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网络通讯中经常需要确定远程主机是否存活，以决定下一部进行的操作。可以直接使用ICMP协议来实现，但是要考虑许多协议细节，实现起来比较麻烦。Windows 自带的ICMP库里有现成的函数可以使用，只要在使用前填充相应的数据结构就可以了。 以下是要使用的数据结构。这些结构MSDN里有C形式的声明，这里给出的是Delphi的形式。
//用到的协议数据结构PIPOptionInfo = ^TIPOptionInfo; // IP 头选项TIPOptionInfo = packed recordTTL: Byte;//存活时间TOS: Byte;//Type of Service，请求类型Flags: Byte;//标志OptionsSize: Byte;//选项长度OptionsData: PChar;//选项数据end;PIcmpEchoReply = ^TIcmpEchoReply;TIcmpEchoReply = packed record // ICMP 返回信息Address: DWORD;//IP地址Status: DWORD;//状态RTT: DWORD;DataSize: Word;//数据长度Reserved: Word;//保留Data: Pointer;//数据Options: TIPOptionInfo;//选项区end;//动态库中的函数声明TIcmpCreateFile = function: THandle; stdcall; //创建ICMP句柄TIcmpCloseHandle = function(IcmpHandle: THandle): Boolean; stdcall; //关闭ICMP句柄TIcmpSendEcho = function(IcmpHandle:THandle; DestinationAddress:DWORD;RequestData:Pointer; RequestSize:Word; RequestOptions:PIPOptionInfo;ReplyBuffer:Pointer; ReplySize:DWord; Timeout:DWord):DWord; stdcall;//发送ICMP探测数据报//要用到的变量声明hICMPDll,hICMP:THandle;wsaData:TWSADATA;ICMPCreateFile:TICMPCreateFile;IcmpCloseHandle:TIcmpCloseHandle;IcmpSendEcho:TIcmpSendEcho;//destip:要探测的远程地址，形如 192.168.1.1procedure f_CheckOnline(destip:string); var IPOpt:TIPOptionInfo;// 发包的 IP 选项 IPAddr:DWORD; pReqData,pRevData:PChar; pIPE:PIcmpEchoReply;// ICMP Echo 回复缓冲区 FSize: DWORD; MyString:string; FTimeOut:DWORD; BufferSize:DWORD; i:integer; begin hICMPdll := LoadLibrary('icmp.dll'); //调取icmp 动态库 if hICMPDll<>NULL then begin WSAStartup($101,wsaData);//初始化网络协议栈 @ICMPCreateFile := GetProcAddress(hICMPdll, 'IcmpCreateFile'); //取动态库中的导出函数 @IcmpCloseHandle := GetProcAddress(hICMPdll, 'IcmpCloseHandle'); @IcmpSendEcho := GetProcAddress(hICMPdll, 'IcmpSendEcho'); hICMP := IcmpCreateFile; //创建 icmp句柄 IPAddr:= inet_addr(PChar(destip)); //取要探测的远端主机ip地址 FSize := 40; BufferSize := SizeOf(TICMPEchoReply) FSize; GetMem(pRevData,FSize); GetMem(pIPE,BufferSize); FillChar(pIPE^, SizeOf(pIPE^), 0); pIPE^.Data := pRevData; MyString := 'Hi, OnLine?';//任意字符串 pReqData := PChar(MyString); FillChar(IPOpt, Sizeof(IPOpt), 0); IPOpt.TTL := 64; FTimeOut := 500;//等待时长 i:=IcmpSendEcho(hICMP, IPAddr, pReqData, Length(MyString), @IPOpt, pIPE, BufferSize, FTimeOut);//如果有返回，返回值表示收到的回复的个数。如果为0表示没有回复，主机无法到达 FreeMem(pRevData); FreeMem(pIPE); IcmpCloseHandle(hicmp); FreeLibrary(hICMPdll);//释放动态库 WSAcleanup();//清理协议栈 end;end;
