(Delphi DLL) Read Bitfinex WebSocket Ticker Channel

Subscribes to the public Bitfinex websocket ticker channel and receives ticker updates.

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, Rest, WebSocket, JsonObject;

...

procedure TForm1.Button1Click(Sender: TObject);
var
ws: HCkWebSocket;
rest: HCkRest;
success: Boolean;
responseBody: PWideChar;
json: HCkJsonObject;
finalFrame: Boolean;
receivedFinalFrame: Boolean;
numUpdatesReceived: Integer;
receivedText: 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 api.bitfinex.com
success := CkRest_Connect(rest,'api.bitfinex.com',443,True,False);
CkWebSocket_UseConnection(ws,rest);
CkWebSocket_AddClientHeaders(ws);

responseBody := CkRest__fullRequestNoBody(rest,'GET','/ws');
success := CkWebSocket_ValidateServerHandshake(ws);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkWebSocket__lastErrorText(ws));
    Memo1.Lines.Add(responseBody);
    Memo1.Lines.Add(CkRest__responseHeader(rest));
    Exit;
  end;

//  After connecting, the bitfinex websocket server will send
//  an info message that contains the actual version of the websocket stream.
//  Receive that message..
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;

//  We should get this:
//  {"event":"info","version":1.1,"platform":{"status":1}}
Memo1.Lines.Add(CkWebSocket__getFrameData(ws));

//  Subscribe to the public ticker feed.
//  See https://docs.bitfinex.com/docs for more information.
json := CkJsonObject_Create();
CkJsonObject_AppendString(json,'event','subscribe');
CkJsonObject_AppendString(json,'channel','ticker');
CkJsonObject_AppendString(json,'pair','BTCUSD');

finalFrame := True;
success := CkWebSocket_SendFrame(ws,CkJsonObject__emit(json),finalFrame);

//  Read the response.
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;

//  Examine the response
//  We should get this:
//  {"event":"subscribed","channel":"ticker","chanId":2751,"pair":"BTCUSD"}
Memo1.Lines.Add(CkWebSocket__getFrameData(ws));

//  Begin reading the ticker feed.
//  We'll just read the 1st 5 updates and then exit..
receivedFinalFrame := False;
numUpdatesReceived := 0;
while numUpdatesReceived < 5 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;

    //  The responses we desire are in Text frames, where the opcode = 1.
    if (CkWebSocket_getFrameOpcodeInt(ws) = 1) then
      begin
        receivedText := CkWebSocket__getFrameData(ws);
        Memo1.Lines.Add(receivedText);
        //  Should receive a line of text such as this:
        //  [2751,7349,36.34269559,7349.1,41.01777063,-116.2,-0.0156,7349.1,22188.26055319,7560,7270.5]
        numUpdatesReceived := numUpdatesReceived + 1;
      end;

  end;

//  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;

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

CkWebSocket_Dispose(ws);
CkRest_Dispose(rest);
CkJsonObject_Dispose(json);

end;