Delphi uses ICMP to detect whether the remote host is alive

Delphi uses ICMP to detect whether the remote host is alive

2005-03-10 jlbnet

In network communication, it is often necessary to determine whether the remote host is alive to determine the operation performed in the next part. It can be implemented directly using the ICMP protocol, but many protocol details need to be considered, which is more troublesome to implement. There are ready-made functions in the ICMP library that comes with Windows, just populate the corresponding data structure before use.

The following is the data structure to be used. These structures MSDN have declarations in form C, and the form of Delphi is given here.

//The protocol data structure used

PipOptionInfo = ^TIPOptionInfo; // IP header options

TIPOptionInfo = packed record

TTL: Byte;//Life time

TOS: Byte;//Type of Service, request type

Flags: Byte;//Lottery

OptionsSize: Byte;//Option length

OptionsData: PChar;//Options Data

end;

PIcmpEchoReply = ^TIcmpEchoReply;

TIcmpEchoReply = packed record // ICMP Return information

Address: DWord;//IP address

Status: DWORD;//Status

RTT: DWORD;

DataSize: Word;//Data length

Reserved: Word;//Reserve

Data: Pointer;//Data

Options: TIPOptionInfo;//Options area

end;

// Function declaration in dynamic library

TIcmpCreateFile = function: THandle; stdcall; //Create ICMP handle

TIcmpCloseHandle = function(IcmpHandle: THandle): Boolean; stdcall; //Close the ICMP handle

TIcmpSendEcho = function(IcmpHandle:THandle; DestinationAddress:DWORD;

RequestData:Pointer; RequestSize:Word; RequestOptions:PIPOptionInfo;

ReplyBuffer:Pointer; ReplySize:DWord; Timeout:DWord):DWord; stdcall;//Send ICMP probe datagram

//The variable declaration to be used

hICMPDll,hICMP:THandle;

wsaData:TWSADATA;

ICMPCreateFile:TICMPCreateFile;

IcmpCloseHandle:TIcmpCloseHandle;

IcmpSendEcho:TIcmpSendEcho;

//destip: The remote address to be detected is as 192.168.1.1

PRocedure f_CheckOnline(destip:string);

var

IPOpt:TIPOptionInfo;// Package IP options

IPAddr:DWORD;

pReqData,pRevData:PChar;

pIPE:PIcmpEchoReply;// ICMP Echo Reply Buffer

FSize: DWORD;

MyString:string;

FTimeOut:DWORD;

BufferSize:DWORD;

i:integer;

Begin

hICMPdll := LoadLibrary('icmp.dll');//Click the icmp dynamic library

if hICMPDll<>NULL then

Begin

WSAStartup($101,wsaData);//Initialize the network protocol stack

@ICMPCreateFile := GetProcAddress(hICMPdll, 'IcmpCreateFile');//Please the export function in the dynamic library

@IcmpCloseHandle := GetProcAddress(hICMPdll, 'IcmpCloseHandle');

@IcmpSendEcho := GetProcAddress(hICMPdll, 'IcmpSendEcho');

hICMP := IcmpCreateFile;//Create an icmp handle

IPAddr:= inet_addr(PChar(destip));//Get the IP address of the remote host to be detected

FSize := 40;

BufferSize := SizeOf(TICMPEchoReply) + FSize;

GetMem(pRevData,FSize);

GetMem(pIPE,BufferSize);

FillChar(pIPE^, SizeOf(pIPE^), 0);

pIPE^.Data := pRevData;

MyString := 'Hi, OnLine?';//Arbitrary string

pReqData := PChar(MyString);

FillChar(IPOpt, Sizeof(IPOpt), 0);

IPOpt.TTL := 64;

FTimeOut := 500;//Waiting time

i:=IcmpSendEcho(hICMP, IPAddr, pReqData, Length(MyString), @IPOpt, pIPE, BufferSize, FTimeOut);//If there is a return, the return value indicates the number of replies received. If 0 means no reply, the host cannot reach

FreeMem(pRevData);

FreeMem(pIPE);

IcmpCloseHandle(hicmp);

FreeLibrary(hICMPdll);//Release dynamic library

WSAcleanup();//Clean the protocol stack

end;

end;