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I need to write a small utility for receiving logging data from an embedded WiFi device.
The device (based on ESP8266) is programmed to work as a TCP<=>Serial bridge for channeling data between a data collection unit and a network connected master (can be a PC program or an Android App using TCP socket communications).
We have problems in certain operating modes with the device and so I need to check the data handled by the device. Dropped bytes is a killer here...

So I added two TCP servers to the device each listening on different ports and dedicated to log data sent to and from the serial port of the device. Every time there is any data in either of these sources it will be sent to the logging client in addition to the relaying destination.

Now I need to add two instances of a "logging client" to my configuration program (written with Lazarus/FPC and using the indylaz package components) and the plan is to do this as follows:

- Write a TCP logging class I can instantiate twice for the two logging directions
- Each class instance shall connect to the server on one of the two ports dedicated for logging
- While connected it shall wait for incoming data and dump all received bytes to a log file.
- The running count of the received bytes shall be reported to the main application for display (event function)

In order to do the above I probably need to use a threaded approach since I must keep the application live and responsive.

But I have not succeeded to find any good example to start from where the TCP client is threaded and does not send anything at all by itself, it shall just receive and write to disk whatever comes along. And generate an event with the current byte count.

Any suggestions on how this can be accomplished?

This is as far as I have come as of now:

Code:
type

  TRxEvent = procedure (const Buffer: TIdBytes) of object;

  { TWiFiCommLogger }

  TWiFiCommLogger = class(TThread)

  private

    FComm: TIdTcpClient;

    FServer: string;

    FPort: TIdPort;

    FTcpConnected: boolean;

    FOnRxData: TRxEvent;

    FBuffer: TIdBytes;

    FActive: boolean;

    procedure OnConnected(Sender: TObject);

    procedure OnDisConnected(Sender: TObject);

  protected

    procedure Execute; override;

  public

    constructor Create;

    destructor Destroy; override;

    procedure Connect(Server: string; Port: word);

    procedure Disconnect;

    property Active: boolean read FActive write FActive;

    property Connected: boolean read FTcpConnected;

    property OnRxData: TRxEvent read FOnRxData write FOnRxData;

  end;

implementation

{ TWiFiCommLogger }

procedure TWiFiCommLogger.OnConnected(Sender: TObject);

begin

  FTcpConnected := true;

end;

procedure TWiFiCommLogger.OnDisConnected(Sender: TObject);

begin

  FTcpConnected := false;

end;

procedure TWiFiCommLogger.Execute;

begin

  while not Terminated do

  begin

    if FActive and FTcpConnected then

    begin

      //What do I put here?

      FComm.IOHandler.ReadBytes(FBuffer, -1, true); //Append indata to buffer

      if Length(FBuffer) > 0 then

        if Assigned(FOnRxData) then

        begin

          FOnRxData(FBuffer); //Data are supposed to be saved in the main thread

          SetLength(FBuffer, 0); //So after executing the evnt procedure, erase existing data

        end; 

    end;  

  end; //while

end;

constructor TWiFiCommLogger.Create;

begin

  FActive := false;

  FComm := TIdTCPClient.Create(NIL);

  FComm.IPVersion := Id_IPv4;

  FComm.ReadTimeout := 100;

  FComm.ConnectTimeout := 5000;

  FTcpConnected := false;

  FComm.OnConnected := OnConnected;

  FComm.OnDisconnected := OnDisconnected;

end;

destructor TWiFiCommLogger.Destroy;

begin

  if Connected then

    Disconnect;

  FComm.Free;

  inherited Destroy;

end;

procedure TWiFiCommLogger.Connect(Server: string; Port: word);

begin

  FServer := Server;

  FPort := Port;

  FComm.Connect(FServer, FPort);

end;

procedure TWiFiCommLogger.Disconnect;

begin

  FComm.Disconnect;

end;

Usage in main form:

Code:
procedure TfrmCommTest.FormCreate(Sender: TObject);

begin

  ...

  FLogSS := TWiFiCommLogger.Create;

  FLogSS.OnRxData := OnRxSS;

  ...

end;

procedure TfrmCommTest.btnStartLogClick(Sender: TObject);

begin

  if (FLogSS.Connected and FLogSSM.Connected) then

  begin

    FLogSS.Active := false;

    FLogSS.Disconnect;

    ledLog.Brush.Color := clRed;

    btnStartLog.Caption := 'Start Log';

  end

  else

  begin

    FLogSS.Connect(edAddress.Text, speTcpPort.Value + 10);

    if FLogSS.Connected then

    begin

      ledLog.Brush.Color := clLime;

      btnStartLog.Caption := 'Stop Log';

      FLogSS.Active := true;

    end;

  end;

end;

procedure TfrmCommTest.OnRxSS(const Buf: TBytes);

var

  len, lbuf: integer;

begin

  len := Length(Buf);

  lbuf := Length(FLogBufSS);

  SetLength(FLogBufSS, lbuf + len);

  Move(Buf[0], FLogBufSS[lbuf], len); //Append data to log buffer

  SaveLogFile(Buf); //Append data to file

  SetLength(Buf, 0);  //Clear data after save

  FSSDataRx := true;

end;

The data received (into a TIdBytes container) is sent to the main thread in the event function if defined to be stored into a file (file save not shown above).

Do I need some exception handling inside the Execute method?

BosseB