Delphi download multithreading

Question

My initial question was misleading, I'll try to improve it:

I was able to write a small delphi programme, which is able to do a threaded download by using indy's idHTTP. It consists of 2 files:

• the form:

  interface
  
  type
    TForm1 = class(TForm)
      Button1: TButton;
      Label1: TLabel;
      Button2: TButton;
      IdSSLIOHandlerSocketOpenSSL1: TIdSSLIOHandlerSocketOpenSSL;
      IdAntiFreeze1: TIdAntiFreeze;
      IdHTTP: TIdHTTP;
      ProgressBar1: TProgressBar;
      procedure Button1Click(Sender: TObject);
      procedure Button2Click(Sender: TObject);
    private
      { Private-Deklarationen }
    public
      { Public-Deklarationen }
       procedure UpdateLabel(BytesDone: Integer);
       procedure UpdateProgressBar(AWorkCount: Int64);
       procedure InitProgressBar(AWorkCountMax: Int64);
       procedure ResetProgressBar;
    end;
  
  var
    Form1: TForm1;
    uStopDownloading: Boolean;
  
  implementation
  
  {$R *.dfm}
  
  uses Unit2;
  
  
  procedure TForm1.Button1Click(Sender: TObject);
  var
    HTTPThread: TIdHTTPThread;
  begin
    HTTPThread := TIdHTTPThread.Create(True);
    HTTPThread.Url := 'https://www.bot-factory.de/tmp/lorem7.txt';
    HTTPThread.EncodedStr := '';
    HTTPThread.Filename := 'C:\test.txt';
    HTTPThread.FreeOnTerminate := True;
    HTTPThread.Resume;
  end;
  
  procedure TForm1.Button2Click(Sender: TObject);
  begin
   idhttp.Disconnect;
  end;
  
  procedure TForm1.UpdateLabel(BytesDone: Integer);
  begin
    Label1.caption := format('%.0n',[extended(BytesDone+0.0)]) +' bytes loaded.';
  end;
  
  procedure TForm1.UpdateProgressBar(AWorkCount: Int64);
  begin
    ProgressBar1.Position := AWorkCount;
  end;
  
  procedure TForm1.InitProgressBar(AWorkCountMax: Int64);
  begin
    Screen.Cursor := crHourGlass;
    ProgressBar1.Max := AWorkCountMax;
    ProgressBar1.Position := 0;
  end;
  
  procedure TForm1.ResetProgressBar;
  begin
   Screen.Cursor := crDefault;
   showmessage('Job is done');
  end;
  
  END.
  

• And the Thread-Unit:

  interface
  
  uses
    Classes, IdBaseComponent, IdComponent, IdTCPConnection, IdTCPClient, IdHTTP, sysutils;
  
  type
    TIdHTTPThread = class(TThread)
    private
      FURL: AnsiString;
      FencodedStr: string;
      FFilename: AnsiString;
      FBytesDone,FProgress,FWorkCountMax: Int64;
      IdHTTP: TIdHTTP;
      procedure OnWork(ASender: TObject; AWorkMode: TWorkMode; AWorkCount: Int64);
      procedure OnWorkBegin(ASender: TObject; AWorkMode: TWorkMode; AWorkCountMax: Int64);
      procedure OnWorkEnd(ASender: TObject; AWorkMode: TWorkMode);
      procedure Updatelabel;
      procedure UpdateProgressBar;
      procedure InitProgressBar;
      procedure ResetProgressBar;
      procedure Disconnect;
    public
      Constructor Create(CreateSuspended: Boolean);
      Destructor Destroy; override;
      property Url: AnsiString read FURL write FUrl;
      property encodedstr: String read FencodedStr write FencodedStr;
      property Filename: AnsiString read FFilename write FFilename;
    protected
      procedure Execute; override;
    end;
  
  implementation
  
  uses
    Unit1; // Formular Unit
  
  constructor TIdHTTPThread.Create(CreateSuspended: Boolean);
  begin
    inherited Create(Suspended);
    IdHTTP := TIdHTTP.Create;
    IdHTTP.OnWork := OnWork;
    IdHTTP.OnWorkBegin := OnWorkBegin;
    IdHTTP.OnWorkEnd := OnWorkEnd;
    //IdHTTP.Disconnect := Disconnect;
  end;
  
  destructor TIdHTTPThread.Destroy;
  begin
    IdHTTP.Free;
    inherited;
  end;
  
  procedure TIdHTTPThread.Execute;
  var
    DestStream: TFileStream;
  begin
    DestStream := TFileStream.Create(Filename, fmCreate);
    try
      IdHTTP.Get(Url, DestStream);
    finally
      DestStream.Free;
    end;
  end;
  
  procedure TIdHTTPThread.OnWork(ASender: TObject; AWorkMode: TWorkMode; AWorkCount: Int64);
  begin
    FBytesDone := AWorkCount;
    FProgress := AWorkCount;
    Synchronize(Updatelabel);
    Synchronize(UpdateProgressBar);
  end;
  
  procedure TIdHTTPThread.OnWorkBegin(ASender: TObject; AWorkMode: TWorkMode; AWorkCountMax: Int64);
  begin
    FWorkCountMax := AWorkCountMax;
    Synchronize(InitProgressBar);
  end;
  
  procedure TIdHTTPThread.Disconnect;
  begin
    idhttp.Disconnect;
  end;
  
  procedure TIdHTTPThread.OnWorkEnd(ASender: TObject; AWorkMode: TWorkMode);
  begin
    Synchronize(ResetProgressBar);
  end;
  
  procedure TIdHTTPThread.Updatelabel;
  begin
    Form1.UpdateLabel(FBytesDone);
  end;
  
  procedure TIdHTTPThread.UpdateProgressBar;
  begin
    Form1.UpdateProgressBar(FProgress);
  end;
  
  procedure TIdHTTPThread.InitProgressBar;
  begin
    Form1.initProgressBar(FWorkCountMax);
  end;
  
  procedure TIdHTTPThread.resetProgressBar;
  begin
    Form1.resetProgressBar;
  end;
  
  END.
  

I have in fact 2 questions:

1. How can I interrupt the download of a (large) file ? I know that idhttp.disconnect should do the trick, but I do not know how to use it properly in my thread.
2. And furthermore: how can I use POST instead of GET?

I need to run this POST in a thread:

{++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
//submit_post
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++}
Procedure submit_post(url_string,EncodedStr,filename:string);
var
  aStream: TMemoryStream;
  Params: TStringStream;
begin
  astream := TMemoryStream.create;
  Params := TStringStream.create('');
  Form1.IdHTTP.Request.Clear;
  Form1.IdHTTP.HandleRedirects := TRUE;

  try
    with Form1.IdHTTP do
    begin
      Params.WriteString(EncodedStr);
      Request.ContentType := 'application/x-www-form-urlencoded';
      Request.Charset := 'utf-8';
      try
        Response.KeepAlive := False;
        Post(url_string, params, astream);
      except
        on E: Exception do
        begin
          exit;
        end;
      end;
    end;
    astream.WriteBuffer(#0' ', 1);
    astream.Position := 0;
    astream.SaveToFile(filename);
  finally
    astream.Free;
    Params.Free;
  end;
end;