1、尝试了 gethostbyname(...) 和 Qt598中的qhostinfo::fromname(...)，都可以解析出来IP，但是有一个问题：域名指向的IP改变了，这两种方式需要等较长时间 才会解析到更新后的ip地址。而CMD中 nslookup却一下子就解析到了更新后的IP...
1.1、查了一下资料，貌似原因如下（大概的说下原理，可能不严谨准确）：
（1）域名服务器在 域名的TTL时间段内 它不会去实时的查找域名对应的IP，而是要等到TTL超时 域名服务器才回去再次查询 然后更新新的地址。
（2）又∵ gethostbyname 和 qhostinfo::fromname 都没有参数可以输入 DNS服务器地址，猜测可能使用的是 OS中设置的DNS服务器。
ZC：综上2个原因 造成了这个现象
ZC：改 OS的DNS设置的话，如果 这个DNS服务器不是 常用上网的DNS服务器的话，到时候还要改回来，比较麻烦，暂不考虑使用
1.2、于是猜测，指定 DNS解析服务器的话，就能解决这个现象
2、C++实现DNS域名解析 - Snser - 博客园.html（https://www.cnblogs.com/snser/p/4101729.html）
ZC：DNS解析的 数据包结构、原理、代码 都在这个文章中查看
ZC：只解析IPv4地址的精简版代码在 2.2
2.1、这是文章中的代码（少许改动，运行OK）（项目->属性->C/C++->预处理器->"预处理器定义"中添加 "_ITERATOR_DEBUG_LEVEL=0"）
（1）CDNSLookup.h
#pragma once // C++实现DNS域名解析 - Snser - 博客园.html (https://www.cnblogs.com/snser/p/4101729.html) #define _CRT_SECURE_NO_WARNINGS //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 <winsock2.h> #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); private: BOOL m_bIsInitOK; SOCKET m_sock; };
（2）CDNSLookup.cpp
#include "CDNSLookup.h" #include <stdio.h> #include <string.h> CDNSLookup::CDNSLookup() : m_bIsInitOK(FALSE), m_sock(INVALID_SOCKET) { 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) { ULONG ul = (*iter); BYTE *pbyIPSegment = (BYTE*)(&ul); //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) { printf("WSAStartup(...) err : %d\n", ::GetLastError()); return FALSE; } if ((m_sock = socket(AF_INET, SOCK_DGRAM, 0)) == INVALID_SOCKET) { printf("socket(...) err : %d\n", ::GetLastError()); return FALSE; } DWORD dwTimeOut = 1000 * 5; if (setsockopt(m_sock, SOL_SOCKET, SO_RCVTIMEO, (char*)&dwTimeOut, sizeof(dwTimeOut)) == SOCKET_ERROR) { printf("setsockopt(...) err : %d\n", ::GetLastError()); return FALSE; } return TRUE; } BOOL CDNSLookup::UnInit() { WSACleanup(); 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 addrDnsServer; addrDnsServer.sin_family = AF_INET; addrDnsServer.sin_addr.s_addr = ulDNSServerIP; addrDnsServer.sin_port = htons(DNS_PORT); //DNS查询与解析 if (!SendDNSRequest(addrDnsServer, szDomainName)) { return FALSE; } if (!RecvDNSResponse(addrDnsServer, ulTimeout, pveculIPList, pvecstrCNameList, pulTimeSpent)) { return FALSE; } return TRUE; } BOOL CDNSLookup::SendDNSRequest(sockaddr_in _addrDnsServer, char *_szDomainName) { char bufSend[DNS_PACKET_MAX_SIZE] = {0}; char* pcSend = &bufSend[0]; //填充DNS查询报文头部 DNSHeader *pDnsHdr = (DNSHeader*)pcSend; pDnsHdr->usTransID = (USHORT)GetCurrentProcessId(); pDnsHdr->usFlags = htons(0x0100); pDnsHdr->usQuestionCount = htons(0x0001); pDnsHdr->usAnswerCount = 0x0000; pDnsHdr->usAuthorityCount = 0x0000; pDnsHdr->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(pcSend += sizeof(DNSHeader), szEncodedDomainName, nEncodedDomainNameLen); memcpy(pcSend += nEncodedDomainNameLen, (char*)(&usQType), DNS_TYPE_SIZE); memcpy(pcSend += 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, bufSend, nDNSPacketSize, 0, (sockaddr*)&_addrDnsServer, sizeof(_addrDnsServer)) == SOCKET_ERROR) { return FALSE; } return TRUE; } BOOL CDNSLookup::RecvDNSResponse(sockaddr_in _addrDnsServer, ULONG ulTimeout, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG *pulTimeSpent) { if (pveculIPList != NULL) pveculIPList->clear(); if (pvecstrCNameList != NULL) pvecstrCNameList->clear(); char bufRecv[1024] = { 0 }; char szDotName[128] = { 0 }; USHORT nEncodedNameLen = 0; int iAddrDnsServer = sizeof(_addrDnsServer); DWORD dw1 = ::GetTickCount(); //接收响应报文 if (recvfrom(m_sock, bufRecv, sizeof(bufRecv), 0, (struct sockaddr*)&_addrDnsServer, &iAddrDnsServer) == SOCKET_ERROR) { //WSAETIMEDOUT printf("DNS recvfrom(...) failed : %d\n", ::GetLastError()); return FALSE; } DNSHeader *pDnsHdr = (DNSHeader*)bufRecv; USHORT usQuestionCount = 0; USHORT usAnswerCount = 0; if (pDnsHdr->usTransID == (USHORT)GetCurrentProcessId() && (ntohs(pDnsHdr->usFlags) & 0xfb7f) == 0x8100 //RFC1035 4.1.1(Header section format) && (usQuestionCount = ntohs(pDnsHdr->usQuestionCount)) >= 0 && (usAnswerCount = ntohs(pDnsHdr->usAnswerCount)) > 0) { char *pDNSData = bufRecv + 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), bufRecv)) { 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), bufRecv)) { return FALSE; } pvecstrCNameList->push_back(szDotName); } pDNSData += (usAnswerDataLen); } } DWORD dw2 = ::GetTickCount(); if (pulTimeSpent != NULL) *pulTimeSpent = dw2 - dw1; 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; }
（3）main.cpp
#include <iostream>//#define _CRT_SECURE_NO_WARNINGS #define _WINSOCK_DEPRECATED_NO_WARNINGS #include <stdio.h> #include "CDNSLookup.h" int main(void) { //char szDomainName[] = "www.baidu.com"; char szDomainName[] = "hopeex.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); //BOOL bRet = dnslookup.DNSLookup(inet_addr("221.228.255.1"), 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; }
2.2、只解析IPv4地址的精简版代码
（1）dms_z.h
#pragma once // C++实现DNS域名解析 - Snser - 博客园.html (https://www.cnblogs.com/snser/p/4101729.html) #define _CRT_SECURE_NO_WARNINGS #define _WINSOCK_DEPRECATED_NO_WARNINGS //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 <winsock2.h> #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 DnsLookup { public: DnsLookup(); ~DnsLookup(); ULONG LookupIPv4(const char* pcDnsServerIP, char *szDomainName, ULONG ulTimeout = 1000 * 5); private: BOOL Init(); BOOL UnInit(); BOOL LookupCore(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIP, ULONG ulTimeOut, ULONG *pulTimeSpent); BOOL SendDNSRequest(sockaddr_in sockAddrDNSServer, char *szDomainName); BOOL RecvDNSResponse(sockaddr_in sockAddrDNSServer, std::vector<ULONG> *pveculIP, ULONG ulTimeOut, ULONG *pulTimeSpent); BOOL EncodeDotStr(char *szDotStr, char *szEncodedStr, USHORT nEncodedStrSize); BOOL DecodeDotStr(char *szEncodedStr, USHORT *pusEncodedStrLen, char *szDotStr, USHORT nDotStrSize, char *szPacketStartPos = NULL); private: BOOL m_bIsInitOK; SOCKET m_sock; };
（2）dns_z.cpp
#include "dns_z.h" #include <stdio.h> #include <string.h> DnsLookup::DnsLookup() : m_bIsInitOK(FALSE), m_sock(INVALID_SOCKET) { m_bIsInitOK = Init(); } DnsLookup::~DnsLookup() { UnInit(); } ULONG DnsLookup::LookupIPv4(const char* pcDnsServerIP, char *szDomainName, ULONG ulTimeout) { std::vector<ULONG> veculIP; ULONG ulTimeSpent; if (LookupCore(inet_addr(pcDnsServerIP), szDomainName, &veculIP, ulTimeout, &ulTimeSpent)) { if (veculIP.size() > 0) return veculIP.front(); } return 0; } BOOL DnsLookup::Init() { WSADATA wsaData; if (WSAStartup(MAKEWORD(2, 2), &wsaData) == SOCKET_ERROR) { printf("WSAStartup(...) err : %d\n", ::GetLastError()); return FALSE; } if ((m_sock = socket(AF_INET, SOCK_DGRAM, 0)) == INVALID_SOCKET) { printf("socket(...) err : %d\n", ::GetLastError()); return FALSE; } return TRUE; } BOOL DnsLookup::UnInit() { WSACleanup(); return TRUE; } BOOL DnsLookup::LookupCore(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIP, ULONG ulTimeOut, ULONG *pulTimeSpent) { if (m_bIsInitOK == FALSE || szDomainName == NULL) return FALSE; //配置SOCKET sockaddr_in addrDnsServer; addrDnsServer.sin_family = AF_INET; addrDnsServer.sin_addr.s_addr = ulDNSServerIP; addrDnsServer.sin_port = htons(DNS_PORT); //DNS查询与解析 if (!SendDNSRequest(addrDnsServer, szDomainName)) return FALSE; if (!RecvDNSResponse(addrDnsServer, pveculIP, ulTimeOut, pulTimeSpent)) return FALSE; return TRUE; } BOOL DnsLookup::SendDNSRequest(sockaddr_in _addrDnsServer, char *_szDomainName) { char bufSend[DNS_PACKET_MAX_SIZE] = { 0 }; char* pcSend = &bufSend[0]; //填充DNS查询报文头部 DnsHeader *pDnsHdr = (DnsHeader*)pcSend; pDnsHdr->usTransID = (USHORT)GetCurrentProcessId(); pDnsHdr->usFlags = htons(0x0100); pDnsHdr->usQuestionCount = htons(0x0001); pDnsHdr->usAnswerCount = 0x0000; pDnsHdr->usAuthorityCount = 0x0000; pDnsHdr->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(pcSend += sizeof(DnsHeader), szEncodedDomainName, nEncodedDomainNameLen); memcpy(pcSend += nEncodedDomainNameLen, (char*)(&usQType), DNS_TYPE_SIZE); memcpy(pcSend += 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, bufSend, nDNSPacketSize, 0, (sockaddr*)&_addrDnsServer, sizeof(_addrDnsServer)) == SOCKET_ERROR) { return FALSE; } return TRUE; } BOOL DnsLookup::RecvDNSResponse(sockaddr_in _addrDnsServer, std::vector<ULONG> *_pveculIP, ULONG _ulTimeOut, ULONG *_pulTimeSpent) { if (_pveculIP != NULL) _pveculIP->clear(); if (setsockopt(m_sock, SOL_SOCKET, SO_RCVTIMEO, (char*)&_ulTimeOut, sizeof(_ulTimeOut)) == SOCKET_ERROR) { printf("setsockopt(...) err : %d\n", ::GetLastError()); return FALSE; } char bufRecv[1024] = { 0 }; char szDotName[128] = { 0 }; USHORT nEncodedNameLen = 0; int iAddrDnsServer = sizeof(_addrDnsServer); DWORD dw1 = ::GetTickCount(); //接收响应报文 if (recvfrom(m_sock, bufRecv, sizeof(bufRecv), 0, (struct sockaddr*)&_addrDnsServer, &iAddrDnsServer) == SOCKET_ERROR) { //WSAETIMEDOUT printf("DNS recvfrom(...) failed : %d\n", ::GetLastError()); return FALSE; } DnsHeader *pDnsHdr = (DnsHeader*)bufRecv; USHORT usQuestionCount = 0; USHORT usAnswerCount = 0; if (pDnsHdr->usTransID == (USHORT)GetCurrentProcessId() && (ntohs(pDnsHdr->usFlags) & 0xfb7f) == 0x8100 //RFC1035 4.1.1(Header section format) && (usQuestionCount = ntohs(pDnsHdr->usQuestionCount)) >= 0 && (usAnswerCount = ntohs(pDnsHdr->usAnswerCount)) > 0) { char *pDnsData = bufRecv + 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), bufRecv)) { 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 && _pveculIP != NULL) { ULONG ulIP = *(ULONG*)(pDnsData); _pveculIP->push_back(ulIP); } pDnsData += (usAnswerDataLen); } } DWORD dw2 = ::GetTickCount(); if (_pulTimeSpent != NULL) *_pulTimeSpent = dw2 - dw1; 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 DnsLookup::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 DnsLookup::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; }
（3）main.cpp
//#define _CRT_SECURE_NO_WARNINGS #define _WINSOCK_DEPRECATED_NO_WARNINGS #include <stdio.h> #include "dns_z.h" int main(void) { //char szDomainName[] = "www.baidu.com"; char szDomainName[] = "hopeex.com"; DnsLookup dnslookup; ULONG ul = dnslookup.LookupIPv4("114.114.114.114", szDomainName, 1000); //BOOL bRet = dnslookup.DNSLookup(inet_addr("221.228.255.1"), szDomainName, &vecstrIPList, &vecCNameList, 1000, &ulTimeSpent); in_addr* pAddr = (in_addr*)&ul; printf("%s\n", inet_ntoa(*pAddr)); return 0; }
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