Differences
This shows you the differences between two versions of the page.
| — |
public:howto:activeconnection [2007/11/30 14:30] (current) |
||
|---|---|---|---|
| Line 1: | Line 1: | ||
| + | ====== 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; | ||
| + | begin | ||
| + | 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 | ||
| + | end; | ||
| + | |||
| + | //[...] | ||
| + | |||
| + | procedure TForm1.Button1Click(Sender: TObject) | ||
| + | begin | ||
| + | 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 | ||
| + | //[...] | ||
| + | end; | ||
| + | </code> | ||