网络通讯中经常需要确定远程主机是否存活，以决定下一部进行的操作。可以直接使用ICMP协议来实现，但是要考虑许多协议细节，实现起来比较麻烦。Windows 自带的ICMP库里有现成的函数可以使用，只要在使用前填充相应的数据结构就可以了。 以下是要使用的数据结构。这些结构MSDN里有C形式的声明，这里给出的是Delphi的形式。
//用到的协议数据结构PIPOptionInfo = ^TIPOptionInfo; // IP 头选项TIPOptionInfo = packed recordTTL: Byte;//存活时间TOS: Byte;//Type of Service，请求类型Flags: Byte;//标志OptionsSize: Byte;//选项长度OptionsData: PChar;//选项数据end;PIcmpEchoReply = ^TIcmpEchoReply;TIcmpEchoReply = packed record // ICMP 返回信息Address: DWORD;//IP地址Status: DWORD;//状态RTT: DWORD;DataSize: Word;//数据长度Reserved: Word;//保留Data: Pointer;//数据Options: TIPOptionInfo;//选项区end;//动态库中的函数声明TIcmpCreateFile = function: THandle; stdcall; //创建ICMP句柄TIcmpCloseHandle = function(IcmpHandle: THandle): Boolean; stdcall; //关闭ICMP句柄TIcmpSendEcho = function(IcmpHandle:THandle; DestinationAddress:DWORD;RequestData:Pointer; RequestSize:Word; RequestOptions:PIPOptionInfo;ReplyBuffer:Pointer; ReplySize:DWord; Timeout:DWord):DWord; stdcall;//发送ICMP探测数据报//要用到的变量声明hICMPDll,hICMP:THandle;wsaData:TWSADATA;ICMPCreateFile:TICMPCreateFile;IcmpCloseHandle:TIcmpCloseHandle;IcmpSendEcho:TIcmpSendEcho;//destip:要探测的远程地址，形如 192.168.1.1procedure f_CheckOnline(destip:string); var IPOpt:TIPOptionInfo;// 发包的 IP 选项 IPAddr:DWORD; pReqData,pRevData:PChar; pIPE:PIcmpEchoReply;// ICMP Echo 回复缓冲区 FSize: DWORD; MyString:string; FTimeOut:DWORD; BufferSize:DWORD; i:integer; begin hICMPdll := LoadLibrary('icmp.dll'); //调取icmp 动态库 if hICMPDll<>NULL then begin WSAStartup($101,wsaData);//初始化网络协议栈 @ICMPCreateFile := GetProcAddress(hICMPdll, 'IcmpCreateFile'); //取动态库中的导出函数 @IcmpCloseHandle := GetProcAddress(hICMPdll, 'IcmpCloseHandle'); @IcmpSendEcho := GetProcAddress(hICMPdll, 'IcmpSendEcho'); hICMP := IcmpCreateFile; //创建 icmp句柄 IPAddr:= inet_addr(PChar(destip)); //取要探测的远端主机ip地址 FSize := 40; BufferSize := SizeOf(TICMPEchoReply) FSize; GetMem(pRevData,FSize); GetMem(pIPE,BufferSize); FillChar(pIPE^, SizeOf(pIPE^), 0); pIPE^.Data := pRevData; MyString := 'Hi, OnLine?';//任意字符串 pReqData := PChar(MyString); FillChar(IPOpt, Sizeof(IPOpt), 0); IPOpt.TTL := 64; FTimeOut := 500;//等待时长 i:=IcmpSendEcho(hICMP, IPAddr, pReqData, Length(MyString), @IPOpt, pIPE, BufferSize, FTimeOut);//如果有返回，返回值表示收到的回复的个数。如果为0表示没有回复，主机无法到达 FreeMem(pRevData); FreeMem(pIPE); IcmpCloseHandle(hicmp); FreeLibrary(hICMPdll);//释放动态库 WSAcleanup();//清理协议栈 end;end;
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