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linux中查询dns示例

    来源: 互联网  发布时间：2014-10-25

    本文导语:  dns.c 代码如下:/* * DNS Query Program on Linux * * Author : ismdeep@live.com * * *///Header Files#include //printf#include //strlen#include //malloc#include //you know what this is for#include //inet_addr , inet_ntoa , ntohs etc#include#include //getpid //List of DNS Servers regi...

dns.c

代码如下:

/*
 * DNS Query Program on Linux
 *
 * Author : ismdeep@live.com
 *
 * */
//Header Files
#include //printf
#include //strlen
#include //malloc
#include //you know what this is for
#include //inet_addr , inet_ntoa , ntohs etc
#include
#include //getpid

//List of DNS Servers registered on the system
char dns_servers[10][100];
int dns_server_count = 0;
//Types of DNS resource records :)

#define T_A 1 //Ipv4 address
#define T_NS 2 //Nameserver
#define T_CNAME 5 // canonical name
#define T_SOA 6 /* start of authority zone */
#define T_PTR 12 /* domain name pointer */
#define T_MX 15 //Mail server

//Function Prototypes
void ngethostbyname (unsigned char* , int);
void ChangetoDnsNameFormat (unsigned char*,unsigned char*);
unsigned char* ReadName (unsigned char*,unsigned char*,int*);
void get_dns_servers();

//DNS header structure
struct DNS_HEADER
{
 unsigned short id; // identification number

 unsigned char rd :1; // recursion desired
 unsigned char tc :1; // truncated message
 unsigned char aa :1; // authoritive answer
 unsigned char opcode :4; // purpose of message
 unsigned char qr :1; // query/response flag

 unsigned char rcode :4; // response code
 unsigned char cd :1; // checking disabled
 unsigned char ad :1; // authenticated data
 unsigned char z :1; // its z! reserved
 unsigned char ra :1; // recursion available

 unsigned short q_count; // number of question entries
 unsigned short ans_count; // number of answer entries
 unsigned short auth_count; // number of authority entries
 unsigned short add_count; // number of resource entries
};

//Constant sized fields of query structure
struct QUESTION
{
 unsigned short qtype;
 unsigned short qclass;
};

//Constant sized fields of the resource record structure
#pragma pack(push, 1)
struct R_DATA
{
 unsigned short type;
 unsigned short _class;
 unsigned int ttl;
 unsigned short data_len;
};
#pragma pack(pop)

//Pointers to resource record contents
struct RES_RECORD
{
 unsigned char *name;
 struct R_DATA *resource;
 unsigned char *rdata;
};

//Structure of a Query
typedef struct
{
 unsigned char *name;
 struct QUESTION *ques;
} QUERY;

int main( int argc , char *argv[])
{
 unsigned char hostname[100];

 //Get the DNS servers from the resolv.conf file
 get_dns_servers();

 //Get the hostname from the terminal
 printf("Enter Hostname to Lookup : ");
 scanf("%s" , hostname);

 //Now get the ip of this hostname , A record
 ngethostbyname(hostname , T_A);

 return 0;
}

/*
 * Perform a DNS query by sending a packet
 * */
void ngethostbyname(unsigned char *host , int query_type)
{
 unsigned char buf[65536],*qname,*reader;
 int i , j , stop , s;

 struct sockaddr_in a;

 struct RES_RECORD answers[20],auth[20],addit[20]; //the replies from the DNS server
 struct sockaddr_in dest;

 struct DNS_HEADER *dns = NULL;
 struct QUESTION *qinfo = NULL;

 printf("Resolving %s" , host);

 s = socket(AF_INET , SOCK_DGRAM , IPPROTO_UDP); //UDP packet for DNS queries

 dest.sin_family = AF_INET;
 dest.sin_port = htons(53);
 dest.sin_addr.s_addr = inet_addr(dns_servers[0]); //dns servers

 //Set the DNS structure to standard queries
 dns = (struct DNS_HEADER *)&buf;

 dns->id = (unsigned short) htons(getpid());
 dns->qr = 0; //This is a query
 dns->opcode = 0; //This is a standard query
 dns->aa = 0; //Not Authoritative
 dns->tc = 0; //This message is not truncated
 dns->rd = 1; //Recursion Desired
 dns->ra = 0; //Recursion not available! hey we dont have it (lol)
 dns->z = 0;
 dns->ad = 0;
 dns->cd = 0;
 dns->rcode = 0;
 dns->q_count = htons(1); //we have only 1 question
 dns->ans_count = 0;
 dns->auth_count = 0;
 dns->add_count = 0;

