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Ping的C++实现
这是一个老话题了,但是我刚学会...
我们的目的是实现这么个东西:
之所以用红框框一下是因为,从baidu.com到123.125.114.144的过程是DNS解析,我们暂时先实现ping的部分。
基础知识
ping的过程是向目的IP发送一个type=8的ICMP响应请求报文,目标主机收到这个报文之后,会向源IP(发送方,我)回复一个type=0的ICMP响应应答报文。
那上面的字节、往访时间、TTL之类的信息又是从哪来的呢?这取决于IP和ICMP的头部。
IP头部:
头部内容有点多,我们关心的只有以下几个:
IHL:首部长度。因为IP的头部不是定长的,所以需要这个信息进行IP包的解析,从而找到Data字段的起始点。
Time to Live:生存时间,这个就是TTL了。
Data:这部分是IP包的数据,也就是ICMP的报文内容。
ICMP响应请求/应答报文头部:
Type:类型,type=8表示响应请求报文,type=0表示响应应答报文。
Code:代码,与type组合,表示具体的信息,参考这里。
Checksum:检验和,这个是整个ICMP报文的检验和,包括Type、Code、...、Data。
Identifier:标识符,这个一般填入本进程的标识符。
Sequence Number:序号
Data:数据部分
上面是标准的ICMP报文,一般而言,统计ping的往返时间的做法是,在ICMP报文的Data区域写入4个字节的时间戳。
在收到应答报文时,取出这个时间戳与当前的时间对比即可。
代码实现
1 #pragma once 2 3 #include <windows.h> 4 5 //这里需要导入库 Ws2_32.lib,在不同的IDE下可能不太一样 6 //#pragma comment(lib, "Ws2_32.lib") 7 8 #define DEF_PACKET_SIZE 32 9 #define ECHO_REQUEST 810 #define ECHO_REPLY 011 12 struct IPHeader13 {14 BYTE m_byVerHLen; //4位版本+4位首部长度15 BYTE m_byTOS; //服务类型16 USHORT m_usTotalLen; //总长度17 USHORT m_usID; //标识18 USHORT m_usFlagFragOffset; //3位标志+13位片偏移19 BYTE m_byTTL; //TTL20 BYTE m_byProtocol; //协议21 USHORT m_usHChecksum; //首部检验和22 ULONG m_ulSrcIP; //源IP地址23 ULONG m_ulDestIP; //目的IP地址24 };25 26 struct ICMPHeader27 { 28 BYTE m_byType; //类型29 BYTE m_byCode; //代码30 USHORT m_usChecksum; //检验和 31 USHORT m_usID; //标识符32 USHORT m_usSeq; //序号33 ULONG m_ulTimeStamp; //时间戳(非标准ICMP头部)34 };35 36 struct PingReply37 {38 USHORT m_usSeq;39 DWORD m_dwRoundTripTime;40 DWORD m_dwBytes;41 DWORD m_dwTTL;42 };43 44 class CPing45 {46 public:47 CPing();48 ~CPing();49 BOOL Ping(DWORD dwDestIP, PingReply *pPingReply = NULL, DWORD dwTimeout = 2000);50 BOOL Ping(char *szDestIP, PingReply *pPingReply = NULL, DWORD dwTimeout = 2000);51 private:52 BOOL PingCore(DWORD dwDestIP, PingReply *pPingReply, DWORD dwTimeout);53 USHORT CalCheckSum(USHORT *pBuffer, int nSize);54 ULONG GetTickCountCalibrate();55 private:56 SOCKET m_sockRaw; 57 WSAEVENT m_event;58 USHORT m_usCurrentProcID;59 char *m_szICMPData;60 BOOL m_bIsInitSucc;61 private:62 static USHORT s_usPacketSeq;63 };
1 #include "ping.h" 2 3 USHORT CPing::s_usPacketSeq = 0; 4 5 CPing::CPing() : 6 m_szICMPData(NULL), 7 m_bIsInitSucc(FALSE) 8 { 9 WSADATA WSAData; 10 WSAStartup(MAKEWORD(1, 1), &WSAData); 11 12 m_event = WSACreateEvent(); 13 m_usCurrentProcID = (USHORT)GetCurrentProcessId(); 14 15 if ((m_sockRaw = WSASocket(AF_INET, SOCK_RAW, IPPROTO_ICMP, NULL, 0, 0)) != SOCKET_ERROR) 16 { 17 WSAEventSelect(m_sockRaw, m_event, FD_READ); 