实现一个简单的sniffer

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#include<stdio.h> #include<pcap.h> #include<unistd.h> #include<stdlib.h> //#include<pcap/bpf.h> #include<netinet/ip.h> #include<netinet/ip_icmp.h> #include<netinet/tcp.h> #include<netinet/udp.h> #include<netinet/ether.h> #include<arpa/inet.h> #define ETHER_SIZE 14   ///get_packet()回调函数 ///header:收到的数据包的pcap_pkthdr类型的指针 ///packet:收到的数据包数据 void get_packet(u_char*args, const struct pcap_pkthdr *header,const u_char *packet){           static int count = 1;     const char * payload;     printf("==================================packet number: %d=============================\n",count++);           ///ETHER_SIZE：以太帧首部长度14个字节     ///IP包头(tcp包头(数据))     ///IP包头(udp包头(数据))     ///IP包头(icmp包头(数据))     struct ip * ip = (struct ip *)(packet + ETHER_SIZE);     printf("IP header length: %d\n",ip->ip_hl<<2);     printf("From %s\n",inet_ntoa(ip->ip_src));     printf("To %s\n",inet_ntoa(ip->ip_dst));     int ip_hl = ip->ip_hl<<2;       ///对报文类型进行了扩展     ///可以分析IP包、ICMP包、TCP包、UDP包     switch(ip->ip_p){           case IPPROTO_TCP:         {             printf("----Protocol TCP----\n");             struct tcphdr *tcp = (struct tcphdr *)(packet + 14 + ip_hl);                        printf("tcp -> source:%d\n",ntohs(tcp -> source));             printf("tcp -> dest:%d\n",ntohs(tcp -> dest));             printf("tcp -> seq:%d\n",ntohs(tcp -> seq));             printf("tcp -> ack_seq:%d\n",ntohs(tcp -> ack_seq));                  printf("tcp -> headerLenth:%d\n",tcp -> doff << 2);             printf("tcp -> fin:%d\n",tcp -> fin);             printf("tcp -> syn:%d\n",tcp -> syn);             printf("tcp -> rst:%d\n",tcp -> rst);             printf("tcp -> psh:%d\n",tcp -> psh);             printf("tcp -> ack:%d\n",tcp -> ack);             printf("tcp -> urg:%d\n",tcp -> urg);             printf("tcp -> window:%d\n",ntohs(tcp -> window));             printf("tcp -> check:%d\n",ntohs(tcp -> check));              //printf("tcp -> urg_ptr:%d\n",tcp -> urg_ptr);                           int h_size = tcp->doff<< 2;             int payload_size = ntohs(ip->ip_len) - ip_hl - h_size;                           int i = payload_size;             printf("payload is:%d\n",i);                           while(i > 0)             {                 printf("%02x  ", packet[i]);                 if( i % 16 == 0 )                     printf("\n");                 i--;             }             printf("\n");             break;         }         case IPPROTO_UDP:         {             printf("----Protocol UDP----\n");             struct udphdr *udp = (struct udphdr *)(packet + 14 + ip_hl);                        printf("udp -> source:%d\n",ntohs(udp -> source));             printf("udp -> dest:%d\n",ntohs(udp -> dest));             printf("udp -> length:%d\n",ntohs(udp -> len));             printf("udp -> check:%d\n",ntohs(udp -> check));             int payload_size = ntohs(ip->ip_len) - ip_hl - 8;             int i = payload_size;             printf("payload is:%d\n",i);                           while(i > 0)             {                 printf("%02x  ", packet[i]);                 if( i % 16 == 0 )                     printf("\n");                 i--;             }             printf("\n");             break;         }         case IPPROTO_ICMP:         {             printf("----Protocol ICMP----\n");             struct icmphdr *icmp = (struct icmphdr *)(packet + 14 + ip_hl);               if(icmp -> type == 8)             {                 printf("--icmp_echo request--\n");                 printf("icmp -> type:%d\n",icmp -> type);                 printf("icmp -> code:%d\n",icmp -> code);                 printf("icmp -> checksum:%d\n",icmp -> checksum);                       printf("icmp -> id:%d\n",icmp -> un.echo.id);                 printf("icmp -> sequence:%d\n",icmp -> un.echo.sequence);                 int payload_size = ntohs(ip->ip_len) - ip_hl - 8;                 int i = payload_size;                 printf("payload is:%d\n",i);                               while(i > 0)                 {                     printf("%02x  ", packet[i]);                     if( i % 16 == 0 )                         printf("\n");                     i--;                 }                 printf("\n");             }             else if(icmp -> type == 0)             {                 printf("--icmp_echo reply--\n");                 printf("icmp -> type:%d\n",icmp -> type);                 printf("icmp -> code:%d\n",icmp -> code);                 printf("icmp -> checksum:%d\n",icmp -> checksum);                               printf("icmp -> id:%d\n",icmp -> un.echo.id);                 printf("icmp -> sequence:%d\n",icmp -> un.echo.sequence);                 int payload_size = ntohs(ip->ip_len) - ip_hl - 8;                 int i = payload_size;                 printf("payload is:%d\n",i);                               while(i > 0)                 {                     printf("%02x  ", packet[i]);                     if( i % 16 == 0 )                         printf("\n");                     i--;                 }                 printf("\n");             }             else             {                 printf("icmp -> type:%d\n",icmp -> type);                 printf("icmp -> code:%d\n",icmp -> code);                 printf("icmp -> checksum:%d\n",icmp -> checksum);                 int payload_size = ntohs(ip->ip_len) - ip_hl - 8;                 int i = payload_size;                 printf("payload is:%d\n",i);                               while(i > 0)                 {                     printf("%02x  ", packet[i]);                     if( i % 16 == 0 )                         printf("\n");                     i--;                 }                 printf("\n");                   }             break;              }         case IPPROTO_IP:         {             printf("----Protocol IP----\n");             //printf("IP header length: %d\n",ip -> ip_hl<<2);             printf("IP version: %d\n",ip -> ip_v);             printf("IP type of service: %d\n",ip -> ip_tos);             printf("IP total length: %d\n",ip -> ip_len);             printf("IP identification: %d\n",ip -> ip_id);             printf("IP fragment offset field: %d\n",ip -> ip_off);             printf("IP time to live: %d\n",ip -> ip_ttl);             printf("IP protocol: %d\n",ip -> ip_p);             printf("IP checksum: %d\n",ip -> ip_sum);             int payload_size = ntohs(ip->ip_len) - ip_hl;             int i = payload_size;             printf("payload is:%d\n",i);                        while(i > 0)             {                 printf("%02x  ", packet[i]);                 if( i % 16 == 0 )                     printf("\n");                 i--;             }             printf("\n");             break;                  }                   default:printf("Protocol unknown\n");         return;             } }               int main(int argc,char*argv[]){       char *dev, errbuf[PCAP_ERRBUF_SIZE];     struct bpf_program fp;     char filter_exp[] = "port 23";     bpf_u_int32 mask;     bpf_u_int32 net;     struct pcap_pkthdr header;     const u_char *packet;       int num_packets = 10;           ///pcap_lookupdev()自动获取网络接口，返回一个网络接口的字符串指针     ///如果出错，errbuf存放出错信息     ///若想手动指定，则跳过此步，将要监听的网络字符串硬编码到pcap_open_live中     dev = pcap_lookupdev(errbuf);     if(dev==NULL){         printf("ERROR:%s\n",errbuf);         exit(2);     }     printf("The sniff interface is:%s\n",dev);       ///pcap_lookupnet()获得设备的IP地址，子网掩码等信息     ///net：网络接口的IP地址     ///mask：网络接口的子网掩码     if(pcap_lookupnet(dev,&net,&mask,errbuf)==-1){         printf("ERROR:%s\n",errbuf);         net = 0;         mask = 0;     }         ///pcap_open_live()打开网络接口     ///BUFSIZ:抓包长度     ///第三个参数：0代表非混杂模式，1代表混杂模式     ///第四个参数：等待的毫秒数，超过这个值，获取数据包的函数会立即返回，0表示一直等待直到有数据包到来     pcap_t * handle = pcap_open_live(dev,BUFSIZ,1,0,errbuf);     if(handle == NULL){         printf("ERROR:%s\n",errbuf);         exit(2);     } /*这里我们测试发现不能过滤，注释掉这部分代码，程序可以正常运行了。     ///pcap_compile()编译过滤表达式     ///fp指向编译后的filter_exp     ///filter_exp过滤表达式     ///参数四：是否需要优化过滤表达式     if(pcap_compile(handle,&fp,filter_exp,0,net)==-1){         printf("Can't parse filter %s:%s\n",filter_exp,pcap_geterr(handle));         return(2);     }           ///pcap_setfilter()应用这个过滤表达式     ///完成过滤表达式后，我们可以使用pcap_loop()或pcap_next()登抓包函数抓包了     if(pcap_setfilter(handle,&fp)==-1){         printf("cant' install filter %s:%s\n",filter_exp,pcap_geterr(handle));         return(2);     }   */     printf("Hello\n");    //  packet = pcap_next(handle,&header); //  printf("Get a packet with length %d.\n",header.len);       ///     ///num_packets:需要抓的数据包的个数，一旦抓到了num_packets个数据包，pcap_loop立即返回。负数表示永远循环抓包，直到出错     ///get_packet：回调函数指针     //pcap_loop(handle,num_packets,get_packet,NULL);     pcap_loop(handle,-1,get_packet,NULL);           pcap_freecode(&fp);           ///pcap_close()释放网络接口     ///关闭pcap_open_live()获取的pcap_t的网络接口对象并释放相关资源     pcap_close(handle);     return(0); }