 //point to the query portion
 qname =(unsigned char*)&buf[sizeof(struct DNS_HEADER)];

 ChangetoDnsNameFormat(qname , host);
 qinfo =(struct QUESTION*)&buf[sizeof(struct DNS_HEADER) + (strlen((const char*)qname) + 1)]; //fill it

 qinfo->qtype = htons( query_type ); //type of the query , A , MX , CNAME , NS etc
 qinfo->qclass = htons(1); //its internet (lol)

 printf("nSending Packet...");
 if( sendto(s,(char*)buf,sizeof(struct DNS_HEADER) + (strlen((const char*)qname)+1) + sizeof(struct QUESTION),0,(struct sockaddr*)&dest,sizeof(dest)) < 0)
 {
  perror("sendto failed");
 }
 printf("Done");

 //Receive the answer
 i = sizeof dest;
 printf("nReceiving answer...");
 if(recvfrom (s,(char*)buf , 65536 , 0 , (struct sockaddr*)&dest , (socklen_t*)&i ) < 0)
 {
  perror("recvfrom failed");
 }
 printf("Done");

 dns = (struct DNS_HEADER*) buf;

 //move ahead of the dns header and the query field
 reader = &buf[sizeof(struct DNS_HEADER) + (strlen((const char*)qname)+1) + sizeof(struct QUESTION)];

 printf("nThe response contains : ");
 printf("n %d Questions.",ntohs(dns->q_count));
 printf("n %d Answers.",ntohs(dns->ans_count));
 printf("n %d Authoritative Servers.",ntohs(dns->auth_count));
 printf("n %d Additional records.nn",ntohs(dns->add_count));

 //Start reading answers
 stop=0;

 for(i=0;ians_count);i++)
 {
  answers[i].name=ReadName(reader,buf,&stop);
  reader = reader + stop;

  answers[i].resource = (struct R_DATA*)(reader);
  reader = reader + sizeof(struct R_DATA);

  if(ntohs(answers[i].resource->type) == 1) //if its an ipv4 address
  {
   answers[i].rdata = (unsigned char*)malloc(ntohs(answers[i].resource->data_len));

   for(j=0 ; jdata_len) ; j++)
   {
    answers[i].rdata[j]=reader[j];
   }

   answers[i].rdata[ntohs(answers[i].resource->data_len)] = '';

   reader = reader + ntohs(answers[i].resource->data_len);
  }
  else
  {
   answers[i].rdata = ReadName(reader,buf,&stop);
   reader = reader + stop;
  }
 }

 //read authorities
 for(i=0;iauth_count);i++)
 {
  auth[i].name=ReadName(reader,buf,&stop);
  reader+=stop;

  auth[i].resource=(struct R_DATA*)(reader);
  reader+=sizeof(struct R_DATA);

  auth[i].rdata=ReadName(reader,buf,&stop);
  reader+=stop;
 }

 //read additional
 for(i=0;iadd_count);i++)
 {
  addit[i].name=ReadName(reader,buf,&stop);
  reader+=stop;

  addit[i].resource=(struct R_DATA*)(reader);
  reader+=sizeof(struct R_DATA);

  if(ntohs(addit[i].resource->type)==1)
  {
   addit[i].rdata = (unsigned char*)malloc(ntohs(addit[i].resource->data_len));
   for(j=0;jdata_len);j++)
   addit[i].rdata[j]=reader[j];

   addit[i].rdata[ntohs(addit[i].resource->data_len)]='';
   reader+=ntohs(addit[i].resource->data_len);
  }
  else
  {
   addit[i].rdata=ReadName(reader,buf,&stop);
   reader+=stop;
  }
 }

 //print answers
 printf("nAnswer Records : %d n" , ntohs(dns->ans_count) );
 for(i=0 ; i < ntohs(dns->ans_count) ; i++)
 {
  printf("Name : %s ",answers[i].name);

  if( ntohs(answers[i].resource->type) == T_A) //IPv4 address
  {
   long *p;
   p=(long*)answers[i].rdata;
   a.sin_addr.s_addr=(*p); //working without ntohl
   printf("has IPv4 address : %s",inet_ntoa(a.sin_addr));
  }

  if(ntohs(answers[i].resource->type)==5)
  {
   //Canonical name for an alias
   printf("has alias name : %s",answers[i].rdata);
  }

  printf("n");
 }

 //print authorities
 printf("nAuthoritive Records : %d n" , ntohs(dns->auth_count) );
 for( i=0 ; i < ntohs(dns->auth_count) ; i++)
 {

  printf("Name : %s ",auth[i].name);
  if(ntohs(auth[i].resource->type)==2)
  {
   printf("has nameserver : %s",auth[i].rdata);
  }
  printf("n");
 }

