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public:howto:activeconnection [2007/11/30 14:30] (current)
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 +====== How Can I Determine, If The TCP Connection Is Still Active? ======
 +Direct testing is impossible. Determining if a connection is still alive can only be done at the moment of communicating. If you try to send or receive data on a broken TCP channel, then an error is returned. This is the only way to test for a broken TCP channel! There are not any event what can be raised when connection was broken.
 +If connection is closed gracefully, then CanRead is signalled, but the read operation reads 0 bytes.
 +Yes, other packages have an 'active' property, but the true value of this property is determined using the previous principles. It is not a direct determination of the live TCP connection status. It is a faked value!
 +To determinate if FTP connection is still alive you can use that function:
 +<code delphi>
 +function CheckFtpConnection(AFtpSend: TFtpSend): Boolean;
 +  if AFtpSend.Sock.Socket = NOT(0) then // Check if socked was ever opened
 +    Result := AFtpSend.Login            // If not, then connect and login to FTP
 +  else
 +    if AFtpSend.NoOp then               // Send NOOP (No Operation) FTP command to check FTP connection
 +      Result := True                    // If it response without error then connection works fine
 +    else
 +      Result := AFtpSend.Login;         // If fails (for some reasos, timeout, etc), then connect and login to FTP
 +procedure TForm1.Button1Click(Sender: TObject)
 +  if not CheckFtpConnection(FtpSend) then // Check if connection works fine, if not then it will reconnect as needed
 +  begin
 +    ShowMessage('Connection to FTP failed!');
 +    Exit;
 +  end;
 +  // Do FTP action(s)
 +  //[...]
 +  if FtpSend.List('/', False) then
 +  //[...]
public/howto/activeconnection.txt · Last modified: 2007/11/30 14:30 (external edit)
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