Get the source code on Github

This example uses a Delphi 2009 VCL application with a main form, which contains only one visual component, a TMemo named “MemoLog”.

Client and server are both started in the FormCreate event.

procedure TServerPushExampleForm.FormCreate(Sender: TObject);
begin
  ExampleServer := TMyPushServer.Create;
  ExampleServer.DefaultPort := 8088;
  ExampleServer.Active := True;

  ExampleClient := TMyPushClientThread.Create('localhost', 8088,
    MemoLog.Lines);
end;

Server

The server code uses a TIdTCPCustomServer subclass which waits for a random time and then sends a string to the client.

function TMyPushServer.DoExecute(AContext: TIdContext): Boolean;
begin
  Result := inherited;

  // simulate hard work
  Sleep(Random(3000));

  AContext.Connection.IOHandler.WriteLn(
    'Completed at ' + TimeToStr(Now), IndyTextEncoding_UTF8);
end;

Client

The client code uses a TThread subclass to run asynchronously without blocking the main VCL thread. It contains a private TIdTCPClient instance, and periodically tries to receive a string from the connection.

...
  S := TCPClient.IOHandler.ReadLn(IndyTextEncoding_UTF8);
...

Full Delphi Form Code

Below is the full code for the example main form.

unit Unit1;

interface

uses
  IdCustomTCPServer, IdTCPClient, IdContext,
  SysUtils, Classes, Forms, StdCtrls, Controls;

type
  TMyPushClientThread = class(TThread)
  private
    TCPClient: TIdTCPClient;
    FLog: TStrings;
  public
    constructor Create(AHost: string; APort: Word; ALog: TStrings);
    destructor Destroy; override;
    procedure Execute; override;
  end;

  TMyPushServer = class (TIdCustomTCPServer)
  protected
    function DoExecute(AContext: TIdContext): Boolean; override;
  end;

  TServerPushExampleForm = class(TForm)
    MemoLog: TMemo;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    ExampleClient: TMyPushClientThread;
    ExampleServer: TMyPushServer;
  end;

var
  ServerPushExampleForm: TServerPushExampleForm;

implementation

uses
  IdGlobal;

{$R *.dfm}

procedure TServerPushExampleForm.FormCreate(Sender: TObject);
begin
  ExampleServer := TMyPushServer.Create;
  ExampleServer.DefaultPort := 8088;
  ExampleServer.Active := True;

  ExampleClient := TMyPushClientThread.Create('localhost', 8088, MemoLog.Lines);
end;

procedure TServerPushExampleForm.FormDestroy(Sender: TObject);
begin
  ExampleServer.Free;
  ExampleClient.Terminate;
  ExampleClient.WaitFor;
  ExampleClient.Free;
end;

{ TMyPushServer }

function TMyPushServer.DoExecute(AContext: TIdContext): Boolean;
begin
  Result := inherited;

  // simulate hard work
  Sleep(Random(3000));

  AContext.Connection.IOHandler.WriteLn(
    'Completed at ' + TimeToStr(Now), IndyTextEncoding_UTF8);
end;

{ TMyPushClientThread }

constructor TMyPushClientThread.Create(AHost: string; APort: Word; ALog: TStrings);
begin
  inherited Create(False);

  FLog := ALog;

  TCPClient := TIdTCPClient.Create;
  TCPClient.Host := AHost;
  TCPClient.Port := APort;
  TCPClient.ReadTimeout := 500;
end;

destructor TMyPushClientThread.Destroy;
begin
  TCPClient.Free;
  inherited;
end;

procedure TMyPushClientThread.Execute;
var
  S: string;
begin
  TCPClient.Connect;

  while not Terminated do
  begin
    S := TCPClient.IOHandler.ReadLn(IndyTextEncoding_UTF8);

    if not TCPClient.IOHandler.ReadLnTimedout then
    begin
      TThread.Queue(nil,
        procedure
        begin
          FLog.Append(S);
        end);
    end;

  end;

  TCPClient.Disconnect;
end;

end.