(Delphi DLL) Send and Receive WebSocket Messages

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.

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();

// 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 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 := CkWebSocket_SendFrame(ws,'This is the 1st frame' + #13#10,finalFrame);
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 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.
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));
  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;