/*********************************************************************************
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* Copyright: (C) 2018 LingYun IoT Studio
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* All rights reserved.
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*
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* Filename: dns_api.c
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* Description: This file is DNS client API based on UDP socket
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*
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* Version: 1.0.0(10/29/2018)
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* Author: Guo Wenxue <guowenxue@gmail.com>
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* ChangeLog: 1, Release initial version on "2018-10-28 01:38:08 PM"
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*
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********************************************************************************/
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#include <stdio.h>
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#include <errno.h>
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#include <string.h>
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#include <time.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <sys/types.h>
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#include <sys/socket.h>
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#include <netinet/in.h>
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#include <arpa/inet.h>
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#include "dns_api.h"
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/*+-----------------------------------------------------------------------------------+
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*| DNS Protocal packet format definition
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*| Reference: https://www.ietf.org/rfc/rfc1035.txt
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*| https://www2.cs.duke.edu/courses/fall16/compsci356/DNS/DNS-primer.pdf
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*+-----------------------------------------------------------------------------------+
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*/
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/*
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DNS packet format:
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+---------------------+
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| Header |
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+---------------------+
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| Question | the question for the name server
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+---------------------+
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| Answer | RRs answering the question
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+---------------------+
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| Authority | RRs pointing toward an authority
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+---------------------+
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| Additional | RRs holding additional information
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+---------------------+
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Header section format：
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1 1 1 1 1 1
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| ID |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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|QR| Opcode |AA|TC|RD|RA| Z | RCODE |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| QDCOUNT |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| ANCOUNT |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| NSCOUNT |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| ARCOUNT |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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Question section format：
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| |
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/ QNAME /
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/ /
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| QTYPE |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| QCLASS |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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Resource record format：
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1 1 1 1 1 1
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| |
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/ /
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/ NAME /
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| |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| TYPE |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| CLASS |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| TTL |
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| |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| RDLENGTH |
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--|
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/ RDATA /
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/ /
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+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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*/
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void dump_buf(const char *prompt, char *data, int len)
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{
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int i;
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if(prompt)
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{
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printf("%s", prompt);
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}
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for(i=0; i<len; i++)
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{
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printf("%02x ", data[i]);
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}
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printf("\n");
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}
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int fill_dns_head(char *packet, int size)
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{
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unsigned short tmp;
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int ofset = 0;
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if( !packet || size<DNS_HEAD_MIN )
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{
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printf("Invalid input arguments in %s()\n", __FUNCTION__);
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return -1;
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}
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/* DNS Head: Transaction ID */
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srand((int)time(0));
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tmp = (unsigned short)random();
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memcpy(&packet[ofset], &tmp, 2);
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ofset += 2;
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/* DNS Head: Flags */
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tmp = 0x0001; /* MSB */
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memcpy(&packet[ofset], &tmp, 2);
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ofset += 2;
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/* DNS Head: Questions */
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tmp = 0x0100; /* MSB */
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memcpy(&packet[ofset], &tmp, 2);
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ofset += 2;
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/* DNS Head: Answer RRs */
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tmp = 0x0000;
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memcpy(&packet[ofset], &tmp, 2);
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ofset += 2;
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/* DNS Head: Authority RRs */
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tmp = 0x0000;
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memcpy(&packet[ofset], &tmp, 2);
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ofset += 2;
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/* DNS Head: Additional RRs */
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tmp = 0x0000;
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memcpy(&packet[ofset], &tmp, 2);
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ofset += 2;
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//dump_buf("DNS packet head: \n", packet, ofset);
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return ofset;
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}
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int fill_dns_question_qtype_qclass(char *packet, int size)
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{
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unsigned short tmp;
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int ofset = 0;
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if( !packet || size<DNS_HEAD_MIN )
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{
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printf("Invalid input arguments in %s()\n", __FUNCTION__);
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return -1;
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}
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/* DNS QType: 0x0001(A record) 0x0005(CNAME)*/
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tmp = 0x0100; /* MSB */
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memcpy(&packet[ofset], &tmp, 2);
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ofset += 2;
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/* DNS QClass, 0x0001: representing Internet addresses */
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tmp = 0x0100; /* MSB */
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memcpy(&packet[ofset], &tmp, 2);
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ofset += 2;
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//dump_buf("DNS packet tail: \n", packet, ofset);
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return ofset;
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}
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/* www.baidu.com ==> 3www5baidu3com0 */
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int fill_dns_question_qname(char *domain, char *packet, int size)
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{
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int ofset = 0;
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const char *start;
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char *ptr;
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int len;
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/* Check arguments */
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if( !domain || !packet || size<strlen(domain) )
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{
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return -1;
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}
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start = domain;
