遇到使用asp.net中的流将文件下载到客户端的问题

Question

I was trying to create (stream) and download a html file on the client in asp.net using Http Response.

Went through many related posts here but nothing really helped. After spending almost over two days, I stumbled upon a solution.

However, would now want to understand the reason, why it failed earlier.

Here is the story:

Please consider the following ASP.net codebehind handler..

protected void UploadButton_Click(object sender, EventArgs e)
{
    if (FileUploadControl.HasFile)
    {
        try
        {
            if (FileUploadControl.PostedFile.ContentType == MIMEAssistant.GetMIMEType(".xls"))
            {
                string filename = "log.htm";
                string logContent = "This is a test log..";

                // Some upload processing..

                // Send log file for download
                Response.Clear();
                Response.ContentType = MIMEAssistant.GetMIMEType(filename);
                Response.AppendHeader("Content-Disposition", "attachment; filename=" + filename);

                using (StreamWriter writer = new StreamWriter(Response.OutputStream, Encoding.ASCII))
                {
                    writer.Write(logContent);
                }

                //Response.OutputStream.Write(buf1, 0, buf1.Length);
                HttpContext.Current.ApplicationInstance.CompleteRequest();
                Response.End();
            }
            else
                StatusLabel.Text = "Upload status: Only .xls files are accepted!";
        }
        catch (Exception ex)
        {
            StatusLabel.Text = "Upload status: The file could not be uploaded. The following error occured: " + ex.Message;
        }
    }
}

Nothing really helped to make IE download the file and save it from getting stuck. In the end, extracting the code under "// Send log file for download" from innermost to outermost in the function resolved the issue.

EDIT: Facing the issue again even after removing the culprits explained below..

Please help me understand why?

Note: In the code above, the statement Response.End() threw an exception that read :

[System.Threading.ThreadAbortException] = {Unable to evaluate expression because the code is optimized or a native frame is on top of the call stack.}

More info: After further investigation and creating a sample application, I found that putting the download code inside the following code causes the issue:

if (FileUploadControl.HasFile)
 {
     try
     {
         this.HtmlLogDownload();
     }
     catch (Exception ex)
     {
         throw ex;
     }
 }

It works fine if I remove:

if (FileUploadControl.HasFile)

Here is the webform code too:

<form id="form1" runat="server">
    <asp:FileUpload ID="FileUploadControl" runat="server" />
    <asp:Button runat="server" ID="UploadButton" Text="Upload" OnClick="UploadButton_Click" />
    <div>

    </div>
    </form>

Edit: The above works in Chrome and Mozilla. Fails in IE 11

Answer 1

I noticed IE11 returns an uploaded .png image as: "application/png" when checking it like this: LabelStatus.Text = "Ongeldig afbeeldingstype: " & FileUploadKleinLogo.PostedFile.ContentType

It used to be "image/png"

My guess is that that's whats causing the issue in IE11 and not FF or Chrome