向DNS服务器发送域名信息处理返回数据报得到IP地址

merabbit

     仔细看了TCP/IP详解中DNS部分，了解了DNS数据报的发送和接收，粗粗的写了段源码用来获取一个域名的IP地址。源码仅仅是用来获取一个域名的IP地址，因此在处理返回数据报时，只考虑了3种类型。

#include
#include
#include
#include
#include
//#include
//#include
//#include
//#include
//#include
//#include
//#include
//#include
#define ADDRESS "192.168.0.1"
#define PORT 53
#define IPADDR 4
#define IPNUMBER 10
//定义发送和接收数据的结构体
typedef struct{
     unsigned short id;
     unsigned short flags;
     unsigned short questNum;
     unsigned short answerNum;
     unsigned short authorNum;
     unsigned short additionNum;
}DNSHDR,*pDNSHDR;

/*typedef struct{
     unsigned short name;
     unsigned short type;
     unsigned short classes;
     unsigned int ttl;
     unsigned short length;
     unsigned int addr;
}RESPONSE,*pRESPONSE;
*/
typedef struct{
//   unsigned char *name;
     unsigned short type;
     unsigned short class;
}QUERYHDR,*pQUERYHDR;

int chagDname(char *Dname,char *name)
{
     int pos[4],posnum[5];
     pos[0] = -1;
     if( Dname[0] == '.')
         {
                 printf("input error!\n");
                 return -1;
        }
     int i,slen=0,num=1;
     slen=strlen(Dname);
     for(i=0;i='a'&&Dname='A'&&Dname
void genDNSPacket(char *Dname,char *DNSsendBuff)//返回要发送的数据报
{
     memset(DNSsendBuff,' ',sizeof(DNSsendBuff));
     pDNSHDR pDnsHdr = (pDNSHDR)malloc(sizeof(DNSHDR));
     pQUERYHDR pQueryHdr = (pQUERYHDR)malloc(sizeof(QUERYHDR));
     pDnsHdr->id = htons(0x3344);printf("pDnsHdr->id=%d\n",pDnsHdr->id);
     pDnsHdr->flags = htons(0x0100);printf("pDnsHdr->flags=%d\n",pDnsHdr->flags);
     pDnsHdr->questNum = htons(0x0001);printf("pDnsHdr->questNum=%d\n",pDnsHdr->questNum);
     pDnsHdr->answerNum = htons(0x0000);printf("pDnsHdr->answerNum=%d\n",pDnsHdr->answerNum);
     pDnsHdr->authorNum = htons(0x0000);printf("pDnsHdr->authorNum=%d\n",pDnsHdr->authorNum);
     pDnsHdr->additionNum = htons(0x0000);printf("pDnsHdr->additionNum=%d\n",pDnsHdr->additionNum);
     memcpy(DNSsendBuff,pDnsHdr,sizeof(DNSHDR));
     int len;
     len = strlen(Dname)+2;
     char *name = (char *)malloc(len *sizeof(char));
     chagDname(Dname,name);
//   printf("%d,%d\n",sizeof(DNSsendBuff),sizeof(DNSHDR));
     memcpy(DNSsendBuff + sizeof(DNSHDR),name,len);
     pQueryHdr->type = htons(0x0001);
     pQueryHdr->class = htons(0x0001);
     memcpy(DNSsendBuff + sizeof(DNSHDR) + len,pQueryHdr,sizeof(QUERYHDR));
}

int main(int argc, char **argv)
{
     unsigned  char sendBuff[64];
     unsigned  char recvBuff[64*10];
     unsigned  char IpFromDname[IPNUMBER][IPADDR];
     bzero(sendBuff,sizeof(sendBuff));
     if (argc \n", argv[0]);
          exit(1);
     }
     char *s;
     s = (char *)malloc(20*sizeof(char));
     int pos = 12;
     int ipnum = 0;
     int posi[IPNUMBER];
     int SocketFd;
     int ServerLen;
     struct sockaddr_in ServerAddr;
     bzero(&ServerAddr,sizeof(struct sockaddr_in));
     SocketFd = socket(AF_INET,SOCK_DGRAM,0);
     ServerAddr.sin_family = AF_INET;
     if (inet_aton(ADDRESS,&ServerAddr.sin_addr) == 0)
             return  -1;               
     ServerAddr.sin_port = htons(PORT);
     ServerLen = sizeof(ServerAddr);

     genDNSPacket(argv[1],sendBuff);
     int res;
     res = sendto(SocketFd,sendBuff,sizeof(sendBuff),0,(struct sockaddr*)&ServerAddr,ServerLen);
     printf("\nsend to %d",res);
     res = recvfrom(SocketFd,recvBuff,sizeof(recvBuff),0,(struct sockaddr*)&ServerAddr,&ServerLen);
     printf("recv %d\n",res);
     int i;
     for (i=0;i
//下面代码找到这个包中是IP的起始位子，并记下该位子
     while( posval != 0 )//0表示表示域名的段结束，如
www.sina.com.cn
，在数据报中是3www4sina3com2cn0
          {
          pos+=posval+1;
          posval=recvBuff[pos];
          printf("pos=%d,posvalue=%d\n",pos,posval);
     }
     pos+=8;
     while(pos

现在不知道怎么用定义结构体来保持接收的数据报，有达人知道指点下，万分感谢！


本文来自ChinaUnix博客，如果查看原文请点：http://blog.chinaunix.net/u2/78880/showart_1901711.html