回-2. 过滤数据包 根据过滤器表达式生成过滤器 int * pcap_compile( pcap_t * p,//pcap_open_live返回的句柄 struct bpf_program * fp,//保存过滤器的结构体指针 const char * str,//要转换的过滤器表达式 int optimize,//过滤程序是否优化 bpf_u_int32 netmask )//子网掩码 返回值: 成功返回0, 失败返回-1。 为指定的捕捉句柄安装过滤器 int pcap_next ( pcap_t * p//pcap_open_live返回的句柄 struct bpf_program * fp);//指向要安装的过滤器的指针 返回值: 成功返回0; 失败返回-1. 捕获数据包流程 示例程序: //ping.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 5 #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 f(int signo) {} 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"); printf("%d packets transmitted, %d received , %%%.2f lostn",nsend,nreceived,(float)(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; //char sendpacket[4096]; icmp->icmp_type=ICMP_ECHO; icmp->icmp_code=0; #if 1 icmp->icmp_seq=pack_no; icmp->icmp_cksum = 0; #endif 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; //while(nsend) //{ 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"); return; } // sleep(1); /*每隔一秒发送一个ICMP报文*/ // } } /*接收所有ICMP报文*/ void recv_packet() { int n,fromlen; extern int errno; struct sigaction act; sigaction(SIGALRM, NULL, &act); act.sa_handler = f; sigaction(SIGALRM, &act, NULL); fromlen=sizeof(from); while(1) { alarm(5); if( (n=recvfrom(sockfd,recvpacket,sizeof(recvpacket),0,(struct sockaddr *)&from,&fromlen)) <0) { if (errno == EINTR) { printf("errno=%dn", errno); break; } else exit(-1); } gettimeofday(&tvrecv,NULL); /*记录接收时间*/ if(unpack(recvpacket,n)==-1) { continue; } else { nreceived++; break; } } } /*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 8n"); 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+(float)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 msn", len,inet_ntoa(from.sin_addr),icmp->icmp_seq,ip->ip_ttl,rtt); } 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 addressn",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*/ dest_addr.sin_addr.s_addr = inaddr; //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[1], inet_ntoa(dest_addr.sin_addr),datalen); int i = 0; bzero(sendpacket, PACKET_SIZE); bzero(recvpacket, PACKET_SIZE); while (i < 3) { send_packet(); /*发送所有ICMP报文*/ recv_packet(); /*接收所有ICMP报文*/ sleep(1); i++; } 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 -----------*/ 查看本栏目更多精彩内容:http://www.bianceng.cn/OS/unix/ (编辑:云计算网_泰州站长网) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |