C++实现DNS域名解析

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“nslookup www.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

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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

 

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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

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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;
};

#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] = {''};
        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] = {''};
    char szDotName[128] = {''};
    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 "x03wwwx05baidux03com"
 * 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 "x03wwwx05baidux03comx00" to "www.baidu.com"
 * 0x0000 03 77 77 77 05 62 61 69 64 75 03 63 6f 6d 00 ff
 * convert "x03wwwx05baiduxc0x13" 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] = '';
    *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);
}

#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):
", szDomainName);
    if (!bRet)
    {
        printf("timeout!
");
        return -1;
    }

    for (int i = 0; i != veculIPList.size(); ++i)
    {
        printf("IP%d(ULONG) = %u
", i + 1, veculIPList[i]);
    }
    for (int i = 0; i != vecstrIPList.size(); ++i)
    {
        printf("IP%d(string) = %s
", i + 1, vecstrIPList[i].c_str());
    }
    for (int i = 0; i != vecCNameList.size(); ++i)
    {
        printf("CName%d = %s
", i + 1, vecCNameList[i].c_str());
    }
    printf("time spent = %ums
", ulTimeSpent);
    
    return 0;
}

 [转载请保留本文地址：http://www.cnblogs.com/goagent/p/4101729.html]