iTextSharp 出现“不支持指定的方法”错误

Question

我正在使用iTextSharp 生成 PDF。我在下面添加了一个测试方法，它可以创建一个包含一个段落的简单页面。它可以工作，生成 PDF，但是，在 PDF 发送到浏览器后的某个时间，我在事件日志中收到 NotSupportedException（或者如果我自己从 Application_Error 中捕获它们）。以下是导致此错误的最简单代码：

public FileStreamResult TestPdf()
{
  using (var ms = new MemoryStream())
  {
    using (var document = new Document())
    {
      PdfWriter.GetInstance(document, ms);
      document.Open();
      document.Add(new Paragraph("Hello World!"));
      document.Close();
    }
    Response.ContentType = "application/pdf";
    Response.AddHeader("content-disposition", "attachment;filename=test.pdf");
    Response.Buffer = true;
    Response.Clear();
    Response.OutputStream.Write(ms.GetBuffer(), 0, ms.GetBuffer().Length);
    Response.OutputStream.Flush();
    Response.End();
  }
  return new FileStreamResult(Response.OutputStream, "application/pdf");
}

以及它抛出的错误（请求完成后的某个时间）

Exception information: 
Exception type: NotSupportedException 
Exception message: Specified method is not supported.
at System.Web.HttpResponseStream.Read(Byte[] buffer, Int32 offset, Int32 count)
at System.Web.Mvc.FileStreamResult.WriteFile(HttpResponseBase response)
at System.Web.Mvc.FileResult.ExecuteResult(ControllerContext context)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult)
at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass1c.<InvokeActionResultWithFilters>b__19()
at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation)
at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass1c.<>c__DisplayClass1e.<InvokeActionResultWithFilters>b__1b()
at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList`1 filters, ActionResult actionResult)
at System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)
at System.Web.Mvc.Controller.ExecuteCore()
at System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext)
at System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext)
at System.Web.Mvc.MvcHandler.<>c__DisplayClass6.<>c__DisplayClassb.<BeginProcessRequest>b__5()
at System.Web.Mvc.Async.AsyncResultWrapper.<>c__DisplayClass1.<MakeVoidDelegate>b__0()
at System.Web.Mvc.Async.AsyncResultWrapper.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.End()
at System.Web.Mvc.MvcHandler.<>c__DisplayClasse.<EndProcessRequest>b__d()
at System.Web.Mvc.SecurityUtil.<GetCallInAppTrustThunk>b__0(Action f)
at System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action)
at System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult)
at System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result)
at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

关于如何解决此问题的任何想法？是图书馆有问题还是其他什么问题？

谢谢！

编辑：

为了解决这个问题，我可以通过控制器的 File 方法使用 FileContentResult 而不是返回 FileStreamResult。这是工作代码：

public ActionResult TestPdf()
{
  using (var ms = new MemoryStream())
  {
    using (var document = new Document())
    {
      PdfWriter.GetInstance(document, ms);

      document.Open();
      document.Add(new Paragraph("Hello World!"));
      document.Close();
    }
    Response.ContentType = "application/pdf";
    Response.AddHeader("content-disposition", "attachment;filename=test.pdf");
    Response.Buffer = true;
    Response.Clear();        
    return File(ms.ToArray(), "application/pdf");
  }
}

Answer 1

此行有错误：

Response.OutputStream.Write(ms.GetBuffer(), 0, ms.GetBuffer().Length);

使用ToArray 而不是GetBuffer。像这样：

var bytes = ms.ToArray();
Response.OutputStream.Write(bytes, 0, bytes.Length);

MemoryStream.GetBuffer 返回分配的字节，而不是填充的字节。

问题示例：

using (var memoryStream = new MemoryStream())
{
    memoryStream.WriteByte(1);
    var length = memoryStream.ToArray().Length; // returns 1
   var bufferLength = memoryStream.GetBuffer().Length; // returns 256
}

虽然增加了一个字节，GetBuffer 将返回 256 个字节。