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7 files changed

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‎CMakeLists.txt

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cmake_minimum_required(VERSION 3.3)
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project(DNS)
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set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
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set(SOURCE_FILES main.cpp base/dns.cpp base/util.cpp)
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INCLUDE_DIRECTORIES(include)
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add_executable(DNS ${SOURCE_FILES})

‎README.md

Whitespace-only changes.

‎base/dns.cpp

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#include "../include/dns.h"
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//construct a binary datagram which is used to request the dns server.
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DNSMessage::DNSMessageData DNSMessage::toRequestData() {
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unsigned char data[4096];
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DNSHeader *newDNSHeader = reinterpret_cast<DNSHeader *> (data);
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//construct dns request header
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newDNSHeader->authorizationRecordCount = this->dnsHeader.authorizationRecordCount;
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newDNSHeader->descriptor = this->dnsHeader.descriptor;
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newDNSHeader->extraSourceCount = this->dnsHeader.extraSourceCount;
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newDNSHeader->questionCount = this->dnsHeader.questionCount;
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newDNSHeader->resourceRecourdCount = this->dnsHeader.resourceRecourdCount;
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newDNSHeader->flag = this->dnsHeader.flag;
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//construct queryQuestion Name of dns request
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char *queryName = reinterpret_cast<char *>(&data[sizeof(DNSHeader)]);
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size_t queryNameLength = strlen((const char *) dnsQuestion.queryName);
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memcpy(queryName, dnsQuestion.queryName, queryNameLength);//copy query name
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//construct queryQuestion type of dns request
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DNSType *newDNSQuestion = reinterpret_cast<DNSType *>(&data[sizeof(DNSHeader) + queryNameLength + 1]);
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newDNSQuestion->type = dnsQuestion.type.type;
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newDNSQuestion->typeClass = dnsQuestion.type.typeClass;
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return DNSMessageData(new std::pair<unsigned char *, int>(data, 12 + queryNameLength + 1 + 4));
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}
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// DNSQuestion* newDNSQuestion=reinterpret_cast<DNSQuestion*>(&data2[sizeof(DNSHeader)]);
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// using namespace std;
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// cout<<newDNSQuestion<<endl;
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//
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// cout<<&newDNSQuestion->queryName<<endl;
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// char* aaa=reinterpret_cast<char*>(&data2[sizeof(DNSHeader)]);
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// printf("%p\n",aaa);
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//assign values to DNSQuestion is too complex work it done perfectly... try another way: encapsulate the type and class to a entity.
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// char* newDNSQuestion=reinterpret_cast<char*>(&data2[sizeof(DNSHeader)+queryNameLength+1]);
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// char* oldDNSQuestion=reinterpret_cast<char*>(((char*)&dnsQuestion)+8);
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// memcpy(newDNSQuestion,oldDNSQuestion,4);

‎base/util.cpp

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#include <cassert>
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#include "../include/util.h"
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#include <stdexcept>
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#include <netinet/in.h>
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#include "../include/dns.h"
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void split(const std::string &str, char c, std::vector<std::string> &v) {
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if (str.size() == 0) {
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throw std::invalid_argument("parameter str is empty");
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}
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std::string::size_type i = 0;
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std::string::size_type j = str.find(c);
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while (j != std::string::npos) {
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v.push_back(str.substr(i, j - i));
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i = ++j;
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j = str.find(c, j);
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}
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if (j == std::string::npos)
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v.push_back(str.substr(i, str.length()));
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}
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void constructQueryName(std::string &hostName, unsigned char *host) {
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if (hostName.size() == 0) {
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throw std::invalid_argument("parameter hostName is invalid.");
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}
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if (!host) {
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throw std::invalid_argument("parameter host is invalid.");
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}
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std::vector<std::string> v;
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split(hostName, '.', v);
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hostName.clear();
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for_each(v.begin(), v.end(), [&hostName, &host](std::string &s) {
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*host = s.size();
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host++;
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memcpy(host, s.c_str(), s.size());
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host += s.size();
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});
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}
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// client has the responsibility to ensure the correctnes of the length of queryName,because of 2 bytes after domain name field;
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std::string restoreQueryName(const unsigned char *domainName, size_t length) {
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if (!domainName) {
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throw std::invalid_argument("parameter queryName is null or empty.");
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}
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if(*domainName=='\0'||length==0){
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return std::string(".");
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}
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// assert(hostName);
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// assert(hostNameLength>2);
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unsigned char newQueryName[length*2]={0};
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unsigned char *newHostPos = newQueryName;
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const unsigned char *hostPos = domainName;
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while (hostPos != (domainName + length + 1)) {
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size_t count = *hostPos++;
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if(count>63){
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break;
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}
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if(count==0){
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*newHostPos++ = ' ';
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continue;
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}
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for (int i = 0; i < count; i++) {
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*newHostPos++ = *hostPos++;
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}
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*newHostPos++ = '.';
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}
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newHostPos='\0';
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return std::string((char*)newQueryName);
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}
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bool isIPType(int type) {
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assert(type >= 1);
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if (type == 1) {
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return true;
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}
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return false;
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}
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bool isCNAMEType(int type){
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assert(type >= 1);
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if (type == 5) {
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return true;
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}
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return false;
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}
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//bool ValidateHostName( std::string hostName) {
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// if (hostName.size() > 63 || hostName.size() == 0) {
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// return false;
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// }
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// std::regex urlRegex("^(www.)?[a-z0-9\\-]+\\.(com|cn)$");
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// if(std::regex_match(hostName,urlRegex)){
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// return true;
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// }
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// return false;
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//}
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void fillDNSQuestion(std::string &hostName, QueryType queryType, DNSQuestion &dnsQuestion) {
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assert(hostName.size() > 0);
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constructQueryName(hostName, dnsQuestion.queryName);
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//dnsQuestion.queryName="3www5baidu3com";
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dnsQuestion.type.typeClass = htons(1);//used to be 1, a internet address.
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dnsQuestion.type.type = htons(queryType);
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}
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void fillDNSHeaeder(DNSHeader &header) {
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header.descriptor = htons(9);//a magic number...
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header.questionCount = htons(1);
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header.resourceRecourdCount = 0;
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header.authorizationRecordCount = 0;
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header.extraSourceCount = 0;
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header.flag.QR = 0;// indicate that the message is used to request
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header.flag.OPCODE = 0;//standard query
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header.flag.AA = 1;//authoritative answer
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header.flag.TC = 0;//can be truncated or not
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header.flag.RD = 1;//tell the dns server that this query must be handled and the method is 'recursive'
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header.flag.RA = 1;//if dns server's query method is 'recursive', asign it 1
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header.flag.ZERO = 0;//it must be 0
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header.flag.RCODE = 0;//returned and assigned by dns server
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}
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void fillDNSRequest(std::string &hostName, QueryType queryType, DNSMessage &dnsMesssage) {
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assert(hostName.size() > 0);
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fillDNSHeaeder(dnsMesssage.dnsHeader);
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fillDNSQuestion(hostName, queryType, dnsMesssage.dnsQuestion);
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}

