C++如何实现DNS域名解析

2020-05-23 14:16:41

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这片文章介绍了C++如何实现DNS域名解析，还有对相关技术的介绍，代码很详细,需要的朋友可以参考下

一、概述

现在来搞定DNS域名解析，其实这是前面一篇文章C++实现Ping里面的遗留问题，要干的活是ping的过程中画红线的部分：

cmd下域名解析的命令是nslookup，比如“nslookupwww.baidu.com”的结果如下：

其中，Address返回的就是www.baidu.com对应的IP地址，这个可能有多个

Alias指别名，也就是说www.baidu.com是www.a.shifen.com的别名，而www.a.shifen.com则是www.baidu.com的规范名(Canonical Name，CName)，具体参考RFC1035 3.2.2 & wikipedia

二、实现结果预览

先看一下最终搞成了什么样子

输入：域名字符串

输出：IP列表、CName列表、DNS查询所用时间

三、相关技术

3.1、UDP or TCP ? (RFC1035 4.2)

UDP：DNS查询和回复采用低开销高性能的UDP，端口号为53。

TCP：辅助DNS服务器从主DNS服务器拉取最新数据时，采用可靠的TCP传输，端口号也为53。

我们这里做DNS查询采用UDP，53端口。

3.2、DNS查询/回复包头部解析 (RFC1035 4.1.1)

重点介绍一下我们关心的部分：

ID(16bits)：标识符，一般填入本进程的标识符

QR(1bits)：标志位，查询包为0，回复包为1

Opcode(4bits)：查询的种类，标准查询为0

QDCOUNT(16bits)：DNS查询/回复包数据部分Question字段的个数

ANCOUNT(16bits)：DNS查询/回复包数据部分Answer字段的个数

3.2、DNS查询/回复包数据部分解析 (RFC1035 4.1.2 & 4.1.3)

查询/回复包的数据部分依次为QDCOUNT个Question字段、ANCOUNT个Answer字段....

对于任意字段，其格式如下：

Name(不定长)：域名，这部分的格式比较复杂，后面单独说。

TYPE(16bits)：查询类型/回复包RDATA类型，比如TYPE=1表示主机IP地址、TYPE=5表示CNAME，详见RFC1035 3.2.2

CLASS(16bits)：类，一般情况下CLASS=1表示Internet，详见RFC1035 3.2.4

TTL(32bits，仅回复包)：生存时间

RDLENGTH(16bits，仅回复包)：RDATA部分的字节数

RDATA(不定长，仅回复包)：资源数据，具体格式取决于TYPE和CLASS，比如TYPE=1、CLASS=1时，RDATA为四个字节的IP地址

3.3、Name解析&消息压缩

3.3.1、一般格式 (RFC1035 4.1.2)

标签内容长度(1个字节) + 标签内容，以标签内容长度0作为Name的结束符，例如：

3.3.2、消息压缩格式 (RFC1035 4.1.4)

如果标签内容长度的二进制前两位是11，则表示消息压缩。

此时，标签内容长度1个字节+后面的1个字节一共16位，后14位表示相对DNS包起始地址的偏移(Byte)，例如：

上述例子中，DNS包起始地址为0x0000，c0 13的二进制为11000000 00010003，即跳转偏移为0x13个字节，对应的数据为03 63 6f 6d 00。

RFC1035中规定，支持的消息压缩规则为：

①以内容长度0结尾的标签序列

②偏移指针

③标签序列+偏移指针

也就是说，Name的消息压缩要求偏移指针必须在Name的尾部，且不支持同一级存在多个偏移指针(偏移指针序列)，

但Name的消息压缩支持嵌套的偏移指针，即指针指向的偏移位置仍然是以偏移指针结尾的数据

四、代码实现

#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;

}