C++如何实现DNS域名解析

#pragma once//这里需要导入库 Ws2_32.lib，在不同的IDE下可能不太一样//#pragma comment(lib, "Ws2_32.lib")#include <windows.h>#include <string>#include <vector>#define MAX_DOMAINNAME_LEN 255#define DNS_PORT  53#define DNS_TYPE_SIZE 2#define DNS_CLASS_SIZE 2#define DNS_TTL_SIZE 4#define DNS_DATALEN_SIZE 2#define DNS_TYPE_A  0x0001 //1 a host address#define DNS_TYPE_CNAME 0x0005 //5 the canonical name for an alias#define DNS_PACKET_MAX_SIZE (sizeof(DNSHeader) + MAX_DOMAINNAME_LEN + DNS_TYPE_SIZE + DNS_CLASS_SIZE)struct DNSHeader{ USHORT usTransID; //标识符 USHORT usFlags; //各种标志位 USHORT usQuestionCount; //Question字段个数  USHORT usAnswerCount; //Answer字段个数 USHORT usAuthorityCount; //Authority字段个数 USHORT usAdditionalCount; //Additional字段个数};class CDNSLookup{public: CDNSLookup(); ~CDNSLookup(); BOOL DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList = NULL, std::vector<std::string> *pvecstrCNameList = NULL, ULONG ulTimeout = 1000, ULONG *pulTimeSpent = NULL); BOOL DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<std::string> *pvecstrIPList = NULL, std::vector<std::string> *pvecstrCNameList = NULL, ULONG ulTimeout = 1000, ULONG *pulTimeSpent = NULL);private: BOOL Init(); BOOL UnInit(); BOOL DNSLookupCore(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent); BOOL SendDNSRequest(sockaddr_in sockAddrDNSServer, char *szDomainName); BOOL RecvDNSResponse(sockaddr_in sockAddrDNSServer, ULONG ulTimeout, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG *pulTimeSpent); BOOL EncodeDotStr(char *szDotStr, char *szEncodedStr, USHORT nEncodedStrSize); BOOL DecodeDotStr(char *szEncodedStr, USHORT *pusEncodedStrLen, char *szDotStr, USHORT nDotStrSize, char *szPacketStartPos = NULL); ULONG GetTickCountCalibrate();private: BOOL m_bIsInitOK; SOCKET m_sock; WSAEVENT m_event; USHORT m_usCurrentProcID; char *m_szDNSPacket;}; [DNSLookup.h] #include "DNSLookup.h"#include <stdio.h>#include <string.h>CDNSLookup::CDNSLookup() :  m_bIsInitOK(FALSE),  m_sock(INVALID_SOCKET), m_szDNSPacket(NULL){ m_bIsInitOK = Init();}CDNSLookup::~CDNSLookup(){ UnInit();}BOOL CDNSLookup::DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent){ return DNSLookupCore(ulDNSServerIP, szDomainName, pveculIPList, pvecstrCNameList, ulTimeout, pulTimeSpent);}BOOL CDNSLookup::DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<std::string> *pvecstrIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent){ std::vector<ULONG> *pveculIPList = NULL; if (pvecstrIPList != NULL) { std::vector<ULONG> veculIPList; pveculIPList = &veculIPList; } BOOL bRet = DNSLookupCore(ulDNSServerIP, szDomainName, pveculIPList, pvecstrCNameList, ulTimeout, pulTimeSpent); if (bRet) { pvecstrIPList->clear(); char szIP[16] = {'/0'}; for (std::vector<ULONG>::iterator iter = pveculIPList->begin(); iter != pveculIPList->end(); ++iter) {  BYTE *pbyIPSegment = (BYTE*)(&(*iter));  //sprintf_s(szIP, 16, "%d.%d.%d.%d", pbyIPSegment[0], pbyIPSegment[1], pbyIPSegment[2], pbyIPSegment[3]);  sprintf(szIP, "%d.%d.%d.%d", pbyIPSegment[0], pbyIPSegment[1], pbyIPSegment[2], pbyIPSegment[3]);  pvecstrIPList->push_back(szIP); } } return bRet;}BOOL CDNSLookup::Init(){ WSADATA wsaData; if (WSAStartup(MAKEWORD(2, 2), &wsaData) == SOCKET_ERROR) { return FALSE; }  if ((m_sock = socket(AF_INET, SOCK_DGRAM, 0)) == INVALID_SOCKET) { return FALSE; } m_event = WSACreateEvent(); WSAEventSelect(m_sock, m_event, FD_READ); m_szDNSPacket = new (std::nothrow) char[DNS_PACKET_MAX_SIZE]; if (m_szDNSPacket == NULL) { return FALSE; } m_usCurrentProcID = (USHORT)GetCurrentProcessId(); return TRUE;}BOOL CDNSLookup::UnInit(){ WSACleanup(); if (m_szDNSPacket != NULL) { delete [] m_szDNSPacket; } return TRUE;}BOOL CDNSLookup::DNSLookupCore(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent){ if (m_bIsInitOK == FALSE || szDomainName == NULL) { return FALSE; } //配置SOCKET sockaddr_in sockAddrDNSServer;  sockAddrDNSServer.sin_family = AF_INET;  sockAddrDNSServer.sin_addr.s_addr = ulDNSServerIP; sockAddrDNSServer.sin_port = htons( DNS_PORT ); //DNS查询与解析 if (!SendDNSRequest(sockAddrDNSServer, szDomainName) || !RecvDNSResponse(sockAddrDNSServer, ulTimeout, pveculIPList, pvecstrCNameList, pulTimeSpent)) { return FALSE; } return TRUE;}BOOL CDNSLookup::SendDNSRequest(sockaddr_in sockAddrDNSServer, char *szDomainName){ char *pWriteDNSPacket = m_szDNSPacket; memset(pWriteDNSPacket, 0, DNS_PACKET_MAX_SIZE);  //填充DNS查询报文头部 DNSHeader *pDNSHeader = (DNSHeader*)pWriteDNSPacket; pDNSHeader->usTransID = m_usCurrentProcID; pDNSHeader->usFlags = htons(0x0100); pDNSHeader->usQuestionCount = htons(0x0001); pDNSHeader->usAnswerCount = 0x0000; pDNSHeader->usAuthorityCount = 0x0000; pDNSHeader->usAdditionalCount = 0x0000; //设置DNS查询报文内容 USHORT usQType = htons(0x0001); USHORT usQClass = htons(0x0001); USHORT nDomainNameLen = strlen(szDomainName); char *szEncodedDomainName = (char *)malloc(nDomainNameLen + 2); if (szEncodedDomainName == NULL) { return FALSE; } if (!EncodeDotStr(szDomainName, szEncodedDomainName, nDomainNameLen + 2)) { return FALSE; } //填充DNS查询报文内容 USHORT nEncodedDomainNameLen = strlen(szEncodedDomainName) + 1; memcpy(pWriteDNSPacket += sizeof(DNSHeader), szEncodedDomainName, nEncodedDomainNameLen); memcpy(pWriteDNSPacket += nEncodedDomainNameLen, (char*)(&usQType), DNS_TYPE_SIZE); memcpy(pWriteDNSPacket += DNS_TYPE_SIZE, (char*)(&usQClass), DNS_CLASS_SIZE); free (szEncodedDomainName); //发送DNS查询报文 USHORT nDNSPacketSize = sizeof(DNSHeader) + nEncodedDomainNameLen + DNS_TYPE_SIZE + DNS_CLASS_SIZE; if (sendto(m_sock, m_szDNSPacket, nDNSPacketSize, 0, (sockaddr*)&sockAddrDNSServer, sizeof(sockAddrDNSServer)) == SOCKET_ERROR) { return FALSE; } return TRUE;}BOOL CDNSLookup::RecvDNSResponse(sockaddr_in sockAddrDNSServer, ULONG ulTimeout, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG *pulTimeSpent){ ULONG ulSendTimestamp = GetTickCountCalibrate(); if (pveculIPList != NULL) { pveculIPList->clear(); } if (pvecstrCNameList != NULL) { pvecstrCNameList->clear(); } char recvbuf[1024] = {'/0'}; char szDotName[128] = {'/0'}; USHORT nEncodedNameLen = 0; while (TRUE) { if (WSAWaitForMultipleEvents(1, &m_event, FALSE, 100, FALSE) != WSA_WAIT_TIMEOUT) {  WSANETWORKEVENTS netEvent;  WSAEnumNetworkEvents(m_sock, m_event, &netEvent);  if (netEvent.lNetworkEvents & FD_READ)  {  ULONG ulRecvTimestamp = GetTickCountCalibrate();  int nSockaddrDestSize = sizeof(sockAddrDNSServer);  //接收响应报文  if (recvfrom(m_sock, recvbuf, 1024, 0, (struct sockaddr*)&sockAddrDNSServer, &nSockaddrDestSize) != SOCKET_ERROR)  {   DNSHeader *pDNSHeader = (DNSHeader*)recvbuf;   USHORT usQuestionCount = 0;   USHORT usAnswerCount = 0;   if (pDNSHeader->usTransID == m_usCurrentProcID   && (ntohs(pDNSHeader->usFlags) & 0xfb7f) == 0x8100 //RFC1035 4.1.1(Header section format)   && (usQuestionCount = ntohs(pDNSHeader->usQuestionCount)) >= 0   && (usAnswerCount = ntohs(pDNSHeader->usAnswerCount)) > 0)   {   char *pDNSData = recvbuf + sizeof(DNSHeader);   //解析Question字段   for (int q = 0; q != usQuestionCount; ++q)   {    if (!DecodeDotStr(pDNSData, &nEncodedNameLen, szDotName, sizeof(szDotName)))    {    return FALSE;    }    pDNSData += (nEncodedNameLen + DNS_TYPE_SIZE + DNS_CLASS_SIZE);   }   //解析Answer字段   for (int a = 0; a != usAnswerCount; ++a)   {    if (!DecodeDotStr(pDNSData, &nEncodedNameLen, szDotName, sizeof(szDotName), recvbuf))    {    return FALSE;    }    pDNSData += nEncodedNameLen;    USHORT usAnswerType = ntohs(*(USHORT*)(pDNSData));    USHORT usAnswerClass = ntohs(*(USHORT*)(pDNSData + DNS_TYPE_SIZE));    ULONG usAnswerTTL = ntohl(*(ULONG*)(pDNSData + DNS_TYPE_SIZE + DNS_CLASS_SIZE));    USHORT usAnswerDataLen = ntohs(*(USHORT*)(pDNSData + DNS_TYPE_SIZE + DNS_CLASS_SIZE + DNS_TTL_SIZE));    pDNSData += (DNS_TYPE_SIZE + DNS_CLASS_SIZE + DNS_TTL_SIZE + DNS_DATALEN_SIZE);    if (usAnswerType == DNS_TYPE_A && pveculIPList != NULL)    {    ULONG ulIP = *(ULONG*)(pDNSData);    pveculIPList->push_back(ulIP);    }    else if (usAnswerType == DNS_TYPE_CNAME && pvecstrCNameList != NULL)    {    if (!DecodeDotStr(pDNSData, &nEncodedNameLen, szDotName, sizeof(szDotName), recvbuf))    {     return FALSE;    }    pvecstrCNameList->push_back(szDotName);    }    pDNSData += (usAnswerDataLen);   }   //计算DNS查询所用时间   if (pulTimeSpent != NULL)   {    *pulTimeSpent = ulRecvTimestamp - ulSendTimestamp;   }   break;   }  }  } } //超时退出 if (GetTickCountCalibrate() - ulSendTimestamp > ulTimeout) {  *pulTimeSpent = ulTimeout + 1;  return FALSE; } } return TRUE;}/* * convert "www.baidu.com" to "/x03www/x05baidu/x03com" * 0x0000 03 77 77 77 05 62 61 69 64 75 03 63 6f 6d 00 ff */BOOL CDNSLookup::EncodeDotStr(char *szDotStr, char *szEncodedStr, USHORT nEncodedStrSize){ USHORT nDotStrLen = strlen(szDotStr); if (szDotStr == NULL || szEncodedStr == NULL || nEncodedStrSize < nDotStrLen + 2) { return FALSE; } char *szDotStrCopy = new char[nDotStrLen + 1]; //strcpy_s(szDotStrCopy, nDotStrLen + 1, szDotStr); strcpy(szDotStrCopy, szDotStr); char *pNextToken = NULL; //char *pLabel = strtok_s(szDotStrCopy, ".", &pNextToken); char *pLabel = strtok(szDotStrCopy, "."); USHORT nLabelLen = 0; USHORT nEncodedStrLen = 0; while (pLabel != NULL) { if ((nLabelLen = strlen(pLabel)) != 0) {  //sprintf_s(szEncodedStr + nEncodedStrLen, nEncodedStrSize - nEncodedStrLen, "%c%s", nLabelLen, pLabel);  sprintf(szEncodedStr + nEncodedStrLen, "%c%s", nLabelLen, pLabel);  nEncodedStrLen += (nLabelLen + 1); } //pLabel = strtok_s(NULL, ".", &pNextToken); pLabel = strtok(NULL, "."); } delete [] szDotStrCopy;  return TRUE;}/* * convert "/x03www/x05baidu/x03com/x00" to "www.baidu.com" * 0x0000 03 77 77 77 05 62 61 69 64 75 03 63 6f 6d 00 ff * convert "/x03www/x05baidu/xc0/x13" to "www.baidu.com" * 0x0000 03 77 77 77 05 62 61 69 64 75 c0 13 ff ff ff ff * 0x0010 ff ff ff 03 63 6f 6d 00 ff ff ff ff ff ff ff ff */BOOL CDNSLookup::DecodeDotStr(char *szEncodedStr, USHORT *pusEncodedStrLen, char *szDotStr, USHORT nDotStrSize, char *szPacketStartPos){ if (szEncodedStr == NULL || pusEncodedStrLen == NULL || szDotStr == NULL) { return FALSE; } char *pDecodePos = szEncodedStr; USHORT usPlainStrLen = 0; BYTE nLabelDataLen = 0;  *pusEncodedStrLen = 0; while ((nLabelDataLen = *pDecodePos) != 0x00) { if ((nLabelDataLen & 0xc0) == 0) //普通格式，LabelDataLen + Label {  if (usPlainStrLen + nLabelDataLen + 1 > nDotStrSize)  {  return FALSE;  }  memcpy(szDotStr + usPlainStrLen, pDecodePos + 1, nLabelDataLen);  memcpy(szDotStr + usPlainStrLen + nLabelDataLen, ".", 1);  pDecodePos += (nLabelDataLen + 1);  usPlainStrLen += (nLabelDataLen + 1);  *pusEncodedStrLen += (nLabelDataLen + 1); } else //消息压缩格式，11000000 00000000，两个字节，前2位为跳转标志，后14位为跳转的偏移 {  if (szPacketStartPos == NULL)  {  return FALSE;  }  USHORT usJumpPos = ntohs(*(USHORT*)(pDecodePos)) & 0x3fff;  USHORT nEncodeStrLen = 0;  if (!DecodeDotStr(szPacketStartPos + usJumpPos, &nEncodeStrLen, szDotStr + usPlainStrLen, nDotStrSize - usPlainStrLen, szPacketStartPos))  {  return FALSE;  }  else  {  *pusEncodedStrLen += 2;  return TRUE;  } } } szDotStr[usPlainStrLen - 1] = '/0'; *pusEncodedStrLen += 1; return TRUE;}ULONG CDNSLookup::GetTickCountCalibrate(){ static ULONG s_ulFirstCallTick = 0; static LONGLONG s_ullFirstCallTickMS = 0; SYSTEMTIME systemtime; FILETIME filetime; GetLocalTime(&systemtime);  SystemTimeToFileTime(&systemtime, &filetime); LARGE_INTEGER liCurrentTime; liCurrentTime.HighPart = filetime.dwHighDateTime; liCurrentTime.LowPart = filetime.dwLowDateTime; LONGLONG llCurrentTimeMS = liCurrentTime.QuadPart / 10000; if (s_ulFirstCallTick == 0) { s_ulFirstCallTick = GetTickCount(); } if (s_ullFirstCallTickMS == 0) { s_ullFirstCallTickMS = llCurrentTimeMS; } return s_ulFirstCallTick + (ULONG)(llCurrentTimeMS - s_ullFirstCallTickMS);} [DNSLookup.cpp] #include <stdio.h>#include <windows.h>#include "DNSLookup.h"int main(void){ char szDomainName[] = "www.baidu.com"; std::vector<ULONG> veculIPList; std::vector<std::string> vecstrIPList; std::vector<std::string> vecCNameList; ULONG ulTimeSpent = 0; CDNSLookup dnslookup; BOOL bRet = dnslookup.DNSLookup(inet_addr("114.114.114.114"), szDomainName, &vecstrIPList, &vecCNameList, 1000, &ulTimeSpent); printf("DNSLookup result (%s):/n", szDomainName); if (!bRet) { printf("timeout!/n"); return -1; } for (int i = 0; i != veculIPList.size(); ++i) { printf("IP%d(ULONG) = %u/n", i + 1, veculIPList[i]); } for (int i = 0; i != vecstrIPList.size(); ++i) { printf("IP%d(string) = %s/n", i + 1, vecstrIPList[i].c_str()); } for (int i = 0; i != vecCNameList.size(); ++i) { printf("CName%d = %s/n", i + 1, vecCNameList[i].c_str()); } printf("time spent = %ums/n", ulTimeSpent);  return 0;}