 //print additional resource records
 printf("nAdditional Records : %d n" , ntohs(dns->add_count) );
 for(i=0; i < ntohs(dns->add_count) ; i++)
 {
  printf("Name : %s ",addit[i].name);
  if(ntohs(addit[i].resource->type)==1)
  {
   long *p;
   p=(long*)addit[i].rdata;
   a.sin_addr.s_addr=(*p);
   printf("has IPv4 address : %s",inet_ntoa(a.sin_addr));
  }
  printf("n");
 }
 return;
}

/*
 *
 * */
u_char* ReadName(unsigned char* reader,unsigned char* buffer,int* count)
{
 unsigned char *name;
 unsigned int p=0,jumped=0,offset;
 int i , j;

 *count = 1;
 name = (unsigned char*)malloc(256);

 name[0]='';

 //read the names in 3www6google3com format
 while(*reader!=0)
 {
  if(*reader>=192)
  {
   offset = (*reader)*256 + *(reader+1) - 49152; //49152 = 11000000 00000000 ;)
   reader = buffer + offset - 1;
   jumped = 1; //we have jumped to another location so counting wont go up!
  }
  else
  {
   name[p++]=*reader;
  }

  reader = reader+1;

  if(jumped==0)
  {
   *count = *count + 1; //if we havent jumped to another location then we can count up
  }
 }

 name[p]=''; //string complete
 if(jumped==1)
 {
  *count = *count + 1; //number of steps we actually moved forward in the packet
 }

 //now convert 3www6google3com0 to www.google.com
 for(i=0;iopcode = 0; //This is a standard query
 dns->aa = 0; //Not Authoritative
 dns->tc = 0; //This message is not truncated
 dns->rd = 1; //Recursion Desired
 dns->ra = 0; //Recursion not available! hey we dont have it (lol)
 dns->z = 0;
 dns->ad = 0;
 dns->cd = 0;
 dns->rcode = 0;
 dns->q_count = htons(1); //we have only 1 question
 dns->ans_count = 0;
 dns->auth_count = 0;
 dns->add_count = 0;

 //point to the query portion
 qname =(unsigned char*)&buf[sizeof(struct DNS_HEADER)];

 ChangetoDnsNameFormat(qname , host);
 qinfo =(struct QUESTION*)&buf[sizeof(struct DNS_HEADER) + (strlen((const char*)qname) + 1)]; //fill it

 qinfo->qtype = htons( query_type ); //type of the query , A , MX , CNAME , NS etc
 qinfo->qclass = htons(1); //its internet (lol)

 printf("nSending Packet...");
 if( sendto(s,(char*)buf,sizeof(struct DNS_HEADER) + (strlen((const char*)qname)+1) + sizeof(struct QUESTION),0,(struct sockaddr*)&dest,sizeof(dest)) < 0)
 {
  perror("sendto failed");
 }
 printf("Done");

 //Receive the answer
 i = sizeof dest;
 printf("nReceiving answer...");
 if(recvfrom (s,(char*)buf , 65536 , 0 , (struct sockaddr*)&dest , (socklen_t*)&i ) < 0)
 {
  perror("recvfrom failed");
 }
 printf("Done");

 dns = (struct DNS_HEADER*) buf;

 //move ahead of the dns header and the query field
 reader = &buf[sizeof(struct DNS_HEADER) + (strlen((const char*)qname)+1) + sizeof(struct QUESTION)];

 printf("nThe response contains : ");
 printf("n %d Questions.",ntohs(dns->q_count));
 printf("n %d Answers.",ntohs(dns->ans_count));
 printf("n %d Authoritative Servers.",ntohs(dns->auth_count));
 printf("n %d Additional records.nn",ntohs(dns->add_count));

