Closing a TCP/IP component connection the right way

[rlebeau]

The way I know it is that to close the connection from the client side, I have to do something similar to this:

Code:

IdHTTP->IOHandler->WriteBufferClear();
IdHTTP->IOHandler->InputBuffer->Clear();
IdHTTP->IOHandler->Close();
IdHTTP->DisconnectNotifyPeer();

Most of that stuff is unnecessary:

• You don't need to call WriteBufferClear() if you don't call WriteBufferOpen() first. Even then, you don't need to call WriteBufferClear() directly if you are using WriteBuffer(Close|Cancel|Flush)() properly to begin with. Also, IOHandler->Open() and IOHandler->Close() both call WriteBufferClear() for you.
  
  
• You don't need to Close() the IOHandler manually, let Disconnect() handle that for you.
  
  
• The only time you should ever need to call InputBuffer->Clear() directly is if you need to reconnect a client after closing a connection prematurely and left unread data in the InputBuffer. The Connect() method raises an exception if Connected() returns True, which it does if there is unread data in the InputBuffer. Under normal usages, if a client follows its protocol properly and you Disconnect() cleanly, there should not be any unread data left behind. Typically, you would Clear() the InputBuffer only after an error had occurred that made you forcibly close the socket.
  
  
• You don't need to Close() the IOHandler manually, let Disconnect() handle that for you.
  
  
• Don't call DisconnectNotifyPeer() directly, call Disconnect() instead with its ANotifyPeer parameter set to true. But in your particular example, that doesn't matter because DisconnectNotifyPeer() doesn't do anything in TIdHTTP, as there is no goodbye message to send to an HTTP server. But even if it did, calling DisconnectNotifyPeer() after Close() is just plain backwards, you can't send anything to the peer after closing the connection.
  

That being said, HTTP is not a stateful protocol, and TIdHTTP manages the socket connection internally for you, connecting and disconnecting it as needed. You should never have to disconnect TIdHTTP manually.