Implementing PING Without Using Raw Sockets

Windows supports an Internet Control Message Protocol (ICMP) to determine whether or not a particular host is available. ICMP is a network layer protocol that delivers flow control, error messages, routing, and other data between Internet hosts. ICMP is primarily used by application developers for a network ping.

What Is a Ping?

A ping is the process of sending an echo message to an IP address and reading the reply to verify a connection between TCP/IP hosts. If you are writing a new application, you will be better to use the Winsock 2 raw sockets support, implemented in Indy, for example.

Please note, however, that for Windows NT and Windows 2000 implementations, Raw Sockets are subject to security checks and are accessible only to members of the administrator's group. Icmp.dll provides functionality that allows developers to write Internet ping applications on Windows systems without Winsock 2 support. 

Note that the Winsock 1.1 WSAStartup function must be called prior to using the functions exposed by ICMP.DLL. If you do not do this, the first call to IcmpSendEcho will fail with error 10091 (WSASYSNOTREADY).

Below you can find the Ping unit's source code. Here are two examples of usage.

Example 1: Code Snippet

uses Ping;...​
const ADP_IP = '208.185.127.40'; (* http://delphi.about.com *)
beginIf  Ping.Ping(ADP_IP) then ShowMessage('About Delphi Programming reachable!');
end;

Example 2: Console Mode Delphi Program

Our next example is a console mode Delphi program that uses the Ping unit: . Here's the Ping unit's source:

unit Ping;​
interfaceuses
Windows, SysUtils, Classes;
type
TSunB = packed record
s_b1, s_b2, s_b3, s_b4: byte;
end;
TSunW = packed record
s_w1, s_w2: word;
end;
PIPAddr = ^TIPAddr;
TIPAddr = record
case integer of
0: (S_un_b: TSunB);1: (S_un_w: TSunW);2: (S_addr: longword);
end;IPAddr = TIPAddr;
function IcmpCreateFile : THandle; stdcall; external 'icmp.dll';
function IcmpCloseHandle (icmpHandle : THandle) : boolean;
stdcall; external 'icmp.dll'
function IcmpSendEcho
(IcmpHandle : THandle; DestinationAddress : IPAddr;
RequestData : Pointer; RequestSize : Smallint;
RequestOptions : pointer;
ReplyBuffer : Pointer;
ReplySize : DWORD;
Timeout : DWORD) : DWORD; stdcall; external 'icmp.dll';
function Ping(InetAddress : string) : boolean;
implementationuses
WinSock;
function Fetch(var AInput: string;
const ADelim: string = ' ';
const ADelete: Boolean = true)
: string;
var
iPos: Integer;
begin
if ADelim = #0 then begin
// AnsiPos does not work with #0
iPos := Pos(ADelim, AInput);
end else begin
iPos := Pos(ADelim, AInput);
end;
if iPos = 0 then begin
Result := AInput;
if ADelete then begin
AInput := '';
end;
end else begin
result := Copy(AInput, 1, iPos - 1);
if ADelete then begin
Delete(AInput, 1, iPos + Length(ADelim) - 1);
end;
end;
end;
procedure TranslateStringToTInAddr(AIP: string; var AInAddr);
var
phe: PHostEnt;pac: PChar;GInitData: TWSAData;
begin
WSAStartup($101, GInitData);
try
phe := GetHostByName(PChar(AIP));
if Assigned(phe) thenbegin
pac := phe^.h_addr_list^;
if Assigned(pac) then
begin
with TIPAddr(AInAddr).S_un_b do begin
s_b1 := Byte(pac[0]);s_b2 := Byte(pac[1]);s_b3 := Byte(pac[2]);s_b4 := Byte(pac[3]);
end;
end
else
begin
raise Exception.Create('Error getting IP from HostName');
end;
end
else
begin
raise Exception.Create('Error getting HostName');
end;
except
FillChar(AInAddr, SizeOf(AInAddr), #0);
end;WSACleanup;
end;
function Ping(InetAddress : string) : boolean;
var
Handle : THandle;
InAddr : IPAddr;
DW : DWORD;
rep : array[1..128] of byte;
begin
result := false;Handle := IcmpCreateFile;
if Handle = INVALID_HANDLE_VALUE then
Exit;
TranslateStringToTInAddr(InetAddress, InAddr);
DW := IcmpSendEcho(Handle, InAddr, nil, 0, nil, @rep, 128, 0);Result := (DW 0);IcmpCloseHandle(Handle);
end;​
end.