Pascal (Lazarus/Delphi)

Read Bitfinex WebSocket Ticker Channel

See more WebSocket Examples

Subscribes to the public Bitfinex websocket ticker channel and receives ticker updates. 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.Rest,
  Chilkat.WebSocket,
  Chilkat.JsonObject;

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

procedure RunDemo;
var
  success: Boolean;
  ws: TWebSocket;
  rest: TRest;
  responseBody: string;
  json: TJsonObject;
  finalFrame: Boolean;
  receivedFinalFrame: Boolean;
  numUpdatesReceived: Integer;
  receivedText: 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 api.bitfinex.com
  success := rest.Connect('api.bitfinex.com',443,True,False);
  ws.UseConnection(rest);
  ws.AddClientHeaders();

  responseBody := rest.FullRequestNoBody('GET','/ws');
  success := ws.ValidateServerHandshake();
  if (success <> True) then
    begin
      WriteLn(ws.LastErrorText);
      WriteLn(responseBody);
      WriteLn(rest.ResponseHeader);
      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 := ws.ReadFrame();
  if (success <> True) then
    begin
      WriteLn('Failed to receive a frame');
      WriteLn('ReadFrame fail reason = ' + ws.ReadFrameFailReason);
      WriteLn(ws.LastErrorText);
      Exit;
    end;

  //  We should get this:
  //  {"event":"info","version":1.1,"platform":{"status":1}}
  WriteLn(ws.GetFrameData());

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

  finalFrame := True;
  success := ws.SendFrame(json.Emit(),finalFrame);

  //  Read the response.
  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;

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

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

      //  The responses we desire are in Text frames, where the opcode = 1.
      if (ws.FrameOpcodeInt = 1) then
        begin
          receivedText := ws.GetFrameData();
          WriteLn(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 := 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;

  WriteLn('Success.');


  ws.Free;
  rest.Free;
  json.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.