将图像上传到HTTP服务器

Question

在我的HTTP服务器上，我试图允许用户通过以下形式上传图像：

<form action="/?command=saveImage" method="post" enctype="multipart/form-data">
  <input type="file" name="images" multiple="multiple"/>
  <input type="submit">
</form>

我正在使用此源上传图像： http ： //embarcadero.newsgroups.archived.at/public.delphi.internet.winsock/201107/1107276163.html并更改了ProcessMimePart过程以便以正确的格式保存图像：

procedure ProcessMimePart(var aDecoder: TIdMessageDecoder;
  var aMsgEnd: Boolean);
var
  LMStream: TMemoryStream;
  LNewDecoder: TIdMessageDecoder;
  fileName, fileExtension: string;
begin
  fileName := aDecoder.fileName;
  fileExtension := GetFileExtension(fileName);

  if (fileExtension <> 'jpg') and (fileExtension <> 'png') 
    and (fileExtension <> 'bmp') then
  begin
    Exit;
  end;

  LMStream := TMemoryStream.Create;
  try
    LNewDecoder := aDecoder.ReadBody(LMStream, aMsgEnd);
    try
      LMStream.Position := 0;
      TSaveImageController.WriteImage(fileName, fileExtension, LMStream);
    except
      LNewDecoder.Free;
      raise;
    end;
    aDecoder.Free;
    aDecoder := LNewDecoder;
  finally
    FreeAndNil(LMStream);
  end;
end;

当我上传一个文件时，此代码工作正常，但当我尝试上传更多图像时，我保存了第一个图像，并且我得到了：'模块'App.exe'中地址004BAD86处的访问冲突。 读取地址00000000'

编辑：

function GetFileExtension(aFileName: string): string;
var
  isValidImageFileExtension: Boolean;
  lastIndexOfComa: integer;
  fileExtension: string;
begin
  lastIndexOfComa := aFileName.LastIndexOf('.');
  if lastIndexOfComa <= 0 then
  begin
    Result := '';
  end
  else
  begin
    fileExtension := LowerCase(aFileName.Substring(lastIndexOfComa + 1));
    if (fileExtension = 'jpg') or (fileExtension = 'bmp') or
      (fileExtension = 'png') then
    begin
      Result := fileExtension;
      Exit;
    end
    else
    begin
      Result := '';
    end;
  end;
end;