保存图像时出现Ruby中的IOError（关闭流）

在这里，我尝试使用ajax将图像保存在mysql数据库中，但是每次上传图像失败时，请帮我解决这个问题。

Controller.rb

def image_converter
        sub = TestimonialPicture.new
        decoded_file = Base64.decode64(params[:picdata]) unless params[:picdata].nil?
        if request.post?
          begin
            tmpfilename = "#{params[:id]}#{Time.now.to_i.to_s}"
            file = Tempfile.new([tmpfilename, '.jpg'])  
            file.binmode
            file.write decoded_file
            file.close
            sub.testimonialpic = file
            if sub.save
              sub.update_attributes(:testimonial_id => params[:tid])
              msg = "YOur image has been successfully uploaded"
            else
              msg = "Failed to create submission. Please try again"
            end
          ensure
            file.unlink
          end
          render :text=>msg
        end
      end

我创建的图像我要将该图像转换为画布并单击保存按钮，通过执行两个功能来保存图像，使用该控制器可以获取图像但无法存储到数据库。

view.html.erb

$(document).ready(function(){
    var element = $("#bgcolor"); // global variable
    var getCanvas; // global variable

    $("#save_btn").on('click', function () {
         html2canvas(element, {
         onrendered: function (canvas) {
                $("#previewImage").append(canvas);
                getCanvas = canvas;
             }
         });
    });

    $("#btn-Convert-Html2Image").on('click', function () {
      $("#popDiv").hide();
      var picdata = getCanvas.toDataURL("image/png");
      var pic = picdata.replace(/^data:image\/(png|jpg);base64,/, ""); 
        var tid = $("#tid").val();
        $.ajax({ 
          url: "/businessdb/image_converter",
          type: "POST",
          data: {"pic" : pic, "tid" : tid},
          dataType: "json",
          success: function(data) {
            location.reload();
            alert("success");
          }
        });
    });

每次我收到类似IOError的错误时（关闭流）

我需要通过单击保存按钮将图片保存到mysqldatabase中