18 m_bIsInitSucc = TRUE; 19 20 m_szICMPData = http://www.mamicode.com/(char*)malloc(DEF_PACKET_SIZE + sizeof(ICMPHeader)); 21 22 if (m_szICMPData =http://www.mamicode.com/= NULL) 23 { 24 m_bIsInitSucc = FALSE; 25 } 26 } 27 } 28 29 CPing::~CPing() 30 { 31 WSACleanup(); 32 33 if (NULL != m_szICMPData) 34 { 35 free(m_szICMPData); 36 m_szICMPData =http://www.mamicode.com/ NULL; 37 } 38 } 39 40 BOOL CPing::Ping(DWORD dwDestIP, PingReply *pPingReply, DWORD dwTimeout) 41 { 42 return PingCore(dwDestIP, pPingReply, dwTimeout); 43 } 44 45 BOOL CPing::Ping(char *szDestIP, PingReply *pPingReply, DWORD dwTimeout) 46 { 47 if (NULL != szDestIP) 48 { 49 return PingCore(inet_addr(szDestIP), pPingReply, dwTimeout); 50 } 51 return FALSE; 52 } 53 54 BOOL CPing::PingCore(DWORD dwDestIP, PingReply *pPingReply, DWORD dwTimeout) 55 { 56 //判断初始化是否成功 57 if (!m_bIsInitSucc) 58 { 59 return FALSE; 60 } 61 62 //配置SOCKET 63 sockaddr_in sockaddrDest; 64 sockaddrDest.sin_family = AF_INET; 65 sockaddrDest.sin_addr.s_addr = dwDestIP; 66 int nSockaddrDestSize = sizeof(sockaddrDest); 67 68 //构建ICMP包 69 int nICMPDataSize = DEF_PACKET_SIZE + sizeof(ICMPHeader); 70 ULONG ulSendTimestamp = GetTickCountCalibrate(); 71 USHORT usSeq = ++s_usPacketSeq; 72 memset(m_szICMPData, 0, nICMPDataSize); 73 ICMPHeader *pICMPHeader = (ICMPHeader*)m_szICMPData; 74 pICMPHeader->m_byType = ECHO_REQUEST; 75 pICMPHeader->m_byCode = 0; 76 pICMPHeader->m_usID = m_usCurrentProcID; 77 pICMPHeader->m_usSeq = usSeq; 78 pICMPHeader->m_ulTimeStamp = ulSendTimestamp; 79 pICMPHeader->m_usChecksum = CalCheckSum((USHORT*)m_szICMPData, nICMPDataSize); 80 81 //发送ICMP报文 82 if (sendto(m_sockRaw, m_szICMPData, nICMPDataSize, 0, (struct sockaddr*)&sockaddrDest, nSockaddrDestSize) == SOCKET_ERROR) 83 { 84 return FALSE; 85 } 86 87 //判断是否需要接收相应报文 88 if (pPingReply == NULL) 89 { 90 return TRUE; 91 } 92 93 char recvbuf[256] = {"\0"}; 94 while (TRUE) 95 { 96 //接收响应报文 97 if (WSAWaitForMultipleEvents(1, &m_event, FALSE, 100, FALSE) != WSA_WAIT_TIMEOUT) 98 { 99 WSANETWORKEVENTS netEvent;100 WSAEnumNetworkEvents(m_sockRaw, m_event, &netEvent);101 102 if (netEvent.lNetworkEvents & FD_READ)103 {104 ULONG nRecvTimestamp = GetTickCountCalibrate();105 int nPacketSize = recvfrom(m_sockRaw, recvbuf, 256, 0, (struct sockaddr*)&sockaddrDest, &nSockaddrDestSize);106 if (nPacketSize != SOCKET_ERROR)107 {108 IPHeader *pIPHeader = (IPHeader*)recvbuf;109 USHORT usIPHeaderLen = (USHORT)((pIPHeader->m_byVerHLen & 0x0f) * 4);110 ICMPHeader *pICMPHeader = (ICMPHeader*)(recvbuf + usIPHeaderLen);111 112 if (pICMPHeader->m_usID == m_usCurrentProcID //是当前进程发出的报文113 && pICMPHeader->m_byType == ECHO_REPLY //是ICMP响应报文114 && pICMPHeader->m_usSeq == usSeq //是本次请求报文的响应报文115 )116 {117 pPingReply->m_usSeq = usSeq;118 pPingReply->m_dwRoundTripTime = nRecvTimestamp - pICMPHeader->m_ulTimeStamp;119 pPingReply->m_dwBytes = nPacketSize - usIPHeaderLen - sizeof(ICMPHeader);120 pPingReply->m_dwTTL = pIPHeader->m_byTTL;121 return TRUE;122 }123 }124 }125 }126 //超时127 if (GetTickCountCalibrate() - ulSendTimestamp >= dwTimeout)128 {129 return FALSE;130 }131 }132 }133 134 USHORT CPing::CalCheckSum(USHORT *pBuffer, int nSize)135 {136 unsigned long ulCheckSum=0; 137 while(nSize > 1) 138 { 139 ulCheckSum += *pBuffer++; 140 nSize -= sizeof(USHORT); 141 }142 if(nSize ) 143 { 144 ulCheckSum += *(UCHAR*)pBuffer; 145 } 146 147 ulCheckSum = (ulCheckSum >> 16) + (ulCheckSum & 0xffff); 148 ulCheckSum += (ulCheckSum >>16); 149 150 return (USHORT)(~ulCheckSum); 151 }152 153 ULONG CPing::GetTickCountCalibrate()154 {155 static ULONG s_ulFirstCallTick = 0;156 static LONGLONG s_ullFirstCallTickMS = 0;157 158 SYSTEMTIME systemtime;159 FILETIME filetime;160 GetLocalTime(&systemtime); 161 SystemTimeToFileTime(&systemtime, &filetime);162 LARGE_INTEGER liCurrentTime;163 liCurrentTime.HighPart = filetime.dwHighDateTime;164 liCurrentTime.LowPart = filetime.dwLowDateTime;165 LONGLONG llCurrentTimeMS = liCurrentTime.QuadPart / 10000;166 167 if (s_ulFirstCallTick == 0)168 {169 s_ulFirstCallTick = GetTickCount();170 }171 if (s_ullFirstCallTickMS == 0)172 {173 s_ullFirstCallTickMS = llCurrentTimeMS;174 }175 176 return s_ulFirstCallTick + (ULONG)(llCurrentTimeMS - s_ullFirstCallTickMS);177 }
1 #include <windows.h> 2 #include <stdio.h> 3 #include "ping.h" 4 5 int main(void) 6 { 7 CPing objPing; 8 9 char *szDestIP = "123.125.114.144";10 PingReply reply;11 12 printf("Pinging %s with %d bytes of data:\n", szDestIP, DEF_PACKET_SIZE);13 while (TRUE)14 {15 objPing.Ping(szDestIP, &reply);16 printf("Reply from %s: bytes=%ld time=%ldms TTL=%ld\n", szDestIP, reply.m_dwBytes, reply.m_dwRoundTripTime, reply.m_dwTTL);17 Sleep(500);18 }19 20 return 0;21 }
执行结果
附录:如何计算校验和
ICMP中校验和的计算算法为:
1、将校验和字段置为0
2、把需校验的数据看成以16位为单位的数字组成,依次进行二进制反码求和
3、把得到的结果存入校验和字段中
所谓二进制反码求和,就是:
1、将源数据转成反码
2、0+0=0 0+1=1 1+1=0进1
3、若最高位相加后产生进位,则最后得到的结果要加1
在实际实现的过程中,比较常见的代码写法是:
1、将校验和字段置为0
2、把需校验的数据看成以16位为单位的数字组成,依次进行求和,并存到32位的整型中
3、把求和结果中的高16位(进位)加到低16位上,如果还有进位,重复第3步[实际上,这一步最多会执行2次]
4、将这个32位的整型按位取反,并强制转换为16位整型(截断)后返回
Ping的C++实现