Indy/lazarus TIdTCPServer how to close properly - sockets

Question

How to close properly a TIdTCPServer with Indy/Lazarus if we press a 'Close' button in the GUI?. Thanks for helping! (Changed my original question)
How to close the TIdTCPServer if a client disconnects?
Should the exception handle anything?
The IO works but it's a bit unstable yet.
Here is the code below:
unit pt_socket;
{$mode objfpc}//{$H+}
interface
uses
Classes, SysUtils,
Forms,
IdGlobal,
IdContext, IdComponent,
IdTCPServer, IdTCPClient,
Controls, Graphics, Dialogs;
type
TSocket = class
private
IdTcpServer1: TIdTCPServer;
IdTcpClient1: TIdTCPClient;
procedure IdTCPServer1Connect(AContext: TIdContext);
procedure IdTCPServer1Disconnect(AContext: TIdContext);
//procedure IdTCPServer1Exception(AContext: TIdContext; AException: Exception);
procedure IdTCPServer1Execute(AContext: TIdContext);
public
procedure init;
function Open: boolean;
procedure Close;
function Write(str: TByteArray; len: integer): integer;
end;
var
lst: Tlist;
implementation
uses main, pt_settings, pt_ctlpanel, pt_terminal;
procedure TSocket.init;
begin
end;
procedure TSocket.IdTCPServer1Connect(AContext: TIdContext);
begin
MainApp.GuiPortOpen;
lst := IdTcpServer1.Contexts.LockList;
end;
procedure TSocket.IdTCPServer1Disconnect(AContext: TIdContext);
begin
IdTcpServer1.Contexts.UnlockList;
MainApp.GuiPortClose;
end;
//procedure TSocket.IdTCPServer1Exception(AContext: TIdContext; AException: Exception);
//begin
// MainApp.GuiPortClose;
//end;
procedure TSocket.IdTCPServer1Execute(AContext: TIdContext);
var
Socket_Receive_Buffer: TIdBytes;
Socket_Input_Length: integer;
Input_Buffer: TByteArray;
begin
with AContext.Connection do
begin
IOHandler.ReadBytes(Socket_Receive_Buffer, -1, false);
Socket_Input_Length := Length(Socket_Receive_Buffer);
if Socket_Input_Length > 0 then
begin
BytesToRaw(Socket_Receive_Buffer,Input_Buffer,Socket_Input_Length);
Terminal.GuiTerminalPutInput(Input_Buffer, Socket_Input_Length);
end;
end;
end;
function TSocket.Open: boolean;
begin
if Settings.SocketModeRadioGroup.ItemIndex = 0 then
begin
IdTcpServer1 := TIdTCPServer.Create(nil);
IdTCPServer1.OnExecute := #IdTCPServer1Execute;
IdTCPServer1.OnConnect := #IdTCPServer1Connect;
IdTCPServer1.OnDisconnect := #IdTCPServer1Disconnect;
//IdTcpServer1.OnException := #IdTCPServer1Exception;
IdTcpServer1.DefaultPort := StrToInt(Settings.SocketPortEdit.Text);
IdTcpServer1.MaxConnections := 1;
IdTCPServer1.Bindings.Add.IPVersion := Id_IPv4;
IdTcpServer1.Active := True;
end
else
begin
IdTcpClient1 := TIdTCPClient.Create(nil);
//IdTcpClient1.DefaultPort := StrToInt(Settings.SocketPortEdit.SelText);
end;
end;
procedure TSocket.Close;
begin
if Settings.SocketModeRadioGroup.ItemIndex = 0 then
begin
IdTcpServer1.Destroy;
end
else
begin
IdTcpClient1.Destroy;
end;
end;
function TSocket.Write(str: TByteArray; len: integer): integer;
var
Socket_Transmit_Buffer: TIdBytes;
begin
Socket_Transmit_Buffer := RawToBytes(str,len);
if len > 0 then
// Only one connection by design
with TIdContext(lst.Items[0]).Connection do
begin
IOHandler.Write(Socket_Transmit_Buffer);
end;
Result := len;
end;
end.

Answer 1

This code has tons of mistakes in it. Misuse of the Contexts list. Improper use of BytesToRaw() and RawToBytes(). Thread-unsafe GUI logic in worker threads. This code is very prone to memory corruption and deadlocks. It is no wonder your code is unstable. You need to fix that.
To answer your specific questions:
How to close properly a TIdTCPServer with Indy/Lazarus if we press a 'Close' button in the GUI?.
Simply deactivate/destroy the server. It will automatically close any active client connection. However, due to the multi-threaded nature of TIdTCPServer you have to make sure NOT to block any of the server's event handlers during deactivation, or you will deadlock your code. If the event handlers have to sync with the main thread while the main thread is deactivating the server, use asynchronous syncs (TThread.Queue(), TIdNotify, etc) or do the deactivation in a worker thread so the main thread is not blocked. Also, if you need to catch exceptions in your event handlers, be sure to re-raise any EIdException-derived exception you catch and let the server handle it, otherwise the client threads will not terminate correctly, deadlocking deactivation as well.
How to close the TIdTCPServer if a client disconnects?
The server cannot be deactivated from inside its own events (deadlock). You will have to perform the deactivation asynchronously. In the OnDisconnect event, you can send yourself an asynchronous signal so the event handler can exit, and then deactivate the server when the signal is processed. Or spawn a worker thread to perform the deactivation.