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
1 #pragma once 2 3 //这里需要导入库 Ws2_32.lib，在不同的IDE下可能不太一样 4 //#pragma comment(lib, "Ws2_32.lib") 5 6 #include <windows.h> 7 #include <string> 8 #include <vector> 9 10 #define MAX_DOMAINNAME_LEN 255 11 #define DNS_PORT 53 12 #define DNS_TYPE_SIZE 2 13 #define DNS_CLASS_SIZE 2 14 #define DNS_TTL_SIZE 4 15 #define DNS_DATALEN_SIZE 2 16 #define DNS_TYPE_A 0x0001 //1 a host address 17 #define DNS_TYPE_CNAME 0x0005 //5 the canonical name for an alias 18 #define DNS_PACKET_MAX_SIZE (sizeof(DNSHeader) + MAX_DOMAINNAME_LEN + DNS_TYPE_SIZE + DNS_CLASS_SIZE) 19 20 struct DNSHeader 21 { 22 USHORT usTransID; //标识符 23 USHORT usFlags; //各种标志位 24 USHORT usQuestionCount; //Question字段个数 25 USHORT usAnswerCount; //Answer字段个数 26 USHORT usAuthorityCount; //Authority字段个数 27 USHORT usAdditionalCount; //Additional字段个数 28 }; 29 30 class CDNSLookup 31 { 32 public: 33 CDNSLookup(); 34 ~CDNSLookup(); 35 36 BOOL DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList = NULL, std::vector<std::string> *pvecstrCNameList = NULL, ULONG ulTimeout = 1000, ULONG *pulTimeSpent = NULL); 37 BOOL DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<std::string> *pvecstrIPList = NULL, std::vector<std::string> *pvecstrCNameList = NULL, ULONG ulTimeout = 1000, ULONG *pulTimeSpent = NULL); 38 39 private: 40 BOOL Init(); 41 BOOL UnInit(); 42 BOOL DNSLookupCore(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent); 43 BOOL SendDNSRequest(sockaddr_in sockAddrDNSServer, char *szDomainName); 44 BOOL RecvDNSResponse(sockaddr_in sockAddrDNSServer, ULONG ulTimeout, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG *pulTimeSpent); 45 BOOL EncodeDotStr(char *szDotStr, char *szEncodedStr, USHORT nEncodedStrSize); 46 BOOL DecodeDotStr(char *szEncodedStr, USHORT *pusEncodedStrLen, char *szDotStr, USHORT nDotStrSize, char *szPacketStartPos = NULL); 47 ULONG GetTickCountCalibrate(); 48 49 private: 50 BOOL m_bIsInitOK; 51 SOCKET m_sock; 52 WSAEVENT m_event; 53 USHORT m_usCurrentProcID; 54 char *m_szDNSPacket; 55 };
1 #include "DNSLookup.h" 2 #include <stdio.h> 3 #include <string.h> 4 5 CDNSLookup::CDNSLookup() : 6 m_bIsInitOK(FALSE), 7 m_sock(INVALID_SOCKET), 8 m_szDNSPacket(NULL) 9 { 10 m_bIsInitOK = Init(); 11 } 12 13 CDNSLookup::~CDNSLookup() 14 { 15 UnInit(); 16 } 17 18 BOOL CDNSLookup::DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent) 19 { 20 return DNSLookupCore(ulDNSServerIP, szDomainName, pveculIPList, pvecstrCNameList, ulTimeout, pulTimeSpent); 21 } 22 23 BOOL CDNSLookup::DNSLookup(ULONG ulDNSServerIP, char *szDomainName, std::vector<std::string> *pvecstrIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent) 24 { 25 std::vector<ULONG> *pveculIPList = NULL; 26 if (pvecstrIPList != NULL) 27 { 28 std::vector<ULONG> veculIPList; 29 pveculIPList = &veculIPList; 30 } 31 32 BOOL bRet = DNSLookupCore(ulDNSServerIP, szDomainName, pveculIPList, pvecstrCNameList, ulTimeout, pulTimeSpent); 33 34 if (bRet) 35 { 36 pvecstrIPList->clear(); 37 char szIP[16] = {'\0'}; 38 for (std::vector<ULONG>::iterator iter = pveculIPList->begin(); iter != pveculIPList->end(); ++iter) 39 { 40 BYTE *pbyIPSegment = (BYTE*)(&(*iter)); 41 //sprintf_s(szIP, 16, "%d.