Code for implementing ICMP monitoring using Delphi

Remote monitoring is an effective measure for us to manage settings and networks. This method has been introduced into more and more fields. Here we will introduce how to use ICMP to detect the status of remote hosts in Delphi. In network communication, you often need to determine whether the remote host is alive to determine the next operation. You can directly use the ICMP protocol for implementation, but you need to consider a lot of protocol details, it is more difficult to implement. There are ready-made functions available in the ICMP library that comes with Windows. You only need to fill in the corresponding data structure before use. The following is the data structure to use. The C-form statements are provided in MSDN. Here, the Delphi statements are provided.

// The Protocol Data Structure Used
PIPOptionInfo = ^ TIPOptionInfo; // IP header Option
TIPOptionInfo = packed record
TTL: Byte; // TTL
TOS: Byte; // Type of Service, request Type
Flags: Byte; // flag
OptionsSize: Byte; // Option Length
OptionsData: PChar; // option data
End;
PIcmpEchoReply = ^ TIcmpEchoReply;
TIcmpEchoReply = packed record // ICMP returned information
Address: DWORD; // ip Address
Status: DWORD; // Status
RTT: DWORD;
DataSize: Word; // Data Length
Reserved: Word; // Reserved
Data: Pointer; // Data
Options: TIPOptionInfo; // option Area
End;
// Function declaration in the dynamic library
TIcmpCreateFile = function: THandle; stdcall; // create an 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 detection Datagram
// Variable declaration to be used
HICMPDll, hICMP: THandle;
WsaData: TWSADATA;
ICMPCreateFile: TICMPCreateFile;
IcmpCloseHandle: TIcmpCloseHandle;
IcmpSendEcho: TIcmpSendEcho;
// Destip: the remote address to be detected, such as 192.168.1.1
Procedure f_CheckOnline (destip: string );
Var
IPOpt: TIPOptionInfo; // IP address option for packet sending
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 '); // retrieves the icmp dynamic library
If hICMPDll <> NULL then
Begin
WSAStartup ($101, wsaData); // initialize the network protocol stack
@ ICMPCreateFile: = GetProcAddress (hICMPdll, 'icmpcreatefile'); // obtain the export function from the dynamic library
@ IcmpCloseHandle: = GetProcAddress (hICMPdll, 'icmpclosehandle ');
@ IcmpSendEcho: = GetProcAddress (hICMPdll, 'icmpsendecho ');
HICMP: = IcmpCreateFile; // create an icmp handle
IPAddr: = inet_addr (PChar (destip); // obtain the IP address of the remote host to be tested.
FSize: = 40;
BufferSize: = SizeOf (TICMPEchoReply) + FSize;
GetMem (pRevData, FSize );
GetMem (pIPE, BufferSize );
FillChar (pIPE ^, SizeOf (pIPE ^), 0 );
PIPE ^. Data: = pRevData;
MyString: = 'Hi, OnLine? '; // Any string
PReqData: = PChar (MyString );
FillChar (IPOpt, Sizeof (IPOpt), 0 );
IPOpt. TTL: = 64;
FTimeOut: = 500; // waiting duration
I: = IcmpSendEcho (hICMP, IPAddr, pReqData, Length (MyString), @ IPOpt, pIPE, BufferSize, FTimeOut); // If yes, the return value indicates the number of replies received. If the value is 0, no response is returned and the host cannot arrive.
FreeMem (pRevData );
FreeMem (pIPE );
IcmpCloseHandle (hicmp );
FreeLibrary (hICMPdll); // release the dynamic library
WSAcleanup (); // clear the protocol stack
End;
End;

The code above shows how Delphi uses ICMP to detect the status of a remote host.