linux中查询dns示例

dns.c

复制代码 代码如下:
/*
 * DNS Query Program on Linux
 *
 * Author : ismdeep@live.com
 *
 * */
//Header Files
#include<stdio.h> //printf
#include<string.h> //strlen
#include<stdlib.h> //malloc
#include<sys/socket.h> //you know what this is for
#include<arpa/inet.h> //inet_addr , inet_ntoa , ntohs etc
#include<netinet/in.h>
#include<unistd.h> //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