Asp.net File Upload control

With ASP.NET, users have been easy to accept uploading files. With FileUpload control, this can be done with a few code lines, as you will see in the following example. However, please note that users take security concerns when accepting files! Markup is required at:

Demo.aspx

<form id="form1" runat="server">
    <asp:FileUpload id="FileUploadControl" runat="server" />
    <asp:Button runat="server" id="UploadButton" text="Upload" onclick="UploadButton_Click" />
    <br /><br />
    <asp:Label runat="server" id="StatusLabel" text="Upload status: " />
</form>

And here is the CodeBehind code required to handle the upload:

Demo.aspx.c#

protected void UploadButton_Click(object sender, EventArgs e)
{
    if(FileUploadControl.HasFile)
    {
        try
        {
            string filename = Path.GetFileName(FileUploadControl.FileName);
            FileUploadControl.SaveAs(Server.MapPath("~/") + filename);
            StatusLabel.Text = "Upload status: File uploaded!";
        }
        catch(Exception ex)
        {
            StatusLabel.Text = "Upload status: The file could not be uploaded. The following error occured: " + ex.Message;
        }
    }
}

As you can see, all this is relatively simple. Once uploadButton is clicked, we check to see if an upload is specified in the upload control or not. If it is, then we use the FileUpload ControlSave method to save the file. We use the root of our project (we use the mappath method to obtain it) as well as the part of the name of the path that the user has specified, if everything goes well, then we Let's notify the user by setting the StatusLabel's text property - if not, an exception will be thrown, and we will also inform the user.

This example will get the job done, but as you can see, nothing is checked. The user can upload any kind of file, and the size of the file is only limited by the server configuration. A more robust example could look like this:

protected void UploadButton_Click(object sender, EventArgs e)
{
    if(FileUploadControl.HasFile)
    {
        try
        {
            if(FileUploadControl.PostedFile.ContentType == "image/jpeg")
            {
                if(FileUploadControl.PostedFile.ContentLength < 102400)
                {
                    string filename = Path.GetFileName(FileUploadControl.FileName);
                    FileUploadControl.SaveAs(Server.MapPath("~/") + filename);
                    StatusLabel.Text = "Upload status: File uploaded!";
                }
                else
                    StatusLabel.Text = "Upload status: The file has to be less than 100 kb!";
            }
            else
                StatusLabel.Text = "Upload status: Only JPEG files are accepted!";
        }
        catch(Exception ex)
        {
            StatusLabel.Text = "Upload status: The file could not be uploaded. The following error occured: " + ex.Message;
        }
    }
}

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