Network Programming Snippets

Part 1 - Use TTcpServer and TTcpClient to exchange messages

Snippet to read and return your current IP address

Function GetIPAddress():String;
type
  pu_long = ^u_long;
var
  varTWSAData : TWSAData;
  varPHostEnt : PHostEnt;
  varTInAddr : TInAddr;
  namebuf : Array[0..255] of ansichar;
begin
  If WSAStartup($101,varTWSAData) <> 0 Then   //Windows sockets data
  Result := 'No. IP Address'
  Else Begin
    gethostname(namebuf,sizeof(namebuf));     //Local Host name
    varPHostEnt := gethostbyname(namebuf);    //Structure returned by Windows
    varTInAddr.S_addr := u_long(pu_long(varPHostEnt^.h_addr_list^)^);
    Result := inet_ntoa(varTInAddr);
  End;
  WSACleanup;
end;

More information about the PHostEnt structure returned by windows is here

---

Snippet to programmatically set Server LocalHost IP address and Port

begin
    lport := inttostr(portnumber);
    IPAddress := ansistring(GetIPAddress);
    TCPServer1.Active := false;
    TCPServer1.LocalHost := IPAddress;
    TCPServer1.LocalPort := lport;
    TCPServer1.Active := true;

    tcpclient1.RemoteHost := IPAddress;
    tcpclient1.RemotePort := lport;
   label1.Caption := '>'+IPAddress+':'+lport;

end;

---

Receive and display server messages

procedure TForm1.TcpServer1Accept(Sender: TObject;
  ClientSocket: TCustomIpClient);
begin
  Memo1.Lines.add(ClientSocket.Receiveln);
end;

---

Send messages from the Client

begin
  if TcpClient1.Connect then
  begin
    TcpClient1.Sendln('Message sent using port '+lport);
    TcpClient1.Disconnect;
  end else
  begin
    ShowMessage('Not connected');
  end;
end;