%d.%d.%d", pbyIPSegment[0], pbyIPSegment[1], pbyIPSegment[2], pbyIPSegment[3]); 42 sprintf(szIP, "%d.%d.%d.%d", pbyIPSegment[0], pbyIPSegment[1], pbyIPSegment[2], pbyIPSegment[3]); 43 pvecstrIPList->push_back(szIP); 44 } 45 } 46 47 return bRet; 48 } 49 50 51 BOOL CDNSLookup::Init() 52 { 53 WSADATA wsaData; 54 if (WSAStartup(MAKEWORD(2, 2), &wsaData) == SOCKET_ERROR) 55 { 56 return FALSE; 57 } 58 59 if ((m_sock = socket(AF_INET, SOCK_DGRAM, 0)) == INVALID_SOCKET) 60 { 61 return FALSE; 62 } 63 64 m_event = WSACreateEvent(); 65 WSAEventSelect(m_sock, m_event, FD_READ); 66 67 m_szDNSPacket = new (std::nothrow) char[DNS_PACKET_MAX_SIZE]; 68 if (m_szDNSPacket == NULL) 69 { 70 return FALSE; 71 } 72 73 m_usCurrentProcID = (USHORT)GetCurrentProcessId(); 74 75 return TRUE; 76 } 77 78 BOOL CDNSLookup::UnInit() 79 { 80 WSACleanup(); 81 82 if (m_szDNSPacket != NULL) 83 { 84 delete [] m_szDNSPacket; 85 } 86 87 return TRUE; 88 } 89 90 BOOL CDNSLookup::DNSLookupCore(ULONG ulDNSServerIP, char *szDomainName, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG ulTimeout, ULONG *pulTimeSpent) 91 { 92 if (m_bIsInitOK == FALSE || szDomainName == NULL) 93 { 94 return FALSE; 95 } 96 97 //配置SOCKET 98 sockaddr_in sockAddrDNSServer; 99 sockAddrDNSServer.sin_family = AF_INET; 100 sockAddrDNSServer.sin_addr.s_addr = ulDNSServerIP; 101 sockAddrDNSServer.sin_port = htons( DNS_PORT ); 102 103 //DNS查询与解析 104 if (!SendDNSRequest(sockAddrDNSServer, szDomainName) 105 || !RecvDNSResponse(sockAddrDNSServer, ulTimeout, pveculIPList, pvecstrCNameList, pulTimeSpent)) 106 { 107 return FALSE; 108 } 109 110 return TRUE; 111 } 112 113 BOOL CDNSLookup::SendDNSRequest(sockaddr_in sockAddrDNSServer, char *szDomainName) 114 { 115 char *pWriteDNSPacket = m_szDNSPacket; 116 memset(pWriteDNSPacket, 0, DNS_PACKET_MAX_SIZE); 117 118 //填充DNS查询报文头部 119 DNSHeader *pDNSHeader = (DNSHeader*)pWriteDNSPacket; 120 pDNSHeader->usTransID = m_usCurrentProcID; 121 pDNSHeader->usFlags = htons(0x0100); 122 pDNSHeader->usQuestionCount = htons(0x0001); 123 pDNSHeader->usAnswerCount = 0x0000; 124 pDNSHeader->usAuthorityCount = 0x0000; 125 pDNSHeader->usAdditionalCount = 0x0000; 126 127 //设置DNS查询报文内容 128 USHORT usQType = htons(0x0001); 129 USHORT usQClass = htons(0x0001); 130 USHORT nDomainNameLen = strlen(szDomainName); 131 char *szEncodedDomainName = (char *)malloc(nDomainNameLen + 2); 132 if (szEncodedDomainName == NULL) 133 { 134 return FALSE; 135 } 136 if (!EncodeDotStr(szDomainName, szEncodedDomainName, nDomainNameLen + 2)) 137 { 138 return FALSE; 139 } 140 141 //填充DNS查询报文内容 142 USHORT nEncodedDomainNameLen = strlen(szEncodedDomainName) + 1; 143 memcpy(pWriteDNSPacket += sizeof(DNSHeader), szEncodedDomainName, nEncodedDomainNameLen); 144 memcpy(pWriteDNSPacket += nEncodedDomainNameLen, (char*)(&usQType), DNS_TYPE_SIZE); 145 memcpy(pWriteDNSPacket += DNS_TYPE_SIZE, (char*)(&usQClass), DNS_CLASS_SIZE); 146 free (szEncodedDomainName); 147 148 //发送DNS查询报文 149 USHORT nDNSPacketSize = sizeof(DNSHeader) + nEncodedDomainNameLen + DNS_TYPE_SIZE + DNS_CLASS_SIZE; 150 if (sendto(m_sock, m_szDNSPacket, nDNSPacketSize, 0, (sockaddr*)&sockAddrDNSServer, sizeof(sockAddrDNSServer)) == SOCKET_ERROR) 151 { 152 return FALSE; 153 } 154 155 return TRUE; 156 } 157 158 BOOL CDNSLookup::RecvDNSResponse(sockaddr_in sockAddrDNSServer, ULONG ulTimeout, std::vector<ULONG> *pveculIPList, std::vector<std::string> *pvecstrCNameList, ULONG *pulTimeSpent) 159 { 160 ULONG ulSendTimestamp = GetTickCountCalibrate(); 161 162 if (pveculIPList != NULL) 163 { 164 pveculIPList->clear(); 165 } 166 if (pvecstrCNameList != NULL) 167 { 168 pvecstrCNameList->clear(); 169 } 170 171 char recvbuf[1024] = {'\0'}; 172 char szDotName[128] = {'\0'}; 173 USHORT nEncodedNameLen = 0; 174 175 while (TRUE) 176 { 177 if (WSAWaitForMultipleEvents(1, &m_event, FALSE, 100, FALSE) != WSA_WAIT_TIMEOUT) 178 { 179 WSANETWORKEVENTS netEvent; 180 WSAEnumNetworkEvents(m_sock, m_event, &netEvent); 181 182 if (netEvent.lNetworkEvents & FD_READ) 183 { 184 ULONG ulRecvTimestamp = GetTickCountCalibrate(); 185 int nSockaddrDestSize = sizeof(sockAddrDNSServer); 186 187 //接收响应报文 188 if (recvfrom(m_sock, recvbuf, 1024, 0, (struct sockaddr*)&sockAddrDNSServer, &nSockaddrDestSize) != SOCKET_ERROR) 189 { 190 DNSHeader *pDNSHeader = (DNSHeader*)recvbuf; 191 USHORT usQuestionCount = 0; 192 USHORT usAnswerCount = 0; 193 194 if (pDNSHeader->usTransID == m_usCurrentProcID 195 && (ntohs(pDNSHeader->usFlags) & 0xfb7f) == 0x8100 //RFC1035 4.1.1(Header section format) 196 && (usQuestionCount = ntohs(pDNSHeader->usQuestionCount)) >= 0 197 && (usAnswerCount = ntohs(pDNSHeader->usAnswerCount)) > 0) 198 { 199 char *pDNSData = recvbuf + sizeof(DNSHeader); 200 201 //解析Question字段 202 for (int q = 0; q != usQuestionCount; ++q) 203 { 204 if (!DecodeDotStr(pDNSData, &nEncodedNameLen, szDotName, sizeof(szDotName))) 205 { 206 return FALSE; 207 } 208 pDNSData += (nEncodedNameLen + DNS_TYPE_SIZE + DNS_CLASS_SIZE); 209 } 210 211 //解析Answer字段 212 for (int a = 0; a != usAnswerCount; ++a) 213 { 214 if (!DecodeDotStr(pDNSData, &nEncodedNameLen, szDotName, sizeof(szDotName), recvbuf)) 215 { 216 return FALSE; 217 } 218 pDNSData += nEncodedNameLen; 219 220 USHORT usAnswerType = ntohs(*(USHORT*)(pDNSData)); 221 USHORT usAnswerClass = ntohs(*(USHORT*)(pDNSData + DNS_TYPE_SIZE)); 222 ULONG usAnswerTTL = ntohl(*(ULONG*)(pDNSData + DNS_TYPE_SIZE + DNS_CLASS_SIZE)); 223 USHORT usAnswerDataLen = ntohs(*(USHORT*)(pDNSData + DNS_TYPE_SIZE + DNS_CLASS_SIZE + DNS_TTL_SIZE)); 224 pDNSData += (DNS_TYPE_SIZE + DNS_CLASS_SIZE + DNS_TTL_SIZE + DNS_DATALEN_SIZE); 225 226 if (usAnswerType == DNS_TYPE_A && pveculIPList != NULL) 227 { 228 ULONG ulIP = *(ULONG*)(pDNSData); 229 pveculIPList->push_back(ulIP); 230 } 231 else if (usAnswerType == DNS_TYPE_CNAME && pvecstrCNameList != NULL) 232 { 233 if (!DecodeDotStr(pDNSData, &nEncodedNameLen, szDotName, sizeof(szDotName), recvbuf)) 234 { 235 return FALSE; 236 } 237 pvecstrCNameList->push_back(szDotName); 238 } 239 240 pDNSData += (usAnswerDataLen); 241 } 242 243 //计算DNS查询所用时间 244 if (pulTimeSpent != NULL) 245 { 246 *pulTimeSpent = ulRecvTimestamp - ulSendTimestamp; 247 } 248 249 break; 250 } 251 } 252 } 253 } 254 255 //超时退出 256 if (GetTickCountCalibrate() - ulSendTimestamp > ulTimeout) 257 { 258 *pulTimeSpent = ulTimeout + 1; 259 return FALSE; 260 } 261 } 262 263 return TRUE; 264 } 265 266 /* 267 * convert "www.baidu.com" to "\x03www\x05baidu\x03com" 268 * 0x0000 03 77 77 77 05 62 61 69 64 75 03 63 6f 6d 00 ff 269 */ 270 BOOL CDNSLookup::EncodeDotStr(char *szDotStr, char *szEncodedStr, USHORT nEncodedStrSize) 271 { 272 USHORT nDotStrLen = strlen(szDotStr); 273 274 if (szDotStr == NULL || szEncodedStr == NULL || nEncodedStrSize < nDotStrLen + 2) 275 { 276 return FALSE; 277 } 278 279 char *szDotStrCopy = new char[nDotStrLen + 1]; 280 //strcpy_s(szDotStrCopy, nDotStrLen + 1, szDotStr); 281 strcpy(szDotStrCopy, szDotStr); 282 283 char *pNextToken = NULL; 284 //char *pLabel = strtok_s(szDotStrCopy, ".", &pNextToken); 285 char *pLabel = strtok(szDotStrCopy, "."); 286 USHORT nLabelLen = 0; 287 USHORT nEncodedStrLen = 0; 288 while (pLabel != NULL) 289 { 290 if ((nLabelLen = strlen(pLabel)) != 0) 291 { 292 //sprintf_s(szEncodedStr + nEncodedStrLen, nEncodedStrSize - nEncodedStrLen, "%c%s", nLabelLen, pLabel); 293 sprintf(szEncodedStr + nEncodedStrLen, "%c%s", nLabelLen, pLabel); 294 nEncodedStrLen += (nLabelLen + 1); 295 } 296 //pLabel = strtok_s(NULL, ".", &pNextToken); 297 pLabel = strtok(NULL, "."); 298 } 299 300 delete [] szDotStrCopy; 301 302 return TRUE; 303 } 304 305 /* 306 * convert "\x03www\x05baidu\x03com\x00" to "www.baidu.com" 307 * 0x0000 03 77 77 77 05 62 61 69 64 75 03 63 6f 6d 00 ff 308 * convert "\x03www\x05baidu\xc0\x13" to "www.baidu.com" 309 * 0x0000 03 77 77 77 05 62 61 69 64 75 c0 13 ff ff ff ff 310 * 0x0010 ff ff ff 03 63 6f 6d 00 ff ff ff ff ff ff ff ff 311 */ 312 BOOL CDNSLookup::DecodeDotStr(char *szEncodedStr, USHORT *pusEncodedStrLen, char *szDotStr, USHORT nDotStrSize, char *szPacketStartPos) 313 { 314 if (szEncodedStr == NULL || pusEncodedStrLen == NULL || szDotStr == NULL) 315 { 316 return FALSE; 317 } 318 319 char *pDecodePos = szEncodedStr; 320 USHORT usPlainStrLen = 0; 321 BYTE nLabelDataLen = 0; 