‎include/dns.h

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#ifndef _DNS_INCLUDE
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#define _DNS_INCLUDE
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#include <memory>
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#include <cstring>
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enum QueryType {
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A = 1,
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PTR = 12
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};
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struct DNSFlag {
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unsigned char RD:1;
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unsigned char TC:1;
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unsigned char AA:1;
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unsigned char OPCODE:4;
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unsigned char QR:1;
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unsigned char RCODE:4;
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unsigned char ZERO:3;
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unsigned char RA:1;
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// unsigned char QR:1;
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// unsigned char OPCODE:4;
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// unsigned char AA:1;
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// unsigned char TC:1;
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// unsigned char RD:1;
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// unsigned char RA:1;
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// unsigned char ZERO:3;
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// unsigned char RCODE:4;
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};
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struct DNSHeader {
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unsigned short descriptor;
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DNSFlag flag;
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unsigned short questionCount;
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unsigned short resourceRecourdCount;
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unsigned short authorizationRecordCount;
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unsigned short extraSourceCount;
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};
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struct DNSType {
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unsigned short type;
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unsigned short typeClass;
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};
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struct DNSQuestion {
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unsigned char queryName[4096];
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DNSType type;
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// unsigned short queryType=QueryType::A;
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// unsigned short queryClass=1;
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};
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struct DNSMessage {
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typedef std::shared_ptr<std::pair<unsigned char *, int>> DNSMessageData;
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DNSHeader dnsHeader;
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DNSQuestion dnsQuestion;
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DNSMessageData toRequestData();
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};
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struct DNSResourceExtraInfo {
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DNSType type;
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int liveTime;
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unsigned short resourceDataLength;
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};
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struct DNSResourceRecord {
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char domainName[4096];
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DNSResourceExtraInfo extraInfo;
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char dataResrouce[4096];
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};
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#endif

‎include/util.h

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#ifndef DNS_UTILITY_H
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#define DNS_UTILITY_H
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#include <string>
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#include <vector>
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#include <algorithm>
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#include <cstring>
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#include <netinet/in.h>
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#include "../include/dns.h"
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void split(const std::string &s, char c, std::vector<std::string> &v);
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//when constructing dns query name, using a byte to store the count of the query name, not char!
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//note that because of the validation of hostName , so we can assume that hostName if valid.
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void constructQueryName(std::string &hostName, unsigned char *host);
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//restore the query name, for example , 3www5baidu3com -> www.baidu.com
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std::string restoreQueryName(const unsigned char *queryName, size_t length);
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//indicating current whether the dns response type is IP or not
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bool isIPType(int type);
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bool isCNAMEType(int type);
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//bool ValidateHostName(std::string hostName);
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void fillDNSQuestion(std::string &hostName, QueryType queryType, DNSQuestion &dnsQuestion);
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void fillDNSHeaeder(DNSHeader &header);
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void fillDNSRequest(std::string &hostName, QueryType queryType, DNSMessage &dnsMesssage);
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#endif

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