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while( (ptr=(strchr(start, '.'))) != NULL )
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{
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len=ptr-start; /* get segemnent length by '.' */
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packet[ofset++] = len;
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len = ptr-start;
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strncpy(&packet[ofset], start, len); /* copy segemnent string */
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ofset += len;
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start = ptr + 1; /* let start point to next character follow '.' */
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}
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/* last segemnent by '.' is pointed by start */
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len = strlen(domain)- (start-domain);
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packet[ofset++] = len;
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/* check strncpy buffer limits */
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if(size-ofset < len)
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len = size-ofset;
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strncpy(&packet[ofset], start, len);
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ofset += len;
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packet[ofset++] = 0x00;
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return ofset;
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}
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int query_dns(char *dns_server_ip, char *domain, char *ipaddr, int ipaddr_size)
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{
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int sockfd;
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char msg_buf[512];
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int ofset = 0;
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int rv = -1;
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short records;
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struct sockaddr_in servaddr;
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if(!domain || !ipaddr || strlen(domain)<=0 || ipaddr_size<IPADDR_LEN)
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{
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printf("Invalid input arguments\n");
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return -1;
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}
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memset(ipaddr, 0, ipaddr_size);
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/*+--------------------------------------------------------------------------------------------------------------
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*| Parser baidu.com:
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*| Send DNS Query Packet:
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*| a7 c3 01 00 00 01 00 00 00 00 00 00 05 62 61 69 64 75 03 63 6f 6d 00 00 01 00 01
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*|
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*| Header section format:
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*| Session ID(2B): A7 C3
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*| Flag(2B): 01 00
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*| QDCOUNT(2B): 01 00 1 entry in the question section
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*| ANCOUNT(2B): 00 00 0 resource records in the answer section
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*| NSCOUNT(2B): 00 00 0 resource records in the authority records section
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*| ARCOUNT(2B): 00 00 0 resource records in the additional records section
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*|
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*| Question section format:
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*| QNAME(nB): 05 62 61 69 64 75 03 63 6f 6d 00: 05baidu03com0
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*| QTYPE(2B): 00 01 1: (A record)
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*| QCLASS(2B): 00 01 1: (Internet addresses)
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*+--------------------------------------------------------------------------------------------------------------
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*/
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rv=fill_dns_head(&msg_buf[ofset], sizeof(msg_buf)-ofset);
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if( rv < 0 )
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{
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printf("Fill DNS head failure\n");
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return -2;
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}
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ofset += rv;
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rv = fill_dns_question_qname(domain, &msg_buf[ofset], sizeof(msg_buf)-ofset);
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if(rv < 0)
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{
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printf("Fill DNS Question Qname failure\n");
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return -2;
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}
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ofset += rv;
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rv= fill_dns_question_qtype_qclass(&msg_buf[ofset], sizeof(msg_buf)-ofset);
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if( rv < 0 )
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{
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printf("Fill DNS Question QType and QClass\n");
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return -3;
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}
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ofset += rv;
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//dump_buf("DNS packet : \n", msg_buf, ofset);
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if ( (sockfd=socket(PF_INET, SOCK_DGRAM, 0)) < 0 )
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{
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printf("Create UDP socket failure: %s\n", strerror(errno));
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return -4;
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}
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memset(&servaddr, 0, sizeof(servaddr));
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servaddr.sin_family = AF_INET;
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servaddr.sin_port = htons(53); /*DNS default port 53 */
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servaddr.sin_addr.s_addr = inet_addr(dns_server_ip);
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if( sendto(sockfd, msg_buf, ofset, 0, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0 )
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{
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printf("Send DNS packet to DNS server[%s] failure: %s\n", dns_server_ip, strerror(errno));
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return -5;
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}
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if( (rv=recvfrom(sockfd, msg_buf, sizeof(msg_buf), 0, NULL, NULL) ) < 0 )
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{
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printf("Receive DNS reply from DNS server[%s] failure: %s\n", dns_server_ip, strerror(errno));
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return -6;
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}
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/*+--------------------------------------------------------------------------------------------------------------
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*| Receive DNS Server Reply Packet:
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*| a7 c3 81 80 00 01 [00 02] 00 00 00 00 05 62 61 69 64 75 03 63 6f 6d 00 00 01 00 01
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*| c0 0c 00 01 00 01 00 00 00 21 00 04 dc b5 39 d8 c0 0c 00 01 00 01 00 00 00 21 00 04 7b 7d 73 6e
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*| Question Section: a7 c3 ... 00 01, but bytes[8:7] is reply resource entries, here is [00 02] so get 2 entries
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*|
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*| First resource
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*| Name Pointer(2B): c0 0c
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*| Type(2B): 01 00
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*| Class: 01 00
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*| TTL(4B): 00 00 00 21
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*| RDLENGTH(2B): 00 04
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*| IP address: dc b5 39 d8 "220.181.57.216"
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*|
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*| Second resource
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*| Name Pointer(2B): c0 0c
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*| Type(2B): 01 00
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*| Class: 01 00
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*| TTL(4B): 00 00 00 21
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*| RDLENGTH(2B): 00 04
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*| IP address: 7b 7d 73 6e "123.125.115.110"
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*|
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*+--------------------------------------------------------------------------------------------------------------
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*/
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//dump_buf("Recieve DNS reply: \n", msg_buf, rv);
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records = *(short *)&msg_buf[7];
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/* 1, Reply resource will followed by request packet
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* 2, 2B Name Pointer + 2B Type+2B Class + 4B TTL + 2B RDlength = 12B */
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ofset += 12;
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snprintf(ipaddr, ipaddr_size, "%d.%d.%d.%d",msg_buf[ofset],msg_buf[ofset+1],msg_buf[ofset+2],msg_buf[ofset+3]);
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#if 0
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printf("DNS server[%s] resolve domain \"%s\" get %d records:\n", dns_server_ip, domain, records);
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while( records-- )
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{
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printf("%d.%d.%d.%d\n",msg_buf[ofset],msg_buf[ofset+1],msg_buf[ofset+2],msg_buf[ofset+3]);
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ofset += 16;
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}
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#endif
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close(sockfd);
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return 0;
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}
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