How to check if a TCP port is available with Delphi?

Question

Is there a more elegant way of checking if a TCP port is available with Delphi other than catching a netstat call?

Answer 1

I guess you can use Indy's components to do that. For instance a TIdHTTPServer will raise an exception if a port is in use when it is being opened.

So basically you could create such component, bind it to localhost:<yourport> and if an exception is raised ( catch it and check it ) then the port is probably in use, else it is free.

I guess other indy components can tell if a port is open or not, but I can't look at it right now.

This was just to give you an approach.

Answer 2

@Mattl, if Available means open for you, you can use this code.

program CheckTCP_PortOpen;

{$APPTYPE CONSOLE}

uses
  Winsock; //Windows Sockets API Unit

    function PortTCPIsOpen(dwPort : Word; ipAddressStr:string) : boolean;
    var
      client : sockaddr_in;//sockaddr_in is used by Windows Sockets to specify a local or remote endpoint address
      sock   : Integer;
    begin
        client.sin_family      := AF_INET;
        client.sin_port        := htons(dwPort);//htons converts a u_short from host to TCP/IP network byte order.
        client.sin_addr.s_addr := inet_addr(PChar(ipAddressStr)); //the inet_addr function converts a string containing an IPv4 dotted-decimal address into a proper address for the IN_ADDR structure.
        sock  :=socket(AF_INET, SOCK_STREAM, 0);//The socket function creates a socket 
        Result:=connect(sock,client,SizeOf(client))=0;//establishes a connection to a specified socket.
    end;

var
  ret    : Integer;
  wsdata : WSAData;
begin
  Writeln('Init WinSock');
  ret := WSAStartup($0002, wsdata);//initiates use of the Winsock
  if ret<>0 then exit;
  try
    Writeln('Description : '+wsData.szDescription);
    Writeln('Status      : '+wsData.szSystemStatus);

    if PortTCPIsOpen(80,'127.0.0.1') then
    Writeln('Open')
    else
    Writeln('Close');

  finally
  WSACleanup; //terminates use of the Winsock
  end;

  Readln;
end.