 //Start reading answers
 stop=0;

 for(i=0;ians_count);i++)
 {
  answers[i].name=ReadName(reader,buf,&stop);
  reader = reader + stop;

  answers[i].resource = (struct R_DATA*)(reader);
  reader = reader + sizeof(struct R_DATA);

  if(ntohs(answers[i].resource->type) == 1) //if its an ipv4 address
  {
   answers[i].rdata = (unsigned char*)malloc(ntohs(answers[i].resource->data_len));

   for(j=0 ; jdata_len) ; j++)
   {
    answers[i].rdata[j]=reader[j];
   }

   answers[i].rdata[ntohs(answers[i].resource->data_len)] = '';

   reader = reader + ntohs(answers[i].resource->data_len);
  }
  else
  {
   answers[i].rdata = ReadName(reader,buf,&stop);
   reader = reader + stop;
  }
 }

 //read authorities
 for(i=0;iauth_count);i++)
 {
  auth[i].name=ReadName(reader,buf,&stop);
  reader+=stop;

  auth[i].resource=(struct R_DATA*)(reader);
  reader+=sizeof(struct R_DATA);

  auth[i].rdata=ReadName(reader,buf,&stop);
  reader+=stop;
 }

 //read additional
 for(i=0;iadd_count);i++)
 {
  addit[i].name=ReadName(reader,buf,&stop);
  reader+=stop;

  addit[i].resource=(struct R_DATA*)(reader);
  reader+=sizeof(struct R_DATA);

  if(ntohs(addit[i].resource->type)==1)
  {
   addit[i].rdata = (unsigned char*)malloc(ntohs(addit[i].resource->data_len));
   for(j=0;jdata_len);j++)
   addit[i].rdata[j]=reader[j];

   addit[i].rdata[ntohs(addit[i].resource->data_len)]='';
   reader+=ntohs(addit[i].resource->data_len);
  }
  else
  {
   addit[i].rdata=ReadName(reader,buf,&stop);
   reader+=stop;
  }
 }

 //print answers
 printf("nAnswer Records : %d n" , ntohs(dns->ans_count) );
 for(i=0 ; i < ntohs(dns->ans_count) ; i++)
 {
  printf("Name : %s ",answers[i].name);

  if( ntohs(answers[i].resource->type) == T_A) //IPv4 address
  {
   long *p;
   p=(long*)answers[i].rdata;
   a.sin_addr.s_addr=(*p); //working without ntohl
   printf("has IPv4 address : %s",inet_ntoa(a.sin_addr));
  }

  if(ntohs(answers[i].resource->type)==5)
  {
   //Canonical name for an alias
   printf("has alias name : %s",answers[i].rdata);
  }

  printf("n");
 }

 //print authorities
 printf("nAuthoritive Records : %d n" , ntohs(dns->auth_count) );
 for( i=0 ; i < ntohs(dns->auth_count) ; i++)
 {

  printf("Name : %s ",auth[i].name);
  if(ntohs(auth[i].resource->type)==2)
  {
   printf("has nameserver : %s",auth[i].rdata);
  }
  printf("n");
 }

 //print additional resource records
 printf("nAdditional Records : %d n" , ntohs(dns->add_count) );
 for(i=0; i < ntohs(dns->add_count) ; i++)
 {
  printf("Name : %s ",addit[i].name);
  if(ntohs(addit[i].resource->type)==1)
  {
   long *p;
   p=(long*)addit[i].rdata;
   a.sin_addr.s_addr=(*p);
   printf("has IPv4 address : %s",inet_ntoa(a.sin_addr));
  }
  printf("n");
 }
 return;
}

/*
 *
 * */
u_char* ReadName(unsigned char* reader,unsigned char* buffer,int* count)
{
 unsigned char *name;
 unsigned int p=0,jumped=0,offset;
 int i , j;

 *count = 1;
 name = (unsigned char*)malloc(256);

 name[0]='';

 //read the names in 3www6google3com format
 while(*reader!=0)
 {
  if(*reader>=192)
  {
   offset = (*reader)*256 + *(reader+1) - 49152; //49152 = 11000000 00000000 ;)
   reader = buffer + offset - 1;
   jumped = 1; //we have jumped to another location so counting wont go up!
  }
  else
  {
   name[p++]=*reader;
  }

  reader = reader+1;

  if(jumped==0)
  {
   *count = *count + 1; //if we havent jumped to another location then we can count up
  }
 }

 name[p]=''; //string complete
 if(jumped==1)
 {
  *count = *count + 1; //number of steps we actually moved forward in the packet
 }

 //now convert 3www6google3com0 to www.google.com
 for(i=0;i


    
 
 

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