Using ICMP to detect remote host status in Delphi

In network communications, it is often necessary to determine whether a remote host survives to determine the next operation. Can be implemented directly using ICMP protocol, but to consider a lot of protocol details, to achieve more cumbersome. There are ready-made functions available in Windows ' own ICMP library, so just fill in the appropriate data structure before using it.

The following is the data structure to use. These structures MSDN has a C form of the statement, here is the form of Delphi.

//Used protocol data structure


pipoptioninfo = ^tipoptioninfo; IP Header Option


tipoptioninfo = packed record


ttl:byte;//Survival Time


Tos:byte;//type of Service, request type


flags:byte;//logo


optionssize:byte;//Option Length


optionsdata:pchar;//Option Data


end;


picmpechoreply = ^ticmpechoreply;


ticmpechoreply = packed record//ICMP return information


ADDRESS:DWORD;//IP Address


status:dword;//State


Rtt:dword;


datasize:word;//Data Length


reserved:word;//reserved


data:pointer;//Data


options:tipoptioninfo;//Option Area


end;

function declarations in
//dynamic Libraries


ticmpcreatefile = Function:thandle; stdcall; Create ICMP handle


Ticmpclosehandle = function (icmphandle:thandle): Boolean; stdcall; Close ICMP handle


Ticmpsendecho = function (icmphandle:thandle; Destinationaddress:dword;


Requestdata:pointer; Requestsize:word; Requestoptions:pipoptioninfo;


Replybuffer:pointer; Replysize:dword; Timeout:dword):D Word; stdcall;//send ICMP probing datagram


//variable declaration to be used


Hicmpdll,hicmp:thandle;


Wsadata:twsadata;


Icmpcreatefile:ticmpcreatefile;


Icmpclosehandle:ticmpclosehandle;


Icmpsendecho:ticmpsendecho;


//destip: Remote address to probe, shaped like 192.168.1.1


procedure F_checkonline (destip:string);


var

IP options for the
ipopt:tipoptioninfo;//contract


Ipaddr:dword;


Preqdata,prevdata:pchar;


pipe:picmpechoreply;//ICMP Echo Recovery buffer


Fsize:dword;


mystring:string;


Ftimeout:dword;


Buffersize:dword;


I:integer;


begin


Hicmpdll: = LoadLibrary (' Icmp.dll '); Fetch ICMP Dynamic library


if Hicmpdll<>null then


begin


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


@ICMPCreateFile: = GetProcAddress (Hicmpdll, ' icmpcreatefile '); Take the exported function in the dynamic library


@IcmpCloseHandle: = GetProcAddress (Hicmpdll, ' icmpclosehandle ');


@IcmpSendEcho: = GetProcAddress (Hicmpdll, ' Icmpsendecho ');


hicmp: = Icmpcreatefile; Create ICMP handle


ipaddr:= inet_addr (Pchar (Destip)); The remote host IP address to be probed


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;//Wait Long


I:=icmpsendecho (hicmp, ipaddr, Preqdata, Length (MyString), @IPOpt, PIPE, buffersize, ftimeout);/If there is a return, the return value indicates the received reply Number of. If 0 indicates no reply, the host cannot reach


Freemem (Prevdata);


Freemem (PIPE);


Icmpclosehandle (HICMP);


FreeLibrary (hicmpdll)/free Dynamic library


WSACleanup ()//cleaning protocol stack


end;


end;