Pascal (Lazarus/Delphi)

Send and Receive WebSocket Messages

See more WebSocket Examples

This example how to send and receive websocket messages.

A WebSocket message can be composed of one or more frames. The simple case is where a single frame is both the first and last frame in a message. This is the case where the 1st frame in the message has the "final frame" bit set.

This example demonstrates sending and receiving multi-frame messages.

Note: The websockets.chilkat.io server imposes the following limitations:
Messages must be 16K or less, and each connection is limited to a max of 16 echoed messages.

Pascal (Lazarus/Delphi)

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.WebSocket,
  Chilkat.Rest;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  ws: TWebSocket;
  rest: TRest;
  responseBodyIgnored: string;
  finalFrame: Boolean;
  receivedFinalFrame: Boolean;
  receivedMsg: string;

begin
  success := False;

  //  This example requires the Chilkat API to have been previously unlocked.
  //  See Global Unlock Sample for sample code.

  ws := TWebSocket.Create;

  //  For brevity, this example does not check for errors when etablishing the WebSocket connection.
  //  See Establish WebSocket Connection for more complete sample code for making the connection.

  rest := TRest.Create;
  //  Connect to websockets.chilkat.io
  //  IMPORTANT: websockets.chilkat.io accepts frames of up to 16K in size and echoes them back.
  //  IMPORTANT: The websockets.chilkat.io server imposes the following limitations: 
  //  ---------- Messages must be 16K or less, and each connection is limited to a max of 16 echoed messages.
  success := rest.Connect('websockets.chilkat.io',80,False,False);
  ws.UseConnection(rest);
  ws.AddClientHeaders();
  responseBodyIgnored := rest.FullRequestNoBody('GET','/wsChilkatEcho.ashx');
  success := ws.ValidateServerHandshake();
  if (success <> True) then
    begin
      WriteLn(ws.LastErrorText);
      Exit;
    end;

  //  This example demonstrates sending and receiving a multi-frame message.

  //  The websocket message will be composed of three text lines, each frame will contain a single line.

  //  Send the 1st frame in the message.
  finalFrame := False;
  success := ws.SendFrame('This is the 1st frame' + #13#10,finalFrame);
  if (success <> True) then
    begin
      WriteLn(ws.LastErrorText);
      Exit;
    end;

  //  Send the 2nd frame in the message.
  success := ws.SendFrame('This is the 2nd frame' + #13#10,finalFrame);
  if (success <> True) then
    begin
      WriteLn(ws.LastErrorText);
      Exit;
    end;

  //  Send the 3rd and final frame in the message.
  finalFrame := True;
  success := ws.SendFrame('This is the 3rd frame' + #13#10,finalFrame);
  if (success <> True) then
    begin
      WriteLn(ws.LastErrorText);
      Exit;
    end;

  //  Read an incoming frames until we receive the final frame.
  //  Note: It may be that the echo server (websockets.chilkat.io) responds with 
  //  the full message in a single final frame.
  receivedFinalFrame := False;
  while receivedFinalFrame = False do
    begin

      success := ws.ReadFrame();
      if (success <> True) then
        begin
          WriteLn('Failed to receive a frame');
          WriteLn('ReadFrame fail reason = ' + ws.ReadFrameFailReason);
          WriteLn(ws.LastErrorText);
          Exit;
        end;

      receivedFinalFrame := ws.FinalFrame;

      //  Show the opcode and final frame bit for the frame just received:
      WriteLn('Frame opcode: ' + ws.FrameOpcode);
      WriteLn('Final frame: ' + receivedFinalFrame);
    end;

  //  Return the message accumulated in the above calls to ReadFrame.
  receivedMsg := ws.GetFrameData();
  WriteLn('Received: ' + receivedMsg);

  //  Close the websocket connection.
  success := ws.SendClose(True,1000,'Closing this websocket.');
  if (success <> True) then
    begin
      WriteLn(ws.LastErrorText);
      Exit;
    end;

  //  Read the Close response.
  success := ws.ReadFrame();
  if (success <> True) then
    begin
      WriteLn('ReadFrame fail reason = ' + ws.ReadFrameFailReason);
      WriteLn(ws.LastErrorText);
      Exit;
    end;

  //  Should receive the "Close" opcode.
  WriteLn('Received opcode: ' + ws.FrameOpcode);
  //  Should be the same status code we sent (1000)
  WriteLn('Received close status code: ' + ws.CloseStatusCode);
  //  The server may echo the close reason.  If not, this will be empty.
  WriteLn('Echoed close reason: ' + ws.CloseReason);

  WriteLn('Success.');


  ws.Free;
  rest.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.