(Delphi DLL) Send a WebSocket Ping Control Frame

Ping and Pong messages are the heartbeat of websockets. See Pings and Pongs

"At any point after the handshake, either the client or the server can choose to send a ping to the other party. When the ping is received, the recipient must send back a pong as soon as possible. You can use this to make sure that the client is still connected, for example. A ping or pong is just a regular frame, but it's a control frame. Pings have an opcode of 0x9, and pongs have an opcode of 0xA. When you get a ping, send back a pong with the exact same Payload Data as the ping (for pings and pongs, the max payload length is 125). You might also get a pong without ever sending a ping; ignore this if it happens."

This example demonstrates how to send a Ping in the midst of sending a message.

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.

Chilkat for Delphi Downloads Chilkat non-ActiveX DLL for Delphi Chilkat ActiveX DLL for Delphi * The examples here use the non-ActiveX DLL.

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, WebSocket, Rest;

...

procedure TForm1.Button1Click(Sender: TObject);
var
ws: HCkWebSocket;
rest: HCkRest;
success: Boolean;
responseBodyIgnored: PWideChar;
finalFrame: Boolean;
receivedFinalFrame: Boolean;
receivedMsg: PWideChar;

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

ws := CkWebSocket_Create();

// The PongAutoConsume property is True by default.  This means that any Pong frames that are received 
// will automatically be consumed, and the ReadFrame method will continue reading the next incoming frame before it returns.
CkWebSocket_putPongAutoConsume(ws,True);

// 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 := CkRest_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 := CkRest_Connect(rest,'websockets.chilkat.io',80,False,False);
CkWebSocket_UseConnection(ws,rest);
CkWebSocket_AddClientHeaders(ws);
responseBodyIgnored := CkRest__fullRequestNoBody(rest,'GET','/wsChilkatEcho.ashx');
success := CkWebSocket_ValidateServerHandshake(ws);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkWebSocket__lastErrorText(ws));
    Exit;
  end;

// This example sends a multi-frame message to the Chilkat echo server, and reads the response.
// In the midst of sending the message, we'll send a Ping control frame.  The server should respond with a Pong frame,
// and we'll automatically consume it.

// Send the 1st frame in the message.
finalFrame := False;
success := CkWebSocket_SendFrame(ws,'This is the 1st frame' + #13#10,finalFrame);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkWebSocket__lastErrorText(ws));
    Exit;
  end;

// Let's send a Ping frame here...
success := CkWebSocket_SendPing(ws,'This is a ping');
if (success <> True) then
  begin
    Memo1.Lines.Add(CkWebSocket__lastErrorText(ws));
    Exit;
  end;

// Send the 2nd frame in the message.
success := CkWebSocket_SendFrame(ws,'This is the 2nd frame' + #13#10,finalFrame);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkWebSocket__lastErrorText(ws));
    Exit;
  end;

// Send the 3rd and final frame in the message.
finalFrame := True;
success := CkWebSocket_SendFrame(ws,'This is the 3rd and final frame' + #13#10,finalFrame);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkWebSocket__lastErrorText(ws));
    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.
// 
// The Pong response will be consumed automatically because the PongAutoConsume property is True.
// Therefore, we don't need to worry about handling an incoming Pong.
receivedFinalFrame := False;
while receivedFinalFrame = False do
  begin

    success := CkWebSocket_ReadFrame(ws);
    if (success <> True) then
      begin
        Memo1.Lines.Add('Failed to receive a frame');
        Memo1.Lines.Add('ReadFrame fail reason = ' + IntToStr(CkWebSocket_getReadFrameFailReason(ws)));
        Memo1.Lines.Add(CkWebSocket__lastErrorText(ws));
        Exit;
      end;

    receivedFinalFrame := CkWebSocket_getFinalFrame(ws);

    // Show the opcode and final frame bit for the frame just received:
    Memo1.Lines.Add('Frame opcode: ' + CkWebSocket__frameOpcode(ws));
    Memo1.Lines.Add('Final frame: ' + IntToStr(receivedFinalFrame));
    Memo1.Lines.Add('--');
  end;

// Return the message accumulated in the above calls to ReadFrame.
receivedMsg := CkWebSocket__getFrameData(ws);
Memo1.Lines.Add('Received: ' + receivedMsg);

// Close the websocket connection.
success := CkWebSocket_SendClose(ws,True,1000,'Closing this websocket.');
if (success <> True) then
  begin
    Memo1.Lines.Add(CkWebSocket__lastErrorText(ws));
    Exit;
  end;

// Read the Close response.
success := CkWebSocket_ReadFrame(ws);
if (success <> True) then
  begin
    Memo1.Lines.Add('ReadFrame fail reason = ' + IntToStr(CkWebSocket_getReadFrameFailReason(ws)));
    Memo1.Lines.Add(CkWebSocket__lastErrorText(ws));
    Exit;
  end;

// Should receive the "Close" opcode.
Memo1.Lines.Add('Received opcode: ' + CkWebSocket__frameOpcode(ws));
// Should be the same status code we sent (1000)
Memo1.Lines.Add('Received close status code: ' + IntToStr(CkWebSocket_getCloseStatusCode(ws)));
// The server may echo the close reason.  If not, this will be empty.
Memo1.Lines.Add('Echoed close reason: ' + CkWebSocket__closeReason(ws));

Memo1.Lines.Add('Success.');

CkWebSocket_Dispose(ws);
CkRest_Dispose(rest);

end;