I was looking for MQTT (Mosquitto protocol implementation) using Indy components (that supports FMX [Delphi Firemonkey framework]).

I found this repo https://github.com/wizinfantry/delphi-mqtt-client — which seems to work after adding the following fix:

On file .\delphi-mqtt-client\LIB\MQTT.pas on function ‘function TMQTT.WriteData(AData: TBytes): boolean;’ using proper TMemoryStream something like that:

function TMQTT.WriteData(AData: TBytes): boolean;
var
  sentData: integer;
  attemptsToWrite: integer;
  Stream: TMemoryStream;
  nCount: Integer;
  pData: TArray<byte>;
begin

// :
// ;

    try
      Stream := TMemoryStream.create;
      nCount := Length(AData) - sentData;
      pData := Copy(AData, sentData - 1, Length(AData) + 1);
      Stream.Write(pData, nCount);
      Stream.Seek(0,0);
      FSocket.IOHandler.Write(Stream, Length(AData) - sentData);
      Stream.Free;
      Result := True;
      FisConnected := true;
    except
      raise;
      Result := False;
      FisConnected := false;
    end;

// :
// ;
end;

Although it is only Alpha version, it does seem to do the basic functionality.

Seems to me this repo is a forked version of https://github.com/jamiei/Delphi-TMQTT2 which is the VCL version using Synapse TCP components.

I ran basic tests on Win, Android and Linux (using Delphi Sydney 10.4.2 with Linux GetIt addon)… all seems to work properly — (Linux had a little free memory issue when subscribing a topic — which required try except — as a fast fix)