322 *pusEncodedStrLen = 0; 323 324 while ((nLabelDataLen = *pDecodePos) != 0x00) 325 { 326 if ((nLabelDataLen & 0xc0) == 0) //普通格式，LabelDataLen + Label 327 { 328 if (usPlainStrLen + nLabelDataLen + 1 > nDotStrSize) 329 { 330 return FALSE; 331 } 332 memcpy(szDotStr + usPlainStrLen, pDecodePos + 1, nLabelDataLen); 333 memcpy(szDotStr + usPlainStrLen + nLabelDataLen, ".", 1); 334 pDecodePos += (nLabelDataLen + 1); 335 usPlainStrLen += (nLabelDataLen + 1); 336 *pusEncodedStrLen += (nLabelDataLen + 1); 337 } 338 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 339 { 340 if (szPacketStartPos == NULL) 341 { 342 return FALSE; 343 } 344 USHORT usJumpPos = ntohs(*(USHORT*)(pDecodePos)) & 0x3fff; 345 USHORT nEncodeStrLen = 0; 346 if (!DecodeDotStr(szPacketStartPos + usJumpPos, &nEncodeStrLen, szDotStr + usPlainStrLen, nDotStrSize - usPlainStrLen, szPacketStartPos)) 347 { 348 return FALSE; 349 } 350 else 351 { 352 *pusEncodedStrLen += 2; 353 return TRUE; 354 } 355 } 356 } 357 358 szDotStr[usPlainStrLen - 1] = '\0'; 359 *pusEncodedStrLen += 1; 360 361 return TRUE; 362 } 363 364 ULONG CDNSLookup::GetTickCountCalibrate() 365 { 366 static ULONG s_ulFirstCallTick = 0; 367 static LONGLONG s_ullFirstCallTickMS = 0; 368 369 SYSTEMTIME systemtime; 370 FILETIME filetime; 371 GetLocalTime(&systemtime); 372 SystemTimeToFileTime(&systemtime, &filetime); 373 LARGE_INTEGER liCurrentTime; 374 liCurrentTime.HighPart = filetime.dwHighDateTime; 375 liCurrentTime.LowPart = filetime.dwLowDateTime; 376 LONGLONG llCurrentTimeMS = liCurrentTime.QuadPart / 10000; 377 378 if (s_ulFirstCallTick == 0) 379 { 380 s_ulFirstCallTick = GetTickCount(); 381 } 382 if (s_ullFirstCallTickMS == 0) 383 { 384 s_ullFirstCallTickMS = llCurrentTimeMS; 385 } 386 387 return s_ulFirstCallTick + (ULONG)(llCurrentTimeMS - s_ullFirstCallTickMS); 388 }
1 #include <stdio.h> 2 #include <windows.h> 3 #include "DNSLookup.h" 4 5 int main(void) 6 { 7 char szDomainName[] = "www.baidu.com"; 8 std::vector<ULONG> veculIPList; 9 std::vector<std::string> vecstrIPList; 10 std::vector<std::string> vecCNameList; 11 ULONG ulTimeSpent = 0; 12 CDNSLookup dnslookup; 13 BOOL bRet = dnslookup.DNSLookup(inet_addr("114.114.114.114"), szDomainName, &vecstrIPList, &vecCNameList, 1000, &ulTimeSpent); 14 15 printf("DNSLookup result (%s):\n", szDomainName); 16 if (!bRet) 17 { 18 printf("timeout!\n"); 19 return -1; 20 } 21 22 for (int i = 0; i != veculIPList.size(); ++i) 23 { 24 printf("IP%d(ULONG) = %u\n", i + 1, veculIPList[i]); 25 } 26 for (int i = 0; i != vecstrIPList.size(); ++i) 27 { 28 printf("IP%d(string) = %s\n", i + 1, vecstrIPList[i].c_str()); 29 } 30 for (int i = 0; i != vecCNameList.size(); ++i) 31 { 32 printf("CName%d = %s\n", i + 1, vecCNameList[i].c_str()); 33 } 34 printf("time spent = %ums\n", ulTimeSpent); 35 36 return 0; 37 }
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