function TOEMConversion.ConvertReadStream(Stream: TStream; Buffer: PChar; BufSize: Integer): Integer;
var
  Mem: TMemoryStream;
begin
  Mem := TMemoryStream.Create;
  try
    Mem.SetSize(BufSize);
    Result := inherited ConvertReadStream(Stream, PChar(Mem.Memory), BufSize);
    OemToCharBuff(PChar(Mem.Memory), Buffer, Result);
  finally
    Mem.Free;
  end;
end;

  TConversion = class(TObject)
  public
    constructor Create; virtual;
    function ConvertReadStream(Stream: TStream; Buffer: TConversionBuffer; BufSize: Integer): Integer; virtual;
    function ConvertWriteStream(Stream: TStream; Buffer: TConversionBuffer; BufSize: Integer): Integer; virtual;
  end;